Method for manufacturing a three-dimensional object

Abstract

Provided herein is a method for producing a three-dimensional object by bottom-up additive manufacturing, the method may include providing a carrier platform, a light source, and a light-transmitting window therebetween, the light-transmitting window comprising a gas-permeable member having a top surface and a bottom surface; depositing a liquid resin onto the window, the resin comprising a cyclic olefin monomer and a ring-opening metathesis polymerization (ROMP) photocatalyst; contacting the gas with the bottom surface of the gas-permeable member; and exposing the resin to light from the light source while advancing the carrier platform away from the window to form the three-dimensional object on the carrier platform. The invention also provides apparatus useful for performing the method and methods useful for recycling the three-dimensional object.

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for manufacturing an object by additive manufacturing. [Background technology]

[0002] A group of additive manufacturing techniques, also known as "stereolithography," builds three-dimensional objects by the sequential polymerization of photopolymerizable resins. Such techniques can be "bottom-up" techniques, where light is projected through a light-transmitting window onto the resin at the bottom of a growing object, or "top-down" techniques, where light is projected onto the resin on top of a growing object, and the growing object is then dipped downward into a pool of resin.

[0003] The recent introduction of a faster stereolithography technique known as continuous liquid interface manufacturing (CLIP), coupled with the introduction of "dual-cure" resins for additive manufacturing, has expanded the utility of stereolithography from prototyping to manufacturing (see, e.g., U.S. Patent Nos. 9,211,678, 9,205,601, and 9,216,546 to DeSimone et al., and J. Tumbleston, D. Shirvanyants, N. Ermoshkin et al., Continuous liquid interface production of 3D Objects, Science 347, 1349-1352 (2015); see also Rolland et al., U.S. Patent Nos. 9,676,963, 9,453,142, and 9,598,606).

[0004] Additional additive manufacturing techniques can further expand the variety of materials suitable for stereolithography. Summary of the Invention

[0005] According to some embodiments, there is provided a method for producing a three-dimensional object by bottom-up additive manufacturing, the method may include providing a carrier platform, a light source, and a light-transmissive window therebetween, wherein the light-transmissive window comprises a gas-permeable member having a top surface and a bottom surface; depositing a liquid resin onto the window, wherein the resin comprises a cyclic olefin monomer and a ring-opening metathesis polymerization (ROMP) photocatalyst; contacting a gas with the bottom surface of the gas-permeable member; and exposing the resin to light from the light source while advancing the carrier platform away from the window to form the three-dimensional object on the carrier platform. In some embodiments, the activation of the ROMP photocatalyst for the polymerization of the cyclic olefin monomer is inhibited by oxygen. As further described below, in some embodiments, the gas contains oxygen, but at a low level. The oxygen is present in an amount sufficient to reduce stray cure, skirt formation, or flaring around the growing three-dimensional object (which increases the defect rate), but insufficient to suppress activation of the ROMP photocatalyst in the resin to the extent that it prevents the formation of the three-dimensional object (e.g., oxygen is present at a partial pressure of 0.1, 0.2, 0.4, 1, 1.5, 2, or 2.5 kilopascals up to 8, 9, 10, or 11 kilopascals). In some embodiments, the gas contacts the bottom surface of the gas-permeable member at a pressure lower than that of ambient air. In some embodiments, the liquid resin deposited on the window is in contact with ambient air, while in other embodiments, the liquid resin deposited on the window is in contact with a controlled atmosphere (or second gas) containing low levels of oxygen (e.g., substantially the same level of oxygen as contained in the gas in contact with the bottom surface of the gas permeable member, by placing the window in a sealed chamber containing air at reduced pressure).

