PRODUCTION OF OBJECTS WITH MIXED TENSILE PROPERTIES

Field of the Invention

The present invention concerns additive manufacturing resins, methods of using the same, and products made from such resins.

Background of the Invention

The introduction of more rapid additive manufacturing processes sometimes referred to as "continuous liquid interface production" (or "CLIP"), coupled with the introduction of dual cure additive manufacturing resins that produce objects with practical functional properties, have accelerated the transition of additive manufacturing from a tool for producing prototype objects, to a tool for making objects suitable for real-world use. See J. Tumbleston et al., Continuous liquid interface production of 3D objects , SCIENCE 347, 1349-1352 (2015); US Patent Nos. 9,211,678; 9,205,601; and 9,216,546 to DeSimone et al.; and R. Janusziewicz, et al., Layerless fabrication with continuous liquid interface production, PNAS 113, 11703-11708 (2016); See also Rolland et al., US Patent Nos. 9,676,963, 9,453,142 and 9,598,606; J. Poelma and J. Rolland, Rethinking digital manufacturing with polymers, SCIENCE 358, 1384-1385 (2017).

Current dual cure additive manufacturing resins are tailored to the production of objects with a particular set of tensile properties, such as rigid objects, flexible objects, and elastomeric objects. Examples of such resins include the RPU, FPU, EPU, and MPU family of resins available from Carbon Inc. (Redwood City, California). There are, however, situations where it would be desirable to produce an object with different tensile properties in different regions thereof. Previously, such objects could be produced by switching the resin (e.g, by swapping window cassettes containing different resins) during the course of producing an object (see, e.g, Rolland et al., above). It would speed and simplify production of such objects to have a single resin that could produce an object with different tensile properties in different regions thereof, and, where necessary, produce an object where the transition between those regions is not planar (as is necessarily the case where windows containing the resin are switched during production). Summary

Provided herein according to some embodiments is a dual cure additive manufacturing resin useful to produce objects with mixed tensile properties, the resin comprising: (a) light polymerizable component comprised of: (i) a reactive blocked prepolymer, said prepolymer comprised of a rigid or elastic polyurethane, polyurea, or copolymer thereof ( e.g ., in an amount of from 5, 10, or 20 percent by weight to 70, 80, or 90 percent by weight); (ii) a volatile (meth)acrylate monomer, wherein said monomer is rigid when said prepolymer is elastic, or said monomer is elastic when said prepolymer is rigid (e.g., in an amount of from 90, 80, or 70 percent by weight to 20, 10, or 5 percent by weight); (Hi) a photoinitiator (e.g, in an amount of from 0.1 to 4 percent by weight); and (iv) optionally, but preferably, an ultraviolet light absorber and/or pigment (e.g, in an amount when present of from 0.01 or 0.1 to 1 or 2 percent by weight); (v) optionally, a crosslinker (e.g, a volatile or non-volatile (meth)acrylate, acrylamide, or vinyl crosslinker, which can be rigid or elastomeric) (e.g, in an amount when present of from 0.1 or 1 percent by weight to 30 or 50 percent by weight); said resin further comprising: (b) a heat polymerizable component comprised of: (i) a chain extender selected from the group consisting of polyols, polyamines, and combinations thereof (e.g, in an amount of from 5 or 10 percent by weight to 30 or 40 percent by weight); and (ii) optionally, an organometallic catalyst (e.g, in an amount when present of 0.01 or 0.1 percent by weight to 2 or 3 percent by weight).

In some embodiments, the reactive blocked prepolymer is produced by reaction of a polyisocyanate oligomer with an amine (meth)acrylate, alcohol (meth)acrylate, maleimide, or n-vinyl formamide blocking agent. In some embodiments, the reactive blocked prepolymer is produced by reaction of a polyisocyanate oligomer with an amine (meth)acrylate, maleimide, or n-vinyl formamide blocking agent.

In some embodiments, the glass transition temperature of a polymer formed only from one of said elastomeric monomers, prepolymers, or crosslinkers is 25 degrees Celsius or less; and the glass transition temperature of a polymer formed from only one of said rigid monomers, prepolymers, or crosslinkers is 50 degrees Celsius or more.

