Photocurable composition for additive manufacturing and use thereof

Abstract

A thermoreversible photocurable composition is disclosed that has high strength at low temperatures but melts at high temperatures, making it suitable as a composition for additive manufacturing.

Description

[Technical Field]

[0001] The present invention relates to photocurable, three-dimensional printable compositions that polymerize to a solid when exposed to UV light and then soften and melt when heated. The photocurable compositions are useful in additive manufacturing processes, particularly for producing three-dimensional objects that require demountability. [Background technology]

[0002] Additive manufacturing, also known as 3D printing, has gained more attention over the past decade. Layer-by-layer production allows for the creation of small or large-scale, highly precise, custom-made products by linking together simple 3D models or using 3D scanners. Additive manufacturing is used in the production of medical devices, automotive parts, aerospace equipment and components, electronics, jewelry, fashion, and more.

[0003] Materials for additive manufacturing can be liquid-based, solid-based, or power-based to build freestanding structures. Based on the starting material, additive manufacturing can be performed using digital light processing, stereolithography, slot-die coating, spray coating, wet coating, screen printing UV nanoimprint lithography or photo-nanoimprint lithography, step and flash imprint lithography, selective laser sintering, fused deposition modeling, fused filament fabrication, polyjet, or inkjet printing. Reworkability is important for the removal and reuse of certain parts from a cost or efficiency standpoint.

[0004] Fused deposition modeling (FDM) is one of the most common methods of additive manufacturing, where molten thermoplastic material is extruded through a nozzle to form an object. The precision of the part is limited by the nozzle diameter, which is typically 0.2-1 mm. Additive manufacturing using digital light processing (DLP) and stereolithography can achieve higher accuracy and resolution compared to FDM, with comparable strength, but the part does not melt when heated.

[0005] There is a need in the art for high precision, high strength, and easily removable materials for three-dimensional printing processes, and the present invention fills this need. Summary of the Invention [Means for solving the problem]

[0006] The present invention provides thermoreversible photocurable compositions for printing three-dimensional or additively manufactured objects that require strong mechanical strength when formed, but soften and melt when heated, which is useful for reworking or removing parts or the entire object.

[0007] In one embodiment, the reworkable three-dimensional composition comprises: A) a monomer A having at least one functionality with a glass transition temperature value of less than about 25°C; B) a monomer B having at least one functionality with a glass transition temperature value greater than about 25°C; C) a thermoreversible crosslinker having a UV-curable functional group and a thermoreversible covalent bond; D) a photoinitiator; and E) additives selected from the group consisting of chain transfer agents, irreversible chain transfer agents, antioxidants, hindered amine light stabilizers, amine synergists, optical brighteners, UV screeners, fillers, dyes, waxes, plasticizers or mixtures thereof; Includes:

[0008] The reworkable three-dimensional composition may be the basis for forming an object. The photocurable composition maintains high mechanical strength at temperatures below about 130°C due to the thermoreversible bonds in the composition, and softens and melts at temperatures above about 130°C.

[0009] Another embodiment is directed to forming a reworkable three-dimensional composite object, comprising the steps of: 1) preparing a reworkable three-dimensional composition comprising: A) a monomer A having at least one functionality with a glass transition temperature value of less than about 25°C; B) a monomer B having at least one functionality with a glass transition temperature value greater than about 25°C; C) a thermoreversible crosslinker having a UV-curable functional group and a thermoreversible covalent bond; D) a photoinitiator; and E) an additive selected from the group consisting of a chain transfer agent, an irreversible chain transfer agent, an antioxidant, a hindered amine light stabilizer, an amine synergist, an optical brightener, a UV blocker, a filler, a dye, a wax, a plasticizer, or a mixture thereof; and 2) Applying the reworkable three-dimensional composition onto a substrate or depositing the mixture as a free-standing three-dimensional structure, thereby forming an object of the reworkable three-dimensional composition.

[0010] Another embodiment is directed to a method of manufacturing a reworkable three-dimensional object, comprising the steps of: 1) preparing a reworkable three-dimensional composition comprising: A) a monomer A having at least one functionality with a glass transition temperature value of less than about 25°C; B) a monomer B having at least one functionality with a glass transition temperature value greater than about 25°C; C) a thermoreversible crosslinker having a UV-curable functional group and a thermoreversible covalent bond; D) a photoinitiator; and E) additives selected from the group consisting of chain transfer agents, irreversible chain transfer agents, antioxidants, hindered amine light stabilizers, amine synergists, optical brighteners, UV screeners, fillers, dyes, waxes, plasticizers or mixtures thereof; 2) applying the reworkable three-dimensional composition onto a substrate or depositing the mixture as a free-standing three-dimensional structure; 3) drying, curing, or solidifying the reworkable three-dimensional composition, thereby forming a reworkable three-dimensional object; 4) optionally, heating a portion of the entire reworkable three-dimensional object at a temperature greater than 130°C to soften the reworkable three-dimensional object; 5) Optionally, removing the reworkable three-dimensional object. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic representation of a hardened reworkable three-dimensional composition. [Figure 2] 2A-2D are differential scanning calorimetry (DSC) curves of various compositions. [Figure 3] Figure 3 is a photograph of a vertically printed tensile specimen of Sample 1 with a height of 63 mm. DETAILED DESCRIPTION OF THE INVENTION

[0012] Three-dimensional (3D) or additive manufacturing (AM) is the creation of tangible objects by printing three-dimensional objects in successive layers from a digital design. Various methods are commonly used to print objects, including FDM (fused deposition modeling), SLA (stereolithography), SLS (selective laser sintering), or LCD (liquid crystal display). The appropriate AM composition is selected depending on the physical properties of the desired object and the printer. This composition can be a powder (thermoplastic, wax, ceramic, or metal), and light or a heat source is used to sinter / melt / fuse layers of powder together. Microdroplet jetting is also an AM technique. PLA or ABS can also be extruded in filament form to build layers and create predetermined shapes. Because objects can be printed and managed by a printer, even highly detailed and complex objects can be produced AM with built-in functionality and no assembly required.

