THREE-DIMENSIONAL PRINTING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001 ] This application claims priority to International Patent Application

Number PCT/US2017/063935 filed November 30, 2017, the contents of which are incorporated by reference herein in its entirety.

BACKGROUND

[0002] Three-dimensional (3D) printing may be an additive printing process used to make three-dimensional solid parts from a digital model. 3D printing is often used in rapid product prototyping, mold generation, mold master generation, and short run manufacturing. Some 3D printing techniques are considered additive processes because they involve the application of successive layers of material (which, in some examples, may include build material, binder and/or other printing liquid(s), or combinations thereof). This is unlike traditional machining processes, which often rely upon the removal of material to create the final part. Some 3D printing methods use chemical binders or adhesives to bind build materials together. Other 3D printing methods involve at least partial curing, thermal merging/fusing, melting, sintering, etc. of the build material, and the mechanism for material coalescence may depend upon the type of build material used. For some materials, at least partial melting may be accomplished using heat-assisted extrusion, and for some other materials (e.g., polymerizable materials), curing or fusing may be accomplished using, for example, ultra-violet light or infrared light. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Features of examples of the present disclosure will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals or features having a previously described function may or may not be described in connection with other drawings in which they appear.

[0004] Fig. 1 is a flow diagram illustrating an example of a method for 3D printing;

[0005] Fig. 2 is a flow diagram illustrating another example of a method for 3D printing;

[0006] Fig. 3 is a cross-sectional view of an example of a part formed using an example of the 3D printing methods disclosed herein;

[0007] Figs. 4A through 4H are schematic views depicting the formation of a part using an example of the 3D printing methods disclosed herein;

[0008] Figs. 5A through 5C are schematic views depicting the formation of a part using another example of the 3D printing methods disclosed herein;

[0009] Figs. 6A and 6B are schematic views depicting the formation of a part using still another example of the 3D printing methods disclosed herein;

[0010] Fig. 7 is a simplified isometric and schematic view of an example of a 3D printing system disclosed herein; and

[0011 ] Figs. 8-11 are black and white photos of example 3D objects (Figs. 8 and 10) and a comparative 3D object (Figs. 9 and 11 ).

DETAILED DESCRIPTION

[0012] Some examples of three-dimensional (3D) printing may utilize a liquid functional agent, such as a fusing agent including an energy absorber, to pattern polymeric build material. In these examples, an entire layer of the polymeric build material is exposed to radiation, but the patterned region (which, in some instances, is less than the entire layer) of the polymeric build material is coalesced/fused and hardened to become a layer of a 3D object. In the patterned region, the fusing agent is capable of at least partially penetrating into voids between the polymeric build material particles, and is also capable of spreading onto the exterior surface of the polymeric build material particles. This fusing agent is capable of absorbing radiation and converting the absorbed radiation to thermal energy, which in turn coalesces/fuses the polymeric build material that is in contact with the fusing agent.

[0013] Other examples of 3D printing may utilize selective laser sintering (SLS) or selective laser melting (SLM). During selective laser sintering or melting, a laser beam is aimed at a selected region (which, in some instances, is less than the entire layer) of a layer of the polymeric build material. Heat from the laser beam causes the polymeric build material under the laser beam to fuse. In selective laser sintering or melting, other liquid functional agents may be applied to at least some of the build material prior to laser beam exposure in order to impart a particular property, such as a physical, mechanical and/or electrical property, to the 3D object being formed.

[0014] Coalescing/fusing (through the use of (i) the fusing agent and radiation exposure, or (ii) the laser beam) causes the polymeric build material to join or blend to form a single entity (i.e., the layer of the 3D object). Coalescing/fusing may involve at least partial thermal merging, melting, binding, and/or some other mechanism that coalesces the polymeric build material to form the layer of the 3D object.

[0015] Liquid functional agent components, which may include a vehicle and an active material (e.g., an energy absorber, a colorant, a conductive material, a semi- conductive material, an insulating material, etc.), may be balanced so that the agent can be inkjetted and so that desirable active material efficiency is achieved. However, the characteristics that may contribute to good jettability may, in some instances, also cause the liquid functional agent to exhibit an undesirable wetting behavior on some polymeric build materials. For example, the liquid functional agent (including the active material) may not penetrate sufficiently through a desired thickness (e.g., a build material layer) in some instances.

[0016] When the liquid functional agent is a fusing agent and does not penetrate sufficiently through the desired thickness, some of the polymeric build material within the desired thickness may remain non-coalesced/non-fused due to the energy absorber not being in contact with that polymeric build material.

Additionally, when the fusing agent does not penetrate sufficiently through the desired thickness, some other of the polymeric build material within the desired thickness may over coalesce/fuse due to the presence of extra energy absorber (that did not sufficiently penetrate). Non-coalesced/non-fused polymeric build material and/or over-coalesced/over-fused polymeric build material within the desired thickness may reduce the mechanical tolerance(s) and mechanical strength of the 3D object, and may also deleteriously affect the surface finish quality and/or accuracy of the 3D object. For example, the 3D object may be brittle and/or fragile. As another example, the 3D object may be warped.

[0017] Insufficient penetration of a property-imparting liquid functional agent through the desired thickness may prevent some of the polymeric build material within the desired thickness from exhibiting the desired property due to the lack of the active material therein. For example, a liquid functional agent including a colorant may be used to impart color to a 3D object or a discrete region thereof. In this example, insufficient liquid functional agent penetration may prevent a portion of the 3D object or 3D object region from exhibiting the desired color. As another example, a liquid functional agent including a conductive material may be used to form a metal trace in a 3D object. In this example, insufficient liquid functional agent penetration may prevent a portion of the area for the trace from exhibiting the conductive property and thus, may prevent the formation of a continuous, conductive trace. [0018] Penetrating agents

[0019] Disclosed herein is a penetrating agent including a surfactant blend, a co-solvent, a humectant, and a balance of water. It has been found that the combination of the surfactant blend, the co-solvent, the humectant, and water allows the penetrating agent to improve the penetration of the liquid functional agent. As such, the penetrating agent, when applied with the liquid functional agent in a single pass, enables the liquid functional agent (including the active material) to penetrate all or substantially all of the desired thickness (e.g., an entire build material layer). Thus, the activity of the liquid functional agent is able to be exhibited throughout all or substantially all of the desired thickness.

[0020] As used herein, the term“desired thickness” refers to the depth of the build material composition that corresponds to a portion of a 3D object model (i.e., in the digital domain) of the 3D object. In some examples, the“desired thickness” may have a depth equal to the thickness of a build material layer. As such, in these examples, when the combination of the penetrating agent and the liquid functional agent penetrates all or substantially all of the desired thickness, the combination penetrates all or substantially all of the build material layer. It is to be understood that the thickness of any individual build material layer may vary from other build material layers, for example, as the 3D object is built up in the Z- direction. As a patterned layer is coalesced (e.g., fused) to form a 3D object layer, it may undergo compaction. As a result, the formed 3D object layer may be thinner than the build material layer used to form the 3D object layer, and thus there may be a difference in thickness between the 3D object layer and any non-coalesced build material that surrounds the 3D object layer. The additional build material that is applied to the 3D object layer and any non-coalesced build material that surrounds the 3D object layer may have to compensate for this thickness difference. As such, the thickness of the build material layer may be increased when it is applied over an already formed 3D object layer(s), as compared to when the build material is applied directly to a surface of the fabrication bed. In these instances, the thickness of this build material layer may be from about 2 times to about 4 times thicker than the underlying 3D object layer. In an example, this layer thickness may be equal to the (3D object layer thickness)*(bulk substrate density)/(powder spread density). The penetrating agents disclosed herein may be used to effectively penetrate these types of build material layers.

[0021 ] In an example, the penetrating agent for a three-dimensional (3D) printing process, comprises: a surfactant blend including: a first non-ionic surfactant having a first hydrophilic chain length; a second non-ionic surfactant, wherein the second non-ionic surfactant is selected from the group consisting of a polyether siloxane and an alkoxylated alcohol; and an anionic surfactant; a co- solvent; a humectant present in an amount ranging from about 2 wt% to about 10 wt%, based on a total weight of the penetrating agent; and a balance of water.

[0022] In some examples, the build material composition consists of the surfactant blend, the co-solvent, the humectant, and water. In other examples, the build material composition may include additional components, such as

antimicrobial agent(s), anti-kogation agent(s), and/or chelating agent(s).

[0023] The surfactant blend includes a first non-ionic surfactant, a second non- ionic surfactant, and an anionic surfactant. In some examples, the surfactant blend further includes a third non-ionic surfactant. In other examples, the surfactant blend may include a fluorosurfactant instead of the second non-ionic surfactant.

[0024] The first non-ionic surfactant has a first hydrophilic chain length. In an example, the first non-ionic surfactant may be TERGITOL™ TMN-6 (available from The Dow Chemical Company). In another example, the first non-ionic surfactant may be TERGITOL™ 15-S-30 (available from The Dow Chemical Company). In still another example, the first non-ionic surfactant may be TERGITOL™ 15-S-12 (available from The Dow Chemical Company). The first non-ionic surfactant may also be selected from the IGEPAL® series (available from Rhodia), the

PLURONIC® series (available from BASF Corp.), the TRITON™ series (available from The Dow Chemical Company), the ECOSURF™ EH series (available from The Dow Chemical Company), and the ECOSURF™ SA series (available from The Dow Chemical Company). [0025] As mentioned above, in some examples, the surfactant blend further includes a third non-ionic surfactant having a second hydrophilic chain length that is different than the first hydrophilic chain length. The third non-ionic surfactant may be selected from any of the examples listed for the first non-ionic surfactant, as long as the two non-ionic surfactants have different hydrophilic chain lengths. In an example, the first non-ionic surfactant may be TERGITOL™ TMN-6, and the second non-ionic surfactant may be TERGITOL™ 15-S-30 (which has a higher HLB number and a longer hydrophilic chain length than TERGITOL™ TMN-6).

[0026] The second non-ionic surfactant is a polyether siloxane or an alkoxylated alcohol. Examples of the polyether siloxane include TEGO® WET 270, TEGO® WET 280, and DYNOL™ 960 available from Evonik. Other examples of the polyether siloxane include BYK®-3455, BYK®-348, and BYK®-347, available from BYK-Chemie. An example of the alkoxylated alcohol includes TEGO® WET 510 available from Evonik.

[0027] As mentioned above, in some examples, the surfactant blend may include a fluorosurfactant instead of the second non-ionic surfactant. As an example, a non-ionic fluorosurfactant (e.g., CAPSTONE® fluorosurfactants, such as CAPSTONE® FS-35, from E. I. du Pont de Nemours and Company, previously known as ZONYL FSO) may be used.

[0028] As mentioned above, the surfactant blend also includes the anionic surfactant. In an example, the anionic surfactant may be alkyldiphenyloxide disulfonate (e.g., the DOWFAX™ series, such a 2A1 , 3B2, 8390, C6L, C10L, and 30599).

[0029] Without being bound to any theory, it is believed that balancing, via different yet complementary mechanisms, the non-ionic surfactants and the anionic surfactant allows for better control of the total surface tension of the penetrating agent. An example of different, yet complementary mechanisms are stabilization of fluid components via steric (non-ionic) and electrostatic (ionic) stabilization. Non- ionic surfactants may be more robust to solutions that contain other ions. Ionic surfactants may retain solubility better in higher temperatures. As such, it is believed that each type (steric and electrostatic) can fill in the gaps of the other.

[0030] In an example, the first non-ionic surfactant is present in an amount ranging from about 0.1 wt% to about 1.5 wt%, based on the total weight of the penetrating agent; the second non-ionic surfactant is present in an amount ranging from about 0.1 wt% to about 1.5 wt%, based on the total weight of the penetrating agent; and the anionic surfactant is present in an amount ranging from about 0.1 wt% to about 1.5 wt%, based on the total weight of the penetrating agent. In another example, the third non-ionic surfactant is present in an amount ranging from about 0.1 wt% to about 1.5 wt%, based on the total weight of the penetrating agent. In still another example, the fluorosurfactant is present in an amount ranging from about 0.1 wt% to about 1.5 wt%, based on the total weight of the penetrating agent.

[0031 ] In an example, the total amount of the surfactants present in the penetrating agent ranges from about 0.25 wt% to about 3 wt%, based on the total weight of the penetrating agent. In another example, the total amount of the surfactants present in the penetrating agent ranges from about 0.4 wt% to about 4.5 wt%, based on the total weight of the penetrating agent.

[0032] As mentioned above, the penetrating agent also includes the co-solvent, the humectant, and water. The combination of these components and any other components of the penetrating agent with the surfactant blend may be referred to as the“liquid vehicle” of the penetrating agent. In other words, the term“liquid vehicle” may refer to the liquid with which the surfactant blend is combined to form the penetrating agent. In some examples, the liquid vehicle includes co-solvent(s), humectant(s), and water. In these examples, the liquid vehicle may include additional components, such as antimicrobial agent(s), anti-kogation agent(s), and/or chelating agent(s). In other examples, the liquid vehicle consists of co- solvents), humectant(s), and water without any other components. [0033] Water may make up the balance of the penetrating agent. As such, the amount of water may vary depending upon the amounts of the other components that are included. As an example, deionized water may be used.

[0034] The liquid vehicle may also include co-solvent(s). In an example, the co- solvent is present in an amount ranging from about 5 wt% to about 25 wt%, based on the total weight of the penetrating agent. In another example, the co-solvent is present in an amount of about 18 wt%, based on the total weight of the penetrating agent.

[0035] Classes of organic co-solvents that may be used in the liquid vehicle include aliphatic alcohols, aromatic alcohols, diols, glycol ethers, polyglycol ethers, 2-pyrrolidones, caprolactams, formamides, acetamides, glycols, and long chain alcohols. Examples of these co-solvents include primary aliphatic alcohols, secondary aliphatic alcohols, 1 ,2-alcohols, 1 ,3-alcohols, 1 ,5-alcohols, 1 ,6- hexanediol or other diols (e.g., 1 ,5-pentanediol, 2-methyl-1 ,3-propanediol, etc.), ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs (C6-C12) of polyethylene glycol alkyl ethers, triethylene glycol, tetraethylene glycol, tripropylene glycol methyl ether, N-alkyl caprolactams, unsubstituted caprolactams, both substituted and unsubstituted formamides, both substituted and unsubstituted acetamides, and the like. Other examples of organic co-solvents include dimethyl sulfoxide (DMSO), isopropyl alcohol, ethanol, pentanol, acetone, or the like.

[0036] Other examples of suitable co-solvents include water-soluble high-boiling point solvents, which have a boiling point of at least 120°C, or higher. Some examples of high-boiling point solvents include 2-pyrrolidone (i.e. , 2-pyrrolidinone, boiling point of about 245°C), 1 -methyl-2-pyrrolidone (boiling point of about 203°C), N-(2-hydroxyethyl)-2-pyrrolidone (boiling point of about 140°C), 2-methyl-1 ,3- propanediol (boiling point of about 212°C), and combinations thereof.

[0037] The co-solvent(s) of the liquid vehicle may depend, in part, upon the jetting technology that is to be used to dispense the penetrating agent. For example, if thermal inkjet printheads are to be used, water and/or ethanol and/or other longer chain alcohols (e.g., pentanol) may be the co-solvent (e.g., making up 35 wt% or more of the penetrating agent. For another example, if piezoelectric inkjet printheads are to be used, water may make up from about 25 wt% to about 30 wt% of the penetrating agent, and co-solvent (e.g., making up 35 wt% or more of the penetrating agent) may be ethanol, isopropanol, acetone, etc.

[0038] The liquid vehicle may also include humectant(s). In an example, the total amount of the humectant(s) present in the penetrating agent ranges from about 2 wt% to about 10 wt%, based on the total weight of the penetrating agent.

In another example, the total amount of the humectant(s) present in the penetrating agent ranges from about 3 wt% to about 8 wt%, based on the total weight of the penetrating agent. In still another example, the total amount of the humectant(s) present in the penetrating agent is about 5 wt%, based on the total weight of the penetrating agent.

[0039] An example of a suitable humectant is ethoxylated glycerin having the following formula:

H ₂ C - 0(CH ₂ CH ₂ 0) _a H

H ₂ C - 0(CH ₂ CH ₂ 0) _b H

H ₂ C - 0(CH ₂ CH ₂ 0) _c H

in which the total of a+b+c ranges from about 5 to about 60, or in other examples, from about 20 to about 30. An example of the ethoxylated glycerin is LIPONIC® EG-1 (LEG-1 , glycereth-26, a+b+c=26, available from Lipo Chemicals). Other examples of suitable humectants include glycerin, propylene glycol, and a polyethylene glycol (PEG) with a molecular weight of about 1000 M _n (number average molecular weight) or less. In an example, the humectant is selected from the group consisting of an ethoxylated glycerin, glycerin, propylene glycol, a polyethylene glycol with a molecular weight of about 1000 M _n or less, and a combination thereof.

[0040] In some examples, the penetrating agent (and/or the liquid vehicle), in addition to the surfactant blend, co-solvent, humectant, and water, may include an antimicrobial agent, an anti-kogation agent, a chelating agent, or a combination thereof.

[0041 ] In some examples, the penetrating agent (and/or the liquid vehicle) includes antimicrobial agent(s). Suitable antimicrobial agents include biocides and fungicides. Example antimicrobial agents may include the NUOSEPT™ (Troy Corp.), UCARCIDE™ (Dow Chemical Co.), ACTICIDE® B20 (Thor Chemicals), ACTICIDE® M20 (Thor Chemicals), ACTICIDE® MBL (blends of 2-methyl-4- isothiazolin-3-one (MIT), 1 ,2-benzisothiazolin-3-one (BIT) and Bronopol) (Thor Chemicals), AXIDE™ (Planet Chemical), NIPACIDE™ (Clariant), blends of 5- chloro-2-methyl-4-isothiazolin-3-one (CIT or CMIT) and MIT under the tradename KATHON™ (Dow Chemical Co.), and combinations thereof. Examples of suitable biocides include an aqueous solution of 1 ,2-benzisothiazolin-3-one (e.g.,

PROXEL® GXL from Arch Chemicals, Inc.), quaternary ammonium compounds (e.g., BARDAC® 2250 and 2280, BARQUAT® 50-65B, and CARBOQUAT® 250-T, all from Lonza Ltd. Corp.), and an aqueous solution of methylisothiazolone (e.g., KORDEK® MLX from Dow Chemical Co.).

[0042] In an example, the penetrating agent may include a total amount of antimicrobial agents that ranges from about 0.05 wt% to about 1 wt%. In an example, the antimicrobial agent(s) is/are a biocide(s) and is/are present in the penetrating in an amount of about 0.25 wt% (based on the total weight of the penetrating agent).

[0043] An anti-kogation agent may be included in the penetrating agent that is to be jetted using thermal inkjet printing. Kogation refers to the deposit of dried printing liquid (e.g., penetrating agent) on a heating element of a thermal inkjet printhead. Anti-kogation agent(s) is/are included to assist in preventing the buildup of kogation. Examples of suitable anti-kogation agents include oleth-3-phosphate (e.g., commercially available as CRODAFOS™ 03A or CRODAFOS™ N-3 acid from Croda), or a combination of oleth-3-phosphate and a low molecular weight (e.g., < 5,000) polyacrylic acid polymer (e.g., commercially available as

CARBOSPERSE™ K-7028 Polyacrylate from Lubrizol). [0044] Whether a single anti-kogation agent is used or a combination of anti- kogation agents is used, the total amount of anti-kogation agent(s) in the penetrating agent may range from greater than 0.20 wt% to about 0.65 wt% based on the total weight of the penetrating agent. In an example, the oleth-3-phosphate is included in an amount ranging from about 0.20 wt% to about 0.60 wt%, and the low molecular weight polyacrylic acid polymer is included in an amount ranging from about 0.005 wt% to about 0.03 wt%.