In some embodiments, the volatile monomer is rigid (e.g, is isobornyl methacrylate (IBOMA), isobornyl acrylate (IBOA), 3,3,5-trimethylcyclohexyl methacrylate; 2- phenoxyethyl methacrylate or a combination thereof); and/or said crosslinker is present and rigid (e.g, is neopentyl glycol dimethacrylate (NPGDMA), ethoxylated bisphenol A dimethacrylate; acrylate ester; 1,4-butanediol dimethacrylate; di ethylene glycol diacrylate; tricyclodecane dimethanol diacrylate; pentaerythritol tetramethacrylate, dipentaerythritol hexaacrylate, or a combination thereof).

In some embodiments, the volatile monomer is elastomeric ( e.g . lauryl methacrylate (LMA), rnethoxy polyethylene glycol (550) monoacrylate; 2(2-ethoxyethoxy) ethyl acrylate; cyclic Trimethylolpropane formal acrylate; caprolactone acrylate; or a combination thereof); and/or said crosslinker is present and is elastomeric (e.g., a polyethylene glycol dimethacrylate crosslinker such as di (ethylene glycol) methyl ether methacrylate (DEGMA); alkoxylated neopentyl glycol diacrylate; polypropylene glycol (400) dimethacrylate; 1,12- dodecanediol dimethacrylate; tetraethylene glycol dimethacrylate, or a combination thereof).

In some embodiments, the chain extender consists essentially of a polyol, said organometallic catalyst is present, and said blocking agent is n-vinyl formamide (and optionally wherein said resin is packaged with ail constituents mixed together in a single container, i.e., as a IK resin).

Also provided is a method of making a three-dimensional object having at least two portions with different glass transition temperatures, comprising: (a) producing an intermediate object by light polymerization of a resin as taught herein in an additive manufacturing process (e.g, stereolithography), with each of the at least two portions receiving a different dose of light during said producing; (b) optionally cleaning said intermediate object; and then (c) heating said intermediate object to produce said 3D object, with the glass transition temperature of each portion defined by the dose of light received by that portion during said producing step.

In some embodiments, one of said portions is rigid, and the other of said portions is flexible or elastomeric.

In some embodiments, the manufacturing process comprises bottom-up stereolithography (e.g, continuous liquid interface production).

Also provided is a three-dimensional object produced by a method as taught herein.

Further provided is a three-dimensional object produced by additive manufacturing from a single dual cure resin, the object comprising at least two portions having different glass transition temperatures, each of said at least two portions comprising: (a) a light polymerization product of (i) a reactive blocked prepolymer, (ii) a volatile reactive monomer, and (iii) optionally, a crosslinker; and (b) a heat polymerization product of: (i) a polyol and/or a polyamine, and (ii) a deblocked prepolymer produced by the thermal degradation of said light polymerization product; with each of said portions differing from one another in: (i) the degree of incorporation of said volatile reactive monomer and/or said crosslinker into said light polymerization product, and (ii) the amount of said heat polymerization product present, with (Hi) the amount of heat polymerization product present in each portion inversely related to the degree of incorporation of said volatile reactive monomer and/or crosslinker into said light polymerization product in that portion.

In some embodiments, the at least two portions meet one another at a non-planar ( e.g curved, angled, or combinations thereof) boundary zone.

In some embodiments, the at least two portions meet one another at a boundary zone having an average thickness of at least one, two, or three millimeters, where said different glass transition temperatures change to one another gradually across said boundary zone.

In some embodiments, the at least two portions meet one another at a boundary zone comprised of an open cell lattice.

In some embodiments, one of said at least two portions is contained within another of said at least two portions.

The foregoing and other objects and aspects of the present invention are explained in greater detail in the drawings herein and the specification set forth below. The disclosures of all United States patent references cited herein are to be incorporated herein by reference.

Brief Descrption of the Drawings

Figure 1A illustrates a first light exposure script for producing objects as described herein.

Figure IB illustrates a second light exposure script for producing objects as described herein.

