阅读说明：本技术 采用孔隙促进剂的三维打印 (Three-dimensional printing with pore promoters ) 是由 E·H·迪塞基奇 S·R·伍德拉夫 S·G·鲁迪西尔 A·S·卡巴尔诺夫 于 2019-06-10 设计创作，主要内容包括：本公开描述了用于三维打印的多流体套装、用于三维打印的材料套装、和用于制造三维打印制品的方法。在一个实例中,用于三维打印的多流体套装可以包含助熔剂和孔隙促进剂。助熔剂可以包含水和辐射吸收剂。该辐射吸收剂可以吸收辐射能量并将辐射能量转化为热量。孔隙促进剂可以包含水和水溶性孔隙促进化合物。该孔隙促进化合物可以在提高的温度下化学反应以产生气体。(The present disclosure describes a multi-fluid kit for three-dimensional printing, a material kit for three-dimensional printing, and a method for manufacturing a three-dimensionally printed article. In one example, a multi-fluid set for three-dimensional printing may contain a fluxing agent and a pore promoting agent. The fluxing agent may comprise water and a radiation absorber. The radiation absorber can absorb radiant energy and convert the radiant energy into heat. The pore promoter may comprise water and a water-soluble pore promoting compound. The pore promoting compound may chemically react at an elevated temperature to produce a gas.)

1. A multi-fluid kit for three-dimensional printing, comprising:

a fluxing agent comprising water and a radiation absorber, wherein the radiation absorber absorbs radiation energy and converts the radiation energy to heat; and

a pore promoter comprising water and a water-soluble pore promoting compound, wherein the pore promoting compound chemically reacts at an elevated temperature to produce a gas.

2. The multi-fluid kit of claim 1, wherein the pore promoting compound is carbohydrazide, urea, a urea homolog, a urea-containing compound, ammonium carbonate, ammonium nitrate, ammonium nitrite, or a combination thereof.

3. The multi-fluid kit of claim 1, wherein the pore promoting compound is present in an amount of about 0.5 wt% to about 10 wt% relative to the total weight of the pore promoting agent.

4. The multi-fluid kit of claim 1, wherein the elevated temperature at which the pore promoting compound chemically reacts is from about 100 ℃ to about 250 ℃.

5. The multi-fluid kit of claim 1, wherein the radiation absorber is a metal dithiolene complex, carbon black, a near-infrared absorbing dye, a near-infrared absorbing pigment, a metal nanoparticle, a conjugated polymer, or a combination thereof.

6. The multi-fluid kit of claim 1, further comprising a refining agent comprising a refining compound, wherein the refining compound reduces the temperature of the powder bed material on which the refining agent is applied.

7. A kit of materials for three-dimensional printing, comprising:

a powder bed material comprising polymer particles;

a fluxing agent comprising water and a radiation absorber for selective application to the powder bed material, wherein the radiation absorber absorbs radiant energy and converts the radiant energy to heat; and

a pore promoter comprising water and a water-soluble pore promoting compound for selective application to the powder bed material, wherein the pore promoting compound chemically reacts at an elevated temperature to produce a gas.

8. The kit of materials of claim 6, wherein the polymer particles have an average particle size of about 20 μm to about 100 μm and comprise nylon 6, nylon 9, nylon 11, nylon 12, nylon 6, nylon 6,12, polyethylene, thermoplastic polyurethane, polypropylene, polyester, polycarbonate, polyetherketone, polyacrylate, polystyrene powder, wax, or a combination thereof.

9. The kit of materials of claim 6, wherein the pore promoting compound is carbohydrazide, urea, a urea homolog, a urea-containing compound, ammonium carbonate, ammonium nitrate, ammonium nitrite, or a combination thereof.

10. The kit of materials of claim 6, wherein the radiation absorber is a metal dithiolene complex, carbon black, a near-infrared absorbing dye, a near-infrared absorbing pigment, a metal nanoparticle, a conjugated polymer, or a combination thereof.

11. The kit of claim 6, wherein the elevated temperature at which the pore promoting compound chemically reacts is about 100 ℃ to about 250 ℃.

12. A method of making a three-dimensionally printed article, comprising:

repeatedly applying layers of build material of individual polymer particles onto the powder bed;

selectively jetting a flux onto the individual layers of build material based on a three-dimensional object model, wherein the flux comprises water and a radiation absorber;

selectively jetting a pore promoter onto the separate layer of build material based on the three-dimensional object model, wherein the pore promoter comprises water and a water-soluble pore promoting compound, wherein the pore promoting compound chemically reacts at an elevated temperature to generate a gas; and are

Exposing the powder bed to energy to selectively fuse polymer particles contacting the radiation absorber to form a fused polymer matrix at the individual layers of build material, whereby the pore promoting compound is heated to an elevated temperature to generate a gas distributed in the fused polymer matrix.

13. The method of claim 12, wherein the pore promoting compound is carbohydrazide, urea, a urea homolog, a urea-containing compound, ammonium carbonate, ammonium nitrate, ammonium nitrite, or a combination thereof.

14. The method of claim 12, wherein the elevated temperature is from about 100 ℃ to about 250 ℃.

15. The method of claim 12, wherein the gas forms isolated pores in the fused polymer matrix, the pores having an average diameter of about 1 micron to about 500 microns.

Background

Three-dimensional (3D) digital printing methods, an additive manufacturing, have evolved over the past few decades. However, 3D printing systems have historically been very expensive, although these costs have recently decreased to more affordable levels. In general, 3D printing techniques can shorten product development cycles by allowing rapid generation of prototype models for inspection and testing. Unfortunately, this concept is limited in commercial throughput because the range of materials used in 3D printing is also limited. Therefore, it may be difficult to 3D print a functional part having desired properties (such as mechanical strength, visual appearance, and the like). Nevertheless, several commercial sectors (e.g., the aerospace and medical industries) have benefited from the ability to quickly manufacture prototypes and custom parts for consumers.

Brief description of the drawings

Fig. 1 is a schematic illustration of an exemplary multi-fluid kit for three-dimensional printing according to an example of the present disclosure.

Fig. 2 is a schematic view of another exemplary multi-fluid kit for three-dimensional printing according to an example of the present disclosure.

Fig. 3 is a schematic diagram of an exemplary three-dimensional printing suite, according to an example of the present disclosure.

Fig. 4A-4C show schematic diagrams of an exemplary three-dimensional printing method using an exemplary multi-fluid set, according to an example of the present disclosure.

Fig. 5 is a flow chart illustrating an exemplary method of manufacturing a three-dimensional printed article according to an example of the present disclosure.

Fig. 6A-6B show exemplary three-dimensional printed articles and cross-sections of three-dimensional printed articles according to examples of the present disclosure.

