Three-dimensional printing using porosity promoters and acidic reagents

Abstract

The present disclosure includes a multi-fluid kit for three-dimensional printing. The multi-fluid kit can include a fusing agent including water and a radiation absorber that absorbs and converts radiation energy into heat, an acidic agent including water and an acidic component having a pH of about pH 1 to about pH 6.9, and a porosity promoter including water and a porosity promoting compound. The porosity promoting compound can chemically react with the acidic component to generate a gas, and can be selected from sodium bicarbonate, potassium bicarbonate, or a combination thereof.

Description

[0001] background

[0002] Three-dimensional (3D) digital printing, a type of additive manufacturing, has evolved over the past few decades. However, systems used for 3D printing have historically been expensive, although these costs have recently decreased to more affordable levels. Generally, 3D printing technology can shorten product development cycles by allowing the rapid creation of prototype models for inspection and testing. Unfortunately, this concept is somewhat limited in terms of commercial production capabilities because the range of materials available for 3D printing is also limited. Therefore, it can be difficult to print 3D functional parts with desired properties such as mechanical strength, visual appearance, etc. Nevertheless, some commercial sectors, such as the aerospace and medical industries, have already benefited from the ability to rapidly prototype and customize parts for clients. Brief description of the attached diagram

[0004] Figure 1 This is a schematic diagram of an exemplary multifluid suit for 3D printing, according to an example of this disclosure.

[0005] Figure 2 This is a schematic diagram of an exemplary 3D printing material kit according to an example of this disclosure.

[0006] Figures 3A-3C A schematic diagram showing an exemplary 3D printing method using an exemplary multifluid suit according to an example of this disclosure.

[0007] Figure 4 This is a flowchart illustrating an exemplary method for manufacturing a 3D printed object according to an example of this disclosure.

[0008] The accompanying drawings illustrate examples of the technology disclosed herein. However, it should be understood that the technology is not limited to the illustrated examples.

[0009] Detailed Explanation

[0010] Methods for adjusting the mechanical properties of 3D-printed or additively manufactured parts without altering the polymer build material can include the use of various fluid reagents and / or manufacturing methods. The multifluid kits and other material kits, as well as the 3D printing methods and systems disclosed herein, provide the ability to generate parts with increased porosity through 3D printing, or, in some instances, porous cores with solid shells, without significant powder trapping within the pores. This can be achieved by generating gas in situ during the build process, which also provides specified locational and spatial control over pore density.

[0011] Accordingly, in one example, a multifluidic kit for 3D printing may include a flux, an acidic reagent, and a pore promoter. The flux may contain water and a radiation absorber, wherein the radiation absorber absorbs radiation energy and converts the radiation energy into heat. The acidic reagent may contain water and an acidic component and may have a pH of approximately 1 to approximately 6.9. The pore promoter may contain water and a pore-promoting compound. The pore-promoting compound may chemically react with the acidic component from the acidic reagent to generate a gas. The pore-promoting compound may, for example, be selected from sodium bicarbonate, potassium bicarbonate, or combinations thereof. The pore-promoting compound may be, for example, sodium bicarbonate and may be present in an amount of approximately 1% to approximately 10% by weight relative to the total weight of the pore promoter. Alternatively, the pore-promoting compound may be potassium bicarbonate and may be present in an amount of approximately 1% to approximately 20% by weight relative to the total weight of the pore promoter. Both the acidic reagent and the pore promoter may independently contain an organic co-solvent and a surfactant (which may be the same or different from each other). The acidic component can be, for example, an organic acid selected from lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid, malic acid, tartaric acid, or combinations thereof. In another example, the acidic component can be an inorganic acid selected from hydrochloric acid, hydrobromic acid, hydroiodic acid, perchloric acid, phosphoric acid, sulfuric acid, boric acid, nitric acid, nitrous acid, or combinations thereof. The pore-promoting compound can generate gas at elevated temperatures from about 80°C to about 200°C in some instances; therefore, the pore-promoting compound can generate a higher gas volume density (relative to the volume density of the pore-promoting compound at the same concentration without the application of the acidic component) at elevated temperatures when in contact with the acidic component. More specifically, for example, the radiation absorber can include metal dithiolide complexes, carbon black, near-infrared absorbing dyes, near-infrared absorbing pigments, metal nanoparticles, conjugated polymers, or combinations thereof.

[0012] In another example, the 3D printing kit may include a building material comprising polymer particles and a binder comprising water and a radiation absorber that absorbs and converts radiant energy into heat. The 3D printing kit may also include an acidic reagent having a pH of about 1 to about 6.9 and comprising water and an acidic component, and a pore promoter comprising water and a pore-promoting compound. The pore-promoting compound may chemically react with the acidic component to generate a gas. The pore-promoting compound may be selected from sodium bicarbonate, potassium bicarbonate, or combinations thereof. In one example, the polymer particles may have a D50 particle size of about 20 μm to about 150 μm and may include polyamide-6, polyamide-9, polyamide-11, polyamide-12, polyamide-6,6, polyamide-6,12, polyethylene, thermoplastic polyurethane, thermoplastic polyamide, polypropylene, polyester, polycarbonate, polyetherketone, polyacrylate, polystyrene powder, wax, or combinations thereof. Pore-promoting compounds can generate gas at elevated temperatures, from about 80°C to about 200°C, or at lower temperatures when in contact with acidic components, or at elevated temperatures with higher gas volume densities. For example, sodium bicarbonate can generate gas at about 80°C.

[0013] In another example, the 3D printing method may include repeatedly applying individual build material layers of polymer particles to a powder bed, and selectively applying a fusion agent to the individual build material layers based on a 3D object model, wherein the fusion agent comprises water and a radiation absorber. The method may further include selectively applying a pore promoter to the individual build material layers based on the 3D object model. The pore promoter may comprise water and a pore-promoting compound selected from sodium bicarbonate, potassium bicarbonate, or combinations thereof. Furthermore, based on the 3D object model, the method may include selectively applying an acidic agent to the individual build material layers at the application site of the pore promoter. At this site, the pore-promoting compound chemically reacts with the acidic component to generate bubbles within the individual build material layers. The method may further include exposing the build material to energy, the heat of which selectively fuses the polymer particles in contact with the radiation absorber to form a fused polymer matrix at the individual build material layers, wherein bubbles are distributed within the fused polymer matrix. In one example, in addition to the bubble-generating reaction between the pore-promoting compound and the acidic compound, the heat of selectively fusing the polymer particles may further contribute to bubble generation. The discrete pores in the fused polymer matrix, generated by the reaction with an acidic compound and the application of heat, have a D50 diameter, for example, from about 1 μm to about 500 μm. This method can result in the formation of a 3D printed object having a first portion of the fused polymer matrix with a first pore volume at a first location where a flux, a pore accelerator, and an acidic agent have been applied and subsequently thermally fused. The 3D printed object may also include a second portion of the fused polymer matrix having a second pore volume lower than the first pore volume, where a flux has been applied but no acidic agent has been applied. More specifically, a pore accelerator may also not have been applied at the second portion. In this example, the 3D printed object may further include a third portion, where a flux and a pore accelerator have been applied but no acidic agent has been applied, the third portion having a third pore volume lower than the first pore volume but higher than the second pore volume.

[0014] The multifluid kits, material kits, and methods described herein can be used to manufacture porous or porous three-dimensional (3D) printed objects, or objects comprising multiple porous portions with different pore volume densities. In particular, methods relating to 3D printing using polymer particle build materials allow for the selective application of pore promoters and acidic agents to the build material. A flux can also be selectively applied to the build material to promote the fusion of the three-dimensional polymer particles during the build process. The flux may contain a radiation absorber capable of absorbing radiation and converting it into heat. At the layer level, for example, in addition to applying the flux, pore promoter, and acidic agent, the build material can be exposed to radiation. The acidic component of the acidic agent and the pore-promoting compound of the pore promoter can chemically react to generate bubbles. Furthermore, portions of the build material to which the flux has been applied can be heated to the extent that the polymer particles fuse together to form a solid layer. Simultaneously, in addition to gases generated or being generated by the chemical reaction between the pore-promoting compound and the acidic compound, heat can cause the pore-promoting compound in the pore promoter to react and form gas.

[0015] In some instances, gas can be trapped as tiny bubbles within the molten polymer. As the polymer hardens, these bubbles can remain as pores within the polymer matrix. In some cases, pore promoters and / or acidic agents can be applied to the same region as the flux to create a 3D printed object with uniform porosity throughout. In other instances, pore promoters and / or acidic agents can be printed on a limited portion of the region where the flux is printed. This results in a 3D printed object with both porous and non-porous portions. In still other instances, pore promoters can be applied to even more limited portions, and acidic agents can be applied to even more limited sub-portions. This produces a 3D printed object with two (or more) porosity levels within the porous portions and non-porous portions. By selectively applying pore promoters, porous portions of any size, shape, and number can be designed and fabricated within a 3D printed object.

[0016] Forming 3D printed objects with porosity as described herein can be challenging because particulate materials are used as the primary material for forming 3D objects. In methods that use polymer particles as build materials to form 3D printed objects with internally closed pores without ejecting powder or molten powder, a fused polymer with powder trapped within the pores can be obtained. Furthermore, 3D printing methods using polymer particles as build materials are typically limited by the printing resolution of the method in terms of the feature sizes that can be formed. Pores essentially free of build material can be generated by generating gas within the molten polymer during the build process.