[0045] Chelating agents (or sequestering agents) may be included in the penetrating agent to eliminate the deleterious effects of heavy metal impurities. Examples of chelating agents include disodium ethylenediaminetetraacetic acid (EDTA-Na), ethylene diamine tetra acetic acid (EDTA), and methylglycinediacetic acid (e.g., TRILON® M from BASF Corp.).

[0046] Whether a single chelating agent is used or a combination of chelating agents is used, the total amount of chelating agent(s) in the penetrating agent may range from greater than 0 wt% to about 2 wt% based on the total weight of the penetrating agent. In an example, the chelating agent(s) is/are present in the penetrating agent in an amount of about 0.04 wt% (based on the total weight of the penetrating agent).

[0047] In an example, the penetrating agent has a surface tension ranging from about 19 dynes/cm to about 29 dynes/cm. In another example, the penetrating agent has a surface tension ranging from about 20 dynes/cm to about 28 dynes/cm. In still another example, the penetrating agent has a surface tension ranging from about 23 dynes/cm to about 25 dynes/cm.

[0048] A surface tension of the penetrating agent within the ranges disclosed herein may allow the penetrating agent (and thus, the active material of the liquid functional agent applied in a single pass therewith) to penetrate all of a desired thickness (e.g., an entire layer of the build material composition). For example, the penetrating agent and the active material of the liquid functional agent applied in a single pass therewith may penetrate a thickness of the build material composition ranging from greater than 0 pm to about 500 pm. Penetration of all or substantially all of a desired thickness allows the activity of the active material to be exhibited throughout all or substantially all of the desired thickness. As used herein, “substantially all” of a desired thickness means 95% or more (in the z-direction) of a desired thickness. As such, the surface tension of the penetrating agent being within the disclosed ranges may assist in the placement of the active material in desirable locations within a layer of build material and upon the surfaces of the build material.

[0049] 3D Printing Kits and Compositions

[0050] The penetrating agent described herein may be part of a 3D printing kit and/or a 3D printing composition.

[0051 ] In an example, the three-dimensional (3D) printing kit, comprises: a build material composition including a polymer; a liquid functional agent to be applied to at least a portion of the build material composition during 3D printing, the liquid functional agent including an active material; and a penetrating agent to be applied with the liquid functional agent to the at least the portion of the build material composition during 3D printing, the penetrating agent including: a surfactant blend including: a first non-ionic surfactant having a first hydrophilic chain length; a second non-ionic surfactant, wherein the second non-ionic surfactant is selected from the group consisting of a polyether siloxane and an alkoxylated alcohol; and an anionic surfactant; and a liquid vehicle including a humectant present in an amount ranging from about 2 wt% to about 10 wt%, based on a total weight of the penetrating agent. In another example of the 3D printing kit, the build material composition has a surface energy density ranging from about 0.02 J/m ² to about 0.046 J/m ² ; and the penetrating agent has a surface tension ranging from about 19 dynes/cm to about 29 dynes/cm.

[0052] In some examples, the 3D printing kit consists of the build material composition, the liquid functional agent, and the penetrating agent with no other components. In other examples, the kit includes additional components, such as another liquid functional agent. The components of the kit may be maintained separately until used together in examples of the 3D printing method disclosed herein.

[0053] Any example of the penetrating agent may be used in the examples of the 3D printing kit. As mentioned above, the penetrating agent includes at least the surfactant blend and the liquid vehicle including a humectant present in an amount ranging from about 2 wt% to about 10 wt% (based on a total weight of the penetrating agent), and may additionally include water, the co-solvent, the humectant, the antimicrobial agent, the anti-kogation agent, the chelating agent, or combinations thereof.

[0054] As mentioned above, the build material composition includes at least the polymer, and in some examples, the build material composition has a surface energy density ranging from about 0.02 J/m ² to about 0.046 J/m ² and includes at least the polymer. Any of the example compositions of the build material composition described below may be used in the examples of the 3D printing kit.

[0055] The liquid functional agent includes at least the active material.

[0056] In some examples, the liquid functional agent is a fusing agent and the active material is an energy absorber to absorb electromagnetic radiation to coalesce the polymer in the at least the portion. In some of these examples, one of: the fusing agent is a core fusing agent and the energy absorber has absorption at least at wavelengths ranging from 400 nm to 780 nm; or the fusing agent is a primer fusing agent and the energy absorber has absorption at wavelengths ranging from 800 nm to 4000 nm and has transparency at wavelengths ranging from 400 nm to 780 nm. The core fusing agent may also have absorption at wavelengths ranging from 800 nm to 4000 nm. In some examples, the 3D printing kit may include both a core fusing agent and a primer fusing agent. Example compositions of the fusing agent (e.g., example compositions of the core fusing and example compositions of the primer fusing agent) are described below.

[0057] In some examples, the liquid functional agent is a coloring agent selected from the group consisting of a black agent, a cyan agent, a magenta agent, and a yellow agent, and the active material is a colorant. In some examples, the 3D printing kit may include multiple coloring agents. For example, the 3D printing kit may include a coloring agent for each desired color (e.g., black, cyan, magenta, yellow, etc.). Any of the example compositions of the coloring agent described below may be used in the examples of the 3D printing kit.

[0058] In some examples, the liquid functional agent imparts a property, such as an electronic property or a mechanical property. In some examples, the 3D printing kit may include multiple property-imparting liquid functional agents. Any of the example compositions of the property-imparting liquid functional agent described below may be used in the examples of the 3D printing kit.

[0059] In some examples, the 3D printing kit may include multiple liquid functional agents. In an example the 3D printing kit may include one or more fusing agents, one or more coloring agents, one or more property-imparting liquid functional agents, or a combination thereof.

[0060] In another example, the three-dimensional (3D) printing composition comprises: a build material composition a build material composition including a polymer; a liquid functional agent to be applied to at least a portion of the build material composition during 3D printing, the liquid functional agent including an active material; and a penetrating agent to be applied with the liquid functional agent to the at least the portion of the build material composition during 3D printing, the penetrating agent including: a surfactant blend including: a first non-ionic surfactant having a first hydrophilic chain length; a second non-ionic surfactant, wherein the second non-ionic surfactant is selected from the group consisting of a polyether siloxane and an alkoxylated alcohol; and an anionic surfactant; and a liquid vehicle including a humectant present in an amount ranging from about 2 wt% to about 10 wt%, based on a total weight of the penetrating agent. In an example of the 3D printing composition, the build material composition has a surface energy density ranging from about 0.02 J/m ² to about 0.046 J/m ² ; and the penetrating agent has a surface tension ranging from about 19 dynes/cm to about 29 dynes/cm. [0061 ] As used herein,“material set” or“kit” may, in some instances, be synonymous with“composition.” Further,“material set” and“kit” are understood to be compositions comprising one or more components where the different components in the compositions are each contained in one or more containers, separately or in any combination, prior to and during printing but these components can be combined together during printing. The containers can be any type of a vessel, box, or receptacle made of any material.

[0062] Build Material Compositions

[0063] In the examples of the 3D printing kit, the 3D printing composition, the 3D printing methods, and the 3D printing system disclosed herein, a build material composition may be used. As mentioned above, the build material composition includes a polymer. In some examples, the build material composition also has a surface energy density ranging from about 0.02 J/m ² to about 0.046 J/m ² .

[0064] In some examples, the build material composition consists of the polymer. In other examples, the build material composition may include additional components, such as glass, a filler, an antioxidant, a whitener, an antistatic agent, a flow aid, or a combination thereof.

[0065] In some examples, the polymer may be a crystalline or semi-crystalline polymer. Some examples of semi-crystalline polymers include polyamides (PAs), such as polyamide 11 (PA 11 / nylon 11 ), polyamide 12 (PA 12 / nylon 12), polyamide 12-GB (PA 12-GB / nylon 12-GB), polyamide 6 (PA 6 / nylon 6), polyamide 4,6 (PA 4,6 / nylon 4,6), polyamide 13 (PA 13 / nylon 13), polyamide 6,13 (PA 6,13 / nylon 6,13), polyamide 8 (PA 8 / nylon 8), polyamide 9 (PA 9 / nylon 9), polyamide 66 (PA 66 / nylon 66), polyamide 612 (PA 612 / nylon 612), polyamide 812 (PA 812 / nylon 812), polyamide (PA 912 / nylon 912), etc. It is to be understood that polyamide 12-GB refers to a polyamide 12 including glass beads or another form of glass disclosed herein (mixed therewith or encapsulated therein, e.g., at a weight ratio of the glass to the polyamide 12 within the ranges set forth herein). Other examples of crystalline or semi-crystalline polymers suitable for use as the polymer include polyethylene, polypropylene, and polyoxomethylene (i.e. , polyacetals). Still other examples of suitable polymers include polystyrene, polycarbonate, polyester, polyurethanes, other engineering plastics, and blends of any two or more of the polymers listed herein. One example of a suitable polyester is polybutylene terephthalate (PBT).

[0066] In some examples, the polymer may be a thermoplastic elastomer.

Some examples of thermoplastic elastomers include a thermoplastic polyamide (TPA), a thermoplastic polyurethane (TPU), a styrenic block copolymer (TPS), a thermoplastic polyolefin elastomer (TPO), a thermoplastic vulcanizate (TPV), and a thermoplastic copolyester (TPC). In an example, the thermoplastic elastomer is a thermoplastic polyamide. Thermoplastic polyamide elastomers are thermoplastic elastomer block copolymers based on nylon and polyethers or polyesters.

Examples of TPA elastomers include polyether block amide elastomers. Polyether block amide elastomers may be obtained by the polycondensation of a carboxylic acid terminated polyamide (PA 6, PA 11 , PA 12) with an alcohol terminated polyether (e.g., polytetramethylene glycol (PTMG), polyethylene glycol (PEG), etc.). Two examples of commercially available PEBA elastomers include those known under the tradename of PEBAX® (Arkema) and VESTAMID® E (Evonik Industries). In another example, the thermoplastic elastomer is a thermoplastic polyurethane. Thermoplastic polyurethane elastomers may be obtained by reaction of: (i) diisocyanates with short-chain diols (so-called chain extenders) and/or (ii) diisocyanates with long-chain diols. Two examples of commercially available TPU elastomers include those known under the tradename of

DESMOPAN® (Covestro) and ELASTOLLAN® (BASF Corp.).

[0067] In some examples, the polymer may be in the form of a powder. In other examples, the polymer may be in the form of a powder-like material, which includes, for example, short fibers having a length that is greater than its width. In some examples, the powder or powder-like material may be formed from, or may include, short fibers that may, for example, have been cut into short lengths from long strands or threads of material. [0068] The polymer may be made up of similarly sized particles and/or differently sized particles. In an example, the average particle size of the polymer ranges from about 2 pm to about 200 pm. In another example, the average particle size of the polymer ranges from about 10 pm to about 110 pm. The term“average particle size”, as used herein, may refer to a number-weighted mean diameter or a volume-weighted mean diameter of a particle distribution.

[0069] When the polymer is a crystalline or semi-crystalline polymer, the polymer may have a wide processing window of greater than 5°C, which can be defined by the temperature range between the melting point and the re- crystallization temperature. In an example, the polymer may have a melting point ranging from about 50°C to about 300°C. As other examples, the polymer may have a melting point ranging from about 155°C to about 225°C, from about 155°C to about 215°C, about 160°C to about 200°C, from about 170°C to about 190°C, or from about 182°C to about 189°C. As still another example, the polymer may be a polyamide having a melting point of about 180°C.

[0070] When the polymer is a thermoplastic elastomer, the thermoplastic elastomer may have a melting range within the range of from about 130°C to about 250°C. In some examples (e.g., when the thermoplastic elastomer is a polyether block amide), the thermoplastic elastomer may have a melting range of from about 130°C to about 175°C. In some other examples (e.g., when the thermoplastic elastomer is a thermoplastic polyurethane), the thermoplastic elastomer may have a melting range of from about 130°C to about 180°C or a melting range of from about 175°C to about 210°C.

[0071 ] In some examples, the polymer does not substantially absorb radiation having a wavelength within the range of 400 nm to 1400 nm. In other examples, the polymer does not substantially absorb radiation having a wavelength within the range of 800 nm to 1400 nm. In still other examples, the polymer does not substantially absorb radiation having a wavelength within the range of 400 nm to 1200 nm. In these examples, the polymer may be considered to reflect the wavelengths at which the polymer does not substantially absorb radiation. The phrase“does not substantially absorb” means that the absorptivity of the polymer at a particular wavelength is 25% or less (e.g., 20%, 10%, 5%, etc.).

[0072] In some examples, the polymer may also include glass therein (e.g., when the polymer is a polyamide 12-GB). In some of these examples, the glass may be dry blended with the polymer. In others of these examples, the glass may be encapsulated by the polymer. When the glass is encapsulated by the polymer, the polymer may form a continuous coating (e.g., none of the glass is exposed) or a substantially continuous coating (e.g., 5% or less of the glass is exposed) on the glass.

[0073] Whether the glass is dry blended with the polymer or encapsulated by the polymer may depend, in part, on (i) the characteristics of the glass, and (ii) the 3D printer with which the build material composition is to be used. As an example, when the glass includes glass fibers and/or crushed glass, the glass may be encapsulated by the polymer. As another example, when segregation of dry blended polymer and glass may occur and cause damage to the 3D printer in which the build material composition is to be used, the glass may be encapsulated by the polymer.

[0074] When the glass is dry blended with the polymer, the average particle size of the glass may range from about 5 pm to about 100 pm.

[0075] When the glass is encapsulated by the polymer, the average particle size of the glass (prior to being coated) may range from about 5 pm to about 100 pm or from about 30 pm to about 50 pm. The average particle size of the encapsulated material (i.e. , the glass coated with the polymer) may depend upon the size of the glass prior to coating and the thickness of the polymer that is applied to the glass.

In an example, the average particle size of the encapsulated build material may range from about 10 pm to about 200 pm. In another example, the average particle size of the encapsulated build material may range from about 20 pm to about 120 pm.

[0076] The weight ratio of the glass to the polymer (e.g., polyamide 12) may range from about 5:95 to about 60:40. In some examples, the weight ratio of the glass to the polymer may range from about 10:90 to about 60:40; or from about 20:80 to about 60:40; or from about 40:60 to about 60:40; or from about 5:95 to about 40:60; or from about 5:95 to about 50:50. In some instances, additives (e.g., antioxidant(s), whitener(s), charging agent(s), flow aid(s), etc.) may be included with the polymer and glass. In these instances, the weight of the polymer, for the purpose of determining the weight ratio of the glass to the polymer, may include the weight of the additives in addition to the weight of the polymer. In other instances, the weight of the polymer, for the purpose of determining the weight ratio of the glass to the polymer, includes the weight of the polymer alone (whether or not additives are included in the build material composition). The weight ratio of the glass to the polymer may depend, in part, on the desired properties of the 3D object to be formed, the glass used, the polymer used, and/or the additives included in the polymer.

[0077] In one example, the glass may be selected from the group consisting of solid glass beads, hollow glass beads, porous glass beads, glass fibers, crushed glass, and a combination thereof. In another example, the glass may be selected from the group consisting of soda lime glass (Na ₂ 0/Ca0/Si0 ₂ ), borosilicate glass, phosphate glass, fused quartz, and a combination thereof. In still another example, the glass may be selected from the group consisting of soda lime glass,

borosilicate glass, and a combination thereof. In yet other examples, the glass may be any type of non-crystalline silicate glass.

[0078] In some examples, a surface of the glass may be modified with a functional group selected from the group consisting of an acrylate functional silane, a methacrylate functional silane, an epoxy functional silane, an ester functional silane, an amino functional silane, and a combination thereof. Examples of the glass modified with such functional groups and/or such functional groups that may be used to modify the glass are available from Potters Industries, LLC (e.g., an epoxy functional silane or an amino functional silane), Gelest, Inc. (e.g., an acrylate functional silane or a methacrylate functional silane), Sigma-Aldrich (e.g., an ester functional silane), etc. In an example, the surface of the glass is modified with an amino functional silane. In another example, the surface of the glass may be modified with an epoxy functional silane. In other examples, a surface of the glass is not modified with any functional group.

[0079] In some examples, the build material composition, in addition to the polymer (and the glass if included), may include a filler, an antioxidant, a whitener, an antistatic agent, a flow aid, or a combination thereof. While several examples of these additives are provided, it is to be understood that these additives are selected to be thermally stable (i.e. , will not decompose) at the 3D printing temperatures.

[0080] Filler(s) may be added to the build material composition to modify the properties of the 3D objects to be printed. Examples of suitable fillers include glass, alumina, silica, talc, and a combination thereof. In an example, the filler may be included in the build material composition in an amount ranging from about 1 wt% to about 60 wt%, based on the total weight of the build material composition.

[0081 ] Antioxidant(s) may be added to the build material composition to prevent or slow molecular weight decreases of the polymer and/or may prevent or slow discoloration (e.g., yellowing) of the polymer by preventing or slowing oxidation of the polymer. In some examples, the antioxidant may discolor upon reacting with oxygen, and this discoloration may contribute to the discoloration of the build material composition. The antioxidant may be selected to minimize discoloration.

In some examples, the antioxidant may be a radical scavenger. In these

examples, the antioxidant may include IRGANOX® 1098 (benzenepropanamide,

N, N'-1 ,6-hexanediylbis(3,5-bis(1 , 1 -dimethylethyl)-4-hydroxy)), IRGANOX® 254 (a mixture of 40% triethylene glycol bis(3-tert-butyl-4-hydroxy-5-methylphenyl), polyvinyl alcohol and deionized water), and/or other sterically hindered phenols. In other examples, the antioxidant may include a phosphite and/or an organic sulfide (e.g., a thioester). The antioxidant may be in the form of fine particles (e.g., having an average particle size of 5 pm or less) that are dry blended with the polymer. In an example, the antioxidant may be included in the build material composition in an amount ranging from about 0.01 wt% to about 5 wt%, based on the total weight of the build material composition. In other examples, the antioxidant may be included in the build material composition in an amount ranging from about 0.01 wt% to about 2 wt% or from about 0.2 wt% to about 1 wt%, based on the total weight of the build material composition.

[0082] Whitener(s) may be added to the build material composition to improve visibility. Examples of suitable whiteners include titanium dioxide (T1O ₂ ), zinc oxide (ZnO), calcium carbonate (CaCOs), zirconium dioxide (Zr0 ₂ ), aluminum oxide (AI ₂ O ₃ ), silicon dioxide (S1O ₂ ), boron nitride (BN), and combinations thereof. In some examples, a stilbene derivative may be used as the whitener and a brightener. In these examples, the temperature(s) of the 3D printing process may be selected so that the stilbene derivative remains stable (i.e., the 3D printing temperature does not thermally decompose the stilbene derivative). In an example, any example of the whitener may be included in the build material composition in an amount ranging from greater than 0 wt% to about 10 wt%, based on the total weight of the build material composition.

