权利要求：
1. A method of fabricating a metal part through additive manufacturing, the method comprising:
depositing a binder formulation onto a powder layer comprising a plurality of metal particles to form a composite layer;
curing the composite layer; and
heating the cured composite layer such that at least a portion of the binder formulation is removed from the cured composite layer,
wherein the binder formulation comprises a polymer comprising a nitrogen-containing repeat unit.
2. A method as in claim 1, wherein the depositing step comprises producing a droplet of the binder formulation having a droplet size of between or equal to 0.5 pL and 20 pL, or between or equal to 2 pL and 20 pL, or between or equal to 0.5 pL and 2 pL.
3. A method as in any preceding claim, wherein the binder formulation is deposited at a velocity of between or equal to 4 m/sec and 12 m/sec.
4. A method as in any preceding claim, wherein depositing the binder formulation does not substantially form satellite droplets with the main droplet.
5. A method as in any preceding claim, wherein the depositing step comprises producing a droplet of the binder formulation using a piezoelectric print head component.
6. A method as in any preceding claim, wherein the depositing step comprises producing a droplet of the binder formulation using a thermal print head component.
7. A method as in any preceding claim, wherein the step of depositing the binder formulation results in the formation of a two-dimensional image layer of a three-dimensional structure.
8. A method as in any preceding claim, wherein the thickness of the composite layer is between or equal to 10 microns and 200 microns, or between or equal to 25 microns and 100 microns.
9. A method as in any preceding claim, further comprising depositing a second powder layer on the deposited binder formulation to form the composite layer.
10. A method as in any preceding claim, wherein the curing step comprises heating an environment in which the composite layer is positioned to a temperature of between or equal to 120° C. and 220° C.
11. A method as in claim 10, wherein the composite layer is heated for between or equal to 0.5 hours and 100 hours.
12. A method as in any preceding claim, wherein the step of heating the cured composite layer comprises heating an environment in which the cured composite layer is positioned to a temperature of between or equal to 220° C. and 1200° C.
13. A method as in any preceding claim, wherein the step of heating the cured composite layer comprises heating an environment in which the cured composite layer is positioned to a temperature of greater than or equal to 220° C. and less than or equal to 300° C. in an oxidative environment.
14. A method as in any one of claims 12-13, wherein the step of heating is performed for between or equal to 4 hours and 10 hours.
15. A method as in any preceding claim, wherein the step of heating an environment in which the composite layer is positioned is performed in air or in inert gas.
16. A method as in any preceding claim, wherein the step of heating an environment in which the composite layer is positioned is performed in a gaseous environment having an oxygen content of at most 10 ppm.
17. A method as in any preceding claim, further comprising sintering the cured composite layer to form the three-dimensional structure.
18. A method as in any preceding claim, wherein the heating step and the sintering step are performed in an environment comprising at least 2 wt % hydrogen.
19. A method as in any one of claims 17-18, wherein sintering is performed at a temperature of greater than or equal to 750° C. and less than or equal to 1700° C.
20. A method as in any one of claims 17-19, wherein sintering is performed at a temperature of at most 850° C.
21. A method as in any one of claims 17-20, wherein the heating step is performed at a temperature at least 50° C. lower than a temperature at which the sintering step is performed.
22. A method as in claim 17, wherein the three-dimensional structure has a relative density of at least 94%.
23. A binder formulation for use in additive manufacturing, the binder formulation comprising:
polymer comprising a nitrogen-containing repeat unit in an amount of between or equal to 5 wt % and 50 wt %; and
water,
wherein the binder formulation is configured, in the presence of heat, to form a composition with a metal powder.
24. A composition formed in an additive manufacturing system, the composition comprising:
a plurality of metal particles embedded in a polymer comprising a nitrogen-containing repeat unit;
wherein the plurality of metal particles are present in the composition in an amount of greater than or equal to 40 wt % and less than or equal to 99.7 wt %, and
wherein the composition has a transverse rupture strength of greater than or equal to 2 MPa and less than or equal to 100 MPa.
25. A method of fabricating a metal part through additive manufacturing, the method comprising:
depositing a binder formulation onto a powder layer comprising a plurality of metal particles, wherein the binder formulation comprises:
a polymer present in the binder formulation in an amount of greater than or equal to 5 wt % and less than or equal to 50 wt %, wherein the polymer comprises a nitrogen-containing repeat unit; and
water.
26. A composition comprising:
a polymer; and
a metal powder;
wherein the polymer comprises a nitrogen-containing repeat unit.
27. The composition of claim 26, wherein the nitrogen-containing repeat unit is a repeat unit of a polypeptide, a protein, a polyacrylamide, or a glycosaminoglycan.
28. The composition of claim 26, wherein the polymer is a biologically-derived polymer.
29. The composition of claim 28, wherein the biologically-derived polymer is chitosan, chitosan oligosaccharide, collagen, gelatin, collagen hydrolysate, or hyaluronic acid (HA).
30. The composition of claim 26, wherein the polymer is a synthetic polymer.
31. The composition of claim 30, wherein the synthetic polymer is polyvinylpyrrolidone, poly(2-(diethylamino)ethyl methacrylate), polyacrylamide, poly(N-isopropylacrylamide), or N-(2-hydroxypropyl) methacrylamide (HPMA).
