[0001] Methods of three-dimensional (3D) digital printing, a type of additive manufacturing, have continued to be developed over the last few decades. However, systems for three-dimensional printing have historically been very expensive, though those expenses have been coming down to more affordable levels recently. Three-dimensional printing technology can shorten the product development cycle by allowing rapid creation of prototype models for reviewing and testing. Unfortunately, the concept has been somewhat limited with respect to commercial production capabilities because the range of materials used in three-dimensional printing is likewise limited. Accordingly, it can be difficult to three-dimensional print functional parts with desired properties such as mechanical strength, visual appearance, etc. Nevertheless, several commercial sectors such as aviation and the medical industry have benefitted from the ability to rapidly prototype and customize parts for customers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 is a flow diagram illustrating an example method of treating a three-dimensional object in accordance with the present disclosure.

[0003] FIG. 2 is a schematic view of an example three-dimensional printed object being treated with liquid oil in accordance with the present disclosure.

[0004] FIG. 3 is a flowchart illustrating an example method of making a three-dimensional printed object in accordance with the present disclosure.

[0005] FIGS. 4A-4C are schematic views of an example three-dimensional printing system in accordance with the present disclosure. [0006] FIG.5 is a schematic vie of an example three-dimensional printing kit in accordance with the present disclosure. DETAILED DESCRIPTION [0007] The present disclosure describes methods of treating three- dimensional printed objects, methods of making three-dimensional printed objects, and three-dimensional printing kits. In one example, a method of treating a three-dimensional printed object includes applying a liquid oil to a surface of a three-dimensional printed object. The liquid oil includes a long-chain molecule having 12 carbon atoms or more. The three-dimensional printed object includes fused polymer particles with carbon black pigment particles embedded among the fused polymer particles. The surface of the three-dimensional printed object has a darker black appearance after applying the liquid oil than before applying the liquid oil. In some examples, the liquid oil can include a C ₁₂ to C ₃₄ straight- chain alkane, a C ₁₂ to C ₃₄ branched alkane, a silicone oil having alkyl side groups, or a combination thereof. In further examples, the liquid oil can include from about 50 wt% to 100 wt% of a C ₁₈ to C ₃₄ alkane or a polydimethylsiloxane. In some other examples, the fused polymer particles can include polyamide-6, polyamide-9, polyamide-11, polyamide-12, polyamide-6,6, polyamide-6,12, thermoplastic polyamide, polyamide copolymer, polyethylene, thermoplastic polyurethane, polypropylene, polyester, polycarbonate, polyether ketone, polyacrylate, polystyrene, polyvinylidene fluoride, polyvinylidene fluoride copolymer, poly(vinylidene fluoride-trifluoroethylene), poly(vinylidene fluoride- trifluoroethylene-chlorotrifluoroethylene), wax, or a combination thereof. In still other examples, the three-dimensional printed object can include the carbon black pigment particles in an amount from about 0.005 wt% to about 5 wt% with respect to the total weight of the three-dimensional printed object. In certain examples, applying the liquid oil to the surface of the three-dimensional printed object can include soaking the three-dimensional printed object in the liquid oil for a time period from about 1 second to about 30 days. In further examples, the three-dimensional printed object can have a lightness (L*) value from about 35 to about 50 before applying the liquid oil and a lightness (L*) value from about 15 to about 35 after applying the liquid oil. In other examples, the method can also include washing the surface of the three-dimensional printed object after applying the liquid oil. In some examples, the liquid oil can be applied at a temperature from about 0 °C to about 150 °C. [0008] The present disclosure also describes methods of making three- dimensional printed objects. In one example, a method of making a three- dimensional printed object includes iteratively applying individual build material layers of polymer particles to a powder bed. Based on a three-dimensional object model, a fusing agent is selectively applied onto the individual build material layers. The fusing agent includes water and a carbon black pigment dispersion. The powder is exposed to energy to selectively fuse the polymer particles in contact with the carbon black pigment to form a fused polymer matrix at individual build material layers to form a three-dimensional printed object having a black appearance. The method also includes applying a liquid oil to a surface of a three-dimensional printed object. The liquid oil includes a long-chain molecule having 12 carbon atoms or more. The surface of the three-dimensional printed object has a darker black appearance after applying the liquid oil than before applying the liquid oil. In some examples, the liquid oil can include a C ₁₂ to C ₃₄ straight-chain alkane, a C ₁₂ to C ₃₄ branched alkane, a silicone oil having alkyl side groups, or a combination thereof. In further examples, the three-dimensional printed object can have a lightness (L*) value from about 35 to about 50 before applying the liquid oil and a lightness (L*) value from about 15 to about 35 after applying the liquid oil. [0009] The present disclosure also describes three-dimensional printing kits. In one example, a three-dimensional printing kit includes a fusing agent, thermoplastic polymer powder, and a liquid oil. The fusing agent includes from about 75 wt% to about 99 wt% water, and a carbon black pigment dispersion in an amount from about 0.1 wt% to about 15 wt% by solids weight out of the total weight of the fusing agent. The liquid oil includes from about 50 wt% to 100 wt% of a C ₁₂ to C ₃₄ straight-chain alkane, a C ₁₂ to C ₃₄ branched alkane, a silicone oil having alkyl side groups including 12 or more carbon atoms, or a combination thereof. In some examples, the liquid oil can include polyamide-12, polyamide- 6,6, polyamide-6,12, thermoplastic polyamide, polyamide copolymer, polyethylene, thermoplastic polyuretha e, polypropylene, polyester, polycarbonate, polyether ketone, polyacrylate, polystyrene, polyvinylidene fluoride, polyvinylidene fluoride copolymer, poly(vinylidene fluoride- trifluoroethylene), poly(vinylidene fluoride-trifluoroethylene- chlorotrifluoroethylene), wax, or a combination thereof. In certain examples, the liquid oil can include from about 50 wt% to 100 wt% of a C ₁₈ to C ₃₄ alkane or a polydimethylsiloxane having 12 or more carbon atoms. [0010] When discussing the methods of treating three-dimensional printed objects, methods of making three-dimensional printed objects, and three- dimensional printing kits described herein, these discussions can be considered applicable to one another whether or not they are explicitly discussed in the context of that example. Thus, for example, when discussing a polymeric build material related to a three-dimensional printing kit, such disclosure is also relevant to and directly supported in the context of the methods of making three- dimensional printed objects, and vice versa. [0011] Terms used herein will have the ordinary meaning in their 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 can have a meaning as described herein. Methods of Treating Three-dimensional Printed Objects [0012] The methods described herein can be used to treat three- dimensional printed objects to alter the appearance of the object to have a darker black color. In particular, the three-dimensional printed objects can be made using a process that utilizes a carbon black pigment. The three-dimensional printed object can be made up of polymer particles that have fused together. Carbon black pigment particles can be embedded among the fused polymer particles. In many examples, this type of three-dimensional printed object can be black in color due to the carbon black pigment particles. However, many types of polymer particles can be transparent or white in color. Therefore, the overall color of the object can be closer to gray than a true black color. In other examples, the object can have a mottled or patchy appearance with black areas and white areas. However, the methods described herein can be used to give a more even and darker black appearance to such three-dimensional printed objects.