[0013] The three-dimensional object is photocurable with actinic radiation, which is electromagnetic radiation capable of causing a photochemical reaction.

[0014] As used herein, the term melting point of a substance refers to the temperature at which the substance changes state from solid to liquid. At the melting point, the solid and liquid phases exist in equilibrium. As used herein, the term softening point refers to the temperature at which a substance softens, particularly the temperature at which amorphous materials begin to soften.

[0015] As used herein, a monomer is defined as a molecule that can be polymerized to become an oligomer or polymer. A monomer may be a monofunctional monomer having a single functional polymerizable group, or a polyfunctional monomer having multiple functional polymerizable groups. The molecular weight of the monomer may be low (e.g., about 100 to about 1,000 daltons), medium (e.g., about 1,000 to about 5,000 daltons), or high (e.g., about 5,000 to about 20,000 daltons). "Oligomer" refers to a defined small number of repeating monomer units, e.g., 10 to 5,000 units, preferably 10 to 1,000 units, that are polymerized to form a molecule. Oligomer is a subset of the term polymer. "Polymer" refers to any polymerization product with a chain length and molecular weight greater than that of an oligomer. A polymer may have a degree of polymerization of about 50 to about 25,000.

[0016] The present invention provides a thermoreversible photocurable composition for additive manufacturing. The composition maintains high mechanical properties until it is softened and removed. In one embodiment, the photocurable composition comprises: A) a monomer A having at least one functionality with a glass transition temperature value of less than about 25°C; B) a monomer B having at least one functionality with a glass transition temperature value greater than about 25°C; C) a thermoreversible crosslinker having a UV-curable functional group and a thermoreversible covalent bond; D) a photoinitiator; and E) an additive selected from the group consisting of a chain transfer agent, a reversible chain transfer agent (RAFT), an antioxidant, a hindered amine light stabilizer, an amine synergist, an optical brightener, a UV screener, a filler, a dye, a wax, a plasticizer, or a mixture thereof; Includes:

[0017] Photocurable compositions require a combination of cationically or radically curable monomers to form the polymer backbone. The combination of monomer A having a glass transition temperature value below about 25° C. and monomer B having a glass transition temperature value above about 25° C. provides a polymer network suitable for additive manufacturing processes, such as 3D printing.

[0018] The backbone is formed from at least two monomers, each of which independently has at least one functional group selected from (meth)acrylate, acrylate, vinyl ester, vinyl ether, allyl, N-vinyl, vinylamide, thiol, (meth)acrylamide, vinyl carbonate, acryloyl, vinyl carbamate, maleimide, cyanoacrylate, thiol and epoxide, styrenic resin, vinyl halide, acrylonitrile, nadimide, itaconimide, and vinyl ether. The term "backbone" is intended to refer to the chemical moieties to which the functional groups are attached or the chemical moieties present between the functional groups. In another embodiment, the backbone is formed from a single monomer.

[0019] Monomer A has a glass transition (Tg) temperature value of less than about 25°C, preferably less than about 0°C, and most preferably less than about -15°C, and contains at least one of the above-mentioned reactive groups. It is particularly preferred that the functional group of Monomer A is a methacrylate or acrylate. Particularly preferred examples of Monomer A include lauryl acrylate (Tg = 15°C), lauryl methacrylate (Tg = -65°C), isodecyl acrylate (Tg = -58°C), isodecyl methacrylate (Tg = -70°C), 2-propylheptyl acrylate (Tg = -68°C), isobutyl acrylate (Tg = -24°C), ethyl diglycol acrylate (Tg = -53°C), heptadecyl acrylate (Tg = -64°C), and 4-hydroxybutyl acrylate (Tg = -65°C).

[0020] Monomer A is present in the range of about 1% by weight to about 30% by weight, preferably about 3% by weight to about 15% by weight of the entire photocurable composition.

[0021] Monomer B has a glass transition temperature value greater than about 25° C., preferably greater than 50° C., more preferably greater than 75° C. It is particularly preferred that Monomer B contains a methacrylate, acrylate, vinyl ester, vinyl, ether, allyl, N-vinyl, vinylamide, acrylamide, vinyl carbonate, acryloyl, vinyl carbamate, maleimide, cyanoacrylate, thiol, or epoxide functional group.

[0022] Examples of reactive groups of the monomer group B include isobornyl acrylate (Tg=95°C), isobornyl methacrylate (Tg=110°C), N-vinyl caprolactam (Tg=125°C), cyclohexyl methacrylate (Tg=92°C), hydroxyethyl methacrylate (Tg=55°C), hydroxypropyl methacrylate (Tg=76°C), phenyl methacrylate (Tg=110°C), methacrylic acid (Tg=228°C), acrylamide (Tg=165°C), N-vinylpyrrolidone (Tg=150°C), acryloylmorpholine (Tg=145°C), and N,N-dimethylacrylamide (Tg=119°C).

[0023] Monomer B is present in the range of about 10% to about 75% by weight, preferably about 20% to about 60% by weight, and more preferably about 25% to about 55% by weight of the total photocurable composition.

