Production of low-density products using moisture curable resins

Abstract

Provided are methods of making a three-dimensional object that include (a) producing an intermediate object from a polymerizable liquid that includes heat expandable microspheres by additive manufacturing; (b) optionally, cleaning the intermediate object; and (c) moisture curing the intermediate object to form the three-dimensional object, said moisture curing performed before or after heating the object for a time and at a temperature sufficient to expand the microspheres. Objects produced by the methods are also provided.

Description

[0001] Attorney Docket No. 1151.256. WO

[0002] PRODUCTION OF LOW-DENSITY PRODUCTS USING

[0003] MOISTURE CURABLE RESINS

[0004] Cross-reference to Related Applications

[0005] This application claims the benefit of U.S. Provisional Application No. 63 / 696,048, filed September 18, 2024, the disclosure of which is hereby incorporated by reference in its entirety.

[0006] Field of the Invention

[0007] The present invention concerns methods of additive manufacturing and objects made from such methods.

[0008] Background of the Invention

[0009] A group of additive manufacturing techniques sometimes referred to as "stereolithography" create a three-dimensional object by the sequential polymerization of a light polymerizable resin. Such techniques may be "bottom-up" techniques, where light is projected into the resin onto the bottom of the growing object through a light transmissive window, or "top-down" techniques, where light is projected onto the resin on top of the growing object, which is then immersed downward into the pool of resin.

[0010] The introduction of a more rapid stereolithography technique known as continuous liquid interface production (CLIP), coupled with the introduction of "dual cure" resins for additive manufacturing, has expanded the usefulness of stereolithography from prototyping to manufacturing. See, e.g, U.S. Patent Nos. 9,211,678, 9,205,601, 9,216,546, 9,676,963, 9,453,142, and 9,598,606; and J. Tumbleston, D. Shirvanyants, N. Ermoshkin et al., Continuous liquid interface production of 3D Objects, Science 347, 1349-1352 (2015).

[0011] Additive manufacturing using dual cure moisture cure chemistry has been shown to produce high performance parts with one-part resins. See, e.g., U.S. Publication No. 2023 / 0095658 Al. However, producing bright white colored parts that are resistant to discoloration from aging (UV, thermal, etc.) or contact with chemicals (stain resistance) has been challenging for certain additive manufacturing resins, particularly for elastomers. Additionally, although foaming of dual-cured parts has been demonstrated previously with Attorney Docket No. 1151.256. WO thermal cure only (see, e.g., U.S. Publication No. 2022 / 0118689 Al) such processes did not show the significant whitening effects, and the reduction in density was modest.

[0012] Accordingly, new methods and processes for producing lower density and / or stain resistant parts are desirable.

[0013] Summary of the Invention

[0014] Provided according to embodiments of the invention are methods of making a three- dimensional object that include (a) producing an intermediate object from a polymerizable liquid that includes heat expandable microspheres by additive manufacturing (e.g., by bottom- up stereolithography, such as by continuous liquid interface production); (b) optionally, cleaning the intermediate object (e.g., by washing, spinning, etc.); and (c) moisture curing the intermediate object to form the three-dimensional object, said moisture curing performed before or after heating the object for a time and at a temperature sufficient to expand the microspheres.

[0015] In some embodiments of the invention, the moisture curing of the intermediate object is performed before the expansion of the microspheres. For example, in some embodiments, step (c) includes (i) exposing the intermediate to moisture (e.g., at about 90%, about 95%, or more humidity) at a temperature wherein the microspheres are substantially unexpanded and for a time sufficient to moisture cure the object and form a moisture cured object; and then (ii) heating and / or microwave irradiating the moisture cured object for a time and at a temperature sufficient to expand the microspheres.

[0016] In some embodiments, the polymerizable liquid includes (i) at least one reactive blocked prepolymer (e.g., in an amount of from about 1% or about 5% by weight to about 60%, about 70%, about 80%, about 90%, or about 98% by weight); (ii) a photoinitiator (e.g., in an amount of from about 0.05% to about 10% by weight); (iii) heat expandable microspheres (e.g., in an amount of from about 1% or about 2% by weight to about 5%, about 10%, about 20%, about 30%, or about 35% by weight); and (iv) optionally, a reactive diluent, non-reactive diluent, water, and / or crosslinker.

[0017] In some embodiments, the at least one reactive blocked prepolymer is photopolymerized to form the intermediate object; the temperature at which moisture curing occurs is sufficient to degrade the intermediate object to form unblocked prepolymer; and the unblocked prepolymer reacts with water to form the moisture cured intermediate object.

[0018] In some embodiments, the reactive blocked prepolymer is a reactive blocked polyisocyanate, optionally wherein the reactive blocked polyisocyanate comprises the reaction Attorney Docket No. 1151.256. WO product of a polyisocyanate and an amine or hydroxyl (meth)acrylate or meth(acrylamide) blocking agent. In some embodiments, the temperature at which moisture curing occurs is sufficient to degrade the intermediate object to form unblocked polyisocyanate, and the unblocked polyisocyanate reacts with water to generate a polyamine in situ, wherein the polyamine reacts with additional unblocked polyisocyanate to form urea linkages.

[0019] In some embodiments, the reactive blocked prepolymer is a reactive blocked polysiloxane.

[0020] In some embodiments, the heat expandable microspheres comprise a partially or completely hollow thermally expandable shell (e.g., a thermoplastic polymer shell), and a propellant (e.g., a low-boiling point liquid or liquified gas such as a lower alkane) contained in the shell.

[0021] In some embodiments, the microspheres have an expansion start temperature in a range of 90 °C to 140 °C (e.g., 100 °C to 135 °C) and / or a maximum expansion temperature (Tmax) in a range of 120 °C to 220 °C (e.g., 160 °C to 205 °C).

[0022] In some embodiments, the polymerizable liquid is devoid of free amine (or devoid of a primary or secondary amine).

[0023] In some embodiments, a volume of the three-dimensional object is at least 30%, 50%, 75%, 100%, or 125% greater than a volume of the intermediate object and / or the three- dimensional object has a dimensional increase of at least 5%, 10%, 15%, 20%, 30% relative to the intermediate object.

[0024] In some embodiments, the three-dimensional object is comprised of polyurea, polyurethane, silicone, and / or epoxy.

[0025] In some embodiments, the three-dimensional object is rigid, flexible, or elastic.

[0026] In some embodiments, the three-dimensional object comprises a polyurethane and / or polyurea and has an elongation at break of greater than 300%.

[0027] In some embodiments, the intermediate object is moisture cured at a temperature in a range of from 50 °C to 150 °C; and the heating and / or microwave irradiating of the moisture cured object to expand the microspheres is performed at a temperature in a range of from 110 °C to 220 °C.

[0028] In some embodiments, the intermediate object is exposed to moisture at a temperature in a range of from 50 °C to 100 °C (e.g, for a time in a range of 1 or 2 hours to 5, 8, 10, 12, 15, or 18 hours), optionally at a temperature in a range of from 70 °C to 100 °C.

[0029] In some embodiments, the microspheres are present in the polymerizable liquid at a concentration in a range of 1 or 2 percent by weight to 35% by weight (e.g, 1 to 10 or 15 Attorney Docket No. 1151.256. WO percent by weight), optionally wherein the microspheres have an average particle diameter before expansion in a range of 1 pm to 100 pm (and optionally expand upon heating by 2-10 times in diameter and / or 50 to 1000 times in volume).

[0030] In some embodiments, the three-dimensional object comprises a cushion, shock absorber, thermal insulator, or electric insulator.

[0031] In some embodiments, the three-dimensional object comprises a regular or irregular open-cell lattice.

[0032] Objects formed by a method of the invention are also provided herein.

[0033] Detailed Description of Illustrative Embodiments

[0034] The present invention is now described more fully hereinafter with reference to particular 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 the 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.

[0036] 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.

[0037] As used herein, the term “and / or” includes any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative (“or”).

[0038] 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 Attorney Docket No. 1151.256. WO 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.