[0006] In some embodiments, a liquid interface is maintained between the object and the window by the resin during the exposing step. In some embodiments, the gas comprises an inert gas, such as nitrogen, argon, helium, neon, krypton, xenon, radon, or a combination of two or more thereof, hi some embodiments, the gas comprises argon. In some embodiments, the gas is dissolved in the liquid carrier. In some embodiments, the cyclic olefin monomer is selected from the group consisting of cyclopropene, cyclobutene, benzocyclobutene, cyclopentene, norbornene, norbornadiene, cycloheptene, cyclooctene, 7-oxanorbornene, 7-oxanorbornadiene, cyclodecene, 1,3-cyclooctadiene, 1,5-cyclooctadiene, 1,3-cycloheptadiene, [2.2.1]bicycloheptene, [2.2.2]bicyclooctene, norbornene, norbornadiene, ethylidenenorbornene, dicyclopentadiene, vinylnorbornene, cyclohexenylnorbornene, norbornene dicarboxylic anhydride, cyclododecene, 1,5,9-cyclododecatriene, and mixtures of two or more thereof. In some embodiments, the ROMP photocatalyst comprises a transition metal catalyst, hi some embodiments, the ROMP photocatalyst comprises ruthenium, tungsten, or osmium. In some embodiments, the resin further comprises at least one additional component selected from the group consisting of light absorbers, pigments, dyes, matting agents, flame retardants, fillers, non-reactive and photo-reactive diluents, and combinations of two or more thereof. In some embodiments, the resin further comprises a latent thermal ROMP catalyst, and the method further comprises heating the body after its formation to further polymerize the resin. Also provided is an apparatus for additive manufacturing of objects from a photopolymerizable resin, the resin comprising a cyclic olefin monomer and a ring-opening metathesis polymerization (ROMP) photocatalyst, the apparatus comprising: (a) an optically transmissive window including (i) a gas-permeable top member onto which the photopolymerizable resin can be disposed, (ii) a rigid bottom member, and (iii) a gas supply region disposed between the top member and the bottom member; (b) a carrier platform disposed above the window, on which an object can be fabricated from the resin; (c) a drive operably coupled to the carrier platform and the optically transmissive window, the drive configured to advance the carrier platform and the window away from each other; (d) a light source disposed below the window, configured to polymerize the photopolymerizable resin; and (e) an inert gas supply operably coupled to the gas supply region of the window, configured to (i) supply an inert gas to the resin through the top member and (ii) receive oxygen from the resin through the top member. In some embodiments, the inert gas supply comprises a nitrogen generator or nitrogen supply. In some embodiments, the inert gas supply includes an argon supply. In some embodiments, the inert gas supply comprises a bottled gas blend. In some embodiments, the inert gas supply is configured to contact the inert gas with the bottom surface of the gas permeable member at a pressure lower than ambient air pressure (i.e., by including a vacuum pump operably connected to the gas supply). In some embodiments, the inert gas supply is configured to contain oxygen in an amount sufficient to reduce stray curing, skirt formation, or flaring around the growing three-dimensional object (which increases the reject rate during the process), but insufficient to suppress activation of the ROMP photocatalyst in the resin to an extent that prevents the formation of the three-dimensional object (e.g., oxygen is contained at a partial pressure of 0.1, 0.2, 0.4, 1, 1.5, 2, or 2.5 kilopascals up to 8, 9, 10, or 11 kilopascals). In some embodiments, the window is configured to be in contact with oxygen in the ambient air (ie, in a chamber open to and / or in contact with the ambient air). In some embodiments, the apparatus further comprises: (f) a sealed chamber comprising the window; and (g) a gas supply operably coupled to the sealed chamber, the gas supply configured to supply a gas into the chamber, the gas comprising oxygen at substantially the same partial pressure as the gas supplied to the window (e.g., ambient air under reduced pressure). In some embodiments, the apparatus further comprises a liquid carrier in which the inert gas is dissolved. Further provided is a method for recycling an additively manufactured object, wherein the object is comprised of a photopolymerized product of a cyclic olefin monomer, the method optionally comprising the steps of pulverizing the object and then contacting the optionally pulverized object with a liquid acrylate (e.g., acrylic acid, ethyl acrylate) in the presence of a Grubbs catalyst for a time and at a temperature sufficient to depolymerize the photopolymerized product.

[0007] These and other objects and aspects of the present invention are explained in more detail in the following drawings and the specification set forth below, the disclosures of all U.S. patent documents cited herein are hereby incorporated by reference. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of one embodiment of an apparatus described herein. [Figure 2] 2 shows a schematic representation of an inert gas (nitrogen in this example) being exchanged for oxygen in the resin through a window in the apparatus of FIG. 1. [Figure 3] Photograph of a set of test objects produced on the carrier platform, where a significant number of objects failed to print correctly or to complete the print. [Figure 4A]As part of a non-limiting theory for the defect shown in Figure 3, the lateral diffusion of free radicals from the growing object is shown schematically. [Figure 4B] 4B shows schematically the lateral formation of an unintentional polymerized "skirt" around an object, which may be the result of the lateral diffusion of free radicals shown in FIG. 4A. [Figure 5] FIG. 1 is a schematic diagram of another embodiment of an apparatus described herein. [Figure 6] FIG. 1 is a schematic diagram of another embodiment of a device described herein that includes a sealed chamber. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will now be described in more detail with reference to the accompanying drawings, which show embodiments of the invention. However, the present invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that the disclosure will be thorough and complete, and the scope of the invention will be fully understood by those skilled in the art.

[0010] 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 a combination ("or") when interpreted in the alternative.

[0011] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs. Terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning 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 defined herein. Well-known functions or structures are not described in detail for the sake of brevity and / or clarity.

[0012] 1. Resin A polymerizable liquid composition curable by actinic radiation (typically light, in some embodiments, ultraviolet (UV) light) is provided to enable the present invention. The liquid (also referred to as a "liquid resin," "ink," or simply "resin") may include polymerizable monomers, particularly photopolymerizable and / or free-radically polymerizable monomers (e.g., cyclic olefin monomers and / or reactive diluents) and / or prepolymers (i.e., reactive monomers or larger monomers that can be further polymerized), and a suitable catalyst, such as a ring-opening metathesis polymerization (ROMP) photocatalyst.

[0013] Examples of suitable resins are described in O. Burtovyy, "Polycycloolefin monomers and catalyst activated by compound cables of generating photoacid as optical materials," WO 2019 / 147878, which is incorporated herein by reference.

[0014] Further examples of suitable catalysts include, but are not limited to, those described in Stijn Monsaert et al., "Latent olefin metathesis catalysts," Chem Soc. Revie., Vol. 38, p. 3360 (2009) and Y. Vidavsky and N. Lemcoff, "Light-induced olefin metathesis," Beilsein J. Org Chem., 6, pp. 1106-1119 (2010).