Figure 2A illustrates an object produced with a script of Figure 1 A following baking thereof.

Figure 2B illustrates an object produced with a script of Figure 1B following baking thereof.

Figure 3A is a partial cut-away illustration of an object produced as described herein. Figure 3B is a partial cut-away illustration of an object produced as described herein.

Detailed Description of Illustrative Embodiments

The present invention is now described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. 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.

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.

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").

The transitional phrase "consisting essentially of' means that the scope of a claim is to be interpreted to encompass the specified materials or steps recited, and also additional materials or steps that do not materially affect the basic and novel characteristics of the claimed invention as described herein.

Provided herein according to some embodiments is a dual cure additive manufacturing resin useful to produce objects with mixed tensile properties. The resin may have: (a) light polymerizable component comprising: (i) a reactive blocked prepolymer, said prepolymer comprised of a rigid or elastic polyurethane, polyurea, or copolymer thereof; and (ii) a volatile (meth)acrylate monomer, wherein said monomer is rigid when said prepolymer is elastic, or said monomer is elastic when said prepolymer is rigid; and (b) a heat polymerizable component comprising: (i) a chain extender selected from the group consisting of polyols, polyamines, and combinations thereof. The resin may also include a photoinitiator, an ultraviolet light absorber and/or pigment, and/or a crosslinker. An organometallic catalyst may be included in the resin in some embodiments.

In some embodiments, the reactive blocked prepolymer is produced by reaction of a polyisocyanate oligomer with an amine (meth)acrylate, alcohol (meth)acrylate, maleimide, or n-vinyl formamide blocking agent. In some embodiments, the reactive blocked prepolymer is produced by reaction of a polyisocyanate oligomer with an amine (meth)acrylate, maleimide, or n-vinyl formamide blocking agent.

In some embodiments, the glass transition temperature of a polymer formed only from one of said elastomeric monomers, prepolymers, or crosslinkers is 25 degrees Celsius or less; and the glass transition temperature of a polymer formed from only one of said rigid monomers, prepolymers, or crosslinkers is 50 degrees Celsius or more.

"ABPU" or "reactive blocked polyurethane" as used herein refers to UV-curable, (meth)acrylate blocked, polyurethane/polyurea (i.e., reactive blocked polyurethane) such as described in US Patent Nos. 9,453,142 and 9,598,606 to Rolland et al. A particular example of a suitable reactive (or UV-curable) blocking agent is a tertiary amine-containing (meth)acrylate (e.g., /-butyl ami noethyl methacrylate, t-BAEMA).

Polyisocyanates (including diisocyanates) useful in carrying out the present invention include, but are not limited to, l,l'-methylenebis(4-isocyanatobenzene) (MDI), 2,4- diisocyanato-l-methylbenzene (TDI), methylene-bis(4-cyclohexylisocyanate) (H _I2 MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), polymeric MDI, 1,4- phenylene diisocyanate (PPDI), and o-tolidine diisocyanate (TODI). In some embodiments, a preferred diisocyanate is H _I2 MDI, such as Desmodur W, supplied by Covestro AG. Additional examples include but are not limited to those given in US Patent No. 3,694,389 to Levy.

Reactive blocking agents useful in the present invention include amine (meth)acrylate monomer blocking agents (e.g., tertiary -butylaminoethyl methacrylate (TBAEMA), tertiary pentylaminoethyl methacrylate (TPAEMA), tertiary hexylaminoethyl methacrylate (THAEMA), tertiary-butylaminopropyl methacrylate (TBAPMA), acrylate analogs thereof, and mixtures thereof (see, e.g, US Patent Application Publication No. 20130202392). There are, however, many blocking agents for isocyanate, and those skilled in the art can couple (meth)acrylate groups to other blocking agents to create additional blocking agents that can be used to carry out the present invention, such as an alcohol (meth)acrylate, maleimide or substituted maleimide, or n-vinyl formamide blocking agent. See, e.g., U.S. Pat. No. 3,947,426 to Lander.