[0013] In some examples, methods of treating three-dimensional printed objects can include applying a liquid oil to a surface of the three-dimensional printed object. The liquid oil can include a long-chain molecule that has 12 carbon atoms or more. As explained above, the three-dimensional printed object can include fused polymer particles with carbon black pigment particles embedded among the fused polymer particles. Applying the liquid oil to the surface of the three-dimensional printed object can cause the appearance of the surface of the object to become darker black than before applying the oil. A variety of types of liquid oil can be used, including alkanes having 12 or more carbon atoms, motor oils, silicone oils having hydrocarbon side chains, and others.

[0014] The effect of the liquid oil on the three-dimensional printed object is unexpected. The liquid oil can be colorless or have a non-black color. Yet, the liquid oil can still change the color of the three-dimensional printed object to a darker black. It has also been found that the color change persists even after vigorous washing of the three-dimensional printed object. This suggests that the color change is not merely a coating on the surface of the object that may be washed away. Without being bound to a specific mechanism, in some examples the liquid oil can interact with the carbon black pigment particles in some way that results in a lasting color change for the three-dimensional printed object to a darker black color.

[0015] FIG. 1 is a flow diagram illustrating one example method 100 of treating a three-dimensional printed object. The method includes applying 110 a liquid oil to a surface of a three-dimensional printed object, wherein the liquid oil includes a long-chain molecule having 12 carbon atoms or more, wherein the three-dimensional printed object includes fused polymer particles with carbon black pigment particles embedded among the fused polymer particles, and wherein the surface of the three-dimensional printed object has a darker black appearance after applying the liquid oil than before applying the liquid oil.

[0016] FIG. 2 illustrates an example of this method, in which a three- dimensional printed object 120 is being treated with a liquid oil 130. The three- dimensional printed object is made up of fused polymer particles 140 and carbon black pigment particles 150 embedded among the fused polymer particles. In this particular example, the liquid oil is applied to the surface of the three-dimensional printed object by dipping the three-dimensional printed object in the liquid oil.

[0017] In further examples, the liquid oil can be applied to the surface of the three-dimensional printed object in a variety of ways. For example, the three- dimensional printed object can be dipped in the liquid oil, or the liquid oil can be sprayed onto the three-dimensional printed object, or the liquid oil can be applied by a brush or by another method.

[0018] In some examples, a liquid oil application unit can be used, which can include equipment for applying liquid oil to a three-dimensional printed object. A liquid oil application unit can include a tank or well containing liquid oil for dipping a three-dimensional printed object or sprayers for spraying liquid oil onto a three-dimensional printed object. In certain examples, a liquid oil application unit can include a chamber in which a three-dimensional object can be enclosed and internal sprayers within the chamber can apply the liquid oil to the three- dimensional printed object. In further examples, it can be useful to wash excess liquid oil off of the three-dimensional printed object. The liquid oil application unit can also include equipment to wash the object, such as with soap and water. Alternatively, the three-dimensional printed object can be removed from the liquid oil application unit and washed elsewhere. In certain examples, a separate washing unit can be used.

[0019] The liquid oil can be applied to the three-dimensional printed object for a sufficient amount of time to allow the liquid oil to increase the black appearance of the object. In some examples, the three-dimensional printed object can be soaked in the liquid oil for a time period from about 1 second to about 30 days. In other examples, the time can be from about 10 seconds to about 3 days, or from about 1 minutes to about 6 hours, or from about 1 second to about 1 minute, or from about 1 minute to about 10 minutes. When the liquid oil is applied by a method other than soaking, the time period can be from the time the liquid is applied (such as by spraying or brushing) and the time when the object is washed to remove excess liquid oil.

[0020] The liquid oil can be capable of increasing the blackness of the three-dimensional printed object without using high temperature, pressure, or other special conditions. In some examples, the liquid oil can be applied at room temperature under normal conditions. Thus, the treatment can be easy to perform with minimal equipment. In some examples, the temperature of the three- dimensional object and the liquid oil can be from about 0 °C to about 150 °C when the liquid oil is applied.

[0021] Focusing on the liquid oil specifically, the liquid oil can include a variety of oils that include long-chain molecules having 12 carbon atoms or more. In some examples, the oil can include molecules having from 12 to 34 carbon atoms. It is noted that some oils include a mixture of many different compounds, and some compounds in the oil can fall outside of this range. However, a portion of the oil can be made up of molecules having from 12 to 34 carbon atoms. In various examples, the liquid oil can include a C12 to C34 straight-chain alkane or a C12 to C34 branched alkane. Additionally, in some examples, the liquid oil can be a silicone oil that includes carbon atom-containing side groups. Examples can include polymethylhydrosiloxane, polydimethylsiloxane, polydiethylsiloxane, and others.