Detailed Description

The present disclosure describes a multi-fluid set for three-dimensional printing. In one example, a multi-fluid kit for three-dimensional printing may include a fluxing agent comprising water and a radiation absorber. The radiation absorber can absorb radiant energy and convert the radiant energy into heat. The multi-fluid set may also comprise a pore promoting agent comprising water and a water-soluble pore promoting compound. The pore promoting compound may chemically react at an elevated temperature to produce a gas. In further examples, the pore promoting compound can be carbohydrazide, urea homologs, urea-containing compounds, ammonium carbonate, ammonium nitrate, ammonium nitrite, or combinations thereof. In some examples, the pore promoting compound may be present in an amount of about 0.5 wt% to about 10 wt% relative to the total weight of the pore promoting agent. In some examples, the elevated temperature at which the pore promoting compound chemically reacts may be from about 100 ℃ to about 250 ℃. In further examples, the radiation absorber in the fluxing agent can be a metal dithiolene complex, carbon black, a near-infrared absorbing dye, a near-infrared absorbing pigment, a metal nanoparticle, a conjugated polymer, or a combination thereof. In additional examples, the multi-fluid kit may further comprise a refining agent comprising a refining compound. The fining compound may lower the temperature of the powder bed material to which the fining agent is applied.

The present disclosure also describes a kit of materials for three-dimensional printing. In one example, a three-dimensional printing kit may include a powder bed material comprising polymer particles, a fluxing agent comprising water and a radiation absorber for selective application to the powder bed material, and a pore promoting agent comprising water and a water-soluble pore promoting compound for selective application to the powder bed material. The radiation absorber can absorb radiant energy and convert the radiant energy into heat. The pore promoting compound may chemically react at elevated temperatures to produce a gas. In some examples, the polymer particles may have an average particle size of about 20 μm to about 100 μm and may include nylon 6, nylon 9, nylon 11, nylon 12, nylon 66, nylon 612, polyethylene, thermoplastic polyurethane, polypropylene, polyester, polycarbonate, polyetherketone, polyacrylate, polystyrene powder, wax, or combinations thereof. In other examples, the pore promoting compound may be carbohydrazide, urea homologs, urea-containing compounds, ammonium carbonate, ammonium nitrate, ammonium nitrite, or combinations thereof. In further examples, the radiation absorber is a metal dithiolene complex, carbon black, a near-infrared absorbing dye, a near-infrared absorbing pigment, a metal nanoparticle, a conjugated polymer, or a combination thereof. In some examples, the elevated temperature at which the pore promoting compound chemically reacts may be from about 100 ℃ to about 250 ℃.

The present disclosure also describes methods of making three-dimensional printed articles. In one example, a method of making a three-dimensional printed article can include repeatedly applying separate layers of build material of polymer particles onto a powder bed. Flux may be selectively sprayed onto individual layers of build material based on the three-dimensional object model. The fluxing agent may comprise water and a radiation absorber. The pore promoter may also be selectively sprayed onto the separate layer of build material based on the three-dimensional object model. The pore promoter may comprise water and a water-soluble pore promoting compound, wherein the pore promoting compound may chemically react at an elevated temperature to produce a gas. The powder bed may be exposed to energy to selectively fuse the polymer particles in contact with the radiation absorber, forming a fused polymer matrix at the individual layers of build material, thereby heating the pore promoting compound to an elevated temperature to generate a gas distributed in the fused polymer matrix. In certain examples, the pore promoting compound can be carbohydrazide, urea homologs, urea-containing compounds, ammonium carbonate, ammonium nitrate, ammonium nitrite, or combinations thereof. In further examples, the elevated temperature can be from about 100 ℃ to about 250 ℃. In one particular example, the gas can form isolated pores in the fused polymer matrix, wherein the pores have an average diameter of about 1 micron to about 500 microns.

The multi-fluid kits, material kits, and methods described herein can be used to make a three-dimensional (3D) printed article that is porous or has a porous portion. In certain methods involving 3D printing using a powder bed of polymer powder, a pore promoter may be selectively applied to the powder bed. Flux may also be selectively applied to the powder bed. In general, the flux may comprise a radiation absorber that can receive radiation and convert the radiation into heat. After application of the fluxing agent and the pore promoting agent, the powder bed may be exposed to radiation. The portion of the powder bed to which the fluxing agent is applied may be heated to the point where the polymer powders may become fused together to form a solid layer. At the same time, the heat may cause the pore promoting compounds in the pore promoter to react and form a gas. In some examples, the gas may be trapped in the molten polymer in small bubbles. When the polymer hardens, the gas bubbles may remain in the form of pores in the polymer matrix. In some cases, the porosity promoter may be applied in the same area as the fluxing agent to produce a 3D printed article with uniform porosity throughout the article. In other examples, the porosity promoter may be printed on a limited portion of the area where the flux is printed. This may form a 3D printed article having a porous portion and a non-porous portion. By selectively applying the porosity promoter, porous portions of any size, shape, and number can be designed and manufactured in the 3D printed article.

The 3D printed articles having porosity described herein can be difficult to form using many 3D printing methods. In methods using powder beds, forming 3D printed articles with internally closed pores is not desirable because powder build material can become trapped inside the pores and not be able to remove powder after printing the article. Furthermore, 3D printing methods using powder build materials are generally limited in the size of features that can be formed by the printing resolution of the method. For example, a 3D printing method involving applying flux to a powder bed may be used to form pores by designing pores into a 3D object model and then printing an article having pores according to the 3D object model. However, the printing resolution of such methods may be limited by the resolution of the flux applied to the powder bed and the particle size of the powder build material. Thus, the explicit design and printing of apertures using such methods may be limited to apertures greater than the printing resolution.

In turn, the methods and materials described herein may be used to form apertures that are smaller than the printing resolution of 3D printing methods. In some examples, the pores formed using these methods may be smaller than the particle size of the polymer powder build material.

The porosity formed using the methods described herein can affect the bulk properties of the 3D printed article. For example, the 3D printed article may be made porous to reduce the weight of the article. In another example, porosity may be introduced in order to tend to reduce the stiffness and strength of the article. If desired, a portion of the 3D printed article can be made porous to reduce the stiffness of that particular portion. Thus, the ability to selectively form porous portions in a 3D printed article can be used for a variety of applications.

Further, the methods described herein may allow for control and adjustment of the degree of porosity. The pores are formed by the pore promoting compound in the pore promoting agent. The pore promoting compound may be a compound that chemically reacts to form a gas when the compound is heated to an elevated temperature. In some examples, the level of porosity in the 3D printed article can be adjusted by varying the amount of porosity promoter applied to the build material. In other examples, the level of porosity may be adjusted by varying the amount of heating provided to the pore promoting compound. For example, a build material having a pore promoting compound applied thereto may be exposed to more intense radiation or for a longer period of time in order to provide more heat to the pore promoting compound and thereby react more of the pore promoting compound to form a gas. Thus, the methods described herein provide a variety of ways to control the level of porosity in a 3D printed article.

