Photocurable resin composition and cured product thereof

Abstract

To provide a photocurable resin composition having excellent storage stability while suppressing volume shrinkage due to curing.SOLUTION: There is provided a photocurable resin composition which comprises (A) a monofunctional (meth)acrylic monomer, (B) at least one polyfunctional monomer selected from the group consisting of a polyfunctional (meth)acrylic acid ester and a polyfunctional urethane (meth)acrylate, (C) cross-linked poly(meth)acrylic ester particles, (D) resin particles having a specific gravity of 70 to 95% of the component (C), and (E) a photopolymerization initiator.SELECTED DRAWING: None

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a photocurable resin composition and a cured product thereof. [Background technology]

[0002] Photocurable resin compositions are used as raw materials for obtaining stereolithography using, for example, a 3D printer, and are used in a variety of applications. For example, it is known that a stereolithography object obtained using a photocurable resin composition is used as a resin mold (lost model), an inorganic material such as plaster is placed around the resin mold, and the resin mold is heated in this state to lose its shape, thereby producing a casting mold for molding dental prostheses such as dentures.

[0003] For example, Patent Document 1 discloses a curable composition for stereolithography that contains a photopolymerizable component and a photopolymerization initiator, and uses a monofunctional (meth)acrylic monomer and a bifunctional (meth)acrylic monomer as the photopolymerizable component. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 189652 Summary of the Invention [Problem to be solved by the invention]

[0005] When producing stereolithography objects from photocurable resin compositions, it is necessary to suppress volumetric shrinkage due to curing in order to improve the molding accuracy of the stereolithography object. We hypothesized that reducing the amount of liquid (meth)acrylic monomer would reduce the overall shrinkage rate, and therefore considered incorporating a material in which the (meth)acrylic monomer was prepolymerized and solidified. Specifically, we found that incorporating crosslinked poly(meth)acrylic ester particles into a photocurable resin composition is effective in suppressing volumetric shrinkage due to curing. However, we found that crosslinked poly(meth)acrylic ester particles have a different specific gravity than the (meth)acrylic monomer, the photopolymerizable component, and therefore settle during storage of the photocurable resin composition, resulting in poor storage stability. If such settling occurs, a process is required to disperse the bottle containing the photocurable resin composition in a vibrator for a certain period of time before producing a stereolithography object. Aiming to avoid this vibration process as much as possible, we sought a photocurable resin composition that could suppress settling during storage, resulting in the present invention.

[0006] That is, an object of an embodiment of the present invention is to provide a photocurable resin composition that exhibits excellent storage stability while suppressing volumetric shrinkage due to curing. [Means for solving the problem]

[0007] The present invention includes the embodiments shown below. [1] A photocurable resin composition comprising: (A) a monofunctional (meth)acrylic monomer; (B) at least one polyfunctional monomer selected from the group consisting of a polyfunctional (meth)acrylic ester and a polyfunctional urethane (meth)acrylate; (C) crosslinked poly(meth)acrylic ester particles; (D) resin particles having a specific gravity of 70 to 95% of that of the component (C); and (E) a photopolymerization initiator. [2] The photocurable resin composition according to [1], wherein the total content of the component (C) and the component (D) is 60 to 140 parts by mass per 100 parts by mass of the total content of the component (A) and the component (B). [3] The photocurable resin composition according to [1] or [2], wherein the component (D) contains polyethylene particles and / or nylon particles. [4] The photocurable resin composition according to any one of [1] to [3], wherein the component (E) comprises an acylphosphine oxide compound and an alkylphenone compound. [5] The photocurable resin composition according to any one of [1] to [4], which is used in a liquid tank photopolymerization method. [6] A cured product of the photocurable resin composition according to any one of [1] to [5]. [Effects of the Invention]

[0008] The photocurable resin composition according to the embodiment of the present invention can improve storage stability while suppressing volume shrinkage due to curing. DETAILED DESCRIPTION OF THE INVENTION

[0009] The photocurable resin composition according to the embodiment contains (A) a monofunctional (meth)acrylic monomer, (B) at least one polyfunctional monomer selected from the group consisting of polyfunctional (meth)acrylic esters and polyfunctional urethane (meth)acrylates, (C) crosslinked poly(meth)acrylic ester particles, (D) resin particles having a specific gravity of 70 to 95% of that of the component (C), and (E) a photopolymerization initiator.

[0010] As used herein, "(meth)acrylic monomer" refers to one or both of an acrylic monomer and a methacrylic monomer. "(meth)acrylic acid" refers to one or both of an acrylic acid and a methacrylic acid. "(meth)acrylate" refers to one or both of an acrylate and a methacrylate.