[0083] Antistatic agent(s) may be added to the build material composition to suppress tribo-charging. Examples of suitable antistatic agents include aliphatic amines (which may be ethoxylated), aliphatic amides, quaternary ammonium salts (e.g., behentrimonium chloride or cocam idopropyl betaine), esters of phosphoric acid, polyethylene glycolesters, or polyols. Some suitable commercially available antistatic agents include HOSTASTAT® FA 38 (natural based ethoxylated alkylamine), HOSTASTAT® FE2 (fatty acid ester), and HOSTASTAT® HS 1 (alkane sulfonate), each of which is available from Clariant Int. Ltd.). In an example, the antistatic agent is added in an amount ranging from greater than 0 wt% to less than 5 wt%, based upon the total weight of the build material composition.

[0084] Flow aid(s) may be added to improve the coating flowability of the build material composition. Flow aids may be particularly beneficial when the build material composition has an average particle size less than 25 pm. The flow aid improves the flowability of the build material composition by reducing the friction, the lateral drag, and the tribocharge buildup (by increasing the particle conductivity). Examples of suitable flow aids include aluminum oxide (AI2O3), tricalcium phosphate (E341 ), powdered cellulose (E460(ii)), magnesium stearate (E470b), sodium bicarbonate (E500), sodium ferrocyanide (E535), potassium ferrocyanide (E536), calcium ferrocyanide (E538), bone phosphate (E542), sodium silicate (E550), silicon dioxide (E551 ), calcium silicate (E552), magnesium trisilicate (E553a), talcum powder (E553b), sodium aluminosilicate (E554), potassium aluminum silicate (E555), calcium aluminosilicate (E556), bentonite (E558), aluminum silicate (E559), stearic acid (E570), and polydimethylsiloxane (E900). In an example, the flow aid is added in an amount ranging from greater than 0 wt% to less than 5 wt%, based upon the total weight of the build material composition.

[0085] In some examples, the build material composition disclosed herein may be reused/recycled. After a print cycle, some of the build material composition disclosed herein remains non-coalesced/non-fused, and can be reclaimed and used again. This reclaimed build material is referred to as the recycled build material composition. The recycled build material composition may be exposed to 2, 4, 6, 8, 10, or more build cycles (i.e. , heating to a temperature ranging from about 50°C to about 205°C and then cooling), and reclaimed after each cycle.

Between cycles, the recycled build material composition may be mixed with at least some fresh or virgin (i.e., not previously used in a 3D printing process) build material composition. In some examples, the weight ratio of the recycled build material composition to the fresh build material composition may be 90:10, 80:20, 70:30, 60:40, 50:50, or 40:60. The weight ratio of the recycled build material composition to the fresh build material composition may depend, in part, on the stability of the build material composition, the discoloration of the recycled build material composition (as compared to the build material composition), the desired aesthetics for the 3D object being formed, the thermal decomposition of the recycled build material composition (as compared to the build material

composition), and/or the desired mechanical properties of the 3D object being formed. [0086] Fusing Agents

[0087] In the examples of the 3D printing kit, the 3D printing composition, the 3D printing methods, and the 3D printing system disclosed herein, a fusing agent may be used.

[0088] Some examples of the fusing agent have substantial absorption (e.g., 80%) at least in the visible region (400 nm - 780 nm). These examples of the fusing agent are referred to as the core fusing agent, or, in some instances, the black fusing agent. As described herein, the energy absorber in the core fusing agent may also absorb energy in the infrared region (e.g., 800 nm to 4000 nm). This absorption generates heat suitable for coalescing/fusing during 3D printing, which leads to 3D objects (or 3D objects regions) having mechanical integrity and relatively uniform mechanical properties (e.g., strength, elongation at break, etc.). This absorption, however, also results in strongly colored, e.g., black, 3D objects (or 3D objects regions).

[0089] Other examples of the fusing agent include an energy absorber having absorption at wavelengths ranging from 800 nm to 4000 nm and having

transparency at wavelengths ranging from 400 nm to 780 nm. These examples of the fusing agent are referred to as the primer fusing agent, or, in some instances, the low tint fusing agent. This absorption and transparency allows the primer fusing agent to absorb enough radiation to coalesce/fuse the build material composition in contact therewith while causing the 3D objects (or 3D objects regions) to be white or slightly colored.

[0090] As used herein“absorption” means that at least 80% of radiation having wavelengths within the specified range is absorbed. Also used herein,

“transparency” means that 25% or less of radiation having wavelengths within the specified range is absorbed.

[0091 ] Core Fusing Agents

[0092] Some examples of the core fusing agent are dispersions including an energy absorber (i.e. , an active material). In some examples, the active material may be an infrared light absorbing colorant. In an example, the active material is a near-infrared light absorber. Any near-infrared colorants, e.g., those produced by Fabricolor, Eastman Kodak, or BASF, Yamamoto, may be used in the core fusing agent. As one example, the core fusing agent may be a printing liquid formulation including carbon black as the active material. Examples of this printing liquid formulation are commercially known as CM997A, 516458, C18928, C93848, C93808, or the like, all of which are available from HP Inc.

[0093] As another example, the core fusing agent may be a printing liquid formulation including near-infrared absorbing dyes as the active material.

Examples of this printing liquid formulation are described in U.S. Patent No.

9,133,344, incorporated herein by reference in its entirety. Some examples of the near-infrared absorbing dye are water-soluble near-infrared absorbing dyes selected from the group consisting of:





and mixtures thereof. In the above formulations, M can be a divalent metal atom (e.g., copper, etc.) or can have 0S0 ₃ Na axial groups filling any unfilled valencies if the metal is more than divalent (e.g., indium, etc.), R can be hydrogen or any C-i-Cs alkyl group (including substituted alkyl and unsubstituted alkyl), and Z can be a counterion such that the overall charge of the near-infrared absorbing dye is neutral. For example, the counterion can be sodium, lithium, potassium, NH ₄ ⁺ , etc.

[0094] Some other examples of the near-infrared absorbing dye are

hydrophobic near-infrared absorbing dyes selected from the group consisting of:

31

and mixtures thereof. For the hydrophobic near-infrared absorbing dyes, M can be a divalent metal atom (e.g., copper, etc.) or can include a metal that has Cl, Br, or OR’ (R’=H, CHs, COCH ₃ , COCH ₂ COOCH ₃ , COCH ₂ COCH ₃ ) axial groups filling any unfilled valencies if the metal is more than divalent, and R can be hydrogen or any C-i-Cs alkyl group (including substituted alkyl and unsubstituted alkyl).

[0095] Other near-infrared absorbing dyes or pigments may be used. Some examples include anthroquinone dyes or pigments, metal dithiolene dyes or pigments, cyanine dyes or pigments, perylenediimide dyes or pigments, croconium dyes or pigments, pyrilium or thiopyrilium dyes or pigments, boron-dipyrromethene dyes or pigments, or aza-boron-dipyrromethene dyes or pigments.

[0096] Anthroquinone dyes or pigments and metal (e.g., nickel) dithiolene dyes or pigments may have the following structures, respectively:

Anthroquinone dyes/pigments

Nickel Dithiolene dyes/pigments where R in the anthroquinone dyes or pigments may be hydrogen or any CrC ₈ alkyl group (including substituted alkyl and unsubstituted alkyl), and R in the dithiolene may be hydrogen, COOH, SO3, NH ₂ , any C-i-C ₈ alkyl group (including substituted alkyl and unsubstituted alkyl), or the like.

[0097] Cyanine dyes or pigments and perylenediimide dyes or pigments may have the following structures, respectively:

Cyanine dyes/pigments

Perylenediimide dyes/pigments where R in the perylenediimide dyes or pigments may be hydrogen or any CrC ₈ alkyl group (including substituted alkyl and unsubstituted alkyl).

[0098] Croconium dyes or pigments and pyrilium or thiopyrilium dyes or pigments may have the following structures, respectively:

Pyrilium (X=0), thiopyrilium (X=S) dyes/pigments

[0099] Boron-dipyrromethene dyes or pigments and aza-boron-dipyrromethene dyes or pigments may have the following structures, respectively:

boron-dipyrromethene dyes/pigments

aza-boron-dipyrromethene dyes/pigments [0100] The amount of the active material that is present in the core fusing agent ranges from greater than 0 wt% to about 40 wt% based on the total weight of the core fusing agent. In other examples, the amount of the active material in the core fusing agent ranges from about 0.3 wt% to 30 wt%, from about 1 wt% to about 20 wt%, from about 1.0 wt% up to about 10.0 wt%, or from greater than 4.0 wt% up to about 15.0 wt%. It is believed that these active material loadings provide a balance between the core fusing agent having jetting reliability and heat and/or radiation absorbance efficiency.

[0101 ] Primer Fusing Agents

[0102] Some examples of the primer fusing agent are dispersions including the energy absorber that has absorption at wavelengths ranging from 800 nm to 4000 nm and transparency at wavelengths ranging from 400 nm to 780 nm. The absorption of this energy absorber is the result of plasmonic resonance effects. Electrons associated with the atoms of the energy absorber may be collectively excited by radiation, which results in collective oscillation of the electrons. The wavelengths that can excite and oscillate these electrons collectively are

dependent on the number of electrons present in the energy absorber particles, which in turn is dependent on the size of the energy absorber particles. The amount of energy that can collectively oscillate the particle’s electrons is low enough that very small particles (e.g., 1 -100 nm) may absorb radiation with wavelengths several times (e.g., from 8 to 800 or more times) the size of the particles. The use of these particles allows the primer fusing agent to be inkjet jettable as well as electromagnetically selective (e.g., having absorption at wavelengths ranging from 800 nm to 4000 nm and transparency at wavelengths ranging from 400 nm to 780 nm).

[0103] In an example, the energy absorber of the primer fusing agent has an average particle diameter (e.g., volume-weighted mean diameter) ranging from greater than 0 nm to less than 220 nm. In another example, the energy absorber has an average particle diameter ranging from greater than 0 nm to 120 nm. In a still another example, the energy absorber has an average particle diameter ranging from about 10 nm to about 200 nm.

[0104] In an example, the energy absorber of the primer fusing agent is an inorganic pigment. Examples of suitable inorganic pigments include lanthanum hexaboride (LaB ₆ ), tungsten bronzes (A _x W0 ₃ ), indium tin oxide (ln ₂ 0 ₃ :Sn0 ₂ , ITO), antimony tin oxide (Sb ₂ 0 ₃ :Sn0 ₂ , ATO), titanium nitride (TiN), aluminum zinc oxide (AZO), ruthenium oxide (Ru0 ₂ ), silver (Ag), gold (Au), platinum (Pt), iron pyroxenes (A _x Fe _y Si ₂ 0 ₆ wherein A is Ca or Mg, x = 1.5-1.9, and y = 0.1 -0.5), modified iron phosphates (A _x Fe _y P0 ₄ ), modified copper phosphates (A _x Cu _y PO _z ), and modified copper pyrophosphates (A _x Cu _y P ₂ 0 ₇ ). Tungsten bronzes may be alkali doped tungsten oxides. Examples of suitable alkali dopants (i.e. , A in A _x W0 ₃ ) may be cesium, sodium, potassium, or rubidium. In an example, the alkali doped tungsten oxide may be doped in an amount ranging from greater than 0 mol% to about 0.33 mol% based on the total mol% of the alkali doped tungsten oxide. Suitable modified iron phosphates (A _x Fe _y PO) may include copper iron phosphate (A = Cu, x = 0.1 -0.5, and y = 0.5-0.9), magnesium iron phosphate (A = Mg, x = 0.1 -0.5, and y = 0.5-0.9), and zinc iron phosphate (A = Zn, x = 0.1 -0.5, and y = 0.5-0.9). For the modified iron phosphates, it is to be understood that the number of phosphates may change based on the charge balance with the cations. Suitable modified copper pyrophosphates (A _x Cu _y P ₂ 0 ₇ ) include iron copper pyrophosphate (A = Fe, x = 0-2, and y = 0-2), magnesium copper pyrophosphate (A = Mg, x = 0-2, and y = 0- 2), and zinc copper pyrophosphate (A = Zn, x = 0-2, and y = 0-2). Combinations of the inorganic pigments may also be used.

[0105] The amount of the energy absorber that is present in the primer fusing agent ranges from greater than 0 wt% to about 40 wt% based on the total weight of the primer fusing agent. In other examples, the amount of the energy absorber in the primer fusing agent ranges from about 0.3 wt% to 30 wt%, from about 1 wt% to about 20 wt%, from about 1.0 wt% up to about 10.0 wt%, or from greater than 4.0 wt% up to about 15.0 wt%. It is believed that these energy absorber loadings provide a balance between the primer fusing agent having jetting reliability and heat and/or radiation absorbance efficiency.

[0106] The energy absorber of the primer fusing agent may, in some instances, be dispersed with a dispersant. As such, the dispersant helps to uniformly distribute the energy absorber throughout the primer fusing agent. Examples of suitable dispersants include polymer or small molecule dispersants, charged groups attached to the energy absorber surface, or other suitable dispersants. Some specific examples of suitable dispersants include a water-soluble acrylic acid polymer (e.g., CARBOSPERSE® K7028 available from Lubrizol), water-soluble styrene-acrylic acid copolymers/resins (e.g., JONCRYL® 296, JONCRYL® 671 , JONCRYL® 678, JONCRYL® 680, JONCRYL® 683, JONCRYL® 690, etc.

available from BASF Corp.), a high molecular weight block copolymer with pigment affinic groups (e.g., DISPERBYK®-190 available BYK Additives and Instruments), or water-soluble styrene-maleic anhydride copolymers/resins.

[0107] Whether a single dispersant is used or a combination of dispersants is used, the total amount of dispersant(s) in the primer fusing agent may range from about 10 wt% to about 200 wt% based on the weight of the energy absorber in the primer fusing agent.

[0108] A silane coupling agent may also be added to the primer fusing agent to help bond the organic and inorganic materials. Examples of suitable silane coupling agents include the SILQUEST® A series manufactured by Momentive.

[0109] Whether a single silane coupling agent is used or a combination of silane coupling agents is used, the total amount of silane coupling agent(s) in the primer fusing agent may range from about 0.1 wt% to about 50 wt% based on the weight of the energy absorber in the primer fusing agent. In an example, the total amount of silane coupling agent(s) in the primer fusing agent ranges from about 1 wt% to about 30 wt% based on the weight of the energy absorber. In another example, the total amount of silane coupling agent(s) in the primer fusing agent ranges from about 2.5 wt% to about 25 wt% based on the weight of the energy absorber. [0110] One example of the primer fusing agent includes cesium tungsten oxide (CTO, also referred to as CWO) nanoparticles as the energy absorber. The CTO nanoparticles have a formula of Cs _x W0 ₃ , where 0<x<1. The cesium tungsten oxide nanoparticles may give the primer fusing agent a light blue color. The strength of the color may depend, at least in part, on the amount of the CTO nanoparticles in the primer fusing agent. When it is desirable to form an outer white layer on the 3D object, less of the CTO nanoparticles may be used in the primer fusing agent in order to achieve the white color. In an example, the CTO nanoparticles may be present in the primer fusing agent in an amount ranging from about 1 wt% to about 20 wt% (based on the total weight of the primer fusing agent).

[0111 ] The average particle size (e.g., volume-weighted mean diameter) of the CTO nanoparticles may range from about 1 nm to about 40 nm. In some examples, the average particle size of the CTO nanoparticles may range from about 1 nm to about 15 nm or from about 1 nm to about 10 nm. The upper end of the particle size range (e.g., from about 30 nm to about 40 nm) may be less desirable, as these particles may be more difficult to stabilize.

[0112] This example of the primer fusing agent may also include a zwitterionic stabilizer. The zwitterionic stabilizer may improve the stabilization of this example of the primer fusing agent. While the zwitterionic stabilizer has an overall neutral charge, at least one area of the molecule has a positive charge (e.g., amino groups) and at least one other area of the molecule has a negative charge. The CTO nanoparticles may have a slight negative charge. The zwitterionic stabilizer molecules may orient around the slightly negative CTO nanoparticles with the positive area of the zwitterionic stabilizer molecules closest to the CTO

nanoparticles and the negative area of the zwitterionic stabilizer molecules furthest away from the CTO nanoparticles. Then, the negative charge of the negative area of the zwitterionic stabilizer molecules may repel CTO nanoparticles from each other. The zwitterionic stabilizer molecules may form a protective layer around the CTO nanoparticles, and prevent them from coming into direct contact with each other and/or increase the distance between the particle surfaces (e.g., by a distance ranging from about 1 nm to about 2 nm). Thus, the zwitterionic stabilizer may prevent the CTO nanoparticles from agglomerating and/or settling in the primer fusing agent.

[0113] Examples of suitable zwitterionic stabilizers include C ₂ to C ₈ betaines, C ₂ to C ₈ aminocarboxylic acids having a solubility of at least 10 g in 100 g of water, taurine, and combinations thereof. Examples of the C ₂ to C ₈ aminocarboxylic acids include beta-alanine, gamma-aminobutyric acid, glycine, and combinations thereof.

[0114] The zwitterionic stabilizer may be present in the primer fusing agent in an amount ranging from about 2 wt% to about 35 wt% (based on the total weight of the primer fusing agent). When the zwitterionic stabilizer is the C ₂ to C ₈ betaine, the C ₂ to C ₈ betaine may be present in an amount ranging from about 8 wt% to about 35 wt% of the total weight of the primer fusing agent. When the zwitterionic stabilizer is the C ₂ to C ₈ aminocarboxylic acid, the C ₂ to C ₈ aminocarboxylic acid may be present in an amount ranging from about 2 wt% to about 20 wt% of the total weight of the primer fusing agent. When the zwitterionic stabilizer is taurine, taurine may be present in an amount ranging from about 2 wt% to about 35 wt% of the total weight of the primer fusing agent.

[0115] In this example, the weight ratio of the CTO nanoparticles to the zwitterionic stabilizer may range from 1 : 10 to 10: 1 ; or the weight ratio of the CTO nanoparticles to the zwitterionic stabilizer may be 1 :1.

[0116] Fusing Agent Vehicles

[0117] As used herein,“FA vehicle” may refer to the liquid in which the energy absorber is dispersed or dissolved to form the fusing agent (e.g., the core fusing agent or the primer fusing agent). A wide variety of FA vehicles, including aqueous and non-aqueous vehicles, may be used in the fusing agent. In some examples, the FA vehicle may include water alone or a non-aqueous solvent alone with no other components. In other examples, the FA vehicle may include other

components, depending, in part, upon the applicator that is to be used to dispense the fusing agent. Examples of other suitable fusing agent components include co- solvent(s), humectant(s), surfactant(s), antimicrobial agent(s), anti-kogation agent(s), and/or chelating agent(s).

[0118] The solvent of the fusing agent may be water or a non-aqueous solvent (e.g., ethanol, acetone, n-methyl pyrrolidone, aliphatic hydrocarbons, etc.). In some examples, the fusing agent consists of the energy absorber and the solvent (without other components). In these examples, the solvent makes up the balance of the fusing agent.

[0119] The co-solvent(s) that may be used in the fusing agent include any of the co-solvents listed above in reference to the penetrating agent. The co-solvent(s) may be present in the fusing agent in a total amount ranging from about 1 wt% to about 50 wt% based upon the total weight of the fusing agent, depending upon the jetting architecture of the applicator. In an example, the total amount of the co- solvents) present in the fusing agent is 25 wt% based on the total weight of the fusing agent.