"Diluents" as used herein includes both UV-curable diluents (for example monoacrylates, mono-methacrylates, poly acrylates, polymethacrylates, acrylamides, methacrylamides, etc.), and non-UV-curable diluents (for example, plasticizers such as bis(2- ethylhexyl) phthalate, bis(2-propylheptyl) phthalate, diisononyl phthalate, tri-(2-ethylhexyl) trimellitate, bis(2-ethylhexyl) adipate, diisononyl adipate, dibutyl sebacate, diisobutyl maleate, etc.). 1. Dual cure additive manufacturing resins containing ABPUs.

Dual cure additive manufacturing resins containing ABPUs are described in, for example, US Patent Nos. 9,453,142 and 9,598,606 to Rolland et al., the contents of which are incorporated by reference herein.

A. Light-polymerizable monomers and/or prepolymers. Sometimes also referred to as "Part A" of a dual cure resin, these are monomers and/or prepolymers that can be polymerized by exposure to actinic radiation or light. This resin can comprise difunctional or polyfunctional monomers, but can also include monofunctional monomers (to act as "chain stoppers" to control molecular weight). Examples of reactive end groups suitable for Part A constituents, monomers, or prepolymers include, but are not limited to: acrylates, methacrylates, a-olefms, N-vinyls, acrylamides, methacrylamides, styrenics, epoxides, thiols, 1,3-dienes, vinyl halides, acrylonitriles, vinyl esters, maleimides, and vinyl ethers.

In some embodiments, Part A includes monomers that are volatile (i.e., they will volatize, especially upon heating).

In some embodiments, the volatile monomer is rigid ( e.g ., is isobornyl methacrylate (IBOMA), isobornyl acrylate (IBOA), 3,3,5-trimethylcyclohexyl methacrylate; 2- phenoxyethyl methacrylate or combinations thereof); and/or a crosslinker is present and rigid (e.g., is neopentyl glycol dimethacrylate (NPGDMA), ethoxylated bisphenol A dimethacrylate; acrylate ester; 1,4-butanediol dimethacrylate; di ethylene glycol diacrylate; tricyclodecane dimethanol diacrylate; pentaerythritol tetramethacrylate, dipentaerythritol hexaacrylate, or combinations thereof).

In some embodiments, the volatile monomer is elastomeric (e.g. lauryl methacrylate (LMA), methoxy polyethylene glycol (550) monoacrylate; 2(2-ethoxyethoxy) ethyl acrylate; cyclic Trimethylolpropane formal acrylate; caprolactone acrylate; or a combination thereof); and/or a crosslinker is present and is elastomeric (e.g, a polyethylene glycol dimethacrylate crosslinker such as diiethylene glycol) methyl ether methacrylate (DEGMA); alkoxylated neopentyl glycol diacrylate; polypropylene glycol (400) dimethacrylate; 1,12-dodecanediol dimethacrylate; tetraethylene glycol dimethacrylate, or a combination thereof).

In some embodiments, the light polymerizable component, once polymerized, is one which can degrade (e.g, during heating or baking) to form a constituent for further (e.g, heat) cure. Thus, it is converted, in part, to a "Part B" thermally reactive component. In some embodiments, the additional part B thermally reactive components (e.g., chain extenders such as polyols and/or polyamines) are carried in the green, light cured, object, where they can participate in a subsequent cure to impart desired physical properties to the object.

Chain extenders. Examples of polyol ( e.g ., diol, triol) chain extenders include, but are not limited to, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3 -propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, hydroquinone bis(2-hydroxy ethyl) ether (HQEE), glycerol, trimethylolpropane, trimethylolpropane ethoxylate (TPE), 1,2,6-hexanetriol, and pentaerythritol. Natural oil polyols (biopolyols) may also be used. Such polyols may be derived, e.g., from vegetable oils (triglycerides), such as soybean oil, by known techniques. See, e.g. , U.S. Patent No. 6,433,121 to Petrovic et al.

Polyamine {e.g., diamine, triamine) chain extenders are known and include but are not limited to those described in US Patent Nos. 10,190,020; and 9,908,146. A particular example is 4,4’ -methyl enebis(2-methylcy cl ohexyl-amine) (or "MACM").