[0011] The photocurable resin composition contains the photopolymerizable components (A) and (B). Upon exposure to light, these components polymerize (i.e., become resinified) and harden (i.e., solidify) due to the action of component (E). Therefore, the monofunctional (meth)acrylic monomer (A) and the polyfunctional monomer (B) are photocured by the photopolymerization initiator (E). Adding crosslinked poly(meth)acrylic ester particles (C) to the composition reduces the volumetric shrinkage during curing, improving molding accuracy. Furthermore, we have found that using resin particles (D) having the above-mentioned specific gravity in combination with the crosslinked poly(meth)acrylic ester particles (C) can suppress sedimentation of the crosslinked poly(meth)acrylic ester particles (C) and prevent their separation from the photopolymerizable components. This improves the storage stability of the photocurable resin composition.

[0012] [Component (A)] The monofunctional (meth)acrylic monomer of component (A) is a monomer having one (meth)acryloyl group per molecule, where the (meth)acryloyl group represents either or both of an acryloyl group and a methacryloyl group.

[0013] Examples of the monofunctional (meth)acrylic monomer (A) include monofunctional (meth)acrylic acid esters and monofunctional N-substituted (meth)acrylamides, and any one of these may be used alone or in combination of two or more. Here, (meth)acrylamide refers to either or both of acrylamide and methacrylamide.

[0014] Specific examples of monofunctional (meth)acrylic acid esters include ethyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, and cyclohexyl (meth)acrylate. Examples of suitable acrylates include acrylate, tetrahydrofurfuryl (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate, phenylbenzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxytetraethylene glycol (meth)acrylate, nonylphenoxyethyl (meth)acrylate, and phenoxybenzyl (meth)acrylate. These may be used alone or in combination of two or more. Among these, it is preferable to use a (meth)acrylic acid ester having an aromatic ring in the molecule and / or a (meth)acrylic acid ester having an alicyclic structure in the molecule. Here, the alicyclic structure may include a structure having a heteroatom such as an oxygen atom or a nitrogen atom in part thereof.

[0015] Specific examples of monofunctional N-substituted (meth)acrylamides include (meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, etc. These may be used alone or in combination of two or more.

[0016] In one embodiment, the (A) monofunctional (meth)acrylic monomer may contain a (meth)acrylic acid ester (Aa) having an alicyclic structure in the molecule. In this case, the content of the (Aa) component in 100% by mass of the (A) monofunctional (meth)acrylic monomer may be 50 to 100% by mass or 70 to 97% by mass. Furthermore, the (A) monofunctional (meth)acrylic monomer may contain, in addition to the (meth)acrylic acid ester (Aa) having an alicyclic structure in the molecule, a monofunctional (meth)acrylic acid ester (Ab) having an aromatic ring in the molecule and / or a monofunctional N-substituted (meth)acrylamide (Ac). In this case, the content of the (Aa) component in 100% by mass of the (A) monofunctional (meth)acrylic monomer may be 50 to 98% by mass (preferably 70 to 97% by mass), and the content of the (Ab) component and / or the (Ac) component may be 2 to 50% by mass (preferably 3 to 30% by mass).

[0017] In one embodiment, the (A) monofunctional (meth)acrylic monomer may contain a monofunctional (meth)acrylic acid ester (Ab) having an aromatic ring in the molecule. In this case, the content of the (Ab) component in 100% by mass of the (A) monofunctional (meth)acrylic monomer may be 20 to 100% by mass or 50 to 97% by mass. Furthermore, the (A) monofunctional (meth)acrylic monomer may contain, in addition to the monofunctional (meth)acrylic acid ester (Ab) having an aromatic ring in the molecule, a (meth)acrylic acid ester (Aa) having an alicyclic structure in the molecule and / or a monofunctional N-substituted (meth)acrylamide (Ac). In this case, the content of the (Ab) component may be 20 to 98% by mass, and the content of the (Aa) component and / or the (Ac) component may be 2 to 80% by mass, in 100% by mass of the (A) monofunctional (meth)acrylic monomer.

[0018] [(B) Component] Component (B) is at least one polyfunctional monomer selected from the group consisting of polyfunctional (meth)acrylic acid esters and polyfunctional urethane (meth)acrylates, and has multiple (meth)acryloyloxy groups in one molecule. The polyfunctional monomer (B) typically has two or three (meth)acryloyloxy groups in one molecule. Here, the (meth)acryloyloxy groups represent one or both of an acryloyloxy group and a methacryloyloxy group.

[0019] Specific examples of polyfunctional (meth)acrylic acid esters include ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, glycerin di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, alkylene oxide-modified bisphenol A di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, diethylene glycol di(meth)acrylate, 2-hydroxy-3-acryloyloxypropyl (meth)acrylate, polyethylene glycol di(meth)acrylate, tris(acryloyloxyethyl) isocyanurate, trimethylolpropane triacrylate, alkylene oxide-modified trimethylolpropane tri(meth)acrylate, alkylene oxide-modified pentaerythritol penta(meth)acrylate, and alkylene oxide-modified dipentaerythritol hexa(meth)acrylate. These may be used alone or in combination of two or more.