[0024] Combining two monomers with different Tg's can provide a balanced combination of high strength, high ductility, and high modulus. If the Tg of the monomer combination in the photocurable composition is too high (e.g., above 100°C), the resulting polymer will exhibit high viscosity upon heating and will be difficult to soften. In contrast, if the Tg of the monofunctional monomer used is too low (e.g., below 20°C), the mechanical properties of the resulting polymer will be poor, and the photocurable composition will deform under applied stress.

[0025] The monomers in combination with the thermoreversible crosslinking agent in the above ranges provide sufficient mechanical and physical properties in flexibility, tensile strength, and moldability while maintaining meltability.

[0026] The elastic modulus of the backbone, monomer A and monomer B, including the thermoreversible crosslinker, should be greater than about 10 MPa Young's modulus according to ASTM D638.

[0027] The photocurable composition further comprises a thermoreversible crosslinker having a UV-curable functional group and a thermoreversible covalent bond. a) a bismaleimide or a compound having two or more maleimide groups; b) furfuryl methacrylate or furfuryl acrylate, The molar ratio of a to b is 1:0.5 to 1:2.

[0028] In one embodiment, the thermoreversible crosslinker is prepared by reacting a bismaleimide with two molar equivalents of furfuryl methacrylate. In another embodiment, the thermoreversible crosslinker is prepared by reacting a bismaleimide with two molar equivalents of furfuryl acrylate. In yet another embodiment, the thermoreversible crosslinker is prepared by reacting a starting material containing two or more maleimide groups with 0.5 to 1 molar equivalent of furfuryl methacrylate per maleimide. In another embodiment, the thermoreversible crosslinker is prepared by reacting a starting material containing two or more maleimide groups with 0.5 to 1 molar equivalent of furfuryl acrylate per maleimide. In another embodiment, the thermoreversible crosslinker is prepared by reacting a bismaleimide with two molar equivalents of a reactant containing one furfuryl group and one methacrylate group. In yet another embodiment, the thermally reversible crosslinker is prepared by reacting a bismaleimide with two molar equivalents of a reactant containing one furfuryl group and one acrylate group.

[0029] The Diels-Alder reaction forms an adduct between bismaleimide and furfuryl acrylate at temperatures up to about 80°C. The adduct is thermally reversible via a reverse Diels-Alder reaction at temperatures between about 80°C and about 180°C. The adduct forms as the temperature rises to about 80°C, and the bond dissociates when the adduct reaches the inversion temperature between about 80°C and 180°C. The best way to dissociate the adduct is to hold the adduct above the inversion temperature for a minimum amount of time. The temperature and time can be determined by experimentation by those skilled in the art, e.g., higher temperatures for shorter times or lower temperatures for longer times.

[0030] [ka]

[0031] The thermoreversible crosslinker forms a network reaction between the pendant furan and / or maleimide heterocycles and the polymer.

[0032] [ka]

[0033] The stereochemistry and actual location of the furan or bismaleimide within the polymer chain determines its reactivity.

[0034] In one example, the thermoreversible crosslinker is a furan-maleimide Diels-Alder adduct of bismaleimide (1,1'-(methylenedi-4,1-phenylene)bismaleimide), which reacts with two molar equivalents of furfuryl methacrylate to form (methylenebis(4,1-phenylene))bis(1,3-dioxo-2,3,3a,4,7,7a-hexahydro-1H-4,7-epoxyisoindole-2,5-diyl)bis(2-methylacrylate).

[0035] In yet another embodiment, the thermoreversible crosslinker is prepared by reacting a polyimide having pendant maleimide functional groups with a trifuran derivative.

[0036] In one embodiment, the thermoreversible crosslinker is prepared by reacting a bismaleimide with two molar equivalents of furfuryl glycidyl ether. In another embodiment, the thermoreversible crosslinker is prepared by reacting a starting material containing two or more maleimide groups with 0.5 to 1 molar equivalent of furfuryl glycidyl ether per maleimide.

[0037] In another embodiment, the thermoreversible crosslinker is prepared by reacting a bismaleimide with two molar equivalents of a reactant containing one furfuryl group and one epoxy group.

[0038] In another embodiment, the thermoreversible crosslinker is prepared by reacting a bismaleimide with two molar equivalents of a reactant containing one furfuryl group and one acrylamide group.

[0039] In another embodiment, the thermally reversible crosslinker is prepared by reacting a bismaleimide with two molar equivalents of a reactant containing one furfuryl group and one methacrylamide group.

[0040] In another embodiment, the thermally reversible crosslinker is prepared by reacting a bismaleimide with two molar equivalents of a reactant containing one furfuryl group and one vinyl group.

[0041] In another embodiment, the thermally reversible crosslinker is prepared by reacting a bismaleimide with two molar equivalents of a reactant containing one furfuryl group and one vinyl ester group.

[0042] In another embodiment, the thermally reversible crosslinker is prepared by reacting a bismaleimide with two molar equivalents of a reactant containing one furfuryl group and one vinyl ether group.

[0043] In another embodiment, the thermally reversible crosslinker is prepared by reacting a bismaleimide with two molar equivalents of a reactant containing one furfuryl group and one cyanoacrylate group.

[0044] Thermoreversible crosslinkers can have various molecular weight ranges, including low molecular weight (about 500 to about 1,000 daltons), medium molecular weight (about 1,000 to about 5,000 daltons), and high molecular weight (5,000 to about 10,000 daltons). Depending on factors such as viscosity, reaction rate, and miscibility, one skilled in the art can select an appropriate thermoreversible crosslinker having an appropriate molecular weight range.

[0045] The thermoreversible crosslinking agent is present in an amount of about 10% by weight to about 90% by weight, preferably about 20% by weight to about 50% by weight, of the total photocurable composition.

