Photocurable composition and molded article

Abstract

The present invention provides a photocurable composition that maintains excellent photopolymerization properties without causing precipitation of acylphosphine oxide-based photopolymerization initiators, which are poorly soluble in water, even when stored for a long period of time. [Solution] The photocurable composition of the present invention is characterized by comprising a polymerizable compound, an acylphosphine oxide-based photopolymerization initiator, a nonionic surfactant having a polyoxyalkylene skeleton, a branched aliphatic hydrocarbon group having 8 or more carbon atoms, or a sorbitan skeleton in its molecule, and an aqueous medium.

Description

[Technical Field]

[0001] The present invention relates to a photocurable composition and a molded article. [Background technology]

[0002] Conventionally, photocurable compositions containing polymerizable compounds, polymerization initiators, and aqueous media have been used to form gels. By irradiating the photocurable composition with active energy rays such as ultraviolet light, the polymerizable compounds polymerize, and the solvent is incorporated into the resulting polymer, thereby generating a gel.

[0003] Polymerization initiators used in photocurable compositions include alkylphenone-based polymerization initiators and acylphosphine oxide-based polymerization initiators. Acylphosphine oxide-based polymerization initiators are relatively widely used because they have absorption properties in the visible light region.

[0004] As a photocurable composition for gel formation containing such an acylphosphine oxide-based polymerization initiator, Patent Document 1 discloses a hydrogel-forming composition comprising an acrylamide compound having a specific ester structure, a polymerization initiator, water, and a mineral, wherein the hydrogel structure formed from this hydrogel-forming composition has a transmittance of 80% or more in the visible light region, and it is stated that an acylphosphine oxide-based polymerization initiator is used as the polymerization initiator.

[0005] Patent Document 2 discloses a photocurable composition comprising a photopolymerization initiator, a polymerizable monomer, and polymer particles, wherein the photopolymerization initiator contains a phosphinate.

[0006] Non-patent document 1 discloses that diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, an acylphosphine oxide polymerization initiator, is nano-sized and dispersed in water, and that it is used in gel-forming compositions. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2021-66058 [Patent Document 2] WO2019 / 156163 [Non-patent literature]

[0008] [Non-Patent Document 1] A high-absorbance water-soluble photo initiator nanoparticle for hydrogel 3D printing : synthesis, characterization and in vitro cytotoxicity study(https: / / www.nature.com / articles / s41598-023-35865-3.pdf) [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, the hydrogel-forming composition described in Patent Document 1 and the photocurable composition described in Patent Document 2 have the problem that when stored for a long period of time, acylphosphine oxide-based photopolymerization initiators precipitate, reducing the polymerizability of the hydrogel-forming composition and the photocurable composition.

[0010] The nanoparticle-formed diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide described in Non-Patent Document 1 has a complicated manufacturing process and low production efficiency, limiting its use in industrial applications.

[0011] The present invention provides a photocurable composition that does not cause precipitation of acylphosphine oxide-based photopolymerization initiators, which are poorly soluble in water, even when stored for a long period of time, and that has excellent photopolymerization properties. [Means for solving the problem]

[0012] The photocurable composition of the present invention comprises a polymerizable compound, an acylphosphine oxide-based photoinitiator, a nonionic surfactant having a polyoxyalkylene skeleton, a branched aliphatic hydrocarbon group having 8 or more carbon atoms, or a sorbitan skeleton in the molecule, and an aqueous medium, and is characterized in that.

[0013] The molded article of the present invention is characterized by including a cured product of the above photocurable composition.

Effects of the Invention

[0014] The photocurable composition of the present invention uses a nonionic surfactant having a polyoxyalkylene skeleton, a branched aliphatic hydrocarbon group having 8 or more carbon atoms, or a sorbitan skeleton in combination with an acylphosphine oxide-based photoinitiator. The acylphosphine oxide-based photoinitiator is stably solubilized in the micelles formed by the nonionic surfactant. Even when stored for a long period of time, the acylphosphine oxide-based photoinitiator does not precipitate in the photocurable composition, and it has excellent storage stability.

[0015] The above photocurable composition has excellent storage stability, and the acylphosphine oxide-based photoinitiator is stably present in the same phase as the polymerizable compound, so it has excellent photopolymerizability.

[0016] The acylphosphine oxide-based photoinitiator in the above photocurable composition is considered to be solubilized not only inside the micelles formed by the nonionic surfactant but also on the surface of the micelles. The polymerizable compound can be polymerized well by the radicals generated by the decomposition of the acylphosphine oxide-based photoinitiator, and a cured product can be easily produced.

[0017] In cured products produced by curing a photocurable composition, even if the amount of polymerizable compound decreases as polymerization of the polymerizable compound progresses, the precipitation of acylphosphine oxide-based photopolymerization initiators is suppressed, and the photocurable composition exhibits excellent photopolymerizability throughout the entire curing process. [Modes for carrying out the invention]

[0018] In the numerical ranges described stepwise in this specification, the upper or lower limit of one step in the numerical range can be arbitrarily combined with the upper or lower limit of another step in the numerical range. In the numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with values ​​shown in the examples or values ​​that can be uniquely derived from the examples. In this specification, numbers connected by "~" mean a numerical range that includes the numbers before and after "~" as the lower and upper limits.

