Dual cure resins having polyether and polyamide subunits and additive manufacturing methods using the same

Abstract

Provided herein is a resin composition useful for the production of a three-dimensional object by additive manufacturing, said resin composition including one or more of: (a) a reactive blocked prepolymer including at least one ether subunit; (b) a multifunctional amine chain extender including at least one amide subunit; (c) a photoinitiator; and (d) optionally, a reactive and / or non-reactive diluent. Methods of forming a three-dimensional object with the resin composition and three-dimensional objects formed from the resin composition are also provided.

Description

[0001] DUAL CURE RESINS HAVING POLYETHER AND POLYAMIDE SUBUNITS AND ADDITIVE MANUFACTURING METHODS USING THE SAME

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority from U.S. Provisional Application No. 63 / 518,945, filed August 11, 2023, the disclosure of which is hereby incorporated by reference in its entirety.

[0004] FIELD

[0005] The present invention relates to resin compositions useful for additive manufacturing and methods of using the same.

[0006] BACKGROUND

[0007] In conventional additive or three-dimensional fabrication techniques, construction of a three-dimensional object is performed in a stepwise or layer-by-layer manner. Typically, layer formation is performed through solidification of photo curable resin under the action of visible or UV light irradiation. Generally referred to as “stereolithography,” two particular techniques are known: one in which new layers are formed at the top surface of the growing object; the other in which new layers are formed at the bottom surface of the growing object. Examples of such methods include those given in U.S. Pat. No. 5,236,637 to Hull (see, e g., FIGS. 3-4), U.S. Pat. Nos. 5,391,072 and 5,529,473 to Lawton, U.S. Pat. No. 7,438,846 to John, U.S. Pat. No. 7,892,474 to Shkolnik, U.S. Pat. No. 8,110,135 to El-Siblani, U.S. Patent Application Publication No. 2013 / 0292862 to Joyce, and U.S. Patent Application Publication No. 2013 / 0295212 to Chen et al.

[0008] Techniques referred to as “continuous liquid interface production” (or “CLIP”) have also been developed. These techniques enable the rapid production of three-dimensional objects in a layerless manner, by which the parts may have desirable structural and mechanical properties. See, e.g., U.S. Pat. Nos. 9,211,678, 9,205,601, and 9,216,546; J. Tumbleston et al., Continuous liquid interface production of 3D Objects, Science 347, 1349-1352 (2015); and R. Janusziewicz et al., Layerless fabrication with continuous liquid interface production, Proc. Natl. Acad. Sci. USA 113, 11703-11708 (2016). Dual cure stereolithography resins suitable for stereolithography techniques are described, for example, in U.S. Pat. No. 9,453,142, 9,676,963, and 9,598,606. Such resins typically include a first polymerizable system polymerized by light (sometimes referred to as “Part A”) from which an intermediate object is produced, and also include at least a second polymerizable system (“Part B”) which is usually cured after the intermediate object is first formed, and which imparts desirable structural and / or tensile properties to the final object.

[0009] Poly(ether-block-amide) (PEBA) materials are known to have desirable cold temperature flexibility, durability, impact resistance, and elongation at break, due to the polyether (PE) block, while also having desirable phase separation and stiffness from the crystallization of the polyamide (PA) block. In addition, PEBA materials may be varied to have a wide range of moduli, from soft elastomers to semi-rigid material properties (~10 - 300 MPa modulus). Such material properties are desirable for certain applications.

[0010] SUMMARY

[0011] Provided herein is a resin composition useful for the production of a three-dimensional object by additive manufacturing, said resin composition including one or more of: (a) a reactive blocked prepolymer including at least one ether subunit (e.g., a poly ether subunit including at least three ether bonds); (b) a multifunctional amine (e.g., a diamine) chain extender including at least one amide subunit (e.g., a polyamide subunit having at least three amide bonds); (c) a photoinitiator; and (d) optionally, a reactive and / or non-reactive diluent.

[0012] In some embodiments, the reactive blocked prepolymer comprises a polyether (e.g., a poly(ethylene ether), polypropylene ether), poly(trimethylene ether), and / or poly(tetramethylene ether)) subunit. In some embodiments, the reactive blocked prepolymer is formed by (a) reaction of a polyether polyol and a diisocyanate (e.g., hexamethylenediisocyanate, UDI) to form an intermediate; and (b) reaction of diisocyanate groups in the intermediate with a blocking agent that includes a functional group polymerizable by actinic radiation or light.

[0013] In some embodiments, the blocking agent is an amine (meth)acrylate (e.g., TBAEMA), an alcohol (meth)acrylate, maleimide, or n-vinylformamide. In some embodiments, the reactive blocked prepolymer includes a compound having a prepolymer structure of: [reactive blocking group]-[diisocyanate]-[polyether]-[diisocyanate]- [reactive blocking group].

[0014] In some embodiments, the blocking agent is TBAEMA, the diisocyanate is HDI, and / or the polyether is poly(tetramethylene ether glycol) (PTMEG).

[0015] In some embodiments, the multifunctional amine chain extender comprises a polyamide (e.g., a Nylon such as 6,6, 12,12, 6 / 12, 10, 11, or 12) subunit.