[0046] The photocurable composition also contains a photoinitiator, including both Type I and Type II photoinitiators. Suitable photoinitiators include phosphine oxide derivatives, triazines, ketones, peroxides, diketones, azides, azo derivatives, disulfide derivatives, disilane derivatives, thiol derivatives, diselenide derivatives, diphenyl ditelluride derivatives, digermane derivatives, distannane derivatives, carbogermanium compounds, carbon-silicon derivatives, sulfur-carbon derivatives, sulfur-silicon derivatives, peresters, bartone ester derivatives, hydroxamic and thiohydroxamic acids and esters, organic borates, organometallic compounds, titanocenes, chromium complexes, aluminate complexes, carbon-sulfur or sulfur-sulfur iniferter compounds, oxyamines, aldehydes, acetals, silanes, phosphorus-containing compounds, borane complexes, thioxanthone derivatives, coumarins, anthraquinones, fluorenones, and ferrocenium salts. Particularly desirable photoinitiators include benzophenones, anthraquinones, and fluoroenones. In one embodiment, the photoinitiator is a Norrish Type I initiator selected from 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), 1-hydroxycyclohexyl-phenyl ketone, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (BAPO), or ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate (TPO-L) or polymeric derivatives thereof.

[0047] Commercially available photoinitiators include Omnirad TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide), Omnirad 184 (1-hydroxycyclohexyl-phenyl ketone), the Irgacure series, the Chemcure series, and the Daido UV-cure series.

[0048] If used, the photoinitiator is present in an amount of from about 0.01% to about 15% by weight of the total composition.

[0049] The photocurable composition may, but need not, contain a thermal initiator.

[0050] The photocurable composition may further contain additives including chain transfer agents, irreversible chain transfer agents, antioxidants, hindered amine light stabilizers, amine synergists (both reactive and non-reactive), optical brighteners, UV blockers, fillers including both inorganic and organic fillers, dyes (also called pigments), waxes (including wax-like additives), plasticizers, or mixtures thereof. Chain transfer agents or irreversible chain transfer agents reduce the average molecular weight between crosslinks in the cured composition. Antioxidants extend the shelf life of the photocurable composition. Hindered amine light stabilizers improve the weatherability of the photocurable composition. Amine synergists increase the cure rate of the photocurable composition. Optical brighteners control the penetration depth of light during curing of the photocurable composition. UV blockers control the penetration depth of light during curing, improve weatherability, and prevent UV degradation of the composition. Organic and inorganic fillers increase the stiffness or modulus of elasticity, providing mechanical strength by resisting abrasion and tear in the cured composition. Dyes function as colorants and control the penetration depth of light during curing of the photocurable composition. Waxes improve the melt flow and processing of the cured composition. Plasticizers provide mechanical strength by adding flexibility and impact resistance to the cured composition, further aiding in the flow and processability of the cured composition.

[0051] Chain transfer agents include free radical living polymerization catalysts, catalytic chain transfer agents, reversible addition-fragmentation chain transfer (RAFT) agents, and iodine transfer agents for polymerization.

[0052] Particularly preferred additives are addition-fragmentation chain transfer agents. Exemplary agents include allyl sulfide, allylphenyl sulfone, ethyl 2-tosyloxyacrylate, ethyl 2-(1-hydroxyperoxyethyl)propenoate, mono-β-allyl sulfone, alpha-(benzyloxy)styrene, carbon tetrachloride, carbon tetrabromide, bromotrichloromethane, 4-methylbenzenethiol, pentaphenylethane, tert-nonyl mercaptan, 4,4'-thiobisbenzenethiol, n-octyl mercaptan, thioglycolic acid, and mixtures thereof. The addition-fragmentation chain transfer agent can design and promote the reversibility of the photocurable composition.

[0053] During the Diels-Alder reaction of bismaleimide and furfuryl acrylate under free radical polymerization, a side reaction occurs that forms branches in the polymer backbone. This increases the molecular weight and affects the irreversible crosslinking reaction of the photocurable composition. This avoids the branching side reaction of the polymer and effectively reduces the molecular weight. A chain transfer agent is added to the photocurable composition. The addition of this chain transfer agent softens the polymer at temperatures around 130°C. This allows the photocurable composition to soften sufficiently to separate from the master pattern by heat.

[0054] Figure 1 is a schematic diagram of a cured photocurable composition. The squares represent hard segments formed from high Tg monomers. The hard segments provide rigidity and strength to the cured article. The soft segments formed from low Tg monomers are represented by lines, which provide flexibility and toughness to the cured article. The thermoreversible crosslinkers are represented as spheres connected to the hard segments and can be debonded and dissociated upon heating. The chain transfer agent can adjust the molecular weight of the polymer and reduce the unit length (n) of the polymer. Under sufficient heat exposure, the cured photocurable composition softens and melts due to the dissociation of the thermoreversible crosslinkers and the reaching of the glass transition temperature.

[0055] Examples of antioxidants include butylated hydroxytoluene, 4-methoxyphenol, 4,4'-(2-tert-butyl-5-methylphenol), 2,2'-methylenebis(6-tert-butyl-4-methylphenol), 2,5-di(tert-amyl)hydroquinone, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphate, and tris(2,4-di-tert-butylphenyl)phosphite.

[0056] Exemplary hindered amine light stabilizers include N,N',N'',N'''-tetrakis(4,6-bis(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)triazin-2-yl)-4,7-diazadecane-1,10-diamine, bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, decanedioic acid, 1,10-bis(1,2,2,6,6-pentamethyl-4-piperidinyl) ester decanedioic acid, 1-methyl 10-(1,2,2,6,6-pentamethyl-4-piperidinyl), and bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate.

