Three-dimensional printing using reaction-inhibiting additives

Abstract

The present disclosure describes a three-dimensional printing kit, a three-dimensional printing system, and a method of manufacturing a three-dimensional printed object. In one example, a three-dimensional printing kit can include a build material and a binder. The build material can include particles of copper or a copper alloy. The binder can include water, copper (II) nitrate or a hydrate thereof, and a reaction-inhibiting additive. The additive can be a copper oxide etchant, a water-soluble phosphate-containing compound, or a combination thereof.

Description

[0001] background

[0002] 3D printing is an additive manufacturing method that can be used to create three-dimensional solid parts from digital models. 3D printing is commonly used for rapid product prototyping, mold generation, master mold generation, and small-batch manufacturing. Some 3D printing techniques involve applying successive layers of material. This differs from other machining methods—which typically rely on removing material to create the final part. Some 3D printing methods use chemical adhesives or glues to bond the build materials together. Other 3D printing methods involve partial sintering, melting, etc., of the build materials. For some materials, partial melting can be achieved using thermally assisted extrusion; for others, curing or fusion can be achieved using, for example, ultraviolet or infrared light. Brief description of the attached diagram

[0004] Figure 1 This is a schematic diagram of an exemplary 3D printing kit according to the present disclosure;

[0005] Figure 2 This is a schematic diagram of another exemplary 3D printing kit according to this disclosure;

[0006] Figure 3 This is a schematic diagram of an exemplary 3D printing system according to the present disclosure;

[0007] Figure 4 This is a schematic diagram of another exemplary 3D printing system according to the present disclosure; and

[0008] Figure 5 This is a flowchart illustrating an exemplary method for manufacturing 3D printed objects.

[0009] Detailed Explanation

[0010] This disclosure describes a 3D printing kit, a 3D printing system, and a method for manufacturing 3D printed objects. In one example, the 3D printing kit includes a building material and a binder. The building material comprises particles of copper or a copper alloy. The binder comprises water, copper(II) nitrate or its hydrate, and a reaction inhibitor. The additive is a copper oxide etchant, a water-soluble phosphate-containing compound, or a combination thereof. In some examples, the reaction inhibitor may comprise a copper oxide etchant selected from acetic acid, phosphoric acid, formic acid, propionic acid, phosphonoacetic acid, oxalic acid, sulfuric acid, nitric acid, or a combination thereof. In other examples, the reaction inhibitor may comprise a water-soluble phosphate-containing compound selected from ammonium dihydrogen phosphate, ammonium hydrogen phosphate, ammonium phosphate, phosphoric acid, sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, potassium dihydrogen phosphate, lithium dihydrogen phosphate, lithium hydrogen phosphate, cesium phosphate, or a combination thereof. In some examples, the reaction inhibitor may be a copper oxide etchant, and the 3D printing kit may also include a second fluid reagent comprising water and a water-soluble phosphate-containing compound. In some instances, the reaction-inhibiting additive may be present in an amount from about 0.01 wt% to about 5.0 wt% relative to the total weight of the adhesive. In some instances, the adhesive may contain an amount from about 20 wt% to about 70 wt% relative to the total weight of the adhesive. In further instances, the adhesive may also contain an amount from about 0.025 wt% to about 2 wt% relative to the total weight of the adhesive, a surfactant. In some other instances, the adhesive may be substantially free of organic wetting agents or may contain an amount from about 0.1 wt% to about 10 wt% organic wetting agents.

[0011] This disclosure also describes a 3D printing system. In one example, the 3D printing system includes a powder bed, a binder applicator, and a curing heater. The powder bed includes a build material comprising particles of copper or a copper alloy. The binder applicator is fluidly connected to or can be connected to the binder and can be directed to repeatedly apply the binder onto the build material layer. The binder comprises water, copper(II) nitrate or its hydrate, and a reaction inhibitor, wherein the additive is a copper oxide etchant, a water-soluble phosphate-containing compound, or a combination thereof. The curing heater is positioned to heat the powder bed to a curing temperature. In some examples, the reaction inhibitor may be acetic acid, phosphoric acid, formic acid, propionic acid, phosphonoacetic acid, oxalic acid, sulfuric acid, nitric acid, ammonium dihydrogen phosphate, ammonium hydrogen phosphate, ammonium phosphate, sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, potassium dihydrogen phosphate, lithium dihydrogen phosphate, lithium hydrogen phosphate, cesium phosphate, or a combination thereof. In a further example, the reaction inhibitor may be present in an amount of about 0.01% by weight to about 5.0% by weight relative to the total weight of the adhesive, and the adhesive may contain an amount of about 20% by weight to about 70% by weight relative to the total weight of the adhesive, of copper(II) nitrate trihydrate.

[0012] This disclosure also describes a method for manufacturing a 3D printed object. In one example, the method for manufacturing a 3D printed object includes selectively applying an adhesive to a build material comprising particles of copper or a copper alloy. The adhesive comprises water, copper(II) nitrate or a hydrate thereof, and a reaction inhibitor. The additive is a copper oxide etchant, a water-soluble phosphate-containing compound, or a combination thereof. The build material and the selectively applied adhesive are heated to bond layers of the 3D printed object. In some examples, the reaction inhibitor may be acetic acid, phosphoric acid, formic acid, propionic acid, phosphonoacetic acid, oxalic acid, sulfuric acid, nitric acid, ammonium dihydrogen phosphate, ammonium hydrogen phosphate, ammonium phosphate, sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, potassium dihydrogen phosphate, lithium dihydrogen phosphate, lithium hydrogen phosphate, cesium phosphate, or a combination thereof. The reaction inhibitor may be present in an amount from about 0.01% by weight to about 5.0% by weight relative to the total weight of the adhesive. The adhesive may contain an amount from about 20% by weight to about 70% by weight relative to the total weight of the adhesive. In other instances, the method may also include sintering the adhesive layer of the 3D printed object to form a sintered 3D printed object. In still other instances, the method may include adding multiple additional build material layers and selectively applying adhesive to the multiple additional build material layers. Heating the build material and selectively applying the adhesive may include simultaneously heating the build material and the multiple additional build material layers to bond the entire 3D printed object.