[0016] In some embodiments, the multifunctional amine chain extender includes a compound having a structure of wherein a, b, and c are each independently an integer from 4 to 20 (optionally, a = c) and x is an integer from 1 to 60; and / or a compound having a structure of wherein d, e, and f are each independently an integer from 4 to 20, and y and z are each independently an integer from 0 to 60, wherein y + z > 1.

[0017] In some embodiments, the ratio of the weight of the reactive blocked prepolymer to the weight of the multifunctional amine chain extender is in a range of 10: 1 to 1 :2.

[0018] In some embodiments, the multifunctional amine chain extender is a solid at room temperature (e.g., about 25 °C). In some embodiments, the multifunctional amine chain extender has a melting temperature in a range of about 120 °C to about 180 °C.

[0019] In some embodiments, the resin composition further comprises a pigment, dye, and / or filler. Also provided is a method of forming a three-dimensional object, comprising irradiating a resin composition as taught herein with actinic radiation or light (e.g., by a top-down or bottom- up stereolithography method), thereby forming a three-dimensional intermediate, and then further reacting the three-dimensional intermediate to form the three-dimensional object.

[0020] In some embodiments, the method includes one or more steps of:

[0021] (a) providing a carrier and an optically transparent member having a build surface, the carrier and the build surface defining a build region therebetween;

[0022] (b) filling the build region with a resin composition as taught herein;

[0023] (c) irradiating the build region with light through the optically transparent member to solidify at least a portion of the resin composition;

[0024] (d) advancing the carrier away from the build surface;

[0025] (e) repeating steps (b) through (d) to form a solid polymer scaffold that is a three- dimensional intermediate having the same shape as, or a shape to be imparted to, the three- dimensional object;

[0026] (f) optionally, washing the three-dimensional intermediate; and

[0027] (g) further reacting the three-dimensional intermediate to form the three- dimensional object.

[0028] In some embodiments, the further reacting comprises exposing the three-dimensional intermediate to heat, microwave irradiation, irradiation at a same or different wavelength than in step (c), and / or moisture.

[0029] In some embodiments, the multifunctional amine chain extender is a solid and unreacted (or substantially unreacted) after irradiation step (c), and the further reacting step (g) comprises heating the three-dimensional intermediate sufficient to degrade the polymer scaffold and melt the multifunctional amine chain extender, and reacting a portion of the degraded scaffold with the multifunctional amine chain extender.

[0030] In some embodiments, the isocyanate functional groups on the degraded scaffold react with the multifunctional amine chain extender. In some embodiments, the step (c) and / or step (d) is carried out while also concurrently (i) continuously maintaining a dead zone of the resin composition in contact with the build surface; and (ii) continuously maintaining a gradient of polymerization zone between the dead zone and the solidified polymer in contact with the carrier, the gradient of polymerization zone comprising the resin composition in partially cured form.

[0031] In some embodiments, the optically transparent member comprises a semipermeable member (optionally wherein the semipermeable member comprises a fluoropolymer), and continuously maintaining a dead zone is carried out by feeding an inhibitor (e.g., oxygen) through said optionally transparent member (optionally creating a gradient of inhibitor in the dead zone and optionally in at least a portion of the gradient of polymerization zone).

[0032] Also provided is a three-dimensional object formed from a resin composition as taught herein and / or by a method as taught herein.

[0033] DETAILED DESCRIPTION

[0034] The present invention is now described more fully hereinafter with reference to embodiments. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art.

[0035] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements components and / or groups or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups or combinations thereof. The sequence of operations (or steps) is not limited to the order presented in the claims or figures unless specifically indicated otherwise. Any element that comprises certain features, integers, steps, operations, elements, components and / or groups may also “consist of’ or “consist essentially of’ such features, integers, steps, operations, elements, components and / or groups, respectively.

[0036] As used herein, the term “and / or” includes any and all possible combinations or one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative (“or”).

[0037] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and claims and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and / or clarity.

[0038] It will be understood that, although the terms first, second, etc., may be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. Rather, these terms are only used to distinguish one element, component, region, layer and / or section, from another element, component, region, layer and / or section. Thus, a first element, component, region, layer, or section discussed herein could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.

[0039] All publications and patents cited herein are specifically incorporated by reference to disclose the methods and / or materials with which the documents are cited.

[0040] As used herein, the term “about” with reference to a numerical number or range refers to the exact numbers and to values that are + / - 1%, 2%, 5%, or 10% thereof. It is also to be understood that where a range of values is provided, each intervening integer within the upper and lower limit of the range is also explicitly disclosed.

[0041] As used herein, when a particle is not spherical, the diameter of the particle is defined as the longest dimension of the particle "Shape to be imparted to" refers to the case where the shape of the intermediate object slightly changes between formation thereof and forming the subsequent three-dimensional product, typically by shrinkage (e.g., up to 1, 2 or 4 percent by volume), expansion (e.g., up to 1, 2 or 4 percent by volume), removal of support structures, or by intervening forming steps (e.g., intentional bending, stretching, drilling, grinding, cutting, polishing, or other intentional forming after formation of the intermediate product, but before formation of the subsequent three- dimensional product).

[0042] A “reactive diluent,” as used herein, is a type of monomer that may be included in a resin composition and can polymerize or co-polymerize with other component s) during exposure to actinic radiation or light (e.g., via free radical polymerization).