[0020] The polyfunctional urethane (meth)acrylate is a urethane compound having a plurality of (meth)acryloyloxy groups in one molecule. Examples of the polyfunctional urethane (meth)acrylate include those obtained by reacting (meth)acrylic acid with a terminal hydroxyl group-containing urethane prepolymer obtained by reacting a polyisocyanate compound with a polyol compound, those obtained by reacting a terminal isocyanate group-containing urethane prepolymer obtained by reacting a polyisocyanate compound with a polyol compound, and those obtained by reacting a hydroxyl group-containing (meth)acrylate with a polyisocyanate compound.

[0021] Examples of polyisocyanate compounds include aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates. Examples of polyol compounds include polyether polyols, polyester polyols, polycarbonate polyols, and polyolefin polyols. Examples of hydroxy group-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, ethylene glycol mono(meth)acrylate, propylene glycol mono(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane di(meth)acrylate, and dipentaerythritol penta(meth)acrylate.

[0022] The content of component (B) is not particularly limited and may be, for example, 3 to 80 parts by mass, 5 to 60 parts by mass, or 10 to 50 parts by mass relative to 100 parts by mass of the total content of components (A) and (B).The total content of components (A) and (B) relative to 100 parts by mass of the photocurable resin composition is not particularly limited and may be, for example, 20 to 63 parts by mass, 30 to 62 parts by mass, or 41 to 60 parts by mass.

[0023] [(C) component] The crosslinked poly(meth)acrylic acid ester particles of component (C) are fine particles of crosslinked poly(meth)acrylic acid ester. By incorporating component (C), the product has light transmittance close to that of the photopolymerizable component, while suppressing volumetric shrinkage due to curing, thereby improving molding precision.

[0024] Examples of poly(meth)acrylates constituting the (C) crosslinked poly(meth)acrylate particles include poly(alkyl(meth)acrylates) such as poly(methyl(meth)acrylate), poly(ethyl(meth)acrylate), and poly(propyl(meth)acrylate, and these may be used alone or in combination. Among these, poly(alkyl methacrylates) such as poly(methyl methacrylate), poly(ethyl methacrylate), and poly(propyl methacrylate are preferred, i.e., the (C) component according to a preferred embodiment is a crosslinked poly(meth)acrylate particle. The alkyl group of the poly(alkyl(meth)acrylate) preferably has two or fewer carbon atoms.

[0025] The (C) crosslinked poly(meth)acrylic acid ester particles have a specific gravity greater than that of the photopolymerizable components (A) and (B). The specific gravity of the (C) crosslinked poly(meth)acrylic acid ester particles is not particularly limited, but may be, for example, 1.10 to 1.25. In this specification, specific gravity refers to the ratio (true specific gravity) of the mass of a substance to the mass of a standard substance (water at 4°C) of the same volume, and is measured by the method described in JIS Z 8807:2012, Section 6, "Method for measuring density and specific gravity using a pycnometer." The specific gravities of components (A) and (B) herein refer to the weighted average of the specific gravities of the monomers constituting components (A) and (B) based on their mass ratio.

[0026] The average particle size of the (C) crosslinked poly(meth)acrylic acid ester particles is not particularly limited and may be, for example, 1 to 50 μm or 2 to 20 μm. In this specification, the average particle size is the volume average diameter measured by the Coulter counter method.

[0027] [(D) component] Component (D) is a resin particle that is blended into the photocurable resin composition together with the crosslinked poly(meth)acrylic acid ester particles of component (C), and has a specific gravity of 70 to 95% of that of component (C). As the resin particle of component (D), one type of resin particle having a specific gravity of 70 to 95% of that of component (C) may be used, or two or more types of resin particles may be used.

[0028] If only component (C) is used as resin particles, component (C) will settle during storage of the photocurable resin composition, resulting in separation from the photopolymerizable components (A) and (B). However, by using resin particles with a specific gravity of 70 to 95% that of component (C), the settling of component (C) can be suppressed. Furthermore, the floating and settling of component (D) itself can be suppressed, maintaining a uniform dispersion.

[0029] The specific gravity of the resin particles of component (D) is preferably 75 to 90% of the specific gravity of the crosslinked poly(meth)acrylic acid ester particles of component (C), and more preferably 78 to 85%.

[0030] The specific gravity of component (C) referred to here refers to the specific gravity of the crosslinked poly(meth)acrylic ester particles when one type of crosslinked poly(meth)acrylic ester particles is used as component (C), or refers to the weighted average of the specific gravities of the crosslinked poly(meth)acrylic ester particles when multiple types of crosslinked poly(meth)acrylic ester particles are used.