[0017] The porosity created using the methods described herein can influence the overall properties of a 3D printed object. For example, a 3D printed object can be made porous to reduce its weight. In another instance, porosity can be introduced to reduce the stiffness or strength of the object. In yet another instance, porosity can be used to control crack propagation. In other words, porosity can also help determine how cracks might pass through / propagate through a component. If desired, a portion of a 3D printed object can be made porous to reduce the stiffness of that particular portion. Therefore, the ability to selectively form porous portions and even porous portions of varying densities in a 3D printed object is useful in a variety of applications.

[0018] The systems, materials, and methods described herein enable the control and regulation of porosity at temperatures lower than those used for some compounds such as urea. Lower temperatures reduce the oxidation of polymer particles in the building materials, thereby reducing any unwanted oxidation / yellowing problems at temperatures above 200°C. Pores can be formed by a pore-promoting compound in a pore promoter and / or by a combination of a pore-promoting compound and an acidic compound—applied to react at the layers of a three-dimensional object. The pore-promoting compound can be a compound that chemically reacts to form a gas and / or reacts with an acidic component when heated to an elevated temperature of approximately 80°C to approximately 200°C. In one example, the pore-promoting compound can be sodium bicarbonate, potassium bicarbonate, or a combination thereof. More specifically, the acidic component of the acidic reagent can be any component that provides a pH of approximately pH 1 to approximately pH 6.9 for the acidic reagent. Examples may include, for example, organic or inorganic acids. Exemplary organic acids can be lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid, malic acid, tartaric acid, or combinations thereof. Exemplary inorganic acids may be hydrochloric acid, hydrobromic acid, hydroiodic acid, perchloric acid, phosphoric acid, sulfuric acid, boric acid, nitric acid, nitrous acid, or combinations thereof.

[0019] In some instances, the porosity level in a 3D-printed object can be tuned by varying the amount of porosity-promoting compounds and / or the content of acidic compounds applied to the build material by their respective fluid reagents. In other instances, the porosity level can be tuned by varying the amount of heat supplied to the porosity-promoting compounds. For example, a build material to which a porosity-promoting compound has been applied can be exposed to stronger radiation or for a longer period to supply more heat to the porosity-promoting compounds, thereby causing more of the porosity-promoting compounds to react and form gas. Therefore, the methods described herein provide multiple avenues for controlling the porosity level in 3D-printed objects.

[0020] Multifluid kit

[0021] Considering this description, Figure 1A schematic diagram of an exemplary multifluid kit 100 for 3D printing is shown. The multifluid kit includes a flux 110, a pore-promoting agent 120, and an acidic reagent 130. The flux may contain water and a radiation absorber. The radiation absorber can absorb radiation energy and convert it into heat. The pore-promoting agent may contain water and a water-soluble pore-promoting compound selected from sodium bicarbonate, potassium bicarbonate, or combinations thereof. The acidic reagent may contain an acidic component, such as an organic acid, an inorganic acid, or other compound that provides acidity to the acidic reagent, for example, a pH of approximately 1 to approximately 6.9, approximately 2 to approximately 6, or approximately 3 to approximately 5.

[0022] In some instances, other fluid agents may be present in the multifluid kit. For example, the multifluid kit may also include coloring agents and / or refining agents. Coloring agents (if present) may comprise a colorant and a liquid carrier that can be fluidly ejected from the jetting structure. Refining agents (if present) may comprise refining compounds that can lower the temperature of the build material to which the refining agent is applied. In some instances, the refining agent may be applied around the edge of the area where the fusion agent is applied. This prevents the build material around the edge from agglomerating due to heat from the area where the fusion agent is applied. The refining agent may also be applied in the same area where the fusion agent is applied to control the temperature and prevent overheating during the fusion of the build material.

[0023] 3D printing kit

[0024] This disclosure also describes a material kit for 3D printing. In some instances, the material kit may include materials that are available in the 3D printing methods described herein. Figure 2 A schematic diagram of a 3D printing kit 200 according to an embodiment of the present disclosure is provided more specifically. The kit includes a build material 240 comprising polymer particles, a fusion agent 110 selectively applied to the build material, a pore promoter 120 selectively applied to the build material, and an acidic reagent selectively applied to the build material, particularly at some or all locations where the pore promoter has been or will be applied. The pore promoter comprises a pore-promoting compound, which may be a compound that chemically reacts to form a gas when heated at an elevated temperature of about 80°C to about 200°C. The pore-promoting compound may be selected from sodium bicarbonate, potassium bicarbonate, or combinations thereof. The acidic reagent may contain an acidic component, such as an organic acid, an inorganic acid, or other compound that provides acidity to the acidic reagent, for example, a pH of about 1 to about 6.9, about 2 to about 6, or about 3 to about 5. As described above, the fusion agent may be applied to the build material in the powder bed region of the layers to be fused to form a 3D printed object.

[0025] 3D printing methods

[0026] Figures 3A-3C The illustration shows an example of using a multi-fluid suite to create a 3D printed object. Figure 3A In this process, a flux 110, a pore accelerator 120, and an acid reagent 130 are selectively sprayed onto a build material layer 340 of a powder bed. The build material comprises polymer particles, such as those described herein, that can be thermally fused during molding to form a molten polymer. The flux can be sprayed from a flux injector 312, the pore accelerator from a pore accelerator injector 322, and the acid reagent from an acid reagent injector 332. These fluid injectors can move across the polymer particle layer to selectively spray the flux onto areas to be fused, while the pore accelerator can be sprayed onto areas where porosity is to be increased. Furthermore, the acid reagent can be sprayed onto areas where pore accelerators have been or will be applied, having the same footprint or a different (typically smaller) footprint to provide increased porosity, typically more than areas where only pore accelerators have been applied. If other fluid reagents, such as coloring agents and / or refining agents, may be present, containing one or more additional injectors (not shown) to accommodate additional fluid reagents to be applied. For example, coloring agents can be applied to add color to the printed object. Refining agents can be applied to or around the boundary areas of the printed 3D object to aid cooling, or in some cases, applied within the area of ​​the 3D printed object to increase cooling. Figures 3A-3C The image also shows radiation source 352, which can also move across the polymer particle layer.

[0027] Figure 3B The diagram shows a build material layer 340 comprising polymer particles after the flux 110 has been sprayed onto the area to be fused in region 110A. Additionally, a pore promoter 120 has been sprayed onto a portion of the area where the flux is also applied, as shown in region 120A. An acidic agent 130 has been applied in this example to region 130A, where both the flux and the pore promoter have been applied. In this figure, a radiation source 352 is shown emitting radiation 350 toward the polymer particle layer. The flux containing the radiation absorber can thus absorb this radiation and convert the radiative energy into heat, causing the polymer particles of the build material to form a molten polymer. As the molten polymer, bubbles generated by the heat applied to the pore-promoting compound and / or by the reaction of the pore-promoting compound and the acidic component of the corresponding fluid reagent can be embedded within it, leaving pores within the 3D printed object upon cooling.

[0028] Figure 3CThe diagram shows a building material layer 240 comprising polymer particles, having a fusion portion 310 where a flux is applied and irradiated to generate sufficient heat to form a molten polymer. This layer has reached a temperature sufficient to fuse the polymer particles together to form a solid polymer matrix 342 upon cooling or solidification. In areas where a pore-promoting agent is applied and at some locations where an acidic agent is applied, bubbles are formed, leaving multiple pores 344 upon cooling. In this example, a porous region 320 is formed, comprising multiple sub-regions with varying densities of gas-generated bubbles and resulting pores. A first region 320A (shown at two locations) comprises a relatively low pore density and a relatively high material density. A second region 320B comprises a relatively high pore density and a relatively low material density. In this case, pores are generated along the entire porous region shown, but higher pore densities are generated where an acidic agent is applied in addition to heat. Therefore, in the first region, heat is used to generate bubbles in the molten polymer to create pores. However, in the second region, a relatively high bubble density is generated within the molten polymer due to the application of heat generated in addition to the interaction between the radiation absorber and the radiation energy, as well as the chemical reaction between the pore promoter and the acidic reagent. Therefore, in this example, two bubble densities or concentrations are generated, but they are forming or in the process of forming within the molten polymer, and the bubbles are trapped when the polymer re-solidifies or cools to form a solid polymer matrix.

[0029] More in detail, and as Figure 4 As illustrated, an exemplary 3D printing method 400 may include 410 repeatedly applying individual build material layers of polymer particles onto a powder bed, and 420 selectively applying a fusion agent to the individual build material layers based on a 3D object model, wherein the fusion agent comprises water and a radiation absorber. The method may further include 430 selectively applying a pore-promoting agent to the individual build material layers based on the 3D object model. The pore-promoting agent may comprise water and a pore-promoting compound selected from sodium bicarbonate, potassium bicarbonate, or combinations thereof. Furthermore, based on the 3D object model, the method may include 440 selectively applying an acidic agent to the individual build material layers at the application site of the pore-promoting agent. At this site, the pore-promoting compound chemically reacts with the acidic component to generate bubbles within the individual build material layers. The method may also include 450 exposing the build material to energy, which generates heat to selectively fuse polymer particles in contact with the radiation absorber to form a fused polymer matrix at the individual build material layers, wherein bubbles are distributed within the fused polymer matrix.