[0013] It should be noted that when shaping compositions, 3D printing kits, and / or methods are discussed herein, these discussions may be considered to apply to each other, regardless of whether they are explicitly discussed in the context of that instance. Thus, for example, when discussing high-melting-point metal particles in shaping compositions, such disclosures also relate to and are directly supported in the context of 3D printing kits and methods, and vice versa, regardless of the scope of the differences described.

[0014] It should also be understood that, unless otherwise specified, the terms used herein have their common meaning in the relevant technical field. In some cases, certain terms are defined more specifically in various parts of this specification or included at the end of this specification, and therefore these terms may have the meanings as stated herein.

[0015] 3D printing kit

[0016] The 3D printing kits, systems, and methods described herein can be used to manufacture 3D printed objects of copper or copper alloys. Some form of 3D printing or additive manufacturing process can be performed using the materials described herein. In one example, an adhesive can be applied to a layer of metal particles made of copper or copper alloys. Successive layers of metal particles can be added, and an adhesive can be applied to the layers to bond the particles together to form a layer of 3D printed green body. The green body can later be fused together, for example, by sintering, to form a metallic object.

[0017] The binder used in the 3D printing method may include an aqueous solution of copper(II) nitrate. The binder can be applied to certain areas of the metal particle layer. The metal particles and the applied binder can then be heated to an elevated temperature, at which temperature the copper(II) nitrate can decompose (or partially decompose) to form copper(II) hydroxynitrate (Cu₂(OH)₃NO₃). The copper(II) hydroxynitrate binds the metal particles together in the green body. When the green body is subsequently fused at a high temperature, the hydrogen, oxygen, and nitrogen in the copper(II) hydroxynitrate can be released as gases, while the copper can be retained as part of the fused metal object.

[0018] In some cases, a chemical reaction can occur between the metal particles and the binder when the binder is applied to the metal particles. For example, some binder formulations containing water and copper(II) nitrate can cause a reaction with copper or copper alloy particles. This reaction can produce gases such as nitric oxide (NO) and nitrogen dioxide (NO2). The reaction can also oxidize copper or copper alloys to form copper(I) oxide (Cu2O) and / or copper(II) oxide (CuO). If sufficient gas is released through this reaction, it can reduce the density of the 3D-printed green body. For example, the gas may be trapped and form bubbles between the particles in the green body. The gas can also cause dimensional instabilities, such as bulges on the surface of the green body. These defects persist throughout the sintering process. Therefore, the gas released by this reaction can affect the appearance and density of the final sintered metal object. Furthermore, the voids formed by the gas can negatively affect the properties of the final sintered metal object, such as thermal conductivity, electrical conductivity, and strength.

[0019] The binders described herein may contain additives that inhibit the aforementioned reactions. In various examples, the reaction-inhibiting additives may be copper oxide etchants, water-soluble phosphate compounds, or a combination of both. Binders containing reaction-inhibiting additives can reduce gas escape when applied to metal particles compared to binders without such additives. Therefore, 3D printed green bodies made using the binders described herein can have higher densities compared to 3D green bodies made using other binders. Sintered metal objects made by sintering this green body can also have better properties compared to sintered metal objects made using other binders. In some cases, the reaction-inhibiting additives can also remove oxides already present on the metal particles. This can also help sinter the metal particles together with higher density and enhanced properties such as thermal and electrical conductivity.

[0020] In some instances, the binders described herein are particularly useful for metal powder building materials that do not yet contain reaction-inhibiting additives. For example, some copper powders with low phosphorus content (e.g., less than 1% by weight) are available. The phosphorus content in such copper powders can have a similar effect of inhibiting the reaction with the binder. However, different copper powder formulations can consist of pure copper or copper alloys without any phosphorus or other reaction-inhibiting additives. The binders described herein can be used to form 3D printed green bodies from such copper powders without the negative effects of gas selection from the aforementioned reactions.

[0021] Additionally, the amount of reaction-inhibiting additive in the binder can be adjusted to minimize its presence in the final 3D printed metal object. The amount of binder applied during the 3D printing process can also be adjusted to control the amount of reaction-inhibiting additive present in the object. In some instances, the presence of phosphorus in copper objects can cause a significant decrease in the thermal and electrical conductivity of copper. However, a very small amount of phosphate reaction-inhibiting additive can be applied as part of the binder, and such a small amount is sufficient to reduce or prevent the negative effects of the aforementioned gas escape. This very small amount of phosphate reaction-inhibiting additive can also be so small that its effect on the thermal or electrical conductivity of the copper object is negligible. Furthermore, some phosphorus can be removed during high-temperature debinding and sintering. Therefore, using a binder containing reaction-inhibiting additives allows for better control of the amount of reaction-inhibiting additive present in the build material. In some instances, the binder can be formulated and applied such that, relative to the total weight of the build material, the amount of phosphorus added to the powdered build material is less than about 0.1% by weight, or less than about 0.01% by weight, or less than about 0.005% by weight. In a further example, the concentration of the water-soluble phosphate compound in the adhesive may be from about 0.01 wt% to about 5 wt%, or from about 0.01 wt% to about 2.5 wt%, or from about 0.025 wt% to about 1 wt%, or from about 0.025 wt% to about 0.5 wt%.

[0022] Figure 1 This diagram illustrates an exemplary 3D printing kit 100 according to the present disclosure. The 3D printing kit includes a build material 110 and an adhesive 120. The build material may contain particles of copper or a copper alloy. The adhesive may contain water, copper(II) nitrate or its hydrate, and a reaction inhibitor. The reaction inhibitor may be a copper oxide etchant, a water-soluble phosphate compound, or a combination thereof.