Multi-fluid set for three-dimensional printing

With this description in mind, fig. 1 shows a schematic diagram of an exemplary multi-fluid kit 100 for three-dimensional printing. The multi-fluid set contains a fluxing agent 110 and a pore promoter 120. The fluxing agent may comprise water and a radiation absorber. The radiation absorber can absorb radiant energy and convert the radiant energy into heat. The pore promoter may comprise water and a water-soluble pore promoting compound. As described above, the fluxing agent may be applied to the powder bed material in the areas to be fused to form the 3D printed article layer. The porosity promoter may be applied to the area of the powder bed where porosity is to be formed.

Fig. 2 shows a schematic view of another exemplary multi-fluid set 200 for three-dimensional printing. This multi-fluid set also contains flux 210 and pore promoter 220. Additionally, the multi-fluid set comprises a refiner 230. The fining agent may include a fining compound, which is a compound that can lower the temperature of the powder bed material to which the fining agent is applied. In some examples, the fining agent may be applied around the edges of the area where the flux is applied. This prevents the powder bed material around the edges from agglomerating due to heat from the areas where flux is applied. The refiner may also be applied in the same area as the fusion is applied in order to control the temperature and prevent excessive temperatures when the powder bed material fuses.

Material set for three-dimensional printing

The present disclosure also describes a kit of materials for three-dimensional printing. In some examples, the kit of materials may contain materials that may be used in the three-dimensional printing methods described herein. Fig. 3 shows a schematic diagram of an exemplary three-dimensional printing suite 300, according to an example of the present disclosure. The kit includes a powder bed material 340 comprising polymer particles, a fluxing agent 310 to be selectively applied to the powder bed material, and a pore promoting agent 320 to be selectively applied to the powder bed material.

Three-dimensional printing with multi-fluid set and material set

Fig. 4A-4C illustrate one example of forming a 3D printed article using a multi-fluid suit. In fig. 4A, a fluxing agent 310 and a pore promoter 320 are sprayed onto a powder bed material layer 340 comprising polymer particles. Flux is sprayed by flux sprayer 312 and pore promoter is sprayed by pore promoter sprayer 322. These fluid ejectors can be moved across the layer of polymer particles to selectively eject the fluxing agent over the area to be fused, while the porosity promoter can be ejected over the area to be made porous. If a refiner is to be used, there may be additional refiner ejectors (not shown) that contain a refiner applied at or around the boundary region of the three-dimensional article to be printed. In addition, the radiation source 352 can also move across the polymer particle layer.

Fig. 4B shows the powder bed material layer 340 after the fluxing agent 310 has been sprayed onto the area of the layer to be fused, which contains polymer particles. In addition, a pore promoter 320 has been sprayed onto a portion of the area where the fluxing agent is also sprayed. In this figure, the radiation source 352 is shown emitting radiation 350 towards the polymer particle layer. The flux may contain a radiation absorber that can absorb the radiation and convert the radiant energy into heat.

Fig. 4C shows a powder bed material layer 340 comprising polymer particles having a fused portion 342 sprayed with a flux. The part has reached a temperature sufficient to fuse the polymer particles together to form a solid polymer matrix. The area where the pore promoter is sprayed becomes the porous portion 344. The portion includes a plurality of pores formed when a pore promoting compound in the pore promoter reacts to form a gas upon heating. The reaction forms bubbles in the molten polymer and the bubbles become trapped as the polymer resolidifies to form a solid polymer matrix.

As used herein, "pore" refers to a void space in a solid polymer matrix. The void space may be a separate, enclosed void space that is separated from other void spaces by the solid polymer. In other examples, the void spaces may interconnect with other void spaces. Thus, in various instances, the pores may range from a fully interconnected network of pores to a discrete, disconnected set of pores, depending on the degree of porosity. In further examples, the void space may be filled with a gas generated by a chemical reaction of the pore promoting compound.

As used herein, "porosity" may refer in general context to the presence of pores in a fused polymer matrix. In the context of a particular value, "porosity" may be defined as the volume fraction of void space in the fused polymer relative to the entire volume of the fused polymer together with the void space. Void space may refer to voids formed by chemical reactions of the pore promoting compound, rather than void space designed into a 3D model of the article in question for 3D printing. Any geometry designed into the 3D object model may be considered a feature of the "entire volume of fused polymer" and the fraction of void space may be based on voids formed by gas generated by the pore-promoting compound. Further, porosity can be measured relative to the entire 3D printed article or relative to the porous portion of the 3D printed article (where the porosity promoting agent is applied). In some examples, the porous portion of a 3D printed article manufactured using the methods described herein may have a porosity of about 0.5 vol% to about 50 vol%. In further examples, the porous portion can have a porosity of about 1% to about 30% by volume or about 5% to about 20% by volume. In addition, the size of the pores may vary. In some examples, the pores may have an average diameter of about 1 micron to about 500 microns. In further examples, the pores may have an average diameter of about 2 microns to about 300 microns or about 5 microns to about 50 microns.

Powder bed material

In certain examples, the powder bed material may include polymer particles having a variety of shapes, such as substantially spherical particles or irregularly shaped particles. In some examples, the polymer powder may be capable of forming a 3D printed object having 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 3D printed object. The polymer powder may form a layer about 20 to about 100 μm thick such that the fused layer of the printed part has about the same thickness. This may provide a resolution in the z-axis (i.e., depth) direction of about 20 μm to about 100 μm. The polymer powder may also have a sufficiently small particle size and a sufficiently regular particle shape to provide resolution of about 20 μm to about 100 μm along the x-axis and y-axis (i.e., the axis parallel to the top surface of the powder bed). For example, the polymer powder may have an average particle size of about 20 μm to about 100 μm. In other examples, the average particle size may be about 20 μm to about 50 μm. Other resolutions along these axes may be about 30 μm to about 90 μm or 40 μm to about 80 μm.

The polymer powder may have a melting or softening point of about 70 ℃ to about 350 ℃. In further examples, the polymer may have a melting or softening point of about 150 ℃ to about 200 ℃. A variety of thermoplastic polymers having melting or softening points within these ranges may be used. For example, the polymer powder may be polyamide 6 powder, polyamide 9 powder, polyamide 11 powder, polyamide 12 powder, polyamide 6,6 powder, polyamide 6,12 powder, polyethylene powder, wax, thermoplastic polyurethane powder, acrylonitrile butadiene styrene powder, amorphous polyamide powder, polymethyl methacrylate powder, ethylene-vinyl acetate powder, polyarylate powder, silicone rubber, polypropylene powder, polyester powder, polycarbonate powder, a copolymer of polycarbonate and acrylonitrile butadiene styrene, a copolymer of polycarbonate and polyethylene terephthalate polyether ketone powder, polyacrylate powder, polystyrene powder, or a mixture thereof. In a particular example, the polymer powder can be polyamide 12, which can have a melting point of about 175 ℃ to about 200 ℃. In another embodiment, the polymer powder may be a thermoplastic polyurethane.