[0030] In one example, in addition to the bubble-generating reaction between the pore-promoting compound and the acidic compound, the heat of selectively fused polymer particles can further contribute to bubble generation. The discrete pores in the fused polymer matrix generated by the reaction with the acidic compound and the application of heat have, for example, a D50 particle size of about 1 μm to about 500 μm. This method can result in the formation of a 3D printed object having a first portion of a fused polymer matrix with a first pore volume at a first location where a flux, pore promoter, and acidic agent have been applied and subsequently thermally fused. The 3D printed object may also include a second portion of the fused polymer matrix having a second pore volume lower than the first pore volume, where a flux has been applied but no acidic agent has been applied. More specifically, a pore promoter may also not have been applied at the second portion. In this example, the 3D printed object may further include a third portion where a flux and pore promoter have been applied but no acidic agent has been applied, the third portion having a third pore volume lower than the first pore volume but higher than the second pore volume.

[0031] In some instances, a refiner can also be sprayed onto the build material. As mentioned above, the refiner can be a fluid that lowers the maximum temperature of the polymer particles on which it has been printed. Specifically, the maximum temperature reached by the powder during exposure to electromagnetic energy can be lower in the area where the refiner is applied. In some instances, the refiner may contain a solvent that evaporates from the polymer particles to cool them. The refiner can be printed in areas of the powder bed where the build material is not desired to fuse. In certain instances, the refiner can be printed along the edge of the fusion agent printing area. This provides a clean, defined edge to the fused layer, where the fused polymer particles end and adjacent polymer particles remain unfused. In other instances, the refiner can be printed in the same area where the fusion agent is printed to control the temperature of the area to be fused. In some instances, some areas to be fused may tend to overheat, especially in the central region of large fusion sections. To control the temperature and avoid overheating (which can lead to melting and collapse of the build material), a refiner can be applied to these areas.

[0032] As mentioned above, in some instances, the elevated temperature that can cause the pore-promoting compound to chemically react (in the absence of acidic reagents) can be from approximately 80°C to approximately 200°C. As mentioned, when acidic reagents are present, the reaction can occur at even lower temperatures. In some instances, the pore-promoting compound and the building material to which it is sprayed can reach this elevated temperature when radiant energy is applied to the building material. However, in some instances, the powder bed can be elevated to a temperature below the melting or softening temperature of the polymer particles in the building material, and then elevated above the softening or melting temperature upon application of heat. For example, the entire building material can be preheated to a temperature below the melting or softening point of the polymer particles. Therefore, the preheating temperature can be within 50°C of the melting or softening point, for example, from approximately 10°C to approximately 30°C below the melting or softening point. In a particular instance, the preheating temperature can be from approximately 100°C to approximately 120°C, and the polymer particles can be thermoplastic polyamide polymer particles. In another example, the preheating temperature may be from approximately 90°C to approximately 100°C, and the polymer particles may be thermoplastic polyurethane. Preheating can be achieved using one or more lamps, ovens, heated support beds, or other types of heaters. In some examples, the entire building material may be heated to a substantially uniform temperature. Regardless of the method followed, 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 react with the acidic component and, in some cases, may be heated to a temperature sufficient to react and form gas while the polymer particles are in a molten or softened state, such that bubbles can form in the molten polymer (which may be a melted or softened polymer).

[0033] As mentioned above, various variables of the "print mode" can be adjusted to affect the porosity level in a 3D printed object. In some instances, methods for manufacturing 3D printed objects may include adjusting these variables to change the porosity level. In some instances, variables may include the amount of fusion agent applied to the build material, the amount of porosimeter agent applied to the build material, the thickness of each layer of the build material, the intensity and duration of radiation applied to the build material, the preheating temperature of the build material, etc.

[0034] Various fluid reagents can be jetted onto the build material using a fluid jet printhead. The amount of pore promoter and / or acidic reagent jetted onto the powder can be calibrated based on factors such as the concentration of the pore-promoting compound in the pore promoter, the desired porosity of the porous portion to be printed, etc. Similarly, the amount of flux used can be calibrated based on the concentration of the radiation absorber in the flux, the required level of fusion of the polymer particles, and other factors. In some instances, the amount of flux printed may be sufficient to bring the radiation absorber into contact with the entire layer of polymer particles. For example, if a single layer of the build material is 100 μm thick, the flux may penetrate 100 μm into the build material, or in some cases, may penetrate less than 100 μm. Therefore, in some instances, the flux may heat the polymer particles throughout the entire layer, even without 100% penetration in some cases. Through sufficient penetration and the heat generated, the layer can coalesce and bond to the layer below. After the solid layer has been formed, a new loose powder layer can be formed by lowering the build material or by raising the height of the powder roller and rolling a new powder layer.

[0035] The build material can be irradiated with a fusion lamp. Suitable fusion lamps used in the methods described herein may include commercially available infrared lamps and halogen lamps. The fusion lamp can be a stationary lamp or a mobile lamp. For example, the lamp can be mounted on a track to move horizontally across the build material. Such a fusion lamp can pass over the bed multiple times, depending on the exposure required to coalesce the individual printed layers. The fusion lamp can be configured to irradiate the entire build material with a substantially consistent amount of energy. This allows for selective coalescing of portions printed with the fusion agent, keeping the polymer particles in the unprinted portions below their melting or softening point.

[0036] In one example, the fusion lamp can be matched with a radiation absorber in the fusion flux so that the wavelength of the light emitted by the fusion lamp matches the peak absorption wavelength of the radiation absorber. A radiation absorber with a narrow peak at a specific near-infrared wavelength can be used with a fusion lamp that emits light over a narrow wavelength range approximately at the peak wavelength of the radiation absorber. Similarly, a radiation absorber that absorbs a wide range of near-infrared wavelengths can be used with a fusion lamp that emits light over a wide wavelength range. Matching the radiation absorber and the fusion lamp in this way can improve the efficiency of polymer particle agglomeration with the flux printed on it, while unprinted polymer particles do not absorb as much light and remain at a lower temperature.

[0037] Depending on the amount of radiation absorber present in the polymer particles, the absorbance of the radiation absorber, the preheating temperature, and the melting or softening point of the polymer, the appropriate irradiation dose can be supplied by the fusion lamp. In some instances, the fusion lamp can irradiate each layer for approximately 0.5 to approximately 10 seconds per pass.

[0038] 3D printed objects can be formed by spraying a flux onto a layer of build material based on a 3D object model. In some instances, computer-aided design (CAD) software can be used to create the 3D object model. The 3D object model can be stored in any suitable file format. In some instances, as described herein, a 3D printed object can be based on a single 3D object model. The 3D object model can define the 3D shape of the object and the 3D shape of the porous portions to be formed in the 3D printed object. In other instances, the object can be defined by a first 3D object model, while the porous portions can be defined by a second 3D object model. Other information may also be included, such as the structure formed by additional different materials or color data regarding printing the object in various colors at different locations on the object. The 3D object model may also include features or materials specifically related to the fluid sprayed onto the build material layer, such as the required amount of fluid to be applied to a given area. This information can be in the form of droplet saturation, for example, which can instruct the 3D printing system to spray a certain number of fluid droplets onto a specific area. This allows the 3D printing system to precisely control radiation absorption, cooling, color saturation, the concentration of porosilicates, the concentration of acidic compounds, etc. All information can be contained in a single 3D object file or a combination of multiple files. 3D printed objects can be made based on 3D object models. As used herein, "based on 3D object models" can refer to printing using a single 3D object model file or a combination of multiple 3D object models that together define the object. In some instances, software can be used to convert 3D object models into instructions for a 3D printer to form the object by accumulating individual layers of building material.

[0039] In one example of a 3D printing method, thin layers of polymer particles are spread onto a bed to form a build material. At the start of the process, the build material can be empty, as no polymer particles have been spread yet. For the first layer, 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 3D printing process, such as metal. Therefore, “applying individual build material layers of polymer particles to a powder bed” includes spreading polymer particles onto an empty build platform to form the first layer. In other instances, multiple initial layers of polymer particles can be spread before printing begins. The number of these “blank” layers of build material can be approximately 10 to approximately 500, approximately 10 to approximately 200, or approximately 10 to approximately 100 in some instances. In some cases, spreading multiple powder layers before printing can improve the temperature uniformity of the 3D printed object. A fluid jet printhead, such as an inkjet printhead, can then be used to print a binder containing a radiation absorber onto portions of the build material corresponding to the thin layers of the 3D object to be formed. The bed can then be exposed to electromagnetic energy, typically the entire bed. Electromagnetic energy can include light, infrared radiation, etc. Radiation absorbers can absorb more energy from electromagnetic energy compared to unprinted powder. The absorbed light energy can be converted into heat energy, softening and fusing the printed portions of the powder together to form a forming layer. After the first layer is formed, new thin layers of polymer particles can be spread onto the build material, and this process can be repeated to form additional layers until a complete three-dimensional object is printed. Therefore, "applying individual build material layers of polymer particles to a powder bed" also includes spreading polymer particle layers onto a loose object and fused layer beneath the new polymer particle layers.