[0023] In some instances, the adhesive may comprise both a copper oxide etchant and a water-soluble phosphate-containing compound. In other instances, the adhesive may comprise either a copper oxide etchant or a water-soluble phosphate-containing compound, but not both. Some examples of copper oxide etchants may include acids such as acetic acid, phosphoric acid, formic acid, propionic acid, phosphonoacetic acid, oxalic acid, sulfuric acid, nitric acid, etc. Some exemplary water-soluble phosphate-containing compounds may include ammonium dihydrogen phosphate, ammonium hydrogen phosphate, ammonium phosphate, phosphoric acid, sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, potassium dihydrogen phosphate, lithium dihydrogen phosphate, lithium hydrogen phosphate, cesium phosphate, etc.

[0024] In a further example, the 3D printing kit may include an adhesive and a second fluid reagent. The adhesive may contain a copper oxide etchant or a water-soluble phosphate-containing compound. Any type of reaction-inhibiting additive not included in the adhesive may be included in the second fluid reagent. Therefore, the amount of different reaction-inhibiting additives applied to the build material can be controlled independently. In one example, the adhesive may contain a copper oxide etchant, while the second fluid reagent may contain a water-soluble phosphate-containing compound.

[0025] Figure 2 Another exemplary 3D printing kit 100 is shown. This kit includes a build material 110, an binder 120, and a second fluid reagent 130. In this example, the build material contains particles of copper or a copper alloy. The binder contains water, copper(II) nitrate or its hydrate, and a copper oxide etchant. The second fluid reagent contains water and a water-soluble phosphate-containing compound. This kit can be used in 3D printing methods where the binder and the second fluid reagent can be independently and selectively applied to the build material. Therefore, the amounts of copper oxide etchant and the phosphate-containing compound can be independently controlled in different parts of the 3D printed green body object. In some instances, the second fluid reagent may also contain copper(II) nitrate or its hydrate. In such instances, the second fluid reagent can act as a second binder.

[0026] In some instances, the build materials and adhesives can be packaged together in separate containers. Specifically, the container holding the build materials and the container holding the adhesive can be packaged together. For 3D printing kits that include a second fluid reagent, a container holding the second fluid reagent may also be included. In other instances, the build materials, adhesives, and second fluid reagent (if present) can be packaged separately. However, these materials can be combined during 3D printing by loading materials into the 3D printing system.

[0027] The following describes in more detail specific examples of building materials, binders, other fluid agents, and components that may be contained therein.

[0028] 3D printing system

[0029] 3D printing systems can be used with the build materials and binders described herein to fabricate 3D printed objects. In some instances, the 3D printing system may include a powder bed for supporting layers of build material. A binder applicator may be positioned to selectively apply binder to the build material layers. For example, the binder applicator may be controllable to apply binder at specific x / y coordinates of the build material layer. Additionally, the 3D printing system may include a curing heater. As used herein, “curing” can refer to the process of heating the build material and binder to evaporate the solvent in the binder and to dehydrate or partially dehydrate the copper(II) nitrate in the binder. In one specific instance, the binder may contain copper(II) nitrate trihydrate, and curing may include heating the binder until the copper(II) nitrate trihydrate decomposes to form copper(II) hydroxynitrate.

[0030] Figure 3 This is a schematic diagram of an exemplary 3D printing system 200 according to the present disclosure. The system includes a powder bed 210 comprising a build material 110. The build material comprises particles of copper or a copper alloy. The system also includes an adhesive applicator 220. The adhesive applicator is fluidly connected to an adhesive 120 and is directed to repeatedly apply the adhesive onto the build material layer. The adhesive may comprise water, copper(II) nitrate or its hydrate, and a reaction inhibitor. As explained above, the reaction inhibitor may be a copper oxide etchant, a water-soluble phosphate-containing compound, or a combination thereof. The system also includes a curing heater 230 positioned to heat the powder bed to a curing temperature.

[0031] It should be pointed out that, except Figure 3 In addition to the components shown, a 3D printing system may also include various additional components. Examples of additional components include a build material dispenser, a supply source of additional build material, a fluid applicator for applying a second fluid reagent, a hardware controller for sending instructions to other components in the system, a non-transitory computer-readable medium having stored computer-executable instructions to enable the hardware controller to send instructions to other components in the system to perform the 3D printing method, a sintering furnace, etc.

[0032] Figure 4Another exemplary 3D printing system 200 is shown, which includes some of these additional components. In this example, the system includes a powder bed 210 having a build material platform 202 and sidewalls 204. A build material applicator 208 is configured to deposit individual build material layers 110 on the build material platform or on top of a previous build material layer. The system also includes an adhesive applicator 220 disposed above the powder bed. The adhesive applicator is movable to allow it to apply adhesive 120 onto the build material layers. A curing heater 230 is disposed to heat the powder bed. In this example, the curing heater can heat the individual build material layers after the application of adhesive to form individual green body layers 212 composed of bonded metal particles. A hardware controller 240 communicates with the curing heater, adhesive applicator, and build material applicator to send instructions to these components to execute the 3D printing method.

[0033] In some instances, the adhesive applicator can move along two axes, such as the x-axis and y-axis, to selectively apply the adhesive to any desired location on the build material layer. In other instances, the adhesive applicator can be large enough to span an entire dimension of the powder bed, and the adhesive applicator can move along one axis. For example, the adhesive applicator may include multiple nozzles along the length of the adhesive applicator, and the adhesive can be selectively sprayed from each nozzle. The adhesive applicator can then scan across the powder bed and can selectively spray the adhesive from the nozzles to apply the adhesive to any desired location on the powder bed. In other instances, the powder bed itself can be movable. For example, the powder bed can be movable, while the adhesive applicator can be stationary. In either instance, the adhesive applicator and the powder bed can be configured such that the adhesive can be selectively applied to specific portions of the powder bed. In some instances, the adhesive applicator can be configured to print adhesive droplets at a resolution of approximately 300 dots per inch (DPI) to approximately 1200 DPI. Higher or lower resolutions can also be used. The volume of each adhesive droplet can be approximately 1 pL to approximately 400 pL in some instances. The spray frequency of the nozzle of the adhesive applicator can be from about 1 kHz to about 100 kHz in some instances.