In some embodiments, the chain extender is or consists essentially of a polyol, the organometallic catalyst is present, and the blocking agent is n-vinyl formamide (and optionally wherein the resin is packaged with all constituents mixed together in a single container, i.e., as a IK resin).

Catalysts. In the present invention, one or more metal organometallic chelate catalysts, such as non-tin catalysts, can be incorporated into the resin composition. Such catalysts are known and described in, for example, US Patent No. 5,965,686 to Blank et al., 8,912,113 to Ravichandran et al.; 9,066,316 to Hsieh et al., and 10,023,764 to Hsieh et al.; 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); J. Florio et al., Novel Bismuth Carboxylate Catalysts with Good Hydrolytic Stability and HFO Compatibility (2017); the disclosures of which are incorporated herein by reference in their entirety.

In some embodiments, the catalyst comprises a metal carboxylate such as a zinc carboxylate and/or a bismuth carboxylate.

In some embodiments, the organometallic catalyst comprises a metal amidine complex and/or a second compound, wherein the second compound is a metal carboxylate or a carboxylic acid, and/or a third compound wherein the third compound is a metal chelate complex of an acetylacetonate {e.g., pentanedione), optionally wherein the metal of the metal amidine complex and the metal of the metal carboxylate and/or the metal of the metal acetylacetonate (when present) are not identical. Note that the various organic groups can be substituted or unsubstituted. For example, the acetylacetonate can be further substituted, for instance with one to six methyl groups or one to six fluorines at the 1 and 5 positions.

In some embodiments, the metal amidine complex is of the chemical formula metal(amidine) _w (carboxylate) ₂ , wherein w is an integer from 1 to 4.

In some embodiments, the metal of the metal amidine complex, the metal of the metal carboxylate, and the metal of the chelate complex are independently copper, zinc, lithium, sodium, magnesium, barium, potassium, calcium, bismuth, cadmium, aluminum, zirconium, tin, hafnium, titanium, lanthanum, vanadium, niobium, tantalum, tellurium, molybdenum, tungsten, or cesium.

In some embodiments, the metal of the metal amidine complex and the metal of the metal carboxylate are independently zinc or bismuth.

In some embodiments, the amidine is 1,1,3,3-tetramethyl guanidine or 1- methylimidazole.

In some embodiments, the chelate is pentanedione, hexafluoropentanedione or tetramethy 1 octanedi one .

In some embodiments, the carboxylate is octoate, neodecanoate, naphthenate, stearate, or oxalate.

In some embodiments, the second compound comprises a zinc carboxylate and/or a bismuth carboxylate.

Particular examples of suitable catalysts include, but are not limited to K-KAT® catalysts XK-348, XK-635, XK-651, XK-661, XK-672, and XK-678, available from King Industries, 1 Science Road, Norwalk, CT 06852 USA ( See generally King Industries, K- KAT® Guide to Tin-Free Catalysts for Urethane Coatings (2018)).

Photoinitiators. Photoinitiators included in the polymerizable liquid (resin) can be any suitable photoiniator, including type I and type II photoinitiators and including commonly used UV photoinitiators, examples of which include but are not limited to such as 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, etc. See, e.g, US Patent No. 9,453,142 to Rolland et al.

The liquid resin or polymerizable material can have solid particles suspended or dispersed therein. Any suitable solid particle can be used, depending upon the end product being fabricated. The particles can be metallic, organic/polymeric, inorganic, or composites or mixtures thereof. The particles can 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. The particles can be of any suitable size (for example, ranging from 1 nm to 20 pm average diameter).

The particles can comprise an active agent or detectable compound as described below, though these may also be provided dissolved or solubilized in the liquid resin as also discussed below. For example, magnetic or paramagnetic particles or nanoparticles can be employed.

The liquid resin can have additional ingredients solubilized therein, including pigments, dyes, diluents, active compounds or pharmaceutical compounds, detectable compounds ( e.g ., fluorescent, phosphorescent, radioactive), etc., again depending upon the particular purpose of the product being fabricated. Examples of such additional ingredients include, but are not limited to, proteins, peptides, nucleic acids (DNA, RNA) such as siRNA, sugars, small organic compounds (drugs and drug-like compounds), etc., including combinations thereof.