[0039] It will be understood that, although the terms first, second, etc. (or the use of “additional”) may be used herein to describe various elements or components, these elements and components should not be limited by these terms. Rather, these terms are only used to distinguish one element or component from another element or component. Thus, a first element or component could be termed a second element or component without departing from the teachings of the present invention.

[0040] All publications and patents cited herein are specifically incorporated by reference to disclose the methods and / or materials with which the documents are cited.

[0041] 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.

[0042] Provided according to embodiments of the present invention are methods of making a three-dimensional object that include: (a) producing an intermediate object from a polymerizable liquid comprising heat expandable microspheres by additive manufacturing; (b) optionally, cleaning the intermediate object; and (c) moisture curing the intermediate object to form the three-dimensional object before or after heating the object for a time and at a temperature sufficient to expand the microspheres.

[0043] In some embodiments, the moisture curing of the intermediate object is performed before the expansion of the microspheres. For example, in some embodiments, the intermediate is first exposed to moisture (e.g. , at 90%, 95%, 98% or more humidity) at a temperature wherein the microspheres are substantially unexpanded and for a time sufficient to moisture cure the object. Then, the moisture cured intermediate is heated and / or microwave irradiated for a time and at a temperature sufficient to expand the microspheres. In particular embodiments, an additional heating step may be included to remove residual moisture or other volatile compounds in the resin composition. For example, this heating step may be performed after moisture curing but before expansion of the microspheres. However, this moisture / volatile removal step could also or alternatively be performed after expansion of the microspheres. In certain embodiments, the moisture cured (but not yet expanded) object may be placed onto a conveyor belt having controlled heat zones so that microsphere expansion can be more closely controlled. Heat control of the microsphere expansion may include both controlled heating and Attorney Docket No. 1151.256. WO controlled cooling to provide desired expansion and polymer properties. The conveyor speed may also be adjusted to account for any lot-to-lot variation to hit the same expansion target.

[0044] In other embodiments, moisture curing of the intermediate object is performed before and / or during the expansion of the microspheres. For example, in some embodiments, the intermediate is first heated and / or microwave irradiated for a time and at a temperature sufficient to expand or substantially expand the microspheres. Then, the intermediate may be exposed to moisture (e.g., at 90%, 95%, 98% or more humidity) for a time and at a temperature sufficient to moisture cure the intermediate. Again, an additional heating step may be included before and / or after moisture curing to remove moisture and / or other volatiles in the resin composition.

[0045] As used herein, “substantially unexpanded” means that (a) the microspheres have, on average, substantially the same (e.g., within 10%) diameter as at room temperature; and / or (b) are exposed to a temperature that is below their expansion start temperature, the temperature at which they begin to expand.

[0046] In the present invention, by using heat expandable microspheres in combination with moisture curing, the color of a three-dimensional object has shown to be significantly whitened and the object is more resistant to discoloration. Additionally, the part’s density may be significantly reduced, which can potentially lower the resin usage for the same part or provide the ability to make larger final parts and / or result in reduced print times. The present inventors have unexpectedly discovered that expansion of the microspheres before or after moisture curing not only is possible but affects the properties in the final formed object.

[0047] Additive Manufacturing Processes

[0048] Polymerizable liquids or resins as described herein may be used to make three- dimensional objects in an additive manufacturing process that generates a "green" or intermediate object using a first curing process (e.g., curing with UV light), followed by moisture curing of that intermediate object to form the three-dimensional object.

[0049] Techniques for additive manufacturing are known and the invention is not limited to a particular type. However, suitable techniques include bottom-up or top-down additive manufacturing, generally known as stereolithography. Such methods are known and described in, for example, U.S. Patent No. 5,236,637 to Hull, U.S. Patent Nos. 5,391,072 and 5,529,473 to Lawton, U.S. Patent No. 7,438,846 to John, U.S. 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 U.S. Patent Application Publication No. 2013 / 0295212 to Chen et al. Attorney Docket No. 1151.256. WO

[0050] In particular embodiments, the intermediate object is formed by a continuous liquid interface production (CLIP) process. CLIP is known and described in, for example, U.S. Patent No. 9,211,678, U.S. Patent No. 9,205,601, U.S. Patent No. 9,216,546, and in J. Tumbleston, D. Shirvanyants, N. Ermoshkin et al., Continuous liquid interface production of 3D Objects, Science 347, 1349-1352 (2015). See also R. Janusziewcz 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 polymerizable liquid in partially-cured form.

[0051] In some embodiments of CLIP, the optically transparent member comprises a semipermeable 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. 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 L. Robeson et al., WO Publication No. 2015 / 164234), generating oxygen as an inhibitor by electrolysis (see I. Craven et al., WO Publication No. 2016 / 133759), and incorporating magnetically positionable particles to which the photoactivator is coupled into the polymerizable liquid (see J. Rolland, WO Publication No. 2016 / 145182).

[0052] Other examples of methods and apparatus for carrying out particular embodiments of CLIP include but are not limited to U.S. Patent No. 10,384,439; U.S. Patent Application Pub. No. US 2016 / 0288376; U.S. Patent No. 9,782,934; U.S. Patent No. 10,073,424; U.S. Patent No. 10,118,377; U.S. Publication No. 2018 / 0243976; U.S. Patent No. 11,117,316; and U.S. Patent No. 10,213,956.

[0053] Polymerizable Liquids (Resins)

[0054] The polymerizable liquids of the invention include (i) at least one reactive blocked prepolymer; (ii) at least one photoinitiator; and (iii) heat expandable microspheres. Further, Attorney Docket No. 1151.256. WO additional optional additives, including but not limited to, reactive diluents, crosslinkers, non- reactive diluents, UV absorbers, pigments, dyes, antioxidants, plasticizers, fillers, radical inhibitors, and thermal inhibitors, may also be present in the polymerizable liquid.

[0055] The polymerizable liquids of the present invention (which may also be referred to as “polymer resins” or “resins”) include one or more components that are first cured by actinic radiation or light (e.g., UV light) during an additive manufacturing process to form an intermediate object; and include one or more components, the same component that is cured by actinic radiation or light and / or different component(s), that cure by exposure to moisture to form a final three-dimensional object. The second curing process may be facilitated by using heat to deblock the reactive blocked prepolymer, and optionally, to expand the heat expandable microspheres, but the curing of the intermediate object to form the final three-dimensional object is achieved by moisture curing. In general, the polymerizable liquid is a one-part (IK) resin, but in some embodiments, the polymerizable liquid may be a two-part (2K) resin.

[0056] Reactive Blocked Prepolymers

[0057] Many different possible reactive blocked prepolymers may be used in embodiments of the invention, and combinations of different reactive blocked prepolymers may also be used. In general, the reactive blocked prepolymer includes a prepolymer that is blocked by a functional group that reacts (e.g., polymerizes) upon exposure to actinic radiation or light (e.g., UV light exposure during additive manufacturing). The prepolymer is any oligomer or polymer (e.g., having a molecular weight in a range of 500 g / mL to 50,000 g / L, in some embodiments, in a range of 500 g / mL to 5,000 g / mL) that can react with water when the reactive blocking group is removed / unblocked. In some embodiments, the prepolymer includes a polyisocyanate, a polyurethane, a polyurea, a polyether, a polysiloxane, or any combination thereof. In particular embodiments, the prepolymer has one or more isocyanate end groups that are blocked by a reactive blocking group. In some embodiments, when unblocked, a portion of such isocyanate groups may then react with water to form a primary amine, which may then react with other isocyanate groups to form a urea linkage.