The thermoplastic polymer particles may also be blended with fillers in some cases. The filler may include inorganic particles such as alumina, silica, fibers, carbon nanotubes, or combinations thereof. When thermoplastic polymer particles are fused together, the filler particles may become embedded in the polymer, forming a composite. In some examples, the filler may comprise a free-flowing agent, an anti-caking agent, or the like. Such agents may prevent powder particles from stacking, coat powder particles and smooth edges to reduce inter-particle friction, and/or absorb moisture. In some examples, the weight ratio of thermoplastic polymer particles to filler particles can be about 100:1 to about 1:2 or about 5:1 to about 1: 1.

Fluxing agent

The multi-fluid kits and material kits for three-dimensional printing described herein may include a fluxing agent to be applied to the polymeric build material. The flux may comprise a radiation absorber that can absorb radiation energy and convert the energy into heat. In certain examples, the fluxing agent may be used with the powder bed material in certain 3D printing methods. A thin layer of powder bed material may be formed and flux may then be selectively applied to regions of the powder bed material that are desired to be consolidated into a component of a solid 3D printed object. The fluxing agent may be applied, for example, by printing, such as with a fluid ejector or a fluid ejection printhead. Fluid-ejection printheads can eject fluxing agents in a manner similar to ink-jet printheads that eject ink. Thus, the fluxing agent can be applied with great precision on certain areas of the powder bed material intended to form the layer of the final 3D printed object. After application of the flux, the powder bed material may be irradiated with radiant energy. The radiation absorber from the fluxing agent can absorb this energy and convert it to heat, thereby heating any polymer particles that come into contact with the radiation absorber. The appropriate amount of radiant energy may be applied so that the area of the powder bed material printed with the fluxing agent is heated sufficiently to melt the polymer particles, consolidating the particles into a solid layer, while the powder bed material not printed with the fluxing agent remains as a loose powder with individual particles.

In some examples, the amount of applied radiant energy, the amount of flux applied to the powder bed, the concentration of radiation absorber in the flux, and the preheat temperature of the powder bed (i.e., the temperature of the powder bed material prior to printing the flux and irradiating) may be adjusted to ensure that the portions of the powder bed printed with flux will fuse to form a solid layer, and the unprinted portions of the powder bed will remain loose powder. These variables may be referred to as part of the "print mode" of the 3D printing system. In general, the printing mode may include any variable or parameter that may be controlled during 3D printing to affect the outcome of the 3D printing method.

In general, the method of forming a single layer by applying flux and irradiating the powder bed may be repeated with additional layers of fresh powder bed material to form additional layers of the 3D printed article, thereby building up the final object one layer at a time. In this method, the powder bed material surrounding the 3D printed article may act as a support material for the object. When the 3D printing is complete, the article may be removed from the powder bed and any loose powder on the article may be removed.

Thus, in some examples, the flux may include a radiation absorber capable of absorbing electromagnetic radiation to generate heat. The radiation absorber may be colored or colorless. In various examples, the radiation absorber can be a pigment such as carbon black pigment, 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 a combination thereof. Examples of near infrared absorbing dyes include ammonium dyes, tetraaryldiamine dyes, cyanine dyes, phthalocyanine (pthalocyanine) dyes, dithiolene dyes, and others. In further examples, the radiation absorber can be a near-infrared absorbing conjugated polymer such as poly (3, 4-ethylenedioxythiophene) -poly (styrenesulfonate) (PEDOT: PSS), polythiophene, poly (p-phenylene sulfide), polyaniline, poly (pyrrole), poly (acetylene), poly (p-phenylene vinylene), poly (polyparaphenylene) or a combination thereof. As used herein, "conjugated" refers to alternating double and single bonds between atoms in a molecule. Thus, a "conjugated polymer" refers to a polymer having a main chain with alternating double bonds 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.

A variety of near infrared pigments may also be used. Non-limiting examples can include phosphates with various counterions (e.g., copper, zinc, iron, magnesium, calcium, strontium, etc.), and combinations thereof. Non-limiting specific examples of the phosphate may include M₂P₂O₇、M₄P₂O₉、M₅P₂O₁₀、M₃(PO₄)₂、M(PO₃)₂、M₂P₄O₁₂And combinations thereof, wherein M represents a counterion having an oxidation state of +2, such as those listed above or combinations thereof. For example, M₂P₂O₇ May include compounds such as Cu₂P₂O₇、Cu/MgP₂O₇、Cu/ZnP₂O₇Or any other suitable combination of counterions. It is noted that the phosphate salts 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.

The additional near infrared pigment may include a silicate. The silicate may have the same or similar counter ion as the phosphate. One non-limiting example may include M₂SiO₄、M₂Si₂O₆And other silicates in which M is a counterion with an oxidation state of + 2. For example, silicate M₂Si₂O₆May include Mg₂Si₂O₆、Mg/CaSi₂O₆、MgCuSi₂O₆、Cu₂Si₂O₆、Cu/ZnSi₂O₆Or other suitable combinations 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.

In a further example, the radiation absorber can include a metal dithiolene complex. The transition metal dithiolene complexes may exhibit strong absorption bands in the region of 600 nm to 1600 nm of the electromagnetic spectrum. In some examples, the central metal atom may be any metal that can form a planar tetragonal complex. Non-limiting specific examples include nickel, palladium and platinum based complexes.

In some examples, a dispersant may be included in the fluxing agent. The dispersing agent may help disperse the radiation absorbing pigment described above. In some examples, the dispersant itself may also absorb radiation. Non-limiting examples of dispersants that may be included as radiation absorbers, either alone or with pigments, may include polyoxyethylene glycol octylphenol ethers, ethoxylated aliphatic alcohols, carboxylic acid esters, polyethylene glycol esters, sorbitan esters, carboxamides, polyoxyethylene fatty acid amides, poly (ethylene glycol) p-isooctylphenyl ether, sodium polyacrylate, and combinations thereof.

The amount of radiation absorber in the flux may vary depending on the type of radiation absorber. In some examples, the concentration of the radiation absorber in the flux may be about 0.1 wt% to about 20 wt%. In one example, the concentration of the radiation absorber in the flux may be about 0.1 wt% to about 15 wt%. In another example, the concentration may be about 0.1 wt% to about 8 wt%. In yet another example, the concentration may be about 0.5 wt% to about 2 wt%. In one particular example, the concentration may be about 0.5 wt% to about 1.2 wt%. In one example, the concentration of the radiation absorber in the fluxing agent is such that after the fluxing agent is sprayed 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%, relative to the weight of the polymer powder.

In some examples, a fluid ejection device, such as an inkjet printing architecture, may be used to eject the fluxing agent onto the polymer powder build material. Thus, in some examples, the flux may be formulated to impart good jetting properties to the flux. The components that may be included in the flux to provide good jetting performance may include a liquid vehicle. Thermal spraying may function by heating the flux to form vapor bubbles that displace fluid around the bubbles and thereby force fluid droplets out of the spray nozzle. Thus, in some examples, the liquid vehicle can include a sufficient amount of evaporative liquid that can form vapor bubbles upon heating. The evaporative liquid may be a solvent such as water, alcohol, ether or a combination thereof.