[0015] Non-limiting examples of suitable cyclic olefin monomers include, but are not limited to, cyclopropene, cyclobutene, benzocyclobutene, cyclopentene, norbornene, norbornadiene, cycloheptene, cyclooctene, 7-oxanorbornene, 7-oxanorbornadiene, cyclodecene, 1,3-cyclooctadiene, 1,5-cyclooctadiene, 1,3-cycloheptadiene, [2.2.1]bicycloheptene, [2.2.2]bicyclooctene, norbornene, norbornadiene, ethylidenenorbornene, dicyclopentadiene, vinylnorbornene, cyclohexenylnorbornene, norbornene dicarboxylic anhydride, cyclododecene, 1,5,9-cyclododecatriene, (these terms include derivatives of any of the foregoing compounds), or mixtures of two or more thereof. Suitable examples include, but are not limited to, those described in U.S. Pat. Nos. 10,767,002, 10,693,072, 10,245,562, 9,765,180, 9,468,890, 9,415,354, 9,328,179, 9,181,360, and 8,765,894, the disclosures of which are incorporated herein by reference in their entireties.

[0016] In some embodiments, the ROMP photocatalyst is inhibited by oxygen. In some embodiments, the ROMP photocatalyst comprises a transition metal catalyst. In some embodiments, the ROMP photocatalyst comprises ruthenium, tungsten, or osmium. Diluents. Known in the art, diluents are compounds used to reduce viscosity in resin compositions and may be photoreactive or non-reactive diluents. Reactive diluents undergo a reaction during photocuring that becomes part of the polymer network. In some embodiments, reactive diluents may react at approximately the same rate as other reactive monomers and / or prepolymers in the composition. Fillers. Any suitable filler may be used in connection with the present invention, depending on the properties desired for the part or object being manufactured. Thus, fillers may be solid or liquid, organic or inorganic, and may include reactive and non-reactive rubbers, such as siloxanes, acrylonitrile-butadiene rubbers; reactive and non-reactive thermoplastics (including, but not limited to, poly(etherimides), maleimide-styrene terpolymers, polyarylates, polysulfones, polyethersulfones, and the like); inorganic fillers, such as silicates (e.g., talc, clay, silica, mica), glass, carbon nanotubes, graphene, cellulose nanocrystals, and the like, as well as combinations of all of the above. Suitable fillers include reinforcing agents, such as core-shell rubbers, as described below. Reinforcing Agents. One or more polymeric and / or inorganic reinforcing agents may be used as fillers in the present invention. The reinforcing agent may be in the form of particles uniformly distributed throughout the cured product. The particles may be less than 5 microns (μm) in diameter. Such reinforcing agents include, but are not limited to, those formed from elastomers, with or without surface modification or functionalization, branched polymers, hyperbranched polymers, dendrimers, rubbery polymers, rubbery copolymers, block copolymers, core-shell particles, oxides, or inorganic materials such as clays, polyhedral oligomeric silsesquioxanes (POSS), carbonaceous materials (e.g., carbon black, carbon nanotubes, carbon nanofibers, fullerenes), ceramics, and silicon carbide. Examples of block copolymers include those whose compositions are described in U.S. Patent No. 6,894,113 (Court et al., Atofina, 2005), and "NANOSTRENTH®" SBM (polystyrene-polybutadiene-polymethacrylate) and AMA (polymethacrylate-polybutylacrylate-polymethacrylate), both manufactured by Arkema, Inc. (King of Prussia, Pennsylvania). Other suitable block copolymers include FORTEGRA® and the amphiphilic block copolymers described in U.S. Patent No. 7,820,760 B2, assigned to Dow Chemical Company.Examples of known core-shell particles include core-shell (dendrimer) particles (the composition of which is described in U.S. Patent Application Publication No. 2010 / 0280151 (Nguyen et al., Toray Industries, Inc., 2010) in which an amine-branched polymer is grafted as a shell onto a core polymer polymerized from a polymerizable monomer having an unsaturated carbon-carbon bond), core-shell rubbery particles (the composition of which is described in European Patent Applications Publication Nos. 1632533 and 2123711 by Kaneka Corporation), and particle / epoxy blends in the "Kane Ace MX" product line (these particles have a polymer core polymerized from a polymerizable monomer, such as butadiene, styrene, other unsaturated carbon-carbon bond monomers, or combinations thereof, and an epoxy-compatible polymer shell, typically polymethyl methacrylate, polyglycidyl methacrylate, polyacrylonitrile, or similar polymers as described in more detail below). Also suitable as block copolymers in the present invention are the "JSR SX" series of carboxylated polystyrene / polydivinylbenzene manufactured