[0058] In some embodiments of the invention, the reactive blocked prepolymer includes a polyisocyanate oligomer produced by the reaction of at least two diisocyanates with at least one polyol (e.g., a polyether or polyester or polybutadiene diol). “Diisocyanate” and “polyisocyanate” are used interchangeably herein and refer to aliphatic, cycloaliphatic, and aromatic isocyanates that have at least 2, or in some embodiments more than 2, isocyanate (NCO) groups per molecule, on average. In some embodiments, the isocyanates have, on Attorney Docket No. 1151.256. WO average, 3 to 6, 8 or 10 or more isocyanate groups per molecule. Examples of suitable isocyanates include, but are not limited to, methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI)), para-phenyl diisocyanate (PPDI), 4,4'-dicyclohexylmethane-diisocyanate (HMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), triphenylmethane-4,4'4"-triisocyanate, toluene-2,4,6-triyl triisocyanate, l,3,5-triazine-2,4,6- triisocyanate, ethyl ester L-lysine triisocyanate, including combinations thereof. Numerous additional examples are known and are described in, for example, U.S. Pat. Nos. 9,200,108; 8,378,053; 7,144,955; 4,075,151, 3,932,342, and in US Patent Application Publication Nos. US 20040067318 and US 20140371406. Examples of polyisocyanates include Lupranate® series by BASF (Ludwigshafen, Germany), Adiprene® series by Lanxess (Cologne, Germany) Desmodur® series by Covestro (Leverkusen, Germany), Imuthane® series by COIM (Offanengo, Italy), and Ongronat® series by BorsodChem (Kazincbarcika, Hungary).

[0059] Reactive blocking groups are known in the art and include, but are not limited to, those formed from an amine (meth)acrylate monomer blocking agent (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., U.S. Patent Application Publication No. 20130202392)), alcohol (meth)acrylate blocking agents, maleimide blocking agents, and n-vinylformamide blocking agents.

[0060] Examples of known blocking agents which can be substituted on or covalently coupled to (meth)acrylate or maleimide to form reactive blocking groups include, but are not limited to, phenol type blocking agents (e.g., phenol, cresol, xylenol, nitrophenol, chlorophenol, ethyl phenol, t-butylphenol, hydroxy benzoic acid, hydroxy benzoic acid esters, 2,5-di-t-butyl-4- hydroxy toluene), lactam type blocking agents (e.g., 8-caprolactam, 5-valerolactam, y- butyrolactam, P-propiolactam), active methylene type blocking agents (e.g., diethyl mal onate, dimethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetyl acetone, and the like), alcohol type blocking agents (e.g., methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, n-amyl alcohol, t-amyl alcohol, lauryl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, methoxyethanol, glycolic acid, glycolic acid esters, lactic acid, lactic acid ester, methylol urea, methylol melamine, diacetone alcohol, ethylene chlorohydrine, ethylene bromhydrine, l,3-dichloro-2-propanol, co-hydroperfluoro alcohol, acetocyanhydrine), mercaptan type blocking agents (e.g., butyl mercaptan, hexyl mercaptan, t-butyl mercaptan, t- Attorney Docket No. 1151.256. WO dodecyl mercaptan, 2-mercapto-benzothiazole, thiophenol, methyl thiophenol, ethyl thiophenyl), acid amide type blocking agents (e.g., acetoanilide, acetoanisidine amide, acrylamide, methacrylamide, acetic amide, stearic amide, benzamide), imide type blocking agents (e.g., succinimide, phthalimide, mal eimide), amine type blocking agents (e.g., diphenylamine, phenylnaphthylamine, xylidine, N-phenyl xylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, butyl phenylamine), imidazole type blocking agents (e.g., imidazole, 2-ethylimidazole), urea type blocking agents (e.g., urea, thiourea, ethylene urea, ethylene thiourea, 1,3 -diphenyl urea), carbamate type blocking agents (e.g., N-phenyl carbamic acid phenyl ester, 2-oxazolidone), imine type blocking agents (e.g., ethylene imine, etc.), oxime type blocking agents (e.g., formaldoxime, acetaldoximine, acetoxime, methylethyl ketoxime, diacetylomonoxime, benzophenoxime, cyclohexanonoxime) and sulfurous acid salt type blocking agents (e.g., sodium bisulfite, potassium bisulfite).

[0061] Reactive blocked prepolymers that may be used in some embodiments of the invention include but are not limited to those described in U.S. Patent Nos. 9,453,142, 11,299,579, and 9,982,164.

[0062] In particular embodiments, the reactive blocked prepolymer is a reactive blocked polyisocyanate, optionally wherein the reactive blocked polyisocyanate comprises the reaction product of a polyisocyanate and an amine or hydroxyl (meth)acrylate or meth(acrylamide) blocking agent.

[0063] In some embodiments, the reactive blocked prepolymer comprises polysiloxane linkages, and when the reactive blocked prepolymer is deblocked, the polysiloxane prepolymer undergoes a condensation reaction to form the three-dimensional object.

[0064] The amount of the reactive blocked prepolymer(s) in the polymerizable liquid may vary depending on the end use of the three-dimensional object being formed. However, in some embodiments, the reactive blocked prepolymer is present in the polymerizable liquid at a concentration of from about 1%, about 5%, or about 10% by weight to about 50%, about 60%, about 70%, about 80%, about 90%, or about 98% by weight. In some embodiments, the reactive blocked prepolymer is about 1%, about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 98% weight percent, or a range defined between any two of the foregoing values, of the polymerizable liquid. Attorney Docket No. 1151.256. WO

[0065] Photoinitiators

[0066] Any suitable photoinitiator may be included in the polymerizable liquids of the present invention. In some embodiments, the photoinitiator is a free radical photoinitiator. “Free radical photoinitiator” as used herein includes type I free radical photoinitiators, such as phosphineoxide (TPO) or hydroxyacetophenone (HAP), and / or type II free radical photoinitiators, such as a benzophenone photoinitiator (optionally but preferably in combination with a co-initiator (e.g., an alcohol or amine)). Particular examples include, but are not limited to, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), diphenylphosphinyl(2,4,6-trimethylphenyl)methanone; benzophenone; substituted benzophenones; acetophenone; substituted acetophenones; benzoin; benzoin alkyl esters; xanthone; substituted xanthones; diethoxy-acetophenone; benzoin methyl ether; benzoin ethyl ether; benzoin isopropyl ether; diethoxyxanthone; chloro-thio-xanthone; N-methyl diethanol- amine-benzophenone; 2-hydroxy-2-m ethyl- 1 -phenyl-propan- 1 -one; 2-benzyl-2-

[0067] (dimethylamino)- 1 -[4-(4-morpholinyl)phenyl]-l -butanone; 2-isopropylthi oxanthone (ITX); and mixtures thereof. See, e.g., U.S. Pat. No. 9,090,765 for additional photoinitiator examples.

[0068] The amount of photoinitiator in the polymerizable liquid may vary, but in some embodiments of the invention, the photoinitiator is present in the polymerizable liquid at a concentration of from about 0.05% to about 10% by weight, including about 0.05%, about 0.1%, about 0.5%, about 1%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10% by weight, or a range defined between any two of the foregoing values.

[0069] Heat Expandable Microspheres

[0070] As used herein, the term “heat expandable microsphere” (sometimes referred to as a microballoon, polymeric microsphere, or hollow microbead) refers to a polymer shell (e.g., an elastic and / or thermoplastic polymer shell) having a void space therein that includes a core material (propellant) in the form of a gas, liquid or combination thereof that expands upon heating. The heat expandable microspheres are typically in the micro size range (about 1 pm to about 100 pm) but may in some embodiments be smaller (e.g., about 500 nm to about 1 pm) or larger (about 100 pm to 500 pm) prior to heat expansion. In some embodiments, the polymer shell of the heat expandable microspheres expands without breaking. However, in some embodiments, some or all of the expandable microspheres may break or burst upon expansion. Heat expandable microspheres are typically approximately spherical hollow bodies but may be other shapes and may, in some embodiments, not be entirely hollow and so may be considered Attorney Docket No. 1151.256. WO partially hollow. In some embodiments, upon heating, the heat expandable microspheres expand so that the diameter is increased by at least 2-10 times and / or the volume is increased by at least 50-fold to 1000-fold. Examples of heat expandable microspheres include but at not limited to those described in U.S. Patent Nos. 10,030,115, 10,023,712, 9,902,829, 9,062,170, 8,388,809, 10,029,550, and 3,615,972. See also U.S. Patent No. 11,292,186 to Poelma et al.