32. The composition of claim 26, wherein the polymer has a weight-average molecular weight of between or equal to 1 kDa and 40 kDa.
33. The composition of claim 32, wherein the polymer has a weight-average molecular weight of between or equal to 2 kDa and 20 kDa.
34. The composition of claim 32, wherein the polymer has a weight-average molecular weight of between or equal to 1 kDa and 15 kDa.
35. The composition of claim 26, further comprising a first liquid that forms a binder formulation with the polymer.
36. The composition of claim 35, wherein the first liquid comprises water.
37. The composition of claim 35, wherein the binder formulation has a weight percent of polymer of between or equal to 5 wt % and 50 wt %, relative to the total weight of the binder formulation.
38. The composition of claim 35, wherein the binder formulation has a weight percent of polymer of between or equal to 7 wt % and 50 wt %, relative to the total weight of the binder formulation.
39. The composition of claim 35, wherein the binder formulation has a weight percent of polymer of between or equal to 15 wt % and 40 wt %, relative to the total weight of the binder formulation.
40. The composition of claim 35, wherein the binder formulation is a solution.
41. The composition of claim 35, wherein the binder formulation further comprises a second liquid.
42. The composition of claim 41, wherein the second liquid comprises an organic solvent.
43. The composition of claim 42, wherein the organic solvent comprises an alcohol, a diol, a triol, a ketone, or an ester.
44. The composition of claim 41, wherein the binder formulation has a weight percent of the second liquid of between or equal to 2 wt % and 10 wt %, relative to the total weight of the binder formulation.
45. The composition of claim 41, wherein the binder formulation has a weight percent of the second liquid of between or equal to 2 wt % and 20 wt %, relative to the total weight of the binder formulation.
46. The composition of claim 35, wherein the binder formulation further comprises an additive.
47. The composition of claim 46, wherein the additive comprises a surfactant or biocide.
48. The composition of claim 46, wherein the binder formulation has a weight percent of the additive of between or equal to 0.1 wt % and 0.5 wt %, relative to the total weight of the binder formulation.
49. The composition of claim 35, wherein the binder formulation has a viscosity of between or equal to 3.5 cP and 30 cP.
50. The composition of claim 49, wherein the binder formulation has a viscosity of between or equal to 4 cP and 7 cP.
51. The composition of claim 49, wherein the binder formulation has a viscosity of between or equal to 4 cP and 15 cP.
52. The composition of claim 35, wherein the binder formulation has a surface tension of between or equal to 20 dyn/cm and 80 dyn/cm.
53. The composition of claim 52, wherein the binder formulation has a surface tension of between or equal to 30 dyn/cm and 70 dyn/cm.
54. The composition of claim 52, wherein the binder formulation has a surface tension of between or equal to 40 dyn/cm and 74 dyn/cm.
55. The composition of claim 26, wherein the metal powder comprises a noble metal.
56. The composition of claim 55, wherein the noble metal comprises gold, silver, or platinum.
57. The composition of claim 26, wherein the metal powder comprises copper.
58. The composition of claim 26, wherein the metal powder has a particle size of between or equal to 5 microns and 50 microns.
59. The composition of claim 58, wherein the metal powder has a particle size of between or equal to 7 microns and 20 microns.
60. The composition of claim 26, having between or equal to 40 wt % and 99.6 wt % of metal powder, relative to the total weight of the composition.
61. The composition of claim 60, having between or equal to 40 wt % and 99.7 wt % of metal powder, relative to the total weight of the composition.
62. The composition of claim 60, having between or equal to 94 wt % and 98 wt % of metal powder, relative to the total weight of the composition.
63. The composition of claim 60, having between or equal to 98 wt % and 99.7 wt % of the metal powder, relative to the total weight of the composition.
64. A method comprising:
combining a metal powder with a binder formulation;
where the binder formulation comprises:
a first liquid; and
a polymer; and
where the polymer comprises a nitrogen-containing repeat unit.
65. The method of claim 64, comprising combining the metal powder with the binder formulation to form a two-dimensional object.
66. The method of claim 65, comprising forming the two-dimensional object in a first layer of metal powder.
67. The method of claim 66, further comprising providing the first layer of metal powder.
68. The method of claim 67, where the first layer of metal powder has a thickness of between or equal to 10 microns and 100 microns.
69. The method of claim 68, where the first layer of metal powder has a thickness of between or equal to 25 microns and 100 microns.
70. The method of claim 67, where providing the first layer of metal powder comprises spreading a powder onto a horizontal surface to form a layer.
71. The method of claim 66, further comprising spreading a second layer of powder directly on top of the first layer.
72. The method of claim 71, further comprising alternating, for a plurality of cycles to form a three-dimensional object, the steps of:
(i) combining the metal powder with the binder formulation to form a two-dimensional object in a currently exposed layer of metal powder, and
(ii) spreading a next layer of powder directly on top of the currently exposed layer.
73. The method of claim 64, where combining the metal powder with the binder formulation comprises depositing droplets of binder formulation onto a selected area of a first layer of metal powder to form a two-dimensional object.
74. The method of claim 73, where depositing the droplets of binder formulation comprises flowing the binder formulation through a print head nozzle to form droplets.