[0040] In some instances, a 3D printed object can be formed having pores throughout the object or having porous portions of any desired shape located at any desired location within the object. In one instance, the 3D printed object may have a porous interior and a solid outer surface. For example, the 3D printed object may be designed with a solid layer or shell free of any applied pore promoters and acidic agents, and the interior portion may include locations where pore promoters or both pore promoters and acidic agents have been applied. In some instances, the solid shell may be approximately 20 μm to approximately 2,000 μm thick, or any other desired thickness. In further instances, pores may be formed in the 3D printed object for purposes such as reducing the object's weight, increasing its buoyancy, reducing its strength, or improving its flexibility. In one instance, a portion of the object may be made highly porous to form a fracture segment that can be broken by moderate force. In another instance, a portion of the object may be made porous while other portions are non-porous to provide a more flexible porous segment connected to a more rigid non-porous segment. In another example, pore promoters, or a combination of pore promoters and acidic reagents, can be used to form hidden tags, codes, or identification markers. For instance, a porous portion of a specific shape can be formed inside a 3D-printed object below its surface, making it invisible to the human eye. This porous portion can be detected using a detection device to find or read the hidden identification tag or code. In this way, the porous tag or code can be used to verify the authenticity of the 3D-printed object or to store information about the 3D-printed object. Besides these examples, 3D-printed objects with porous portions can be used for a variety of other applications.

[0041] Pore ​​promoters and / or acidic agents can be applied to the areas of the build material where pores are to be formed. When applying the pore promoter and acidic agent to the build material, the concentrations of the respective pore-promoting and acidic compounds, or other factors such as the choice of acid used, can determine how much of each fluid agent should be applied. However, in some instances, there may be 3D printing kits, systems, and methods that use approximately 1 / 20 to 3 parts (by volume) of acidic agent with approximately 1 part (by volume) of pore promoter. If, for example, the formulation and printed architecture provide similar droplet volumes during printing, the volume ratio can depend on how many drops are applied.

[0042] More specifically, in some instances, the applied volume of the corresponding fluid reagent may be such that the pore-promoting compound and the acidic compound in contact in the powder bed containing one or more layers of build material for printing are approximately in equimolar ratio. In other instances, the molar ratio of the pore-promoting compound to the acidic compound may be from about 5:1 to about 1:1, such that there is no excess acidic compound, but there may be excess pore-promoting compound, which can generate bubbles upon heating, even if all the acidic compound reacts with the other pore-promoting compound molecules. In still other instances, the molar ratio of the pore-promoting compound to the acidic compound to be applied to the build material may be, for example, from about 1:2 to about 5:1, from about 1:1 to about 4:1, from about 1:1 to about 3:1, from about 1:1 to about 2:1, or from about 2:1 to about 5:1.

[0043] As used herein, “pore” refers to the void space within a solid polymer matrix. A void space can be a single, closed void space separated from other void spaces by the solid polymer. In other instances, void spaces can be interconnected with other void spaces. In some cases, more interconnected void spaces or even larger voids may exist where the void facilitates the reaction of the acidic component. Therefore, in various instances, depending on porosity, a void can range from a fully interconnected network of voids to a collection of discrete, unconnected voids. In further instances, void spaces can be filled with gases generated by the chemical reaction of void-facilitating compounds.

[0044] The term "porosity" as used in this article generally refers to the presence of pores in the fused polymer matrix. In specific values, "porosity" can be defined as the volume fraction of the void space in the fused polymer relative to the total volume of the fused polymer and the void space together. The void space can refer to the voids formed by the chemical reaction of the pore-promoting compound, rather than the void space designed into the 3D model of the object involved in 3D printing. Any geometry designed into the 3D object model can be considered a feature of the "total volume of the fused polymer," and the fraction of void space can be based on the voids formed by the gases generated by the pore-promoting compound. Furthermore, porosity can be measured relative to the entire 3D printed object or relative to the porous portion of the 3D printed object (where the pore-promoting agent is applied).

[0045] In some instances, the porous portions of a 3D printed object fabricated using the methods described herein can have a porosity of approximately 0.1 volume% to approximately 50 volume% (in discrete regions or globally). In further instances, the porous portions can have a porosity of approximately 1 volume% to approximately 30 volume% or approximately 5 volume% to approximately 20 volume%. Additionally, the pore sizes can vary. In 3D printed objects exhibiting multiple porosities, such as those containing a substantially non-porous region (at the edge of 310), a first region 320A with moderate porosity, and a second region 320B with increased porosity... Figure 3C In the 3D printed object shown, the first region may have a porosity of approximately 0.1 volume% to approximately 25 volume%, approximately 0.1 volume% to approximately 15 volume%, or approximately 0.1 volume% to approximately 10 volume%, and the second region may have a porosity of approximately 1 volume% to approximately 50 volume%, approximately 10 volume% to approximately 50 volume%, approximately 20 volume% to approximately 10 volume%, or approximately 30 volume% to approximately 50 volume%, provided that the porosity of the second region is greater than that of the first region. Regardless of their location or region, more specifically, the pores may have a D50 particle size of approximately 1 μm to approximately 500 μm, approximately 1 μm to approximately 300 μm, approximately 1 μm to approximately 200 μm, or approximately 5 μm to approximately 100 μm.

[0046] Construction materials

[0047] Regarding the building materials in more detail, polymer particles may be present in the building materials in amounts of approximately 80% to 100% by weight, approximately 90% to 100% by weight, approximately 95% to 100% by weight, approximately 80% to approximately 90% by weight, approximately 85% to approximately 95% by weight, or approximately 100% by weight. As described in detail below, other particles (if present) may be included, such as fillers, charged particles, flow-aiding particles, etc.

[0048] The polymer particles may be selected from polyacetal, polyacrylate, polyamide, polybutylene terephthalate, polycarbonate, polyester, polyetherketone, polyethylene terephthalate, polyethylene, polypropylene, polystyrene, polyurethane, thermoplastic polyamide, thermoplastic polyurethane, copolymers thereof, blends of any polymer listed herein, and mixtures thereof. In one example, the polymer particles may include polyamide, and the polyamide may be selected from polyamide-6, polyamide-9, polyamide-11, polyamide-12, polyamide-66, polyamide-612, or combinations thereof. In other examples, the polymer particles may include polyacrylate, polybutylene terephthalate, polycarbonate, polyester, polyethylene, polystyrene, polyurethane, copolymers thereof, blends of any polymer listed herein, and mixtures thereof. Core-shell polymer particles using these materials may also be used. In some examples, amorphous materials may be excluded from the building materials.

[0049] The polymer particles (and other particles, if present) of the building material may have a D50 particle size ranging from about 10 μm to about 150 μm. The polymer particles may have, for example, a D50 particle size ranging from about 10 μm to about 150 μm, about 10 μm to about 100 μm, about 20 μm to about 80 μm, about 30 μm to about 50 μm, about 25 μm to about 75 μm, about 40 μm to about 80 μm, about 50 μm to about 75 μm, about 75 μm to about 150 μm, about 60 μm to about 90 μm, or about 100 μm to about 150 μm. As used herein, the terms “size” or “particle size” refer to the diameter of a substantially spherical particle, or the effective diameter of a non-spherical particle, such as the diameter of a sphere having the same mass and density (e.g., by weight) as the non-spherical particle. Particle size information can be determined and / or verified using scanning electron microscopy (SEM), or using a particle analyzer, such as the MASTERSIZER available from Malvern Panalytical. TM 3000 Measurement. Particle analyzers can measure particle size using laser diffraction. A laser beam passes through the particle sample and the angle variation of the intensity of light scattered by the particles can be measured. Larger particles scatter light at smaller angles, while smaller particles scatter light at larger angles. The particle analyzer can then analyze the angular scattering data to calculate the particle size using Mie light scattering theory. Particle size can be reported as the volume equivalent sphere diameter. In some instances, the particle size range can be considered here as a mathematical average of the particle size, which is typically roughly the same as the D50 particle size, but can vary depending on the particle size distribution.

[0050] Therefore, an exemplary Gaussian-like distribution of particles can typically be characterized using particle size distribution values ​​such as "D10," "D50," and "D90," where D10 refers to the particle size at the 10th percentile, D50 to the 50th percentile, and D90 to the 90th percentile. For example, a D50 value of approximately 25 μm means that approximately 50% of the particles (by quantity) have a particle size greater than approximately 25 μm, and approximately 50% of the particles have a particle size smaller than approximately 25 μm. Particle size distribution values ​​are not necessarily correlated with a Gaussian distribution curve. In practice, a true Gaussian distribution typically does not exist due to potential skewness, but a Gaussian-like distribution can still be considered a "Gaussian" distribution used in practice. The particle size distribution can be represented by the D50 particle size, which can approximate the average particle size but may not be identical to it.

[0051] The shape of the particles used to construct the material can be spherical, irregularly spherical, circular, semi-circular, disc-shaped, angular, semi-angular, cubic, cylindrical, or any combination thereof. In one instance, the particles may include spherical particles, irregularly spherical particles, or circular particles. In some instances, the shape of the particles may be uniform or substantially uniform, which allows the particles to melt relatively uniformly.