[0034] exist Figure 4 In some examples, the curing heater is used to cure individual layers of building material after the adhesive has been applied to each layer. In other examples, the curing heater can apply heat to cure multiple layers at once. For example, these layers can be cured after every five layers, or after every ten layers, or after every twenty layers, and so on. Alternatively, the curing heater can be used after all layers have been deposited and the adhesive has been applied to them. The entire powder bed can then be heated to the curing temperature to cure the entire green body object at once.

[0035] A build material applicator can deposit build material layers onto a build platform, wherein the build material layers can be planarized or smoothed layer by layer, for example, by mechanical rollers, spreading blades, or other planarization techniques. The build material layers can be deposited and uniformly spread on the top surface. As mentioned above, the build material may contain copper or copper alloy particles. The build material layers may have layer thicknesses of, for example, approximately 25 μm to approximately 400 μm, 75 μm to approximately 400 μm, approximately 100 μm to approximately 400 μm, approximately 150 μm to approximately 350 μm, or approximately 30 μm to approximately 100 μm. A binder can be used, for example, to generate a green body object layer by layer. As explained above, the binder can be applied to certain portions of the build material layers in the shape of the green body object layers. The shape of the green body object layers may, for example, be based on a three-dimensional computer model. After each layer has been printed with adhesive, the build platform can be lowered a distance corresponding to the thickness of the applied build material layer, for example, approximately 50 μm to approximately 200 μm, so that another build material layer can be added on top and printed with adhesive, and so on. This method can be repeated on a layer-by-layer basis until a green body object is formed. As described above, a curing heater can be used to cure the green body object in a single curing operation, either on a layer-by-layer basis or after the entire green body object has been formed in a powder bed. The green body object can be stabilized enough to be moved into a furnace suitable for fusion, such as sintering, annealing, etc.

[0036] Methods for manufacturing 3D printed objects

[0037] The 3D printing kit and system described in this article can be used as a method for manufacturing 3D printed objects. Figure 5 This is a flowchart illustrating an exemplary method 300 for manufacturing a 3D printed object. The method includes: 310 selectively applying an adhesive to a build material comprising particles of copper or a copper alloy, wherein the adhesive comprises water, copper(II) nitrate or a hydrate thereof, and a reaction inhibitory additive, wherein the additive is a copper oxide etchant, a water-soluble phosphate compound, or a combination thereof; and 320 heating the build material and the selectively applied adhesive to bond layers of the 3D printed object.

[0038] The amount of copper(II) nitrate introduced into the building material by the binder is sufficient to bind the building material particles together. In some instances, after the binder has been applied, the concentration of copper(II) nitrate in the building material may be from about 0.2 wt% to about 20 wt% based on the total weight of the building material particles and copper(II) nitrate. In other instances, the concentration of copper(II) nitrate may be from about 0.2 wt% to about 15 wt%, or from about 0.2 wt% to about 10 wt%, or from about 0.2 wt% to about 5 wt%, or from about 0.2 wt% to about 1 wt%.

[0039] In a further example, the build material to which the binder is applied can be heated to a curing temperature. As explained above, this can dehydrate or partially dehydrate the copper(II) nitrate in the binder, forming a compound that binds the build material particles together. The 3D printed body of the build material particles held together in this way can be referred to as a “green body” or “green body object.” In some examples, the individual build material layers and binder can be heated and cured to form the individual layers of the final green body object. In other examples, multiple build material layers may have an binder applied thereto, and then the multiple layers can be cured simultaneously. In one example, all layers can be formed in a powder bed without curing, and then at the end of the 3D printing method, the entire powder bed can be heated to a curing temperature to simultaneously cure the entire green body object. The green body object can consist of build material particles and binder prior to fusion (e.g., by sintering or annealing), but they are sufficiently held together to allow the object to be processed and moved to a sintering furnace or other apparatus for fusing green body objects.

[0040] The heat used for curing can be provided by a curing heater positioned to heat the build material in the powder bed. In some instances, the curing heater can be positioned above the powder bed. In other instances, a build platform below the powder bed can be heated. The heater can also be positioned on the side of the powder bed. Combinations of these heaters can also be used. In some instances, the curing temperature for the build material and adhesive can be from about 70°C to about 250°C. In further instances, the curing temperature can be from about 70°C to about 160°C, or from about 70°C to about 120°C, or from about 100°C to about 160°C, or from about 140°C to about 160°C, or from about 140°C to about 250°C. The curing time can be from about 1 second to about 4 hours. In some instances, individual build material layers can be cured, and the curing time can be from about 1 second to about 1 minute per layer. In other instances, the entire green body can be cured simultaneously, and the curing time can be from about 15 minutes to about 4 hours, or from about 20 minutes to about 3 hours, or from about 30 minutes to about 2 hours, or from about 1 hour to about 2 hours.

[0041] In some instances, the green body can be fully cured in the powder bed of the 3D printing system. In other instances, the first curing stage can be performed in the powder bed, followed by a second curing stage at another location, such as in a curing oven. In some instances, the second curing stage can expose the green body to a higher curing temperature than the first curing stage. In one instance, the green body can be cured in the powder bed during the first curing stage at a first curing temperature of approximately 70°C to approximately 160°C, and then further cured in the second curing stage at a second curing temperature of approximately 140°C to approximately 250°C.

[0042] After the 3D printed green body has solidified, it can be fused together. The terms "fusion" and "fused" refer to the thermal bonding of the metal particles in the green body at a high temperature, which depends on various variables such as particle size, metal type, metal purity, and weight percentage of metal content. Fusion can take the form of melting, sintering, annealing, etc., and can include the complete fusion of adjacent particles into a common structure, such as melting them together, or it can include surface fusion, where the particles are not completely melted to their liquefaction point but can still bond the individual particles of the building material together, such as forming material bridges between particles at or near contact points. Fusion can include particles melting together into a single entity, or it can include the softening or melting of the surfaces of the metal building particles to bond them together at the particle interfaces. In either case, the metal object with bonded and fused metal building particles can be treated and / or used as a rigid component or object without the fragility of the green body.