75. The method of claim 73, further comprising spreading a second layer of powder directly on top of the first layer.
76. The method of claim 75, further comprising alternating, for a plurality of cycles to form a three-dimensional object, the steps of:
(i) depositing droplets of binder formulation onto a selected area of a currently exposed layer of metal powder to form a two-dimensional object, and
(ii) spreading a next layer of powder directly on top of the currently exposed layer.
77. The method of claim 73, wherein the droplets have a volume of between or equal to 2 pL and 100 pL.
78. The method of claim 74, wherein the droplets have a velocity of between or equal to 4 m/s and 20 m/s measured at 0.5 mm from an outlet of the print head nozzle.
79. The method of claim 72, further comprising heating the three-dimensional object, by exposing the three-dimensional object to an environment having a first heating temperature and a first pressure, to convert the three-dimensional object into a self-supporting composite.
80. The method of claim 79, wherein the self-supporting composite has a transverse rupture strength of between or equal to 5 MPa and 30 MPa.
81. The method of claim 79, wherein the self-supporting composite has a transverse rupture strength of between or equal to 2 MPa and 30 MPa.
82. The method of claim 79, wherein the self-supporting composite has a transverse rupture strength of between or equal to 2 MPa and 100 MPa.
83. The method of claim 79, further comprising heating the self-supporting composite, by exposing the self-supporting composite to an environment having a second heating temperature greater than or equal to the first heating temperature and a second pressure less than or equal to the first pressure, to convert the self-supporting composite into a pre-sintered part.
84. The method of claim 83, wherein the pre-sintered part has a carbon content of less than 0.5 wt %, relative to the weight of the pre-sintered part.
85. The method of claim 84, wherein the pre-sintered part has a carbon content of less than 0.2 wt %, relative to the weight of the pre-sintered part.
86. The method of claim 83, further comprising heating the pre-sintered part, by exposing the pre-sintered part to an environment having a third heating temperature greater than or equal to the second heating temperature and a third pressure less than or equal to the second pressure, to convert the pre-sintered part into a final part.
87. The method of claim 86, wherein the final part has a relative density of at least 95% relative to the bulk density of the metal powder material.
88. The method of claim 86, wherein the final part has a relative density of at least 92% relative to the bulk density of the metal powder material.
89. A method for additive manufacturing, the method comprising:
spreading a layer of a metallic base powder across a powder bed;
jetting a fluid to the layer along a controlled two-dimensional pattern associated with the layer, the fluid including a first liquid and a polymer including a nitrogen-containing repeat unit;
for each layer of a plurality of layers, repeating the steps of spreading a respective layer of the metallic base powder and jetting the fluid to the respective layer to form a three-dimensional green part; and
for each layer of a plurality of layers, repeating the steps of spreading a respective layer of the metallic base powder and jetting the fluid to the respective layer to form a three-dimensional green part.
具体实施方式：
[0022]Compositions comprising a binder and a powder, and associated methods are described herein. The inventors have recognized and appreciated that the material characteristics and/or chemical characteristics of a binder and/or binder formulation used in a powder metallurgical process (e.g., a powder-based additive manufacturing process, a method of fabricating a metal part through additive manufacturing) can have a significant impact on the performance of the process and the quality of the manufactured parts. For example, the adhesion properties of at least one component (e.g., a polymer) of a binder formulation to a powder (e.g., metal powder) can impact the ability to form strong pre-sintered parts (also referred to herein as “green” parts). In particular, poor adhesion between a polymer binder and a metal powder may result in a pre-sintered part without enough strength for the part to be handled, making the process of forming a final part more difficult. For example, conventional binder formulations may provide adequate strength of pre-sintered parts including steel powders, but may not provide adequate strength of pre-sintered parts including other powder materials. In addition, the viscosity of a binder formulation can impact the ability of the binder formulation to jet and spread evenly onto a metal powder bed, in the case of binder jetting, which in turn can affect ability to control the shape and homogeneity of the final printed part. In particular, a viscosity above a certain threshold may preclude the ability to jet the binder formulation or increase the heterogeneity of jetting. The viscosity of the binder formulation may impact the flow characteristics of a binder-powder mixture in an injection molding process. In particular, a lower viscosity increases the rate at which the mixture can be injected into the mold.
[0023]In view of the foregoing, the inventors have appreciated advantages associated with compositions and processes for powder metallurgical processing (e.g., a binder jetting process, a method of fabricating a metal part through additive manufacturing) in which a binder formulation comprising a water-soluble polymer comprising a nitrogen-containing repeat unit is combined with a metal powder to facilitate control over the mechanical properties of a pre-sintered part. The water-soluble polymer comprising a nitrogen-containing repeat unit may enhance the adhesion properties with the metal powder such that a pre-sintered part comprising the nitrogen-containing water-soluble polymer in the metal powder has a greater strength as compared to a pre-sintered parts comprising the metal powder and a water-soluble polymer without a nitrogen-containing repeat unit. For example, the electron-donating nitrogen along the polymer chains improves adhesion to metal powders relative to water-soluble polymers that do not contain nitrogen, thereby increasing the strength of a resulting pre-sintered part. This enhanced strength may result in an improved ability to handle the pre-sintered part, which may improve the quality of the process and manufactured part. Moreover, the inventors have recognized that binder formulations comprising a water-soluble polymer comprising a nitrogen-containing repeat unit may be particularly suitable for certain powder metallurgical processes, such as those processes involving metal powders comprising copper or a noble metal. In some embodiments, the binder formulations that enhance the mechanical characteristics of a pre-sintered part without interfering with other aspects of a powder metallurgical process. Non-limiting applications of the compositions and binder formulation powder metallurgical processes disclosed herein include jewelry, catalysis, and biomedical applications.
