BACKGROUND

[0001] Methods of three-dimensional (3D) digital printing, a type of additive manufacturing, have continued to be developed over the last few decades. In general, 3D printing technology can change the product development cycle by allowing rapid creation of prototype models or even finished products. For example, several commercial sectors such as aviation and the medical industry, to name a few, have benefitted from rapid prototyping and/or the production of customized parts. There are various methods for 3D printing that have been developed, including heat-assisted extrusion, selective laser sintering, photolithography, additive manufacturing, as well as others. As technology advances, higher demands with respect to production speed, part consistency, rigidity, method flexibility, color options, etc., are requested by customers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 schematically illustrates an example three-dimensional printing kit in accordance with the present disclosure;

[0003] FIG. 2 illustrates an example method for three-dimensional printing in accordance with the present disclosure; and

[0004] FIG. 3 schematically illustrates an example three-dimensional printing system in accordance with the present disclosure.

DETAILED DESCRIPTION

[0005] The present disclosure is drawn to three-dimensional (3D) fusing agents, 3D printing kits, and 3D printing methods. More particularly, the three- dimensional fusing agent can be used in three-dimensional methods and three- dimensional printing kits where a polymer build material can be spread on a powder bed on a layer by layer basis. The various layers can be selectively contacted with the fusing agent. The fusing agent can be ejected from a print head, such as a fluid ejector similar to an inkjet print head, for example, and then the layer can be exposed to electromagnetic radiation, e.g., ultraviolet energy, to heat the layer of the polymer build material. This can be repeated layer by layer until a three-dimensional object is formed.

[0006] In accordance with this, the present disclosure is drawn to a fusing agent. The fusing agent can include from about 0.5 wt% to about 30 wt% optically transparent metal oxide particles that can have a D50 particle size from about 3 nm to about 90 nm and an aqueous liquid vehicle. The aqueous liquid vehicle can include water, surfactant, and from about 1 wt% to 50 wt% organic co-solvent.

The organic co-solvent can consist essentially of a C2 to C10 alkylene diol, C3 to C10 alkylene triol, C4 to C10 alkylene glycol, or a mixture thereof. In on example, the fusing agent can be devoid of nitrogen-containing compounds. In another example, the transparent metal oxide particles can include zirconium oxide, titanium dioxide, zinc oxide, cerium oxide, or a combination thereof. In yet another example, the optically transparent metal oxide binder particles can have a D50 particle size ranging from about 3 nm to about 60 nm.

[0007] In another example, a three-dimensional printing kit is presented. The three-dimensional printing kit can include a polymer build material and a fusing agent. The polymer build material can include from about 80 wt% to 100 wt% of nitrogen-containing polymer particles. The fusing agent can include from about 0.5 wt% to about 30 wt% optically transparent metal oxide particles and an aqueous liquid vehicle. The aqueous liquid vehicle can include water, surfactant, and from about 1 wt% to about 50 wt% organic co-solvent. The organic co solvent can include a C2 to C10 alkylene diol, C3 to C10 alkylene triol, or a C4 to C10 alkylene glycol. The aqueous liquid vehicle can be devoid of nitrogen- containing organic co-solvent. In an example, the nitrogen-containing polymer particles can include polyamide polymer particles. In another example, the optically transparent metal oxide particles can include zirconium oxide, titanium dioxide, zinc oxide, cerium oxide, or a combination thereof. In yet another example, the optically transparent metal oxide binder particles can have a D50 particle size ranging from about 3 nm to about 90 nm. In a further example, the organic co-solvent can be the C2 to C10 alkylene diol or the C3 to C10 alkylene triol, and can include 1 ,2-ethanediol, 1 ,2-propanediol, 1 ,3-propane diol, 2-methyl- 1 , 3-propanediol, glycerol, propylene glycol, or a combination thereof. In one example, the organic co-solvent can be the C4 to C10 alkylene glycol and can include diethylene glycol, triethylene glycol, tetraethylene glycol, or a combination thereof.