[0043] As used herein, the term “prepolymer” refers to an oligomer or polymer (e.g., has a Mw in a range of 250 to 10,000 g / mol) that may further react (e.g., with a chain extender) to form a longer polymer chain and / or a polymer network. Non-limiting examples include polyisocyanate prepolymers, polyurethane prepolymers, polyurea prepolymers, and polyisocyanurate prepolymers.

[0044] As used herein, the term “(meth)acrylate” includes a methacrylate and / or an acrylate. Likewise, the term “di(meth)acrylate” includes a dimethacrylate and / or a diacrylate.

[0045] Resin Compositions

[0046] Provided according to some embodiments of the invention are resin compositions useful for producing a three-dimensional object by additive manufacturing. Such compositions may also be referred to herein as a “polymerizable liquid,” “liquid resin,” “ink,” or simply “resin.” In some embodiments of the invention, resin compositions include (a) a reactive blocked prepolymer that includes at least one ether subunit (e.g., a polyether subunit); (b) a multifunctional amine (e.g., a diamine) chain extender that includes at least one amide subunit (e.g., a polyamide subunit); (c) a photoinitiator; and (d) optionally, a reactive diluent.

[0047] In some embodiments of the present invention, the reactive blocked prepolymer includes a urethane, urea, isocyanurate, or any combination thereof. In some embodiments, the reactive blocked prepolymer includes two or more urethane linkages produced by the reaction of a polyisocyanate (e.g., a diisocyanate) with at least one polyether polyol (e.g., a polyether diol) to form an isocyanate-functional urethane polyether intermediate. Poly isocyanates include, but are not limited to, l,l'-methylenebis(4-isocyanatobenzene) (MDI), 2,4-diisocyanato-l -methylbenzene (TDI), methylene-bis(4-cyclohexylisocyanate) (H12MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 2,2,4-(2,4,4-) trimethylhexane 1,6-diisocyanate (TMHDI, e.g., VESTANAT® TMDI, available from Evonik (Essen, Germany)), polymeric MDI, 1,4-phenylene diisocyanate (PPDI), and o-tolidine diisocyanate (TODI). Additional examples include but are not limited to those given in U.S. Pat. No. 3,694,389.

[0048] Examples of polyether polyols include but are not limited to polyethylene ether glycol (e.g., diethylene ether glycol, trimethylene ether glycol, tetraethylene ether glycol, pentaethylene ether glycol (e.g., dipropylene glycol, tripropylene glycol, and 1,3-propanediol), etc. The length of the polyether polyol chain may be varied based on the desired properties of the three-dimensional object to be produced. However, in some embodiments, the poly ether polyol has a molecular weight in a range of 250 to 6000 g / mol (e.g., between 650-2000 g / mol). A particular polyether polyol of interest is poly(tetramethylene ether glycol) (PTMEG). While in general, the polyether subunit is formed using a polyether polyol, other end groups reactive with isocyanates (e.g., amines) could be used in lieu of the terminal alcohol functional groups in the polyether.

[0049] In some embodiments, the isocyanate-functional intermediate is then reacted with a reversible blocking agent that includes a functional group polymerizable by actinic radiation or light (e.g., in combination with a photoinitiator and / or via free radical polymerization). In some embodiments, the blocking agent is an amine functional (meth)acrylate (e.g., tertiary- butylaminoethyl methacrylate (TBAEMA), tertiary pentylaminoethyl methacrylate (TPAEMA), tertiary hexylaminoethyl methacrylate (THAEMA), tertiary-butylaminopropyl methacrylate (TBAPMA), an acrylate analog of any of the foregoing, or mixtures of two or more of the foregoing). In such a case, the reactive blocked prepolymer may include two or more urea linkages produced by the reaction of the isocyanate-functional intermediate with the amine portion of such blocking agents.

[0050] Other blocking agents may be used, including other methacrylates and acrylates that may have functional groups that are reactive with the isocyanate-functional intermediate. Other blocking agents include but are not limited to maleimide, or substitute mal eimide on other known blocking agents, for use in the present invention. Examples of known blocking agents which can be substituted on or covalently coupled to (meth)acrylate or maleimide for use in the present invention include, but are not limited to, phenol type blocking agents, lactam type blocking agents, active methylene type blocking agents, alcohol type blocking agents, mercaptan type blocking agents, acid amide type blocking agents, imide type blocking agents, amine type blocking agents, imidazole type blocking agents, urea type blocking agents, carbamate type blocking agents, imine type blocking agents, oxime type blocking agents, and sulfurous acid salt type blocking agents.

[0051] In some embodiments, an isocyanate-functional intermediate may be blocked with an aldehyde blocking agent, such as a formyl blocking agent. Examples include but are not limited to 2-formyloxyethyl(meth)acrylate (FEMA)(or other aldehyde-containing acrylate or methacrylate) with a diisocyanate or isocyanate functional oligomer or polymer. See, e.g., X. Tassel et al., A New Blocking Agent of isocyanates, European Polymer Journal 36(9), 1745-1751 (2000); T. Haig, P. Badyrka et al., U.S. Pat. No. 8,524,816; and M. Sullivan and D. Bulpett, U.S. Pat. Appl. Pub. No. 2012 / 0080824.