In some examples, the liquid vehicle formulation may include one or more co-solvents present in a total of about 1 wt% to about 50 wt%, depending on the jetting architecture. In addition, nonionic, cationic, and/or anionic surfactants can be present, present at about 0.01% to about 5% by weight. In one example, the surfactant may be present in an amount of about 1% to about 5% by weight. The liquid vehicle may also include a dispersant in an amount of about 0.5 wt% to about 3 wt%. The balance of the formulation may be purified water, and/or other vehicle components such as biocides, viscosity modifiers, materials for pH adjustment, sequestering agents, preservatives, and the like. In one example, the liquid vehicle may be primarily water.

In some examples, a water-dispersible or water-soluble radiation absorber can be used with the aqueous vehicle. Because the radiation absorber is dispersible or soluble in water, an organic co-solvent may not be present, as an organic co-solvent may not be included to render the radiation absorber soluble. Thus, in some examples, the fluid may be substantially free of organic solvents, such as primarily water. However, in other examples, co-solvents may be used to help disperse other dyes or pigments, or to enhance the jetting properties of the respective fluids. In yet a further example, the non-aqueous vehicle may be used with an organic soluble or organic dispersible fluxing agent.

In certain examples, high boiling co-solvents may be included in the fluxing agent. The high boiling co-solvent may be an organic co-solvent that boils at a temperature above the powder bed temperature during printing. In some examples, the high boiling co-solvent may have a boiling point above about 250 ℃. In yet a further example, the high boiling co-solvent may be present in the fluxing agent at a concentration of from about 1 wt% to about 4 wt%.

Classes of co-solvents that can be used can include organic co-solvents including aliphatic alcohols, aromatic alcohols, glycols, glycol ethers, polyglycol ethers, caprolactams, formamides, acetamides, and long chain alcohols. Examples of such compounds include higher homologs (C) of 1-aliphatic alcohols, secondary aliphatic alcohols, 1, 2-alcohols, 1, 3-alcohols, 1, 5-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, polyethylene glycol alkyl ethers₆-C₁₂) N-alkyl caprolactam, unsubstituted caprolactam, substituted and unsubstituted formamide bisThese are, both substituted and unsubstituted acetamides, and the like. Specific examples of the solvent that can be used include, but are not limited to, 2-pyrrolidone, N-methylpyrrolidone, 2-hydroxyethyl-2-pyrrolidone, 2-methyl-1, 3-propanediol, tetraethylene glycol, 1, 6-hexanediol, 1, 5-hexanediol, and 1, 5-pentanediol.

As regards the surfactants which may be present, one or more surfactants may 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 amides, dimethicone copolyols, substituted amine oxides, and the like. The amount of surfactant added to the fluxing agent can be from about 0.01% to about 20% by weight. Suitable surfactants may include, but are not limited to, lipid ketone esters (liponic acids), such as Tergitol ™ 15-S-12, Tergitol ™ 15-S-7, LEG-1 and LEG-7, available from the Dow Chemical Company (Michigan); triton ™ X-100 available from Dow Chemical Company (Michigan); triton ™ X-405; and sodium lauryl sulfate.

Various other additives may be employed to enhance certain properties of the fluxing agent for particular applications. Examples of such additives are those added to inhibit the growth of harmful microorganisms. These additives may be biocides, fungicides, and other microbial agents (microbial agents), which may 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 America, New Jersey), and combinations thereof.

Chelating agents such as EDTA (ethylenediaminetetraacetic acid) may be included to eliminate the deleterious effects of heavy metal impurities, and buffers may be used to control the pH of the fluid. For example, about 0.01 wt% to about 2 wt% can be used. Viscosity modifiers and buffers may also be present, as well as other additives to modify the properties of the fluid as desired. Such additives may be present at about 0.01 wt% to about 20 wt%.

Pore promoters

The pore promoter may comprise a water-soluble pore promoting compound that can chemically react at elevated temperatures to produce a gas. As used herein, "chemical reaction" refers to a change in chemical composition, and not merely a phase change from a liquid or solid to a gas. Many liquid solvents can evaporate at elevated temperatures to form a gas. However, the pore promoting compounds described herein do not refer to liquids that evaporate at elevated temperatures. Rather, the pore promoting compound undergoes a chemical reaction to form a different compound. The product of the chemical reaction may be a gas, and the gas may remain in a gaseous state even after cooling to room temperature. In some examples, the chemical reaction of the pore promoting compound may be conducted without any other reactant other than the pore promoting compound. In certain examples, the pore promoting compound may chemically decompose to form smaller molecules, and the product molecules may include a gas.

Non-limiting examples of pore promoting compounds may include carbohydrazide, urea homologs, urea-containing compounds, ammonium carbonate, ammonium nitrate, ammonium nitrite, and combinations thereof. As used herein, "urea homologues" may refer to methyl ureas and dimethyl ureas. These compounds may chemically decompose to form a gas when heated to decomposition temperatures. In some examples, the formed gas may include carbon dioxide gas.

In some examples, the pore promoter may react to form a gas at the elevated temperature reached in the 3D printing process. In some examples, the elevated temperature at which the pore promoting compound reacts may be from about 100 ℃ to about 250 ℃. In further examples, the elevated temperature can be from about 150 ℃ to about 250 ℃ or from about 190 ℃ to about 240 ℃. In certain examples, the elevated temperature may be at or near the melting or softening point temperature of the polymer particles in the powder bed. For example, the elevated temperature may be within 20 ℃, within 15 ℃, or within 10 ℃ of the melting point or softening point of the polymer particles. Thus, the pore promoting compound may react when the polymer particles fuse during the 3D printing method. In other examples, the elevated temperature at which the pores facilitate the reaction may be above the melting or softening point of the polymer particles. During the 3D printing process, a sufficient amount of the fusing agent may be applied to the polymer particles, and a sufficient amount of radiant energy may be applied to heat the pore promoting compound to a temperature at which the pore promoting compound will react.

In some cases, the pore promoting compound applied to the powder bed may react completely to form a gas when the powder bed is heated during fusion of the polymer particles. In other words, all or substantially all of the pore promoting compound may react to produce a gas. In other examples, a portion of the pore promoting compound may react and another portion may remain unreacted. In certain examples, from about 50% to about 100% by weight of the pore promoting compound may react. In other examples, from about 60% to about 95% or from about 70% to about 90% by weight of the pore promoting compound may react. In yet a further example, less of the pore promoting compound may react. For example, from about 10 wt% to about 70 wt%, or from about 20 wt% to about 60 wt%, or from about 30 wt% to about 50 wt% of the pore promoting compound may react. The amount of the reactive pore-promoting compound may in some cases depend on the temperature to which the powder bed is heated, the length of time the powder is held at that temperature, the total amount of radiant energy applied to the powder bed, and the like. Thus, in some examples, the amount of radiant energy applied, the length of time the powder bed is heated, the temperature to which the powder bed is brought, the amount of flux applied to the powder bed, and other variables can affect the extent of reaction of the pore promoting compound. Thus, these variables can affect the porosity of the final 3D printed article. These variables may be part of the "print mode" of the 3D printing method. Porosity can also be affected by varying the amount of porosity promoter applied to the powder bed. Thus, the printing mode may be adjusted to affect the level of porosity in the 3D printed article.