[0008] In yet another example, a method for three dimensional printing is presented. The method can include iteratively applying polymer build material as individual layers, the polymer build material can include from about 80 wt% to 100 wt% nitrogen-containing polymer particles to a powder bed; based on a three-dimensional object model, selectively dispensing a fusing agent to the individual layers of the polymer build material, the fusing agent can include from about 0.5 wt% to about 30 wt% optically transparent metal oxide particles and an aqueous liquid vehicle including water, surfactant, and from about 1 wt% to about 50 wt% organic co-solvent including a C2 to C10 alkylene diol, C3 to C10 alkylene triol, or a C4 to C10 alkylene glycol. The aqueous liquid vehicle can be devoid of nitrogen-containing organic co-solvent. The method can further include exposing the powder bed to ultraviolent radiation to selectively fuse portions of individual layers of the polymer build material in contact with the fusing agent to form a three-dimensional object. In another example, the nitrogen-containing polymer particles can include polyamide-6 powder, polyamide-9 powder, polyamide-11 powder, polyamide-12 powder, polyamide-66 powder, polyamide- 612 powder, thermoplastic polyamide polymer, thermoplastic polyamide copolymer, thermoplastic polyurethane, or a combination thereof. In yet another example, the organic co-solvent can include 1 ,2-ethanediol, 1 ,2-propanediol, 1 ,3- propane diol, 2-methyl-1 , 3-propanediol, glycerol, diethylene glycol, triethylene glycol, propylene glycol, tetraethylene glycol, di-alcohols, tri-alcohols, poly alcohols, oligomeric glycol solvents, or a combination thereof. In one example, the transparent metal oxide binder particles can have a D50 particle size ranging from about 3 nm to about 90 nm. In another example, the three-dimensional object formed can have a b ^* value ranging from 0 units to about 17 units. [0009] It is noted that when discussing the fusing agent, the three- dimensional printing kit, and the method for three-dimensional printing of the present disclosure, these discussions can be considered applicable to other examples, whether or not they are explicitly discussed in the context of that example. Thus, for example, in discussing optically transparent metal oxide particles related to the fusing agent, such disclosure is also relevant to and directly supported in context of a three-dimensional printing kit, the method for three-dimensional printing, and vice versa.

[0010] It is also understood that terms used herein will have the ordinary meaning in the relevant technical field unless specified otherwise. In some instances, there are terms defined more specifically throughout the specification or included at the end of the present specification, and thus, these terms have a meaning consistent with these more specific definitions.

Three-Dimensional Printing Kit

[0011] In accordance with examples of the present disclosure, a three- dimensional (3D) printing kit 100 is shown in FIG. 1. The three-dimensional printing kit can include a polymer build material 110 and a fusing agent 120. The polymer build material can include from about 80 wt% to about 100 wt% of nitrogen-containing polymer particles 112 based on the total weight of the polymer build material. The fusing agent can include optically transparent metal oxide particles 122 and an aqueous liquid vehicle 124. The aqueous liquid vehicle can include water, surfactant, and an organic so-solvent. In an example relative to the fusing agent examples of the present disclosure, the aqueous liquid vehicle can include from about 1 wt% to about 50 wt% of the organic co solvent and the organic co-solvent can consist essentially of a C2 to C10 alkylene diol, C3 to C10 alkylene triol, or a C4 to C10 alkylene glycol. In other examples, such as when the fusing agent is used in the context of the three-dimensional printing kit, the aqueous liquid vehicle can include a C2 to C10 alkylene diol, C3 to C10 alkylene triol, or a C4 to C10 alkylene glycol, and can also be devoid of nitrogen-containing organic co-solvent. The polymer build material may be packaged or co-packaged with the fusing agent in separate containers and/or can be combined with one another at the time of printing, e.g. loaded together in a three-dimensional printing system.

Methods of Three-dimensional Printing

[0012] A flow diagram of an example method 200 of three-dimensional (3D) printing is shown in FIG. 2. The method can include iteratively applying 210 polymer build material as individual layers. The polymer build material can include from about 80 wt% to 100 wt% nitrogen-containing polymer particles to a powder bed. The method can additionally include, based on a three-dimensional object model, selectively 220 dispensing a fusing agent to the individual layers of the polymer build material. The fusing agent can include from about 1 wt% to about 30 wt% optically transparent metal oxide particles and an aqueous liquid vehicle. The aqueous liquid vehicle can include water, surfactant, and from about 1 wt% to about 50 wt% organic co-solvent. The organic co-solvent can include a C2 to C10 alkylene diol, C3 to C10 alkylene triol, or a C4 to C10 alkylene glycol. The aqueous liquid vehicle can be devoid of nitrogen-containing organic co solvent. The method can further include exposing 230 the powder bed to ultraviolent radiation to selectively fuse portions of individual layers of the polymer build material in contact with the fusing agent to form a three-dimensional object.