[0022] In some examples, the liquid oil can include alkanes having from 12 carbon atoms to 34 carbon atoms. In other examples, the liquid oil can include alkanes having from 18 carbon atoms to 34 carbon atoms. In certain examples, the alkanes having from 18 carbon atoms to 34 carbon atoms can make up from about 50 wt% to 100 wt% of the total weight of the liquid oil. Examples of alkanes that can be included in the liquid oil can include n-dodecane, n-tridecane, n- tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n- nanodecane, n-icosane, n-henicosane, n-docosane, n-tricosane, n-tetracosane, n-pentacosane, n-hexacosane, n-heptacosane, n-octacosane, n-nonacosane, n- triacontane, n-hentriacontane, n-dotriacontane, n-tritriacontane, n- tetratriacontane, hexylcyclohexane, heptylcyclohexane, octylcyclohexane, nonylcyclohexane, decylcyclohexane, undecylcyclohexane, dodecyclohexane, 3- methyl-1 -hexylcyclohexane, 1-ethyl-2-hexylcyclohexane, 1 -tert-butyl-4- hexylcyclohexane, and others. A variety of other branched alkanes can be included in the liquid oil.

[0023] In certain examples, the liquid oil can include motor oil. Motor oil is a mixture of compounds used as a lubricant for automotive engines. Many types of motor oil include 50 wt% or more of long-chain molecules having 12 carbon atoms or more, as described above. Examples of motor oils that can be used include non-synthetic motor oil, synthetic blends, and full-synthetic motor oil. Motor oils are available in a variety of weights and viscosities, such as 5W-20, 10W-30, etc.

[0024] Notably, the liquid oil can be free of colorants. In particular, the liquid oil may not include any black colorants. Therefore, the increased black appearance provided by the liquid oil is not caused by a color in the oil itself, but rather by an interaction between the liquid oil and the carbon black pigment present in the three-dimensional printed object. The darkness or blackness of the three-dimensional printed object can be quantified as an “L*” value. The L* value corresponds to the lightness of the object. Therefore, a lower value (closer to zero) corresponds to a darker black appearance. In some examples, the three- dimensional printed object can have an L* value from about 35 to about 50 before applying the liquid oil. The L* value can be reduced to a lower value after applying the liquid oil. In some examples, the lower value can be from about 15 to about 35. The definition of the L* value can be in accordance with standard CIELAB values, which include L*, a*, and b*. The L* value can be measured using appropriate equipment, such as an X-Rite® spectrophotometer from X-Rite (USA).

Methods of Making Three-dimensional Printed Objects

[0025] The present disclosure also describes methods of making three- dimensional printed objects. These methods can include a treatment with a liquid oil as described above to increase the black appearance of the objects. FIG. 3 is a flowchart illustrating one example method 200 of making a three-dimensional printed object. This method includes iteratively applying 210 individual build material layers of polymer particles to a powder bed, and based on a three- dimensional object model, selectively applying 220 a fusing agent onto the individual build material layers, wherein the fusing agent includes water and a carbon black pigment dispersion. The method further includes exposing 230 the powder bed to energy to selectively fuse the polymer particles in contact with the carbon black pigment to form a fused polymer matrix at individual build material layers to form a three-dimensional printed object having a black appearance, and applying 240 a liquid oil to a surface of the three-dimensional printed object. The liquid oil in this example includes a long-chain molecule having 12 carbon atoms or more, and the surface of the three-dimensional printed object can have a darker black appearance after applying the liquid oil than before applying the liquid oil.

[0026] To illustrate the process of forming the three-dimensional printed object, FIGS. 4A-5C illustrate an example system 300, e.g., illustrating one example method that can be used to form a three-dimensional printed object. In FIG. 4A, a fusing agent 310 is applied, e.g., jetted, onto a layer of powder bed material 340, which is a bed including polymeric particles for fusing. The fusing agent is jetted from a fusing agent ejector 312 that can move across the layer of powder bed material to selectively jet fusing agent on areas that are to be fused. A radiation source 350 is also shown, which is described in more detail in the context of FIG. 4B.

[0027] The system 300 is further described in FIG. 4B, which shows the layer of powder bed material 340 after the fusing agent 310 has been jetted onto an area of the layer that is to be fused. In this figure, the radiation source 350 is shown emitting radiation 352 toward the layer of polymer particles. The fusing agent can include carbon black pigment particles as a radiation absorber that can absorb this radiation and convert the radiation energy to heat.

[0028] FIG. 4C shows a layer of powder bed material 340 with a fused portion 342 where the fusing agent was jetted. This portion has reached a sufficient temperature to fuse the polymer particles together to form a solid polymer matrix. For context, the fusing agent ejector 312 and the radiation source 350 are shown in place to apply the next applications of fusing agent and radiation to the next layer of powder bed material, to thereby continue to build the three-dimensional object iteratively.

[0029] In some examples, a detailing agent can also be jetted onto the powder bed. The detailing agent can be a fluid that reduces the maximum temperature of the polymer powder on which the detailing agent is printed. In particular, the maximum temperature reached by the powder during exposure to radiation energy can be less in the areas where the detailing agent is applied. In certain examples, the detailing agent can include a solvent that evaporates from the polymer powder to evaporatively cool the polymer powder. The detailing agent can be printed in areas of the powder bed where fusing is not desired. In particular examples, the detailing agent can be printed along the edges of areas where the fusing agent is printed. This can give the fused layer a clean, defined edge where the fused polymer particles end and the adjacent polymer particles remain unfused. In other examples, the detailing agent can be printed in the same area where the fusing agent is printed to control the temperature of the area to be fused. In certain examples, some areas to be fused can tend to overheat, especially in central areas of large fused sections. To control the temperature and avoid overheating (which can lead to melting and slumping of the build material), the detailing agent can be applied to these areas

[0030] The fusing agent and, in some cases, detailing agent can be applied onto the powder bed using fluid jet print heads, e.g., jetting or ejecting from printing architecture. The amount of the fusing agent used can be calibrated based the concentration of radiation absorber in the fusing agent, the level of fusing desired for the polymer particles, and other factors. In some examples, the amount of fusing agent printed can be sufficient to contact the radiation absorber with the entire layer of polymer powder. For example, if individual layers of polymer powder are 100 microns thick, then the fusing agent can penetrate 100 microns into the polymer powder. Thus the fusing agent can heat the polymer powder throughout the entire layer so that the layer can coalesce and bond to the layer below. After forming a solid layer, a new layer of loose powder can be formed, either by lowering the powder bed or by raising the height of a powder roller and rolling a new layer of powder.