[0019] The photocurable composition of the present invention comprises a polymerizable compound, an acylphosphine oxide-based photopolymerization initiator, a nonionic surfactant having a polyoxyalkylene skeleton, a branched aliphatic hydrocarbon group having 8 or more carbon atoms, or a sorbitan skeleton in its molecule, and an aqueous medium.

[0020] [Polymerizable compound] The photocurable composition contains a polymerizable compound. The polymerizable compound has an ethylenically unsaturated bond (preferably an ethylenically unsaturated double bond) in its molecule, and a monomer that can be radically polymerized by a radical generated by an acylphosphine oxide-based photopolymerization initiator is used.

[0021] Polymerizable compounds require a monofunctional monomer having one ethylenically unsaturated bond in its molecule as an essential component, and may optionally contain polyfunctional monomers having two or more ethylenically unsaturated bonds in their molecule.

[0022] The polymerizable compound may be dissolved or dispersed in the aqueous medium, but it is preferable that it be dissolved in the aqueous medium (water-soluble) because the photocurable composition exhibits excellent photopolymerization properties.

[0023] The monofunctional monomer is not particularly limited and includes, for example, (meth)acrylamide monomers, (meth)acrylic acid ester monomers, monomers having a lactam structure, (meth)acrylic acid or its salts, with (meth)acrylamide monomers being preferred. The monofunctional monomer may be used alone or in combination of two or more. In this specification, (meth)acrylic means acrylic or methacrylic.

[0024] Examples of (meth)acrylamide monomers include N,N-dialkyl(meth)acrylamides such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide; N-alkyl(meth)acrylamides such as N-isopropyl(meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, and N-butyl(meth)acrylamide; N-hydroxyalkyl(meth)acrylamides such as N-hydroxyethyl(meth)acrylamide and N-hydroxymethyl(meth)acrylamide; cationic acrylamide compounds containing amino groups such as dimethylaminopropyl(meth)acrylamide; anionic monofunctional monomers containing sulfonic acid groups such as 4-acryloylmorpholin and tert-butylacrylamidesulfonic acid, or their salts; and derivatives thereof, with N-hydroxyalkyl(meth)acrylamide and N,N-dialkyl(meth)acrylamide being preferred. (Meth)acrylamide monomers may be used alone or in combination of two or more.

[0025] Each alkyl group in N,N-dialkyl(meth)acrylamide, N-alkyl(meth)acrylamide, and N-hydroxyalkyl(meth)acrylamide may be linear or branched, and the number of carbon atoms in the alkyl group is preferably 1 to 6, and more preferably 1 to 4.

[0026] Examples of (meth)acrylic acid ester monomers include alkyl (meth)acrylate esters in which the alkyl group has 1 to 18 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-pentyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-lauryl (meth)acrylate, tridecyl (meth)acrylate, and n-stearyl (meth)acrylate. Alkyl methacrylates; cyclohexyl methacrylate, isobornyl methacrylate, 1-adamantyl methacrylate, and other alicyclic methacrylates; alkoxy group-containing methacrylates such as 2-methoxyethyl methacrylate, ethoxyethoxyethyl methacrylate, methoxytriethylene glycol methacrylate, and other methoxypolyethylene glycol methacrylates; hydroxyalkyl methacrylates such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxy-3-phenoxypropyl methacrylate, and 2-hydroxybutyl methacrylate (which may have an aryl group bonded to the hydroxyalkyl group via an ether link); 2- Examples include aminoalkyl (meth)acrylates such as (dimethylamino)ethyl; glyceryl mono(meth)acrylate; polyalkylene glycols such as polyethylene glycol mono(meth)acrylate and polyethylene glycol-polypropylene glycol copolymers; (meth)acrylate esters having aromatic rings such as benzyl (meth)acrylate; and (meth)acrylate esters having heterocyclic rings such as tetrahydrofurfuryl (meth)acrylate. Note that (meth)acrylate ester monomers may be used alone or in combination of two or more.

[0027] From the viewpoint of water solubility, the lactam structure of a monomer having a group containing a lactam structure is preferably a 5-membered ring lactam structure, a 6-membered ring lactam structure, or a 7-membered ring lactam structure, more preferably a 5-membered ring lactam structure or a 6-membered ring lactam structure, and most preferably a 5-membered ring lactam structure.

[0028] Examples of monomers having a lactam structure include vinyl lactams such as N-vinyl-2-pyrrolidone and N-vinyl-ε-caprolactam.

[0029] Examples of (meth)acrylic acid or its salts include acrylic acid, methacrylic acid, sodium acrylate, potassium acrylate, and potassium methacrylate. (Meth)acrylic acid or its salts may be used alone or in combination of two or more types.