Dyes/non-reactive light absorbers. In some embodiments, polymerizable liquids for carrying out the present invention 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 0.05 or 0.1 to 1 or 5 percent by weight), (ii) carbon black (e.g, included in an amount of from 0.05 or 0.1 to 1 or 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) (e.g, included in an amount of 0.001 or 0.005 to 1, 2 or 4 percent by weight). Examples of suitable organic ultraviolet light absorbers include, but are not limited to, those described in US Patent Nos. 3,213,058; 6,916,867; 7,157,586; and 7,695,643, the disclosures of which are incorporated herein by reference.

Fillers. Any suitable filler may be used in connection with the present invention, depending on the properties desired in the part or object to be made. Thus, fillers may be solid or liquid, organic or inorganic, and 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, polyarylates, 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.

Tougheners. One or more polymeric and/or inorganic tougheners can be used as a filler in the present invention. The toughener may be uniformly distributed in the form of particles in the cured product. The particles could be less than 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.

Core-shell rubbers. Core-shell rubbers are particulate materials (particles) having a rubbery core. Such materials are known and described in, for example, US Patent Application Publication No. 20150184039, as well as US Patent Application Publication No. 20150240113, and US Patent Nos. 6,861,475, 7,625,977, 7,642,316, 8,088,245, and elsewhere. In some embodiments, the core-shell rubber particles are nanoparticles (i.e., having an average particle size of less than 1000 nanometers (nm)). Generally, the average particle size of the core-shell rubber nanoparticles is less than 500 nm, e.g., less than 300 nm, less than 200 nm, less than 100 nm, or even less than 50 nm. Typically, such particles are spherical, so the particle size is the diameter; however, if the particles are not spherical, the particle size is defined as the longest dimension of the particle. Suitable core-shell rubbers include, but are not limited to, those sold by Kaneka Corporation under the designation Kaneka Kane Ace, including the Kaneka Kane Ace 15 and 120 series of products, including Kaneka Kane Ace MX 120, Kaneka Kane Ace MX 153, Kaneka Kane Ace MX 154, Kaneka Kane Ace MX 156, Kaneka Kane Ace MX170, Kaneka Kane Ace MX 257 and Kaneka Kane Ace MX 120 core-shell rubber dispersions, and mixtures thereof.

Organic diluents. In some embodiments, diluents for use in the present invention are preferably reactive organic diluents; that is, diluents that will degrade, isomerize, cross-react, or polymerize, with themselves or a light polymerizable component, during the additive manufacturing step. In general, the diluent(s) are included in an amount sufficient to reduce the viscosity of the polymerizable liquid or resin (e.g., to not more than 15,000, 10,000, 6,000, 5,000, 4,000, or 3,000 centipoise at 25 degrees Centigrade). Suitable examples of diluents include, but are not limited to, isobornyl methacrylate, TBAEMA (tert-butyl amino ethyl methacrylate), tetrahydrofurfuryl methacrylate, N, A-di methyl acryl a i de, A-vinyl-2- pyrrolidone, and A -vinyl formamide, or a mixture of two or more thereof. The diluent may be included in the polymerizable liquid in any suitable amount, typically from 1, 5 or 10 percent by weight, up to about 30 or 40 percent by weight, or more.

Resin packaging. The resin may be packaged as two separate precursors, which are mixed together and dispensed prior to use (sometimes referred to as "2K resins") or in some embodiments may be packaged in a premixed form, in the same chamber of a single container (sometimes referred to as a " IK" resin). In either case, the resin is dispensed into an additive manufacturing apparatus for production of a "green" intermediate object.