[0031] In some examples, the powder bed as a whole can be preheated to a temperature below the melting or softening point of the polymer powder. In one example, the preheat temperature can be from about 10°C to about 30°C below the melting or softening point. In another example, the preheat temperature can be within 50°C of the melting or softening point. In a particular example, the preheat temperature can be from about 160°C to about 170°G and the polymer powder can be polyamide-12 powder. In another example, the preheat temperature can be about 90°C to about 100°C and the polymer powder can be thermoplastic polyurethane. Preheating can be accomplished with a lamp or lamps, an oven, a heated support bed, or other types of heaters. In some examples, the entire powder bed can be heated to a substantially uniform temperature.

[0032] The powder bed can be irradiated with a fusing lamp. Suitable fusing lamps for use in the methods described herein can include commercially available infrared lamps and halogen lamps. The fusing lamp can be a stationary lamp or a moving lamp. For example, the lamp can be mounted on a track to move horizontally across the powder bed. Such a fusing lamp can make multiple passes over the bed depending on the amount of exposure to coalesce printed layers. The fusing lamp can be configured to irradiate the entire powder bed with a substantially uniform amount of energy. This can selectively coalesce the printed portions with fusing agent leaving the unprinted portions of the polymer powder below the melting or softening point.

[0033] In one example, the fusing lamp can be matched with the radiation absorber in the fusing agent so that the fusing lamp emits wavelengths of light that match the peak absorption wavelengths of the radiation absorber. A radiation absorber with a narrow peak at a particular near-infrared wavelength can be used with a fusing lamp that emits a narrow range of wavelengths at approximately the peak wavelength of the radiation absorber. Similarly, a radiation absorber that absorbs a broad range of near-infrared wavelengths can be used with a fusing lamp that emits a broad range of wavelengths. Matching the radiation absorber and the fusing lamp in this way can increase the efficiency of coalescing the polymer particles with the fusing agent printed thereon, while the unprinted polymer particles do not absorb as much light and remain at a lower temperature.

[0034] Depending on the amount of radiation absorber present in the polymer powder, the absorbance of the radiation absorber, the preheat temperature, and the melting or softening point of the polymer, an appropriate amount of irradiation can be supplied from the fusing lamp. In some examples, the fusing lamp can irradiate individual layers from about 0.5 to about 10 seconds per pass.

[0035] The three-dimensional printed object can be formed by jetting a fusing agent onto layers of powder bed build material according to a 3D object model. 3D object models can in some examples be created using computer aided design (CAD) software. 3D object models can be stored in any suitable file format. In some examples, a three-dimensional printed object as described herein can be based on a single 3D object model. The 3D object model can define the three-dimensional shape of the article. Other information may also be included, such as structures to be formed of additional different materials or color data for printing the article with various colors at different locations on the article. The 3D object model may also include features or materials specifically related to jetting fluids on layers of powder bed material, such as the desired amount of fluid to be applied to a given area. This information may be in the form of a droplet saturation, for example, which can instruct a three-dimensional printing system to jet a certain number of droplets of fluid into a specific area. This can allow the three-dimensional printing system to finely control radiation absorption, cooling, color saturation, and so on. All this information can be contained in a single 3D object file or a combination of multiple files. The three-dimensional printed object can be made based on the 3D object model. As used herein, “based on the 3D object model” can refer to printing using a single 3D object model file or a combination of multiple 3D object models that together define the article. In certain examples, software can be used to convert a 3D object model to instructions for a three-dimensional printer to form the article by building up individual layers of build material.

[0036] In an example of the three-dimensional printing process, a thin layer of polymer powder can be spread on a bed to form a powder bed. At the beginning of the process, the powder bed can be empty because no polymer particles have been spread at that point, or the first layer can be applied onto an existing powder bed, e.g., support powder that is not used to form the three- dimensional object. For the first layer, the polymer particles can be spread onto an empty build platform. The build platform can be a flat surface made of a material sufficient to withstand the heating conditions of the three-dimensional printing process, such as a metal. Thus, “applying individual build material layers of polymer particles to a powder bed” includes spreading polymer particles onto the empty build platform for the first layer. In other examples, a number of initial layers of polymer powder can be spread before the printing begins. These “blank” layers of powder bed material can in some examples number from about 10 to about 500, from about 10 to about 200, or from about 10 to about 100. In some cases, spreading multiple layers of powder before beginning the printing can increase temperature uniformity of the three-dimensional printed object. A fluid jet printing head, such as an inkjet print head, can then be used to print a fusing agent including a radiation absorber over portions of the powder bed corresponding to a thin layer of the 3D article to be formed. Then the bed can be exposed to electromagnetic energy, e.g., typically the entire bed. The electromagnetic energy can include light, infrared radiation, and so on. The radiation absorber can absorb more energy from the electromagnetic energy than the unprinted powder. The absorbed light energy can be converted to thermal energy, causing the printed portions of the powder to soften and fuse together into a formed layer. After the first layer is formed, a new thin layer of polymer powder can be spread over the powder bed and the process can be repeated to form additional layers until a complete 3D article is printed. Thus, “applying individual build material layers of polymer particles to a powder bed” also includes spreading layers of polymer particles over the loose particles and fused layers beneath the new layer of polymer particles.

[0037] After the three-dimensional object has been initially formed using the process described above, the object can be treated with a liquid oil using any of the application methods described above. For example, the object can be dipped in liquid oil for a period of time as shown in FIG. 2. In further examples, the method can also include washing excess liquid oil off of the three-dimensional printed object, such as using soap and water. In various examples, the object can be washed by spraying with soap and water, soaking, scrubbing, or other methods.