The total amount of the porosity promoting compound present in the powder bed may directly affect the porosity of the 3D printed article. As mentioned above, this variable can be adjusted by varying the amount of pore promoter applied to the powder bed. Alternatively, the amount of pore promoting compound applied to the powder bed may be varied by varying the concentration of the pore promoting compound in the pore promoting agent. The amount of the pore promoting compound can be selected to allow the pore promoting compound to be jettable from the fluid ejection printhead. In certain examples, the concentration of the pore promoting compound in the pore promoter may be from about 0.5 wt% to about 10 wt% relative to the total weight of the pore promoter. In further examples, the concentration of the pore promoting compound may be 1 to 8 weight percent or 2 to 7 weight percent.

The pore promoter may also include a component that allows the pore promoter to be ejected by the fluid ejection printhead. In some examples, the pore promoter may contain ingredients that impart jettability, such as those described above in the fluxing agent. These ingredients may include liquid vehicles, surfactants, dispersants, co-solvents, biocides, viscosity modifiers, materials for pH adjustment, chelating agents, preservatives, and the like. These ingredients may be included in any of the amounts described above.

Refining agent

In further examples, a multi-fluid kit or a material kit for three-dimensional printing may comprise a refiner. The refining agent may comprise a refining compound. The refining compound may be capable of lowering the temperature of the powder bed material to which the refining agent is applied. In some examples, the refiner may be printed around the edges of the powder portion where the fluxing agent is printed. The refiner may increase the selectivity between fused and unfused portions of the powder bed by lowering the powder temperature around the edges of the portions to be fused.

In some examples, the refining compound may be a solvent that evaporates at the powder bed temperature. In some cases, the powder bed may be preheated to a preheating temperature within about 10 ℃ to about 70 ℃ of the fusion temperature of the polymer powder. Depending on the type of polymer powder used, the preheating temperature may be from about 90 ℃ to about 200 ℃ or higher. The thinning compound may be a solvent that evaporates when in contact with the powder bed at the pre-heating temperature, thereby cooling the printed portion of the powder bed by evaporative cooling. In certain examples, the refiner may comprise water, a co-solvent, or a combination thereof. Non-limiting examples of co-solvents used in the refiner may include xylene, methyl isobutyl ketone, 3-methoxy-3-methyl-1-butyl acetate, ethyl acetate, butyl acetate, propylene glycol monomethyl ether, ethylene glycol mono-t-butyl ether, dipropylene glycol methyl ether, diethylene glycol butyl ether, ethylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol, isobutanol, 1, 4-butanediol, N-dimethylacetamide, and combinations thereof. In some examples, the refiner may be primarily water. In one particular example, the refiner may be about 85% by weight water or more. In further examples, the refiner may be about 95% by weight water or more. In yet further examples, the refiner may be substantially free of radiation absorbers. That is, in some examples, the refiner may be substantially free of components that absorb radiation energy sufficient to fuse the powder. In certain examples, the refiner may include a colorant such as a dye or pigment, but in a small enough amount that the colorant does not fuse the powder on which the refiner is printed upon exposure to radiant energy.

The detailing agent can also include a component that allows the detailing agent to be ejected through the fluid ejection printhead. In some examples, the refiner may comprise a jettability-imparting ingredient, such as those described above in the flux. These ingredients may include liquid vehicles, surfactants, dispersants, co-solvents, biocides, viscosity modifiers, materials for pH adjustment, chelating agents, preservatives, and the like. These ingredients may be included in any of the amounts described above.

Manufacture ofMethod for 3D printing of an article

The present disclosure also describes methods of making three-dimensional printed articles. Fig. 5 shows a flow chart illustrating one exemplary method 500 of manufacturing a three-dimensional printed article. The method comprises the following steps: repeatedly applying 510 separate layers of build material of polymer particles onto the powder bed; selectively jetting a flux onto the individual layers of build material based on the three-dimensional object model, wherein the flux comprises water and a radiation absorber 520; selectively spraying a pore promoter onto the separate layer of build material based on the three-dimensional object model, wherein the pore promoter comprises water and a water-soluble pore promoting compound, wherein the pore promoting compound chemically reacts at an elevated temperature to generate a gas 530; and exposing the powder bed to energy to selectively fuse the polymer particles contacting the radiation absorber to form a fused polymer matrix at the individual layers of build material, thereby heating the pore promoting compound to an elevated temperature to generate a gas 540 distributed in the fused polymer matrix. The polymer particles, fluxing agent and pore promoter may have the components and properties described above.

In some examples, a refiner may also be sprayed onto the powder bed. As mentioned above, the refiner may be a fluid that reduces the maximum temperature of the polymer powder on which the refiner is printed. In particular, the maximum temperature reached by the powder during exposure to electromagnetic energy may be lower in the area where the fining agent is applied. In certain examples, the refiner may include a solvent that evaporates from the polymer powder to evaporate the cooling polymer powder. The refiner can be printed in areas of the powder bed where fusion is not desired. In a particular example, the refiner may be printed along the edges of the areas where flux is printed. This may provide a clean, defined edge for the fused layer, where the fused polymer particles are at the end and adjacent polymer particles remain unfused. In other examples, the refiner may be printed in the same area as the printing flux to control the temperature of the area to be fused. In some instances, some areas to be fused may be prone to overheating, particularly in the central area of a large fused section. To control the temperature and avoid excessive heating, which can lead to melting and collapse of the build material, a refiner can be applied in these areas.

As described above, in some examples, the elevated temperature at which the pore promoting compound chemically reacts may be from about 100 ℃ to about 250 ℃. The elevated temperature may be reached by the pore promoting compound and the powder bed material onto which the pore promoting compound is sprayed when radiant energy is applied to the powder bed. In some examples, the elevated temperature may be at or near the melting or softening point of the polymer particles in the powder bed. In other examples, the elevated temperature may be above or below the melting or softening point of the polymer particles. In any of these examples, the pore promoting compound may be heated to a temperature sufficient to react and form a gas while the polymer particles are in a molten or softened state, such that bubbles may be formed in the molten or softened polymer.

Also as described above, a number of variables of the "print mode" can be adjusted to affect the level of porosity in the 3D printed article. In some examples, a method of making a 3D printed article may include adjusting these variables to change the porosity level. In certain examples, the variables may include the amount of flux applied to the powder bed, the amount of pore promoter applied to the powder bed, the thickness of the individual layers of build material, the intensity and duration of the radiation applied to the powder bed, the preheat temperature of the powder bed, and the like.