[0030] The polyfunctional monomer is not particularly limited and includes, for example, polyfunctional (meth)acrylamides such as N,N'-methylenebis(meth)acrylamide and N,N'-ethylenebis(meth)acrylamide, polyethylene glycol di(meth)acrylate, glycerin tri(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polyglycerin di(meth)acrylate, glycerin tri(meth)acrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and polyoxyethylene polyglyceryl ether acrylic acid adducts. The polyfunctional monomer may be used alone or in combination of two or more. In this specification, (meth)acrylate means acrylate or methacrylate.

[0031] Polymers produced by polymerizing polymerizable compounds containing polyfunctional monomers can stably retain aqueous media (retention properties), and hydrogels, which are cured products, can be easily produced from photocurable compositions. The hydrogels have excellent shape retention properties, and hydrogels with desired shapes can be obtained. The polyfunctional monomers preferably have a glycerol skeleton shown in Formula 1 in their molecules. In Formula 1, n is an integer from 1 to 20, and preferably an integer from 2 to 20. * represents a bond, meaning a single bond.

[0032] [ka]

[0033] Polyfunctional monomers are preferable because they can stably retain an aqueous medium in the polymer produced by the polymerization of polymerizable compounds, and the resulting hydrogel has excellent shape retention properties.

[0034] In this specification, the polyoxyalkylene skeleton has the structure shown in Formula 2 below. -(R 1 -O)m- Formula 2 (In formula 2, R 1 (where m represents an alkylene group with 1 to 14 carbon atoms, and m is a positive integer representing the number of repeating units.)

[0035] In this specification, an alkylene group is a divalent group of atoms formed by removing (extracting) one hydrogen atom from each of the different carbon atoms bonded to aliphatic saturated hydrocarbons, or a divalent group of atoms formed by removing (extracting) two hydrogen atoms from methane, and includes both linear and branched groups of atoms.

[0036] Examples of alkylene groups include methylene group [-CH2-], ethylene group [-CH2-CH2-], propylene group [-CH(CH3)-CH2-], trimethylene group [-CH2-CH2-CH2-], butylene group, amylene group [-(CH2)5-], and hexylene group, with ethylene group being preferred.

[0037] Polyfunctional monomers are preferable because they can stably retain an aqueous medium in the polymer produced by the polymerization of polymerizable compounds, and the resulting hydrogel has excellent shape retention. They preferably have a glycerol skeleton and a polyoxyalkylene skeleton within the molecule, and more preferably have the structure shown in Formula 3. However, n is an integer from 2 to 20, m1 is an integer from 50 to 200, m2 is an integer from 50 to 200, and m3 is an integer from 50 to 200.

[0038] [ka]

[0039] When the proportion of monofunctional monomers in the polymerizable compound is high, the cured product of the photocurable composition tends to become more flexible. Conversely, when the proportion of polyfunctional monomers in the polymerizable compound is high, the cured product of the photocurable composition becomes harder. The blending ratio of monofunctional monomers and polyfunctional monomers can be appropriately adjusted depending on the intended use of the cured product of the photocurable composition.

[0040] In polymerizable compounds, the polyfunctional monomer content is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, and more preferably 0.4 parts by mass or more, per 100 parts by mass of monofunctional monomer. The polyfunctional monomer content is preferably 3 parts by mass or less, more preferably 3.5 parts by mass or less, more preferably 3 parts by mass or less, more preferably 2.5 parts by mass or less, more preferably 2 parts by mass or less, and more preferably 1.5 parts by mass or less, per 100 parts by mass of monofunctional monomer.

[0041] The content of polymerizable compounds in the photocurable composition is preferably 20% by mass or more, and more preferably 25% by mass or more. The content of polymerizable compounds in the photocurable composition is preferably 50% by mass or less, and more preferably 45% by mass or less. When the content of polymerizable compounds in the photocurable composition is 50% by mass or less, acylphosphine oxide-based photopolymerization initiators tend to precipitate. However, by using a nonionic surfactant described later in combination with an acylphosphine oxide-based photopolymerization initiator, the precipitation of the acylphosphine oxide-based photopolymerization initiator can be suppressed, and the state in which it is solubilized in an aqueous medium can be stably maintained.

[0042] [Acylphosphine oxide-based photopolymerization initiators] The photocurable composition contains an acylphosphine oxide-based photopolymerization initiator. Acylphosphine oxide-based photopolymerization initiators have absorption in the ultraviolet (wavelength 10 nm or more, less than 380 nm) and visible (wavelength 380 nm or more, less than 760 nm) regions and exhibit excellent polymerization efficiency, but they have low stability in aqueous media and tend to precipitate in aqueous media.

[0043] Therefore, the photocurable composition uses an acylphosphine oxide-based photopolymerization initiator in combination with a specific nonionic surfactant to stably dissolve the acylphosphine oxide-based photopolymerization initiator in an aqueous medium over a long period of time, and to largely prevent precipitation in the aqueous medium.

[0044] By using an acylphosphine oxide-based photopolymerization initiator in combination with a specific nonionic surfactant, the precipitation of the acylphosphine oxide-based photopolymerization initiator is suppressed during storage of the photocurable composition. Since the photocurable composition contains the polymerizable compound and the acylphosphine oxide-based photopolymerization initiator in the same phase, photopolymerization of the polymerizable compound can be easily carried out.