[0024]As mentioned above, according to some aspects, a composition is provided. Compositions provided herein may comprise one or more of a polymer, a binder formulation, and/or a powder (e.g., a metal powder). Compositions herein may or may not comprise a liquid.
[0025]In some embodiments, a composition comprises a polymer. The polymer generally acts as a binder (e.g., to hold powder particles together to form an object comprising the binder and the powder particles). As used herein, a “binder” may be a substance that holds other materials together by chemical interactions (e.g., adhesion, cohesion, hydrogen bonding, metallic bonding, dipole-dipole interactions, Van der Waals forces, electrostatic interactions) between the binder and the other materials. In some embodiments, it may be preferred that the polymer comprises a nitrogen-containing repeat unit. As used herein, a “nitrogen-containing repeat unit” may be a repeat unit located within a polymer chain having one or more nitrogen atoms.
[0026]A polymer described herein may comprise polymer chains having any suitable architecture. In some embodiments, a polymer comprises a homopolymer having a single type of repeat unit. In some embodiments, the polymer comprises a homopolymer, wherein each repeat unit of the homopolymer is a nitrogen-containing repeat unit. In some embodiments, a polymer comprises a copolymer having more than one type of repeat unit. In some embodiments, the polymer comprises a copolymer (e.g., a statistical copolymer, a block copolymer, a gradient copolymer), wherein at least 40% (e.g., at least 50%) of the repeat units of the copolymer are nitrogen-containing repeat units. In some embodiments, at least 50%, at least 60%, or at least 70% of the repeat units of the copolymer are nitrogen-containing repeat units. In some embodiments, at most 100%, at most 90%, or at most 80% of the repeat units of the copolymer are nitrogen-containing repeat units. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 50% and 100%, between or equal to 60% and 90%, between or equal to 70% and 80%). Other ranges are also possible. In some cases, 100% of the repeat units of the copolymer are nitrogen-containing repeat units. The remainder of the repeat units of the copolymer may comprise nitrogen-free repeat units. In some embodiments, the polymer is a copolymer comprising two or more nitrogen-containing repeat units. In some embodiments, the polymer is a polymer blend of one or more homopolymers, one or more copolymers, and/or a combination thereof.
[0027]In some embodiments, the polymer comprises the following structure:
-[A]n—[B]m—
wherein [A] is a nitrogen-containing repeat unit or a combination of nitrogen-containing repeat units and [B] is a nitrogen-free repeat unit or a combination of nitrogen-free repeat units, n>0.5, and n+m=1. As used herein, a “nitrogen-free repeat unit” may be a repeat unit having no nitrogen atoms, wherein the repeat unit is located within a polymer chain.
[0028]A nitrogen-containing repeat unit may have any suitable chemical structure, for example, so as to impart desired solubility or polarity characteristics of the polymer chain. In some embodiments, the nitrogen-containing repeat unit is a repeat unit having a nitrogen-containing side group, a nitrogen-containing backbone, or a suitable combination thereof. The nitrogen-containing side group may comprise a primary amine, a secondary amine, a tertiary amine, an amide, an imide, a urethane, a urea, or a nitrogen-containing heterocyclic moiety. The nitrogen-containing backbone may comprise a peptide bond, an amine, an amide, an imide, a urethane, a urea, or a nitrogen-containing heterocyclic moiety.
[0029]A nitrogen-containing repeat unit may be a repeat unit of any suitable class of nitrogen-containing polymers. In some embodiments, the nitrogen-containing repeat unit is a repeat unit of a polypeptide, a protein (e.g., collagen, gelatin), a polyacrylamide, a glycosaminoglycan (e.g., hyaluronic acid), a polyvinyl lactam (e. g. polyvinyl pyrrolidone, poly vinyl caprolactam), a polyoxazoline, a poly(aminoalkyl acrylate), a poly(aminoalkyl methacrylate), a poly(amidoamine), a melamine resin, a polyamide, or a polyimide. For example, the nitrogen-containing repeat unit may be a repeat unit of polyvinylpyrrolidone, chitosan, collagen, gelatin, poly(2-(diethylamino)ethyl methacrylate), polyacrylamide, poly(N-isopropylacrylamide), N-(2-hydroxypropyl) methacrylamide (HPMA), hyaluronic acid (HA), polyvinylcaprolactam, poly(2-ethyl-2-oxazoline), melamine, or polycaprolactam.
[0030]A nitrogen-free repeat unit may be a repeat unit of any suitable class of nitrogen-free polymers. In some embodiments, the nitrogen-free repeat unit is a repeat unit of an acrylate polymer, or a repeat unit of a vinyl polymer comprising nitrogen-free repeat units comprising an ester. In some embodiments, the nitrogen-free repeat unit comprises an alkyl, an aryl, a hydroxyl group, or a heterocyclic group. In some embodiments, the nitrogen-free repeat unit was formed from a difunctional repeat unit, such as a diacid, configured to react and form a repeat unit of a condensation polymer. For example, the nitrogen-free repeat unit may be a repeat unit of polyvinyl acetate, poly(acrylic acid), poly(methacrylic acid), poly(2-hydroxyethyl acrylate), poly (methyl methacrylate), polyvinyl alcohol, polyhydroxystyrene, maleic acid, or adipic acid.