[0052] The reactive blocked prepolymer may take a variety of different forms based on the polyether polyol (or other reactive polyether), the polyisocyanate, and the blocking agent. However, in some embodiments, the reactive blocked prepolymer has the general structure of

[0053] [reactive blocking group]-[diisocyanate]-[polyether]-[diisocyanate]-[reactive blocking group].

[0054] In some embodiments, the at least one polyether subunit in the reactive blocked prepolymer includes a poly(ethylene ether), polypropylene ether), poly(trimethylene ether), and / or poly(tetramethylene ether). In some embodiments, the weight of such polyether subunits is in a range of about 250 to about 6000 g / mol (e.g., between about 650 to about 2000 g / mol). In some embodiments, the reactive blocked prepolymer includes a compound of the formula A-X- A, where X is a polyether and each A is an independently selected substituent of Formula (X): where R is a hydrocarbyl group, R' is O or NH, and Z is a blocking group, the blocking group having a functional group that is polymerizable by actinic radiation or light (e.g., a polymerizable end group such as an alkene or alkyne end group). In a particular example, each A is an independently selected substituent of Formula (XI): where R and R' are as given above.

[0055] In some embodiments, the blocking group is 2-(tert-butylamino)ethyl methacrylate (TBAEMA), the diisocyanate is HDI (wherein R in the formula above is -(CH2)e-), and the polyether is poly(tetramethylene ether glycol) (PTMEG).

[0056] In some embodiments, the multifunctional amine chain extender is a diamine that includes a polyamide subunit (e.g., a Nylon subunit such as Nylon 6,6, Nylon 12,12, Nylon 6 / 12, Nylon 10, Nylon 11, or Nylon 12). In some embodiments, the multifunctional amine chain extender includes at least 2, at least 3, or at least 4 polyamide subunits. A polyamide subunit is a repeating unit (if more than one) that includes at least one amide bond therein. In some embodiments, a portion of the multifunctional amine chain extender is formed from the reaction of a dicarboxylic acid and a diamine. In some embodiments, the multifunctional amine chain extender includes a compound having a general structure of: wherein a, b, and c are each independently an integer in a range of 4 to 20 (optionally, a = c) and x is an integer in a range of 1 to 10, 20, 30, 40, 50 or 60.

[0057] In some embodiments, the multifunctional amine chain extender includes a compound having the general structure of: wherein d, e, and f are each independently an integer in a range of 4 to 20 and y and z are each independently an integer in a range of 0 or 1 to 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or 60, and wherein y + z > 1.

[0058] In some embodiments, the multifunctional amine chain extender is a solid at room temperature (e.g., about 25 °C at about 1 atm) and / or at the operating conditions of the light polymerization portion of an additive manufacturing process in which the resin is used. In some embodiments, the multifunctional amine chain extender has a melting temperature in a range of about 120 °C to about 180 °C. In some embodiments, the multifunctional amine chain extender is a dispersed micronized solid suspended in the resin composition. In some embodiments, the dispersed micronized solid has a particle size in a range of about 0.1 pm to about 100 pm (e.g., about 0.5 pm to about 20 pm)

[0059] In some embodiments, the ratio of the weight of reactive blocked prepolymer to the weight of the multifunctional amine chain extender is in a range of about 10: 1 to about 1 :2. In particular embodiments, the ratio of the weight of reactive blocked prepolymer to the weight of the multifunctional amine chain extender is in a range of about 7: 1 to about 3:1 (e.g., about 5:1).

[0060] In general, the resin compositions include a photoinitiator that initiates polymerization once exposed to actinic radiation or light (e.g., UV radiation). Photoinitiators included in the polymerizable liquid (resin) can be any suitable photoinitiator, including type I and type TI photoinitiators and including commonly used UV photoinitiators, examples of which include but are not limited to acetophenones (diethoxyacetophenone for example), phosphine oxides such as diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide (PPO), Irgacure® 369 (Omnirad® 369, IGM Resins, Charlotte, North Carolina, U.S.A.) (2- benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone, CAS number 119313-12-1), etc. See, e.g., U.S. Pat. No. 9,453,142, incorporated by reference in its entirety, for other non-limiting examples.

[0061] In some embodiments, one or more reactive diluents may be included in the resin composition. In some embodiments, the reactive diluent includes an acrylate, a methacrylate, a styrene, a vinylamide, a vinyl ether, a vinyl ester, or a combination of one or more of the foregoing (e g., acrylonitrile, styrene, divinyl benzene, vinyl toluene, methyl acrylate, ethyl acrylate, butyl acrylate, methyl (meth)acrylate, isobornyl acrylate (IBOA), isobornyl methacrylate (IBOMA), 4- t-butyl-cyclohexyl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, 3,3,5- trimethylcyclohexyl (meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, an alkyl ether of mono-, di- or tri ethylene glycol acrylate or methacrylate (e.g., polyethylene glycol diacrylate), a fatty alcohol acrylate or methacrylate such as lauryl (meth)acrylate, and mixtures thereof, TBAEMA (tert-butyl amino ethyl methacrylate), tetrahydrofurfuryl methacrylate, N,N- dimethylacrylamide, N-vinyl-2-pyrrolidone, N-vinylformamide, and Michael adducts of N- vinylformamide with (meth)acrylates (known and described in, for example, U.S. Pat. No. 5,672,731)).