[0031] It is preferable to use resin particles of component (D) that have a specific gravity equal to or smaller than that of components (A) and (B). The specific gravities of components (A) and (B) referred to here are the weighted average of the specific gravities of the monomers constituting components (A) and (B) based on their mass ratio.

[0032] The specific gravity of the resin particles of component (D) may be, for example, 0.90 to 1.10, 0.92 to 1.05, or 0.93 to 1.02.

[0033] There are no particular restrictions on the average particle size of the resin particles of component (D), and it may be, for example, 1 to 50 μm, or 2 to 20 μm.

[0034] The resin particles of component (D) are not particularly limited as long as they are resin particles other than the crosslinked poly(meth)acrylic acid ester particles of component (C) and have a specific gravity in the range of 70 to 95% of that of component (C). The resin particles are insoluble in components (A) and (B) and therefore maintain a particulate state in the photopolymerizable component. Furthermore, the resin particles used are those that do not undergo polymerization upon irradiation with light.

[0035] Specific examples of component (D) include polyethylene particles, polypropylene particles, polystyrene particles, nylon particles, AS resin (acrylonitrile-styrene copolymer) particles, ABS resin (acrylonitrile-butadiene-styrene copolymer) particles, and epoxy resin particles. These may be used alone or in combination of two or more. The resins constituting these resin particles may be crosslinked, or may not be crosslinked as long as they are insoluble in components (A) and (B).

[0036] As component (D), it is preferable to use polyethylene particles and / or nylon particles. That is, in a preferred embodiment, component (D) includes at least one particle selected from the group consisting of polyethylene particles and nylon particles.

[0037] As the polyethylene particles, it is preferable to use particles (ultra-high molecular weight polyethylene resin particles) made of ultra-high molecular weight polyethylene (UHMWPE) having an average molecular weight of 1 million or more. The weight-average molecular weight of the ultra-high molecular weight polyethylene is not particularly limited and may be, for example, 1 million to 4 million, or 1.2 million to 2.5 million. The average particle size of the polyethylene particles is not particularly limited and may be, for example, 1 to 50 μm, or 2 to 20 μm. In this specification, the weight-average molecular weight is measured by GPC (gel permeation chromatography) using a refractometer (RI detector). The weight-average molecular weight is calculated based on a calibration curve created using standard polystyrene.

[0038] The nylon particles are preferably, for example, nylon 11 particles or nylon 12 particles. The average particle size of the nylon particles is not particularly limited, and may be, for example, 1 to 50 μm or 2 to 20 μm.

[0039] The contents of the above components (C) and (D) are preferably set as follows: The total content of components (C) and (D) is preferably 60 to 140 parts by mass per 100 parts by mass of the total content of components (A) and (B). When the total content of components (C) and (D) is 60 parts by mass or more, the effect of suppressing volumetric shrinkage due to curing can be enhanced. Furthermore, when the total content is 140 parts by mass or less, the viscosity of the photocurable resin composition can be reduced. From these perspectives, the total content of components (C) and (D) is more preferably 65 to 130 parts by mass, even more preferably 70 to 120 parts by mass, and particularly preferably 80 to 100 parts by mass.

[0040] The ratio of the contents of the (C) component and the (D) component, for example, the mass ratio (D) / (C) of the (D) component to the (C) component, is preferably 5 / 1 to 1 / 5, and more preferably 4 / 1 to 1 / 2.

[0041] The content of component (C) is not particularly limited, but is preferably 5 to 130 parts by mass, more preferably 10 to 100 parts by mass, and even more preferably 20 to 60 parts by mass, per 100 parts by mass of the total content of components (A) and (B).

[0042] The content of component (D) is not particularly limited, but is preferably 10 to 80 parts by mass, more preferably 20 to 70 parts by mass, and even more preferably 20 to 60 parts by mass, per 100 parts by mass of the total content of components (A) and (B).

[0043] [(E) component] The photopolymerization initiator (E) is not particularly limited as long as it can initiate photoradical polymerization of components (A) and (B). Examples of photopolymerization initiators (E) include alkylphenone compounds, acylphosphine oxide compounds, oxime ester compounds, thioxanthone compounds, and anthraquinone compounds. These may be used alone or in combination of two or more.

[0044] Examples of alkylphenone compounds include benzyl methyl ketal compounds such as 2,2'-dimethoxy-1,2-diphenylethan-1-one, α-hydroxyalkylphenone compounds such as 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one, and 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methylpropan-1-one, and aminoalkylphenone compounds such as 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one and 2-benzylmethyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone. Examples of the acylphosphine oxide compound include phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, etc. These can be used alone or in combination of two or more.

[0045] In one embodiment, the (E) photopolymerization initiator contains an acylphosphine oxide compound (Ea), which is a long-wavelength component, in order to be compatible with an LED (light-emitting diode) light source, and more preferably contains phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide. In this case, the content of the (Ea) component (more preferably phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide) in 100% by mass of the (E) photopolymerization initiator may be 10 to 50% by mass or 15 to 45% by mass.