[0045] Furthermore, by using an acylphosphine oxide-based photopolymerization initiator in combination with a specific nonionic surfactant, the precipitation of the acylphosphine oxide-based photopolymerization initiator is suppressed during the polymerization process of the photocurable composition, resulting in a photocurable composition with excellent photopolymerization properties.

[0046] The mechanism by which acylphosphine oxide-based photopolymerization initiators are suppressed by using them in combination with specific nonionic surfactants has not been clearly elucidated, but it is thought to be due to the following mechanism.

[0047] Nonionic surfactants having a polyoxyalkylene skeleton, a branched aliphatic hydrocarbon group with 8 or more carbon atoms, or a sorbitan skeleton within their molecule are thought to have high micelle-forming ability and large micelle size, and are presumed to either solubilize acylphosphine oxide-based photopolymerization initiators within the micelles with their polar portion (-P(=O)CO-) facing the micelle surface, or additionally solubilize acylphosphine oxide-based photopolymerization initiators on the micelle surface.

[0048] The acylphosphine oxide-based photopolymerization initiator is not particularly limited as long as it has the structure shown in Formula 5 below. Examples include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO) and 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO), with (2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO) being preferred. The acylphosphine oxide-based photopolymerization initiator may be used alone or in combination of two or more. The acylphosphine oxide-based photopolymerization initiator does not contain salts. In Formula 5, * represents a bond, meaning a single bond.

[0049] [ka]

[0050] In the photocurable composition, the content of the acylphosphine oxide-based photopolymerization initiator is preferably 0.05 parts by mass or more, more preferably 0.08 parts by mass or more, more preferably 0.1 parts by mass or more, and more preferably 0.15 parts by mass or more, per 100 parts by mass of the polymerizable compound. In the photocurable composition, the content of the acylphosphine oxide-based photopolymerization initiator is preferably 0.3 parts by mass or less, more preferably 0.25 parts by mass or less, more preferably 0.23 parts by mass or less, more preferably 0.21 parts by mass or less, and more preferably 0.20 parts by mass or less, per 100 parts by mass of the polymerizable compound. When the content of the acylphosphine oxide-based photopolymerization initiator is within the above range, the photocurable composition exhibits excellent photopolymerization properties while suppressing the precipitation of the acylphosphine oxide-based photopolymerization initiator.

[0051] The photopolymerization initiator preferably contains both an acylphosphine oxide-based photopolymerization initiator and an alkylphenone-based photopolymerization initiator. The inclusion of an alkylphenone-based photopolymerization initiator further suppresses the precipitation of the acylphosphine oxide-based photopolymerization initiator.

[0052] Alkylphenone-based photopolymerization initiators refer to photopolymerization initiators having the structure shown in formula 6 below. However, R 4 This is a monovalent substituent containing a carbon atom that is directly bonded to the keto group (-CO-) and does not have a hydrogen atom bonded to it. The hydrogen atom of the phenyl group directly bonded to the keto group may be substituted by another atom or substituent. 4 This may be a chain-like structure, a ring-like structure, or may include a ring-like structure.

[0053] [ka]

[0054] The alkylphenone-based photopolymerization initiator is not particularly limited, and examples include benzyldimethyl ketal, 2-hydroxy-2-methylpropiophenone, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, methyl phenylglyoxyate, 1-[4-(hydroxyethoxy)-phenyl]-2-hydroxy-2-methylpropan-1-one, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholino)phenyl]-1-butanone, and 2-(dimethylamino)-2-(4-methylphenyl)methyl-1-4-(4-morpholino)phenyl-1-butanone. 2-hydroxy-2-methylpropiophenone and methyl phenylglyoxyate are preferred, and 2-hydroxy-2-methylpropiophenone is more preferred. The alkylphenone-based photopolymerization initiator may be used alone or in combination of two or more.

[0055] The mass ratio of the alkylphenone-based photopolymerization initiator to the acylphosphine oxide-based photopolymerization initiator (alkylphenone-based photopolymerization initiator content / acylphosphine oxide-based photopolymerization initiator content) is preferably 1 or more, more preferably 2 or more, and more preferably 3 or more. The mass ratio of the alkylphenone-based photopolymerization initiator to the acylphosphine oxide-based photopolymerization initiator (alkylphenone-based photopolymerization initiator content / acylphosphine oxide-based photopolymerization initiator content) is preferably 10 or less, more preferably 8 or less, more preferably 6 or less, and more preferably 5 or less. When the mass ratio of the alkylphenone-based photopolymerization initiator to the acylphosphine oxide-based photopolymerization initiator is within the above range, the precipitation of the acylphosphine oxide-based photopolymerization initiator can be more effectively suppressed.

[0056] The particle size of the acylphosphine oxide-based photopolymerization initiator is preferably 0.5 μm or larger, more preferably 1 μm or larger, and even more preferably 5 μm or larger. The particle size of the acylphosphine oxide-based photopolymerization initiator is preferably 2000 μm or smaller, more preferably 1000 μm or smaller, and even more preferably 500 μm or smaller.