[0052] The polymer particles in the building material may have a melting point ranging from about 75°C to about 350°C, from about 100°C to about 300°C, or from about 150°C to about 250°C. As an example, the building material may be a polyamide with a melting point of about 170°C to about 190°C, or a thermoplastic polyurethane with a melting point of about 100°C to about 165°C. Various thermoplastic polymers with melting points or softening points within these ranges may be used. In a specific example, the building material may include polyamide particles, such as polyamide-12, which may have a melting point of about 175°C to about 200°C. In another example, an elastomer, such as a thermoplastic polyamide, may be used, which in some instances may have a melting point of about 135°C to about 210°C.

[0053] In addition to polymer particles, the building blocks may also include other particles, such as filler particles, charged particles, flow-aiding particles, or combinations thereof. For example, charged particles can be added to suppress triboelectric charging. Examples of suitable charged particles include aliphatic amines (which may be ethoxylated), aliphatic amides, quaternary ammonium salts (e.g., behenyltrimethylammonium chloride or cocamidopropyl betaine), phosphate esters, polyethylene glycol esters, or polyols. Some suitable commercially available charged particles include... FA 38 (Natural ethoxylated alkylamine), FE2 (fatty acid esters) and HS 1 (alkane sulfonates / esters) are all from Clariant Int. Ltd. (North America). In one instance, if added, charged particles may be included in an amount from more than 0 wt% to about 20 wt%, from about 0.1 wt% to about 10 wt%, or from about 0.2 wt% to about 5 wt% of the total weight of the building material.

[0054] Flow-aiding particles can be added to increase the flowability of the build material coating. Flow-aiding particles can be particularly useful when the build material particles are at the smaller end of the particle size range. Flow-aiding particles can increase the flowability of the build material by reducing friction, lateral drag, and triboelectric charge accumulation (by increasing particle conductivity). Examples of suitable flow aids include tricalcium phosphate (E341), powdered cellulose (E460(ii)), magnesium stearate (E470b), sodium bicarbonate (E500), sodium ferrocyanide (E535), potassium ferrocyanide (E536), calcium ferrocyanide (E538), bone phosphate (E542), sodium silicate (E550), silica (E551), calcium silicate (E552), magnesium trisilicate (E553a), talc (E553b), sodium aluminosilicate (E554), potassium aluminum silicate (E555), calcium aluminosilicate (E556), bentonite (E558), aluminum silicate (E559), stearic acid (E570), or polydimethylsiloxane (E900). In one instance, if added, the flow-aiding particles may be included in an amount from more than 0% to about 20% by weight, from about 0.1% to about 10% by weight, or from about 0.2% to about 5% by weight of the total weight of the building material.

[0055] Fuel

[0056] The multifluidic kits and material kits for 3D printing described herein may include a fusion agent to be applied to a polymeric build material. The fusion agent may contain a radiation absorber capable of absorbing radiant energy and converting it into heat. In some instances, the fusion agent may be used in conjunction with the build material in a specific 3D printing method. A thin layer of the build material may be formed, and then the fusion agent may be selectively applied to areas of the build material that are desired to solidify into part of a solid 3D printed object. The fusion agent may be applied, for example, by printing with a fluid jet or a fluid jet printhead. A fluid jet printhead may jet the fusion agent in a manner similar to how an inkjet printhead jets ink. Therefore, the fusion agent can be applied with high precision to certain areas of the build material to which layers of the final 3D printed object are desired to form. After the fusion agent is applied, the build material may be irradiated with radiant energy. The radiation absorber from the fusion agent may absorb this energy and convert it into heat, thereby heating any polymer particles in contact with the radiation absorber. An appropriate amount of radiant energy can be applied to heat the build material region with the fusible linker to a temperature sufficient to melt the polymer particles and solidify the object into a solid layer, while the build material without the fusible linker remains a loose powder with individual particles.

[0057] In some instances, the amount of applied radiation energy, the amount of flux applied to the build material, the concentration of radiation absorber in the flux, and the preheating temperature of the build material (i.e., the temperature of the build material before printing the flux and irradiation) can be adjusted to ensure that the portion of the build material with the flux printed will fuse to form a solid layer, while the unprinted portion of the build material remains loose powder. These variables can be referred to as part of the “printing mode” of the 3D printing system. Typically, the printing mode can include any variables or parameters that can be controlled during the 3D printing process to affect the outcome of the 3D printing method.

[0058] Typically, additional layers of fresh build material are formed by repeatedly applying a fusion agent and irradiating the build material to create individual layers, thus building the final object layer by layer. During this process, the build material surrounding the 3D printed object acts as a support material for that object. When 3D printing is complete, the object can be removed from the build material (e.g., build material not bonded to the 3D printed object), and any loose powder on the object can be removed.

[0059] Therefore, in some instances, the fusing agent may include a radiation absorber capable of absorbing electromagnetic radiation to generate heat. The radiation absorber may be colored or colorless. In various instances, the radiation absorber may be pigments such as carbon black pigments, glass fibers, titanium dioxide, clay, mica, talc, barium sulfate, calcium carbonate, near-infrared absorbing dyes, near-infrared absorbing pigments, conjugated polymers, dispersants, or combinations thereof. Examples of near-infrared absorbing dyes include ammonium dyes, tetraaryldiamine dyes, cyanine dyes, phthalocyanine dyes, dithioene dyes, and others. In further instances, the radiation absorber may be near-infrared absorbing conjugated polymers such as poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT: PSS), polythiophene, poly(p-phenylene sulfide), polyaniline, poly(pyrrole), poly(acetylene), poly(p-phenylenevinylene), poly(p-phenylene), or combinations thereof. As used herein, "conjugation" refers to alternating double and single bonds between atoms in a molecule. Therefore, a "conjugated polymer" refers to a polymer whose main chain has alternating double and single bonds. In many cases, radiation absorbers can have peak absorption wavelengths in the range of approximately 800 nm to approximately 1400 nm.

[0060] A variety of near-infrared pigments can also be used. Non-limiting examples may include phosphates, or combinations thereof, having a variety of counterions (such as copper, zinc, iron, magnesium, calcium, strontium, etc.). Specific non-limiting examples of phosphates may include M2P2O7, M4P2O9, and M5P2O. 10 M3(PO4)2, M(PO3)2, M2P4O 12 Or combinations thereof, where M represents a counterion having an oxidation state of +2, such as those or combinations thereof listed above. For example, M2P2O7 can include compounds such as Cu2P2O7, Cu / MgP2O7, Cu / ZnP2O7, or any other suitable combination of counterions. It should be noted that the phosphates described herein are not limited to counterions having an oxidation state of +2. Other phosphate counterions can also be used to prepare other suitable near-infrared pigments.

[0061] Additional near-infrared pigments may include silicates. Silicates may have counterions that are the same as or similar to those of phosphates. A non-limiting example may include M₂SiO₄, M₂Si₂O₆, and other silicates wherein M is a counterion having an oxidation state of +2. For example, silicate M₂Si₂O₆ may include Mg₂Si₂O₆, Mg / CaSi₂O₆, MgCuSi₂O₆, Cu₂Si₂O₆, Cu / ZnSi₂O₆, or other suitable combinations of counterions. It should be noted that the silicates described herein are not limited to counterions having an oxidation state of +2. Other silicate counterions may also be used to prepare other suitable near-infrared pigments.

[0062] In further examples, the radiation absorber may include metal dithioene complexes. Transition metal dithioene complexes can exhibit strong absorption bands in the 600 nm to 1600 nm region of the electromagnetic spectrum. In some examples, the central metal atom can be any metal capable of forming a planar tetragonal complex. Non-limiting specific examples include nickel-, palladium-, and platinum-based complexes.

[0063] In some instances, a dispersant may be included in the fusing agent. The dispersant helps disperse the aforementioned radiation-absorbing pigments. In some instances, the dispersant itself may also absorb radiation. Non-limiting examples of dispersants that may be included alone or together with the pigment as a radiation absorber include polyoxyethylene glycol octylphenol ether, ethoxylated aliphatic alcohols, carboxylic acid esters, polyethylene glycol esters, sorbitan esters, carboxamides, polyoxyethylene fatty acid amides, poly(ethylene glycol) p-isooctylphenyl ether, sodium polyacrylate, or combinations thereof.

[0064] The amount of radiation absorber in the flux varies depending on the type of radiation absorber. In some examples, the concentration of the radiation absorber in the flux can be from about 0.1 wt% to about 20 wt%. In one example, the concentration of the radiation absorber in the flux 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 concentration of the radiation absorber in the flux is such that, after the flux is sprayed onto the polymer particles, the amount of radiation absorber in the polymer particles relative to the weight of the polymer particles can be from about 0.0003 wt% to about 10 wt%, or from about 0.005 wt% to about 5 wt%.

[0065] In some instances, fluid jetting devices, such as inkjet printing architectures, can be used to jet the flux onto polymer particles of the building material. Therefore, in some instances, the flux can be formulated to impart good jetting properties. Components that can be included in the flux to provide good jetting properties may include a liquid carrier. Thermal jetting works by heating the flux to form vapor bubbles, which displace the fluid around the bubbles and thereby force fluid droplets away from the jet nozzle. Thus, in some instances, the liquid carrier may include a sufficient quantity of evaporating liquid that can form vapor bubbles upon heating. The evaporating liquid may be a solvent such as water, alcohol, ether, or a combination thereof.