The flux and pore promoter may be sprayed onto the powder bed using a fluid jet print head. The amount of the pore promoting compound sprayed onto the powder may be calibrated based on the concentration of the pore promoting compound in the pore promoting compound, the desired porosity of the resulting porous portion to be printed, among other factors. Similarly, the amount of flux used may be calibrated based on the concentration of radiation absorber in the flux, the desired level of fusion of the polymer particles, and other factors. In some examples, the amount of flux printed may be sufficient to bring the radiation absorber into contact with the entire polymer powder layer. For example, if a single polymer powder layer is 100 microns thick, the fluxing agent can penetrate 100 microns into the polymer powder. Thus, the fluxing agent may heat the polymer powder throughout the layer so that the layer may coalesce and bond to the underlying layer. After the solid layer is formed, a new layer of loose powder may be formed by lowering the powder bed or by raising the height of the powder roller and rolling a new layer of powder.

In some examples, the entire powder bed may be preheated to a temperature below the melting or softening point of the polymer powder. In one example, the preheating temperature may be about 10 ℃ to about 30 ℃ below the melting or softening point. In another example, the preheating temperature may be within 50 ℃ of the melting or softening point. In one particular example, the pre-heat temperature may be about 160 ℃ to about 170 ℃, and the polymer powder may be nylon 12 powder. In another example, the preheat temperature may be about 90 ℃ to about 100 ℃, and the polymer powder may be a thermoplastic polyurethane. Preheating may be accomplished with one or more lamps, ovens, heated support beds, or other types of heaters. In some examples, the entire powder bed may be heated to a substantially uniform temperature.

The powder bed may be irradiated with a fusion lamp. Suitable fusion lamps for use in the methods described herein may include commercially available infrared and halogen lamps. The fusion lamp may be a fixed lamp or a moving lamp. For example, the lamps may be mounted on rails to move horizontally through the powder bed. Such fusion lamps may be passed multiple times over the bed, depending on the exposure used to coalesce the individual printed layers. The fusion lamp may be configured to irradiate the entire powder bed with a substantially uniform amount of energy. This can selectively coalesce the printed portions with the fluxing agent, leaving unprinted portions of the polymer powder below the melting or softening point.

In one example, the fusion lamp may be matched to the radiation absorber in the flux, such that the fusion lamp emits a wavelength of light that matches the peak absorption wavelength of the radiation absorber. Radiation absorbers having a narrow peak at a particular near infrared wavelength may be used with fusion lamps that emit a narrow range of wavelengths at approximately the peak wavelength of the radiation absorber. Similarly, radiation absorbers that absorb a wide range of near-infrared wavelengths may be used with fusion lamps that emit a wide range of wavelengths. Matching the radiation absorber with the fusion lamp in this manner can improve the efficiency of the fusing agent coalescing polymer particles for printing on the polymer particles, while unprinted polymer particles do not absorb as much light and remain at a lower temperature.

Depending on the amount of radiation absorber present in the polymer powder, the absorbance of the radiation absorber, the preheating temperature, and the melting or softening point of the polymer, an appropriate amount of radiation can be provided by the fusion lamp. In some examples, the fusion lamp may irradiate a single layer for about 0.5 to about 10 seconds at a time.

The 3D printed article may be formed by spraying a flux onto a layer of powder bed build material according to a 3D object model. In some instances, the 3D object model may be generated using computer-aided design (CAD) software. The 3D object model may be stored in any suitable file format. In some examples, the 3D printed article described herein may be based on a single 3D object model. The 3D object model may define a three-dimensional shape of the article and a three-dimensional shape of a porous portion to be formed in the 3D printed article. In other examples, the article may be defined by a first 3D object model and the porous portion may be defined by a second 3D object model. Other information may also be included, such as additional different materials of the structure to be formed or color data for printing the article in various colors at different locations on the article. The 3D object model may also include features or materials that are specifically related to the ejected fluid on the powder bed material layer, such as a desired amount of fluid to be applied to a given area. This information may be in the form of, for example, drop saturation, which may instruct the 3D printing system to eject a certain number of fluid drops into a particular area. This allows the 3D printing system to finely control radiation absorption, cooling, color saturation, pore promoting compound concentration, and the like. All this information may be contained in a single 3D object file or a combination of multiple files. A 3D printed article may be manufactured based on the 3D object model. As used herein, "based on a 3D object model" may refer to printing using a single 3D object model file or a combination of multiple 3D object models (which together define an article of manufacture). In some instances, software may be used to convert the 3D object model into instructions for a 3D printer to form an article of manufacture by building a single layer of build material.

In one example of a 3D printing method, a thin layer of polymer powder may be spread over a bed to form a powder bed. At the start of the process, the powder bed may be empty, since at this point the polymer particles have not yet spread. For the first layer, the polymer particles may be spread onto an empty build platform. The build platform may be a flat surface of a material (e.g., metal) sufficient to withstand the heating conditions of the 3D printing method. Thus, "applying separate layers of build material of polymer particles onto the powder bed" includes spreading the polymer particles onto an empty build platform for the first layer. In other examples, multiple initial layers of polymer powder may be spread before printing begins. These "blank" layers of powder bed material may be in some examples in an amount of about 10 to about 500, about 10 to about 200, or about 10 to about 100. In some cases, spreading multiple layers of powder before printing begins can improve the temperature uniformity of the 3D printed article. A fluid-jet print head (e.g., an inkjet print head) can then be used to print a flux containing a radiation absorber on the portion of the powder bed corresponding to the thin layer of the 3D article to be formed. The bed, for example typically the entire bed, may then be exposed to electromagnetic energy. The electromagnetic energy may include light, infrared radiation, and the like. Radiation absorbers can absorb more energy from electromagnetic energy than 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 shaped 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 the complete 3D article is printed. Thus, "applying a layer of build material of individual polymer particles to the powder bed" also includes spreading a layer of polymer particles on a layer of loose particles and fused particles below the layer of new polymer particles.

In certain examples, a 3D printed article can be formed having a porosity throughout the 3D printed article, or having porous portions of any desired shape located at any desired location in the 3D printed article. In one example, the 3D printed article may have a porous interior and a solid exterior surface. For example, a 3D printed article may be designed with a solid layer or shell that does not contain any pore promoting agent, and then an inner portion to which the pore promoting agent is applied. In some examples, the solid shell may be about 20 microns to about 2,000 microns thick, or any other desired thickness. In further examples, porosity may be formed in the 3D printed article for the purpose of reducing weight of the article, increasing buoyancy of the article, decreasing strength of the article, increasing flexibility of the article, and the like. In one example, certain portions of the article may be made highly porous to form a break section that can be broken with an appropriate force. In another example, a portion of the article may be made porous while other portions are non-porous to provide a more flexible porous section connected to a more rigid non-porous section. In yet another example, a hidden label, code, or identifying indicia may be formed using a pore promoting agent. For example, a porous portion of a particular shape can be formed within the interior of the 3D printed article below the surface such that the porous portion is not visible to the human eye. The porous portion may be detected using a detection device to discover or read a hidden identification tag or code. In this manner, the porous label or code may be used to verify the authenticity of the 3D printed article or to store information related to the 3D printed article. In addition to these examples, the 3D printed article having a porous portion may be used for a variety of additional applications.