[0013] In an example, the method can further include preheating the polymer build material to a temperature ranging from about 4 °C to about 30°C, from about 10 °C to about 30 °C, or from about 10 °C to about 20 °C lower than the melting or softening point of the polymer. In another example the method can further include, based on the three-dimensional object model, jetting a detailing agent onto individual layers laterally at a border between a first area of the polymer build material contacted by the fusing agent and an area of the polymer build material uncontacted by the fusing agent. Printing a detailing agent laterally at a border can increase the definition of the three-dimensional object at the lateral edge and can permit a formation of a smooth edge at the printed three- dimensional object.

[0014] Following jetting of the fluid agents (fusing agent and/or fusing agent and detailing agent), an electromagnetic radiation source can be used to selectively fuse portions of individual layers of the polymer build material. The electromagnetic radiation source, for example, can include a scanning lamp energy source with one or multiple high watt bulbs which emits ultraviolet light energy, for example. In some examples, exposing the powder bed to the ultraviolet radiation energy or some other frequency of electromagnetic energy can raise a temperature of an individual layer of the polymer build material to a temperature ranging from about 1 °C to about 100 °C above a melting temperature of the polymer build material. A portion of the polymer build material having the fusing agent applied thereto can thus be fused, while areas outside of where the fusing agent was applied can remain free flowing or substantially free flowing (e.g., they do not become part of the three-dimensional object or part being fabricated).

[0015] In further detail regarding the three-dimensional printing methods, as an example, methods can be carried out using a three-dimensional printing system 300 or apparatus, as illustrated in FIG. 3. Thus, the polymer build material 110 can be iteratively applied to a powder bed support 310 or platform (typically with side walls to hold the powder build material therein). A fluid ejector 320 can selectively jet a fusing agent 120, or in some examples, multiple fluid ejectors may be present to jet fluid agents other than the fusing agent, e.g., ink compositions, detailing agent, etc. The fluid ejectors can be any type of printing apparatus capable of selectively applying the jettable fluid(s). For example, the fluid ejector(s) can be an inkjet applicator(s) (thermal, piezo, etc.), a sprayer(s), etc.

[0016] Following jetting, an electromagnetic radiation source 330 can be used to expose the powder bed to electromagnetic radiation (e), such as ultraviolet radiation, to selectively fuse portions of individual layers 130 of the polymer build material together to form the three-dimensional object. The electromagnetic radiation source can be a static lamp or can travel latterly by carriage along with the fluid ejectors. In further detail, the build platform can drop in height (shown by x), thus allowing for successive layers of polymer build material to be applied and the respective layers to be patterned one layer at a time and exposed to electromagnetic radiation until the three-dimensional object is formed. [0017] The three-dimensional object formed with the three-dimensional printing kit herein can exhibit less yellowing than three-dimensional objects formed with pyrrolidone based solvents and metal oxides. Yellowing of three- dimensional objects can result from a side reaction of pyrrolidone solvents with metal oxides which can result from ring opening of the pyrrolidone solvents. Yellowing can also result from free amines that may result from pyrrolidone degradation. These free amines can then react with aldehyde end groups of degraded polyamide powders, resulting in a concentration of enamines which can provide yellowing. The fusing agents herein can exclude pyrrolidone solvents and can thus result in a three-dimensional object that can exhibit significantly less yellowing. In one example, the three-dimensional object can have a b ^* value ranging from 0 units to about 17 units. As used herein, a b ^* value indicates a yellowness of a polymer powder as a function of powder age and/or thermal stress. An x-rite eXact™ spectrometer can measure b ^* values which can range from blue (negative values) to yellow (positive values). The higher the b ^* value, the greater the yellowing. In yet other examples, the three-dimensional object have a b ^* value ranging from about 1 unit to about 10 units, or from about 8 units to about 17 units.

Fusing Agent

[0018] The fusing agent 120 that may be utilized in three-dimensional printing kit or the method of three-dimensional printing, as described herein, can include from about 0.5 wt% to about 30 wt% optically transparent metal oxide particles dispersed in an aqueous liquid vehicle. In yet other examples, the fusing agent can include from about 1 wt% to about 25 wt%, from about 1 wt% to about 20 wt%, from about 5 wt% to about 15 wt%, or from about 3 wt% to about 12 wt% of optically transparent metal oxide particles.