[0043] Sintering of metal building blocks is a form of metal particle fusion. Annealing is another form of metal particle fusion. A third type of fusion involves melting metal building blocks together to form a unitary mass. The terms "sintering," "sintered," etc., refer to the solidification and physical bonding of metal building blocks through solid-state diffusion bonding, partial melting of metal building blocks, or a combination of solid-state diffusion bonding and partial melting (after temporary bonding with an adhesive). The term "annealing" refers to the controlled heating and cooling processes, such as slowing down cooling in some cases, to remove internal stresses and / or toughen the fused metal object.

[0044] In some instances, the green body can be sintered in a sintering furnace. Sintering can be carried out at a variety of temperatures, depending on the specific type of metal particles present in the building material. In some instances, the sintering temperature can be from about 750°C to about 1300°C. In further instances, the sintering temperature can be from about 800°C to about 1300°C, or from about 900°C to about 1300°C, or from about 1000°C to about 1300°C, or from about 1100°C to about 1300°C, or from about 1200°C to about 1300°C, or from about 800°C to about 1200°C, or from about 900°C to about 1200°C, or from about 1000°C to about 1200°C, or from about 1100°C to about 1200°C, or from about 800°C to about 1100°C, or from about 900°C to about 1100°C, or from about 1000°C to about 1100°C. In some instances, sintering can be carried out for approximately 10 minutes to approximately 20 hours, or approximately 30 minutes to approximately 10 hours, or approximately 1 hour to approximately 5 hours. Sintering can be performed in an atmosphere or in a vacuum. In some instances, the sintering atmosphere can be an inert gas, a low-reactivity gas, a reducing gas, or a combination thereof. Some gases that can be used in a sintering atmosphere include hydrogen, helium, argon, neon, xenon, krypton, nitrogen, carbon monoxide, and combinations thereof.

[0045] Construction materials

[0046] The build materials used in the 3D printing kits described herein may contain metallic particles. As mentioned above, in some instances, the build materials may contain copper or copper alloy particles. In some instances, copper alloys may include brass, copper-zinc alloys, bronze, copper-tin alloys, aluminum bronze, magnesium bronze, silicon bronze, phosphor bronze, copper-nickel alloys, copper-chromium alloys, Monel alloys, nickel-copper alloys, copper-gold alloys, copper-silver alloys, etc. Other metals that may be included in the build materials include steel, stainless steel, titanium, titanium alloys, aluminum, aluminum alloys, nickel, nickel alloys, cobalt, cobalt alloys, iron, iron alloys, gold, gold alloys, silver, silver alloys, platinum, platinum alloys, and combinations thereof. Specific examples of copper powder include copper powder available from Goodfellow Corporation (USA) and copper powder available from Sandvik AB (Sweden).

[0047] As mentioned above, some copper powders may contain trace amounts of phosphorus to inhibit oxidation. However, in some instances, the build materials used in the 3D printing kits described herein may be phosphorus-free or essentially phosphorus-free. In some instances, the build material may be pure copper powder.

[0048] In various instances, the building material may contain particles of similar or different sizes. In some instances, the building material may have a D50 particle size of approximately 1 micrometer to approximately 150 micrometers, or approximately 5 micrometers to approximately 50 micrometers, or approximately 10 micrometers to approximately 30 micrometers. As used herein, particle size may refer to the diameter value of spherical particles, or, in non-spherical particles, the longest dimension of the particle. The particle size may exhibit a Gaussian or Gaussian-like distribution (or a normal or quasi-normal distribution). A Gaussian-like distribution is a distribution curve that may appear Gaussian in shape but is slightly skewed in one or the other direction (towards the smaller or larger end of the particle size distribution range). That is, an exemplary Gaussian-like distribution of metallic building particles can be characterized using particle size distribution values ​​of “D10,” “D50,” and “D90,” where D10 refers to the 10th percentile particle size, D50 refers to the 50th percentile particle size, and D90 refers to the 90th percentile particle size. For example, a D50 value of 25 μm means that 50% of the particles (by number) have a particle size greater than 25 μm and 50% of the particles have a particle size less than 25 μm. The particle size distribution value may not be related to a Gaussian distribution curve, but in one example of this disclosure, the metallic building blocks may have a Gaussian distribution or, more generally, a Gaussian-like distribution with a shifted peak near D50. In practice, a true Gaussian distribution is not usually present because some skewness may exist, but a Gaussian-like distribution can still be considered "Gaussian-type" in practice. The shape of the building block particles can be spherical, non-spherical, random, or a combination thereof.

[0049] adhesives

[0050] The adhesive used in this 3D printing kit may contain water, copper(II) nitrate or its hydrate, and a reaction inhibitor. As explained above, the reaction inhibitor may be a copper oxide etchant, a water-soluble phosphate compound, or a combination thereof. In some instances, the content of copper(II) nitrate or its hydrate may be from about 20% to about 70% by weight, or from about 30% to about 60% by weight, or from about 35% to about 50% by weight. In some instances, copper(II) nitrate may be in the form of anhydrous copper(II) nitrate, copper(II) nitrate monohydrate, copper(II) nitrate sesquihydrate, copper(II) nitrate disesquihydrate, copper(II) nitrate trihydrate, or copper(II) nitrate hexahydrate. In one particular instance, the adhesive may contain an amount of copper(II) nitrate trihydrate from about 20% to about 70% by weight.

[0051] In some instances, the content of the reaction inhibitor additive may be from about 0.01 wt% to about 5.0 wt% relative to the total weight of the adhesive. In further instances, the amount of the reaction inhibitor additive may be from about 0.05 wt% to about 5 wt%, or from about 0.075 wt% to about 5 wt%, or from about 0.1 wt% to about 5 wt%, or from about 0.25 wt% to about 5 wt%, or from about 0.5 wt% to about 5 wt%. In some instances, the adhesive may contain both a copper oxide etchant and a water-soluble phosphate-containing compound. In such instances, the concentration ranges given above may be combined concentrations of the copper oxide etchant and the phosphate-containing compound. In some instances, the amount of copper oxide etchant may be greater than the amount of water-soluble phosphate-containing compound contained in the adhesive. In some instances, the weight ratio of copper oxide etchant to water-soluble phosphate-containing compound may be from about 2:1 to about 10:1, or from about 2:1 to about 5:1.