[0038] As explained above, the three-dimensional printed object can have a darker black appearance after the treatment with the liquid oil compared to before the treatment. In some examples, the dark black appearance can be indicated by an L* value that is lower than the L* value before the treatment. In certain examples, the three-dimensional printed object can have an L* value from about 35 to about 50 before the liquid oil treatment and a reduced L* value from about 15 to about 35 after the liquid oil treatment. Three-dimensional Printing Kits [0039] The present disclosure also describes three-dimensional printing kits. The kits can include materials used in the methods described herein. FIG.5 shows a schematic illustration of one example three-dimensional printing kit 400 in accordance with examples of the present disclosure. The kit includes a powder bed material of thermoplastic polymer powder 420, a fusing agent 410, and a liquid oil 430. In some examples, the fusing agent can include from about 75 wt% to about 99 wt% water, and a carbon black pigment dispersion in an amount from about 0.1 wt% to about 15 wt% by solids weight out of the total weight of the fusing agent. The thermoplastic polymer powder can be suitable for use as a powder bed material in the methods described herein. Further details about the composition of the fusing agent and the polymer powder are described below. The liquid oil can be any of the liquid oils described above. In certain examples, the liquid oil can include from about 50 wt% to 100 wt% of a C ₁₂ to C ₃₄ straight- chain alkane, a C ₁₂ to C ₃₄ branched alkane, a silicone oil having alkyl side groups including 12 or more carbon atoms, or a combination thereof. [0040] In further detail regarding the powder bed material, e.g., the thermoplastic polymer powder or particles, this material can include polymer particles having a variety of shapes, such as substantially spherical particles or irregularly-shaped particles. In some examples, the polymer powder can be capable of being formed into three-dimensional printed objects with a resolution of about 20 μm to about 100 μm, about 30 μm to about 90 μm, or about 40 μm to about 80 μm. As used herein, “resolution” refers to the size of the smallest feature that can be formed on a three-dimensional printed object. The polymer powder can form layers from about 20 μm to about 100 μm thick, allowing the fused layers of the printed part to have roughly the same thickness. This can provide a resolution in the z-axis (i.e., depth) direction of about 20 μm to about 100 μm. The polymer powder can also have a sufficiently small particle size and sufficiently regular particle shape to provide about 20 μm to about 100 μm resolution along the x-axis and y-axis (i.e., the axes parallel to the top surface of the powder bed). For example, the polymer powder can have an average particle size from about 20 μm to about 100 μm. In other examples, the average particle size can be from about 20 pm to about 50 pm. Other resolutions along these axes can be from about 30 pm to about 90 pm or from 40 pm to about 80 pm.

[0041] The polymer powder can have a melting or softening point from about 70°C to about 350°C. In further examples, the polymer can have a melting or softening point from about 150°C to about 200°C. A variety of thermoplastic polymers with melting points or softening points in these ranges can be used. For example, the polymer powder can be polyamide-6 powder, polyamide-9 powder, polyamide-11 powder, polyamide-12 powder, polyamide-6, 6 powder, polyamide- 6,12 powder, thermoplastic polyamide powder, polyamide copolymer powder, polyethylene powder, wax, thermoplastic polyurethane powder, acrylonitrile butadiene styrene powder, amorphous polyamide powder, polymethylmethacrylate powder, ethylene-vinyl acetate powder, polyarylate powder, aromatic polyesters, silicone rubber, polypropylene powder, polyester powder, polycarbonate powder, copolymers of polycarbonate with acrylonitrile butadiene styrene, copolymers of polycarbonate with polyethylene terephthalate, polyether ketone powder, polyacrylate powder, polystyrene powder, polyvinylidene fluoride powder, polyvinylidene fluoride copolymer powder, poly(vinylidene fluoride-trifluoroethylene) powder, poly(vinylidene fluoride- trifluoroethylene-chlorotrifluoroethylene) powder, or mixtures thereof. In a specific example, the polymer powder can be polyamide-12, which can have a melting point from about 175°C to about 200°C. In another specific example, the polymer powder can be thermoplastic polyurethane.

[0042] The thermoplastic polymer particles can also in some cases be blended with a filler. The filler can include inorganic particles such as alumina, silica, fibers, carbon nanotubes, or combinations thereof. When the thermoplastic polymer particles fuse together, the filler particles can become embedded in the polymer, forming a composite material. In some examples, the filler can include a free-flow agent, anti-caking agent, or the like. Such agents can prevent packing of the powder particles, coat the powder particles and smooth edges to reduce inter-particle friction, and/or absorb moisture. In further examples, a filler can be encapsulated in polymer to form polymer encapsulated particles. For example, glass beads can be encapsulated in a polymer such as a polyamide to form polymer encapsulated particles. In some examples, a weight ratio of thermoplastic polymer to filler in the powder bed material can be from about 100: 1 to about 1 :2 or from about 5: 1 to about 1 :1.

[0043] In more specific detail regarding the fusing agent, these fusing agents can be applied to the powder bed in areas that are to be fused together during three-dimensional printing. The fusing agent can include carbon black pigment particles as a radiation absorber. The carbon black pigment particles can absorb radiant energy and convert the energy to heat. As explained above, the fusing agent can be used with a powder bed material in a particular three- dimensional printing process. A thin layer of powder bed material can be formed, and then the fusing agent can be selectively applied to areas of the powder bed material that are desired to be consolidated to become part of the solid three- dimensional printed object. The fusing agent can be applied, for example, by printing such as with a fluid ejector or fluid jet printhead. Fluid jet printheads can jet the fusing agent in a similar way as an inkjet printhead jetting ink. Accordingly, the fusing agent can be applied with great precision to certain areas of the powder bed material that are desired to form a layer of the final three-dimensional printed object. After applying the fusing agent, the powder bed material can be irradiated with radiant energy. The carbon black pigment particles from the fusing agent can absorb this energy and convert it to heat, thereby heating any polymer particles in contact with the pigment particles. An appropriate amount of radiant energy can be applied so that the area of the powder bed material that was printed with the fusing agent heats up enough to melt the polymer particles to consolidate the particles into a solid layer, while the powder bed material that was not printed with the fusing agent remains as a loose powder with separate particles.

[0044] In some examples, the amount of radiant energy applied, the amount ef fusing agent applied to the powder bed, the concentration of radiation absorber in the fusing agent, and the preheating temperature of the powder bed (i.e., the temperature of the powder bed material prior to printing the fusing agent and irradiating) can be tuned to ensure that the portions of the powder bed printed with the fusing agent will be fused to form a solid layer and the unprinted portions of the powder bed will remain a loose powder. These variables can be referred to as parts of the “print mode” of the three-dimensional printing system. The print mode can include any variables or parameters that can be controlled during three-dimensional printing to affect the outcome of the three-dimensional printing process.