by JSR Corporation, "Kureha Paraloid" EXL-2655 (manufactured by Kureha Corporation), which is a butadiene alkyl methacrylate styrene copolymer, "Stafiloid" AC-3355 and TR-2122 (both manufactured by Takeda Pharmaceutical Company Limited), which are acrylate methacrylate copolymers, and "PARALOID" EXL-2611 and EXL-3387 (both manufactured by Rohm & Haas), which are butyl acrylate methyl methacrylate copolymers. Examples of suitable oxide particles include NANOPOX® manufactured by Nanoresins. Core-shell rubber. Core-shell rubber is a granular material (particle) having a rubbery core. Such materials are known and are described, for example, in U.S. Patent Application Publication Nos. 2015 / 0184039 and 2015 / 0240113, as well as U.S. Patent Nos. 6,861,475, 7,625,977, 7,642,316, and 8,088,245, among others. In some embodiments, the core-shell rubber particles are nanoparticles (i.e., have an average particle size of less than 1000 nanometers (nm)). Generally, the average particle size of 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 particle is not spherical, the particle size is defined as the longest dimension of the particle. In some embodiments, the rubbery core may have a glass transition temperature (Tg) of less than -25°C, more preferably less than -50°C, and even more preferably less than -70°C. The Tg of the rubbery core may be less than -100°C. The core-shell rubber also preferably has at least one shell portion having a Tg of at least 50°C. "Core" refers to the inner portion of the core-shell rubber. The core may form the center of the core-shell particle or an inner shell or domain of the core-shell rubber. The shell is the portion of the core-shell rubber that is outside the rubbery core. The shell portion typically forms the outermost portion of the core-shell rubber particle. The shell material may be grafted onto the core or crosslinked. The rubbery core may constitute 50 to 95%, or 60 to 90%, by weight of the core-shell rubber particle. The core of the core-shell rubber may be a polymer or copolymer of a conjugated diene such as butadiene or a lower alkyl acrylate such as n-butyl, ethyl, isobutyl, or 2-ethylhexyl acrylate. The core polymer may further contain up to 20% by weight of other copolymerized monounsaturated monomers, such as styrene, vinyl acetate, vinyl chloride, or methyl methacrylate. The core polymer is optionally crosslinked. The core polymer may optionally contain up to 5% of a copolymerized graft-linking monomer having two or more unsaturated sites of different reactivity, such as diallyl maleate, monoallyl fumarate, or allyl methacrylate, where at least one reactive site is non-conjugated. The core polymer may also be a silicone rubber. These materials often have a glass transition temperature below -100°C. Core-shell rubbers with a silicone rubber core include those commercially available under the trade name GENIOPERL® from Wacker Chemie, Munich, Germany. The shell polymer, optionally chemically grafted or crosslinked to the rubber core, can be polymerized from at least one lower alkyl methacrylate, such as methyl methacrylate, ethyl methacrylate, or t-butyl methacrylate. Homopolymers of such methacrylate monomers can be used. Additionally, up to 40% by weight of the shell polymer can be formed from other monovinylidene monomers, such as styrene, vinyl acetate, vinyl chloride, methyl acrylate, ethyl acrylate, and butyl acrylate. The molecular weight of the grafted shell polymer can be 20,000 to 500,000. One suitable type of core-shell rubber has reactive groups in the shell polymer that can react with epoxy resins or epoxy resin hardeners. Glycidyl groups are preferred. The glycidyl groups can be provided by monomers such as glycidyl methacrylate. An example of a suitable core-shell rubber is the type described in U.S. Patent Application Publication No. 2007 / 0027233 (European Patent Application Publication No. 1632533). The core-shell rubber particles described therein comprise a crosslinked rubber core, which is most often a crosslinked copolymer of butadiene, and a shell, preferably a copolymer of styrene, methyl methacrylate, glycidyl methacrylate, and optionally acrylonitrile. The core-shell rubber is preferably dispersed in a polymer or epoxy resin, as also described therein. Suitable core-shell rubbers include, but are not limited to, those sold by Kaneka Corporation under the trade name Kaneka Kane Ace, for example, the Kaneka Kane Ace 15 and 120 series of products, such as Kaneka Kane Ace MX 120, Kaneka Kane Ace MX 153, Kaneka Kane Ace MX 154, Kaneka Kane Ace MX 156, Kaneka Kane Ace MX 170, Kaneka Kane Ace MX 257 and Kaneka Kane Ace MX 120 core-shell rubber dispersions, and mixtures of two or more thereof.