[0062] In general, the reactive diluent(s) are included in an amount sufficient to reduce the viscosity of the polymerizable liquid or resin (e.g., to not more than about 15,000, about 10,000, about 6,000, about 5,000, about 4,000, or about 3,000 centipoise at about 25 °C). The diluent may be included in the polymerizable liquid in any suitable amount, typically from about 1, about 5 or about 10 percent by weight, up to about 30 or about 40 percent by weight, or more.

[0063] Non-reactive diluents may also be included in the resin composition in some embodiments. In some embodiments, the non-reactive diluent includes a glycol ether (e.g., dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol methyl ether acetate, propylene glycol methyl ether, diethyleneglycol monomethyl ether, ethylene glycol ethyl ether, propylene glycol monomethyl ether, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol butyl ether, etc., including combinations thereof). In some embodiments, the non-reactive diluent includes an ester (e.g., butyl acetate, hexyl acetate, octyl acetate, decyl acetate, dodecyl acetate, etc. including combinations thereof). In some embodiments, the non-reactive diluent includes an alcohol (e.g., butanol, amyl alcohol, hexanol, 1 -octanol, 2-ethylhexanol, decyl alcohol, dodecanol, etc., including combinations thereof). In some embodiments, the non-reactive diluent includes N-methyl-2-pyrrolidone, N,N- dimethylformamide, heavy naptha, toluene, xylene, mineral spirits or white spirits, or a combination thereof. In some embodiments, the non-reactive diluent includes dipropylene glycol dimethyl ether, dipropylene glycol methyl ether acetate, or a combination thereof.

[0064] In some embodiments, the non-reactive diluent has: (i) a boiling point less than 160, 200, or 240 degrees Centigrade at a pressure of one bar; and / or (ii) an autoignition temperature less than 300, 400, or 600 degrees Centigrade (i.e., as measured in accordance with the procedure described in ASTM E659); and / or (iii) a flash point less than 50, 80, 100, or 140 degrees Centigrade as measured by the Pensky-Martens closed cup method (e.g., ASTM D93, EN ISO 2719, or IP 34).

[0065] In some embodiments, the non-reactive diluent is included in the resin composition in an amount of from 1 or 5 percent by weight to 10, 15 or 20 percent by weight. Mixtures of reactive and non-reactive diluents may also be included in resin compositions of the invention.

[0066] Other Resin Components

[0067] The resin compositions may include other components as needed for the particular application of interest. For example, in some embodiments, the resin compositions include solid particles suspended or dispersed therein. Any suitable solid particle can be used, depending upon the three-dimensional object being fabricated. In some embodiments, the particles are metallic, organic / polymeric, inorganic, or composites or mixtures thereof. For example, the particles may be nonconductive, semi-conductive, or conductive (including metallic and non-metallic or polymer conductors); and the particles can be magnetic, ferromagnetic, paramagnetic, or nonmagnetic. The particles can be of any suitable shape, including spherical, elliptical, cylindrical, etc. In some embodiments, the particles may include an active agent or detectable compound, though these may also be provided dissolved solubilized in the liquid resin as also discussed below. In a particular embodiment, magnetic or paramagnetic particles or nanoparticles can be employed. The filler particles included in the resin compositions may be of any suitable size (for example, about 1 nm to about 20 pm average diameter).

[0068] In some embodiments, the fillers may include reactive and non-reactive rubbers, siloxanes, acrylonitrile-butadiene rubbers, reactive and non-reactive thermoplastics (including but not limited to: poly(ether imides), maleimide-styrene terpolymers, polyacrylates, polysulfones and polyethersulfones, etc.), inorganic fillers such as silicates (such as talc, clays, silica, mica), glass, carbon nanotubes, graphene, cellulose nanocrystals, etc., including combinations of all of the foregoing. Suitable fillers include tougheners, such as core-shell rubbers, as discussed below.

[0069] One or more polymeric and / or inorganic tougheners can be used as a filler in some embodiments of the present invention. The toughener may be uniformly distributed in the form of particles in the cured product. In some embodiments, such particles are less than about 5 microns (pm) in diameter. Such tougheners include, but are not limited to, those formed from elastomers, branched polymers, hyperbranched polymers, dendrimers, rubbery polymers, rubbery copolymers, block copolymers, core-shell particles, oxides or inorganic materials such as clay, polyhedral oligomeric silsesquioxanes (POSS), carbonaceous materials (e.g., carbon black, carbon nanotubes, carbon nanofibers, fullerenes), ceramics and silicon carbides, with or without surface modification or functionalization.