[0071] The propellant in the core of the heat expandable microspheres is typically a low- boiling liquid (e.g., a liquid with a boiling point at standard pressure of less than 75 °C, 100 °C, 120 °C, 140 °C, 160 °C, or 200 °C) or with liquefied gas. In some embodiments, the core includes a lower alkane hydrocarbon (C1-C6), for example isobutane and / or isopentane, which are enclosed as liquefied gas under pressure in the polymer shell. The polymer shell is generally formed of a polymer that can expand under the pressure of the encapsulated propellant. In some embodiments, the polymer shell of the heat expandable microsphere includes a polyacrylonitrile, polyvinyl dichloride (PVDC), polyvinyl chloride (PVC), a polyamide and / or a polyacrylate.

[0072] In some embodiments, action on the microspheres — more particularly by supply of heat or generation of heat, as for example by ultra-sound or microwave radiation — causes, first, a softening of the outer polymer shell, while at the same time the liquid blowing gas present in the shell undergoes transitions of its gaseous state. At a particular pairing of pressure and temperature the microspheres undergo irreversible expansion and expand three-dimensionally. The expansion ends when the internal pressure equals the external pressure. Since the polymeric shell is maintained, a closed-celled foam may be achieved in this way.

[0073] A large number of types of microspheres are available commercially, such as, for example, from Nouryon (Amsterdam, Netherlands), the EXPANCEL® DU (dry unexpanded) products, which differ essentially in their size (6 to 45 pm in diameter in the unexpanded state) and in the starting temperature they require for expansion (75 °C to 220 °C). Another example is Advanced® Microspheres from Sekisui Specialty Chemicals (Osaka, Japan).

[0074] Unexpanded types of microballoons are also available in the form of an aqueous dispersion (e.g., with a solids fraction or microballoon fraction of around 40% to 45% by weight), and also in the form of polymer-bound microballoons (masterbatches), for example in ethylene-vinyl acetate (e.g., with a microballoon concentration of around 65% by weight). Obtainable, furthermore, are what are called microballoon slurry systems, in which the microballoons are present in the form of an aqueous dispersion (e.g., with a solids fraction of 60% to 80% by weight). The microballoon dispersions, the microballoon slurries, and the masterbatches, like the DU products, can be used in the process described herein. Attorney Docket No. 1151.256. WO

[0075] The concentration of the heat expandable microspheres in the polymerizable liquid may vary depending on the three-dimensional object and its end use. However, in some embodiments, the heat expandable microspheres are present in the polymerizable liquid at a concentration in a range of about 1% or about 2% by weight to about 35% by weight (e.g., about 1%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35% by weight, or a range defined between any two of the foregoing values).

[0076] In some embodiments, the microspheres have an expansion start temperature in a range of 90 °C to 140 °C (e.g., 100 °C to 135 °C) and / or a maximum expansion temperature (Tmax) in a range of 120 °C to 220 °C (e.g., 160 °C to 205°C).

[0077] Additional Components

[0078] The polymerizable liquid may include a number of additional components depending on the three-dimensional object being made and its intended use. In some embodiments, the polymerizable liquid includes at least one additional component, including but not limited to, a reactive diluent, a non-reactive diluent, a crosslinker, a UV absorber (e.g., a pigment and / or dye), an antioxidant, a plasticizer, a filler, a radical inhibitor, and / or a thermal inhibitor.

[0079] In some embodiments, the polymerizable liquid includes at least one reactive diluent. Suitable examples of reactive diluents include, but are not limited to, a (meth)acrylate (e.g., isobornyl methacrylate, PEG methacrylate), / A-dimethylacrylamide, A-vinyl-2-pyrrolidone, and TV- vinyl formamide, or a mixture of two or more thereof. In some embodiments, the reactive diluent is present in the resin in an amount sufficient to reduce the viscosity to not more than 15,000, 10,000, 6,000, 5,000, 4,000, or 3,000 centipoise at 25 °C. In some embodiments, the reactive diluent is present in the polymerizable liquid at a concentration in a range of from about 1%, about 5%, or about 10% by weight to about 30%, about 40%, or about 50% by weight (e.g., about 1%, about 2%, about 3%, about 4%, about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50% by weight, or a range defined between any two of the foregoing values).

[0080] In some embodiments, the polymerizable liquid includes a non-reactive diluent. Non- reactive diluents that may be useful are, in general, organic liquids that can be polar or nonpolar, and protic or aprotic. In particular embodiments, the non-reactive diluent comprises an alkane (e.g., a C7-C15 alkane) and / or a volatile silicone diluent, and / or an acetate (e.g., a C3-C25 acetate such as di(propylene glycol)methyl ether acetate and diisononyl adipate). The non-reactive diluents are preferably non-flammable, non-hygroscopic, low odor, and low Attorney Docket No. 1151.256. WO viscosity. In some embodiments, the non-reactive diluent has an autoignition temperature greater than about 300 °C, greater than about 400 °C, or greater than about 600 °C (z.e., as measured in accordance with the procedure described in ASTM E659). In some embodiments, the non-reactive diluent has a flash point of greater than about 50 °C, greater than about 80 °C, greater than about 100 °C, or greater than about 140 °C as measured by the Pensky -Martens closed cup method (e.g., ASTM D93, EN ISO 2719, or IP 34). In some embodiments, the non- reactive diluent may be volatile (e.g., evaporates during the heating and / or moisture curing steps described herein). In some embodiments, the non-reactive diluent may act as a plasticizer.

[0081] In some embodiments, the non-reactive diluent is present in the polymerizable liquid at a concentration in a range from about 5% by weight to about 50% by weight, including in an amount of about 5% by weight to about 20% by weight. In some embodiments, the non-reactive diluent is included in the resin composition in an amount of from about 1% or about 5% by weight to about 10%, about 15% or about 20% by weight (e.g., about 1%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19% and about 20% by weight, or a range defined between any two of the foregoing values).

[0082] In some embodiments, the polymerizable liquid includes a crosslinking agent (e.g., a monomer having two or more reactive functional groups). Examples include but are not limited to polyol poly(meth)acrylates, including diol di(meth)acrylates (e.g., glycol poly (meth)acrylates such as PEG dimethacrylate and trimethylolpropane tri(meth)acrylate (TMPTA or TMPTMA)). The presence and concentration of the crosslinker may vary according to the three-dimensional part being produced and its end use. However, in some embodiments, a crosslinker is included in the polymerizable liquid in an amount of about 1% to about 20% by weight (e.g., about 1%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19% and about 20% by weight, or a range defined between any two of the foregoing values).

[0083] In some embodiments, the polymerizable liquid includes a non-reactive pigment or dye that absorbs and / or scatters light, particularly UV light. Suitable examples of such light absorbers and / or scatterers include, but are not limited to: (i) titanium dioxide (e.g., included in an amount of from about 0.001% or about 0.1% to about 1% or about 5% by weight), (ii) carbon black (e.g., included in an amount of from about 0.001% or about 0.1% to about 1% or about 5% by weight), and / or (iii) an organic ultraviolet light absorber such as a hydroxybenzophenone, hydroxyphenylbenzotriazole, oxanilide, benzophenone, thioxanthone, Attorney Docket No. 1151.256. WO hydroxyphenyltriazine, benzotriazole ultraviolet light absorber (e.g., Mayzo BLS® 1326), and / or bis(l,2,2,6,6-pentamethyl-4-piperidinyl)sebacate (Tinuvin 765, BASF), hydroxyphenyl-triazine (HPT)n and the like. Examples of suitable organic ultraviolet light absorbers include, but are not limited to, those described in U.S. Patent Nos. 3,213,058, 6,916,867, 7,157,586, and 7,695,643. The amount of such light absorbers may vary but, in some embodiments, the polymerizable liquid includes a non-reactive pigment or dye that absorbs light at a concentration in a range of about 0.001% or about 0.005% to about 1%, about 2% or about 4% percent by weight.