[0017] Additional Resin Component. The liquid resin or polymeric material may have solid particles suspended or dispersed therein. Any suitable solid particles may be used depending on the final product being fabricated. The particles may be metallic, organic / polymeric, inorganic, or composites or mixtures thereof. The particles may be non-conductive, semi-conductive, or conductive (including metallic and non-metallic or polymeric conductors), and the particles may be magnetic, ferromagnetic, paramagnetic, or non-magnetic. The particles may have any suitable shape, including spherical, ellipsoidal, cylindrical, etc. The particles may be of any suitable size (e.g., average diameter of 1 nm to 20 μm).

[0018] The particles may comprise an active agent or a detectable compound, as described below, which may also be provided dissolved or solubilized in a liquid resin, as described below. For example, magnetic or paramagnetic particles or nanoparticles may be used.

[0019] The liquid resin may have additional components solubilized therein, including pigments, dyes, active or pharmaceutical compounds, detectable compounds (e.g., fluorescent, phosphorescent, radioactive), etc., again depending on the particular purpose of the product being fabricated. Examples of such additional components include, but are not limited to, proteins, peptides, nucleic acids (DNA, RNA), e.g., siRNA, sugars, small organic compounds (drugs and drug-like compounds), etc., and combinations thereof.

[0020] Light Absorbers. In some embodiments, polymerizable liquids for practicing the present invention include non-reactive pigments or dyes that absorb light, particularly UV light. Suitable examples of such light absorbers include, but are not limited to, (i) titanium dioxide (e.g., in an amount of 0.05 or 0.1 to 1 or 5 wt %), (ii) carbon black (e.g., in an amount of 0.05 or 0.1 to 1 or 5 wt %), and / or (iii) organic ultraviolet light absorbers, such as hydroxybenzophenone, hydroxyphenylbenzotriazole, oxanilide, benzophenone, thioxanthone, hydroxyphenyltriazine, and / or benzotriazole ultraviolet absorbers (e.g., Mayzo BLS1326) (e.g., in an amount of 0.001 or 0.005 to 1, 2, or 4 wt %). Examples of suitable organic ultraviolet light absorbers include, but are not limited to, those described in U.S. Pat. No. 3,213,058, U.S. Pat. No. 6,916,867, U.S. Pat. No. 7,157,586, and U.S. Pat. No. 7,695,643, which are incorporated by reference in their entireties. Flame Retardants. Flame retardants that can be included in the polymerizable liquids of the present invention can include monomers or prepolymers containing flame retardant groups. For example, in some embodiments, a component can be brominated, i.e., contain one, two, three, four, or more bromine groups covalently bonded thereto (e.g., 1, 2, or 5 to 15 or 20 weight percent of the total bromine groups). Flame retardant oligomers, which can be reactive or non-reactive, can also be included in the resins of the present invention. Examples include, but are not limited to, brominated oligomers such as ICL flame retardants F-3100, F-3020, F-2400, F-2016, and the like (ICL Industrial Products). See also U.S. Patent Application Publication No. 2013 / 0032375 to Pierre et al. Flame retardant synergists can also be included, which provide flame retardancy synergism when combined with a halogen, such as bromine. Examples include, but are not limited to, antimony synergists, such as antimony oxides (e.g., antimony trioxide, antimony pentoxide, etc.), and aromatic amines, such as melamine. See U.S. Pat. No. 9,782,947. In some embodiments, the resin composition may contain a synergist in an amount of 0.1, 0.5, or 1% to 3, 4, or 5% by weight. In some embodiments, antimony pentoxide functionalized with triethanolamine or ethoxylated amine can be used, which is available as BurnEX® colloidal additives, such as BurnEX® A1582, BurnEX® ADP480, and BurnEX® ADP494 (Nyacol® Nano Technologies, Ashland, Massachusetts). Matting Agents: Examples of suitable matting agents include, but are not limited to, barium sulfate, magnesium silicate, silicon dioxide, aluminosilicates, alkali aluminosilicate ceramic microspheres, aluminosilicate glass microspheres or flakes, polymer wax additives (e.g., polyolefin waxes in combination with salts of organic anions), and the like. Latent Thermal Catalyst. In some embodiments, the resin further comprises a latent thermal ROMP catalyst, and the method further comprises heating the body after molding to further polymerize the resin. Many examples of such catalysts are known, including, but not limited to, those described in U.S. Patent No. 6,107,420 to Grubbs and Wilhelm and U.S. Patent No. 9,610,572 to Grela and Czarnocki, both of which are incorporated herein by reference.

[0021] 2. Equipment Apparatus for carrying out the methods described herein may be adapted from apparatus used to perform continuous liquid interface manufacturing (CLIP) by replacing the oxygen or enriched oxygen supply with an inert gas supply. CLIP is known and is described, for example, in U.S. Pat. Nos. 9,211,678, 9,205,601, 9,216,546, Feller and Griffin, WO 2019 / 084112, and Feller et al., WO 2018 / 006018, the disclosures of all of which are incorporated herein by reference.

[0022] A non-limiting example of an apparatus is shown in Figure 1. The apparatus (10) typically comprises a frame or chassis (17), a resin cassette (window (11) + frame (12)) operably coupled to the frame (typically by a cassette mount (not shown)), a light source (e.g., 13) positioned below the resin cassette and arranged to project a magnified image through the window (11), a removable carrier platform (14) on which an object (31) may be fabricated from resin (21), and / or a carrier platform coupling member (14a) to which the carrier platform is attached, positioned above the window (11), which may be operably coupled to the frame (17), and a drive (15) operably coupled to the carrier and the frame and configured to advance the carrier platform and the resin cassette away from each other (typically in a "Z" or vertical direction, typically by moving the platform upward and away from an otherwise fixed window).

[0023] Any suitable light source can be used, for example ultraviolet light can be used and projected from a micromirror array or through a liquid crystal display (LCD) panel.

[0024] A suitable inert gas supply (36) may be used, including tanks or bottles of compressed inert gas or gas blend, nitrogen generators, etc. Examples of suitable inert gases include nitrogen (e.g., 95 percent, 99 percent, or 99.9 percent or greater purity), argon, helium, neon, krypton, xenon, radon, or combinations of two or more thereof. The inert gas supply may include a return line (as shown), and / or may be provided with valves and channels for two-way flow of the inert gas through a window, and / or the inert gas may simply be vented after use.

[0025] In some embodiments, the inert gas may be provided dissolved in a liquid carrier.