2. Methods.

Suitable additive manufacturing methods and apparatus in which resins as described herein can be used include bottom-up and top-down additive manufacturing apparatus, as known and described in, for example, U.S. Patent No. 5,236,637 to Hull, US Patent Nos. 5,391,072 and 5,529,473 to Lawton, U.S. Patent No. 7,438,846 to John, US Patent No. 7,892,474 to Shkolnik, U.S. Patent No. 8,110,135 to El-Siblani, U.S. Patent Application Publication No. 2013/0292862 to Joyce, and US Patent Application Publication No. 2013/0295212 to Chen et al. The disclosures of these patents and applications are incorporated by reference herein in their entirety.

In some embodiments, the additive manufacturing step is carried out by one of the family of methods sometimes referred to as continuous liquid interface production (CLIP). CLIP is known and described in, for example, US Patent Nos. 9,211,678; 9,205,601; 9,216,546; and others; in J. Tumbleston et al., Continuous liquid interface production of 3D Objects, Science 347, 1349-1352 (2015); and in R. Janusziewcz et al., Layerless fabrication with continuous liquid interface production, Proc. Natl. Acad. Sci. USA 113, 11703-11708 (2016). Other examples of methods and apparatus for carrying out particular embodiments of CLIP include, but are not limited to: Batchelder et al., US Patent Application Pub. No. US 2017/0129169; Sun and Lichkus, US Patent Application Pub. No. US 2016/0288376; Willis et al., US Patent Application Pub. No. US 2015/0360419; Lin et al., US Patent Application Pub. No. US 2015/0331402; D. Castanon, US Patent Application Pub. No. US 2017/0129167. B. Feller, US Pat App. Pub. No. US 2018/0243976 (Aug 30, 2018); M. Panzer and J. Tumbleston, US Pat App Pub. No. US 2018/0126630 (May 10, 2018); and K. Willis and B. Adzima, US Pat App Pub. No. US 2018/0290374 (Oct. 11, 2018). Following additive manufacturing, objects can, if desired, be cleaned ( e.g ., wiped, washed, spun to centrifugally separate unpolymerized resin from the object, etc.) and further cured (e.g., by baking), in accordance with known techniques.

3. Objects.

The resins and methods described herein can be used to make a variety of objects, including but not limited to cushions, bumpers, and shock absorbers, with particular examples including helmet pads and liners, seat cushions, bed cushions, body pads such as shoulder pads, knee pads, and shin guards, balls having cores or internal layers with different tensile properties than the outer shell thereof, etc. and the like.

In some embodiments, the object includes at least two portions having different glass transition temperatures, each portion comprising: (a) a light polymerization product of (i) a reactive blocked prepolymer, (ii) a volatile reactive monomer, and (iii) optionally, a crosslinker; and (b) a heat polymerization product of: (i) a polyol and/or a polyamine, and (ii) a deblocked prepolymer produced by the thermal degradation of the light polymerization product. Each portion may differ from one another in: (i) the degree of incorporation of the volatile reactive monomer and/or crosslinker into the light polymerization product, and (ii) the amount of heat polymerization product present, with (iii) the amount of heat polymerization product present in each portion inversely related to the degree of incorporation of the volatile reactive monomer and/or crosslinker into the light polymerization product in that portion.

In some embodiments, the at least two portions meet one another at a non-planar (e.g, curved, angled, or combinations thereof) boundary zone.

In some embodiments, the at least two portions meet one another at a boundary zone having an average thickness of at least one, two, or three millimeters, where said different glass transition temperatures change to one another gradually across said boundary zone.

In some embodiments, the at least two portions meet one another at a boundary zone comprised of an open cell lattice.

In some embodiments, one of the at least two portions is contained within another of the at least two portions.

The regions or portions of the object with different tensile properties can join to one another as a homogeneous lattice structure (that is, without intervening walls or solid layers), as seen in Figure 2A, although it will be appreciated that various unit cells within the homogeneous lattice can differ from one another. A particular example is a helmet liner that transitions from an elastomeric internal (or body facing) portion to a rigid external portion.

The regions or portions of the object with different tensile properties can connect to one another along a gradual or extended transition zone (in contrast to the more sudden transition obtained when switching cassettes with different resins as described in Rolland et al., noted above).