[0084] In some embodiments, the polymerizable liquid includes an antioxidant. A number of possible antioxidants may be used. Examples of antioxidants include, but are not limited to, phenols, hindered phenols (e.g., Irganox 245 by BASF), phosphites, thiosynergists, and combinations thereof (available, for example, from Mayzo, Suwanee, Georgia, U.S.A.). The amount of antioxidant may vary but, in some embodiments, the polymerizable liquid includes an antioxidant at a concentration in a range of about 0.001% or about 0.005% to about 1% or about 2% percent by weight.

[0085] In some embodiments of the invention, the polymerizable liquid may include a filler. A number of possible fillers may be used, including, but not limited to, tougheners and / or coreshell rubbers. 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 two or more of the foregoing. Suitable fillers include tougheners, such as core-shell rubbers, as discussed below. In some embodiments, the filler is a hydrophobic or hydrophilic fumed or precipitated silica, titanium dioxide, or carbon black, and may be present in the composition at a concentration of about 5 wt% to about 30 wt% (e.g., about 10 wt% to about 20 wt %).

[0086] 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 Attorney Docket No. 1151.256. WO

[0087] (POSS), carbonaceous materials e.g., carbon black, carbon nanotubes, carbon nanofibers, fullerenes), ceramics and silicon carbides, with or without surface modification or functionalization.

[0088] 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. 2015 / 0184039, as well as US Patent Application Publication No. 2015 / 0240113, and U.S. 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 (Osaka, Japan) 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 of two or more thereof.

[0089] The resin composition may include other solid particles suspended or dispersed therein. 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 about 1 nm to about 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.

[0090] Resin compositions of the invention may optionally have other ingredients solubilized therein, including active compounds or pharmaceutical compounds, detectable compounds (e.g., fluorescent, phosphorescent, radioactive), 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. Attorney Docket No. 1151.256. WO

[0091] In some embodiments, the liquid may include a deoxygenating compound as an accelerator of stereolithography (particularly CLIP). An example of an accelerator is triphenylphosphine.

[0092] In some embodiments, the polymerizable liquid is devoid or substantially devoid of free amines (e.g., substantially devoid of primary and / or secondary amines). As used herein, “substantially devoid” refers to compositions with less than 5%, less than 4%, less than 3%, less than 2%, or less than 1% of a primary and / or secondary amine. The lack of such free amines may render the intermediate object more stable and facilitate processing during the moisture cure process.

[0093] In some embodiments of the invention, the polymerizable liquid includes water. The inclusion of the water during the printing process may be desirable for the further curing with moisture. In particular embodiments, the polymerizable liquid includes water at a concentration of about 0.2 to about 5 weight percent.

[0094] Optional Cleaning and / or Washing

[0095] As described above, intermediate objects may optionally be cleaned and / or washed prior to moisture curing to form the three-dimensional object. In doing so, the intermediate object may be cleaned or washed in any suitable apparatus. In some embodiments, the intermediate object is washed with a wash liquid as described herein, and additionally or alternatively, in some embodiments, the intermediate object may be cleaned by wiping (with an absorbent, air blade, etc.), spinning, or variations thereof. In some embodiments, cleaning the intermediate object includes removing excess resin therefrom.

[0096] Wash liquids that may be used to carry out the present invention include, but are not limited to, water, organic solvents, and combinations thereof (e.g., combined as co-solvents), optionally containing additional ingredients such as surfactants, chelants (ligands), enzymes, borax, dyes or colorants, fragrances, etc., including combinations thereof. The wash liquid may be in any suitable form, such as a solution, emulsion, dispersion, etc. In some preferred embodiments, where the residual resin has a boiling point of at least 90 or 100 °C (e.g., up to 250 °C or 300 °C, or more), the wash liquid has a boiling point of at least 30 °C, but not more than 80 °C or 90 °C. Boiling points are given herein for a standard pressure of 1 bar or 1 atmosphere.

[0097] In some embodiments, the wash liquid consists of a 50:50 (volume: volume) solution of water and an alcohol organic solvent such as isopropanol (2-propanol). Attorney Docket No. 1151.256. WO

[0098] In some embodiments, a hydrofluorcarbon solvent may be used. Examples of hydrofluorocarbon solvents include, but are not limited to, 1, 1,1, 2, 3, 4, 4, 5,5,5- decafluoropentane (Vertrel® XF, DuPont™ Chemours, Wilmington, Delaware,

[0099] U.S.A.), 1,1,1,3,3-pentafluoropropane, 1,1,1,3,3-pentafluorobutane, 3, 3 -Diehl oro-1, 1,1, 2,2- pentafluoropropane, 1 ,3 -Dichloro- 1 , 1 ,2,2,3 -pentafluoropropane, 1 , 1 -Dichloro- 1 - fluoroethane, and mixtures thereof.

[0100] Examples of hydrofluoroether solvents that may be used to wash the intermediate object include, but are not limited to, methyl nonafluorobutyl ether (HFE-7100), methyl nonafluoroisobutyl ether (HFE-7100), ethyl nonafluorobutyl ether (HFE-7200), ethyl nonafluoroisobutyl ether (HFE-7200), l,l,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, etc., including mixtures thereof. Commercially available examples of this solvent include 3M™ Novec™ 7100 and 3M™ Novec™ 7200 (3M, Maplewood, Minnesota, U.S.A.).

[0101] Examples of volatile methyl siloxane solvents that may be used to wash the intermediate object include, but are not limited to, hexamethyldisiloxane (OS- 10, Dow Corning, Midland, Michigan), octamethyltrisiloxane (OS-20, Dow Corning), decamethyltetrasiloxane (OS-30, Dow Corning), etc., including mixtures thereof. Other siloxane solvents (e.g., NAVSOLVE® solvent, Ecolink, Tucker, Georgia, U.S.A.) that may be used to wash the intermediate object include but are not limited to those set forth in US Patent No. 7,897,558.

[0102] In some embodiments, the wash liquid comprises an azeotropic mixture comprising, consisting of, or consisting essentially of a first organic solvent (e.g., a hydrofluorocarbon solvent, a hydrochlorofluorocarbon solvent, a hydrofluoroether solvent, a methylsiloxane solvent, or a combination thereof; e.g. in an amount of from 80 or 85 to 99 percent by weight) and a second organic solvent (e.g, a C1-C4 or C6 alcohol such as methanol, ethanol, isopropanol, tert-butanol, etc.; e.g, in an amount of from 1 to 15 or 20 percent by weight). Additional ingredients such as surfactants or chelants may optionally be included. In some embodiments, the azeotropic wash liquid may provide superior cleaning properties, and / or enhanced recyclability, of the wash liquid. Additional examples of suitable azeotropic wash liquids include, but are not limited to, those set forth in U.S. Patent Nos. 6,008,179; 6,426,327; 6,753,304; 6,288,018; 6,646,020; 6,699,829; 5,824,634; 5,196,137; 6,689,734; and 5,773,403, the disclosures of which are incorporated by reference herein in their entirety.

[0103] When the wash liquid includes ingredients that are not desired for carrying into the further curing step, in some embodiments, the initial wash with the wash liquid can be followed with a further rinsing step with a rinse liquid, such as water (e.g., distilled and / or deionized water), or a mixture of water and an alcohol such as isopropanol. Attorney Docket No. 1151.256. WO

[0104] In some embodiments, the intermediate object is spun in a spinning apparatus to remove excess resin and / or wash liquid prior to moisture curing. Suitable spinning apparatus include, but are not limited to, those described in U.S. Publication No. 2021 / 0394399 and U.S. Patent No. 11,491,725.

[0105] Moisture Curing of Intermediate Objects

[0106] In some embodiments of the present invention, the intermediate object(s) of the invention are substantially, predominantly, or completely moisture cured before the microspheres are expanded (or substantially expanded). For example, in some embodiments, more than 50%, 60%, 70%, 80%, 90%, 95%, 99%, or 99.9% (or any range between any two of the foregoing values) of the final polymer formation is completed before the microspheres are expanded.