[0026] The device may include a controller (16), such as a general-purpose computer located on the device, in the cloud, or a combination thereof, operably coupled to the light source and drive devices and containing programming for performing additive manufacturing on the device as known in the art. The apparatus may optionally include a heater and / or cooler operably coupled to the window and controller. Any suitable device may be used, including resistive heaters, Peltier coolers, infrared heaters, etc. The heater / cooler is preferably contained directly within the resin cassette and is preferably in direct contact with the window itself or, in the case of an infrared heater, may be positioned to protrude through the window into the resin. Alternatively or additionally, the heater and / or cooler may be in direct contact with the inert gas supply, such as the liquid carrier thereof.

[0027] As described above, the cassette generally includes a light-transmitting window (11) configured to pass an image through the cassette, the window having internal structures that define a fluid flow path within the cassette, the internal structures distributed across the length and width of the window, and optionally, the internal structures forming reflective and refractive surfaces within the window. A peripheral frame (12) connects to and surrounds the window, and the window and frame together form a well (e.g., 21) configured to receive a photopolymerizable resin. Various geometric shapes for these internal structures may be used. In some embodiments, the internal structures include walls, and the passageways include laterally aligned (e.g., parallel) channels. In some embodiments, the internal structures include pillars (of any shape, width, and length), and the passageways may include regularly or irregularly intersecting channels. The channels themselves may have any suitable cross-section, for example, triangular and / or quadrangular (e.g., square, rectangular, parallelogram, etc.) cross-sections. See, for example, U.S. Patent Application Publication Nos. 2016 / 0200052 and 2018 / 0133959 to Moore et al., which are incorporated herein by reference. The cassette window may be configured in any suitable manner, but preferably provides or includes a gas permeable member through which the inert gas in the fluid flow path can reach the resin on top of the window, and oxygen in the resin can flow in the opposite direction from the resin, through the window, and into the channels carrying the inert gas. The oxygen can exit the cassette via a return line and / or a vent. In some embodiments, as shown schematically in Figure 2, the window comprises a sandwich of at least a gas permeable top portion or member (11a), a middle portion or member (11b), and a bottom portion or member (11c), with an internal structure formed in the middle portion or member. In some embodiments, the window bottom or member (11c) is rigid and may comprise glass, sapphire, quartz, or clear aluminum (ALON, aluminum oxynitride).

[0028] In some embodiments, the gas permeable window top or member (11a) comprises a polymer (eg, an oxygen permeable polymer, such as an amorphous fluoropolymer).

[0029] In some embodiments, the middle portion or member (11b) comprises a second polymer layer, a polydimethylsiloxane (PDMS) layer.

[0030] In some embodiments, as shown in FIG. 2, channels may be formed in the middle portion or member (11b) that are in fluid communication with the gas supply (36) so that an inert gas (e.g., nitrogen) flows from the channels in the middle portion or member (11b) through the gas permeable top portion or member (11a) and oxygen flows in the opposite direction.

[0031] 3. Manufacturing method Suitable techniques for additive manufacturing include bottom-up and top-down additive manufacturing, commonly known as stereolithography. Such methods are known and are described, for example, in 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. See also U.S. Patent Nos. 9,211,678, 9,205,601, and 9,216,546 to DeSimone et al. The disclosures of these patents and applications are incorporated herein by reference in their entireties. As noted above, the apparatus in some embodiments preferably includes an inert gas supply (including an inert gas with a low level of oxygen), which can generally be conveniently implemented by replacing the oxygen or enriched oxygen supply with the CLIP apparatus with an inert gas supply. Note in particular Feller and Griffin, WO 2019 / 084112, and Felle et al., WO 2018 / 006018, cited above. (See also G. Price and B. Feller, Window Cassettes for Reduced Polymerization Inhibitor Irregularity During Additive Manufacturing, U.S. Patent Application Publication No. 2020 / 0061919 (February 27, 2020), and B. Feller and G. Price, Reduction of Polymerization Inhibitor Irregularity on Additive Manufacturing Windows, U.S. Patent Application Publication No. 2020 / 0094468 (March 26, 2020)).

[0032] A method for producing a three-dimensional object by bottom-up additive manufacturing taught herein may include providing a carrier platform, a light source, and a light-transmissive window therebetween, wherein the light-transmissive window comprises a gas-permeable member having a top surface and a bottom surface; depositing a liquid resin onto the window, wherein the resin comprises a cyclic olefin monomer and a ring-opening metathesis polymerization (ROMP) photocatalyst; contacting the bottom surface of the gas-permeable member with an inert gas; and advancing the carrier platform away from the window while exposing the resin to light from the light source to form the three-dimensional object on the carrier platform. In some embodiments, activation of the ROMP photocatalyst for polymerization of the cyclic olefin monomer is inhibited by oxygen, and the liquid resin deposited on the window may be contacted with ambient oxygen by contacting the bottom surface of the gas permeable member with an inert gas in an amount sufficient to purge the resin of residual oxygen in the resin and / or ambient oxygen absorbed in the resin.

[0033] 4. Reduced defect rate by introducing low levels of oxygen While it was surprising to be able to successfully practice the invention with the resin pool open to the atmosphere, it was nevertheless observed that some attempts to practice this method resulted in significant print defects, an example of which is shown in the photograph in Figure 3.

[0034] [Table 1]

[0035] While not wishing to be bound by theory to explain such failures, it is currently believed that, as summarized in Figures 4A-4B, excess photogenerated radicals (or HCl) diffuse into the unilluminated areas around the growing object due to the absence of the chain termination mechanism described above in Table 1. This results in initiation around the growing object and the production of a sticky gel-like substance that adheres to the object, which inhibits resin refilling beneath the growing object and promotes undesirable adhesion to the window.