[0070] Core-shell rubbers are particulate materials (particles) having a rubbery core. Such materials are known and described in, for example, U.S. Patent Application Publication Nos. 2015 / 0184039 and 2015 / 0240113, and U.S. Pat. Nos. 6,861,475, 7,625,977, 7,642,316, and 8,088,245. In some embodiments, the core-shell rubber particles are nanoparticles (i.e., having an average particle size of less than about 1000 nm). Generally, the average particle size of the coreshell rubber nanoparticles is less than about 500 nm, e.g., less than about 300 nm, less than about 200 nm, less than about 100 nm, or even less than about 50 nm. Suitable core-shell rubbers include, but are not limited to, those sold by Kaneka Corporation (Kaneka Pharma America LLC, New York, New York, U.S.A.) under the designation Kaneka KaneAce®, including the Kaneka KaneAce® 15 and 120 series of products, including Kaneka KaneAce® MX 120, Kaneka KaneAce® MX 153, Kaneka KaneAce® MX 154, Kaneka KaneAce® MX 156, Kaneka KaneAce® MX170, Kaneka KaneAce® MX 257 and Kaneka KaneAce® MX 120 core-shell rubber dispersions, and mixtures thereof. In some embodiments, the resin compositions are devoid of core-shell rubbers.

[0071] In some embodiments, the resin compositions may include one or more polymerization (or other reaction) inhibitors, including liquid or gas inhibitors. For free radical polymerizable monomers, in some cases, the inhibitor is oxygen, which can be provided in the form of a gas such as air, a gas enriched in oxygen (optionally including an inert gas with oxygen to reduce combustibility thereof), or pure oxygen gas.

[0072] In some embodiments, resin compositions include a non-reactive pigment or dye that absorbs light, particularly UV light. Suitable examples of such light absorbers include, but are not limited to: (i) titanium dioxide (e.g., included in an amount of from about 0.05 or about 0.1 to about 1 or about 5 percent by weight), (ii) carbon black (e.g., included in an amount of from about 0.05 or about 0.1 to about 1 or about 5 percent by weight), and / or (iii) an organic ultraviolet light absorber such as a hydroxybenzophenone, hydroxyphenylbenzotriazole, oxanilide, benzophenone, thioxanthone, hydroxyphenyltriazine, and / or benzotriazole ultraviolet light absorber (e.g., Mayzo BLS1326 (Mayzo Specialty Chemicals Plus, Suwanee, Georgia, U.S.A.) or UVS-1101 (Kawasaki Kasei Chemical)) (e.g., included in an amount of about 0.001 or about 0.005 to about 1, about 2 or about 4 percent by weight). Examples of suitable organic ultraviolet light absorbers include, but are not limited to, those described in U.S. Pat. Nos. 3,213,058; 6,916,867; 7,157,586; and 7,695,643, the disclosures of which are incorporated herein by reference.

[0073] In some embodiments of the invention, the resin compositions include one or more metal organometallic chelate catalysts, including tin and non-tin catalysts. Such catalysts are known and described in, for example, U.S. Pat. Nos. 5,965,686, 8,912,113, 9,066,316, and 10,023,764; and in W. Blank et al., Catalysis of the Isocyanate-Hydroxyl Reaction by Non-Tin Catalysts (1999); W. Blank et al., Catalysis of Blocked Isocyanates with Non-Tin Catalysts (2000); and J. Florio et al., Novel Bismuth Carboxylate Catalysts with Good Hydrolytic Stability and HFO Compatibility (2017). Particular examples of suitable catalysts include but are not limited to K-KAT® catalysts 4205, XK-348, XK-635, XK-651, XK-661, XK-672, and XK-678, available from King Industries, 1 Science Road, Norwalk, Conn. 06852 USA. In some embodiments, the resin composition includes from about 5, about 20, or about 40 percent by weight to about 60, about 80, or about 90 percent by weight of the reactive blocked prepolymer; from about 10 or about 20 percent by weight to about 30 or about 40 or about 50 percent by weight of a reactive diluent and / or non-reactive diluent; from about 5 or about 10 percent by weight to about 20 or about 30 percent by weight of the multifunctional chain extender; and from about 0.1 or about 0.2 percent by weight to about 1, about 2 or about 4 percent by weight of photoinitiator.

[0074] In addition to the catalysts described above, additional constituents for a dual cure resin of the present invention are described in, for example, in U.S. Pat. Nos. 9,453,142, 9,598,606, 9,676,963, and 9,982,164.

[0075] In some embodiments, the resin compositions of the invention may be packaged as two separate precursors, which are mixed together and dispensed prior to use (sometimes referred to as “2K resins”). In some embodiments, the resin composition may be packaged in a premixed form in the same chamber of a single container (sometimes referred to as a “IK” resin).

[0076] In some embodiments, the resin compositions produce a polymeric material that can have similar properties to poly(ether-block-amide) (PEBA) and such properties may be adjusted by varying the “blocks” of polyether and polyamide as with other PEBA materials. For example, the polymer formed by a resin composition of the invention may have the general structure of poly(isocyanate-ether-isocyanate-block-amide) or (isocyanate-ether-isocyanate-block-amide)n wherein n is in a range of about 3 to about 10, about 15, or about 20, or more. The moduli of the polymers of the present invention can be adjusted from soft to semi-rigid (e.g., ~10 to 300 MPa modulus) by varying the length of the polyether or polyamide block / portion of the polymer and the ratio of the polyether to the polyamide.

[0077] In some embodiments of the invention, provided are three-dimensional objects formed from a resin composition of the invention. Additive Manufacturing Methods

[0078] Resin compositions of the invention may be used to form three-dimensional objects by a variety of additive manufacturing methods. Techniques for additive manufacturing are known. Suitable techniques include bottom-up and top-down additive manufacturing, generally known as stereolithography. Such methods are known and described in, for example, U.S. Pat. Nos. 5,236,637, 5,391,072, 5,529,473, 7,438,846, 7,892,474, 8,110,135, 9,636,873, and 9,120,270.