[0019] Optically transparent” as used herein, can indicate that the metal oxide particles appear transparent when viewed by the naked eye when applied to a polymer build material, and in some cases, appears optically transparent as a fusing agent fluid. This appearance can be due to the size of the metal oxide particles, which may otherwise appear white if sized appropriately for light scattering. For example, optically transparent metal oxide particles can have a D50 particle size that can range from about 3 nm to about 90 nm, from about 3 nm to about 75 nm, from about 3 nm to about 60 nm, from about 5 nm to about 50 nm, from about 5 nm to about 25 nm, or from about 3 nm to about 12 nm. Particles within these size ranges can exhibit less light scattering than larger sized particles, can exhibit better light absorption than larger sized particles, and can tend to have less agglomeration, e.g. clumping, than larger sized particles.

[0020] As used herein, the D50 particle size can refer to a value of the diameter of spherical particles or in particles that are not spherical can refer to the volumetric equivalent spherical diameter of that particle. Thus, the particle volume can be converted to a spherical shape having the same volume at the same density, and that diameter can be said to be the particle size of irregular other otherwise non-spherical particles. The particle size can be in a Gaussian distribution or a Gaussian-like distribution (or normal or normal-like distribution). Gaussian-like distributions are distribution curves that can appear Gaussian in distribution curve shape, but which can be slightly skewed in one direction or the other (toward the smaller end or toward the larger end of the particle size distribution range). In these or other types of particle distributions, the particle size can be characterized in one way using the 50 ^th percentile of the particle size, sometimes referred to as the “D50” particle size. “D50” particle size is defined as the particle size at which about half of the particles are larger than the D50 particle size and about half of the other particles are smaller than the D50 particle size (by weight based on the particle content). As used herein, particle size with respect to the optically transparent metal oxide particles can be based on volume of the particle size normalized to a spherical shape for diameter measurement, for example. Particle size can be collected using a Malvern ZETASIZER™ from Malvern Panalytical (United Kingdom), for example.

[0021] The optically transparent metal oxides can be selected from metal oxides that can be UV absorbing or near UV absorbing. In an example, the optically transparent metal oxide particles can include zirconium oxide, titanium dioxide, zinc oxide, cerium oxide, or a combination thereof. In another example, the optically transparent metal oxide particles can include titanium dioxide. In yet another example, the optically transparent metal oxide particles can include zinc oxide. [0022] The optically transparent metal oxide in the fusing agent can provide a temperature boosting capacity to the fusing agent sufficient to increase a temperature of the polymer build material above the melting or softening point of the polymer build material. As used herein, “temperature boosting capacity” refers to the ability of an optically transparent metal oxide to convert electromagnetic energy, e.g., ultraviolet light energy, into thermal energy to increase a temperature of the printed polymer build material over and above the temperature of the unprinted portion of the polymer build material. Typically, the polymer build material can be fused together when the temperature increases to or above the melting or softening temperature of the polymer, but fusion can also occur in some instance below the melting point. As used herein, “melting point” refers to the temperature at which a polymer transitions from a crystalline phase to a pliable, amorphous phase. Some polymers do not have a melting point, but rather have a range of temperatures over which the polymers soften. This range can be segregated into a lower softening range, a middle softening range, and an upper softening range. In the lower and middle softening ranges, the particles can coalesce to form a part while the remaining polymer powder remains loose. If the upper softening range was used, the whole powder bed can become cake like. The “softening point,” as used herein, refers to the temperature at which the polymer particles coalesce while portions of the polymer build material that are not contacted by the fusing agent remain separate and loose.

[0023] In one example, optically transparent metal oxide particles can have a temperature boosting capacity ranging from about 5 °C to about 30 °C for a polymer build material with a melting or softening point from about 75 °C to about 350 °C. If the polymer build material is at a temperature within about 5 °C to about 30 °C of the melting or softening point, then an optically transparent metal oxide can boost the temperature of the printed polymer build material up to or above the melting or softening point of the polymer build material, while the unprinted polymer build material can remain at a lower temperature.

[0024] The optically transparent metal oxide can be dispersed in an aqueous liquid vehicle. In one example, the liquid vehicle can include water as a major solvent, e.g., the solvent present at the highest concentration when compared to other co-solvents. The water can be deionized, in some examples. An amount of water in the aqueous liquid vehicle can range from about 20 wt% to about 98 wt%, from about 40 wt% to about 95 wt%, from about 65 wt% to about 95 wt%, from about 70 wt% to about 98 wt%, or from about 80 to about 98 wt%.