[0045] The process of forming a single layer by applying fusing agent and irradiating the powder bed can be repeated with additional layers of fresh powder bed material to form additional layers of the three-dimensional printed object, thereby building up the final object one layer at a time. In this process, the powder bed material surrounding the three-dimensional printed object can act as a support material for the object. When the three-dimensional printing is complete, the article can be removed from the powder bed and any loose powder on the article can be removed.

[0046] Accordingly, in some examples, the fusing agent can include a radiation absorber that is capable of absorbing electromagnetic radiation to produce heat. The radiation absorber can include carbon black pigment particles. These particles can effectively absorb radiation to generate heat. The particles also give the finished three-dimensional printed object a black appearance. In further examples, additional radiation absorbers may also be included. The radiation absorbers can be colored or colorless. In various examples, the radiation absorber can include glass fiber, titanium dioxide, clay, mica, talc, barium sulfate, calcium carbonate, a near-infrared absorbing dye, a near-infrared absorbing pigment, a conjugated polymer, a dispersant, or combinations thereof. Examples of near-infrared absorbing dyes include aminium dyes, tetraaryldiamine dyes, cyanine dyes, pthalocyanine dyes, dithiolene dyes, and others. In further examples, radiation absorber can be a near-infrared absorbing conjugated polymer such as poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonate) (PEDOT:PSS), a polythiophene, poly(p-phenylene sulfide), a polyaniline, a poly(pyrrole), a poly(acetylene), poly(p-phenylene vinylene), polyparaphenylene, or combinations thereof. As used herein, “conjugated” refers to alternating double and single bonds between atoms in a molecule. Thus, “conjugated polymer” refers to a polymer that has a backbone with alternating double and single bonds. In many cases, the radiation absorber can have a peak absorption wavelength in the range of about 800 nm to about 1400 nm. [0047] A variety of near-infrared igments can also be used. Non-limiting examples can include phosphates having a variety of counterions such as copper, zinc, iron, magnesium, calcium, strontium, the like, and combinations thereof. Non-limiting specific examples of phosphates can include M2P2O7, M ₄ P ₂ O ₉ , M ₅ P ₂ O ₁₀ , M ₃ (PO ₄ ) ₂ , M(PO ₃ ) ₂ , M ₂ P ₄ O ₁₂ , and combinations thereof, where M represents a counterion having an oxidation state of +2, such as those listed above or a combination thereof. For example, M ₂ P ₂ O ₇ can include compounds such as Cu ₂ P ₂ O ₇ , Cu/MgP ₂ O ₇ , Cu/ZnP ₂ O ₇ , or any other suitable combination of counterions. It is noted that the phosphates described herein are not limited to counterions having a +2 oxidation state. Other phosphate counterions can also be used to prepare other suitable near-infrared pigments. [0048] Additional near-infrared pigments can include silicates. Silicates can have the same or similar counterions as phosphates. One non-limiting example can include M ₂ SiO ₄ , M ₂ Si ₂ O ₆ , and other silicates where M is a counterion having an oxidation state of +2. For example, the silicate M ₂ Si ₂ O ₆ can include Mg ₂ Si ₂ O ₆ , Mg/CaSi ₂ O ₆ , MgCuSi ₂ O ₆ , Cu ₂ Si ₂ O ₆ , Cu/ZnSi ₂ O ₆ , or other suitable combination of counterions. It is noted that the silicates described herein are not limited to counterions having a +2 oxidation state. Other silicate counterions can also be used to prepare other suitable near-infrared pigments. [0049] In further examples, the radiation absorber can include a metal dithiolene complex. Transition metal dithiolene complexes can exhibit a strong absorption band in the 600 nm to 1600 nm region of the electromagnetic spectrum. In some examples, the central metal atom can be any metal that can form square planer complexes. Non-limiting specific examples include complexes based on nickel, palladium, and platinum. [0050] In further examples, the radiation absorber can include a tungsten bronze or a molybdenum bronze. In certain examples, tungsten bronzes can include compounds having the formula M _x WO ₃ , where M is a metal other than tungsten and x is equal to or less than 1. Similarly, in some examples, molybdenum bronzes can include compounds having the formula M _x MoO ₃ , where M is a metal other than molybdenum and x is equal to or less than 1. [0051] A dispersant can be included in the fusing agent in some examples. Dispersants can help disperse the radiation absorbing pigments described above. In some examples, the dispersant itself can also absorb radiation. Non-limiting examples of dispersants that can be included as a radiation absorber, either alone or together with a pigment, can include polyoxyethylene glycol octylphenol ethers, ethoxylated aliphatic alcohols, carboxylic esters, polyethylene glycol ester, anhydrosorbitol ester, carboxylic amide, polyoxyethylene fatty acid amide, poly (ethylene glycol) p-isooctyl-phenyl ether, sodium polyacrylate, and combinations thereof.

[0052] The amount of radiation absorber in the fusing agent can vary depending on the type of radiation absorber. In some examples, the concentration of radiation absorber in the fusing agent can be from about 0.1 wt% to about 20 wt%. In one example, the concentration of radiation absorber in the fusing agent can be from about 0.1 wt% to about 15 wt%. In another example, the concentration can be from about 0.1 wt% to about 8 wt%. In yet another example, the concentration can be from about 0.5 wt% to about 2 wt%. In a particular example, the concentration can be from about 0.5 wt% to about 1 .2 wt%. In one example, the radiation absorber can have a concentration in the fusing agent such that after the fusing agent is jetted onto the polymer powder, the amount of radiation absorber in the polymer powder can be from about 0.0003 wt% to about 10 wt%, or from about 0.005 wt% to about 5 wt%, with respect to the weight of the polymer powder.

[0053] In some examples, the fusing agent can be jetted onto the polymer powder build material using a fluid jetting device, such as inkjet printing architecture. Accordingly, in some examples, the fusing agent can be formulated to give the fusing agent good jetting performance. Ingredients that can be included in the fusing agent to provide good jetting performance can include a liquid vehicle. Thermal jetting can function by heating the fusing agent to form a vapor bubble that displaces fluid around the bubble, and thereby forces a droplet of fluid out of a jet nozzle. Thus, in some examples the liquid vehicle can include a sufficient amount of an evaporating liquid that can form vapor bubbles when heated. The evaporating liquid can be a solvent such as water, an alcohol, an ether, or a combination thereof.