[0107] While the intermediate object is cured with water to produce the three-dimensional object, the intermediate object may also be heated so that the reactive blocked prepolymer can be deblocked and / or the moisture curing process is otherwise facilitated. However, when moisture curing occurs prior to microsphere expansion, the microspheres remain substantially unexpanded at the temperature used to deblock the reactive blocked prepolymer and facilitate the moisture curing process.

[0108] In some embodiments, at least one reactive blocked prepolymer is photopolymerized to form the intermediate object, the intermediate object degrades on heating and / or microwave irradiation to form the unblocked prepolymer, and the unblocked prepolymer reacts with water to cure the intermediate object and form the three-dimensional object. In particular embodiments, the unblocked prepolymer reacts with water to generate a polyamine in situ that reacts with further unblocked prepolymer to form urea linkages and thereby form a three- dimensional object comprising polyurea. In some embodiments, the prepolymer is a reactive blocked polyisocyanate. In such embodiments, up to 50% of the unblocked polyisocyanate will react with water directly to generate an amine and such formed amines will then react with the remaining unblocked polyisocyanate to convert to the final polyurethane / urea.

[0109] The temperature at which moisture curing occurs may be varied based on the particular composition being used and whether expansion is to be performed after moisture curing, in which case, the expansion start temperature for the microspheres included therein may affect the moisture cure temperature. For example, in some embodiments, the intermediate object is exposed to moisture at a temperature in a range of 50 °C or 70 °C to 100 °C, 120 °C, or 150 °C (e.g., for a time in a range of 1 or 2 hours to 5, 8, 10, 12, 15, or 18 hours), optionally at a Attorney Docket No. 1151.256. WO temperature in a range of 70 °C to 100 °C. The application of water to the intermediate object may be varied, as well. However, in some embodiments, water is applied by placing the intermediate object in a humid environment (e.g., at least 50% humidity, 60% humidity, 70% humidity, 80% humidity, 90% humidity, 95% humidity, or 98% humidity). In some embodiments, the moisture cure process is performed in a steam autoclave or by using steam injection.

[0110] Expansion of the Heat Expandable Microspheres

[0111] The heat expansion of the microspheres is performed by heating and / or microwave irradiating the intermediate object for a time and at a temperature sufficient to expand said microspheres. The temperature at which microsphere expansion occurs may be varied based on the particular composition being used and the expansion start temperature for the microspheres included therein. In some embodiments, the three-dimensional object is heated to a temperature in a range of 110 °C or 120 °C to 150 °C, 170 °C, 180 °C, 200 °C, or 220 °C (e.g., for a time in a range of 5, 10, or 30 seconds to 2, 6, 8, 10, 12, 15, or 18 hours), optionally at a temperature in a range of 110 °C to 150 °C.

[0112] Heating for Moisture Curing, Moisture Removal and / or Microsphere Expansion

[0113] Heating may be performed by any suitable method, for example, by placing the object in an oven, such as an electric, gas, solar oven or microwave oven, placing the object in a heated bath, or combination thereof. In some embodiments, the heating step is carried out with at least a first (oven) temperature and a second (oven) temperature, with the first temperature greater than ambient temperature, the second temperature greater than the first temperature, and the second temperature less than 200 °C (e.g., with ramped or step-wise increases between ambient temperature and the first temperature, and / or between the first temperature and the second temperature).

[0114] In some embodiments, the heating step is carried out in an inert gas atmosphere. Inert atmosphere ovens are known, and generally employ an atmosphere enriched in nitrogen, argon, or carbon dioxide in the oven chamber. Suitable examples include but are not limited to those available from Grieve Corporation (Round Lake, Illinois, U.S.A.), Davron Technologies, (Chattanooga, Tennessee, U.S.A.), Despatch Thermal Processing Technology, (Minneapolis, Minnesota, U.S.A.), and others.

[0115] In other embodiments, the heating step is carried out in an inert liquid bath. Suitable inert liquids may be organic liquids (e.g., mineral oil, fluorinated, perfluorinated, and Attorney Docket No. 1151.256. WO polysiloxane organic compounds such as perfluorohexane, perfluoro(2-butyl- tetrahydrofurane), perfluorotripentylamine, etc. (commercially available as PERFLUORINERT® inert liquids from 3M Company)), and mixtures thereof. These inert liquids can be deoxygenated if necessary, such as by bubbling an inert gas such as nitrogen through the liquid, by boiling the inert liquid, by mixing oxygen-scavenging agents with the inert liquid medium (or contacting them to one another), etc., including combinations thereof (see, e.g., US Patent No. 5,506,007).

[0116] In some embodiments, the curing or heating step (whether carried out in a liquid or gas fluid) is carried out at an elevated pressure (e.g., elevated sufficiently to reduce volatilization or out-gassing of residual monomers, prepolymers, chain extenders, and / or reactive diluents, and / or increase the water vapor concentration). Suitable pressure ranges include, but are not limited to, from 10 or 15 psi to 70 or 100 psi, or more.

[0117] In some embodiments of the invention, after the moisture cure and expansion of the microspheres, a further dry (or reduced humidity) heating step may be desirable to remove residual moisture and / or volatiles in and / or on the three-dimensional object. While the time and temperature for this heating step may be varied, in some embodiments, this “dry bake” may be performed at a temperature in a range of 60 °C to 160 °C, or in a range of 100 °C to 130 °C (e.g., for a time in a range of about 10 minutes to about 24 hours).

[0118] Three-Dimensional Objects

[0119] As taught herein, heating to expand the microspheres after moisture cure produced unexpectedly desirable results. Using the methods of the invention, a volume of the three- dimensional object may be at least 30%, 50%, 75%, 100%, or 125% greater (or any range defined between any two of the foregoing values) than the volume of the intermediate object. In some embodiments, the three-dimensional object has a dimensional increase of at least 5%, 10%, 15%, 20%, or 30% relative to the intermediate object.

[0120] In some embodiments, the three-dimensional object shows minimal color change after UV aging, with ISO gray stain values that are 3 or greater (e.g., 4 or 5). In some embodiments, the ISO gray stain is determined using test ISO 105-A03.

[0121] The methods of the invention can be implemented for the production of any object by additive manufacturing. In some embodiments, the three-dimensional object includes polyurethane, polyurea, silicone, and / or epoxy. In some embodiments, the three-dimensional object is rigid, flexible, or elastic. In some embodiments, the three-dimensional object is a rigid Attorney Docket No. 1151.256. WO polyurethane and has an elongation at break of greater than 200%, greater than 250%, or greater than 300%.

[0122] In some embodiments, the three-dimensional object comprises a cushion, shock absorber, thermal insulator, or electric insulator. In some embodiments, the resins are useful for the production of low-k dielectric objects or electrical insulators, such as for use as packaging in the semiconductor industry. In some embodiments, the three-dimensional object comprises a regular or irregular open-cell lattice.

[0123] In some embodiments, the objects are made from a resin prone to shrinking, and the microspheres can be added to offset shrinking that may otherwise occur. In other embodiments, the objects can be additively produced at a smaller size than intended (e.g., to speed the additive manufacturing step), and then expanded to the intended final size during the moisture curing step.

[0124] In some embodiments, prior to the further curing step, the intermediate object is contacted (e.g., in a fixturing apparatus) to another pre-formed object, and the further curing step carried out with the intermediate object contacting the pre-formed object, to produce a composite object. The expansion of the intermediate object by the microspheres may aid in joining the two objects together.

[0125] The resins and methods of the present invention are useful for making objects that comprise lattices, including rigid lattices where no recovery after impact is necessary (e.g., impact absorbers such as in automotive bumpers and body panels, helmets and helmet inserts such as in bicycling and motorcycling helmets which are typically discarded after a single impact, and the like). In some embodiments, the use of the microspheres in the resins as taught herein may increase the stiffness of lattices compared to non-expanded lattices with approximately the same mass and overall dimensions.

[0126] In some embodiments, after the further curing step, the object made is dipped or immersed in a liquid such as a penetrant liquid, so that the pores may fill with another material such as a dye.

[0127] In some embodiments, the three-dimensional objects formed by a method of the invention may have a fine textured or "sand paper" feel, and they can be used to produce objects that have a matte finish, and / or to produce an object having an anti-slip or gripping surface.