[0057] Typical amine synergists or coinitiators commonly used with Type II photoinitiators include, but are not limited to, tertiary aliphatic amines such as methyldiethanolamine, dimethylethanolamine, triethanolamine, triethylamine, and N-methylmorpholine; aromatic amines such as amyl paradimethylaminobenzoate, 2-n-butoxyethyl-4-(dimethylamino)benzoate, 2-(dimethylamino)ethyl benzoate, ethyl-4-(dimethylamino)benzoate, and 2-ethylhexyl-4-(dimethylamino)benzoate; and (meth)acrylated amines such as dialkylaminoalkyl(meth)acrylates (e.g., diethylaminoethyl acrylate) or N-morpholinoalkyl-(meth)acrylates (e.g., N,N-morpholinoethyl-acrylate).

[0058] In certain embodiments, the photocurable composition may include one or more optical brighteners (i.e., optical brightening agents). Optical brightening agents (OBAs), fluorescent brightening agents (FBAs), or fluorescent whitening agents (FWAs) are compounds that absorb light in the ultraviolet and violet regions of the electromagnetic spectrum (usually 340-370 nm) and emit light in the blue region (typically 420-470 nm) by fluorescence. Suitable optical brighteners include, but are not limited to, bisbenzoxazoles; coumarins; stilbenes, including triazine stilbenes and biphenyl stilbenes; diazoles; triazoles; benzoxazolines; combinations thereof; and the like. Optical brighteners are preferred. In some embodiments, the optical brightener acts as a sensitizer. Commercially available optical brighteners include, but are not limited to, Optiblank PL (3V Sigma); Benetex OB, OB Plus, and OB-M1 (Meizo).

[0059] UV blocking agents. Any suitable filler may be used in connection with the various embodiments described herein depending on the desired properties of the part or object being fabricated. Accordingly, the filler may be solid or liquid, organic or inorganic, and may be reactive and non-reactive rubbers, examples of which include siloxanes, organic phosphinates, acrylonitrile butadiene rubber; reactive and non-reactive thermoplastics (such as poly(etherimide), maleimide-styrene terpolymer, polyacrylate, polysulfone, and polyethersulfone), silicates (such as talc, clay, silica, or mica), glass, carbon nanotubes, graphene, carbon fiber, metals, and cellulose nanocrystals, and inorganic fillers such as combinations thereof.

[0060] Any suitable filler may be used in connection with the various embodiments described herein, depending on the desired properties of the part or object being fabricated. Accordingly, fillers may be solid or liquid, organic or inorganic, and may include reactive and non-reactive rubbers, examples of which include siloxanes, organic phosphinates, acrylonitrile butadiene rubbers (such as poly(etherimides), maleimide-styrene terpolymers, polyacrylates, polysulfones, and polyethersulfones), silicates (talc, clay, silica, or mica), glass, carbon nanotubes, graphene, carbon nanostructures, carbon fibers, artificial spider silk and its derivatives, metal and cellulose nanocrystals, core-shell, and combinations thereof. One or more polymeric and / or inorganic reinforcing agents may be included in the photocurable composition. The reinforcing agent may be substantially uniformly dispersed in the polymerization product in the form of particles, with particle sizes ranging from about 1 μm to about 200 μm in diameter. Such reinforcing agents include those formed from elastomers, branched polymers, hyperbranched polymers, dendrimers, rubbery polymers, rubbery copolymers, block copolymers, core-shell particles, oxides, or clays, polyhedral oligomeric silsesquioxanes (POSS), carbonaceous materials (e.g., carbon black, carbon nanotubes, carbon nanofibers, and fullerenes), ceramics, and silicon carbide (with or without surface modification or functionalization). Core-shell particles, the compositions of which are described in U.S. Patent Application Publication Nos. 2010 / 0280151 and 2007 / 0027233 (the entire contents of which are incorporated herein by reference), may also be added as fillers. In some embodiments, the filler has an average particle size of less than 1,000 nanometers (nm). Typically, the average particle size of the filler is less than 500 nm, 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, but if the particle is not spherical, the particle size is defined as the longest dimension of the particle.

[0061] Examples of waxes and wax-like additives include microcrystalline wax, beeswax, carnauba wax, paraffin wax, polyethylene glycol wax, candelilla wax, ozokerite wax, olika wax, microcrystalline wax, amide wax, erucamide wax, polypropylene wax, paraffin wax, polyethylene wax, polytetrafluoroethylene wax, carnauba wax, polyethylene glycol having a molecular weight of more than 1000 daltons, poly(tetramethylene ether) glycol having a molecular weight of more than 650 daltons, etc. The wax may also be a combination of the above waxes. The waxes and wax-like additives may also have reactive or non-reactive functional groups on the waxes and wax-like additives.

[0062] In certain embodiments, the photocurable composition may include one or more plasticizers. Suitable plasticizers include, but are not limited to, phthalates, benzoic acid-based esters, polyketones, esters of diphenic acid, esters of cyclohexanepolycarboxylic acids, dialkyl adipates, or mixtures thereof. Some examples include bis(2-ethylhexyl phthalate) (DEHP or DOP), diisononyl phthalate (DINP), dioctyl phthalate (DnOP), diisodecyl phthalate (DIDP), dipropylheptyl phthalate (DPHP), di-2-ethylhexyl terephthalate (DOTP or DEHT), and diisononyl-1,2 cyclohexanedicarboxylate (DIDC, an example of which is BASF's Hexamol® Dinch®).

[0063] The photocurable composition may have additional components solubilized or dispersed therein, including pigments, dyes, detectable compounds (e.g., fluorescent, phosphorescent, and emissive), fillers, light absorbers, dispersants, slip agents, leveling agents, melt flow modifiers, optical brighteners, defoamers, antistatic agents, UV sensitizers, waxes, plasticizers, amine synergists or coinitiators, or polymerization inhibitors, depending on the particular purpose of the product being made.