As illustrated in the non-limiting Examples of Figures 3A-3B, the object 201 can have different portions or regions 202, 203, 204, 205 of different tensile properties ( e.g rigid versus elastomeric versus flexible) that join to one another at a non-planar interface, such as a curved interface, and can have one region fully or partially contained within another region (for example, as regions 202 is contained within region 203, as region 203 is contained within region 204, as region 204 is contained within region 205). Still more complicated patterns of interrelated regions can be obtained, including checkerboard, spiral, and other intertwined regions, with the variation of tensile properties being attainable by varying light intensity or dose on a voxel-by-voxel basis during additive manufacturing of the object.

The present invention is explained in greater detail in the following non-limiting Examples.

EXAMPLES

The following examples describe a single resin that is capable of producing a gradient of properties depending on the amount of UV light exposure during the printing process. In these examples, an ABPU normally used for the production of elastomeric objects (ATB7 ABPU) was mixed with a monomer normally used for the production of rigid objects (IBOMA). Since the Tg of the reactive monomer was high, when incorporated into the part at a higher level (high light dose areas) it causes that area to have a higher Tg, versus when incorporated at lower levels (low light dose areas) the polyurethane (PU) network is more prevalent and forms a lower Tg.

The following materials and abbreviations are used herein:

IPDI: isophorone diisocyanate;

TB or TBAEMA: tert-butylaminoethyl methacrylate;

P03G2K: 2 kiloDalton poly(trimethylene ether)glycol (a polyether polyol produced by the self condensation polymerization of 1,3-propanediol (PDO)); ATB7 ABPU: a reactive methacrylate blocked polyurethane prepolymer, prepared as described in J. Rolland et al., US Patent No.9,598,606, from the above ingredients in a molar ratio of IPDI:PO3G2K:TB of 3:1:4);

IBOMA: Isobornyl methacrylate, a reactive, volatile monomer;

5  MACM: 4,4’-methylenebis(2-methylcyclohexyl-amine), a polyamine (Part B);

TPO: Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, a photoinitiator; DBA: 9,10-dibromoanthracene, an ultraviolet light absorber. EXAMPLE 1

10  Resin Formulation

A resin was prepared by adding 50g IBOMA, 0.2g DBA, and 1.6g TPO to a 300mL THINKY™ mixer cup and mixing the components together in a planetary centrifugal mixer (Thinky Corporation) for 10-20 minutes, until solids are dissolved.131g of the ATB7 ABPU was then added and mixed for another 4 minutes. Lastly, 17.2g of MACM was added and 15  mixed for 2 minutes. The resin was then tested for basic properties, such as viscosity and dose-to-cure, and prepared for printing by filtering the resin and placing it into the window cassette of a Carbon Inc. M1 printer. EXAMPLE 2

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Print script were constructed that applied an intensity mask to different areas of the build platform during production of one or more objects on the same carrier platform, at the same time, from the same resin.

A first script had a gradient of 100% to 10% of the initial exposure intensity in 10% 25  bands along the X axis, as shown in Figure 1A.

Another script used had 4 different quadrants which were respectively 25%, 50%, 75% and 100% of the initial exposure intensity in the upper right, upper left, lower left and lower right quadrants of the build platform, as shown in Figure 1B, from which four different objects were produced at the same time, from the same pool of resin on the window cassette. 30  Exposure time was kept constant for each slice in this example, but many other methods for controlling dose can be used to achieve these gradient properties, such as by varying intensity in the "Z" or vertical dimension during production of an object, or by using exposure time differences in the Z dimension in combination with an intensity map in the XY dimensions during production of the object.   The script was applied to the relevant test print, in this case, a set of lattices. The print parameters were adjusted to allow for printing even in the lowest-dose areas, and the lattice objects produced from a resin as described in EXAMPLE 1 above.

After production, the "green" objects were washed in isopropyl alcohol for between 5  30 seconds and five minutes, to remove excess resin.

After washing, the objects were baked for about 12 hours at 120 degrees Centigrade in a Yamato convection oven to allow full formation of the thermal network, and to encourage evaporation of the ultraviolet network in the "green" object formed during the additive manufacturing step. The different objects, shown in Figure 2A-2B, had clear 10  differences in feel and properties. 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.

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