[0052] Non-limiting examples of copper oxide etchants that may be included in the binder may include acids such as acetic acid, phosphoric acid, formic acid, propionic acid, phosphonoacetic acid, oxalic acid, sulfuric acid, nitric acid, etc. Non-limiting examples of water-soluble phosphate-containing compounds may include ammonium dihydrogen phosphate, ammonium hydrogen phosphate, ammonium phosphate, phosphoric acid, sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, potassium dihydrogen phosphate, lithium dihydrogen phosphate, lithium hydrogen phosphate, cesium phosphate, etc. In some examples, the binder may contain phosphoric acid, ammonium dihydrogen phosphate, acetic acid, or combinations thereof. In further examples, the binder may contain phosphoric acid without any other reaction-inhibiting additives. In other examples, the binder may contain acetic acid without any other reaction-inhibiting additives. In still other examples, the binder may contain ammonium dihydrogen phosphate without any other reaction-inhibiting additives. In still other examples, the binder may contain a combination of acetic acid and ammonium dihydrogen phosphate or a combination of phosphoric acid and ammonium dihydrogen phosphate without any other reaction-inhibiting additives. In some instances, the adhesive may contain acetic acid in an amount of about 0.5% to about 2.5% by weight, and / or phosphoric acid in an amount of about 0.025% to about 5% by weight, and / or ammonium dihydrogen phosphate in an amount of about 0.2% to about 5% by weight.

[0053] In some instances, adhesives may also contain surfactants. Surfactants can be used to improve the wetting properties and sprayability of the adhesive. Non-limiting examples of surfactants that can be used include DOWFAX from Dow Inc. (USA). TM 2A1; from Air Products and Chemicals, Inc. (USA) SEF; nonionic fluorinated surfactants, such as those from DuPont (USA). Fluorinated surfactants; ethoxylated low-foaming wetting agents, such as those from Air Products and Chemicals Inc. (USA). 440 or CT-111; ethoxylated wetting agents and molecular defoamers, such as those from Air Products and Chemicals, Inc. (USA). 420; Nonionic wetting agents and molecular defoamers, such as those from AirProducts and Chemicals Inc. (USA) 104E; Water-soluble nonionic surfactants, such as TERGITOL from Dow Inc. (USA) TM TMN-6 or TERGITOL TM 15-S-7. A single surfactant or a combination of surfactants may be used. In some instances, the total amount of surfactant in the adhesive may be from about 0.025% by weight to about 2% by weight.

[0054] In some instances, pH-adjusting additives may also be included in the binder. In some instances, the amount of pH-adjusting additive may be sufficient to provide a binder with a pH of about 0 to about 3, or about 1 to about 2. Additionally, the pH-adjusting additive may not contain elements that remain in the metal object after sintering. For example, some pH-adjusting additives, such as potassium hydroxide, may leave unwanted elements, such as potassium, in the metal object after sintering. Therefore, the pH-adjusting additive included in the binder may contain elements that are volatile and / or combustible during sintering to ensure that no unwanted elements are left in the sintered metal object. Some examples of pH-adjusting additives that can be used include ammonium acetate and ammonium hydroxide. In some instances, the amount of pH-adjusting additive may be from about 0.1% by weight to about 5% by weight.

[0055] The adhesive may also contain water. In some instances, water may be used as a solvent for the adhesive without any additional co-solvents. Thus, in some instances, the adhesive may consist of water, copper(II) nitrate or its hydrate, and a reaction-inhibiting additive. In further instances, the adhesive may consist of these components plus a surfactant and / or a pH-adjusting additive. The amount of water in the adhesive may be from about 20% by weight to about 79% by weight.

[0056] In alternative examples, the adhesive may contain water and an organic co-solvent. The organic co-solvent may include 2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, tripropylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, tripropylene glycol mono-n-butyl ether, propylene glycol phenyl ether, dipropylene glycol methyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, ethylene glycol phenyl ether, diethylene glycol mono-n-butyl ether acetate, ethylene glycol mono-n-butyl ether acetate, 2-methyl-1,3-propanediol, or combinations thereof. In some examples, the content of the organic co-solvent may be from about 0.1% by weight to about 20% by weight, or from about 0.1% by weight to about 10% by weight, or from about 0.1% by weight to about 2% by weight. However, in some examples, the adhesive may be free of or substantially free of organic wetting agents. Organic wetting agents may include organic solvents with a boiling point of 120°C or higher. Some organic wetting agents can pose a flammable or explosive hazard during printing or curing. However, some wetting agents are safe to use. Therefore, in some instances, adhesives may be substantially free of organic wetting agents or may contain amounts ranging from about 0.1% to about 10% by weight of organic wetting agents.

[0057] In some cases, adhesives may contain additional additives, such as antimicrobial agents, antiscaling agents, and chelating agents. An example antimicrobial agent may be NUOSEPT. TM (Troy Corp., USA), UCARCIDE TM (Dow Chemical Co., USA) An aqueous solution of M20 (Thor, United Kingdom), 1,2-benzisothiazolin-3-one, such as from Arch Chemicals, Inc. (USA). GXL, quaternary ammonium compounds, such as 2250 and 2280 50-658 and 250-T, all from Lonza Ltd. Corp. (Switzerland), aqueous solutions of methylisothiazolinone, such as those from Dow Chemical Co. (USA). MLX, or combinations thereof. Biocides or antimicrobial agents may be added in any amount from about 0.05% by weight to about 0.5% by weight relative to the total weight of the adhesive.