[0120] Similar to the penetrating agent, the co-solvent(s) of the fusing agent may depend, in part, upon the jetting technology that is to be used to dispense the fusing agent. For example, if thermal inkjet printheads are to be used, water and/or ethanol and/or other longer chain alcohols (e.g., pentanol) may be the solvent (i.e., makes up 35 wt% or more of the fusing agent) or co-solvents. For another example, if piezoelectric inkjet printheads are to be used, water may make up from about 25 wt% to about 30 wt% of the fusing agent, and the solvent (i.e., 35 wt% or more of the fusing agent) may be ethanol, isopropanol, acetone, etc. The co- solvents) of the fusing agent may also depend, in part, upon the build material composition that is being used with the fusing agent. For a hydrophobic powder (such as the polyamides disclosed herein), the FA vehicle may include a higher solvent content in order to improve the flow of the fusing agent into the build material composition.

[0121 ] The FA vehicle may also include humectant(s). In an example, the total amount of the humectant(s) present in the fusing agent ranges from about 3 wt% to about 10 wt%, based on the total weight of the fusing agent. An example of a suitable humectant is the ethoxylated glycerin described above in reference to the penetrating agent. Other examples of suitable humectants include glycerin, propylene glycol, and a polyethylene glycol (PEG) with a molecular weight of about 1000 M _n or less.

[0122] In some examples, the FA vehicle includes surfactant(s) to improve the jettability of the fusing agent. Examples of suitable surfactants include a self- emulsifiable, non-ionic wetting agent based on acetylenic diol chemistry (e.g., SURFYNOL® SEF from Air Products and Chemicals, Inc.), a non-ionic

fluorosurfactant (e.g., CAPSTONE® fluorosurfactants, such as CAPSTONE® FS- 35, from Chemours), and combinations thereof. In other examples, the surfactant is an ethoxylated low-foam wetting agent (e.g., SURFYNOL® 440 or SURFYNOL® CT-111 from Air Products and Chemical Inc.) or an ethoxylated wetting agent and molecular defoamer (e.g., SURFYNOL® 420 from Air Products and Chemical Inc.). Still other suitable surfactants include non-ionic wetting agents and molecular defoamers (e.g., SURFYNOL® 104E from Air Products and Chemical Inc.) or water-soluble, non-ionic surfactants (e.g., TERGITOL™ TMN-6, TERGITOL™ 15- S-7, or TERGITOL™ 15-S-9 (a secondary alcohol ethoxylate) from The Dow Chemical Company or TEGO® Wet 510 (polyether siloxane) available from Evonik Industries).

[0123] Whether a single surfactant is used or a combination of surfactants is used, the total amount of surfactant(s) in the fusing agent may range from about 0.01 wt% to about 10 wt% based on the total weight of the fusing agent. In an example, the total amount of surfactant(s) in the fusing agent may be about 3 wt% based on the total weight of the fusing agent.

[0124] In some examples, the FA vehicle may also include anti-kogation agent(s), antimicrobial agent(s), and/or chelating agent(s) (each of which is described above in reference to the penetrating agent). [0125] Coloring Agents

[0126] In the examples of the 3D printing kit, the 3D printing composition, the 3D printing methods, and the 3D printing system disclosed herein, a coloring agent may be used. The coloring agent may include a colorant (as the active material), a co-solvent, and a balance of water. In some examples, the coloring agent consists of these components, and no other components. In some other examples, the coloring agent may further include a binder (e.g., an acrylic latex binder, which may be a copolymer of any two or more of styrene, acrylic acid, methacrylic acid, methyl methacrylate, ethyl methacrylate, and butyl methacrylate) and/or a buffer. In still other examples, the coloring agent may further include additional components, such as dispersant(s), humectant(s), surfactant(s) (each of which is described above in reference to the fusing agent). In yet other examples, the coloring agent may further include additional components, such as, anti-kogation agent(s), antimicrobial agent(s), and/or chelating agent(s) (each of which is described above in reference to the penetrating agent).

[0127] The coloring agent may be a black agent, a cyan agent, a magenta agent, or a yellow agent. As such, the colorant may be a black colorant, a cyan colorant, a magenta colorant, a yellow colorant, or a combination of colorants that together achieve a black, cyan, magenta, or yellow color.

[0128] In some instances, the colorant of the coloring agent may be transparent to infrared wavelengths. In other instances, the colorant of the coloring agent may not be completely transparent to infrared wavelengths, but does not absorb enough radiation to sufficiently heat the build material composition in contact therewith. In an example, the colorant absorbs less than 10% of radiation having wavelengths in a range of 650 nm to 2500 nm. In another example, the colorant absorbs less than 20% of radiation having wavelengths in a range of 650 nm to 4000 nm.

[0129] The colorant of the coloring agent is also capable of absorbing radiation with wavelengths of 650 nm or less. As such, the colorant absorbs at least some wavelengths within the visible spectrum, but absorbs little or no wavelengths within the near-infrared spectrum. This is in contrast to at least some examples of the energy absorber in the fusing agent, which absorbs wavelengths within the near- infrared spectrum and/or the infrared spectrum (e.g., the fusing agent absorbs 80% or more of radiation with wavelengths within the near-infrared spectrum and/or the infrared spectrum). As such, the colorant in the coloring agent will not substantially absorb the fusing radiation, and thus will not initiate coalescing/fusing of the build material composition in contact therewith when the build material composition is exposed to the fusing radiation.

[0130] Examples of IR transparent colorants include acid yellow 23 (AY 23), AY17, acid red 52 (AR 52), AR 289, and reactive red 180 (RR 180). Examples of colorants that absorb some visible wavelengths and some IR wavelengths include cyan colorants, such as direct blue 199 (DB 199) and pigment blue 15:3 (PB 15:3).

[0131 ] In other examples, the colorant may be any azo dye having sodium or potassium counter ion(s) or any diazo (i.e. , double azo) dye having sodium or potassium counter ion(s).

[0132] Examples of black dyes may include tetrasodium (6Z)-4-acetamido-5- oxo-6-[[7-sulfonato-4-(4-sulfonatophenyl)azo-1 -naphthyl]hydrazono]naphthalene- 1 , 7-disulfonate with a chemical structure of:

(commercially available as

Food Black 1 ); tetrasodium 6-amino-4-hydroxy-3-[[7-sulfonato-4-[(4- sulfonatophenyl)azo]-1 -naphthyl]azo]naphthalene-2, 7-disulfonate with a chemical structure of: (commercially available as Food Black 2); tetrasodium (6E)-4-amino-5-oxo-3-[[4-(2- sulfonatooxyethylsulfonyl)phenyl]diazenyl]-6-[[4-(2- sulfonatooxyethylsulfonyl)phenyl]hydrazinylidene]naphthalene -2, 7-disulfonate with a chemical structure of:

(commercially available as Reactive Black 31 ); tetrasodium (6E)-4-amino-5-oxo-3-[[4-(2- sulfonatooxyethylsulfonyl)phenyl]diazenyl]-6-[[4-(2- sulfonatooxyethylsulfonyl)phenyl]hydrazinylidene]naphthalene -2, 7-disulfonate with a chemical structure of: combinations thereof. Some other commercially available examples of black dyes include multipurpose black azo-dye based liquids, such as PRO-JET® Fast Black 1 (made available by Fujifilm Holdings), and black azo-dye based liquids with enhanced water fastness, such as PRO-JET® Fast Black 2 (made available by Fujifilm Holdings).

[0133] Examples of cyan dyes include ethyl-[4-[[4-[ethyl-[(3-sulfophenyl) methyl] amino] phenyl]-(2-sulfophenyl) ethylidene]-1 -cyclohexa-2,5-dienylidene]-[(3- sulfophenyl) methyl] azanium with a chemical structure of:

(commercially available as Acid Blue 9, where the counter ion may alternatively be sodium counter ions or potassium counter ions); sodium 4-[(E)-{4- [benzyl(ethyl)amino]phenyl}{(4E)-4-[benzyl(ethyl)iminio]cycl ohexa-2,5-dien-1 - ylidene}methyl]benzene-1 ,3-disulfonate with a chemical structure of:

(commercially available as Acid Blue 7); and a phthalocyanine with a chemical structure of:

(commercially available as Direct Blue 199); and combinations thereof.

[0134] An example of the pigment based coloring agent may include from about 1 wt% to about 10 wt% of pigment(s), from about 10 wt% to about 30 wt% of co- solvents), from about 1 wt% to about 10 wt% of dispersant(s), from about 0.1 wt% to about 5 wt% of binder(s), from 0.01 wt% to about 1 wt% of anti-kogation agent(s), from about 0.05 wt% to about 0.1 wt% antimicrobial agent(s), and a balance of water (based upon the total weight of the coloring agent). An example of the dye based coloring agent may include from about 1 wt% to about 7 wt% of dye(s), from about 10 wt% to about 30 wt% of co-solvent(s), from about 1 wt% to about 7 wt% of dispersant(s), from about 0.05 wt% to about 0.1 wt% antimicrobial agent(s), from 0.05 wt% to about 0.1 wt% of chelating agent(s), from about 0.005 wt% to about 0.2 wt% of buffer(s), and a balance of water (based upon the total weight of the coloring agent).

[0135] Some examples of the coloring agent include a set of cyan, magenta, and yellow agents, such as C1893A (cyan), C1984A (magenta), and C1985A (yellow); or C4801A (cyan), C4802A (magenta), and C4803A (yellow); all of which are available from HP Inc. Other commercially available coloring agents include C9384A (printhead HP 72), C9383A (printhead HP 72), C4901A (printhead HP 940), and C4900A (printhead HP 940).

[0136] Property-Imparting Liquid Functional Agents

[0137] In the examples of the 3D printing kit, the 3D printing composition, the 3D printing methods, and the 3D printing system disclosed herein a property- imparting liquid functional agent may be used. The property-imparting liquid functional agent may include any material (as the active material) that will introduce the property to the build material composition to which the active material is applied and/or will enhance that property in the build material composition to which the active material is applied. The property-imparting liquid functional agent may also include a co-solvent, and a balance of water. In some examples, the property- imparting liquid functional agent consists of these components, and no other components. In some other examples, the property-imparting liquid functional agent may further include additional components, such as dispersant(s), humectant(s), surfactant(s) (each of which is described above in reference to the fusing agent). In still other examples, the property-imparting liquid functional agent may further include additional components, such as, anti-kogation agent(s), antimicrobial agent(s), and/or chelating agent(s) (each of which is described above in reference to the penetrating agent). [0138] Examples of electronic property imparting materials include conductive materials, semi-conductive materials, and insulating materials.

[0139] Examples of the conductive material include transition metal (e.g., silver, copper, gold, platinum, palladium, chromium, nickel, zinc, tungsten, etc.)

nanomaterials (e.g., nanoparticles, nanorods, nanowires, nanotubes, nanosheets, etc.), conductive oxides (e.g., indium tin oxide, antimony oxide, zinc oxide, etc.), conducting polymers (e.g., poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOTPSS), polyacetylene, polythiophenes, any other conjugated polymer, etc.), carbonaceous nanomaterials (e.g., graphene (single or multi-layer), carbon- nanotubes (CNTs, single or multi-walled), graphene nanoribbons, fullerenes, etc.), and reactive metal systems.

[0140] Examples of the semi-conductive material that may be used in the property-imparting liquid functional agent include semi-conducting nanomaterials (nanoparticles, nanorods, nanowires, nanotubes, nanosheets, etc.), semi- conducting metal oxides (e.g., tin oxide, antimony oxide, indium oxide, etc.), semi- conducting polymers (e.g., PEDOTPSS, polythiophenes, poly(p-phenylene sulfide), polyanilines, poly(pyrrole)s, poly(acetylene)s, poly(p-phenylene vinylene), polyparaphenylene, and any other conjugated polymer, etc.), and semi-conducting small molecules (i.e. , having a molecular mass less than 5,000 Daltons, e.g., rubrene, pentacene, anthracene, aromatic hydrocarbons, etc.). The previously described fullerenes, conducting or semi-conducting metal oxides, and conducting or semi-conducting polymers may be semi-conductive, in that they have a finite conductivity. However, this conductivity may often be sufficient for conductive applications. The material may be considered conductive or semi-conductive depending upon the geometry and/or in what combination with other electronic components it is utilized.

[0141 ] Examples of the insulating (dielectric) material that may be used include insulating nanomaterials (nanoparticles, nanorods, nanowires, nanotubes, nanosheets, etc.), colloids, or sol-gel precursors, such as hexagonal boron nitride, metal and semiconducting oxides, metal and semiconducting nitrides, metal oxide sol-gel precursors (e.g., metal alkoxides, metal chlorides, etc.), silicon sol-gel precursors (silicates), or solid electrolytes. Other examples of the insulating material include insulating polymers (e.g., polylactic acid, fluoropolymers, polycarbonate, acrylics, polystyrene, SU-8, ete.) and insulating small molecules (i.e. , having a molecular mass less than 5,000 Daltons, e.g., benzocyclobutane, paraffins, organic dyes, etc.).

[0142] Examples of mechanical property imparting materials include any material that can alter the ductility of the 3D object, e.g., by increasing elongation at break, toughness, resilience, elongation at yield, or elongation at maximum stress in tension, compression, shear, or torsion. Examples of mechanical property imparting materials that may alter ductility (e.g., by increasing flexibility) include miscible solids selected from the group consisting of 2-methyl-benzene

sulfonamide, a mixture of 4-methyl-benzene and 2-methyl-benzene sulfonamide, N-butylbenzenesulfonamide (BBSA), N-ethylbenzenesulfonamide (EBSA), N- propylbenzenesulfonamide (PBSA), N-butyl-N-dodecylbenzenesulfonamide

(BDBSA), N,N-dimethylbenzenesulfonamide (DMBSA), p- methylbenzenesulfonamide, o/p-toluene sulfonamide, p-toluene sulfonamide, 2- ethylhexyl-4-hydroxybenzoate, hexadecyl-4-hydroxybenzoate, 1 -butyl-4- hydroxybenzoate, dioctyl phthalate, diisodecyl phthalate, di-(2-ethylhexyl) adipate, tri-(2-ethylhexyl) phosphate, and combinations thereof. Other examples of mechanical property imparting materials include any material that can alter the mechanical strength of the 3D object, e.g., by increasing the rigidity. Examples of mechanical property imparting materials that may alter mechanical strength, e.g., by increasing rigidity, include metal oxides (e.g., ZnO, Fe ₃ 0 ₄ , T1O2, Zr0 ₂ , M0O ₃ , WO ₃ , etc.), graphene, carbon nanotubes, silicon, etc. The mechanical property imparting materials (e.g., metal oxides, carbon, silicon, etc.) may be in the form of nanofibers, nanorods, or nanowires.

[0143] The amount of the active material present in the property-imparting liquid functional agent may range from greater than 0 wt% to about 75 wt% based on the total weight of the property-imparting liquid functional agent. In other examples, the amount of the active material in the property-imparting liquid functional agent ranges from about 10 wt% to 40 wt%, from about 0.3 wt% to 30 wt%, from about 1 wt% to about 20 wt%, from about 1.0 wt% up to about 10.0 wt%, or from greater than 4.0 wt% up to about 15.0 wt%. It is believed that these active material loadings provide a balance between the property-imparting liquid functional agent having jetting reliability and property-imparting efficiency.

[0144] In an example, the property-imparting liquid functional agent may include from about 1 wt% to about 50 wt% of co-solvent(s), from about 3 wt% to about 10 wt% of humectant(s), from about 0.01 wt% to about 10 wt% of surfactant(s), from about 1 wt% to about 10 wt% of dispersant(s), from about 0.2 wt% to about 1 wt% of anti-kogation agent(s), from about 0.05 wt% to about 1 wt% antimicrobial agent(s), from about 0.01 wt% to about 2 wt% of chelating agent(s), and a balance of water (based upon the total weight of the property-imparting liquid functional agent).

[0145] Printing Methods and Methods of Use

[0146] Referring now to Fig. 1 , an example of a method 100 for 3D printing is depicted. The examples of the method 100 may use examples of the 3D printing kit and/or composition disclosed herein. Additionally, the examples of the method 100 may be used to print 3D objects that exhibit a white color, a cyan color, a magenta color, a yellow color, a black color, an electronic property, a mechanical property, or a combination thereof.

[0147] As shown in Fig. 1 , the method 100 for using the three-dimensional (3D) printing kit comprises: applying a build material composition to form a build material layer, the build material composition having a surface energy density ranging from about 0.02 J/m ² to about 0.046 J/m ² and including a polymer (reference numeral 102); based on a 3D object model, selectively applying a plurality of agents on at least a portion of the build material layer, the plurality of agents including a liquid functional agent and a penetrating agent, the penetrating agent having a surface tension ranging from about 19 dynes/cm to about 29 dynes/cm and including: a surfactant blend including: a first non-ionic surfactant having a first hydrophilic chain length; a second non-ionic surfactant, wherein the second non-ionic surfactant is selected from the group consisting of a polyether siloxane and an alkoxylated alcohol; and an anionic surfactant; a co-solvent; a humectant present in an amount ranging from about 2 wt% to about 10 wt%, based on a total weight of the penetrating agent; and a balance of water (reference numeral 104); and based on the 3D object model, forming a 3D object layer from the at least the portion of the build material layer.

[0148] In an example of the method 100, the selectively applying of the plurality of agents is accomplished in a single printing pass. In another example of the method 100, the selectively applying of the plurality of agents is accomplished at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition to about 90 ng/600 ^th of an inch ² of the build material composition. In still another example of the method 100, the selectively applying of the plurality of agents is accomplished at a fluid density ranging from about 45 ng/600 ^th of an inch ² of the build material composition to about 90 ng/600 ^th of an inch ² of the build material composition. In yet another example of the method 100, the selectively applying of the plurality of agents is accomplished at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition to about 144 ng/600 ^th of an inch ² of the build material composition. In yet another example of the method 100, the selectively applying of the plurality of agents is accomplished at a fluid density ranging from about 45 ng/600 ^th of an inch ² of the build material composition to about 144 ng/600 ^th of an inch ² of the build material composition.

[0149] In some examples of the method 100, the liquid functional agent is a coloring agent; the 3D object layer formed is a colored layer having a colorant of the coloring agent embedded therein; and the method 100 further comprises:

applying a sacrificial build material layer on the colored layer; and based on the 3D object model, selectively applying the penetrating agent and the coloring agent on at least a portion of the sacrificial build material layer. [0150] In some other examples of the method 100, the liquid functional agent is a fusing agent; and the forming of the 3D object layer involves exposing the build material layer to electromagnetic radiation to coalesce the build material composition in the at least the portion.

[0151 ] The method 100 may be used to form an object 44 as shown in Fig. 3, which includes several core layers 46, 46’, 46” and an outer white layer 48 (also referred to herein as a primer layer). The core layers 46, 46’, 46” are sequentially formed by selectively patterning respective build material layers with the core fusing agent 28 and exposing each patterned layer to electromagnetic radiation. The core layers 46, 46’, 46” may be black or a dark color due to the absorber in the core fusing agent 28. The outer white layer 48 is formed by applying a build material layer on the outermost core layer 46”, patterning it with the primer fusing agent 26, 26’, and exposing it to electromagnetic radiation. Since the primer fusing agent 26, 26’ has no or low tint, the white color of the polymer is visible, and thus gives the outer white layer 48 its white appearance. The outer white layer 48 provides the object 44 with a white (or slightly tinted) exterior surface. As such, the outer white layer 48 optically isolates the black core layer(s) 46, 46’, 46” that it covers.