[0031]In some embodiments, the polymer is a biologically derived polymer such as chitosan, chitosan oligosaccharide, collagen, gelatin, collagen hydrolysate, or hyaluronic acid (HA). In some embodiments, the polymer is a synthetic polymer such as polyvinylpyrrolidone, poly(2-(diethylamino)ethyl methacrylate), polyacrylamide, poly(N-isopropylacrylamide), or N-(2-hydroxypropyl) methacrylamide (HPMA).
[0032]Polymers described herein generally have a weight-average molecular weight in a range suitable for the powder process application. In some embodiments, a polymer has a weight-average molecular weight low enough such that the desired viscosity of a binder formulation can be achieved and/or high enough that a desired mechanical strength of a green part in a powder process (e.g., powder metallurgical process) can also be achieved. For example, in a binder jetting process, the polymer has a weight-average molecular weight in a range low enough such that the binder formulation has a viscosity suitable for jetting the binder formulation, but high enough that the resulting three-dimensional object has sufficient strength to be handled. In some such embodiments, the binder formulation having these properties may include a sufficient amount of binder (e.g., polymer) to hold a metal powder together in a resulting composition comprising the metal powder and the binder.
[0033]In some embodiments, the polymer has a weight-average molecular weight of at least 1 kiloDalton (kDa), at least 2 kDa, or at least 3 kDa. In some embodiments, the polymer has a weight-average molecular weight of at most 40 kDa, at most 30 kDa, at most 20 kDa, or at most 15 kDa. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 1 kDa and 40 kDa, between or equal to 1 kDa and 15 kDa, between or equal to 2 kDa and 20 kDa, between or equal to 2 kDa and 15 kDa, between or equal to 3 kDa and 15 kDa). Other ranges are also possible. In certain embodiments, it may be preferred that the polymer has a weight-average molecular weight of between or equal to 2 kDa and 20 kDa. In certain embodiments, it may be preferred that the polymer has a weight-average molecular weight of between or equal to 3 kDa and 15 kDa. In certain embodiments, the polymer is polyvinylpyrrolidone with a weight-average molecular weight of around 10 kDa. In certain embodiments, the polymer is chitosan oligosaccharide with a weight-average molecular weight of around 5 kDa, around 2 kDa, or around 1 kDa. In certain embodiments, the polymer is collagen hydrolysate with a weight-average molecular weight of around 5 kDa. Weight-average molecular weight may be determined for example by intrinsic viscosity measurements or gel permeation chromatography with suitable standards, using conventional methods.
[0034]In some embodiments, a composition comprises a binder formulation, in which a polymer described herein is combined with a first liquid (e.g., water; e.g., a solvent) and optionally one or more other components. In some embodiments, a binder formulation additionally comprises one or more other components including but not limited to a second liquid (e.g., a co-solvent) and/or an additive (e.g., a biocide, a surfactant). The binder formulation may be configured to form a composition (e.g., a “brown” part, as described in further detail below) with a metal powder. For instance, the binder formulation may be configured to do so in the presence of heat and/or upon exposure to heat (e.g., and as also described in further detail below, upon exposure to a first heating temperature, during a curing process).
[0035]A binder formulation generally has a weight percent of polymer in a range suitable for the powder process application. In some embodiments, a binder formulation has a weight percent of polymer low enough such that the desired viscosity of a binder formulation can be achieved, e.g., for extrusion (e.g., for injection molding) or for jetting (e.g., for binder jetting). In some embodiments, the binder formulation has a weight percent (wt %) of polymer of at least 5 wt %, at least 7 wt %, at least 10 wt %, or at least 15 wt % of polymer relative to the total weight of the binder formulation. In some embodiments, the binder formulation has a weight percent (wt %) of polymer of at most 50 wt %, at most 40 wt %, or at most 30 wt % of polymer relative to the total weight of the binder formulation. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 5 wt % and 50 wt %, between or equal to 7 wt % and 50 wt %, between or equal to 10 wt % and 40 wt %, between or equal to 15 wt % and 40 wt %, or between or equal to 15 wt % and 30 wt % of polymer). Other ranges are also possible. For example, during a heating step described herein for heating a composition described herein, a binder formulation in a composition may comprise up to 99.9 wt % of polymer once all of the liquid has nearly been removed. In some embodiments, the balance of the binder formulation comprises a first liquid, a second liquid, and/or an additive, or a combination thereof. Weight percent of polymer in a binder formulation may be determined by thermogravimetric analysis.
[0036]A binder formulation generally comprises a first liquid. In certain embodiments, it may be preferred that the first liquid comprises water. The use of water as a first liquid in a binder formulation may present advantages for manufacturing, including minimization of health and environmental and safety hazards of powder processing with the binder formulation (e.g., additive manufacturing processing with the binder formulation) and a reduced cost of engineering protection to control set hazards, relative to other liquids. It should be understood that the current disclosure is not limited to aqueous binder formulations. In some embodiments, the first liquid comprises methanol, ethanol, isopropanol, propylene diol, diglyme, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol methyl ether, or ethylene glycol monomethyl ether.