[0057] The particle size of the acylphosphine oxide-based photopolymerization initiator is determined by measuring the diameter of 100 randomly selected particles from scanning electron microscope images. If the acylphosphine oxide-based photopolymerization initiator appearing in the scanning electron microscope image is not perfectly circular, the diameter of a perfect circle that can completely enclose the particle is taken as the particle size of the acylphosphine oxide-based photopolymerization initiator. To accurately measure the particle size of the acylphosphine oxide-based photopolymerization initiator, scanning electron microscope images are taken at a magnification such that 300 to 2000 particles of the acylphosphine oxide-based photopolymerization initiator are visible.

[0058] [Nonionic surfactants] The photocurable composition contains a nonionic surfactant having a specific structure. Because the nonionic surfactant has a specific structure, the acylphosphine oxide-based photopolymerization initiator can be stably solubilized in an aqueous medium for a long period of time, and the photocurable composition has excellent storage stability. By having the acylphosphine oxide-based photopolymerization initiator in the same phase as the polymerizable compound, the photocurable composition is given excellent photopolymerizability. During the photopolymerization process of the photocurable composition, precipitation of the acylphosphine oxide-based photopolymerization initiator is suppressed, and the photocurable composition has excellent photopolymerizability throughout the entire curing process.

[0059] Nonionic surfactants have a polyoxyalkylene skeleton, a branched aliphatic hydrocarbon group with 8 or more carbon atoms, or a sorbitan skeleton within their molecule.

[0060] When a nonionic surfactant has a polyoxyalkylene skeleton within its molecule, the polyoxyalkylene has the structure of formula 2 above, but it is preferable that the polyoxyalkylene skeleton (polyoxyalkylene block) has a polyoxyethylene skeleton (polyoxyethylene block).

[0061] When the nonionic surfactant has a polyoxyalkylene skeleton, it can effectively solubilize the acylphosphine oxide-based photopolymerization initiator within and / or on the micelle surface through interaction with the polar portion (-P(=O)CO-) of the acylphosphine oxide-based photopolymerization initiator, and maintain that state stably, resulting in a photocurable composition with excellent storage stability.

[0062] In nonionic surfactants, the polyoxyalkylene skeleton [-(R 1 The degree of polymerization of the repeating unit m of formula 2, i.e., the polyoxyalkylene block, is preferably 2 or higher, more preferably 3 or higher, and even more preferably 4 or higher. In acylphosphine oxide-based photopolymerization initiators, the polyoxyalkylene skeleton [-(R 1 The repeating unit m in formula 2 is preferably 120 or less, and more preferably 110 or less.

[0063] When a nonionic surfactant has a branched aliphatic hydrocarbon group with 8 or more carbon atoms in its molecule, the branched structure of the aliphatic hydrocarbon group interacts with the nonpolar (hydrophobic) portion of the acylphosphine oxide-based photopolymerization initiator at multiple points, effectively solubilizing the acylphosphine oxide-based photopolymerization initiator within and / or on the micelle surface, and maintaining that state stably. As a result, the photocurable composition has excellent storage stability.

[0064] A branched aliphatic hydrocarbon group is a monovalent substituent in which carbon atoms are linked in a chain, has a branched structure, and does not have a cyclic structure. The branched aliphatic hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group containing an ethylenically unsaturated double bond. It is preferable that the branched aliphatic hydrocarbon group contains a branched alkyl group. If the branched aliphatic hydrocarbon group contains an ethylenically unsaturated double bond, it is preferable that there is one ethylenically unsaturated double bond. The nonionic surfactant is preferably a mixture of a nonionic surfactant having a branched saturated aliphatic hydrocarbon group with 8 or more carbon atoms in the molecule and a nonionic surfactant having a branched unsaturated aliphatic hydrocarbon group with 8 or more carbon atoms in the molecule.

[0065] In nonionic surfactants, the number of carbon atoms in the branched aliphatic hydrocarbon group is 8 or more, preferably 9 or more. In nonionic surfactants, the number of carbon atoms in the branched aliphatic hydrocarbon group is 34 or less, preferably 32 or less, more preferably 30 or less, more preferably 28 or less, and more preferably 26 or less. When the number of carbon atoms in the branched aliphatic hydrocarbon group is within the above range, the branched structure of the branched aliphatic hydrocarbon group interacts with the nonpolar portion (hydrophobic portion) of the acylphosphine oxide-based photopolymerization initiator, allowing the acylphosphine oxide-based photopolymerization initiator to be well solubilized in an aqueous medium and maintain that state stably, resulting in a photocurable composition with excellent storage stability.

[0066] The branched aliphatic hydrocarbon group may have any hydrogen atom substituted with other substituents, but an unsubstituted branched aliphatic hydrocarbon group in which the hydrogen atom is not substituted with other substituents is preferred. The acylphosphine oxide-based photopolymerization initiator can be well solubilized in an aqueous medium and its state can be stably maintained, and the photocurable composition has excellent storage stability.

[0067] The branched aliphatic hydrocarbon group is not particularly limited and includes, for example, isostearyl group, decyltetradecyl group, and isopalmityl group (14-methylpentadecyl group, 2-hexyldecyl group).