[0152] In the example object 44 shown in Fig. 3, the outer white layer 48 does not completely surround the object 44, but rather may be formed on the outer surface(s) of the core layer 46” that will be visible. For example, in Fig. 3, the surface 50 of the object 44 may not be visible when the object 44 is in use, and thus it may not be desirable to form the outer white layer 48 on this surface 50.

[0153] It is to be understood that the method 100 may include additional processing to form the object 44 with an outer colored layer (not shown in Fig. 3) on at least a portion of the outer white layer 48, or to form another object 44’

(shown in Fig. 4H) which has the core layer(s) 46 completely encapsulated by a primer layer (including primer layer portions 48’, 48”, 48”’, which are referred to herein respectively as primer layers 48, 48’, 48”) and an outer colored layer (including colored layer portions 52, 52’, 52”, which are referred to herein as colored layers 52, 52’, 52”).

[0154] One specific example of the method 100 (i.e. , the method 200) is shown in Fig. 2. As shown in Fig. 2, the method 200 for three-dimensional (3D) printing comprises: based on a 3D object model, selectively applying a core fusing agent on at least a portion of a first layer of a build material composition, the build material composition including a polymer (reference numeral 202); exposing the first layer to electromagnetic radiation to fuse the build material composition in the at least the portion of the first layer to form a core layer (reference numeral 204); applying a second layer of the build material composition on the core layer

(reference numeral 206); based on the 3D object model, selectively applying a primer fusing agent on at least a portion of the second layer (reference numeral 208); exposing the second layer to electromagnetic radiation to fuse the build material composition in the at least the portion of the second layer to form a primer layer (reference numeral 210); applying a third layer of the build material composition on the primer layer (reference numeral 212); based on the 3D object model, selectively applying a plurality of agents on at least a portion of the third layer, the plurality of agents including a penetrating agent, a coloring agent, and (i) the core fusing agent or (ii) the primer fusing agent, wherein the penetrating agent includes a surfactant blend including: a first non-ionic surfactant having a first hydrophilic chain length; a second non-ionic surfactant, wherein the second non- ionic surfactant is selected from the group consisting of a polyether siloxane and an alkoxylated alcohol; and an anionic surfactant; and a liquid vehicle including a humectant present in an amount ranging from about 2 wt% to about 10 wt%, based on a total weight of the penetrating agent (reference numeral 214); and exposing the third layer to electromagnetic radiation to fuse the build material composition in the at least the portion of the third layer to form a colored layer having a colorant of the coloring agent embedded therein (reference numeral 216). [0155] The method 300 to form the object 44’ will now be discussed in reference to Figs. 4A through 4H. It is to be understood that the method 300 may be an example of the method 100 and/or the method 200.

[0156] Prior to execution of any of the methods 100, 200, 300 disclosed herein or as part of the methods 100, 200, 300 a controller 36 (see, e.g., Fig. 7) may access data stored in a data store 34 (see, e.g., Fig. 7) pertaining to a 3D object 44’ that is to be printed. For example, the controller 36 may determine the number of layers of the build material composition 16 that are to be formed, the locations at which the fusing agent(s) 26, 26’, 28 from the applicator(s) 24A, 24B is/are to be deposited on each of the respective layers, etc.

[0157] In Figs. 4A and 4B, a layer 54 of the build material composition 16 is applied on the build area platform 12. As mentioned above, the build material composition 16 includes at least the polymer, and may additionally include the glass, the filler, the antioxidant, the whitener, the antistatic agent, the flow aid, or combinations thereof. As also mentioned above, in some examples, the build material composition 16 has a surface energy density ranging from about 0.02 J/m ² to about 0.046 J/m ² .

[0158] In the example shown in Figs. 4A and 4B, a printing system (e.g., the printing system 10 shown in Fig. 7) may be used to apply the build material composition 16. The printing system 10 may include a build area platform 12, a build material supply 14 containing the build material composition 16, and a build material distributor 18.

[0159] The build area platform 12 receives the build material composition 16 from the build material supply 14. The build area platform 12 may be moved in the directions as denoted by the arrow 20 (see Fig. 7), e.g., along the z-axis, so that the build material composition 16 may be delivered to the build area platform 12 or to a previously formed layer. In an example, when the build material composition 16 is to be delivered, the build area platform 12 may be programmed to advance (e.g., downward) enough so that the build material distributor 18 can push the build material composition 16 onto the build area platform 12 to form a substantially uniform layer of the build material composition 16 thereon. The build area platform 12 may also be returned to its original position, for example, when a new part is to be built.

[0160] The build material supply 14 may be a container, bed, or other surface that is to position the build material composition 16 between the build material distributor 18 and the build area platform 12. In some examples, the methods 100, 200, 300 further include heating the build material composition 16 in the build material supply 14 to a supply temperature. In these examples, the supply temperature may depend, in part, on the build material composition 16 used and/or the 3D printer used. For example, the supply temperature may range from about 25°C to about 175°C when the crystalline or semi-crystalline polymer is used. For another example, the supply temperature may range from about 40°C to about 100°C when the thermoplastic elastomer is used. In these examples, the supply temperature may depend, in part, on the build material composition 16 used and/or the 3D printer used. As such, it is to be understood that higher or lower

temperatures may be used. The heating of the build material composition 16 in the build material supply 14 may be accomplished by heating the build material supply 14 to the supply temperature.

[0161 ] The build material distributor 18 may be moved in the directions as denoted by the arrow 22 (see Fig. 7), e.g., along the y-axis, over the build material supply 14 and across the build area platform 12 to spread the layer 54 of the build material composition 16 over the build area platform 12. The build material distributor 18 may also be returned to a position adjacent to the build material supply 14 following the spreading of the build material composition 16. The build material distributor 18 may be a blade (e.g., a doctor blade), a roller, a combination of a roller and a blade, and/or any other device capable of spreading the build material composition 16 over the build area platform 12. For instance, the build material distributor 18 may be a counter-rotating roller. In some examples, the build material supply 14 or a portion of the build material supply 14 may translate along with the build material distributor 18 such that build material composition 16 is delivered continuously to the material distributor 18 rather than being supplied from a single location at the side of the printing system 10 as depicted in Fig. 4A.

[0162] In Fig. 4A, the build material supply 14 may supply the build material composition 16 into a position so that it is ready to be spread onto the build area platform 12. The build material distributor 18 may spread the supplied build material composition 16 onto the build area platform 12. The controller 34 may process“control build material supply” data, and in response, control the build material supply 14 to appropriately position the particles of the build material composition 16, and may process“control spreader” data, and in response, control the build material distributor 18 to spread the supplied build material composition 16 over the build area platform 12 to form the layer 54 of build material composition 16 thereon. As shown in Fig. 4B, one build material layer 54 has been formed.

[0163] The layer 54 of the build material composition 16 has a substantially uniform thickness across the build area platform 12. In an example, the build material layer 54 has a thickness ranging from about 50 pm to about 120 pm. In another example, the thickness of the build material layer 54 ranges from about 30 pm to about 300 pm. It is to be understood that thinner or thicker layers may also be used. For example, the thickness of the build material layer 54 may range from about 20 pm to about 500 pm. The layer thickness may be about 2x (i.e. , 2 times) the average diameter of the build material composition particles at a minimum for finer part definition. In some examples, the layer thickness may be about 1 2x the average diameter of the build material composition particles.

[0164] To form the object 44 shown in Fig. 3, this layer 54 of build material composition 16 would be patterned with the core fusing agent 28 (i.e., the core fusing agent 28 would be selectively dispensed on the layer 54 according to a pattern of a cross-section for the core layer 46), and then exposed to

electromagnetic radiation to form the core layer 46. As used herein, the cross- section of the layer of the part to be formed refers to the cross-section that is parallel to the contact surface of the build area platform 12. As an example, if the core layer 46 is to be shaped like a cube or cylinder, the core fusing agent 28 will be deposited in a square pattern or a circular pattern (from a top view),

respectively, on at least a portion of the layer 54 of the build material composition 16.

[0165] In the example shown in Fig. 4B, the layer 54 of build material

composition 16 is a sacrificial layer that is used to enhance the color of the first layer (e.g., colored layer 52) of the object 44’ that is being formed. As shown in Fig. 4B, the coloring agent 30 is selectively applied to at least the portion 56 of the layer 54. As such, the particles of the build material composition 16 in this portion 56 of the layer 54 become colored. In this example, this sacrificial layer 54 is not coalesced/fused (as no primer fusing agent 26, 26’ or core fusing agent 28 is applied thereon). Rather, some of the colored particles of the build material composition 16 in the sacrificial layer 54 may become embedded in

coalesced/fused build material composition of the part layer (e.g., colored layer 52) that is formed thereon. In other words, some of the colored build material composition 16 in portion 56 may become embedded in the surface of the part layer that is formed adjacent thereto. The non-coalesced/non-fused, but

embedded colored build material composition 16 may help to maintain saturation at the surface (of the ultimately formed colored layer 52) by providing a colored interface between the colored layer 52 and surrounding non- coalesced/non-fused build material composition 16.

[0166] It is to be understood that when an agent (e.g., the primer fusing agent 26, 26’, the core fusing agent 28, the coloring agent 30, the penetrating agent 42, etc.) is to be selectively applied to the build material composition 16, the agent 26, 26’, 28, 30, 42 may be dispensed from an applicator 24A, 24B, 24C, 24D. The applicator(s) 24A, 24B, 24C, 24D may each be a thermal inkjet printhead, a piezoelectric printhead, a continuous inkjet printhead, etc., and the selective application of the agent(s) 26, 26’, 28, 30, 42 may be accomplished by thermal inkjet printing, piezo electric inkjet printing, continuous inkjet printing, etc. The controller 36 may process data, and in response, control the applicator(s) 24A,

24B, 24C, 24D (e.g., in the directions indicated by the arrow 32, see Fig. 7) to deposit the agent(s) 26, 26’, 28, 30, 42 onto predetermined portion(s) of the build material composition 16. Throughout the method 300, a single applicator may be labeled with multiple reference numbers (24A, 24B, 24C, and/or 24D), although it is to be understood that the applicators may be separate applicators or a single applicator with several individual cartridges for dispensing the respective agents 26, 26’, 28, 30, 42.

[0167] The coloring agent 30 will penetrate at least partially into the sacrificial layer 54. When it is desirable for the coloring agent 30 to penetrate the entire thickness of the sacrificial layer 54, the penetrating agent 42 may be selectively applied on the portion 56 with the coloring agent 30. As mentioned above, the penetrating agent 42 includes at least the surfactant blend, the co-solvent, the humectant present in an amount ranging from about 2 wt% to about 10 wt% (based on a total weight of the penetrating agent), and water, and may additionally include the antimicrobial agent, the anti-kogation agent, the chelating agent, or

combinations thereof. The penetrating agent 42, when applied with the coloring agent 30, enables the coloring agent 30 to penetrate the entire thickness of the sacrificial layer 54. As such, the colorant of the coloring agent 30 is present throughout the entire thickness of the sacrificial layer 54. In some examples, the coloring agent 30 and the penetrating agent 42 may be applied on the portion 56 in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16.

[0168] In some instances, in addition to the penetrating agent 42, a cooling fluid may be applied, e.g., to maintain the temperature of the build material composition 16 in contact therewith below the melting point of the polymer of the build material composition 16. It is to be understood that the penetrating agent 42 is independent of any cooling fluid that may be applied to the build material composition 16.

[0169] The color of the coloring agent 30 that is applied to the portion(s) 56 of the sacrificial layer 54 will depend upon the desired color for the object 44’ or at least the portion of the colored layer 52 formed adjacent thereto. As examples, a black agent, a cyan agent, a magenta agent, or a yellow agent may be applied alone or in combination to achieve a variety of colors.

[0170] Additionally, while one sacrificial layer 54 is shown, it is to be understood that several sacrificial layers 54 may be sequentially formed in contact with one another.

[0171 ] The layer 58 of the build material composition 16 may be applied in the same manner as the layer 54. The layer 58 is shown in Fig. 4C. The layer 58 may be considered to be the first build material layer because at least a portion of this layer 58 will be coalesced/fused to form the first layer of the 3D object 44’ (since the sacrificial layer 54 is not coalesced/fused).

[0172] After the build material composition 16 has been applied, and prior to further processing, the build material layer 58 may be exposed to heating. Heating may be performed to pre-heat the build material composition 16. In an example, the heating temperature may be below the melting point of the crystalline or semi- crystalline polymer of the build material composition 16. In another example, the heating temperature may be below the lowest temperature in the melting range of the thermoplastic elastomer of the build material composition 16. As such, the temperature selected will depend upon the build material composition 16 that is used.

[0173] As examples, the pre-heating temperature may be from about 5°C to about 50°C below the melting point or the lowest temperature in the melting range of the polymer. In an example, the pre-heating temperature ranges from about 20°C (about room temperature) to about 50°C for the thermoplastic elastomers.

In an example, the pre-heating temperature ranges from about 50°C to about 215°C for the crystalline or semi-crystalline polymers, and from about 50°C to about 125°C for the thermoplastic elastomers. In another example, the pre-heating temperature ranges from about 100°C to about 205°C for the crystalline or semi- crystalline polymers, and from about 80°C to about 125°C for the thermoplastic elastomers. In still another example, the pre-heating temperature ranges from about 100°C to about 190°C for the crystalline or semi-crystalline polymers, and from about 80°C to about 110°C for the thermoplastic elastomers. In yet another example, the methods 100, 200, 300 further include, prior to the selectively applying of the fusing agent 26, 26’, 28, pre-heating the build material composition 16 to a pre-heating temperature ranging from about 5°C to about 50°C below the melting point or the lowest temperature in the melting range of the polymer. The low pre-heating temperature may enable the non-patterned build material composition 16 to be easily removed from the 3D object 44’ after completion of the 3D object 44’. In these examples, the pre-heating temperature may depend, in part, on the build material composition 16 used. As such, the ranges provided are some examples, and higher or lower temperatures may be used.

[0174] Pre-heating the layer 58 of the build material composition 16 may be accomplished by using any suitable heat source that exposes all of the build material composition 16 in the layer 58 to the heat. Examples of the heat source include a thermal heat source (e.g., a heater (not shown) integrated into the build area platform 12 (which may include sidewalls)) or the radiation source 38, 38’

(see, e.g., Fig. 7).

[0175] After the layer 58 is formed, and in some instances is pre-heated, the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied on the same portion(s) 60 of the build material composition 16 in the layer 58.

[0176] As mentioned above, the primer fusing agent 26, 26’ includes an aqueous or non-aqueous vehicle and an energy absorber having absorption at wavelengths ranging from 800 nm to 4000 nm and transparency at wavelengths ranging from 400 nm to 780 nm dispersed therein. The fusing agent 26’ is one specific example of the low tint or primer fusing agent, which includes CTO nanoparticles as the energy absorber, a zwitterionic stabilizer, and an aqueous vehicle. Example compositions of the primer fusing agent 26, 26’ are described above.

[0177] When the desired color for the object 44’ or a particular colored layer 52 of the object 44’ is the color of the coloring agent 30, the primer fusing agent 26, 26’ is applied with the coloring agent 30. Since the primer fusing agent 26, 26’ is clear or slightly tinted, the color of the coloring agent 30 will be the color of the resulting colored layer 52, as the colorants of the coloring agent 30 become embedded throughout the coalesced/fused build material composition of the colored layer 52. The primer fusing agent 26, 26’ may be particularly suitable for obtaining lighter colors or white.

[0178] The penetrating agent 42, when applied with the coloring agent 30, enables the coloring agent 30 to penetrate the entire thickness of the layer 58. Further, the penetrating agent 42, when applied with the primer fusing agent 26,

26’, enables the primer fusing agent 26, 26’ to penetrate the entire thickness of the layer 58. As such, colorant of the coloring agent 30 and/or the energy absorber of the primer fusing agent 26, 26’ is/are present throughout the entire thickness of the layer 58. In some examples, the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 may be applied on the portion 56 in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 144 ng/600 ^th of an inch ² of the build material composition 16.

[0179] The primer fusing agent 26, 26’, the coloring agent 30, and the

penetrating agent 42 are selectively applied in a pattern of a cross-section for the colored layer 52 that is to be formed (shown in Fig. 4D). In the example shown in Fig. 4C, the portion 60 is adjacent to the portion 56 of the layer 54 to which the coloring agent 30 has been applied.

[0180] The volume of the primer fusing agent 26, 26’ that is applied per unit of the build material composition 16 in the patterned portion 60 may be sufficient to absorb and convert enough electromagnetic radiation so that the build material composition 16 in the patterned portion 60 will coalesce/fuse. The volume of the primer fusing agent 26, 26’ that is applied per unit of the build material composition 16 may depend, at least in part, on the energy absorber used, the energy absorber loading in the primer fusing agent 26, 26’, and the build material composition 16 used. [0181 ] After the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied in the specific portion(s) 60 of the layer 58, the entire layer 58 of the build material composition 16 is exposed to

electromagnetic radiation (shown as EMR Exposure between Figs. 4C and 4D).

[0182] The electromagnetic radiation is emitted from the radiation source 38,

38’. The length of time the electromagnetic radiation is applied for, or energy exposure time, may be dependent, for example, on one or more of: characteristics of the radiation source 38, 38’; characteristics of the build material composition 16; and/or characteristics of the primer fusing agent 26, 26’.

[0183] It is to be understood that the exposing of the build material composition 16 to electromagnetic radiation may be accomplished in a single radiation event or in multiple radiation events. In an example, the exposing of the build material composition 16 is accomplished in multiple radiation events. In another example, the exposing of the build material composition 16 to electromagnetic radiation may be accomplished in a number of radiation events ranging from 3 to 8. In still another example, the exposing of the build material composition 16 to

electromagnetic radiation may be accomplished in 3 radiation events. It may be desirable to expose the build material composition 16 to electromagnetic radiation in multiple radiation events to counteract a cooling effect that may be brought on by the amount of the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 that is applied to the build material layer 58. Additionally, it may be desirable to expose the build material composition 16 to electromagnetic radiation in multiple radiation events to sufficiently elevate the temperature of the build material composition 16 in the portion(s) 60, without over heating the build material composition 16 in the non-patterned portion(s).

[0184] The primer fusing agent 26, 26’ enhances the absorption of the radiation, converts the absorbed radiation to thermal energy, and promotes the transfer of the thermal heat to the build material composition 16 in contact therewith. In an example, the primer fusing agent 26, 26’ sufficiently elevates the temperature of the build material composition 16 in the layer 58 to a temperature above the melting point of the polymer or a temperature within or above the melting range of the polymer of the build material composition 16, allowing coalescing/fusing (e.g., thermal merging, melting, binding, etc.) of the build material composition 16 to take place. The application of the electromagnetic radiation forms the colored layer 52, shown in Fig. 4D.

[0185] In some examples of the methods 100, 200, 300, the electromagnetic radiation has a wavelength ranging from 800 nm to 4000 nm. In another example the electromagnetic radiation has a wavelength ranging from 800 nm to 1400 nm.

In still another example, the electromagnetic radiation has a wavelength ranging from 800 nm to 1200 nm. Radiation having wavelengths within the provided ranges may be absorbed (e.g., 80% or more of the applied radiation is absorbed) by the primer fusing agent 26, 26’ and may heat the build material composition 16 in contact therewith, and may not be substantially absorbed (e.g., 25% or less of the applied radiation is absorbed) by the non-patterned build material composition 16.