[0066] In some instances, depending on the spray architecture, the liquid carrier formulation may include one or more cosolvents present in a total amount of about 1% to about 50% by weight. Additionally, nonionic, cationic, and / or anionic surfactants may be present in an amount of about 0.01% to about 5% by weight. In one instance, the surfactant may be present in an amount of about 1% to about 5% by weight. The liquid carrier may also contain a dispersant in an amount of about 0.5% to about 3% by weight. The balance of the formulation may be purified water, and / or other carrier components such as biocides, viscosity modifiers, materials for pH adjustment, chelating agents, preservatives, etc. In one instance, the liquid carrier may be primarily water.

[0067] In some instances, water-dispersible or water-soluble radiation absorbers can be used with aqueous carriers. Because the radiation absorber is dispersible or soluble in water, organic co-solvents are not required, as they may not be present to make the radiation absorber soluble. Therefore, in some instances, the fluid may be substantially free of organic solvents, for example, primarily water. However, in other instances, co-solvents may be used to aid in the dispersion of other dyes or pigments, or to enhance the jetting properties of the corresponding fluid. In further instances, non-aqueous carriers can be used with organically soluble or organically dispersible fluxing agents.

[0068] In some instances, the flux may contain a high-boiling-point co-solvent. This high-boiling-point co-solvent may be an organic co-solvent that boils at a temperature higher than the build material temperature during printing. In some instances, the high-boiling-point co-solvent may have a boiling point above approximately 250°C. In even further instances, the high-boiling-point co-solvent may be present in the flux at a concentration of approximately 1% to approximately 10% by weight.

[0069] The types of cosolvents that can be used can include organic cosolvents, including aliphatic alcohols, aromatic alcohols, diols, glycol ethers, polyglycol ethers, caprolactam, formamide, acetamide, and long-chain alcohols. Examples of such compounds include 1-aliphatic alcohols, secondary aliphatic alcohols, 1,2-ols, 1,3-ols, 1,5-ols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, and higher homologues (C6-C) of polyethylene glycol alkyl ethers. 12 ), N-alkyl caprolactam, unsubstituted caprolactam, both substituted and unsubstituted formamide, both substituted and unsubstituted acetamide, etc. Specific examples of solvents 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.

[0070] Regarding the surfactants that may be present, one or more surfactants may be used, such as alkyl polyethylene oxide, alkylphenyl polyethylene oxide, polyethylene oxide block copolymers, alkynyl polyethylene oxide, polyethylene oxide (di) esters, polyethylene oxide amines, protonated polyethylene oxide amines, protonated polyethylene oxide amides, polydimethylsiloxane copolyols, substituted amine oxides, etc. The amount of surfactant added to the flux may be from approximately 0.01% by weight to approximately 20% by weight. Suitable surfactants may include, but are not limited to, liponic acid esters, such as Tergitol, available from Dow Chemical Company (Michigan). TM 15-S-12, Tergitol TM 15-S-7, LEG-1, and LEG-7; available from Triton, Dow Chemical Company (Michigan). TM X-100; Triton TM X-405; and sodium dodecyl sulfate.

[0071] Various other additives can be used to enhance certain properties of the flux for specific applications. Examples of such additives are those added to inhibit the growth of harmful microorganisms. These additives can be biocides, fungicides, and other microbial agents, which can be used in a variety of formulations. Examples of suitable microbial agents include, but are not limited to, those listed below. (Nudex, Inc., New Jersey), UCARCIDE TM (Union carbide Corp., Texas), (RTVanderbilt Co., Connecticut), (ICIAmericas, New Jersey) or a combination thereof.

[0072] It may contain chelating agents such as EDTA (ethylenediaminetetraacetic acid) to eliminate the harmful effects of heavy metal impurities, and the pH of the fluid may be controlled using buffer solutions. For example, it may be used from about 0.01% by weight to about 2% by weight. Viscosity modifiers and buffers, as well as other additives to change the properties of the fluid as needed, may also be present. Such additives may be present from about 0.01% by weight to about 20% by weight.

[0073] Pore ​​promoters

[0074] Pore ​​promoters may comprise water-soluble pore-promoting compounds that can chemically react at elevated temperatures to generate gas, and / or react chemically with the acidic component of an acidic reagent to generate gas. As used herein, “chemical reaction” refers to a change in chemical composition, not merely a phase transition from liquid or solid to gas. Many liquid solvents can evaporate at elevated temperatures to form gas. However, the pore-promoting compounds described herein do not refer to liquids that evaporate at elevated temperatures. Rather, pore-promoting compounds chemically react with heat and / or with the acidic component of an acidic reagent to form different compounds. The products of such chemical reactions may be gases that remain gaseous even after cooling back to room temperature in some cases. In some instances, the chemical reaction of the pore-promoting compound may occur without any other reactants besides the pore-promoting compound exposed to heat; in other instances, the pore-promoting compound may react with the acidic component at temperatures ranging from room temperature to the melting temperature of the polymer particles that make up the material. In some instances, the pore-promoting compound may chemically decompose to form smaller molecules, and the product molecules may include gases.

[0075] Non-limiting examples of pore-promoting compounds may include sodium bicarbonate, potassium bicarbonate, or combinations thereof. These compounds can chemically decompose to form a gas when heated to a decomposition temperature of about 80°C to about 200°C. These compounds can also react with acidic components, such as many organic and / or inorganic acids. In some instances, the gas formed may include carbon dioxide gas.

[0076] In some instances, the porosity promoter can react to form a gas at elevated temperatures reached during the 3D printing process. In some instances, the elevated temperature at which the porosity promoter reacts can be from approximately 80°C to approximately 200°C. In further instances, the elevated temperature can be from approximately 90°C to approximately 190°C or from approximately 100°C to approximately 180°C. In some instances, the elevated temperature can be at or near the melting or softening point of the polymer particles of the building material. For example, the elevated temperature can be within 20°C, 15°C, or 10°C of the melting or softening point of the polymer particles. Thus, the porosity promoter can react when the polymer particles fuse during the 3D printing process. In other instances, the elevated temperature at which the porosity promoter reacts can be above the melting or softening point of the polymer particles. During the 3D printing process, a sufficient amount of flux can be applied to the polymer particles, and sufficient radiant energy can be applied to heat the porosity promoter to the temperature at which it will react.

[0077] In some cases, when the building material is heated during the fusion of polymer particles, the pore-promoting compounds applied to the building material can react completely to form gas. In other words, all or almost all of the pore-promoting compounds can react to produce gas. In other instances, a portion of the pore-promoting compounds can react, while another portion may remain unreacted. In some instances, approximately 50% to approximately 100% by weight of the pore-promoting compounds can react. In other instances, approximately 60% to approximately 95% by weight or approximately 70% to approximately 90% by weight of the pore-promoting compounds can react. In even further instances, a smaller amount of the pore-promoting compounds can react. For example, approximately 10% to approximately 70% by weight, or approximately 20% to approximately 60% by weight, or approximately 30% to approximately 50% by weight of the pore-promoting compounds can react. The amount of reacting pore-promoting compounds can, in some cases, depend on the temperature to which the building material is heated, the length of time the powder is held at that temperature, the total amount of radiant energy applied to the building material, and so on. Therefore, in some instances, the amount of radiant energy applied, the duration of heating the build material, the temperature reached by the build material, the amount of flux applied to the build material, and other variables can affect the extent of the reaction of the porosimeter-promoting compound. Consequently, these variables can influence the porosity of the final 3D-printed object. These variables can be part of the "printing mode" of the 3D printing method. Porosity can also be affected by changing the amount of porosimeter applied to the build material. Therefore, the printing mode can be adjusted to influence the porosity level in the 3D-printed object.

[0078] The total amount of pore-promoting compounds and / or acidic compounds applied and present in the build material layer can affect the porosity of the 3D printed object. As mentioned above, this variable can be adjusted by changing the amount of pore promoter applied to the build material. Alternatively, the amount of pore-promoting compound applied to the build material can be changed by changing the concentration of the pore-promoting compound in the pore promoter. Similarly, changing the concentration of the selected acidic component and / or the applied acidic component can also affect the porosity. The amount of pore-promoting compound can be selected so that the pore promoter can be ejected from the fluid jet printhead. In some instances, the concentration of the pore-promoting compound in the pore promoter can be from about 0.5 wt% to about 10 wt% relative to the total weight of the pore promoter. In further instances, the concentration of the pore-promoting compound can be from 1 wt% to 8 wt% or from 2 wt% to 7 wt%.

[0079] Pore ​​promoters may also contain components that allow the pore promoter to be ejected by a fluid jet printhead. In some instances, pore promoters may contain components that impart jettisonability, such as those described above in the flux. These components may include liquid carriers, surfactants, dispersants, cosolvents, biocides, viscosity modifiers, materials for pH adjustment, chelating agents, preservatives, and so on. These components may be included in any of the amounts described above.