[0128] The foregoing is illustrated in greater detail in the following non-limiting Examples. Attorney Docket No. 1151.256. WO

[0129] EXAMPLES

[0130] Preparation of Resin Compositions

[0131] (Meth)acrylate blocked polyurethane (ABPU) prepolymers were prepared from NCO- capped aromatic polyether oligomers that were reacted with a molar NCO equivalent of TBAEMA, with 2,6-di-tert-butyl-4-methylphenol and 4-methoxyphenol as stabilizers. The molecular weight and chemical structure of the APBUs were varied to change the modulus of resulting elastomer / semi-rigid material formed from the resin. The polyurea / polyurethane resin compositions included additional components including reactive diluent, non-reactive diluent, crosslinker, photoinitiator, pigment, UV absorber, and antioxidant. Except for the control examples, expandable microspheres were added to the compositions, as described in Table 1, using the following designations: MSI - Advanced® EMH204 (Ts = 110-130 °C, Tmax = 160-180 °C); MS2 - Expancel® 920 DU 40 (Ts = 123 -133 °C, Tmax = 168 -178 °C); MS3 - Expancel® 930 DU 120 (Ts = 122 -132 °C, Tmax = 191 - 204 °C); MS4 - Expancel® 43 DU 80 (Ts = 107 °C, Tmax = 144-164 °C); and MS5 - Advanced® EML-101 (Ts = 115-130 °C, Tmax = 155-175 °C).

[0132] The following resin compositions were tested as follows:

[0133] Resin Composition A produces a polyurea / polyurethane polymer having a modulus of 2 MPa after printing, moisture cure, and dry bake. The resin included 66.57 parts by weight of an ABPU. The resins in Examples Al, A2, and A3 were made by adding expandable microspheres to Resin Composition A at the concentration shown in Table 1. Solid parts were then 3D printed using Carbon Inc.’s (Redwood City, California, U.S.A.) continuous liquid interface production (CLIP) technology and spun clean with a centrifugal spinner. The parts were first moisture cured at 70 °C and 98% relative humidity for 18 hours (MCI) and then dry baked at 120 °C for 8 hours. The parts in Examples A2 and A3 were then heated at 120 °C for 2 hours and 140 °C for 90 minutes.

[0134] Resin Composition B produces a polyurea / polyurethane polymer with a modulus of 14 MPa after printing, moisture cure, and dry bake. The resin included 75.74 parts by weight of an APBU. Example Bl is a control wherein no microspheres are added to Resin Composition B. Example B2 includes expandable microspheres in Resin Composition B, as shown in Table 1. Solid parts were then 3D printed using Carbon Inc.’s continuous liquid interface production (CLIP) technology and spun clean with a centrifugal spinner. The parts in Examples Bl and Attorney Docket No. 1151.256. WO

[0135] B2 were first moisture cured at 70 °C and 98% relative humidity for 18 hours (MCI) and then dry baked at 120 °C for 2 hours and 140 °C for 90 minutes.

[0136] Resin Composition C produces a polyurea / polyurethane polymer with a modulus of 25 MPa after printing, moisture cure, and dry bake. The resin included 68.78 parts by weight of an APBU. Example Cl is a control wherein no microspheres are added to Resin Composition

[0137] C. Examples C2 and C3 were made by adding expandable microspheres to Resin Composition C, as shown in Table 1. Solid parts were then 3D printed using Carbon Inc.’s continuous liquid interface production (CLIP) technology and spun clean with a centrifugal spinner. The parts in Control Example Cl were moisture cured at 70 °C and >95% relative humidity for 18 hours (MCI) and then dry baked at 120 °C for 8 hours. The parts in Examples C2 and C3 were heated to 150 °C for 30 minutes for thermal expansion, then moisture cured at 70 °C and >95% relative humidity for 18 hours (MCI) followed by a dry bake at 120 °C for 8 hours.

[0138] Resin Composition D produces a polyurea / polyurethane polymer with a modulus of 145 MPa after printing, moisture cure, and dry bake. The resin included 70.01 parts by weight of an APBU. Example DI is a control wherein no microspheres are added to Resin Composition

[0139] D. Examples D2 and D3 were made by adding expandable microspheres to Resin Composition D, as shown in Table 1. Solid parts were then 3D printed using Carbon Inc.’s continuous liquid interface production (CLIP) technology and spun clean with a centrifugal spinner. The parts in Examples DI and D2 were then moisture cured at 95 °C and >95% relative humidity for 2 hours (MC2), and then dry baked at 120 °C for 8 hours. The parts in Example D3 were heated to 150 °C for 30 minutes for thermal expansion, then moisture cured at 95 °C and >95% relative humidity for 2 hours (MC2), followed by a dry bake at 120 °C for 8 hours.

[0140] Resin Composition E produces a polyurea / polyurethane polymer with a modulus of 430 MPa after printing, moisture cure, and dry bake. The resin included 68.78 parts by weight of an APBU. Example El is a control wherein no microspheres are added to Resin Composition E. Examples E2 and E3 were made by adding expandable microspheres to Resin Composition

[0141] E. as shown in Table 1. Solid parts were then 3D printed using Carbon Inc.’s continuous liquid interface production (CLIP) technology and spun clean with a centrifugal spinner. The parts in control Example El were then moisture cured at 70 °C and >95% relative humidity for 18 hours (MCI) and then dry baked at 120 °C for 8 hours. The parts in Example E2 were moisture Attorney Docket No. 1151.256. WO cured at 70 °C and >95% relative humidity for 18 hours (MCI), followed by thermal expansion at 150 °C for 30 minutes, and dry baked at 120 °C for 8 hours. The parts in Example E3 were heated to 150 °C for 30 minutes for thermal expansion, then moisture cured at 70 °C and >95% relative humidity for 18 hours (MCI) followed by a dry bake at 120 °C for 8 hours.

[0142] Results

[0143] Sample dimensions were measured by a caliper. The tensile properties were measured according to ASTM D 412 using Type IV specimens with a thickness of 0.8mm at 500 mm / min strain rate. UV aging was performed with a Q-SUN Xe-1 Xenon Test Chamber using an Extended UV-Q / B (1.2 W / m2@ 420nm) filter and intensity for 2 hours at elevated temperature. Color measurement of L* / a* / b* values were conducted on a MetaVue™ Noncontact spectrophotometer with a white background paper. Dimensional changes after each step (when measured) are shown in Table 1. ISO gray stain test results and measured mechanical properties are shown in Table 2 and Table 3, respectively.

[0144]

[0145] Table 1. Post-Print Dimensional Changes

[0146] Attorney Docket No. 1151.256. WO

[0147] Table 2. ISO gray stain results comparing before and after UV-aging of select samples

[0148] Sample: ISO gray strain

[0149] Example El 3

[0150] Example E3 4

[0151] Example DI 3.5

[0152] Example D2 4.5

[0153] Example D3 5

[0154] Table 3. Mechanical properties of the final parts from select samples

[0155] Mechanical properties Ex. Bl Ex. B2 Ex. DI Ex. D2

[0156] Young's modulus (MPa) - - 145 59

[0157] Elongation at break (%) >600 590 546 324

[0158] Ultimate tensile strength , „„ „

[0159] MPa ,517.4 7.4 38.9 8.7

[0160] The choice of microspheres based on its expansion temperature and stability in combination with specific process conditions and temperatures can be used to control the step at which expansion occurs. These examples demonstrate that the objects can unexpectedly expand in spite of having a UV-cured and moisture-cured poly(urethane / urea) and the microspheres being subjected to high humidity and temperature prior to the final bake temperature. For instance, Examples Al, A2, A3, and B2 show 4 different compositions that show no significant microsphere expansion during the moisture cure process but that activate at 120°C to 140 °C. Example A2 demonstrates no significant expansion at 120 °C whereas it initiates expansion at 140 °C. Similarly, Example B2 expands +12.7% by dimension relative to the printed size whereas the control Example Bl shows shrinkage from the printed part under the same conditions, demonstrating the significant expansion that is achieved with the specific choice of expandable microsphere. The expansions were observed to be visibly uniform in XYZ dimensions. The ultimate tensile strength for control Example Bl was 17.4 MPa and elongation at break of greater than 600% whereas Example B2 had an ultimate tensile strength of 7.4 MPa with elongation at break of 590%. Thus, the foamed moisture-cured poly(urea / urethane) in Example B2 had decreased tensile strength relative to the unexpanded moisture-cured poly(urea / urethane) in control Example Bl, as would be expected with a Attorney Docket No. 1151.256. WO foamed material but has substantially the same elongation at break, showing that a strong polymer network of poly(urea / urethane) remains after foaming.