[0025] In another example, the aqueous liquid vehicle can further include from about from about 1 wt% to about 50 wt%, from about 1 wt% to about 25 wt%, or from about 15 wt% to about 35 wt% of liquid components other than water. The other liquid components can include organic co-solvent, surfactant, additives that inhibits growth of harmful microorganisms, viscosity modifiers, pH adjuster, sequestering agents, preservatives, and the like. In one example, the other liquid components can consist essentially of an organic co-solvent and surfactant.

[0026] In an example, the aqueous liquid vehicle can include from about 1 wt% to about 50 wt%, from about 5 wt% to about 20 wt%, or from about 15 wt% to about 45 wt% of an organic co-solvent. The organic co-solvent can include a C2 to C10 alkylene diol, C3 to C10 alkylene triol, C4 to C10 alkylene glycol, or a mixture thereof. In an example, the organic co-solvent can consist essentially of a C2 to C10 alkylene diol, C3 to C10 alkylene triol, C4 to C10 alkylene glycol, or a mixture thereof. In an example, the organic co-solvent can be selected from 1 ,2- ethanediol, 1 ,2-propanediol, 1 ,3-propane diol, 2-methyl-1 , 3-propanediol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, or a combination thereof. In yet another example, the organic co-solvent can include 1 ,2-ethanediol, 1 ,2-propanediol, 1 ,3-propane diol, 2-methyl-1 , 3-propanediol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dialcohols, trialcohols, polyalcohols, oligomeric glycol solvents, or a combination thereof. In a further example, the organic co-solvent can include propylene glycol. In some examples, the organic co-solvent can exclude pyrrolidones, amines, lactams, and/or a combination thereof.

[0027] In some examples, the aqueous liquid vehicle can further include a surfactant. Surfactants can be present at from about 0.01 wt% to about 10 wt% or from about 0.1 wt% to about 5 wt%, if present. Example surfactants can include alkyl polyethylene oxides, alkyl phenyl polyethylene oxides, polyethylene oxide block copolymers, acetylenic polyethylene oxides, polyethylene oxide (di)esters, dimethicone copolyols, or the like. Commercially available examples of surfactants can include, but are not limited to, TERGITOL ^® TMN-6, TERGITOL ^® 15S7, TERGITOL ^® 15S9, LEG-1 , LEG-7; Triton™ X-100, and Triton™ X-405 all available from The Dow Chemical Company (USA).

[0028] In some examples, the aqueous liquid vehicle can further include biocides, fungicides, and other microbial agents. Example antimicrobial agents can include the NUOSEPT ^® (Ashland Inc. (USA)), VANCIDE ^® (R.T. Vanderbilt Co. (USA)), ACTICIDE ^® B20 and ACTICIDE ^® M20 (Thor Chemicals (U.K.)), PROXEL ^® GXL (Arch Chemicals, Inc.(USA)), BARDAC ^® 2250, 2280, BARCUAT ^® 50-65B, and CARBOCUAT ^® 250-T, (Lonza Ltd. Corp. (Switzerland)), KORDEK ^® MLX (The Dow Chemical Co. (USA)), and combinations thereof. In an example, a total amount of antimicrobial agents in the liquid vehicle can range from about 0.1 wt% to about 1 wt% or from about 0.25 wt% to about 0.75 wt%.

[0029] Viscosity modifiers and buffers may also be present. For example, a buffer solution(s) can include potassium hydroxide, 2-[4-(2-hydroxyethyl) piperazin-1-yl] ethane sulfonic acid, 2-amino-2-(hydroxymethyl)-1 , 3-propanediol (TRIZMA ^® sold by Sigma-Aldrich (USA)), 3-morpholinopropanesulfonic acid, beta-alanine, betaine, or mixtures thereof. Such additives can be present at from about 0.01 wt% to about 10 wt% or from about 1 wt% to about 5 wt%.

[0030] In some examples, the fusing agent can include less than 2 wt% nitrogen containing solvents. In another example, the fusing agent can be devoid of pyrrolidones, amines, lactams, and/or nitrogen-containing solvents. In an example, the fusing agent can be devoid of pyrrolidones.