[0036] To reduce this stray cure (skirt formation or "flare") and lower the reject rate, a series of experiments were conducted using inert gas with a small amount of oxygen. The results are summarized in Table 2 below. A completely inert (nitrogen gas) environment both above and below the resin pool resulted in a high reject rate, as seen in Figure 3. Ambient air was introduced into the build chamber above the resin pool, but inert gas supplied to a channel below the window also resulted in a high print reject rate, as seen in Figure 3. As expected, the typical environment with air introduced above the window and the oxygen-enriched atmosphere supplied within the cassette and through the window resulted in failed prints. However, introducing a small amount of oxygen through the window was found to lead to successful prints.

[0037] In Table 2 below, the percentage of oxygen refers to relative partial pressure. The current embodiment of the Carbon printer performing CLIP delivers pure oxygen to the window cassette at a reduced pressure of 25 kilopascals (kPa). Therefore, the concentration or partial pressure of oxygen is 25% of pure oxygen gas at standard temperature and pressure (STP: 0°C, 100 kPa).

[0038] In a preferred embodiment, as summarized in Figure 5 described below, a low oxygen supply to the window cassette is achieved by disconnecting the oxygen generator and supplying ambient air into the window at a pressure of 12 kPa. If the ambient air is composed of approximately 21% oxygen and 79% nitrogen at 100 kPa (1 atmosphere), the oxygen supply to the window cassette (for delivery to the resin through the semipermeable member) will be approximately 2.5% oxygen (and 9.5% nitrogen) relative to the ambient air and oxygen (and nitrogen) in the air inlet stream at STP.

[0039] [Table 2]

[0040] A gas or atmosphere having an oxygen level of 2.5% in the above context may be more generally described as a gas (gas mixture, e.g., air at reduced pressure) having an oxygen partial pressure of 0.1, 0.2, 0.4, 1, 2, or 2.5 kilopascals (kPa), up to 8, 9, 10, or 11 kPa.

[0041] It should be noted that the preferred oxygen concentration below the window (for delivery through the semipermeable member) depends on factors such as the size of the object being manufactured, the precision required for the object being manufactured, the desired production rate, and combinations thereof. Air is a convenient source, as described above and below, and compressed gases ranging from pure oxygen (delivered into the window cassette at high vacuum (i.e., very low pressure)) to mixed gases (including combinations of oxygen and inert gases) and combinations of oxygen and / or nitrogen generators can be used. Temperatures can be varied depending on the need to heat and / or cool the window. Those skilled in the art can adjust parameters such as pressure, concentration, temperature, etc., depending on their particular circumstances and the object being manufactured.

[0042] An exemplary apparatus for practicing these embodiments is shown schematically in Figure 5, with control lines (e.g., valves, drives, pumps, and light sources) omitted for clarity. Elements similar to those in Figure 1 are numbered the same in Figure 5. As in Figure 5 and described above, the inert gas supply 36 is here replaced by an ambient air inlet 37, a valve 38 (e.g., to limit air intake and maintain a desired vacuum), and a vacuum source (39), such as a diaphragm pump (although the inert gas supply includes a vacuum source in some embodiments). If desired, enhancements, such as switching the flow of gas supplied into the window cassette, can be implemented similarly as described in G. Price and B. Feller, "Window Cassettes for Reduced Polymerization Inhibitor Irregularity During Additive Manufacturing," U.S. Patent Application Publication No. 2020 / 0061919 (February 27, 2020), and B. Feller and G. Price, "Reduction of Polymerization Inhibitor Irregularity on Additive Manufacturing Windows," U.S. Patent Application Publication No. 2020 / 0094468 (March 26, 2020), the entire disclosures of which are incorporated herein by reference. However, those skilled in the art will understand that the desired oxygen partial pressure can be achieved by various means, including supplying oxygen and supplying a gas mixture containing oxygen (e.g., from an oxygen generator, gas tank, nitrogen generator, and combinations thereof) at reduced or elevated pressures, depending on the amount of oxygen in the gas mixture.

[0043] In some embodiments, it is preferable to fabricate the article in a sealed chamber so that the resin on top of the window can be in contact with a controlled atmosphere. Specifically, the gas or gas mixture has substantially the same partial pressure as the oxygen provided to the window cassette (e.g., the partial pressure of oxygen in the chamber is plus or minus 10 or 20 percent of the partial pressure of oxygen supplied to the window cassette). A non-limiting example of such an apparatus is shown in FIG. 6, which is similar to the example of FIG. 5, but adds a sealed chamber 40, ambient air inlet 37', control valve 38', and vacuum source 39' to provide low levels of oxygen within the chamber, as described above.

[0044] 5. How to reuse The resulting additively manufactured object composed of the photopolymerized product of cyclic olefin monomers can be recycled by contacting the object with a liquid acrylate (e.g., acrylic acid, ethyl acrylate) in the presence of a Grubbs catalyst for a time and at a temperature sufficient to depolymerize the photopolymerized product. In some embodiments, the object may be comminuted (e.g., by grinding, shredding, chopping, or pelletizing), and the contacting may be performed on the comminuted object.