[0058] Antiscaling agents can also be included in the adhesive. Scaling refers to deposits that form on the heating elements of a thermal inkjet printhead. Antiscaling agents can be included to help prevent scale buildup. Examples of suitable antiscaling agents include oil-based polyoxyethylene (3) ether phosphates, such as CRODAFOS from Croda (United Kingdom).TM 03A or CRODAFOS TM N-3 acid, or a combination of oil-based polyoxyethylene (3) ether phosphate and low molecular weight (e.g., <5,000) polyacrylic acid polymers, such as CARBOSPERSE from Lubrizol (USA). TM K-7028 Polyacrylate. Whether using a single antiscaling agent or a combination of antiscaling agents, in some instances, the total amount of antiscaling agent in the adhesive can be from approximately 0.2% to approximately 0.6% by weight based on the total weight of the adhesive.

[0059] Chelating agents, such as EDTA (ethylenediaminetetraacetic acid), may be included to eliminate the harmful effects of heavy metal impurities. In some instances, 0.01% to 2% by weight of such components may be included. Viscosity improvers and buffers, as well as other additives that alter the properties of the adhesive, may also be present. These additives may be present in amounts ranging from about 0.01% to about 20% by weight in various instances.

[0060] definition

[0061] It should be noted that, unless the context clearly specifies otherwise, the singular forms “a,” “an,” and “the” used in this specification and the appended claims include the plural objects.

[0062] As used herein, the term "approximately" allows for a degree of variability in a numerical value or range, such as within 10% of a specified numerical value or range limit, or within 5% in one aspect. When modifying a numerical range, the term "approximately" is also understood to include the range defined by the exact numerical value stated as a subrange, for example, a range of approximately 1 wt% to approximately 5 wt% includes 1 wt% to 5 wt% as a explicitly supported subrange.

[0063] As used herein, “kit” is synonymous with multiple compositions and is understood to include multiple compositions comprising multiple components, wherein different compositions may be contained separately in the same one or more containers before and during use (e.g., printing three-dimensional objects), but these components may be combined together during the printing process. Containers may be any type of vessel, box, or receptacle made of any material.

[0064] As used herein, for convenience, multiple items, structural elements, components, and / or materials may be listed in a general list. However, these lists should be interpreted as if each member of the list were specified as a separate and unique member. Therefore, unless otherwise indicated, no member of such a list should be interpreted as equivalent to any other member of the same list based on their presence in the same group.

[0065] Concentration, size, amount, and other numerical data may be presented in range format herein. It is to be understood that such range format is used for convenience and brevity only and should be flexibly interpreted to include not only the explicitly listed values ​​that define the limits of the range, but also all individual values ​​or subranges contained within the range, just as if they were explicitly listed. For example, a weight ratio range of approximately 1 wt% to approximately 20 wt% should be interpreted to include the explicitly listed limits of 1 wt% and 20 wt%, as well as individual weights such as approximately 2 wt%, approximately 11 wt%, approximately 14 wt%, and subranges such as approximately 10 wt% to approximately 20 wt%, approximately 5 wt% to approximately 15 wt%, etc. Example

[0066] The embodiments of this disclosure are illustrated below. However, it is to be understood that the following examples illustrate the application of the principles of this disclosure. Many modifications and alternative compositions, methods, and systems can be devised without departing from the spirit and scope of this disclosure. The appended claims are intended to cover such modifications and arrangements.

[0067] Example 1 - Adhesive formulation

[0068] A series of sample binder formulations were prepared. Samples no. 1 to no. 42 contained reaction-inhibiting additives, which included copper oxide etchant or phosphate-containing compounds or a combination of both. Comparative samples no. 1 and no. 2 did not contain reaction-inhibiting additives but contained other additives. All samples contained copper(II) nitrate trihydrate as a binder. Table 1 shows the additives present in the sample formulations, along with their concentrations, the concentration of copper(II) nitrate trihydrate, and the pH of the sample formulations.

[0069] Table 1: Adhesive Formulations

[0070]

[0071]

[0072] The amount of KOH added is sufficient to provide a pH of 1.35.

[0073] In Table 1, AdHP refers to diammonium dihydrogen phosphate; AdBP refers to diammonium hydrogen phosphate; 2P refers to 2-pyrrolidone; and DF2A1 refers to DOWFAX, which is available from Dow Inc. (USA). TM 2A1 surfactant; KOH refers to potassium hydroxide; TMN-6 refers to TERGITOL, which is available from Dow Inc. (USA). TMTMN-6 is a surfactant; HE2P refers to 1-(2-hydroxyethyl)-2-pyrrolidone; and FS-35 refers to CAPSTONE, which is available from The Chemours Company (USA). TM FS-35 surfactant. The "N / A" value was not measured.

[0074] Example 2 -Preparation of molded copper rods

[0075] The binder in Table 1 was tested by forming a molded copper rod from a mixture of binder and copper powder. The copper powder contained copper particles with a particle size of 22 micrometers or smaller and contained no phosphorus. One part by weight of binder was mixed with ten parts by weight of copper powder, and the mixture was used to form a rod in a mold. The rod was then cured to form a green body by heating in three stages on a hot plate at 70°C for 1 hour, 100°C for 1 hour, and 150°C for 1 hour. The strength of the green body was measured using a three-point fracture strength test. In this test, the rod was supported on a blade at opposite ends and a shear force was applied to opposite sides until the rod broke. The tensile stress on the outer edge of the rod at the point of fracture was designated as the fracture strength. The density of the green body was also measured as a comparison with a solid copper rod. The amount of phosphorus added to the copper powder by the binder was also calculated. As explained above, a lower phosphorus concentration is useful in some cases to provide higher thermal and electrical conductivity. Table 2 shows the amount of phosphorus added by the binder, the average strength of the molded rod, the strength range of any binder used to manufacture multiple molded rods, and the average density of the molded rod.