[0037]In some embodiments, the first liquid solubilizes the polymer to an extent sufficient to form a solution, such that the binder formulation is a solution comprising the polymer, and the solution can be processed, e.g., by extrusion or jetting. As used herein, the term “solution” may refer to a homogeneous mixture comprising two or more substances in which one substance (e.g., polymer) is homogeneously distributed in the other (e.g., first liquid). In some embodiments, the first liquid acts as a solvent to the polymer. The polymer may be soluble in the first liquid, such that combining the first liquid with the polymer results in a solution of the polymer in the first liquid. In some embodiments, the first liquid can dissolve the polymer in an amount of at least 1 wt %, at least 5 wt %, at least 10 wt % or at least 15 wt %. In some embodiments, the first liquid can dissolve the polymer in an amount of at most 50 wt %, at most 40 wt %, or at most 30 wt %. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 1 wt % and 50 wt %, between or equal to 5 wt % and 50 wt %, between or equal to 10 wt % and 40 wt %, or between or equal to 15 wt % and 30 wt % of polymer). Other ranges are also possible.
[0038]A polymer that dissolves in water at a concentration of at least 1 wt % is also referred to herein as a “water-soluble polymer”.
[0039]In some embodiments, at least a portion of the polymer in the first liquid remains undissolved. In some embodiments, the first liquid suspends the polymer to an extent sufficient to form a suspension, such that the binder formulation is a suspension comprising the polymer, As used herein, the term “suspension” may refer to a heterogeneous mixture that contains a liquid and solid particles or molecules that can separate from the liquid by sedimentation over time.
[0040]A binder formulation generally has a weight percent of a first liquid in a range suitable for a powder process application. In some embodiments, a binder formulation has a weight percent of first liquid high enough such that the desired viscosity of a binder formulation can be achieved, e.g., for extrusion (e.g., for injection molding) or for jetting (e.g., for binder jetting). In some embodiments, the binder formulation has a weight percent (wt %) of first liquid of at least 50 wt %, at least 60 wt %, or at least 70 wt % of first liquid relative to the total weight of the binder formulation. In some embodiments, the binder formulation has a weight percent (wt %) of at most 95%, at most 90 wt %, at most 85 wt %, or at most 80 wt % of first liquid relative to the total weight of the binder formulation. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 50 wt % and 95 wt %, between or equal to 60 wt % and 90 wt %, between or equal to 70 wt % and 85 wt %, or between or equal to 70 wt % and 80 wt %). Other ranges are also possible.
[0041]In some embodiments, the binder formulation optionally comprises a second liquid. The second liquid may act as a co-solvent to the polymer, to increase the solubility of the polymer in the binder formulation. In some embodiments, the second liquid comprises an organic solvent, e.g., a water-soluble organic solvent. In some embodiments, the second liquid comprises a plurality of organic solvents. Non-limiting classes of organic solvents include alcohols, diols, triols, ketones, or esters. Non-limiting examples of alcohols (e.g., water-soluble alcohols) include ethanol, isopropyl alcohol, and 1-propanol. Non-limiting examples of diols (e.g., water-soluble diols) include ethylene glycol, propylene glycol, 1-(1-hydroxypropoxy)propan-1-ol (CAS-25265-71-8), 1-(2-hydroxypropoxy)propan-2-ol, 3,3′-oxybis(propan-1-ol), and dipropylene glycol (a mixture of isomers 1-(1-hydroxypropoxy)propan-1-ol (CAS-25265-71-8), 1-(2-hydroxypropoxy)propan-2-ol, and 3,3′-oxybis(propan-1-ol)). Non-limiting examples of triols (e.g., water-soluble triols) include glycerol and 1,2,4-butanetriol. Non-limiting examples of ketones (e.g., water-soluble ketones) include acetone and butanone. A non-limiting example of an ester is ethyl acetate.
[0042]A binder formulation generally has a weight percent of a second liquid in a range suitable for a powder process application. In some embodiments, a binder formulation has a weight percent of second liquid high enough such that the binder formulation has fully suspended or solubilized the polymer for ease of processing, e.g., for extrusion or for jetting. In some embodiments, the binder formulation has a weight percent (wt %) of second liquid of at least 0 wt %, at least 2 wt %, or at least 4 wt % of second liquid relative to the total weight of the binder formulation. In some embodiments, the binder formulation has a weight percent (wt %) of second liquid of at most 20 wt %, at most 15 wt %, at most 10 wt %, or at most 5 wt % of second liquid relative to the total weight of the binder formulation. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 0 wt % and 20 wt %, between or equal to 0 wt % and 15 wt %, between or equal to 0 wt % and 10 wt %, between or equal to 2 wt % and 20 wt %, between or equal to 2 wt % and 10 wt %, between or equal to 0 wt % and 5 wt %, between or equal to 2 wt % and 5 wt %, or between or equal to 4 wt % and 5 wt %). Other ranges are also possible. In certain embodiments, the binder formulation comprises between or equal to 0 wt % and 5 wt % of second liquid relative to the total weight of the binder formulation.
[0043]In some embodiments, the binder formulation comprises an additive. An “additive,” as used herein, may be a substance included as a component of a binder formulation to improve one or more properties of the binder formulation and/or preserve the binder formulation against degradation. Suitable additives to a binder formulation include but are not limited to surfactants, biocides, defoamers, adhesion promoters, or corrosion inhibitors. Further examples of suitable additives include wetting agents, flow improvers, coatings, and other powder modifications found to be useful in the sintering or infiltration of additively fabricated parts.