[0045] The foregoing is illustrative of the present invention, and is not to be construed as limiting thereof. The present invention is defined by the following claims, including equivalents of the claims.

Claims

1. 1. A method for manufacturing a three-dimensional object by bottom-up additive manufacturing, comprising: (a) providing a carrier platform, a light source, and a light-transmissive window therebetween, the light-transmissive window comprising a gas-permeable member having a top surface and a bottom surface; (b) depositing a liquid resin on the window, the resin comprising a cyclic olefin monomer and a ring-opening metathesis polymerization photocatalyst (hereinafter referred to as "ROMP photocatalyst"); (c) contacting a gas containing oxygen with the bottom surface of the gas permeable member, wherein the gas contains the oxygen at a partial pressure of 0.1 to 11 kilopascals; (d) exposing the resin to light from the light source while advancing the carrier platform away from the window to form the three-dimensional object on the carrier platform; A method comprising:

2. The resin on the window is (i) in contact with ambient air, or 10. The method of claim 1, wherein (ii) said window is contacted with a second gas comprising oxygen at the same partial pressure as said gas supplied to said window.

3. 3. The method of claim 1 or 2, wherein a liquid interface is maintained between the object and the window by the resin during step (d).

4. 4. The method of any one of claims 1 to 3, wherein the gas comprises an inert gas selected from the group consisting of nitrogen, argon, helium, neon, krypton, xenon, radon, and combinations of two or more thereof.

5. The method of claim 4 wherein the gas comprises argon.

6. 6. The method of claim 1, wherein the gas is dissolved in a liquid carrier.

7. 7. The method of any one of claims 1 to 6, wherein the cyclic olefin monomer is selected from the group consisting of cyclopropene, cyclobutene, benzocyclobutene, cyclopentene, norbornene, norbornadiene, cycloheptene, cyclooctene, 7-oxanorbornene, 7-oxanorbornadiene, cyclodecene, 1,3-cyclooctadiene, 1,5-cyclooctadiene, 1,3-cycloheptadiene, [2.2.1]bicycloheptene, [2.2.2]bicyclooctene, norbornene, norbornadiene, ethylidenenorbornene, dicyclopentadiene, vinylnorbornene, cyclohexenylnorbornene, norbornene dicarboxylic anhydride, cyclododecene, 1,5,9-cyclododecatriene, and mixtures of two or more thereof.

8. The method of any one of claims 1 to 7, wherein the ROMP photocatalyst comprises a transition metal catalyst.

9. 9. The method of any one of claims 1 to 8, wherein the ROMP photocatalyst comprises ruthenium, tungsten, or osmium.

10. 10. The method of any one of claims 1 to 9, wherein the resin further comprises at least one additional component selected from the group consisting of light absorbers, pigments, dyes, matting agents, flame retardants, fillers, non-reactive and photo-reactive diluents, and combinations of two or more thereof.

11. 11. The method of any one of claims 1 to 10, wherein the resin further comprises a latent thermal ROMP catalyst, and the method further comprises heating the body after its formation to further polymerize the resin.

12. 1. An apparatus for additive manufacturing of an object from a photopolymerizable resin, the resin comprising a cyclic olefin monomer and a ring-opening metathesis polymerization photocatalyst (hereinafter referred to as "ROMP photocatalyst"), the apparatus comprising: (a) an optically transparent window including (i) a gas-permeable top member onto which a photopolymerizable resin can be disposed, (ii) a rigid bottom member, and (iii) a gas supply region disposed between the top member and the bottom member; (b) a carrier platform positioned above the window, on which an object may be fabricated from the resin; (c) a drive operatively coupled to the carrier platform and the optically transmissive window, the drive configured to advance the carrier platform and the window away from one another; (d) a light source disposed below the window and configured to polymerize the photopolymerizable resin; (e) an inert gas supply operably coupled to the gas supply region of the window, configured to (i) supply an inert gas to the resin through the top member, and (ii) receive oxygen from the resin through the top member; An apparatus comprising:

13. The apparatus of claim 12, wherein the inert gas supply comprises a nitrogen generator or an argon supply.

14. 14. The apparatus of claim 13, wherein the inert gas supply comprises a bottled gas blend.

15. 15. The apparatus of any one of claims 12 to 14, wherein the inert gas supply is configured to contact the inert gas with the bottom surface of the upper member at a pressure less than ambient air pressure.

16. 16. The apparatus of any one of claims 12 to 15, wherein the inert gas supply is configured to include an amount of oxygen sufficient to reduce stray curing, skirt formation, or flare around a growing three-dimensional object that increases defect rates in the process, but insufficient to suppress activation of the ROMP photocatalyst in the resin to an extent that prevents formation of the three-dimensional object.

17. 17. The device of any one of claims 12 to 16, wherein the window is configured to be in contact with oxygen in the ambient air.

18. (f) a sealed chamber containing said window; (g) a gas supply operably connected to the sealed chamber, the gas supply configured to supply a gas into the chamber, the gas containing oxygen at the same partial pressure as the gas supplied to the window; The apparatus of any one of claims 12 to 16, further comprising:

19. 19. The apparatus of any one of claims 12 to 18, further comprising a liquid carrier in which the inert gas is dissolved.

20. 12. The method of any one of claims 1 to 11, wherein the gas comprises the oxygen at a partial pressure of 2.5 to 8 kilopascals.

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