[0186] It is to be understood that portions of the build material composition 16 that do not have the primer fusing agent 26, 26’ applied thereto do not absorb enough radiation to coalesce/fuse. As such, these portions do not become part of the 3D object 44’ that is ultimately formed. However, the generated thermal energy may propagate into the surrounding build material composition 16 that does not have primer fusing agent 26, 26’ applied thereto. The propagation of thermal energy may be inhibited from coalescing/fusing the non-patterned build material composition 16 in the layer 58, for example, when a cooling fluid is applied to portions of the build material composition 16 in the layer 58 that are not exposed to the primer fusing agent 26, 26’. Moreover, the propagation of thermal energy may be inhibited from coalescing/fusing the portions of the build material composition 16 in the layer 54 when the cooling fluid is applied with the coloring agent 30 in the layer 54. As mentioned above, some of the colored build material composition 16 in the layer 54 may become embedded in the adjacent surface of the

coalesced/fused build material composition of the colored layer 52. [0187] While a single colored layer 52 is shown, it is to be understood that several colored layers 52 may be sequentially formed in contact with one another so that a color region (thicker than one voxel) is built up around the core layer(s) 46 in the final object 44’. The outermost colored layer 52 may form a one voxel deep shell, and the other colored layers may create the thicker color region. The levels of the primer fusing agent 26, 26’ and the coloring agent 30 may be higher in the outermost colored layer 52, compared to other colored layers positioned closer to the core layer(s) 46, in order to increase color saturation at the exterior of the formed object 44’.

[0188] Fig. 4D also illustrates yet another layer 62 of the build material composition 16, this time the layer 62 being applied to the colored layer 52 and to any non-coalesced/non-fused build material composition 16 of layer 58. The layer 62 may be applied in the same manner as the layers 54, 58.

[0189] Prior to further processing, the layer 62 of the build material composition 16 may be exposed to pre-heating in the manner previously described.

[0190] After the layer 62 is formed, and in some instances is pre-heated, the primer fusing agent 26, 26’ is selectively applied on portion(s) 64 of the build material composition 16 in the layer 62. The portion(s) 64 of the layer 62 will form the primer layer 48’, which is white, clear, or slightly tinted from the primer fusing agent 26, 26’. This primer layer 48’ is positioned between the colored layer 52 and subsequently formed black core layer(s) 46 in the object 44’ (see Fig. 4H). This primer layer 48’ may be referred to as the initial layer or the first primer layer. The primer layer 48’ optically isolates at least a portion of the black core layer(s) 46.

[0191 ] When it is desirable for the primer fusing agent 26, 26’ to penetrate the entire thickness of the layer 62, the penetrating agent 42 may be selectively applied on the portion(s) 64 with the primer fusing agent 26, 26’. The penetrating agent 42, when applied with the primer fusing agent 26, 26’, enables the primer fusing agent 26, 26’ to penetrate the entire thickness of the layer 62. As such, the energy absorber of the primer fusing agent 26, 26’ is present throughout the entire thickness of the layer 62. In some examples, the primer fusing agent 26, 26’ and the penetrating agent 42 may be applied on the portion(s) 64 in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16.

[0192] In the example shown in Fig. 4D, the portion 64 to which the primer fusing agent 26, 26’ is selectively applied is adjacent to part (but not all) of the already formed colored layer 52. Selectively applying the primer fusing agent 26, 26’ in this manner may be performed when it is desirable to form colored layer(s)

52’ (shown in Fig. 4E) along the sides of the object 44’ that is being formed. To form the colored layer(s) 52’ along the sides of the object 44’, the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied on other portion(s) 66 of the build material composition 16 in the layer 62. As an example, the portion(s) 66 may define the perimeter of that particular layer of the object 44’ that is being formed, and may be outside of a perimeter or an edge boundary E (i.e. , the outermost portions where the primer fusing agent 26, 26’ alone or the primer fusing agent 26, 26’ and the penetrating agent 42 is/are selectively deposited in any build material layer) of the portion 64.

[0193] When it is desirable to form the colored layer 52’ (shown in Fig. 4E) along the sides of the object 44’ that is being formed, it may also be desirable to selectively deposit the coloring agent 30 with the penetrating agent 42 in portion(s) 68 of the non-patterned build material composition 16 which are adjacent to or surround the portion(s) 66 (which when coalesced/fused, will form the colored layer 52’ along the sides of the object 44’). The colored build material composition 16 in the portion(s) 68 may become embedded in coalesced/fused build material composition of the colored layer 52’. This non-coalesced/non-fused, but

embedded colored build material composition 16 may help to maintain saturation at the surface (of the colored layer 52’) by providing a colored interface between the colored layer 52’ and surrounding non-coalesced/non-fused build material composition 16. [0194] After the primer fusing agent 26, 26’ is applied on the portion(s) 64, and in some instances the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied on the portion(s) 66, the entire layer 62 of the build material composition 16 is exposed to electromagnetic radiation (shown as EMR Exposure between Figs. 4D and 4E) in the manner previously described. Exposure to electromagnetic radiation forms the primer layer 48’, as shown in Fig. 4E.

[0195] If the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied on the portion(s) 66, the EMR exposure will form colored layer(s) 52’ at the outer edge(s). This exposure to electromagnetic radiation forms the colored layer(s) 52’, as shown in Fig. 4E.

[0196] The width of the colored layer(s) 52’ may be large enough to form the color region at this portion of the object 44’. The levels of the primer fusing agent 26, 26’, and the coloring agent 30 may be higher at the outermost edge of the colored layer(s) 52’, compared to the innermost edge(s) of the colored layer(s) 52’, in order to increase color saturation at the exterior of the formed object 44’.

[0197] Fig. 4E also illustrates yet another layer 70 of the build material composition 16, this time the layer 70 being applied to the primer layer 48’, the colored layer(s) 52’, and to any non-coalesced/non-fused build material

composition 16 of layer 62. The layer 70 may be applied in the same manner as the layers 54, 58, 62.

[0198] Prior to further processing, the layer 70 of the build material composition 16 may be exposed to pre-heating in the manner previously described.

[0199] After the layer 70 is formed, and in some instances is pre-heated, the core fusing agent 28 is selectively applied on portion(s) 72 of the build material composition 16 in the layer 70. In one example, the method 200 includes: based on a 3D object model, selectively applying a core fusing agent 28 on at least a portion 72 of a (first) layer 70 of a build material composition 16, the build material composition 16 including a polymer. [0200] As mentioned above, the core fusing agent 28 includes at least an aqueous or non-aqueous vehicle and an active material dispersed or dissolved therein.

[0201 ] When it is desirable for the core fusing agent 28 to penetrate the entire thickness of the layer 70, the penetrating agent 42 may be selectively applied on the portion(s) 72 with the core fusing agent 28. The penetrating agent 42, when applied with the core fusing agent 28, enables the core fusing agent 28 to penetrate the entire thickness of the layer 70. As such, the active material of the core fusing agent 28 is present throughout the entire thickness of the layer 70. In some examples, the core fusing agent 28 and the penetrating agent 42 may be applied on the portion(s) 72 in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16.

[0202] The volume of the core fusing agent 28 that is applied per unit of the build material composition 16 in the patterned portion 72 may be sufficient to absorb and convert enough electromagnetic radiation so that the build material composition 16 in the patterned portion 72 will coalesce/fuse. The volume of the core fusing agent 28 that is applied per unit of the build material composition 16 may depend, at least in part, on the energy absorber used, the energy absorber loading in the core fusing agent 28, and the build material composition 16 used.

[0203] The portion(s) 72 of the layer 70 will form the core layer 46 (Fig. 4F), which may be black from the core fusing agent 28. While a single core layer 46 is shown, it is to be understood that several core layers 46 may be sequentially formed in contact with one another so that a core region (or part core) is built up, which makes up the bulk of the object 44’. Several core layers 46 may enhance the mechanical properties of the object 44’.

[0204] In the example shown in Fig. 4E, the portion 72 to which the core fusing agent 28 is selectively applied is adjacent to part (but not all) of the already formed primer layer 48’. Selectively applying the core fusing agent 28 in this manner may be performed when it is desirable to form colored layer(s) 52’ (shown in Fig. 4F) along the sides of the object 44’ that is being formed. Since the core layer 46 being formed may be black, it may also be desirable to form the primer layer 48” between the core layer 46 and the adjacent colored layer(s) 52’.

[0205] To form the primer layer 48” along the perimeter of the core layer 46, the primer fusing agent 26, 26’ is selectively applied on other (or second) portion(s) 74 of the build material composition 16 in the layer 70 that are immediately adjacent to the perimeter or edge boundary E’ (i.e. , the outermost portions where the core fusing agent 28 alone is selectively deposited in any build material layer) of the portion 72. The perimeter/edge boundary E’ is thus defined by the core fusing agent 28. To form the colored layer(s) 52’ along/adjacent to the perimeter of the primer layer 48”, the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied on still other (or third) portion(s) 76 of the build material composition 16 in the layer 70 that are immediately adjacent to the perimeter or edge boundary E of the portion 74 (which is defined by the primer fusing agent 26, 26’).

[0206] When it is desirable to form the colored layer(s) 52’ (shown in Fig. 4F) along the sides of the object 44’ that is being formed, it may also be desirable to selectively deposit the coloring agent 30 with the penetrating agent 42 in portion(s) 78 of the non-patterned build material composition 16 which are adjacent to or surround the portion(s) 76 (which when coalesced/fused, will form the colored layer 52’ along the sides of the object 44’).

[0207] After the layer 70 is patterned in a desirable manner with at least the core fusing agent 28, the entire layer 70 of the build material composition 16 is exposed to electromagnetic radiation (shown as EMR Exposure between Figs. 4E and 4F) in the manner previously described, except that the wavelength range may be expanded to as low as 400 nm because some of the energy absorbers in the core fusing agent 28 can absorb visible light as well as infrared light. In one example, the method 200 includes: exposing the (first) layer 70 to electromagnetic radiation to fuse the build material composition 16 in the at least the portion 72 of the (first) layer 70 to form a core layer 46. [0208] The core fusing agent 28 enhances the absorption of the radiation in portion 72, converts the absorbed radiation to thermal energy, and promotes the transfer of the thermal heat to the build material composition 16 in contact therewith. In an example, the core fusing agent 28 sufficiently elevates the temperature of the build material composition 16 in portion 72 to a temperature or above the melting point of the polymer or a temperature within or above the melting range of the polymer of the build material composition 16, allowing

coalescing/fusing (e.g., thermal merging, melting, binding, etc.) of the build material composition 16 to take place. Exposure to electromagnetic radiation forms the core layer 46, as shown in Fig. 4F.

[0209] If the primer fusing agent 26, 26’ is selectively applied on the portion(s) 74, and the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied on the portion(s) 76, the EMR exposure will also form primer layer(s) 48” and colored layer(s) 52’ at the outer edge(s) of the core layer 46, as shown in Fig. 4F.

[0210] The width of the primer layer(s) 48” may be large enough to optically isolate the black core layer 46.

[021 1 ] Fig. 4F also illustrates yet another layer 80 of the build material composition 16, this time the layer 80 being applied to the core layer 46, the primer layer(s) 48”, the colored layer(s) 52’, and to any non-coalesced/non-fused build material composition 16 of layer 70. The layer 80 may be applied in the same manner as the layers 54, 58, 62, 70. In one example, the method 200 includes: applying a second layer 80 of the build material composition 16 on the core layer 46.

[0212] Prior to further processing, the layer 80 of the build material composition 16 may be exposed to pre-heating in the manner previously described.

[0213] After the layer 80 is formed, and in some instances is pre-heated, the primer fusing agent 26, 26’ is selectively applied on portion(s) 82 of the build material composition 16 in the layer 80. In one example, the method 200 includes: based on the 3D object model, selectively applying a primer fusing agent 26, 26’ on at least a portion 82 of the second layer 80.

[0214] When it is desirable for the primer fusing agent 26, 26’ to penetrate the entire thickness of the layer 80, the penetrating agent 42 may be selectively applied on the portion(s) 82 with the primer fusing agent 26, 26’. The penetrating agent 42, when applied with the primer fusing agent 26, 26’, enables the primer fusing agent 26, 26’ to penetrate the entire thickness of the layer 80. As such, the energy absorber of the primer fusing agent 26, 26’ is present throughout the entire thickness of the layer 80. In some examples, the primer fusing agent 26, 26’ and the penetrating agent 42 may be applied on the portion(s) 82 in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16.

[0215] The portion(s) 82 of the layer 80 will form another primer layer 48”’, which is white or slightly tinted from the primer fusing agent 26, 26’. This primer layer 48”’ is positioned between the black core layer(s) 46 and subsequently formed colored layer(s) 52” in the object 44’ (see Fig. 4H). As such, the primer layer 48”’ optically isolates the black core layer(s) 46 at another end of the formed object 44’.

[0216] In the example shown in Fig. 4F, the portion 82 to which the primer fusing agent 26, 26’ is selectively applied is adjacent to the already formed core layer(s) 46 and primer layer(s) 48”. Selectively applying the primer fusing agent 26, 26’ in this manner may be performed when it is desirable to form colored layer(s) 52’ (shown in Fig. 4G) along the sides of the object 44’ that is being formed. To form the colored layer(s) 52’ along the sides of the object 44’, the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied on portion(s) 84 of the build material composition 16 in the layer 82. As an example, the portion(s) 84 may define the perimeter of that particular layer of the object 44’ that is being formed, and may be outside of an edge boundary E of the portion 82. [0217] When it is desirable to form the colored layer 52’ (shown in Fig. 4G) along the sides of the object 44’ that is being formed, it may also be desirable to selectively deposit the coloring agent 30 with the penetrating agent 42 in portion(s) 86 of the non-patterned build material composition 16 which are adjacent to or surround the portion(s) 84 (which when coalesced/fused, will form the colored layer 52’ along the sides of the object 44’).

[0218] After the primer fusing agent 26, 26’ is applied on the portion(s) 82, and in some instances the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied on the portion(s) 84, the entire layer 80 of the build material composition 16 is exposed to electromagnetic radiation (shown as EMR Exposure between Figs. 4F and 4G) in the manner previously described. Exposure to electromagnetic radiation forms the primer layer 48”’, as shown in Fig. 4G. In one example, the method 200 includes: exposing the second layer 80 to electromagnetic radiation to fuse the build material composition 16 in the at least the portion 82 of the second layer 80 to form a primer layer 48”’.

[0219] If the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied on the portion(s) 84, the EMR exposure will form colored layer(s) 52’ at the outer edge(s) of the primer layer 48”’. This exposure to electromagnetic radiation forms the colored layer(s) 52’, as shown in Fig. 4G.

[0220] Fig. 4G also illustrates yet another layer 88 of the build material composition 16, this time the layer 88 being applied to the primer layer(s) 48”’ and the colored layer(s) 52’ adjacent thereto, and to any non-coalesced/non-fused build material composition 16 of layer 80. The layer 88 may be applied in the same manner as the layers 54, 58, 62, 70, 80. In one example, the method 200 includes: applying a third layer 88 of the build material composition 16 on the primer layer 48”’.

[0221 ] Prior to further processing, the layer 88 of the build material composition 16 may be exposed to pre-heating in the manner previously described. [0222] After the layer 88 is formed, and in some instances is pre-heated, the primer fusing agent 26, 26’, the coloring agent 30, the penetrating agent 42 are selectively applied on the same portion(s) 90 of the build material composition 16 in the layer 88. In one example, the method 200 includes: based on the 3D object model, selectively applying a plurality of agents on at least a portion of the third layer 88, the plurality of agents including a penetrating agent 42, a coloring agent 30, and (i) the core fusing agent 28 or (ii) the primer fusing agent 26, 26’, wherein the penetrating agent 42 includes a surfactant blend including: a first non-ionic surfactant having a first hydrophilic chain length; a second non-ionic surfactant, wherein the second non-ionic surfactant is selected from the group consisting of a polyether siloxane and an alkoxylated alcohol; and an anionic surfactant; and a liquid vehicle including a humectant present in an amount ranging from about 2 wt% to about 10 wt%, based on a total weight of the penetrating agent 42.

[0223] The penetrating agent 42, when applied with the coloring agent 30, enables the coloring agent 30 to penetrate the entire thickness of the layer 88. Further, the penetrating agent 42, when applied with the primer fusing agent 26,

26’, enables the primer fusing agent 26, 26’ to penetrate the entire thickness of the layer 88. As such, colorant of the coloring agent 30 and/or the energy absorber of the primer fusing agent 26, 26’ is/are present throughout the entire thickness of the layer 88. In some examples, the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 may be applied on the portion 90 in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 144 ng/600 ^th of an inch ² of the build material composition 16.

[0224] The primer fusing agent 26, 26’, the coloring agent 30, and the

penetrating agent 42 are selectively applied in a pattern of a cross-section for the colored layer 52” that is to be formed (shown in Fig. 4H). In the example shown in Fig. 4G, the portion 90 is adjacent to the primer layer 48”’ and the colored layer(s) 52’ is adjacent to the primer layer 48”’. [0225] When the desired color for the object 44’ or a particular colored layer 52” of the object 44’ is the color of the coloring agent 30, the primer fusing agent 26,

26’ is applied with the coloring agent 30. Since the primer fusing agent 26, 26’ is clear or slightly tinted and the build material composition 16 is white, the color of the coloring agent 30 will be the color of the resulting colored layer 52”, as the colorants of the coloring agent 30 become embedded throughout the

coalesced/fused build material composition of the colored layer 52”. The primer fusing agent 26, 26’ may be particularly suitable for obtaining lighter colors or white.

[0226] It may also be desirable to selectively deposit the coloring agent 30 with the penetrating agent 42 in portion(s) of the non-patterned build material

composition 16 which are adjacent to or surround the portion(s) 90 (which when coalesced/fused, will form the colored layer 52” along the top surface of object 44’). The colored build material composition 16 in the non-patterned portion(s) may become embedded in coalesced/fused build material composition along the sides or edges of the colored layer 52”. The non-coalesced/non-fused, but embedded colored build material composition 16 may help to maintain saturation at the surface (of the colored layer 52”) by providing a colored interface between the colored layer 52” and surrounding non-coalesced/non-fused build material composition 16.

[0227] After the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied in the specific portion(s) 90 of the layer 88, the entire layer 88 of the build material composition 16 is exposed to

electromagnetic radiation (shown as EMR Exposure between Figs. 4G and 4H). In one example, the method 200 includes: exposing the third layer 88 to

electromagnetic radiation to fuse the build material composition 16 in the at least the portion 90 of the third layer 88 to form a colored layer 52” having a colorant of the coloring agent 30 embedded therein.

[0228] The electromagnetic radiation is emitted from the radiation source 38, 38’ in the manner previously described, with wavelengths suitable for the primer fusing agent 26, 26’. Exposure to electromagnetic radiation forms the colored layer 52”, as shown in Fig. 4H, having colorants of the coloring agent 30 embedded therein.

[0229] While a single colored layer 52” is shown, it is to be understood that several colored layers 52” may be sequentially formed in contact with one another so that a color region (thicker than one voxel) is built up around the core layer(s) 46 in the final object 44’. The outermost colored layer 52” may form a one voxel deep shell, and the other colored layers may create the thicker color region. The levels of the primer fusing agent 26, 26’ and the coloring agent 30 may be higher in the outermost colored layer 52”, compared to other colored layers positioned closer to the core layer(s) 46, in order to increase color saturation at the exterior of the formed object 44’.