[0044]In some embodiments, the additive comprises a surfactant. A surfactant may be included in a binder formulation to decrease the surface tension of the binder formulation (air-formulation surface tension) to improve jetting performance, and/or to improve powder spreading performance. While both ionic surfactants and non-ionic surfactants can be used, surfactants that do not contain such elements as sulfur, phosphorus, silicon, or metals may be preferred. Non-limiting examples of surfactants include Thetawet FS-8150, Polyoxyl 35 castor oil (CAS #61791-12-6), Lauryldimethylamine oxide (CAS #1643-20-5), Triton X-100 (CAS #9002-93-1), Surfynol 440 (CAS-9014-85-1), Surfynol 2502 (CAS-182211-02-5), and Dynol 604 (CAS-169117-72-0).
[0045]In some embodiments, the additive comprises a biocide. A biocide may be included in a binder formulation to prevent growth of biological matter (e.g., bacteria, yeast) in the binder formulation and/or to prevent enzymatic degradation of a polymer in the binder formulation. Biologically derived polymers such as chitosan and gelatin may be particularly vulnerable to enzymatic degradation in the absence of a biocide. In some embodiments, the biocide is a microbicide and/or a fungicide (is configured to kill bacteria and/or fungi). Non-limiting examples of biocides include 1,2-benzisothiazolin-3-one, 4,5-Dichloro-2-octyl-4-isothiazolin-3-one, Lauryldimethylamine oxide (CAS #1643-20-5), Benzalkonium chloride, 2-n-Octyl-4-Isothiazolin-3-One, 3-(3,4-dichlorophenyl)-1,1-dimethylure, 2-bromo-2-nitropropane-1,3-diol, and Rotenone (CAS #83-79-4).
[0046]In some embodiments, the binder formulation comprises an additive composition. As additive composition herein comprises an additive and optionally one or more additional components (e.g., a liquid, a solvent). Non-limiting examples of additive compositions include Thetawet 8150 (supplied by Innovative Chemical Technologies, Inc. at 103 Walnut Grove Rd, Cartersville, Ga. 30120), ProxelGXL (20% aqueous dipropylene glycol solution of 1,2-benzisothiazolin-3-one), methylisothiazolinone, 4,5-Dichloro-2-octyl-4-isothiazolin-3-one, Lauryldimethylamine oxide (CAS #1643-20-5), Benzalkonium chloride, 2-n-Octyl-4-Isothiazolin-3-One, 3-(3,4-dichlorophenyl)-1,1-dimethylure, 2-bromo-2-nitropropane-1,3-diol, Rotenone (CAS #83-79-4), Thetawet-8150, Polyoxyl 35 castor oil (CAS #61791-12-6), Lauryldimethylamine oxide (CAS #1643-20-5), Triton X-100 (CAS #9002-93-1), Surfynol 440 (CAS-9014-85-1), Surfynol 2502 (CAS-182211-02-5), and Dynol 604 (CAS-169117-72-0).
[0047]An additive (e.g., biocide, surfactant) may be present in a binder formulation in any suitable amount. In some embodiments, the binder formulation has a weight percent (wt %) of additive of at most 1 wt %, at most 0.5 wt %, or at most 0.25 wt % of additive relative to the total weight of the binder formulation. In some embodiments, the binder formulation has a weight percent (wt %) of additive of at least 0 wt %, at least 0.1 wt %, or at least 0.2 wt % of additive relative to the total weight of the binder formulation. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 0 wt % and 1 wt %, between or equal to 0 wt % and 0.5 wt %, between or equal to 0.1 wt % and 0.5 wt %, between or equal to 0 wt % and 0.25 wt %, between or equal to 0.1 wt % and 0.25 wt %, or between or equal to 0.2 wt % and 0.5 wt %). Other ranges are also possible. In some embodiments, the binder formulation comprises between or equal to 0 wt % and 0.5 wt % of a surfactant relative to the weight of the entire binder formulation. In some embodiments, the binder formulation comprises between or equal to 0 wt % and 0.25 wt % of a biocide relative to the weight of the entire binder formulation.
[0048]In certain embodiments, the binder formulation comprises between or equal to 5 wt % and 50 wt % of polymer, between or equal to 50 wt % and 95 wt % of first liquid, between or equal to 0 wt % and 10 wt % of second liquid, and between or equal to 0 wt % and 0.5 wt % of additive. In certain embodiments, the binder formulation comprises between or equal to 15 wt % and 30 wt % of polymer, between or equal to 70 wt % and 85 wt % of first liquid, between or equal to 0 wt % and 10 wt % of second liquid, and between or equal to 0 wt % and 0.5 wt % of additive. It should be understood that the binder formulation could include a number of other components, as the current disclosure is not limited in this regard.