[0054] In some examples, the liquid vehicle formulation can include a co- solvent or co-solvents present in total at from about 1 wt% to about 50 wt%, depending on the jetting architecture. Further, a non-ionic, cationic, and/or anionic surfactant can be present, ranging from about 0.01 wt% to about 5 wt%. In one example, the surfactant can be present in an amount from about 1 wt% to about 5 wt%. The liquid vehicle can include dispersants in an amount from about 0.5 wt% to about 3 wt%. The balance of the formulation can be purified water, and/or other vehicle components such as biocides, viscosity modifiers, material for pH adjustment, sequestering agents, preservatives, and the like. In one example, the liquid vehicle can be predominantly water.

[0055] In some examples, a water-dispersible or water-soluble radiation absorber can be used with an aqueous vehicle. Because the radiation absorber is dispersible or soluble in water, an organic co-solvent may not be present, as it may not be included to solubilize the radiation absorber. Therefore, in some examples the fluids can be substantially free of organic solvent, e.g., predominantly water. However, in other examples a co-solvent can be used to help disperse other dyes or pigments, or enhance the jetting properties of the respective fluids. In still further examples, a non-aqueous vehicle can be used with an organic-soluble or organic-dispersible fusing agent.

[0056] Classes of co-solvents that can be used can include organic cosolvents including aliphatic alcohols, aromatic alcohols, diols, glycol ethers, polyglycol ethers, caprolactams, formamides, acetamides, and long chain alcohols. Examples of such compounds include 1 -aliphatic alcohols, secondary aliphatic alcohols, 1 ,2-alcohols, 1 ,3-alcohols, 1 ,5-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs (C6-C12) of polyethylene glycol alkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams, both substituted and unsubstituted formamides, both substituted and unsubstituted acetamides, and the like. Specific examples of solvents that can be used include, but are not limited to, 2-pyrrolidinone, N-methylpyrrolidone, 2-hydroxyethyl-2- pyrrolidone, 2-methyl-1 ,3-propanediol, tetraethylene glycol, 1 ,6-hexanediol, 1 ,5- hexanediol, 1 ,2-propanediol, and 1 ,5-pentanediol.

[0057] In certain examples, a high boiling point co-solvent can be included in the fusing agent. The high boiling point co-solvent can be an organic cosolvent that boils at a temperature higher than the temperature of the powder bed during printing. In some examples, the high boiling point co-solvent can have a boiling point above about 250 °C. In still further examples, the high boiling point co-solvent can be present in the fusing agent at a concentration from about 1 wt% to about 4 wt%.

[0058] In certain examples, the fusing agent can include a polar organic solvent. As used herein, “polar organic solvents” can include organic solvents made up of molecules that have a net dipole moment or in which portions of the molecule have a dipole moment, allowing the solvent to dissolve polar compounds. The polar organic solvent can be a polar protic solvent or a polar aprotic solvent. Examples of polar organic solvents that can be used can include diethylene glycol, triethylene glycol, tetraethylene glycol, C3 to C6 diols, 2- pyrrolidone, hydroxyethyl-2-pyrrolidone, 2-methyl-1 ,3 propanediol, polypropylene glycol) with 1 , 2, 3, or 4 propylene glycol units, glycerol, and others. In some examples, the polar organic solvent can be present in an amount from about 0.1 wt% to about 20 wt% with respect to the total weight of the fusing agent.

[0059] Regarding the surfactant that may be present, a surfactant or surfactants can be used, such as alkyl polyethylene oxides, alkyl phenyl polyethylene oxides, polyethylene oxide block copolymers, acetylenic polyethylene oxides, polyethylene oxide (di)esters, polyethylene oxide amines, protonated polyethylene oxide amines, protonated polyethylene oxide amides, dimethicone copolyols, substituted amine oxides, and the like. The amount of surfactant added to the fusing agent may range from about 0.01 wt% to about 20 wt%. Suitable surfactants can include, but are not limited to, liponic esters such as TERGITOL™ 15-S-12, TERGITOL™ 15-S-7 available from Dow Chemical Company (Michigan), LEG-1 and LEG-7; TRITON ™ X-100; TRITON™ X-405 available from Dow Chemical Company (Michigan); and sodium dodecylsulfate.

[0060] Various other additives can be employed to enhance certain properties of the fusing agent for specific applications. Examples of these additives are those added to inhibit the growth of harmful microorganisms. These additives may be biocides, fungicides, and other microbial agents, which can be used in various formulations. Examples of suitable microbial agents include, but are not limited to, NUOSEPT® (Nudex, Inc., New Jersey), UCARCIDE™ (Union carbide Corp., Texas), VANCIDE® (R.T. Vanderbilt Co., Connecticut), PROXEL® (ICI Americas, New Jersey), and combinations thereof. [0061] Sequestering agents, such as EDTA (ethylene diamine tetra acetic acid), may be included to eliminate the deleterious effects of heavy metal impurities, and buffer solutions may be used to control the pH of the fluid. From about 0.01 wt% to about 2 wt%, for example, can be used. Viscosity modifiers and buffers may also be present, as well as other additives to modify properties of the fluid as desired. Such additives can be present at from about 0.01 wt% to about 20 wt%.

[0062] In some more specific examples, in addition to the fusing agent, there may be other fluid agents used, such as coloring agents, detailing agents or the like. A coloring agent may include a liquid vehicle and a colorant, such as a pigment and/or a dye. On the other hand, the three-dimensional printing kits can include a detailing agent. The detailing agent can include a detailing compound. The detailing compound can be capable of reducing the temperature of the powder bed 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 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.