[0230] While not shown, the methods 100, 200, 300 may further include applying a sacrificial build material layer on the colored layer 52” to enhance the color of the colored layer 52”. The coloring agent 30 and the penetrating agent 42 are selectively applied on at least a portion of the sacrificial build material layer. As such, the particles of the build material composition 16 in the at least the portion of the sacrificial build material layer become colored. The sacrificial build material layer is not coalesced/fused (as no primer fusing agent 26, 26’ or core fusing agent 28 is applied thereon). Rather, some of the colored particles of the build material composition 16 in the sacrificial layer may become embedded in coalesced/fused build material composition of the colored layer 52”. In other words, some of the colored build material composition 16 in the at least the portion may become embedded in the surface of the part layer that is adjacent thereto. The non- coalesced/non-fused, but embedded colored build material composition 16 may help to maintain saturation at the surface of the colored layer 52”.

[0231 ] When a sacrificial build material layer is applied on the colored layer 52”, it is desirable for the coloring agent 30 to penetrate the entire thickness of the sacrificial build material layer so that the particles of the build material composition 16 that become embedded in coalesced/fused build material composition of the colored layer 52” are colored. As such, when the coloring agent 30 is selectively applied on at least a portion of the sacrificial build material layer, the penetrating agent 42 is applied with the coloring agent 30. The penetrating agent 42, when applied with the coloring agent 30, enables the coloring agent 30 to penetrate the entire thickness of the sacrificial build material layer. As such, the colorant of the coloring agent 30 is present throughout the entire thickness of the sacrificial layer. In some examples, the coloring agent 30 and the penetrating agent 42 may be applied on the at least the portion in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16.

[0232] Throughout the methods 100, 200, 300, the color of the coloring agent 30 that is applied will depend upon the desired color for the object 44’ or at least the portion of the colored layer(s) 52, 52’, 52” to be formed. As examples, a black agent, a cyan agent, a magenta agent, or a yellow agent may be applied alone or in combination to achieve a variety of colors.

[0233] It is to be understood that the methods 100, 200, 300 may be modified so that the core fusing agent 28, rather than the primer fusing agent 26, 26’, is applied with the coloring agent 30 to form the colored layers 52, 52’, 52”. The primer fusing agent 26, 26’ may be particularly suitable for obtaining lighter colors or white. When the desired color for colored layer 52 is a darker color or black, the core fusing agent 28 may be applied with the coloring agent 30.

[0234] It is to be further understood that the methods 100, 300 may be modified so that the sacrificial layers (with the coloring agent 30 thereon) and the outer colored layers 52, 52’, 52” are not formed. In this modified form of the methods 100, 300, the primer layer 48’ would be formed first. In the resulting part, all of the primer layers 48’, 48”, 48”’ would be exposed/visible, and thus would form the exterior of the part. In this example, the primer layers 48’, 48”, 48”’ would form an outer white layer which encapsulates the core layer(s) 46. When the methods 100, 300 are modified in this manner, the part that is formed is white or slightly tinted (depending upon the color of the primer fusing agent 26, 26’). In this example, the penetrating agent 42 may be selectively applied with the core fusing agent 28 and/or the primer fusing agent 26, 26’.

[0235] Still further it is to be understood that the methods 100, 300 may be modified so that the layers of the object are formed via selective laser sintering (SLS) or selective laser melting (SLM). In this modified form of the methods 100, 300, no primer fusing agent 26, 26’ or core fusing agent 28 is applied on the build material composition 16. Rather, an energy beam is used to selectively apply radiation to the portions of the build material composition 16 that are to

coalesce/fuse to become part of the object. When the methods 100, 300 are modified in this manner, the layers of the object formed will exhibit the color of the build material composition 16 when the coloring agent 30 is not applied thereon and the color of the coloring agent 30 when the coloring agent 30 is applied thereon. In this example, the penetrating agent 42 is selectively applied with the coloring agent 30.

[0236] Still further it is to be understood that the methods 100, 300 may be modified so that a property-imparting liquid functional agent is selectively applied on at least a region of the portion(s) of the build material composition 16 that is/are to form a layer of the object. In this modified form of the methods 100, 300, the region, when fused, will exhibit the property of the active material in the property- imparting liquid functional agent.

[0237] When the methods 100, 300 are modified in this manner, the penetrating agent 42 may be selectively applied with the property-imparting liquid functional agent. The penetrating agent 42, when applied with the property-imparting liquid functional agent, enables the property-imparting liquid functional agent to penetrate the entire thickness of the layer. As such, the active material of the property- imparting liquid functional agent is present throughout the entire thickness of the layer. In some examples, the property-imparting liquid functional agent and the penetrating agent 42 may be applied on the region(s) in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16.

[0238] It is to be further understood that in any modification of the methods 100, 300, the penetrating agent 42 is applied with at least one of the primer fusing agent 26, 26’, the core fusing agent 28, the coloring agent 30, or the property-imparting liquid functional agent.

[0239] The method 400 to form the object 44” will now be discussed in reference to Figs. 5A through 5C. It is to be understood that the method 400 may be another example of the method 100.

[0240] In Fig. 5A, a layer 94 of the build material composition 16 is applied on the build area platform 12. The layer 94 may be applied in the same manner as described above.

[0241 ] The layer 94 of the build material composition 16 may be exposed to pre- heating in the manner described herein.

[0242] After the layer 94 is applied, and in some instances is pre-heated, the primer fusing agent 26, 26’ is selectively applied on portion(s) 96 of the build material composition 16 in the layer 94. While the primer fusing agent 26’ is shown in Figs. 5A and 5C, it is to be understood that the primer fusing agent 26 may be used instead of the primer fusing agent 26’.

[0243] When it is desirable for the primer fusing agent 26, 26’ to penetrate the entire thickness of the layer 96, the penetrating agent 42 may be selectively applied on the portion(s) 96 with the primer fusing agent 26, 26’. In some examples, the primer fusing agent 26, 26’ and the penetrating agent 42 may be applied on the portion(s) 96 in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16.

[0244] The portion(s) 96 of the layer 94 will form the first layer 98 of the 3D object 44” (Fig. 5C) being formed. As such, the primer fusing agent 26, 26’ is selectively dispensed on the layer 94 according to a pattern of a cross-section for the layer 98. [0245] After the primer fusing agent 26, 26’ is applied on the portion(s) 96, the entire layer 94 of the build material composition 16 is exposed to electromagnetic radiation (shown as EMR Exposure between Figs. 5A and 5B) in the manner previously described.

[0246] In this example, the primer fusing agent 26, 26’ sufficiently elevates the temperature of the build material composition 16 in portion 96 to a temperature above the melting point of the polymer or a temperature within or above the melting range of the polymer of the build material composition 16, allowing

coalescing/fusing (e.g., thermal merging, melting, binding, etc.) of the build material composition 16 to take place. Exposure to electromagnetic radiation forms the layer 98, as shown in Fig. 5B.

[0247] It is to be understood that portions of the build material composition 16 that do not have the primer fusing agent 26, 26’ applied thereto do not absorb enough energy to coalesce/fuse.

[0248] After the layer 98 is formed, additional layer(s) (e.g., 98’, 98”, 98”’ shown in Fig. 5C) may be formed thereon to create an example of the 3D object 44” (shown in Fig. 5C). For example, to form the other layer 98’, additional build material composition 16 may be applied on the layer 98. The primer fusing agent 26, 26’ (with or without the penetrating agent 42) is then selectively applied on at least a portion of the additional build material composition 16, according to a pattern of a cross-section for the layer (e.g., 98’) which is being formed. After the primer fusing agent 26, 26’ is applied, the entire layer of the additional build material composition 16 is exposed to electromagnetic radiation in the manner previously described. The application of additional build material composition 16, the selective application of the primer fusing agent 26, 26’ (with or without the penetrating agent 42), and the electromagnetic radiation exposure may be repeated a predetermined number of cycles to form the object 44”.

[0249] In the example shown in Figs. 5A through 5C, color may be imparted to the entire object 44” by applying the coloring agent 30 and the penetrating agent 42 with the primer fusing agent 26, 26’ in each of the portions of the respective build material layers that form layers 98, 98’, 98”, 98”’.

[0250] The methods 100, 400 may end at the formation of object 44” or color may be imparted to the top surface of the object 44”. This is shown in Figs. 5C.

[0251 ] To impart color, a final layer 1 12 of the build material composition 16 is applied to the object 44”. As shown in Fig. 5C, this layer 1 12 is applied to the outermost layer 98”’ of the object 44”. Prior to further processing, the layer 1 12 may be exposed to pre-heating in the manner previously described.

[0252] After the layer 1 12 is formed, and in some instances is pre-heated, the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied on the same portion(s) 1 14 of the build material composition 16 in the layer 1 12. In some examples, the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 may be applied on the portion(s) 1 14 in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 144 ng/600 ^th of an inch ² of the build material composition 16.

[0253] The primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are selectively applied in a pattern of a cross-section for the colored layer that is to be formed (not shown). The color of the coloring agent 30 that is applied will depend upon the desired color for the part.

[0254] After the primer fusing agent 26, 26’, the coloring agent 30, and the penetrating agent 42 are applied, the entire layer 1 12 of the build material composition 16 is exposed to electromagnetic radiation in the manner previously described. The primer fusing agent 26, 26’ sufficiently elevates the temperature of the build material composition 16 in the portion 1 14 of the layer 1 12 to a

temperature above the melting point of the polymer or a temperature within or above the melting range of the polymer of the build material composition 16, allowing coalescing/fusing (e.g., thermal merging, melting, binding, etc.) of the build material composition 16 (in contact with the primer fusing agent 26, 26’) to take place. Exposure to electromagnetic radiation forms the colored layer (not shown), having colorants of the coloring agent 30 embedded therein.

[0255] It is to be understood that several colored layers may be sequentially formed in contact with one another so that a color region (thicker than one voxel) is built up on the layers 98, 98’, 98”, 98’” in the final part. The outermost colored layer may form a one voxel deep shell, and the other colored layers may create the thicker color region. The levels of the primer fusing agent 26, 26’ and the coloring agent 30 may be higher in the outermost colored layer, as compared to other colored layers positioned closer to the layer 98”’, in order to increase color saturation at the exterior of the formed object 44”.

[0256] While not shown, the methods 100, 400 may further include applying a sacrificial build material layer on the colored layer, and selectively applying the coloring agent 30 and the penetrating agent 42 on at least a portion of the sacrificial build material layer. As such, the particles of the build material composition 16 in the at least the portion of the sacrificial build material layer become colored, and some of those colored particles may become embedded in coalesced/fused build material composition of the colored layer to enhance the color of the colored layer.

[0257] When a sacrificial build material layer is applied on the colored layer, it is desirable for the coloring agent 30 to penetrate the entire thickness of the sacrificial build material layer so that the particles of the build material composition 16 that become embedded in coalesced/fused build material composition of the colored layer are colored. As such, when the coloring agent 30 is selectively applied on at least a portion of the sacrificial build material layer, the penetrating agent 42 is applied with the coloring agent 30. In some examples, the coloring agent 30 and the penetrating agent 42 may be applied on the at least the portion in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16. [0258] It is to be understood that the methods 100, 400 may also be modified similarly to the method 300 in order to form colored layers (e.g., 52 and 52’) so that the part is completely encapsulated by colored layers. In this modified form of the methods 100, 400 sacrificial layer(s) may or may not be used to embed colored, non-coalesced/non-fused particles of the build material composition 16 in the surface(s) of the coalesced/fused part layer(s) that is/are adjacent thereto.

[0259] It is to be further understood that the methods 100, 400 so that the layers of the object are formed via selective laser sintering (SLS) or selective laser melting (SLM). In this modified form of the methods 100, 400, the primer fusing agent 26, 26’ is not applied on the build material composition 16. Rather, an energy beam is used to selectively apply radiation to the portions of the build material composition 16 that are to coalesce/fuse to become part of the object. When the methods 100, 400 are modified in this manner, the layers of the object formed will exhibit the color of the build material composition 16 when the coloring agent 30 is not applied thereon and the color of the coloring agent 30 when the coloring agent 30 is applied thereon.

[0260] Still further it is to be understood that the methods 100, 400 may be modified so that a property-imparting liquid functional agent is selectively applied on at least a region of the portion(s) of the build material composition 16 that is/are to form a layer of the object. In this modified form of the methods 100, 400, the region, when fused, will exhibit the property of the active material in the property- imparting liquid functional agent.

[0261 ] When the methods 100, 400 are modified in this manner, the penetrating agent 42 may be selectively applied with the property-imparting liquid functional agent. In some examples, the property-imparting liquid functional agent and the penetrating agent 42 may be applied on the region(s) in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16. [0262] It is to be further understood that in any modification of the methods 100, 400, the penetrating agent 42 is applied with at least one of the primer fusing agent 26, 26’, the coloring agent 30, or the property-imparting liquid functional agent.

[0263] Another example method 500 to form a 3D object will now be discussed in reference to Figs. 6A and 6B. It is to be understood that the method 500 may be another example of the method 100.

[0264] In Fig. 6A, a layer 95 of the build material composition 16 is applied on the build area platform 12. The layer 95 may be applied in the same manner as described above.

[0265] The layer 95 of the build material composition 16 may be exposed to pre- heating in the manner described herein.

[0266] After the layer 95 is applied, and in some instances is pre-heated, the core fusing agent 28 is selectively applied on portion(s) 97 of the build material composition 16 in the layer 95.

[0267] When it is desirable for the core fusing agent 28 to penetrate the entire thickness of the layer 97, the penetrating agent 42 may be selectively applied on the portion(s) 97 with the core fusing agent 28. In some examples, the core fusing agent 28 and the penetrating agent 42 may be applied on the portion(s) 97 in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16.

[0268] The portion(s) 97 of the layer 95 will form the first layer 99 of the 3D object being formed (not shown). As such, the core fusing agent 28 is selectively dispensed on the layer 95 according to a pattern of a cross-section for the layer 99.

[0269] After the core fusing agent 28 is applied on the portion(s) 97, the entire layer 95 of the build material composition 16 is exposed to electromagnetic radiation (shown as EMR Exposure between Figs. 6A and 6B) in the manner previously described.

[0270] In this example, the core fusing agent 28 sufficiently elevates the temperature of the build material composition 16 in portion 97 to a temperature above the melting point of the polymer or a temperature within or above the melting range of the polymer of the build material composition 16, allowing

coalescing/fusing (e.g., thermal merging, melting, binding, etc.) of the build material composition 16 to take place. Exposure to electromagnetic radiation forms the layer 99, as shown in Fig. 6B.

[0271 ] It is to be understood that portions of the build material composition 16 that do not have the core fusing agent 28 applied thereto do not absorb enough energy to coalesce/fuse.

[0272] After the layer 99 is formed, additional layer(s) may be formed thereon to create an example of the 3D object. For example, to form another layer, additional build material composition 16 may be applied on the layer 99. The core fusing agent 28 (with or without the penetrating agent 42) is then selectively applied on at least a portion of the additional build material composition 16, according to a pattern of a cross-section for the layer which is being formed. After the core fusing agent 28 is applied, the entire layer of the additional build material composition 16 is exposed to electromagnetic radiation in the manner previously described. The application of additional build material composition 16, the selective application of the core fusing agent 28 (with or without the penetrating agent 42), and the electromagnetic radiation exposure may be repeated a predetermined number of cycles to form the part.

[0273] In the example shown in Figs. 6A and 6B, color may be imparted to the entire object 44” by applying the coloring agent 30 and the penetrating agent 42 with the core fusing agent 28 in each of the portions of the respective build material layers that form layers of the part.

[0274] It is to be understood that the methods 100, 500 may also be modified similarly to the method 300 in order to form colored layers (e.g., 52, 52’, 52”) so that the part is completely encapsulated by colored layers. In this modified form of the methods 100, 500 sacrificial layer(s) may or may not be used to embed colored, non-coalesced/non-fused particles of the build material composition 16 in the surface(s) of the coalesced/fused part layer(s) that is/are adjacent thereto. [0275] It is to be further understood that the methods 100, 500 so that the layers of the object are formed via selective laser sintering (SLS) or selective laser melting (SLM). In this modified form of the methods 100, 500, the core fusing agent 28 is not applied on the build material composition 16. Rather, an energy beam is used to selectively apply radiation to the portions of the build material composition 16 that are to coalesce/fuse to become part of the object. When the methods 100, 500 are modified in this manner, the layers of the object formed will exhibit the color of the build material composition 16 when the coloring agent 30 is not applied thereon and the color of the coloring agent 30 when the coloring agent 30 is applied thereon.

[0276] Still further it is to be understood that the methods 100, 500 may be modified so that a property-imparting liquid functional agent is selectively applied on at least a region of the portion(s) of the build material composition 16 that is/are to form a layer of the object. In this modified form of the methods 100, 500, the region, when fused, will exhibit the property of the active material in the property- imparting liquid functional agent.

[0277] When the methods 100, 500 are modified in this manner, the penetrating agent 42 may be selectively applied with the property-imparting liquid functional agent. In some examples, the property-imparting liquid functional agent and the penetrating agent 42 may be applied on the region(s) in a single printing pass and/or at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16.

[0278] It is to be further understood that in any modification of the methods 100, 500, the penetrating agent 42 is applied with at least one of the core fusing agent 28, the coloring agent 30, or the property-imparting liquid functional agent.

[0279] In any of the examples disclosed herein, when the 3D object 44, 44’, 44” is complete, it may be removed from the build material platform 12, and any non- coalesced/non-fused build material composition 16 may be removed from the 3D object 44, 44’, 44”. [0280] In any of the methods 100, 200, 300, 400, 500 disclosed herein, the non- patterned and non-coalesced/non-fused build material composition 16 may be reclaimed to be reused as build material in the printing of another 3D object. In some examples, the methods 100, 200, 300,400, 500 may be accomplished in an air environment. As used herein, an“air environment” or an“environment containing air” refers to an environment that contains 20 vol% or more of oxygen.

[0281 ] Still further, in any of the methods 100, 200, 300, 400, 500 disclosed herein, different shaped objects may be printed in different orientations within the printing system 10. As such, while the object 44, 44’, 44” may be printed from the bottom of the object 44, 44’, 44” to the top of the object 44, 44’, 44”, it may alternatively be printed starting with the top of the object 44, 44’, 44” to the bottom of the object 44, 44’, 44”, or from a side of the object 44, 44’, 44” to another side of the object, 44, 44’, 44”, or at any other orientation that is suitable or desired for the particular geometry of the part being formed. Moreover, the fusing agent(s) 26,

26’, 28 used for any particular layer or portion of a layer may depend, in part, on desired strength characteristics and/or aesthetics of the particular layer being formed.

[0282] Printing System

[0283] Referring now to Fig. 7, an example of a 3D printing system 10 is schematically depicted. It is to be understood that the 3D printing system 10 may include additional components (some of which are described herein) and that some of the components described herein may be removed and/or modified.

Furthermore, components of the 3D printing system 10 depicted in Fig. 7 may not be drawn to scale and thus, the 3D printing system 10 may have a different size and/or configuration other than as shown therein.