Polymer Build Material

[0031] In the three-dimensional printing kit and the method for three- dimensional printing herein, the polymer build material can include from about 80 wt% to about 100 wt%, from about 90 wt% to 100 wt%, from about 95 wt% to 100 wt%, or from about 99 wt% to 100 wt% nitrogen-containing polymer particles. In an example, the nitrogen containing polymer particles can be selected from polyamide-6 powder, polyamide-9 powder, polyamide-11 powder, polyamide-12 powder, polyamide-66 powder, polyamide-612 powder, thermoplastic polyamide polymers, thermoplastic polyamide copolymers, thermoplastic urethanes, or a combination thereof. In one example, the nitrogen-containing polymer particles can include polyamide powders. In another example, the nitrogen-containing polymer particles can include polamide-12 powder.

[0032] The polymer build material can have a melting point that can range from about 75 °C to about 350 °C, from about 100 °C to about 300 °C, or from about 150 °C to about 250 °C. As examples, the polymer build material can be a polyamide having a melting point ranging from about 170 °C to about 190 °C, or a thermoplastic urethane having a melting point ranging from about 100 °C to about 165 °C. A variety of nitrogen-containing thermoplastic polymers with melting points or softening points in these ranges can be used. In a specific example, the nitrogen-containing polymer particles can be polyamide-12 powder, a.k.a. nylon 12, which can have a melting point ranging from about 175 °C to about 200 °C.

[0033] The polymer build material can be made up of similarly sized particles or differently sized particles. An average particle size of the nitrogen- containing polymer particles can range from about 20 pm to about 150 pm but can also be from about 50 pm to about 125 pm, or from about 60 pm to about 100 pm.

[0034] In some examples, the polymer build material may include, in addition to the nitrogen-containing polymer particles, a charging agent, a flow aid, other types of polymer particles, or combinations thereof. Charging agent(s) may be added to suppress tribo-charging. Examples of suitable charging agent(s) include aliphatic amines (which may be ethoxylated), aliphatic amides, quaternary ammonium salts (e.g., behentrimonium chloride or cocamidopropyl betaine), esters of phosphoric acid, polyethylene glycol esters, or polyols. Some suitable commercially available charging agents include HOSTASTA ^t® FA 38 (natural based ethoxylated alkylamine), HOSTASTA ^7® FE2 (fatty acid ester), and HOSTASTAT® HS 1 (alkane sulfonate), both from Clariant Int. Ltd. (North America). In an example, the charging agent can be added in an amount ranging from greater than 0 wt% to about 5 wt% based upon the total wt% of the polymer build material.

[0035] Flow aid(s) may be added to increase the coating flowability of the polymer build material. Flow aid(s) may be particularly desirable when the particles of the polymer build material are on the smaller end of the particle size range. A flow aid can increase the flowability of the polymer build material by reducing friction, lateral drag, and tribocharge buildup (by increasing the particle conductivity). Examples of suitable flow aids include 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), or polydimethylsiloxane (E900). In an example, the flow aid can be added in an amount ranging from greater than 0 wt% to less than about 5 wt% based upon the total wt% of the polymer build material.

Detailing Agent

[0036] In some examples, the three-dimensional printing kit can further include a detailing agent formulation including a detailing compound. The detailing compound can be capable of reducing the temperature of the polymer build material onto which the detailing agent is applied. In some examples, the detailing agent can be printed around the edges of the portion of the polymer build material powder that is printed with the fusing agent. The detailing agent can increase selectivity between the fused and unfused portions of the powder bed by reducing the temperature of the powder around the edges of the portion to be fused.

[0037] The detailing compound can be water or an organic co-solvent that can evaporate at the temperature of the powder bed. In some cases the powder bed can be preheated to a preheat temperature within about 10 °C to about 70 °C of the fusing temperature of the polymer powder. Depending on the type of polymer powder used, the preheat temperature can be in the range of about 90 °C to about 200 °C or higher. When the detailing compound comes into contact with the powder bed at the preheat temperature it can thereby cool the printed portion of the powder bed through evaporative cooling.