[0064] In certain embodiments, the photocurable composition may contain one or more surfactants or dispersants. Surfactants include, but are not limited to, anionic surfactants, nonionic surfactants, cationic surfactants, or amphoteric surfactants. Anionic surfactants include mixed fatty acid sodium soaps and fatty acid sodium salts such as sodium stearate, higher alcohol sodium sulfates, sodium alkyl sulfates, alkylbenzene sulfonates, etc. Cationic surfactants and amphoteric surfactants include alkylamines, alkylbetaines, etc. Examples of dispersants include ethyl cellulose, ethylhydroxyethyl cellulose, etc.

[0065] In certain embodiments, the photocurable composition may include one or more slip agents. Slip agents include, but are not limited to, silicones such as polydimethylsiloxane (PDMS), fluoropolymers, alkyl ketal esters, and fatty acid amides. Generally, fatty acid amides are derived from saturated and / or unsaturated aliphatic fatty acids containing 16 to 22 carbon atoms, including, but not limited to, erucamide, oleamide, stearamide, behenamide, and oleyl palmitamide.

[0066] In certain embodiments, the photocurable composition may include one or more leveling agents, including, but not limited to, polyaminoamides and derivatives thereof, polyalkanolamines and derivatives thereof, polyethyleneimines and derivatives thereof, quaternized polyethyleneimines, polyglycines, poly(allylamine), polyanilines, polyureas, polyacrylamides, poly(melamine-co-formaldehyde), reaction products of amines and epichlorohydrin, reaction products of amines, epichlorohydrin, and polyalkylene oxides, reaction products of amines and polyepoxides, polyvinylpyridines, polyvinylimidazoles, polyvinylpyrrolidones, or copolymers thereof, nigrosine, pentamethyl-para-rosaniline hydrohalide, hexamethyl-pararoaniline hydrohalide, or compounds containing a functional group of the formula NRS, where R is a substituted alkyl, unsubstituted alkyl, substituted aryl, or unsubstituted aryl. Typically, the alkyl group is a (C1-C6) alkyl, preferably a (C1-C4) alkyl. Generally, the aryl group includes a (C6-C20) aryl, preferably a (C6-C10) aryl. Such aryl groups may further include heteroatoms such as sulfur, nitrogen, and oxygen. Preferably, the aryl group is phenyl or naphthyl. Compounds containing a functional group of formula NRS are generally known and generally commercially available, and may be used without further purification.

[0067] The additives are present in an amount of from about 0.01% to about 60%, preferably from about 1% to 25%, more preferably from about 1% to about 10% by weight of the total composition.

[0068] The composition is then prepared by combining the components and mixing until reacted. The reacted mixture is applied to a substrate by either coating, lithography, and / or printing, or deposited as a freestanding 3D structure. Applications include vat polymerization, slot-die coating, spray coating, wet coating, screen printing, UV nanoimprint lithography or photo-nanoimprint lithography, step-and-flash imprint lithography, inkjet printing, and others. One skilled in the art may use solvents, monomers, and rheology modifiers to adjust the viscosity of the composition to suit the selected application method. The height range or thickness of the applied structures varies from about 1 μm to about 2000 μm. Taller or thicker structures may be created by applying multiple layers of the composition onto the structure, increasing the thickness to the desired height.

[0069] To photocure the photocurable composition, the composition is exposed to radiation in the electromagnetic spectrum ranging from about 355 nm to about 405 nm. The radiation may be emitted from an LED light source, which may be selected from a laser, multiple lasers, or one or more projectors. The LED light source may be applied from below or above the reservoir containing the photocurable composition.

[0070] Curing occurs by exposing the composition to actinic, ultraviolet, and visible light, which polymerizes and solidifies the composition. Single-reaction mechanism energy polymerization uses energy to initiate and drive polymerization through a single reaction mechanism. Irradiation involves exposure to actinic, ultraviolet, and visible light. Examples include UV light (100 nm to 405 nm), visible light (405 nm to 700 nm), or electron beams. Examples of suitable light sources include LEDs, laser diodes, laser beams, lamps (e.g., halogen lamps, Xe, and Xe-Hg lamps), LED lasers or LED projectors used in additive manufacturing, LCD, LED, or plasma screens that emit visible light, and mobile or tablet devices. This polymerization is carried out through a single reaction mechanism, such as free radical, cationic, Michael addition, step-growth, or click chemistry, to name a few. Photocurable compositions are typically in a liquid or viscous state and polymerize to form three-dimensional solids.

[0071] Optionally, after curing, the UV-cured photocurable composition may be treated with a solvent or cleaning solution. The solvent or cleaning solution may be selected from glycol ether derivatives, lower alkyl alcohols such as isopropanol, or mild surfactants. The solvent or cleaning solution used here may be heated to an elevated temperature. In this way, any unreacted material on the surface of the part may become fluid, making it easier to remove by solvation or mechanical agitation, such as ultrasonication.

[0072] The UV-cured photocurable composition softens above a specific temperature, particularly in the range of about 120°C to about 200°C, more preferably in the range of about 130°C to about 180°C. The photocurable composition can be designed by fine-tuning the thermoreversible crosslinker and chain transfer agent so that it softens at a specific temperature within the range of 120 to 200°C. In one embodiment, the photocurable composition provides high mechanical strength below 130°C and melts at temperatures above 130°C.