[0063] In some examples, the detailing compound can be a solvent that evaporates 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 more. The detailing compound can be a solvent that evaporates when it comes into contact with the powder bed at the preheat temperature, thereby cooling the printed portion of the powder bed through evaporative cooling. 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, N,N-dimethyl acetamide, and combinations thereof. In some examples, the detailing agent can be mostly water. In a particular example, the detailing agent can be about 85 wt% water or more. In further examples, the detailing agent can be about 95 wt% water or more. 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 powder to fuse. In certain examples, the detailing agent can include colorants such as dyes or pigments, but in small enough amounts that the colorants do not promote fusion of the powder printed with the detailing agent when exposed to the radiation energy.

[0064] The detailing agent can also include ingredients to allow the detailing agent to be jetted by a fluid jet printhead. In some examples, the detailing agent can include jettability imparting ingredients such as those in the fusing agent described above. These ingredients can include a liquid vehicle, surfactant, dispersant, co-solvent, biocides, viscosity modifiers, materials for pH adjustment, sequestering agents, preservatives, and so on. These ingredients can be included in any of the amounts described above.

Definitions

[0065] 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 content clearly dictates otherwise.

[0066] The term "about" as used herein, when referring to a numerical value or range, allows for a degree of variability in the value or range, for example, within 10%, or, in one aspect within 5%, of a stated value or of a stated limit of a range. The term “about” when modifying a numerical range is also understood to include as one numerical subrange a range defined by the exact numerical value indicated, e.g., the range of about 1 wt% to about 5 wt% includes 1 wt% to 5 wt% as an explicitly supported sub-range.

[0067] As used herein, “kit” can be synonymous with and understood to include a plurality of multiple components where the different components can be separately contained (though in some instances co-packaged in separate containers) prior to use, but these components can be combined together during use, such as during the three-dimensional object build processes described herein. The containers can be any type of a vessel, box, or receptacle made of any material.

[0068] As used herein, “applying” when referring to a fluid agent that may be used, for example, refers to any technology that can be used to put or place the fluid, e.g., fusing agent, fluid recycling agent, detailing agent, coloring agent, or the like on the polymeric build material or into a layer of polymeric build material for forming a three-dimensional object. For example, “applying” may refer to a variety of dispensing technologies, including “jetting,” “ejecting,” “dropping,” “spraying,” or the like.

[0069] As used herein, “jetting” or “ejecting” refers to fluid agents or other compositions that are expelled from ejection or jetting architecture, such as ink-jet architecture. Ink-jet architecture can include thermal or piezoelectric architecture. Additionally, such architecture can be configured to print varying drop sizes such as up to about 20 picoliters, up to about 30 picoliters, or up to about 50 picoliters, etc. Example ranges may include from about 2 picoliters to about 50 picoliters, or from about 3 picoliters to about 12 picoliters.

[0070] As used herein, “average particle size” refers to a number average of the diameter of the particles for spherical particles, or a number average of the volume equivalent sphere diameter for non-spherical particles. The volume equivalent sphere diameter is the diameter of a sphere having the same volume as the particle. Average particle size can be measured using a particle analyzer such as the MASTERSIZER™ 3000 available from Malvern Panalytical (United Kingdom). The particle analyzer can measure particle size using laser diffraction. A laser beam can pass through a sample of particles and the angular variation in intensity of light scattered by the particles can be measured. Larger particles scatter light at smaller angles, while small particles scatter light at larger angles. The particle analyzer can then analyze the angular scattering data to calculate the size of the particles using the Mie theory of light scattering. The particle size can be reported as a volume equivalent sphere diameter.

[0071] 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 the individual member of the list is 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 based on presentation in a common group without indications to the contrary.

[0072] Concentrations, dimensions, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include the numerical values explicitly recited as the limits of the range, as well as to include all the individual numerical values or sub-ranges encompassed within that range as the individual numerical value and/or sub- range is explicitly recited. For example, a weight ratio range of about 1 wt% to about 20 wt% should be interpreted to include the explicitly recited limits of 1 wt% and 20 wt% and to include individual weights such as about 2 wt%, about 11 wt%, about 14 wt%, and sub-ranges such as about 10 wt% to about 20 wt%, about 5 wt% to about 15 wt%, etc.

EXAMPLES

[0073] The following illustrates examples of the present disclosure. However, it is to be understood that the following are merely illustrative of the application of the principles of the present disclosure. Numerous modifications and alternative devices, 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.

Example 1 - Treating Three-dimensional Printed Objects

[0074] A series of sample three-dimensional objects were printed using an HP Multi-jet Fusion 3D® printer. The build material was polyamide-11 powder and the fusing agent included carbon black pigment as a radiation absorber. A glass container was filled with SAE 30 motor oil and the sample three- dimensional printed objects were completely immersed in the motor oil for a time period of from 100 hours up to 240 hours. After being immersed in the motor oil, the three-dimensional printed objects had a noticeably darker black color. Observation under a microscope showed that the biack color was more uniform across the surface of the objects. Before treatment, the surface had a mixture of white and black colors due to the white color of the polymer particles and the black color of the carbon black pigment. After the treatment, the polymer appeared to have a more uniform black color across the entire surface. The objects were also washed rigorously, and the washing did not change the darker black appearance of the objects.

Example 2 - Measurement of Lightness (L*)

[0075] The lightness value (L*) of the sample three-dimensional printed objects was measured before and after treatment with the motor oil. Six samples were immersed in the motor oil for 240 hours. The L* values were measured using an X-RITE® MetaVue spectrophotometer from X-Rite (USA). The measured values for these six sample three-dimensional printed objects are shown in Table 1 .

Table 1 - Lightness (L*) Measurements (240 hours)

[0076] An additional group of sample three-dimensional printed objects was immersed in motor oil for 100 hours. The L* value of these samples was measured after treatment with the motor oil. These measurements are shown in Table 2.

Example 3 - Mechanical Properties

[0077] Several mechanical properties of the sample objects were measured before and after the treatment with motor oil, including tensile stress at maximum load, Young’s modulus, and percent strain at break. These properties were measured for six sample objects that were not soaked in motor oil, and then the properties were measured for six objects that had been soaked in motor oil for 240 hours. The mechanical properties did not appear to be significantly changed by the treatment with motor oil. Additionally, the surface roughness of the objects was found to be slightly reduced by the motor oil treatment. The mechanical property data of these samples is shown in Table 3.

Table 3 - Mechanical Property Data