[0049]The binder formulation generally has properties suited to the powder processing application. One of the properties of the binder formulation of relevance to powder processing is viscosity. The weight-average molecular weight of the polymer, the weight percent of the polymer in the binder formulation, and other contributing factors can be selected to tailor the viscosity of the binder formulation to the powder processing application. For example, the binder formulation can be selected to have a viscosity that is within the specifications of a particular print head (e.g., inkjet print head) used in an additive manufacturing process (e.g., three-dimensional (3D) printing process). In some embodiments, the viscosity of the binder formulation is at least 3 centiPoise (cP), at least 3.5 cP, or at least 4 cP. In some embodiments, the viscosity of the binder formulation is at most 30 cP, at most 15 cP, or at most 7 cP. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 3.5 cP and 30 cP, between or equal to 3.5 cP and 15 cP, between or equal to 4 cP and 15 cP, or between or equal to 4 cP and 7 cP). Other ranges are also possible. For example, during a heating step described herein for forming a self-supporting composite, the viscosity of the binder formulation may increase well above the ranges described and then a solid may form, making the viscosity measurement irrelevant. In certain embodiments, it may be preferred that the viscosity of the binder formulation be between or equal to 4 cP and 6 cP. Viscosity of a binder formulation may be determined using a spindle viscometer, a cone-and-plate viscometer, or a capillary viscometer, using conventional methods.
[0050]Another property of the binder formulation of relevance to powder processing is surface tension. Surface tension is measured for the binder formulation (air-formulation surface tension) at normal temperature and pressure (20 degrees Celsius and 1 atm). The binder formulation generally has a surface tension suitable to the powder process application, e.g., suitable to jetting in an additive manufacturing process. As discussed, a surfactant may be used to decrease the surface tension of the binder formulation. In some embodiments, the binder formulation has a surface tension of at most 80 dynes per centimeter (dyn/cm), at most 74 dyn/cm, at most 70 dyn/cm, or at most 60 dyn/cm. In some embodiments, the binder formulation has a surface tension of at least 20 dyn/cm, at least 30 dyn/cm, or at least 40 dyn/cm. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 20 dyn/cm and 80 dyn/cm, between or equal to 30 dyn/cm and 70 dyn/cm, between or equal to 40 dyn/cm and 74 dyn/cm, between or equal to 40 dyn/cm and 60 dyn/cm). Other ranges are also possible. Surface tension of a binder formulation may be determined using such conventional methods and instruments as goniometry, a Du Noiy Ring Tensiometer method, a Wilhelmy Plate Tensiometer method, a Du Nouy-Padday method, or a bubble pressure tensiometer method.
[0051]In some embodiments, a composition comprises a powder. As used herein, a “powder” may be a collection of solid particles that are between or equal to 1 micron and 1 mm in size (e.g., having a D50 value according to ASTM E2651-13 of between or equal to 1 micron and 1 mm). Depending on the particular embodiment, the powder may comprise any suitable metallic and/or ceramic components. In certain embodiments, the powder comprises a metal powder. As used herein, a “metal powder” may be a powder which comprises particles that comprise a metal. In some embodiments, the metal powder comprises particles that comprise a plurality of metals (e.g., particles comprise an alloy of two or more metals). In certain embodiments, it may be preferred that the metal powder comprises a noble metal. In some embodiments, the powder comprises a metal oxide (e.g., alumina, silica). In certain embodiments, it may be preferred that the composition comprises a polymer comprising a nitrogen-containing repeat unit and a metal powder comprising a noble metal, due to the favorable adhesion interactions between the nitrogen of the polymer and the noble metal of the metal powder. It should be understood that other modes of favorable adhesion interactions between polymer and powder are possible, as the current disclosure is not limited is this regard.
[0052]As used herein, the “noble metals” are ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), osmium (Os), iridium (Tr), platinum (Pt), and gold (Au).
[0053]In some embodiments, the metal powder comprises a transition metal. The “transition metal” elements are scandium (Sc), yttrium (Y), lanthanum (La), actinium (Ac), titanium (Ti), zirconium (Zr), hafnium (Hf), rutherfordium (Rf), vanadium (V), niobium (Nb), tantalum (Ta), dubnium (Db), chromium (Cr), molybdenum (Mo), tungsten (W), seaborgium (Sg), manganese (Mn), technetium (Tc), rhenium (Re), bohrium (Bh), iron (Fe), ruthenium (Ru), osmium (Os), hassium (Hs), cobalt (Co), rhodium (Rh), iridium (Ir), meitnerium (Mt), nickel (Ni), palladium (Pd), platinum (Pt), darmstadtium (Ds), copper (Cu), silver (Ag), gold (Au), roentgenium (Rg), zinc (Zn), cadmium (Cd), mercury (Hg), and copernicium (Cn).
[0054]In certain embodiments, particles of the metal powder comprise at least one of silver, gold, or platinum. In certain embodiments, it may be preferred that particles of the metal powder consist essentially of a metal or alloy comprising at least one of silver, gold, or platinum, such that a pure noble metal object may result from powder processing with a binder formulation described herein. In certain embodiments, the metal powder comprises copper. It should be understood that any suitable metal can be used in the metal powder, as the current disclosure is not limited in this regard.
[0055]The powder (e.g., the metal powder) generally has a suitable particle size (e.g., number-average particle size as measured according to ASTM E2651-13) for powder processing. In some embodiments, the powder has a D50 of at least 1 micron, at least 5 microns, or at least 7 microns. In some embodiments, the powder has a D50 of at most 50 microns, at most 40 microns, or at most 20 microns. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 1 micron and 50 microns, between or equal to 5 microns and 50 microns, between or equal to 7 microns and 40 microns, or between or equal to 7 microns and 20 microns). Other ranges are also possible. In certain embodiments, it may be preferred that the powder hav