[0046] In one embodiment, the (E) photopolymerization initiator preferably contains an acylphosphine oxide compound (Ea) and an alkylphenone compound (Eb), more preferably phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and an alkylphenone compound (more preferably an α-hydroxyalkylphenone compound). This allows the outermost surface of the photocurable resin composition to be cured with the alkylphenone compound (Eb) while the acylphosphine oxide compound (Ea) can cure the inner part of the composition when an LED light source is used, thereby improving the curability of the photocurable resin composition. In this case, the content of the (Ea) component (more preferably phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide) in 100% by mass of the (E) photopolymerization initiator may be 10 to 50% by mass or 15 to 45% by mass, and the content of the (Eb) component (more preferably an α-hydroxyalkylphenone compound) in 100% by mass may be 50 to 90% by mass or 55 to 85% by mass.

[0047] The content of component (E) is preferably 1 to 11 parts by mass per 100 parts by mass of the combined content of components (A) and (B). When the content of component (E) is 1 part by mass or more, photopolymerization of components (A) and (B) can be promoted. When the content of component (E) is 11 parts by mass or less, deep curing can be facilitated. The content of component (E) is more preferably 2 to 8 parts by mass, and even more preferably 3 to 7 parts by mass.

[0048] [Component (F)] The photocurable resin composition according to this embodiment may further contain an organic dye (F). By using an organic dye as a colorant, moldability using a 3D printer based on the liquid vat photopolymerization method can be ensured while eliminating sintering residues, for example, when sintering a mold. Specifically, when stereolithography is performed using the liquid vat photopolymerization method, the photocurable resin composition is required to have a light-shielding effect so that it does not harden in areas other than those that should be hardened. If a pigment is used as a colorant for this purpose, for example, when a stereolithography-produced resin mold is used as a master to sinter a mold, sintering residues of the resin mold will remain in the mold, necessitating a process to remove them. Since organic dyes do not leave sintering residues, they can eliminate sintering residues and reduce the process while ensuring moldability using a 3D printer.

[0049] The organic dye is a dye made of an organic compound, and an organic compound pigment that can be dissolved in a liquid photocurable resin composition is used. Specific examples of organic dyes include CI Acid Yellow 1, 3, 11, 36, 42, and 73; CI Acid Red 22, 26, 51, 87, 88, 92, and 94. These can be used alone or in combination of two or more.

[0050] The content of component (F) is preferably 0.01 to 1 part by mass per 100 parts by mass of the total content of components (A) and (B). When the content of component (F) is 0.01 part by mass or more, the shielding effect of the organic dye is enhanced, improving formability using a 3D printer. When the content of component (F) is 1 part by mass or less, deep curing can be facilitated. The content of component (F) is more preferably 0.03 to 0.5 parts by mass, and even more preferably 0.05 to 0.2 parts by mass.

[0051] [Other ingredients] The photocurable resin composition according to this embodiment may contain other components in addition to those described above, as necessary, such as a monofunctional monomer other than the component (A), a polyfunctional monomer other than the component (B), and a plasticizer.

[0052] Depending on the application, inorganic fillers and inorganic pigments such as metal powders (hereinafter collectively referred to as inorganic particles) may be added to improve the design. When such inorganic particles are added, it is preferable to use hollow particles whose specific gravity is small compared to the specific gravities of the above-mentioned components (A) and (B) in order to prevent the inorganic particles from settling during storage of the photocurable resin composition.

[0053] On the other hand, when the photocurable resin composition is used as a resin composition for, for example, photofabrication of resin molds for producing casting molds by liquid tank photopolymerization, it is preferable that the photocurable resin composition is substantially free of inorganic particles that may become sintering residues. Here, "substantially free" means that the content is less than 0.01% by mass relative to 100% by mass of the photocurable resin composition. Therefore, in one embodiment, the content of inorganic filler may be less than 0.01% by mass, and the content of pigment may be less than 0.01% by mass relative to 100% by mass of the photocurable resin composition.

[0054] In one embodiment, the mass ratios of the contents of components (A) and (B), components (C) and (D), component (E), and component (F) in the photocurable resin composition are preferably in the ranges of (A+B) / (C+D) / E / F=41 to 63 / 35 to 58 / 0.4 to 6.5 / 0.0041 to 0.62. That is, when the total content of components (A) to (E) is taken as 100 mass%, the total content of components (A) and (B) is preferably 41 to 63 mass%, the total content of components (C) and (D) is preferably 35 to 58 mass%, the content of component (E) is preferably 0.4 to 6.5 mass%, and the content of component (F) is preferably 0.0041 to 0.62 mass%.