[0076] Table 2

[0077]

[0078]

[0079] The results in Table 2 show that the comparative samples have very low strength and density compared to samples 1-37 (the strength of rods made with samples 38-42 was not measured). This is due to the formation of air bubbles when the comparative binder is mixed with copper powder. These air bubbles significantly reduce the strength and density of the comparative molded rods. Additionally, voids from these air bubbles are visible on the surface of the comparative molded rods. The molded rods made using binder formulations 1-37 show slightly different strengths. Some optimal results were achieved using additives acetic acid, ammonium dihydrogen phosphate, and phosphoric acid, or combinations thereof.

[0080] It was found that when acetic acid is used alone as an additive, it eliminates oxidation from copper powder. However, some reactions occur during curing, generating sufficient gas to cause surface bulging in molded rods made solely with acetic acid. No surface bulging was observed when ammonium dihydrogen phosphate was combined with acetic acid. Therefore, in some cases, a combination of acetic acid and ammonium dihydrogen phosphate can be used as a reaction-inhibiting additive.

[0081] Example 3 - 3D printing

[0082] An adhesive was prepared comprising 40 wt% copper(II) nitrate trihydrate, 1.0 wt% acetic acid, 0.2 wt% ammonium dihydrogen phosphate, and 0.5 wt% DOWFAX from Dow Inc. (USA). TM 2A1 surfactant and the remainder water. The binder was loaded into the experimental metal 3D printing system. The build material was the same copper powder used in Example 1. The sample object was printed using the 3D printing system. The amount of binder applied to the build material was approximately 0.63 grams of binder per cubic centimeter of copper powder. After printing, the printed green body was cured at 100°C for 1 hour. The cured green body strength was approximately 7-10 MPa. An additional curing was performed at 150°C for 2 hours in a curing oven. After the additional curing, the green body strength increased to approximately 8-11 MPa. X-ray diffraction was performed, and a peak corresponding to the presence of copper(II) hydroxynitrate was found. This indicates that copper(II) hydroxynitrate was formed through the decomposition of copper(II) nitrate trihydrate in the binder.

[0083] The 3D printed rods were sintered at 1050°C for 4 hours in an argon and hydrogen atmosphere. The density of the sintered rods was approximately 90%. The rods were then processed by hot isostatic pressing (HIP) at 950°C under argon pressure of 14,750 psi for 2 hours. The density after HIP was approximately 93% to approximately 96%.

[0084] Although the present technology has been described with reference to certain embodiments, various modifications, variations, omissions and substitutions may be made without departing from the present disclosure.

Claims

1. A 3D printing kit, which includes: The building material contains particles of copper or copper alloys; Adhesive, comprising: water, Copper(II) nitrate or its hydrate, and A reaction-inhibiting additive, wherein the reaction-inhibiting additive is a copper oxide etchant, wherein the copper oxide etchant is acetic acid; and The second fluid reagent comprises water and a water-soluble phosphate compound, wherein the binder and the second fluid reagent are independently and selectively applied to the building material, wherein the water-soluble phosphate compound is ammonium dihydrogen phosphate.

2. The 3D printing kit of claim 1, wherein the reaction inhibitor is present in an amount of about 0.01% by weight to about 5.0% by weight relative to the total weight of the adhesive.

3. The 3D printing kit of claim 1, wherein the adhesive comprises copper(II) nitrate trihydrate in an amount of about 20% to about 70% by weight relative to the total weight of the adhesive.

4. The 3D printing kit of claim 1, wherein the adhesive further comprises a surfactant in an amount of about 0.025% to about 2% by weight relative to the total weight of the adhesive.

5. The 3D printing kit of claim 1, wherein the adhesive is free of organic wetting agents or contains an amount of organic wetting agents from about 0.1% by weight to about 10% by weight.

6. A three-dimensional printing system, comprising: A powder bed comprising a building material containing particles of copper or a copper alloy; An adhesive applicator fluidly connected to or capable of being connected to an adhesive and a second fluid reagent, wherein the adhesive applicator is guided to repeatedly apply the adhesive and the second fluid reagent to a build material layer, wherein the adhesive comprises copper(II) nitrate or its hydrate, water, and a reaction inhibitor, wherein the reaction inhibitor is a copper oxide etchant, the second fluid reagent comprises water and a water-soluble phosphate-containing compound, wherein the copper oxide etchant is acetic acid, the water-soluble phosphate-containing compound is ammonium dihydrogen phosphate, and wherein the adhesive and the second fluid reagent are independently and selectively applied to the build material; and A curing heater is installed to heat the powder bed to the curing temperature.

7. The system of claim 6, wherein the reaction inhibitor is present in an amount of about 0.01% by weight to about 5.0% by weight relative to the total weight of the adhesive, and wherein the adhesive comprises about 20% by weight to about 70% by weight relative to the total weight of the adhesive, in an amount of copper(II) nitrate trihydrate.

8. A method for manufacturing 3D printed objects, comprising: An adhesive is selectively and independently applied to a building material containing copper or copper alloy particles, wherein the adhesive comprises: water, Copper(II) nitrate or its hydrate, and A reaction inhibitory additive, wherein the reaction inhibitory additive is a copper oxide etchant, wherein the copper oxide etchant is acetic acid; A second fluid reagent is independently and selectively applied to the building material, wherein the second fluid reagent comprises water and a water-soluble phosphate-containing compound, wherein the water-soluble phosphate-containing compound is ammonium dihydrogen phosphate; and Heating build materials and independently, selectively applied adhesives are used to bond layers of 3D printed objects.

9. The method of claim 8, wherein the reaction inhibitor is present in an amount of about 0.01% by weight to about 5.0% by weight relative to the total weight of the adhesive, and wherein the adhesive comprises about 20% by weight to about 70% by weight relative to the total weight of the adhesive, in an amount of copper(II) nitrate trihydrate.

10. The method of claim 8, further comprising sintering the adhesive layer of the 3D printed object to form a sintered 3D printed object.

11. The method of claim 8, further comprising adding a plurality of additional building material layers and selectively applying an adhesive independently to the plurality of additional building material layers, wherein heating the building material and selectively applying the adhesive includes simultaneously heating the building material and the plurality of additional building material layers to bond the entire 3D printed object.

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