[0073] Without being bound by any particular theory, the addition of a difunctional monomer or oligomer with a balanced Tg provides strength to the polymer backbone. This resembles an irreversibly crosslinked system of difunctional monomers / oligomers, similar to a thermoset resin that does not melt but rather burns when heated. The photocurable compositions herein are designed to decrosslink the difunctional monomers / oligomers via a reversible Diels-Alder reaction upon exposure to heat. The combination of the reversible Diels-Alder reaction and a chain transfer agent that reduces the side chains and the overall molecular weight of the polymer results in the photocurable compositions softening at approximately 130°C. The photocurable compositions described herein are designed to develop mechanical strength below approximately 130°C, yet exhibit ductility above approximately 130°C. This unique property is used in the pharmaceutical, agricultural, adhesive, and packaging industries.

[0074] Heat allows for the thermoreversibility of the photocurable composition. This has many applications, including additive manufacturing and other processes. Three-dimensional printing can be used to apply the thermoreversible photocurable composition when reworkability or removability is required. The composition may be applied in a variety of ways.

[0075] The photocurable composition can be used to form articles and may be applied by slot die coating, spray coating, wet coating, screen printing UV nanoimprint lithography or photo nanoimprint lithography, step and flash imprint lithography, polyjet or inkjet printing to form 3D structures.

[0076] In one embodiment, the photocurable composition can be the basis for an investment shell. A second composition can be formed on the innermost layer of the investment shell and then solidified, essentially taking the shape of the removed pattern. After the second composition has hardened, the investment shell can be removed by heat or broken to separate it from the object.

[0077] It will be apparent to those skilled in the art that many modifications and variations of this invention can be made without departing from its spirit and scope. The specific embodiments described herein are offered by way of example only, and the invention is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. [Example]

[0078] The thermoreversible crosslinker for Sample 1 was prepared by dissolving 1 molar equivalent of BMI-1400 (Designer Molecules) with 2 molar equivalents of furfuryl methacrylate by centrifugal mixing at 2000 RPM for 5 minutes. This solution was transferred to a round-bottom flask and mixed at 100 RPM at 60°C for 8 hours, then cooled to 25°C over 24 hours. The remaining ingredients for Sample 1, listed in Table 1, were then mixed in a container and then mixed using an overhead mixer (Cowles blade) at 800 RPM for 2 hours. The resulting liquid resin was then loaded into a DLP-based 3D printer and printed in 100 micron layers at 75 mJ / cm per layer. 2 The ASTM D638 Type IV specimens were printed using a mercury bulb at a dose of 1500 mJ / cm. The specimens were post-treated by rinsing in isopropanol alcohol for 2 minutes and then air-dried at 25°C for 30 minutes. Each specimen was exposed to a mercury bulb at a dose of 1500 mJ / cm. 2 (total exposure energy) and then stored at 25 °C for 24 h before testing on an Instron Dual Column Universal Testing System for tensile testing. A photograph of a tensile specimen made with Sample 1 (printed vertically, 63 mm high) is shown in Figure 3.

[0079] DSC was performed on each sample according to ASTM E794-06 (heating rate 5°C / min, N2 purge 50 mL / min, range 25-300°C). DSC measurements were performed to determine the melting temperature based on two specimen samples. The samples at the melting temperature were further observed.

[0080] Samples 2 to 4 were prepared in the same manner. The thermoreversible crosslinking agent was prepared using the above starting compound.

[0081] [Table 1]

[0082] Only Sample 1 showed reversibility. After softening, Sample 1 melted at 150°C. Only Sample 1 had a DSC melting temperature and melted. Samples 2 to 4 did not melt.

[0083] The stress at break and 110% strain at break for Sample 1 were measured and are reported in Table 1. Stress and strain values ​​were not measured for Samples 2-4 as they showed no signs of reversibility.

[0084] Sample 1 contains a thermoreversible crosslinker, an additive for MW control, a high Tg component, and a low Tg component. As shown in Figure 2A, there are endothermic peaks at 110 and 130 °C, which correspond to the retro Diels-Alder reaction (thermal decrosslinking). Sample 1 also exhibits additional endothermic transitions at 70 and 100 °C, indicating melting. Sample 1 melted and became liquid above 130 °C. Sample 2, which does not contain an additive for MW control, showed no signs of melting and only softened above 130 °C.

[0085] In Sample 3, the thermoreversible crosslinker was replaced with a standard crosslinker, a urethane methacrylate oligomer. As shown in Figure 2C, no endothermic transition occurred, and this sample remained a thermoset and did not melt or soften even above 150 °C.

[0086] Sample 4 does not contain any low Tg components. Figure 2D shows an endothermic peak at 130 °C, corresponding to the reverse Diels-Alder reaction, but the composition did not melt above 150 °C. In Sample 4, only a gel-like material formed above 130 °C.

Claims

1. A) a monomer A having at least one functionality with a glass transition temperature value of less than about 25°C; B) a monomer B having at least one functionality with a glass transition temperature value greater than about 25°C; C) a thermoreversible crosslinker having a UV-curable functional group and a thermoreversible covalent bond; D) a photoinitiator; and E) additives selected from the group consisting of chain transfer agents, irreversible chain transfer agents, antioxidants, hindered amine light stabilizers, amine synergists, optical brighteners, UV screeners, fillers, dyes, waxes, plasticizers or mixtures thereof; A photocurable composition comprising:

2. 2. The photocurable composition of claim 1, wherein the at least one functional monomer A has a functional group selected from methacrylate, acrylate, vinyl ester, vinyl ether, allyl, N-vinyl, vinylamide, acrylamide, vinyl carbonate, acryloyl, vinyl carbamate, maleimide, cyanoacrylate, thiol, or epoxy.

3. 2. The photocurable composition of claim 1, wherein the at least one functional monomer A has a functional group selected from methacrylate, acrylate, N-vinyl, acrylamide, maleimide, or acryloyl.