[0055] From the viewpoint of moldability by, for example, a liquid bath photopolymerization method, the viscosity of the photocurable resin composition is preferably 20 to 2500 mPa·s at 25°C as measured using an E-type viscometer. A viscosity of 20 mPa·s or more results in good moldability by a liquid bath photopolymerization method. A viscosity of 2500 mPa·s or less results in good moldability of each layer during liquid bath photopolymerization. The viscosity may be 40 mPa·s or more, or 70 mPa·s or more. The viscosity may be 2000 mPa·s or less, or 1500 mPa·s or less.

[0056] The photocurable resin composition according to this embodiment can be used as a raw material for obtaining various stereolithography objects, and its use is not particularly limited. It is preferably used in additive manufacturing (AM) using a 3D printer, such as a liquid vat photopolymerization method or a material jetting method, and more preferably used in a liquid vat photopolymerization method.

[0057] The liquid vat photopolymerization method is a type of additive manufacturing method using a 3D printer. It selectively irradiates light from the top or bottom of a photocurable resin composition stored in a liquid vat, curing and stacking each layer. Examples of light irradiation methods include scanning laser light with a galvanometer mirror (SLA) and DLP (Digital Light Projection), which uses a projector to simultaneously expose the cross-sectional images of each layer. The light used can be ultraviolet light, or a longer-wavelength LED light source.

[0058] For example, a three-dimensional object can be obtained by repeatedly irradiating a photocurable resin composition placed in a liquid vat with a laser beam from above to cure one layer of the photocurable resin composition in the gap between the liquid surface and the modeling table, then lowering the modeling table by one layer to supply a photocurable resin composition on top of the cured product, and irradiating the cured product with a laser beam. Alternatively, a three-dimensional object can be obtained by repeatedly irradiating a photocurable resin composition placed in a transparent liquid vat with a laser beam from below to cure one layer of the photocurable resin composition in the gap between the bottom of the liquid vat and the modeling table, then raising the modeling table by one layer to supply a photocurable resin composition below the cured product, and irradiating the cured product with light. Modeling using this liquid vat photopolymerization method can be performed, for example, using a commercially available liquid vat photopolymerization 3D printer.

[0059] As described above, liquid vat photopolymerization is a process in which a liquid monomer hardens (i.e., solidifies). The shrinkage rate during hardening from the liquid state significantly affects the dimensional accuracy of the product. Products with varying thicknesses or shapes with multiple branching points may require high flatness. For thick-walled shapes, a high shrinkage rate causes the surface to harden before the interior. However, the surface cures faster, resulting in a lower shrinkage rate, while the interior hardens later, resulting in internal distortion. The release of internal distortion can result in defects such as warping and sink marks. Even if a product is produced without warping or sink marks, the release of internal distortion can manifest as product damage over long-term use. For these reasons, a low shrinkage rate is desirable. One application of this embodiment is bridge-shaped products (partial dentures and full dentures) in dentistry. A cast mold is made from a thin wire-shaped model consisting of multiple teeth with different thicknesses, and a low shrinkage rate is beneficial for patients and dentists who want to avoid rework.

[0060] Additive manufacturing using 3D printers is suitable for small-scale production because it does not require molds for molding thermoplastic resins. 3D printers are particularly suitable for products intended for human consumption, as each product varies in size and shape. Even if shrinkage is high in thermoplastic resin molding, it can be somewhat mitigated through mold design. This can be achieved by incorporating shrinkage into computer-aided engineering (CAE) calculations, eliminating warping and welds. This CAE cost is prohibitively expensive and uneconomical for individual products, and is time-consuming, making it practically unfeasible. Therefore, CAD design values ​​are incorporated into 3D printers, where CAD designers adjust the CAD values ​​based on their experience and output them. With the recent advances in digital medicine, there is an overwhelming shortage of CAD designers capable of making adjustments based on experience. Therefore, a material that can faithfully reproduce CAD output, i.e., a photocurable resin composition with a low shrinkage rate, is needed. This embodiment can meet this demand.

[0061] When the photocurable resin composition according to this embodiment is used for additive manufacturing (AM) using a 3D printer, its applications include, for example, dental models, dental cast molds (bridges, partial dentures, full dentures), orthodontic appliances, earphones, hearing aids, eyeglass frames, jewelry, toys, figurines, sculptures, organ models, tools, and prototypes.

[0062] In one embodiment, the photocurable resin composition is used as a resin composition for photolithography by a liquid vat photopolymerization method to produce a resin mold for producing a casting mold. Therefore, a cured product of the photocurable resin composition according to one embodiment is a resin mold (lost model) for producing a casting mold, and is molded from the photocurable resin composition using a liquid vat photopolymerization 3D printer.

[0063] The resin mold is used as a prototype when producing a mold. The mold is produced by sintering an inorganic material such as gypsum, clay, china clay, or metal. The use of the mold is not particularly limited, and in one embodiment, for example, the mold may be used to mold a dental prosthesis such as a denture base.