[0161] Unexpectedly, Example D2 shows that a higher moisture cure process temperature can also be used to achieve expansion without a pre-heating process such as that used in Example D3. This is a surprising result as the moisture cure condition temperature is below that of the reported expansion start temperature, Ts, of 107°C. Without wishing to be bound by theory, our hypothesis is that the moisture uptake of the microspheres during moisture cure lowers the true Ts, allowing for lower temperatures to be used for expansion. Comparing Examples DI and D2 show the expansion of the relatively rigid polyurethane can still maintain an elongation at break of > 300%, indicative of high mechanical performance properties.

[0162] Example E2, containing heat expandable microspheres, has minimal difference in final part size compared to control Example El, indicative of minimal foaming / expansion. It is hypothesized that the lack of expansion for Example E2 is due to the network stiffness being too high to allow for the microsphere to expand above its reported expansion start temperature (Ts). However, the adjustment of the post-process order to have a heating step prior to moisture cure in Example E3 shows a significant volume expansion, from -2% to +133%. This is suspected to be enabled by the use of ABPU chemistry, where the thermally reversible groups can be unblocked at high temperatures, lowering the stiffness of the matrix and allow for expansion, where upon cooling would revert back to the blocked state. This is similarly observed for Examples C2 and C3 compared to control Example Cl. In such instances, expansion prior to moisture cure may be preferable to enable high expansion. However, this adds additional steps to the process, which may become complex compared to expansion after moisture. Additionally, if the expansion can be done after moisture cure is complete, this may be preferable in order to reduce moisture cure times and improve surface finish, consistency, and / or mechanical properties. For example, if expansion is done after moisture cure, the part thicknesses would be thinner during the moisture cure step and would accelerate the time for moisture diffusion into the part, whereas expanded parts prior to moisture may require longer moisture cure times due to thicker (expanded) size.

[0163] For color resistance, the expanded samples (namely Examples E3, D2, and D3) show higher ISO gray stain values (scale from 1 to 5, with 5 being the least amount of change) than their unexpanded control samples (Examples D and E), indicative of foamed samples being more resistant to discoloration from UV aging, despite the foamed samples being a brighter white color than their controls. Attorney Docket No. 1151.256. WO

[0164] 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

1. Attorney Docket No. 1151.

256. WOWE CLAIM:

1. A method of making a three-dimensional object, comprising:(a) producing an intermediate object from a polymerizable liquid by additive manufacturing (c.g, by bottom -up stereolithography, such as by continuous liquid interface production), wherein the polymerizable liquid comprises:(i) at least one reactive blocked prepolymer (e.g., in an amount of from about 1% or about 5% by weight to about 60%, about 70%, about 80%, about 90%, or about 98% by weight);(ii) a photoinitiator (c.g, in an amount of from about 0.05% to about 10% by weight);(iii) heat expandable microspheres (e.g., in an amount of from about 1% or about 2% by weight to about 5%, about 10%, about 20%, about 30%, or about 35% by weight); and(iv) optionally, a reactive diluent, non-reactive diluent, water, and / or crosslinker;(b) optionally, cleaning the intermediate object (e.g., by washing, spinning, etc.); and(c) curing the intermediate object to form the three-dimensional object by:(i) exposing the intermediate object to moisture (e.g., at about 90%, about 95%, or more humidity) at a temperature wherein the microspheres are substantially unexpanded and for a time sufficient to form a moisture cured intermediate object;(ii) optionally, heating the moisture cured intermediate object to remove residual moisture (and / or other volatile compounds); and then(iii) heating and / or microwave irradiating the moisture cured intermediate object for a time and at a temperature sufficient to expand the microspheres, to thereby form the three-dimensional object.

2. The method of claim 1, wherein the at least one reactive blocked prepolymer is photopolymerized to form the intermediate object; the temperature at which moisture curing occurs is sufficient to degrade the intermediate object to form unblocked prepolymer; and the unblocked prepolymer reacts with water to form the moisture cured intermediate object.Attorney Docket No. 1151.

256. WO3. The method of claim 1 or claim 2, wherein the reactive blocked prepolymer is a reactive blocked polyisocyanate, optionally wherein the reactive blocked polyisocyanate comprises the reaction product of a polyisocyanate and an amine or hydroxyl (meth)acrylate or meth(acrylamide) blocking agent.

4. The method of claim 3, wherein the temperature at which moisture curing occurs is sufficient to degrade the intermediate object to form unblocked polyisocyanate, and the unblocked polyisocyanate reacts with water to generate a polyamine in situ, wherein the polyamine reacts with additional unblocked polyisocyanate to form urea linkages.

5. The method of claim 1 or claim 2, wherein the reactive blocked prepolymer is a reactive blocked polysiloxane.

6. The method of any one of the preceding claims, wherein the heat expandable microspheres comprise a partially or completely hollow thermally expandable shell (e.g, a thermoplastic polymer shell), and a propellant (e.g, a low-boiling point liquid or liquified gas such as a lower alkane) contained in the shell.

7. The method of any one of the preceding claims, wherein the microspheres have an expansion start temperature in a range of 90 °C to 140 °C (e.g., 100 °C to 135 °C) and / or a maximum expansion temperature (Tmax) in a range of 120 °C to 220 °C (e.g., 160 °C to 205 °C).

8. The method of any one of the preceding claims, wherein the polymerizable liquid is devoid of free amine (or devoid of a primary or secondary amine).

9. The method of any one of the preceding claims, wherein a volume of the three- dimensional object is at least 30%, 50%, 75%, 100%, or 125% greater than a volume of the intermediate object and / or the three-dimensional object has a dimensional increase of at least 5%, 10%, 15%, 20%, 30% relative to the intermediate object.

10. The method of any one of the preceding claims, wherein the three-dimensional object is comprised of polyurea, polyurethane, silicone, and / or epoxy.Attorney Docket No. 1151.

256. WO11. The method of any one of the preceding claims, wherein the three-dimensional object is rigid, flexible, or elastic.

12. The method of any one of the preceding claims, wherein the three-dimensional object comprises a polyurethane and / or polyurea and has an elongation at break of greater than 300%.

13. The method of any one of the preceding claims, wherein the intermediate obj ect is moisture cured at a temperature in a range of from 50 °C to 150 °C; and the heating and / or microwave irradiating of the moisture cured object to expand the microspheres is performed at a temperature in a range of from 110 °C to 220 °C.

14. The method of claim 13, wherein the intermediate object is exposed to moisture at a temperature in a range of from 50 °C to 100 °C (e.g., for a time in a range of 1 or 2 hours to 5, 8, 10, 12, 15, or 18 hours), optionally at a temperature in a range of from 70 °C to 100 °C.

15. The method of any one of the preceding claims, wherein the microspheres are present in the polymerizable liquid at a concentration in a range of 1 or 2 percent by weight to 35% by weight (e.g., 1 to 10 or 15 percent by weight), optionally wherein the microspheres have an average particle diameter before expansion in a range of 1 pm to 100 pm (and optionally expand upon heating by 2-10 times in diameter and / or 50 to 1000 times in volume).

16. The method of any one of the preceding claims, wherein the three-dimensional object comprises a cushion, shock absorber, thermal insulator, or electric insulator.

17. The method of any one of the preceding claims, wherein the three-dimensional object comprises a regular or irregular open-cell lattice.

18. An object produced by a method of any one of the preceding claims.

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