[0068] In a branched aliphatic hydrocarbon group, the number of carbon atoms in the branched chains branching from the main chain (the carbon chain with the most carbon atoms) is preferably 1 to 15, more preferably 1 to 14, more preferably 1 to 13, more preferably 1 to 12, and more preferably 1 to 11. This allows for good solubilization of the acylphosphine oxide-based photopolymerization initiator in an aqueous medium and stable maintenance of that state, resulting in a photocurable composition with excellent storage stability. The above branched chains are preferably linear (containing methyl groups). The number of branched chains in a branched aliphatic hydrocarbon group is preferably 1 to 4, more preferably 1 to 3. When the number of branched chains in a branched aliphatic hydrocarbon group is 1 to 4, the acylphosphine oxide-based photopolymerization initiator can be better solubilized in an aqueous medium and more stably maintained, resulting in a photocurable composition with excellent storage stability.

[0069] When the nonionic surfactant has a sorbitan skeleton (Formula 4), the interaction between the hydroxyl group and the oxygen atom of the heterocycle and the polar portion (-P(=O)CO-) of the acylphosphine oxide-based photopolymerization initiator allows for good solubilization of the acylphosphine oxide-based photopolymerization initiator within the micelle, and this state can be stably maintained, resulting in a photocurable composition with excellent storage stability. In Formula 4, * represents a bond, meaning a single bond. At least one of the four bonds is bonded to a hydrogen atom.

[0070] [ka]

[0071] The nonionic surfactant is not particularly limited as long as it has a polyoxyalkylene skeleton, a branched aliphatic hydrocarbon group having 8 or more carbon atoms, or a sorbitan skeleton within its molecule.

[0072] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene polyoxypropylene copolymers, polyoxyethylene sterol ethers, polyoxyethylene hydrogenated sterol ethers, polyoxyethylene alkylamino ethers, polyoxyethylene alkylamides, polyoxyethylene alkenyl ethers, fatty acid alkanolamides having branched aliphatic hydrocarbon groups with 8 or more carbon atoms, polyoxyethylene fatty acid alkanolamides, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, ester compounds of polyglycerin and fatty acids having branched aliphatic hydrocarbon groups with 8 or more carbon atoms, polyoxyethylene glycerin fatty acid esters, and methyl glucoside fatty acid esters having branched aliphatic hydrocarbon groups with 8 or more carbon atoms.

[0073] Preferred nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene hydrogenated castor oil, ester compounds of polyglycerin and fatty acids having branched aliphatic hydrocarbon groups with 8 or more carbon atoms, polyoxyethylene sterol ethers, and polyoxyethylene alkenyl ethers.

[0074] This paper describes ester compounds of polyglycerol and fatty acids having branched aliphatic hydrocarbon groups with 8 or more carbon atoms.

[0075] The average degree of polymerization of polyglycerin is preferably 2 or higher, more preferably 4 or higher, more preferably 6 or higher, and more preferably 8 or higher. The average degree of polymerization of polyglycerin is preferably 20 or lower, more preferably 18 or lower, more preferably 16 or lower, more preferably 14 or lower, and more preferably 12 or lower. When the average degree of polymerization of polyglycerin is within the above range, the acylphosphine oxide-based photopolymerization initiator can be well solubilized in the aqueous medium and this state can be stably maintained, and the photocurable composition has excellent storage stability.

[0076] As described above, fatty acids have branched aliphatic hydrocarbon groups with 8 or more carbon atoms, which allows them to effectively solubilize acylphosphine oxide-based photopolymerization initiators and maintain that state stably, resulting in photocurable compositions with excellent storage stability.

[0077] The number of carbon atoms in the branched aliphatic hydrocarbon group in fatty acids is 8 or more, preferably 9 or more. In nonionic surfactants, the number of carbon atoms in the branched aliphatic hydrocarbon group is 34 or less, preferably 32 or less, more preferably 30 or less, more preferably 28 or less, more preferably 26 or less, more preferably 24 or less, more preferably 22 or less, and more preferably 20 or less. When the number of carbon atoms in the branched aliphatic hydrocarbon group is within the above range, the branched structure of the branched aliphatic hydrocarbon group interacts with the nonpolar portion (hydrophobic portion) of the acylphosphine oxide-based photopolymerization initiator, allowing the acylphosphine oxide-based photopolymerization initiator to be well solubilized in an aqueous medium and maintain that state stably, resulting in a photocurable composition with excellent storage stability.

[0078] In fatty acids, the branched aliphatic hydrocarbon group having 8 or more carbon atoms is not particularly limited, and examples include isostearyl group, decyltetradecyl group, isopalmytil group (14-methylpentadecyl group, 2-hexyldecyl group), with isostearyl group being preferred.

[0079] An ester compound of polyglycerol and a fatty acid having a branched aliphatic hydrocarbon group with 8 or more carbon atoms is preferably a diester or a triester, and more preferably a triester. When the ester compound is a diester or a triester, due to the interaction between the branched alkyl chain with 8 or more carbon atoms and the acylphosphine oxide-based photoinitiator, the acylphosphine oxide-based photoinitiator can be solubilized better and its state can be maintained more stably, and the photocurable composition has better storage stability.