4. 2. The photocurable composition of claim 1, wherein the at least one functional monomer B has a functional group selected from methacrylate, acrylate, vinyl ester, vinyl ether, allyl, N-vinyl, vinylamide, acrylamide, vinyl carbonate, acryloyl, vinyl carbamate, maleimide, cyanoacrylate, thiol, or epoxy.

5. 5. The photocurable composition of claim 4, wherein the at least one functional monomer B has a functional group selected from narrow methacrylate, acrylate, N-vinyl, acrylamide, maleimide or acryloyl.

6. The thermoreversible crosslinking agent is a) a bismaleimide or a compound having two or more maleimide groups; b) furfuryl methacrylate or furfuryl acrylate, is prepared by reacting 2. The photocurable composition according to claim 1, wherein the molar ratio of a to b is 0.5 to 2 equivalents.

7. 2. The photocurable composition of claim 1, wherein the photoinitiator is a Norrish Type I initiator selected from 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), 1-hydroxycyclohexyl-phenyl ketone, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (BAPO), or ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate (TPO-L) or polymeric derivatives thereof.

8. 2. The photocurable composition of claim 1, wherein the additive is a chain transfer agent selected from the group consisting of allyl sulfide, allyl phenyl sulfone, ethyl 2-tosyloxyacrylate, ethyl 2-(1-hydroxyperoxyethyl)propenoate, mono-β-allyl sulfone, alpha-(benzyloxy)styrene, carbon tetrachloride, carbon tetrabromide, bromotrichloromethane, 4-methylbenzenethiol, pentaphenylethane, tert-nonyl mercaptan, 4,4′-thiobisbenzenethiol, n-octyl mercaptan, thioglycolic acid, and mixtures thereof.

9. The photocurable composition of claim 1 having a melting temperature of from about 100°C to about 250°C.

10. A) a monomer A having at least one functionality with a glass transition temperature value of less than about 25°C; B) a monomer B having at least one functionality with a glass transition temperature value greater than about 25°C; C) Oligomers having two or more furan-maleimide Diels-Alder adducts; D) a photoinitiator; and E) Additives selected from the group consisting of chain transfer agents, irreversible chain transfer agents, addition-fragmentation chain transfer agents (AFCTs), antioxidants, hindered amine light stabilizers, amine synergists, optical brighteners, UV screeners, fillers, dyes, waxes, plasticizers or mixtures thereof. A photocurable composition comprising:

11. 11. The photocurable composition of claim 10, wherein the at least one functional monomer A has a functional group consisting of methacrylate, acrylate, acryloyl, vinyl ester, vinyl ether, allyl, N-vinyl, and mixtures thereof.

12. 11. The photocurable composition of claim 10, wherein the at least one functional monomer B has a functional group consisting of methacrylate, acrylate, acryloyl, vinyl ester, vinyl ether, allyl, N-vinyl, and mixtures thereof.

13. The oligomer is A) a bismaleimide or a compound having two or more maleimide groups; B) furfuryl methacrylate or furfuryl acrylate, is prepared by reacting 11. The photocurable composition according to claim 10, wherein the molar ratio of a to b is 0.5 to 2 equivalents.

14. 11. The photocurable composition of claim 10, wherein the photoinitiator is a Norrish Type I initiator selected from 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), 1-hydroxycyclohexyl-phenyl ketone, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (BAPO), ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate (TPO-L), or polymeric derivatives thereof.

15. 11. The photocurable composition of claim 10, wherein the additive is a chain transfer agent selected from the group consisting of allyl sulfide, allyl phenyl sulfone, ethyl 2-tosyloxyacrylate, ethyl 2-(1-hydroxyperoxyethyl)propenoate, mono-β-allyl sulfone, alpha-(benzyloxy)styrene, carbon tetrachloride, carbon tetrabromide, bromotrichloromethane, 4-methylbenzenethiol, pentaphenylethane, tert-nonyl mercaptan, 4,4′-thiobisbenzenethiol, n-octyl mercaptan, thioglycolic acid, and mixtures thereof.

16. The photocurable composition of claim 10 having a melting temperature of from about 100°C to about 250°C.

17. 11. An object made from the cured photocurable composition of claim 10.

18. 1) preparing a photocurable composition comprising: a. Monomer A having at least one functionality with a glass transition temperature value of less than about 25°C; b. Monomer B having at least one functionality with a glass transition temperature value greater than about 25°C; c. a thermoreversible crosslinker having a UV-curable functional group and a thermoreversible covalent bond; d. a photoinitiator; and e. an additive selected from the group consisting of a chain transfer agent, an irreversible chain transfer agent, an antioxidant, a hindered amine light stabilizer, an amine synergist, an optical brightener, a UV blocker, a filler, a dye, a wax, a plasticizer, or a mixture thereof; 2) applying the photocurable composition onto a substrate as a free-standing 3D structure; 3) curing the free-standing 3D structure into a photocured composition; 4) heating the photocured composition to a temperature sufficient to soften the photocured composition into a softened composition; 5) removing the softened composition from the substrate; 1. A method for manufacturing a reworkable 3D printed object, comprising:

19. 20. The method of manufacturing a reworkable 3D object of claim 18, wherein applying the photocurable composition is by digital light processing, stereolithography, slot die coating, spray coating, wet coating, screen printing UV nanoimprint lithography, photo nanoimprint lithography, step and flash imprint lithography, selective laser sintering, fused deposition modeling, fused filament fabrication, polyjet, or inkjet printing.

20. 20. The method for manufacturing a reworkable 3D object of claim 18, wherein the temperature in step 4) is from about 130°C to about 250°C.

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