[0038] In certain examples, the detailing agent can include water, co solvents, or combinations thereof. Non-limiting examples of co-solvents for use in the detailing agent can include xylene, methyl isobutyl ketone, 3-methoxy-3- methyl- 1 -butyl acetate, ethyl acetate, butyl acetate, propylene glycol monomethyl ether, ethylene glycol mono tert-butyl ether, dipropylene glycol methyl ether, diethylene glycol butyl ether, ethylene glycol monobutyl ether, 3-Methoxy-3- Methyl-1 -butanol, isobutyl alcohol, 1 ,4-butanediol, and combinations thereof. In some examples, the detailing agent can be mostly water. In a particular example, the detailing agent can be from about 85 wt% to 100 wt%, or from about 85 wt% to about 99 wt% water. In further examples, the detailing agent can be from about 95 wt% to 100 wt%, or from about 95 wt% to 99 wt% water. In still further examples, the detailing agent can be substantially devoid of radiation absorbers. That is, in some examples, the detailing agent can be substantially devoid of ingredients that absorb enough radiation energy to cause the polymer build material to fuse.

Definitions

[0039] It is noted that, as used in this specification and the appended claims, the singular forms ”a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0040] As used herein, “jetting” or “jettable” refers to compositions that are ejectable from jetting architecture, such as ink-jet architecture. Ink-jet architecture can include thermal or piezo pens with printing orifices or openings suitable for ejection of small droplets of fluid. In a few examples, the fluid droplet size can be less than 10 picoliters, less than 20 picoliters, less than 30 picoliters, less than 40 picoliters, less than 50 picoliters, etc.

[0041] As used herein, the term “about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be “a little above” or “a little below” the endpoint. The degree of flexibility of this term can be dictated by the particular variable and determined based on experience and the associated description herein.

[0042] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though members of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

[0043] Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include individual numerical values or sub ranges encompassed within that range as if numerical values and sub-ranges are explicitly recited. As an illustration, a numerical range of “about 1 wt% to about 5 wt%” should be interpreted to include not only the explicitly recited values of about 1 wt% to about 5 wt%, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3.5, and 4 and sub-ranges such as from 1-3, from 2-4, and from 3-5, etc. This same principle applies to ranges reciting only one numerical value. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.

EXAMPLE

[0044] The following illustrates several examples of the present disclosure. However, it is to be understood that the following are only illustrative of the application of the principles of the present disclosure. Numerous modifications and alternative compositions, methods, and systems may be devised without departing from the spirit and scope of the present disclosure. The appended claims are intended to cover such modifications and arrangements.

Yellowing Effect and Print Performance of Fusing Agents with Various Organic Co-solvents in Fusing Agents

[0045] To evaluate the yellowing effect of various organic co-solvents in fusing agents, several admixtures were prepared. The admixtures were prepared by combining the ingredients in the various formulations provided in Table 1 and 2 below. Table 1 : Fusing Agent Formulations A-C

Table 2: Fusing Agent Formulations D-E

[0046] The fusing agents of formulations A-G were ejected from a thermal inkjet printhead onto a paper medium to determine decap performance of the fusing agents. All of the admixtures exhibited acceptable decap performance, in that they did not cause clogging when left uncapped for 16 seconds.

[0047] The fusing agents of formulations A-F were then subsequently admixed with 1 mm x 1 mm blocks of polyamide-12 powder and then ultraviolet light radiation was applied to bring the samples to about 175 °C for about 20 hours. The b ^* values of the individual sample blocks along with a Control (powder only) were determined using an x-rite eXact™ spectrometer to determine the propensity of the respective fusing agent to exhibit yellowing when exposed to ultraviolet radiation. The results are shown in Table 3 below. Table 3: b ^* values

As indicated in Table 3, three-dimensional objects manufactured with fusing agents that incorporated a pyrrolidone (A, B, D, and E) exhibited greater yellowing than the other samples. The fusing agent incorporating titanium dioxide particles and propylene glycol (C) exhibited the least amount of yellowing when compared to the Control.

[0048] As another point of comparison, a control fusing agent formulation containing about 10 wt% titanium dioxide and water as the major solvent was prepared. From this sample, it was confirmed that water does not contribute significantly to yellowing. As the water did not produce much yellowing, it was determined that to the organic co-solvent concentration can be minimized, e.g., selecting organic co-solvents that do not contribute too much to yellowing/discoloration can be added at concentrations high enough for purposes of jettability and print performance, etc. This can be useful in formulating fusing agents, as it is typically the organic co-solvent that contributes the most to yellowing. By selecting the appropriate organic co-solvent in accordance with the present disclosure, and in one example, minimizing the concentration to the extent useful for a given application, minimal yellowing can result with good print performance.

[0049] While the present technology has been described with reference to certain examples, it is appreciated that various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the disclosure. It is intended, therefore, that the disclosure be limited only by the scope of the following claims.