[0064] One method for manufacturing a mold is to use the resin mold as a prototype, arrange an inorganic material for the mold, such as plaster, around the resin mold, and heat it in this state to sinter the inorganic material. The resin mold is then removed by heating during sintering. According to a preferred embodiment, when the resin mold is used to sinter the mold, sintering residue can be removed while minimizing it, thereby reducing or eliminating the step of removing the sintering residue after the sintering process.

[0065] In one embodiment, the following method can be used to manufacture a mold for molding a dental prosthesis such as a denture base. The shape of the patient's oral cavity is measured by three-dimensional measurement. Based on the obtained measurement data, a resin mold is produced from the photocurable resin composition using a liquid vat photopolymerization 3D printer. An inorganic material such as plaster is placed around the resulting resin mold. In this state, the mold is heated to sinter the inorganic material and remove the resin mold, yielding a mold. The dental prosthesis can be produced by pouring the material for forming the dental prosthesis into the resulting mold and allowing it to harden. [Example]

[0066] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0067] <Measurement and evaluation methods> [viscosity] The viscosity of the photocurable resin composition was measured at 25°C using an E-type viscometer.

[0068] [Volumetric shrinkage rate (molding accuracy)] The photocurable resin composition was applied to a thickness of 100 μm and cured under the following UV irradiation conditions. The specific gravity of the resin at 20°C before and after curing was measured using a pycnometer, and the volumetric shrinkage was calculated using the following formula. A smaller volumetric shrinkage indicates better molding precision. Volumetric shrinkage rate (%) = [(specific gravity after curing - specific gravity before curing) / specific gravity after curing] x 100

[0069] [Tensile strength, elongation, elastic modulus] The photocurable resin composition was applied to a thickness of 100 μm and cured under the following UV irradiation conditions: The cured resin was cut into 5 mm wide strips and used as test pieces. The strength at break (tensile strength [MPa]), elongation [%], and elastic modulus [MPa] were measured using an autograph (TENSILON, manufactured by ORIENTEC) when pulled at a speed of 50 mm / min.

[0070] [UV irradiation conditions] The UV irradiation device used was a belt conveyor type UV curing device (World Engineering Co., Ltd.) equipped with a UV-LED lamp. The irradiation conditions were an integrated illuminance of 4500 mJ / cm. 2 It was decided.

[0071] [3D Printability] A 5cm x 5cm x 1cm dental cast was made using the photocurable resin composition under the following 3D printer process conditions. If the dental cast was successfully made, it was rated as "Good" (good moldability), and if it fell during production or the dental cast was not made as expected, it was rated as "Poor moldability."

[0072] [Sintering residue] A 5cm x 5cm x 1cm three-dimensional object was produced using the photocurable resin composition under the following 3D printer process conditions. The resulting three-dimensional object was placed in an electric furnace at 750°C for 1 hour, and then visually evaluated for sintering residue. Those with no sintering residue were rated "Good" (good sintering residue), and those with sintering residue were rated "Poor" (poor sintering residue).

[0073] [3D printer process conditions] A three-dimensional object of a predetermined shape was fabricated from the photocurable resin composition using a DLP (Digital Light Proofing) stereolithography system (TiTan2 manufactured by Kudo3D). The layer pitch for the stereolithography was 0.1 mm, and the light irradiation time was 60 seconds for the first layer, 30 seconds for the second to tenth layers, and 10 seconds for the tenth layer and beyond. The resulting three-dimensional object was ultrasonically cleaned in isopropanol.

[0074] [Storage stability] The photocurable resin composition was left standing overnight and then its appearance was checked. If no interface between the liquid component and the particle-containing liquid component was clearly visible in the photocurable resin composition solution after standing overnight, it was rated as "Good" (separation suppressed), and if it was visible, it was rated as "Poor" (separation not suppressed).

[0075] <Examples 1 to 12 and Comparative Examples 1 to 7> The components were blended together according to the formulation (parts by mass) shown in Tables 1 and 2 below, and mixed and stirred using a disperser to obtain the photocurable resin compositions of Examples 1 to 12 and Comparative Examples 2 to 7. For Comparative Example 1, a commercially available photocurable resin composition, Press-E-Cast (manufactured by EnvisionTEC), which is commonly used in stereolithography, was prepared. Details of each component in Tables 1 and 2 are as follows:

[0076] (A-1) Isobornyl acrylate: trade name "IBXA", manufactured by Osaka Organic Chemical Industry Ltd. (A-2) Acryloylmorpholine: trade name "ACMO", manufactured by KJ Chemicals Co., Ltd. (A-3) Phenoxyethyl acrylate: trade name "New Frontier PHE", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0077] (B-1) 10 mol ethylene oxide-modified bisphenol A diacrylate: trade name "New Frontier BPE-10", manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (B-2) Tris(acryloxyethyl) isocyanurate: trade name "New Frontier TEICA", manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (B-3) Bifunctional urethane acrylate: trade name "New Frontier R-1220", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0078] (C-1) Cross-linked polymethyl methacrylate particles: trade name "ENEOS Unipowder NMB-0520C", manufactured by ENEOS Liquid Crystal Co., Ltd., spherical particles, specific gravity: 1.20, average particle size: 5 μm

[0079] (D-1) Polyethylene particles: trade name "Mipelon PM-200", manufactured by Mitsui Chemicals, Inc., ultra-high molecular weight polyethylene particles, weight average molecular weight: 1.8 million, specific gravity: 0.938, average particle size: 10 μm (D-2) Nylon particles: trade name "SP-500", manufactured by Toray Industries, Inc., nylon 12 spherical powder, specific gravity 1.02, average particle size: 5 μm

[0080] (E-1) 1-Hydroxycyclohexyl phenyl ketone: trade name "Omnirad184", manufactured by IGM Resins B.V. (E-2) Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide: trade name "Omnirad819", manufactured by IGM Resins B.V.

[0081] (F-1) Organic dye: CI Acid Yellow 42-containing dye: Trade name "VARIFAST ORANGE 1225", manufactured by Orient Chemical Industries Co., Ltd.

[0082] The photocurable resin compositions of Examples 1 to 12 and Comparative Examples 1 to 7 were measured and evaluated for viscosity, volumetric shrinkage, tensile strength, elongation, elastic modulus, 3D printability, sintering residue, and storage stability. The results are shown in Tables 1 and 2. In the tables, "(A) + (B)" represents the total content (parts by mass) of components (A) and (B), "(C) + (D)" represents the total content (parts by mass) of components (C) and (D), and "(D) / (C)" represents the mass ratio of component (D) to component (C).

[0083] [Table 1]

[0084] [Table 2]

[0085] As shown in Tables 1 and 2, the commercially available photocurable resin composition of Comparative Example 1 had poor storage stability, and because it contained a pigment as a colorant, sintering residue remained. The photocurable resin compositions of Comparative Examples 2 to 4 did not contain (C) crosslinked polymethyl methacrylate particles, and therefore had a large volume shrinkage rate and poor molding precision. Furthermore, Comparative Examples 3 and 4 had poor 3D printability, and the test piece of Comparative Example 3 was brittle, making it impossible to measure tensile strength, etc. Note that, because Comparative Examples 2 to 4 did not contain resin particles, storage stability was not evaluated.

[0086] The photocurable resin compositions of Comparative Examples 5 and 6 contained crosslinked polymethyl methacrylate particles (C), which prevented volumetric shrinkage during curing. However, the crosslinked polymethyl methacrylate particles (C) settled and separated from the polymerizable components during storage, resulting in poor storage stability. On the other hand, the photocurable resin composition of Comparative Example 7 contained only polyethylene particles (D) as resin particles, resulting in poor 3D printing properties and waxing. Therefore, viscosity measurement was not possible, and storage stability was not evaluated.

[0087] In contrast, the photocurable resin compositions of Examples 1 to 12 all had small volume shrinkage rates, resulting in excellent molding precision, sufficiently low viscosity, good 3D printing properties, and no sintering residue. Furthermore, the photocurable resin compositions of Examples 1 to 12 also had excellent storage stability, with no sedimentation or floating of resin particles observed during storage, and no separation from the liquid polymerizable component.

[0088] The various numerical ranges described in this specification can be arbitrarily combined with their upper and lower limits, and all such combinations are considered to be preferred numerical ranges described in this specification. Furthermore, a numerical range described as "X to Y" means from X to Y.

[0089] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

Claims

1. (A) a monofunctional (meth)acrylic monomer, (B) at least one polyfunctional monomer selected from the group consisting of polyfunctional (meth)acrylic acid esters and polyfunctional urethane (meth)acrylates; (C) crosslinked poly(meth)acrylic acid ester particles, (D) resin particles having a specific gravity of 70 to 95% of that of the component (C); and (E) a photopolymerization initiator, A photocurable resin composition comprising:

2. 2. The photocurable resin composition according to claim 1, wherein the total content of the component (C) and the component (D) is 60 to 140 parts by mass per 100 parts by mass of the total content of the component (A) and the component (B).

3. 3. The photocurable resin composition according to claim 1, wherein the component (D) comprises polyethylene particles and / or nylon particles.

4. 4. The photocurable resin composition according to claim 1, wherein the component (E) comprises an acylphosphine oxide compound and an alkylphenone compound.

5. The photocurable resin composition according to any one of claims 1 to 4, which is used in a liquid tank photopolymerization method.

6. A cured product of the photocurable resin composition according to any one of claims 1 to 5.

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