[0080] The ester compound of polyglycerol and a fatty acid having a branched aliphatic hydrocarbon group with 8 or more carbon atoms is not particularly limited. For example, polyglyceryl triisostearate, polyglyceryl diisostearate, polyglyceryl monoisostearate, polyglyceryl triisopalmitate, polyglyceryl diisopalmitate, polyglyceryl monoisopalmitate, etc. can be mentioned. Polyglyceryl triisostearate, polyglyceryl diisostearate, and polyglyceryl monoisostearate are preferred, polyglyceryl triisostearate and polyglyceryl diisostearate are more preferred, and polyglyceryl triisostearate is even more preferred.

[0081] The polyoxyethylene polyoxypropylene alkyl ether will be described. The polyoxyethylene polyoxypropylene alkyl ether is a compound obtained by adding and polymerizing propylene oxide and ethylene oxide to a higher alcohol (R 2 -OH).

[0082] The alkyl group of the polyoxyethylene polyoxypropylene alkyl ether is a higher alcohol residue (R 2 -). The number of carbon atoms of the alkyl group of the polyoxyethylene polyoxypropylene alkyl ether (the number of carbon atoms of R 2 ) is preferably 8 or more, more preferably 9 or more, more preferably 10 or more, more preferably 12 or more, and more preferably 14 or more. The number of carbon atoms of the alkyl group of the polyoxyethylene polyoxypropylene alkyl ether (R 2The number of carbon atoms in the alkyl group of the polyoxyethylene polyoxypropylene alkyl ether is preferably 40 or less, more preferably 36 or less, more preferably 32 or less, more preferably 30 or less, more preferably 28 or less, and more preferably 26 or less. When the number of carbon atoms in the alkyl group of the polyoxyethylene polyoxypropylene alkyl ether is within the above range, the interaction between the alkyl group and the acylphosphine oxide-based photopolymerization initiator in the polyoxyethylene polyoxypropylene alkyl ether allows for better solubilization of the acylphosphine oxide-based photopolymerization initiator and more stable maintenance of that state, resulting in a photocurable composition with excellent storage stability.

[0083] The alkyl group in polyoxyethylene polyoxypropylene alkyl ether is not particularly limited and includes, for example, linear alkyl groups such as cetyl groups, branched alkyl groups such as isopalmytil groups (14-methylpentadecyl group, 2-hexyldecyl group), isostearyl groups, 6-decyltetradecyl groups, and 13-decyltetradecyl groups.

[0084] In polyoxyethylene polyoxypropylene alkyl ethers, the ratio of the average degree of polymerization of the polyoxyethylene skeleton (polyoxyethylene block) (average number of moles of ethylene oxide added) to the average degree of polymerization of the polyoxypropylene skeleton (polyoxypropylene block) (average number of moles of propylene oxide added) (average degree of polymerization of the polyoxyethylene skeleton / average degree of polymerization of the polyoxypropylene skeleton) is preferably 1 or more, more preferably 1.2 or more, more preferably 1.4 or more, more preferably 1.6 or more, more preferably 1.8 or more, more preferably 1.9 or more, and more preferably 2.0 or more. In polyoxyethylene polyoxypropylene alkyl ethers, the ratio of the average degree of polymerization of the polyoxyethylene skeleton (polyoxyethylene block) (average number of moles of ethylene oxide added) to the average degree of polymerization of the polyoxypropylene skeleton (polyoxypropylene block) (average number of moles of propylene oxide added) (average degree of polymerization of the polyoxyethylene skeleton / average degree of polymerization of the polyoxypropylene skeleton) is preferably 10 or less, more preferably 9 or less, more preferably 8 or less, more preferably 7 or less, and more preferably 6 or less. When the ratio of the average degree of polymerization of the polyoxyethylene skeleton (average number of moles of ethylene oxide added) to the average degree of polymerization of the polyoxypropylene skeleton (average number of moles of propylene oxide added) is within the above range, the interaction between the polyoxyethylene and polyoxypropylene skeletons of the polyoxyethylene polyoxypropylene alkyl ether and the acylphosphine oxide-based photopolymerization initiator allows for better solubilization of the acylphosphine oxide-based photopolymerization initiator, enabling the maintenance of this state more stably, and resulting in a photocurable composition with superior storage stability.

[0085] The polyoxyethylene polyoxypropylene alkyl ether is not particularly limited, and examples include polyoxyethylene polyoxypropylene cetyl ether, polyoxyethylene polyoxypropylene decyltetradecyl ether, and polyoxyethylene polyoxypropylene isostearyl ether, with polyoxyethylene polyoxypropylene cetyl ether and polyoxyethylene polyoxypropylene decyltetradecyl ether being preferred.