Definition of

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.

As used herein, "colorant" may include dyes and/or pigments.

As used herein, "dye" refers to a compound or molecule that absorbs electromagnetic radiation or a particular wavelength thereof. Dyes can impart a visible color to an ink if the dye absorbs wavelengths in the visible spectrum.

As used herein, "pigment" generally includes pigment colorants, magnetic particles, alumina, silica, and/or other ceramic, organometallic, or other opaque particles, whether or not such particles impart color. Thus, although the present specification primarily exemplifies the use of pigment colorants, the term "pigment" may be used more generally to describe pigment colorants, as well as other pigments such as organometallics, ferrites, ceramics, and the like. However, in a particular aspect, the pigment is a pigment colorant.

As used herein, "ink-jet" or "jetting" refers to a composition that is jetted from a jetting architecture, such as an inkjet architecture. The ink-jet architecture may include a thermal or piezoelectric architecture. Further, such architectures may be configured to print different drop sizes, such as less than 10 picoliters, less than 20 picoliters, less than 30 picoliters, less than 40 picoliters, less than 50 picoliters, and so forth.

As used herein, "average particle size" refers to the number average particle diameter for spherical particles or the number average 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. The average particle size can be measured using a particle analyzer, such as a Mastersizer. 3000 available from Malvern Panalytical. Particle analyzers can use laser diffraction to measure particle size. A laser beam may be passed through a sample of particles and the angular change in the intensity of light scattered by the particles may be measured. Larger particles scatter light at smaller angles, while small particles scatter light at larger angles. The particle analyzer may then analyze the angular scattering data to calculate the size of the particles using mie theory of light scattering. Particle size may be reported as the volume equivalent sphere diameter.

As used herein, the term "substantially" or "substantially" when used in reference to an amount or quantity of a material, or a particular characteristic thereof, refers to an amount sufficient to provide the effect that the material or characteristic is intended to provide. The exact degree of deviation allowable may depend on the particular context in some cases. When the terms "substantially" or "substantially" are used in the negative, e.g., substantially free of material, it means that the material is not present, or at most may be present in trace amounts at concentrations that will not affect the function or properties of the composition as a whole.

The term "about" is used herein to provide flexibility to a numerical range endpoint by assuming that a given value can be "slightly above" or "slightly below" the endpoint. The degree of flexibility of this term can be dictated by the particular variable and determined based on the relevant description herein.

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 each member of the list is individually identified as a separate and unique member. Thus, no single 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 with any other member of the same list in the absence of an indication to the contrary.

Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and thus should be interpreted flexibly to include the numerical values explicitly recited as the limits of the range, and also to include individual numerical values or sub-ranges encompassed within that range as if the numerical values and sub-ranges are explicitly recited. By way of illustration, a numerical range of "about 1 wt% to about 5 wt%" should be interpreted to include the explicitly recited values of about 1 wt% to about 5 wt%, and also include individual values and sub-ranges within the indicated range. Accordingly, included in this numerical range are individual values, e.g., 2, 3.5, and 4, and sub-ranges, e.g., 1-3, 2-4, and 3-5, etc. This same principle applies to ranges reciting a single numerical value. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.

Examples

The following illustrates embodiments of the present disclosure. It is to be understood, however, that the following is only 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. It is intended that the appended claims cover such modifications and arrangements.

To test the efficacy of urea as a pore promoting compound, a series of fluxing agents were formulated with the addition of urea. The fluxing agent comprises 5 wt.%, 10 wt.%, or 20 wt.% urea. The flux also contained additional ingredients as shown in Table 1.ski (Table 1. ski).

TABLE 1

Composition (I)	Concentration (% by weight)
		Organic cosolvent	5 - 30
High boiling point solvent	1 - 10
		Wetting agent	0.01 - 1
Emulsifier	0.01 - 1
		Chelating agents	0.01 - 1
Biocide agent	0.01 - 1
		Carbon black pigment	1 - 10
Deionized water	Balance of

Initially, 5 wt.% urea in HP Multi Jet Fusion 3D printing test printing beds was used as a flux. It was found that excessive melting or over-fusing of the layers occurred when a fusing speed of 18 inches/second (i.e., the speed at which the fusing lamp passed through the powder bed) was used. Excessive melting results in the final 3D printed article having inaccurate dimensions. By adjusting the fusing speed to 20 inches/second, much better dimensional accuracy was obtained. A series of four 3D printed articles were formed using the same 3D object model. Two of the articles were printed with flux having 5 wt.% urea and two were printed with control flux without urea. The dimensions and quality of the 3D printed article were measured and are shown in table 2 below.

TABLE 2

Product number	Width (mm)	Thickness (mm)	Area (cm)2)	Quality (g)
					1 (control)	3.18	3.9	0.12	1.677
2 (control)	3.22	3.9	0.13	1.684
					3	3.26	3.95	0.13	1.578
4	3.21	3.97	0.13	1.581

The 3D printed article printed using the urea flux has approximately the same dimensions as the 3D printed article printed using the control flux. However, the articles printed with the urea flux had a reduced mass of about 0.1 grams. This indicates that a portion of the volume of the article may be occupied by the gas-filled pores.

The 3D printed article was then tested for tensile strength and young's modulus. The results are shown in table 3.

TABLE 3

Product number	Yield stress (MPa)	Tensile stress at maximum load (MPa)	Young's modulus (MPa)	Yield strain%	Strain at break%
						1 (control)	46.26	46.26	1323.58	13.09	62.69
2 (control)	46.11	46.11	1244.58	12.73	80.07
						3	36.51	36.51	855.43	14.68	73.28
4	37.34	37.34	915.57	16.1	74.78

Articles printed with urea have significantly lower yield stress and young's modulus. However, elongation at break was not significantly affected, indicating that bulk fusion, crystallization, and polymer stability were not compromised with the incorporation of urea.

One of the control 3D printed articles and one of the articles printed with urea were sliced using a razor blade to observe the cross-section. The article printed with urea was significantly easier to cut because it had a more spongy texture. The control 3D printed article was essentially a completely solid polymer, while the article printed with urea had fairly uniform and monodisperse pores inside the article. Fig. 6A shows a perspective view of a 3D printed article 600 printed using urea flux. The article is cut along plane 610 to view the cross-section, shown at fig. 6B. More specifically, fig. 6B shows a schematic cross-sectional illustration (not to scale) of a 3D printed article having a number of small pores 620 formed through a solid polymer matrix 640.

These results indicate that a fluid agent comprising urea can be used to create porosity in a 3D printed article, and this can also affect properties of the article, such as yield stress and young's modulus.