[0284] In an example, the three-dimensional (3D) printing system 10, comprises: a supply 14 of a build material composition 16 having a surface energy density ranging from about 0.02 J/m ² to about 0.046 J/m ² and including a polymer; a build material distributor 18; a supply of a liquid functional agent including an active material; a first applicator 24A, 24B, 24C for selectively dispensing the liquid functional agent; a supply of a penetrating agent 42 having a surface tension ranging from about 19 dynes/cm to about 29 dynes/cm and including: a surfactant blend including: a first non-ionic surfactant having a first hydrophilic chain length; a second non-ionic surfactant, wherein the second non-ionic surfactant is selected from the group consisting of a polyether siloxane and an alkoxylated alcohol; and an anionic surfactant; and a liquid vehicle including a humectant present in an amount ranging from about 2 wt% to about 10 wt%, based on a total weight of the penetrating agent; a second applicator 24D for selectively dispensing the penetrating agent 42; a source 38, 38’ of electromagnetic radiation; a controller 36; and a non-transitory computer readable medium having stored thereon computer executable instructions to cause the controller 36 to: utilize the build material distributor 18 to dispense the build material composition 16; utilize the first applicator 24A, 24B, 24C and the second applicator 24D to selectively dispense the liquid functional agent and the penetrating agent 42 on at least a portion of the build material composition 16; and utilize the source 38, 38’ of electromagnetic radiation to expose the build material composition 16 to radiation to coalesce/fuse the at least the portion of the build material composition 16. Any example of the build material composition 16 may be used in the examples of the system 10.

[0285] In some examples of the 3D printing system 10, the liquid functional agent is a fusing agent 26, 26’, 28 and the active material is an energy absorber to absorb the electromagnetic radiation to coalesce the polymer in the at least the portion.

[0286] In some other examples of the 3D printing system 10, the liquid functional agent is a coloring agent 30 selected from the group consisting of a black agent, a cyan agent, a magenta agent, and a yellow agent, and the active material is a colorant.

[0287] In still other examples of the 3D printing system 10, the liquid functional agent is a property-imparting liquid functional agent (not shown), and the active material imparts the property. [0288] In some examples, the 3D printing system 10 may include supplies of multiple liquid functional agents. In these examples, the 3D printing system 10 may further include additional applicators for selectively dispensing each of the liquid functional agents, and the computer executable instructions may further cause the controller 36 to utilize the additional applicators to selectively dispense the additional liquid functional agents.

[0289] As shown in Fig. 7, the printing system 10 includes the build area platform 12, the build material supply 14 containing the build material composition 16 disclosed herein, and the build material distributor 18.

[0290] As mentioned above, the build area platform 12 receives the build material composition 16 from the build material supply 14. The build area platform 12 may be integrated with the printing system 10 or may be a component that is separately insertable into the printing system 10. For example, the build area platform 12 may be a module that is available separately from the printing system 10. The build material platform 12 that is shown is one example, and could be replaced with another support member, such as a platen, a fabrication/print bed, a glass plate, or another build surface.

[0291 ] As also mentioned above, the build material supply 14 may be a container, bed, or other surface that is to position the build material composition 16 between the build material distributor 18 and the build area platform 12. In some examples, the build material supply 14 may include a surface upon which the build material composition 16 may be supplied, for instance, from a build material source (not shown) located above the build material supply 14. Examples of the build material source may include a hopper, an auger conveyer, or the like. Additionally, or alternatively, the build material supply 14 may include a mechanism (e.g., a delivery piston) to provide, e.g., move, the build material composition 16 from a storage location to a position to be spread onto the build area platform 12 or onto a previously formed layer of the 3D object. Another example of the mechanism for moving the build material composition 16 is a pneumatic conveying system. [0292] As also mentioned above, the build material distributor 18 may be a blade (e.g., a doctor blade), a roller, a combination of a roller and a blade, and/or any other device capable of spreading the build material composition 16 over the build area platform 12 (e.g., a counter-rotating roller).

[0293] As shown in Fig. 7, the printing system 10 may include the first applicator 24A, 24B, 24C, which may contain the liquid fictional agent (e.g., the primer fusing agent 26, 26’, the core fusing agent 28, the coloring agent 30, or the property- imparting liquid functional agent). As also shown, the printing system 10 further includes the second applicator 24D, which may contain the penetrating agent 42. While not shown, the printing system 10 may further include another applicator (which may contain the additional liquid functional agents).

[0294] The applicators 24A, 24B, 24C, 24D may be scanned across the build area platform 12 in the directions indicated by the arrow 32, e.g., along the y-axis. The applicators 24A, 24B, 24C, 24D may be, for instance, a thermal inkjet printhead, a piezoelectric printhead, a continuous inkjet printhead, etc., and may extend a width of the build area platform 12. While the each applicator 24A, 24B, 24C, 24D is shown in Fig. 7 as a single applicator, it is to be understood that each applicator 24A, 24B, 24C, 24D may include multiple applicators that span the width of the build area platform 12. Additionally, the applicators 24A, 24B, 24C, 24D may be positioned in multiple printbars. The applicators 24A, 24B, 24C, 24D may also be scanned along the x-axis, for instance, in configurations in which the applicators 24A, 24B, 24C, 24D do not span the width of the build area platform 12 to enable the applicators 24A, 24B, 24C, 24D to deposit the respective agents 26, 26’, 28,

30, 42 over a large area of the build material composition 16. The applicators 24A, 24B, 24C, 24D may thus be attached to a moving XY stage or a translational carriage (neither of which is shown) that moves the applicators 24A, 24B, 24C, 24D adjacent to the build area platform 12 in order to deposit the respective agents 26, 26’, 28, 30, 42 in predetermined areas of the build material layer(s) that has/have been formed on the build area platform 12 in accordance with the methods 100, 200, 300, 400, 500 disclosed herein. In some examples, the applicators 24A, 24B, 24C, 24D may be configured so that the respective agents 26, 26’, 28, 30, 42 may be applied in a single printing pass. The applicators 24A, 24B, 24C, 24D may include a plurality of nozzles (not shown) through which the respective agents 26, 26’, 28, 30, 42 are to be ejected.

[0295] The applicators 24A, 24B, 24C, 24D may deliver drops of the respective agents 26, 26’ 28, 30, 42 at a resolution ranging from about 300 dots per inch (DPI) to about 1200 DPI. In other examples, the applicators 24A, 24B, 24C, 24D may deliver drops of the respective agents 26, 26’, 28, 30, 42 at a higher or lower resolution. The drop velocity may range from about 10 m/s to about 24 m/s and the firing frequency may range from about 1 kHz to about 48 kHz. In one example, the volume of each drop may be on the order of about 3 picoliters (pL) to about 18 pL, although it is contemplated that a higher or lower drop volume may be used. In some examples, the applicators 24A, 24B, 24C, 24D are able to deliver variable drop volumes of the respective agents 26, 26’, 28, 30, 42. One example of a suitable printhead has 600 DPI resolution and can deliver drop volumes ranging from about 6 pL to about 14 pL. In some examples, the applicators 24A, 24B, 24C, 24D may deliver the respective agents 26, 26’, 28, 30, 42 at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16. In some other examples, the applicators 24A, 24B, 24C, 24D may deliver the respective agents 26, 26’, 28, 30, 42 at a fluid density ranging from about 45 ng/600 ^th of an inch ² of the build material composition 16 to about 90 ng/600 ^th of an inch ² of the build material composition 16. In still some other examples, the applicators 24A, 24B, 24C, 24D may deliver the respective agents 26, 26’, 28, 30, 42 at a fluid density ranging from about 36 ng/600 ^th of an inch ² of the build material composition 16 to about 144 ng/600 ^th of an inch ² of the build material composition 16. In yet some other examples, the applicators 24A, 24B, 24C, 24D may deliver the respective agents 26, 26’, 28, 30, 42 at a fluid density ranging from about 45 ng/600 ^th of an inch ² of the build material composition 16 to about 144 ng/600 ^th of an inch ² of the build material composition 16. [0296] Each of the previously described physical elements may be operatively connected to a controller 36 of the printing system 10. The controller 36 may process print data that is based on a 3D object model of the 3D object/part to be generated. In response to data processing, the controller 36 may control the operations of the build area platform 12, the build material supply 14, the build material distributor 18, and the applicators 24A, 24B, 24C, 24D. As an example, the controller 36 may control actuators (not shown) to control various operations of the 3D printing system 10 components. The controller 36 may be a computing device, a semiconductor-based microprocessor, a central processing unit (CPU), an application specific integrated circuit (ASIC), and/or another hardware device. Although not shown, the controller 36 may be connected to the 3D printing system 10 components via communication lines.

[0297] The controller 36 manipulates and transforms data, which may be represented as physical (electronic) quantities within the printer’s registers and memories, in order to control the physical elements to create the 3D object. As such, the controller 36 is depicted as being in communication with a data store 34. The data store 34 may include data pertaining to a 3D object to be printed by the 3D printing system 10. The data for the selective delivery of the build material composition 16, the liquid functional agent (e.g., the primer fusing agent 26, 26’, the core fusing agent 28, the coloring agent 30, and/or the property-imparting liquid functional agent), the penetrating agent 42, etc. may be derived from a model of the 3D object to be formed. For instance, the data may include the locations on each build material layer that the first applicator 24A, 24B, 24C is to deposit the liquid functional agent and the second applicator 24D is to deposit the penetrating agent 42. In one example, the controller 36 may use the data to control the first applicator 24A, 24B, 24C to selectively apply the liquid functional agent and to control the second applicator 24D to selectively apply the penetrating agent 42.

The data store 34 may also include machine readable instructions (stored on a non-transitory computer readable medium) that are to cause the controller 36 to control the amount of build material composition 16 that is supplied by the build material supply 14, the movement of the build area platform 12, the movement of the build material distributor 18, the movement of the applicators 24A, 24B, 24C, 24D, etc.

[0298] As shown in Fig. 7, the printing system 10 may also include a source 38, 38’ of electromagnetic radiation. In some examples, the source 38 of

electromagnetic radiation may be in a fixed position with respect to the build material platform 12. The source 38 in the fixed position may be a conductive heater or a radiative heater that is part of the printing system 10. These types of heaters may be placed below the build area platform 12 (e.g., conductive heating from below the platform 12) or may be placed above the build area platform 12 (e.g., radiative heating of the build material layer surface). In other examples, the source 38’ of electromagnetic radiation may be positioned to apply radiation to the build material composition 16 immediately after the fusing agent 26, 26’, 28 has been applied thereto. In the example shown in Fig. 7, the source 38’ of

electromagnetic radiation is attached to the side of the applicators 24A, 24B, 24C, 24D which allows for patterning and heating/exposing to radiation in a single pass.

[0299] In other examples (not shown), the source of electromagnetic radiation may be a laser or other tightly focused energy source that may selectively apply radiation to the build material composition as previously described for selective laser sintering (SLS) or selective laser melting (SLM). The laser may emit light through optical amplification based on the stimulated emission of radiation. The laser may emit light coherently (i.e. , constant phase difference and frequency), which allows the radiation to be emitted in the form of a laser beam that stays narrow over large distances and focuses on a small area. In some example, the laser or other tightly focused energy source may be a pulse laser (i.e., the optical power appears in pluses). Using a pulse laser allows energy to build between pluses, which enable the beam to have more energy. A single laser or multiple lasers may be used.

[0300] The source 38, 38’ of electromagnetic radiation may emit radiation having wavelengths ranging from about 400 nm to about 4000 nm. As one example, the electromagnetic radiation may range from about 800 nm to about 1400 nm. As another example, the electromagnetic radiation may range from about 400 nm to about 1200 nm. As still another example, the electromagnetic radiation may be blackbody radiation with a maximum intensity at a wavelength of about 1100 nm. The source 38, 38’ of electromagnetic radiation may be infrared (IR) or near-infrared light sources, such as IR or near-IR curing lamps, IR or near- IR light emitting diodes (LED), or lasers with the desirable IR or near-IR

electromagnetic wavelengths.

[0301 ] The source 38, 38’ of electromagnetic radiation may be operatively connected to a lamp/laser driver, an input/output temperature controller, and temperature sensors, which are collectively shown as radiation system

components 40. The radiation system components 40 may operate together to control the source 38, 38’ of electromagnetic radiation. The temperature recipe (e.g., radiation exposure rate) may be submitted to the input/output temperature controller. During heating, the temperature sensors may sense the temperature of the build material composition 16, and the temperature measurements may be transmitted to the input/output temperature controller. For example, a thermometer associated with the heated area can provide temperature feedback. The

input/output temperature controller may adjust the source 38, 38’ of

electromagnetic radiation power set points based on any difference between the recipe and the real-time measurements. These power set points are sent to the lamp/laser drivers, which transmit appropriate lamp/laser voltages to the source 38, 38’ of electromagnetic radiation. This is one example of the radiation system components 40, and it is to be understood that other radiation source control systems may be used. For example, the controller 36 may be configured to control the source 38, 38’ of electromagnetic radiation.

[0302] To further illustrate the present disclosure, an example is given herein. It is to be understood this example is provided for illustrative purposes and is not to be construed as limiting the scope of the present disclosure. EXAMPLE

[0303] Eight examples of the penetrating agent disclosed herein were prepared. The general formulations of the example penetrating agents (Ex. PA 1 -8) are shown below in Table 1 , with the wt% of each component that was used.

TABLE 1

[0304] The pH of the penetrating agents ranged from 6.5 to 7.2.

[0305] A comparative example of the penetrating agent was also prepared. The general formulation of the comparative penetrating agent (comparative agent) is shown in Table 2, with the wt% of each component that was used. TABLE 2

[0306] Four white rectangular plates, each including core layers surrounded by primer layers, were printed on a small testbed 3D printer with an example build material composition, an example primer fusing agent, and an example core fusing agent. The example build material composition included a polyamide 12 powder and 3 wt% of titanium dioxide (T1O2). The example primer fusing agent included cesium tungsten oxide (CTO, also referred to as CWO) nanoparticles as the energy absorber, and the example core fusing agent included carbon black as the energy absorber.

[0307] After the final layer of each rectangular plate was fused, a sacrificial layer of the example build material was applied on the final layer. The nominal thickness of the sacrificial layer was 80 pm, creating an about 250 pm sacrificial layer thickness on top of the previously fused part region. Then, different combinations of printing agents, including an example black agent, and either Ex. PA 1 or the comparative agent, were printed in 16 different tiles on each of the rectangular plates.

[0308] Corresponding tiles (e.g., tile 1 , tile 2, etc.) in each rectangular plate had the same amount of printing agents applied thereon. The rectangular plates varied as to whether Ex. PA 1 or the comparative agent was used; and in the number of printing passes used to apply the printing agents. On the first rectangular plate, different combinations of Ex. PA 1 and the example black agent were printed in a single printing pass. On the second rectangular plate, different combinations of the comparative agent and the example black agent were printed in a single printing pass. On the third rectangular plate, different combinations of Ex. PA 1 and the example black agent were printed in two printing passes (i.e. , both agents printed in both passes at ½ the total amount in each pass). On the fourth rectangular plate, different combinations of the comparative agent and the example black agent were printed in two printing passes (i.e., both agents printed in both passes at ½ the total amount in each pass). The amount (i.e., fluid density) of i) the Agent (either Ex. PA 1 or the comparative agent), ii) the example black agent (Ex. BA), and iii) the total fluid that was applied in each tile is shown in Table 3, in ng/600 ^th of an inch ² of the example build material composition.

TABLE 3

[0309] After the different combinations of the printing agents were printed in the 16 different tiles, each rectangular plate was removed from the powder bed and cleaned to remove the sacrificial layer. The amount of penetration (through the sacrificial layer) that was achieved by the different combinations of the printing agents was indicated by the amount of black color that remained in the

corresponding tile after cleaning. [0310] The first rectangular plate is shown in Fig. 8; the second rectangular plate is shown in Fig. 9; the third rectangular plate is shown in Fig. 10; and the fourth rectangular plate is shown in Fig. 11.

[0311 ] With single pass printing (Figs. 8 and 9), it can be seen that using the example penetrating agent increased the amount of penetration of the example black agent (Fig. 8) as compared to the amount of penetration achieved using the same amount of the comparative agent (Fig. 9).

[0312] Comparing Figs. 8 and 9 with Figs. 10 and 11 , it can also be seen that printing the agents in a single pass improves penetration than when printing the agents over multiple passes. As shown in Figs. 8 and 10, applying the example penetrating agent and the example black agent in a single printing pass increased the amount of penetration of the example black agent (Fig. 8) as compared to the amount of penetration achieved applying the same amount of the same agents in two printing passes (Fig. 10). It is believed that the single pass results are better than the two pass results, in part, because solvent from the agents may evaporate between the two printing passes, and thus may not be available to aid in

penetration during the second printing pass.

[0313] Flowever, even with two pass printing (Figs. 10 and 11 ), it can be seen that using the example penetrating agent increased the amount of penetration of the example black agent (Fig. 10) as compared to the amount of penetration achieved using the same amount of the comparative agent (Fig. 11 ).

[0314] Four additional plates were prepared in the same manner described in this example. With the four additional plates, different combinations of printing agents, including the example black agent, and either Ex. PA 2 or the comparative agent, were printed in 16 different tiles on each of the rectangular plates in the same manner set forth in Table 3. The penetration results for these additional plates are not shown. Flowever, the results were similar to the results for Ex. PA 1. In particular, better penetration of the example black agent was achieved using i) Ex. PA 2 in a single pass than the comparative agent in a single pass, ii) Ex. PA 2 in two passes than the comparative agent in two passes, and iii) Ex. PA 2 in a single pass than Ex. PA 2 in two passes.

[0315] The viscosity and surface tension of each of the 8 penetrating agents were also measured. The viscosity was determined using a VISCOLITE™ viscometer and the surface tension was determined using a Kriiss Force

Tensiometer - K11. The results are shown in Table 4.

TABLE 4

[0316] The viscosity and surface tension of each of the Ex. PA 3 through Ex. PA 8 were similar to the viscosity and surface tension of Ex. PA 1 and Ex. PA 2. It is believed that these physical properties indicate that each of the Ex. PA 3 through Ex. PA 8 will behave similarly to Ex. PA 1 and Ex. PA 2 in terms of improving penetration of colored agent(s) through build material layer(s).

[0317] It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range, as if such values or sub- ranges were explicitly recited. For example, from about 2 wt% to about 10 wt% should be interpreted to include not only the explicitly recited limits of from about 2 wt% to about 10 wt%, but also to include individual values, such as about 2.35 wt%, about 3.5 wt%, about 4.67 wt%, about 5 wt%, about 5.74 wt%, about 6 wt%, about 7.15 wt%, about 8 wt%, about 9.86 wt%, etc., and sub-ranges, such as from about 2.3 wt% to about 5.95 wt%, from about 4.5 wt% to about 6.5 wt%, from about 4.75 wt% to about 9.79 wt%, etc. Furthermore, when“about” is utilized to describe a value, this is meant to encompass minor variations (up to +/- 10%) from the stated value.

[0318] Reference throughout the specification to“one example”,“another example”,“an example”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the example is included in at least one example described herein, and may or may not be present in other examples. In addition, it is to be understood that the described elements for any example may be combined in any suitable manner in the various examples unless the context clearly dictates otherwise.

[0319] In describing and claiming the examples disclosed herein, the singular forms“a”,“an”, and“the” include plural referents unless the context clearly dictates otherwise.

[0320] While several examples have been described in detail, it is to be understood that the disclosed examples may be modified. Therefore, the foregoing description is to be considered non-limiting.