[0079] Continuous Liquid Interface Production (CLIP) is known and described in, for example, U.S. Pat. Nos. 9,211,678, 9,205,601, and 9,216,546; and also in J. Tumbleston, D. Shirvanyants, N. Ermoshkin et al., Continuous liquid interface production of 3D Objects, Science 347, 1349- 1352 (2015). See also R. Janusziewicz et al., Layerless fabrication with continuous liquid interface production, Proc. Natl. Acad. Sci. USA 113, 11703-11708 (2016). In some embodiments, CLIP employs features of a bottom-up three dimensional fabrication as described above, but the irradiating and / or advancing steps are carried out while also concurrently maintaining a stable or persistent liquid interface between the growing object and the build surface or window, such as by: (i) continuously maintaining a dead zone of polymerizable liquid in contact with said build surface, and (ii) continuously maintaining a gradient of polymerization zone (such as an active surface) between the dead zone and the solid polymer and in contact with each thereof, the gradient of polymerization zone comprising the light curable component in partially cured form.

[0080] In some embodiments of CLIP, the optically transparent member includes a semiperm eable member (e.g., a fluoropolymer), and the continuously maintaining a dead zone is carried out by feeding an inhibitor of polymerization through the optically transparent member, thereby creating a gradient of inhibitor in the dead zone and optionally in at least a portion of the gradient of polymerization zone. The inhibitor may pass entirely through the semipermeable member, or a “pool” of inhibitor may reside within the semipermeable member and pass through the resin contact surface thereof. While a desirable inhibitor is oxygen, other inhibitors, such as bases (including amines) may also be used. Other approaches for carrying out CLIP that can be used in the present invention and potentially obviate the need for a semipermeable “window” or window structure include utilizing a liquid interface comprising an immiscible liquid (see e.g., U.S. Patent No. 10,434,706) and generating oxygen as an inhibitor by electrolysis (see, e g., U.S. Patent No. 11,000,992). After the intermediate three-dimensional object is formed, it is optionally washed, optionally dried (e.g., air dried) and / or rinsed (in any sequence). In some embodiments, it is then further cured, such as by heating. Heating may be active heating (e.g., baking in an oven, such as an electric, gas, solar oven or microwave oven, or combination thereof), or passive heating. Active heating will generally be more rapid than passive heating and in some embodiments is preferred, but passive heating — such as simply maintaining the intermediate at ambient temperature for a sufficient time to effect further cure — may in some embodiments also be employed. In some embodiments, the three-dimensional intermediate may alternatively or additionally be cured by microwave irradiation, irradiation at a same or different wavelength than that used during the formation of the three-dimensional intermediate, and / or via exposure to moisture.

[0081] In some embodiments, methods of the invention include the steps of (a) providing a carrier and an optically transparent member having a build surface, the carrier and the build surface defining a build region therebetween; (b) filling the build region with the resin composition of the invention; (c) irradiating the build region with light through the optically transparent member to solidify at least a portion of the resin composition; (d) advancing said carrier away from the build surface; (e) repeating steps (b) through (d) to form a solid polymer scaffold that is a three- dimensional intermediate having the same shape as, or a shape to be imparted to, the three- dimensional object; (f) optionally, washing the three-dimensional intermediate; and (g) further reacting to form the three-dimensional object.

[0082] In some embodiments, the solid polymer scaffold is a three-dimensional intermediate having the same shape as, or a shape to be imparted to, the three-dimensional object, and the three- dimensional intermediate is further reacted to form the three-dimensional object. In some embodiments, further reacting comprises heating, microwave irradiation, irradiation at a same or different wavelength than in step (c), and exposure to moisture. In some embodiments, the resin composition is a dual cure resin and wherein the three-dimensional intermediate carries unsolidified and / or uncured component(s) with the solid polymer scaffold and the further reacting solidifies the unsolidified and / or uncured component(s). In some embodiments, further reacting is carried out under conditions in which the polymer scaffold degrades and forms a constituent necessary for the solidification or curing of the unsolidified and / or uncured component(s) (e.g., the multifunctional amine chain extender). In some embodiments, the multifunctional amine chain extender is a solid at room (and / or operating) temperature and unreacted (or substantially unreacted, e.g., less than 5%, 1%, or 0.1% of the amine functional groups reacted) after irradiation step (c), and the further reacting step (g) comprises heating the three-dimensional intermediate sufficient to degrade the polymer scaffold, melt the multifunctional amine chain extender, and react a portion of the degraded scaffold with the multifunctional amine chain extender. In particular, degrading the scaffold may include deblocking the polymer or prepolymer (releasing the blocking agents), thereby reforming the isocyanate functional groups. Thus, reacting the degraded scaffold with the multifunctional amine chain extender may include reacting the isocyanate groups formed upon degradation of the scaffold with the multifunctional amine chain extender.