[0080] Acidifier

[0081] The acidic reagent may comprise water and an acidic component that provides a pH of approximately pH 1 to approximately pH 6.9, approximately pH 2 to approximately pH 6, or approximately pH 3 to approximately pH 5. Examples of the acidic component may include, for example, organic or inorganic acids. More specific examples of organic acids may include lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid, malic acid, tartaric acid, or combinations thereof. Exemplary inorganic acids may be hydrochloric acid, hydrobromic acid, hydroiodic acid, perchloric acid, phosphoric acid, sulfuric acid, boric acid, nitric acid, nitrous acid, or combinations thereof. The concentration of the acid may depend on whether the contained acid is a strong or weak acid and the degree of chemical reaction between the pore-promoting compound and the acidic component that the user may desire. As mentioned, the pore-promoting component may chemically react at elevated temperatures to generate gas; however, according to the details of this disclosure, the pore-promoting compound may alternatively or additionally chemically react with the acidic component of the acidic reagent to generate gas.

[0082] In some cases, acidic compounds applied to the build material can react with pore-promoting compounds and be completely or partially consumed, forming gas, depending on the concentration of the available pore promoter. In other cases, if applied at an appropriate molar ratio, all or almost all of the acidic compounds can react with the pore-promoting compounds to produce gas. In some instances, if some acidic components remain unreacted, it may be desirable to maintain a sufficiently low concentration within the 3D-printed part so that, once the polymer object has solidified, the acidic compounds do not continue to interact with the polymer object to weaken or otherwise damage it.

[0083] The total amount of acidic compounds applied and present in the build material layers can affect the porosity of a 3D printed object. Acidic agents can have concentrations of acidic components that depend on the nature of the acid. The amount of acid included can be based partly on how much acid is needed to react with bicarbonate when applied to the build material, and partly on how much is likely to be healthy for the architecture, such as a fluid ejector or jet printhead. For example, acidifiers can contain water, organic cosolvents, other organic components such as surfactants, and can contain acids at concentrations suitable for achieving a pH range of approximately pH 1 to approximately pH 6.9, or one of other pH subranges listed herein.

[0084] More specifically, in addition to water, acidic reagents may also contain components that allow the pore enhancer to be ejected through the fluid jet printhead. In some instances, acidic reagents may contain components that provide jettisonability. These components may include liquid carrier components such as surfactants, dispersants, organic cosolvents, biocides, viscosity modifiers, materials for pH adjustment, chelating agents, preservatives, etc. These components may be included in any amount that provides acceptable fluid jetting properties. It is worth noting that some components used to enhance jettisonability may themselves be acidic enough to act as acidic components, thus allowing the use of formulations that do not contain conventional organic or inorganic acids, as long as the pH can be in the range of approximately pH 1 to approximately pH 6.9.

[0085] Other fluid reagents

[0086] In a further example, multifluid kits or material kits used for 3D printing may include other types of fluid reagents, such as coloring agents and / or refining agents. Coloring agents may contain water (and in some instances, other liquid carrier components) and colorants, such as pigments and / or dyes. This type of reagent can be used to add color to 3D printed objects, especially if the printed object is light-colored, such as white or off-white.

[0087] On the other hand, a refiner can be used to cool the material during the printing process of the object and may contain, for example, a refiner compound. The refiner compound can lower the temperature of the build material on which the refiner has been applied. In some instances, the refiner can be printed around the edges of the powdered portion of the fusion agent, or, if cooling is useful in a certain location or under certain conditions, it can be printed within the area occupied by the object during printing. The refiner can improve the selectivity between fused and unfused portions of the build material by lowering the temperature around the edges of the portion to be fused.

[0088] In some instances, the refining compound may be a solvent that evaporates at the temperature of the build material. In some cases, the build material may be preheated to a preheating temperature between about 10°C and about 70°C, which is the melting temperature of the polymer particles. Depending on the type of polymer particles used, the preheating temperature may be between about 90°C and about 200°C or higher. The refining compound may be a solvent that evaporates when in contact with the build material at the preheating temperature, thereby cooling the printed portion of the build material by evaporative cooling. In some instances, the refining agent may contain water, a co-solvent, or a combination thereof. Non-limiting examples of co-solvents used in the refining agent may include xylene, methyl isobutyl ketone, 3-methoxy-3-methyl-1-butyl acetate, ethyl acetate, butyl acetate, propylene glycol monomethyl ether, ethylene glycol monotert-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,N-dimethylacetamide, or a combination thereof. In some instances, the refining agent may be primarily water. In one particular instance, the refining agent may be approximately 85% by weight water or more. In further instances, the refining agent may be approximately 95% by weight water or more. In still further instances, the refining agent may be substantially free of radiation absorbers. That is, in some instances, the refining agent may be substantially free of components that absorb sufficient radiant energy to fuse the powder. In some instances, the refining agent may include colorants such as dyes or pigments, but in sufficiently small amounts that the colorant will not cause the powder printed with the refining agent to fuse when exposed to radiant energy.

[0089] The refiner may also contain components that allow it to be ejected through the fluid jet printhead. In some instances, the refiner may contain components that impart jettisonability, such as those described above in the flux. These components may include liquid carriers, surfactants, dispersants, cosolvents, biocides, viscosity modifiers, materials for pH adjustment, chelating agents, preservatives, and so on. These components may be included in any of the amounts described above.

[0090] definition

[0091] It is worth noting that, unless the context clearly specifies otherwise, the singular forms “a,” “an,” and “the” used in this specification and the appended claims include plural objects.

[0092] The term "colorant" as used in this article may include dyes and / or pigments.

[0093] The term "dye" as used in this article refers to a compound or molecule that absorbs electromagnetic radiation or its specific wavelengths. If a dye absorbs wavelengths in the visible spectrum, it can impart visible color to ink.

[0094] As used herein, “pigment” generally includes pigment colorants, magnetic particles, alumina, silica and / or other ceramics, organometallics or other opaque particles, whether or not such particles impart color. Thus, although this specification primarily exemplifies the use of pigment colorants, the term “pigment” can be used more generally to describe pigment colorants, as well as other pigments such as organometallics, ferrites, ceramics, etc. However, in one specific aspect, a pigment is a pigment colorant.

[0095] As used herein, “ink jetting” or “jetting” refers to the ejection of a composition from a jetting architecture, such as an inkjet architecture. Inkjet architectures may include thermal or piezoelectric architectures. Furthermore, such architectures can be configured to print different droplet sizes, such as less than 10 picoliters, less than 20 picoliters, less than 30 picoliters, less than 40 picoliters, less than 50 picoliters, etc.

[0096] As used in this article, "D50 particle size" refers to a particle size distribution in which approximately half of the particles are larger than the D50 value and approximately half are smaller in size than the D50 value. This can be determined based on the particle diameter of spherical particles, or, if not spherical, based on the diameter of equivalent spherical particles by volume. D50 particle size can be determined using a particle analyzer, such as the Mastersizer available from Malvern Panalytical. TM The particle size is measured at 3000. A particle analyzer can use laser diffraction to measure particle size. A laser beam passes through the particle sample, and the angle of change in the intensity of light scattered by the particles can be measured. Larger particles scatter light at smaller angles, while smaller particles scatter light at larger angles. The particle analyzer can then analyze the angular scattering data to calculate the particle size using Mie theory of light scattering. Particle size can be reported as the volume equivalent sphere diameter.

[0097] As used herein, the terms “basically” or “substantially” when referring to the quantity or amount of a material, or a particular characteristic thereof, mean an amount sufficient to provide the effect that the material or characteristic is intended to provide. The exact degree of permissible deviation may vary depending on the specific context in some cases. When the terms “basically” or “substantially” are used negatively, such as substantially free of the material, it means that the material is absent, or may be present at most in trace amounts such that such concentrations would not affect the function or properties of the composition as a whole.

[0098] The term “approximately” as used in this paper is intended to provide flexibility for the endpoints of a numerical range by assuming that a given value may be “slightly above” or “slightly below” the endpoints. This flexibility can be specified by a particular variable and determined based on the relevant descriptions in this paper.

[0099] As used herein, for convenience, multiple items, structural elements, constituent elements, and / or materials may be presented in a common enumeration. However, such enumerations should be interpreted as if each member of the enumeration were individually identified as a separate and unique member. Thus, without indication to the contrary, a single member in such an enumeration should not be construed as a de facto equivalent of any other member of the same enumeration solely based on their presence in the common group (the single member being mentioned alongside any other member of the same enumeration).

[0100] Concentration, amount, and other numerical data may be expressed or presented in range form herein. It is to be understood that such range form is for convenience and brevity only, and therefore should be flexibly interpreted to include not only the explicitly listed values ​​that define the range's boundaries, but also the independent values ​​or subranges encompassed within that range, as if the values ​​and subranges were explicitly listed. For example, the numerical range “about 1 wt% to about 5 wt%” should be interpreted to include not only the explicitly listed values ​​of about 1 wt% to about 5 wt%, but also the independent values ​​and subranges within the indicated range. Thus, this numerical range includes independent values ​​such as 2, 3.5, and 4, and subranges such as 1–3, 2–4, and 3–5, etc. The same principle applies to ranges that list individual values. Furthermore, this interpretation should apply regardless of the range's magnitude or the characteristics described. Example

[0101] The following examples illustrate embodiments of this disclosure. However, it should be understood that the following are merely illustrative examples of the application of the principles of this disclosure. Many modifications and alternative devices, methods, and systems can be designed without departing from the spirit and scope of this disclosure. The appended claims are intended to cover such modifications and arrangements.