[0083] The foregoing is illustrative of the present invention, and is not to be construed as limiting thereof. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims

What is claimed is:

1. A resin composition useful for the production of a three-dimensional object by additive manufacturing comprising:(a) a reactive blocked prepolymer including at least one ether subunit (e.g., a polyether subunit including at least three ether bonds);(b) a multifunctional amine (e.g., a diamine) chain extender including at least one amide subunit (e.g., a polyamide subunit having at least three amide bonds);(c) a photoinitiator; and(d) optionally, a reactive and / or non-reactive diluent.

2. The resin composition of claim 1, wherein the reactive blocked prepolymer comprises a polyether (e.g., a poly(ethylene ether), polypropylene ether), poly(trimethylene ether), and / or poly(tetramethylene ether)) subunit.

3. The resin composition of claim 1 or 2, wherein the reactive blocked prepolymer is formed by (a) reaction of a polyether polyol and a diisocyanate (e.g., hexamethylenediisocyanate, HDI) to form an intermediate; and (b) reaction of diisocyanate groups in the intermediate with a blocking agent that includes a functional group polymerizable by actinic radiation or light.

4. The resin composition of claim 3, wherein the blocking agent is an amine (meth)acrylate (e g., TBAEMA), an alcohol (meth)acrylate, maleimide, or n-vinylformamide.

5. The resin composition of claim 3 or claim 4, wherein the reactive blocked prepolymer includes a compound having a prepolymer structure of:[reactive blocking group]-[diisocyanate]-[polyether]-[diisocyanate]-[reactive blocking group].

6. The resin composition of any one of claims 3-5, wherein the blocking agent is TBAEMA, the diisocyanate is HDI, and the polyether is poly(tetramethylene ether glycol) (PTMEG).

7. The resin composition of any one of claims 1-6, wherein the multifunctional amine chain extender comprises a polyamide (e g., a Nylon such as 6,6, 12,12, 6 / 12, 10, 11, or 12) subunit.

8. The resin composition of claim 7, wherein the multifunctional amine chain extender includes a compound having a structure of o oNH2(CH2)aHNC(CH2)bCNH(CH2)cNH2wherein a, b, and c are each independently an integer from 4 to 20 (optionally, a = c) and x is an integer from 1 to 60; and / or a compound having a structure ofwherein d, e, and f are each independently an integer from 4 to 20, and y and z are each independently an integer from 0 to 60, wherein y + z > 1.

9. The resin composition of any one of claims 1-8, wherein the ratio of the weight of the reactive blocked prepolymer to the weight of the multifunctional amine chain extender is in a range of 10: 1 to 1 :2.

10. The resin composition of any one of claims 1-9, wherein the multifunctional amine chain extender is a solid at room temperature (e.g., about 25 °C).

11. The resin composition of any one of claims 1-10, wherein the multifunctional amine chain extender has a melting temperature in a range of about 120 °C to about 180 °C.

12. The resin composition of any one of claims 1-11, wherein the resin composition further comprises a pigment, dye, and / or fdler.

13. A method of forming a three-dimensional obj ect, comprising: irradiating the resin composition of any one of claims 1-12 with actinic radiation or light (e.g., by a top-down or bottom-up stereolithography method), thereby forming a three-dimensional intermediate, and then further reacting the three-dimensional intermediate to form the three- dimensional object.

14. The method of claim 13, wherein the method comprises:(a) providing a carrier and an optically transparent member having a build surface, the carrier and the build surface defining a build region therebetween;(b) filling the build region with the resin composition of any one of claims 1-12;(c) irradiating the build region with light through the optically transparent member to solidify at least a portion of the resin composition;(d) advancing the carrier away from the build surface;(e) repeating steps (b) through (d) to form a solid polymer scaffold that is a three- dimensional intermediate having the same shape as, or a shape to be imparted to, the three- dimensional object;(f) optionally, washing the three-dimensional intermediate; and(g) further reacting the three-dimensional intermediate to form the three-dimensional object.

15. The method of claim 14, wherein the further reacting comprises exposing the three- dimensional intermediate to heat, microwave irradiation, irradiation at a same or different wavelength than in step (c), and / or moisture.

16. The method of claim 14 or claim 15, wherein the multifunctional amine chain extender is a solid and unreacted (or substantially unreacted) after irradiation step (c), and the further reacting step (g) comprises: heating the three-dimensional intermediate sufficient to degrade the polymer scaffold and melt the multifunctional amine chain extender, and reacting a portion of the degraded scaffold with the multifunctional amine chain extender.

17. The method of claim 16, wherein isocyanate functional groups on the degraded scaffold react with the multifunctional amine chain extender.

18. The method of any one of claims 14-17, wherein step (c) and / or step (d) is carried out while also concurrently (i) continuously maintaining a dead zone of the resin composition in contact with the build surface; and (ii) continuously maintaining a gradient of polymerization zone between the dead zone and the solidified polymer in contact with the carrier, the gradient of polymerization zone comprising the resin composition in partially cured form.

19. The method of claim 18, wherein the optically transparent member comprises a semipermeable member (optionally wherein the semipermeable member comprises a fluoropolymer), and continuously maintaining a dead zone is carried out by feeding an inhibitor (e g., oxygen) through said optionally transparent member (optionally creating a gradient of inhibitor in the dead zone and optionally in at least a portion of the gradient of polymerization zone).

20. A three-dimensional object formed from a resin composition of any one of claims 1-12 and / or by a method of any one of claims 13-19.

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