[0102] Example 1 - Material kit for 3D printing

[0103] Multifluid kits for 3D printing are prepared according to Tables 1-3 below. A typical fuser formulation is shown in Table 1, which includes a near-infrared absorber as a radiation absorber. A more specific example of a pore-promoting agent formulation is provided in Table 2, which includes sodium bicarbonate as a pore-promoting compound. An exemplary acidic reagent formulation is also provided in Table 3, which includes citric acid as an acidic compound that can react with sodium bicarbonate to form bubbles at room temperature and at temperatures above room temperature (where molten polymers may be present during the construction of the 3D printed object). This multifluid kit is suitable for printing from fluid jet architectures onto a variety of build materials, such as those containing polyamide particles, thermoplastic polyamide particles, polypropylene, etc.

[0104] Table 1 - Fusing Agent Formulation

[0105] Component categories Concentration (wt%) Near-infrared absorber (fusion compound) 5-12 Organic cosolvents 15-25 surfactants 0.1-5 biocides 0.01-0.1 Compounding agents 0.001-0.01 Deionized water margin

[0106] Table 2 - Pore promoter formulations

[0107]

[0108] Table 3 - Acidic Reagent Formulations

[0109] Element category Concentration (wt%) Citric acid acidic components 5 Propylene glycol Organic cosolvents 3-15 2-Phenoxyethanol Organic cosolvents 0.1-3 Disodium EDTA Chelating compounds 0-0.5 Dioctyl sulfosuccinate surfactants 0-1 Deionized water solvent margin

[0110] Example 2 - 3D printing

[0111] A thermoplastic polyurethane (TPU) build material with a D50 particle size of approximately 50-80 μm is used to form a powder bed, which is then preheated to approximately 90-100°C. A flux prepared according to Table 1 is repeatedly applied to the build material layers spread to a thickness of approximately 100-120 μm. The flux is applied in a sufficiently continuous manner to substantially completely penetrate each build material layer and to provide sufficient radiation absorber to raise the temperature of the build material by approximately 30-40°C to approximately 120-140°C. In this embodiment, after applying a flux corresponding to the single-layer footprint of the 3D printed object to be formed, a porosimeter-accelerating agent formulation prepared according to Table 2 is applied to a portion of the footprint. At the preheating temperature, for example, below the melt temperature of the TPU, carbon dioxide gas can begin to be generated from sodium bicarbonate. In this embodiment, the polymer particles selected have a relatively low melt temperature, so some gas may form at the preheating temperature. It should be noted that polymer particles can also be selected such that gas generation may not occur at the preheating temperature. However, in this embodiment, it should be noted that although sodium bicarbonate does not generate gas at room temperature, it can generate gas based solely on temperature at approximately 80°C. It is noteworthy that it has been found that when mixed with citric acid, as in the acidic reagent formulations in Table 3, sodium bicarbonate generates carbon dioxide gas at room temperature. This establishes that when applied in the case of this embodiment, more gas can be generated at lower temperatures, such as preheating temperatures or even lower temperatures. Therefore, enhanced or increased bubble generation at this lower temperature can be achieved by applying the acidic reagent together with a pore enhancer to accelerate the chemical reaction or generate additional bubbles (which can be generated more densely than in embodiments where heat is used simply with a pore enhancer). When applied in the same location, if sodium bicarbonate and citric acid are applied in a molar ratio of approximately 1:1, the chemical reaction that occurs may be as follows:

[0112] NaHCO3+HC2H3O2-→NaC2H3O2+H2O+CO2

[0113] Next, an electromagnetic radiation source located above the powder bed applies electromagnetic radiation. The building material region, including the applied flux, is further heated to a level that melts the thermoplastic polyamide particles. Gases generated within the molten polymer then push the polymer away. This process is repeated layer by layer until a three-dimensional object is formed. During cooling (when building occurs at lower layers or after building is complete), the bubbles generated during this process may make parts of the three-dimensional object more porous than areas without porosity promoters (and, if applicable, acidic reagents).

Claims

1. Three-dimensional printing methods, including: The various building material layers of polymer particles are repeatedly applied to the powder bed; Based on a three-dimensional object model, a flux is selectively applied to each building material layer, wherein the flux comprises water and a radiation absorber; Based on a three-dimensional object model, a pore promoter is selectively applied to each building material layer, wherein the pore promoter comprises water and a water-soluble pore-promoting compound, wherein the pore-promoting compound is selected from sodium bicarbonate, potassium bicarbonate or a combination thereof. Based on a three-dimensional object model, acidic reagents are selectively applied to each building material layer at the application location of the pore promoter, wherein at the location, the pore-promoting compound chemically reacts with the acidic component to generate bubbles within each building material layer; and The building material is exposed to energy, which generates heat to selectively fuse polymer particles in contact with a radiation absorber to form a fused polymer matrix at each layer of the building material, wherein bubbles are distributed within the fused polymer matrix.

2. The method of claim 1, wherein, in addition to the pores promoting the bubble-generating reaction between the compound and the acid compound, the heat of the selectively fused polymer particles further contributes to bubble generation, wherein the discrete pores in the fused polymer matrix generated by the reaction with the acid compound and the applied heat have a D50 diameter of 1 µm to 500 µm.

3. A three-dimensional printed object prepared by the method according to claim 1, comprising: A first portion of a fused polymer matrix having a first pore volume at a first location where a fusion agent, a pore promoter, and an acidic reagent have been applied and subsequently thermally fused; and The second part of the fused polymer matrix, having a second pore volume lower than the first pore volume, is where a fusion agent is applied without the application of an acidic reagent.

4. The three-dimensional printed object of claim 3, wherein no pore promoter is applied at the second portion, and wherein the three-dimensional printed object further comprises a third portion to which a fusion agent and a pore promoter are applied without the application of an acidic agent, wherein the third portion has a third pore volume that is lower than the first pore volume but higher than the second pore volume.

5. A multi-fluid assembly for the three-dimensional printing method of claim 1, comprising: A flux containing water and a radiation absorber, wherein the radiation absorber absorbs radiation energy and converts the radiation energy into heat; An acidic reagent comprising water and an acidic component, said acidic reagent having a pH from pH 1 to pH 6.9; and A pore promoter comprising water and a water-soluble pore-promoting compound, wherein the pore-promoting compound chemically reacts with an acidic component to generate a gas, and the pore-promoting compound is selected from sodium bicarbonate, potassium bicarbonate, or combinations thereof.

6. The multifluid kit of claim 5, wherein the pore-promoting compound is sodium bicarbonate and is present in an amount of 1% to 10% by weight relative to the total weight of the pore promoter.

7. The multifluid kit of claim 5, wherein the pore-promoting compound is potassium bicarbonate and is present in an amount of 1% to 20% by weight relative to the total weight of the pore promoter.

8. The multifluid kit of claim 5, wherein both the acidic reagent and the pore promoter independently comprise an organic cosolvent and a surfactant.

9. The multifluid kit of claim 5, wherein the acidic component is an organic acid selected from lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid, malic acid, tartaric acid, or combinations thereof.

10. The multifluid kit of claim 5, wherein the acidic component is an inorganic acid selected from hydrochloric acid, hydrobromic acid, hydroiodic acid, perchloric acid, phosphoric acid, sulfuric acid, boric acid, nitric acid, nitrous acid, or combinations thereof.

11. The multifluid kit of claim 5, wherein the pore-promoting compound generates gas at elevated temperatures from 80°C to 200°C, and wherein the pore-promoting compound generates a higher gas volume density at elevated temperatures upon contact with an acidic component.

12. The multifluid kit of claim 5, wherein the radiation absorber is a metal dithiol olefin complex, carbon black, near-infrared absorbing dye, near-infrared absorbing pigment, metal nanoparticles, conjugated polymer, or a combination thereof.

13. A 3D printing kit for the 3D printing method of claim 1, comprising: Building materials containing polymer particles; A flux containing water and a radiation absorber, wherein the radiation absorber absorbs radiation energy and converts the radiation energy into heat; An acidic reagent comprising water and an acidic component, said acidic reagent having a pH from pH 1 to pH 6.9; and A pore promoter comprising water and a water-soluble pore-promoting compound, wherein the pore-promoting compound chemically reacts with an acidic component to generate a gas, and the pore-promoting compound is selected from sodium bicarbonate, potassium bicarbonate, or combinations thereof.

14. The 3D printing kit of claim 13, wherein the polymer particles have a D50 particle size of 20 µm to 150 µm and comprise polyethylene, thermoplastic polyurethane, thermoplastic polyamide, polypropylene, polyester, polycarbonate, polyetherketone, polyacrylate, polystyrene powder, wax, or combinations thereof.

15. The 3D printing kit of claim 14, wherein the thermoplastic polyamide comprises polyamide-6, polyamide-9, polyamide-11, polyamide-12, polyamide-6,6, polyamide-6,12 or combinations thereof.

16. The 3D printing kit of claim 13, wherein the pore-promoting compound generates gas at an elevated temperature of 80°C to 200°C, and wherein the pore-promoting compound generates a higher gas volume density at the elevated temperature upon contact with an acidic component.

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