[0086] This section describes polyoxyethylene alkyl ethers. Polyoxyethylene alkyl ethers are higher alcohols (R 3 This compound is obtained by addition polymerization of ethylene oxide to -OH. In the alkyl group of the polyoxyethylene alkyl ether, some of the carbon-carbon single bonds may be dehydrogenated to form unsaturated double bonds, but it is preferable that there are no unsaturated bonds. Note that the polyoxyethylene alkyl ether does not have a polyoxypropylene block in its molecule.

[0087] The alkyl group of polyoxyethylene alkyl ether is a higher alcohol residue (R 3 -) The number of carbon atoms in the alkyl group of polyoxyethylene alkyl ether (R 3 The number of carbon atoms (R) of the alkyl group of the polyoxyethylene alkyl ether is preferably 8 or more, more preferably 10 or more, more preferably 12 or more, and more preferably 14 or more. 3 The number of carbon atoms in the alkyl group of the polyoxyethylene alkyl ether is preferably 40 or less, more preferably 36 or less, more preferably 32 or less, more preferably 30 or less, more preferably 28 or less, more preferably 26 or less, more preferably 24 or less, and more preferably 22 or less. When the number of carbon atoms in the alkyl group of the polyoxyethylene alkyl ether is within the above range, the interaction between the alkyl group and the acylphosphine oxide-based photopolymerization initiator in the polyoxyethylene alkyl ether allows for better solubilization of the acylphosphine oxide-based photopolymerization initiator, and this state can be maintained more stably, resulting in a photocurable composition with superior storage stability.

[0088] The alkyl group in polyoxyethylene alkyl ethers is not particularly limited, and examples include linear alkyl groups such as cetyl groups, branched alkyl groups such as isopalmytil groups (14-methylpentadecyl group, 2-hexyldecyl group), isostearyl groups, 6-decyltetradecyl groups, and 13-decyltetradecyl groups. Branched alkyl groups are preferred, and isostearyl groups are more preferred.

[0089] In polyoxyethylene alkyl ethers, the average degree of polymerization of the polyoxyethylene skeleton (polyoxyethylene block) is preferably 11 or higher, more preferably 12 or higher, and even more preferably 13 or higher. In polyoxyethylene alkyl ethers, the average degree of polymerization of the polyoxyethylene skeleton (polyoxyethylene block) is preferably 24 or lower, more preferably 22 or lower, more preferably 20 or lower, more preferably 18 or lower, and even more preferably 17 or lower. When the average degree of polymerization of the polyoxyethylene skeleton (average number of moles of ethylene oxide added) is within the above range, the interaction between the polyoxyethylene block of the polyoxyethylene alkyl ether and the acylphosphine oxide-based photopolymerization initiator allows for better solubilization of the acylphosphine oxide-based photopolymerization initiator, and this state can be maintained more stably, resulting in a photocurable composition with superior storage stability.

[0090] The polyoxyethylene alkyl ether is not particularly limited, and examples include polyoxyethylene isostearyl ether, polyoxyethylene cetyl ether, and polyoxyethylene decyltetradecyl ether, with polyoxyethylene isostearyl ether being preferred.

[0091] This section describes polyoxyethylene alkenyl ethers. Polyoxyethylene alkenyl ethers are higher alcohols (R) that have one unsaturated double bond in their molecule. 5 This is a compound obtained by addition polymerization of ethylene oxide to -OH. 5 A polyoxyethylene alkenyl ether is a monovalent group of atoms formed by removing (extracting) one hydrogen atom from any carbon atom of an alkene, and includes both linear and branched groups. Note that polyoxyethylene alkenyl ethers do not contain polyoxypropylene blocks within their molecules.

[0092] The alkenyl group of polyoxyethylene alkenyl ethers is a higher alcohol residue (R) that has one unsaturated double bond in the molecule. 5 -) The number of carbon atoms in the alkenyl group of polyoxyethylene alkenyl ether (R 5The number of carbon atoms (R) of the alkenyl group of polyoxyethylene alkenyl ether is preferably 8 or more, more preferably 10 or more, more preferably 12 or more, more preferably 14 or more, and more preferably 16 or more. 5 The number of carbon atoms in the alkenyl group of the polyoxyethylene alkenyl ether is preferably 40 or less, more preferably 36 or less, more preferably 32 or less, more preferably 30 or less, more preferably 28 or less, more preferably 26 or less, more preferably 24 or less, more preferably 22 or less, and more preferably 20 or less. When the number of carbon atoms in the alkenyl group of the polyoxyethylene alkenyl ether is within the above range, the interaction between the alkenyl group and the acylphosphine oxide-based photopolymerization initiator in the polyoxyethylene alkenyl ether allows for better solubilization of the acylphosphine oxide-based photopolymerization initiator, and this state can be maintained more stably, resulting in a photocurable composition with superior storage stability.

[0093] The alkenyl group in polyoxyethylene alkenyl ethers is not particularly limited, and examples include oleyl groups and 9-hexadecene groups, with oleyl groups being preferred.

[0094] In polyoxyethylene alkenyl ethers, the average degree of polymerization of the polyoxyethylene skeleton (polyoxyethylene block) is preferably 3 or higher, more preferably 5 or higher, and even more preferably 7 or higher. In polyoxyethylene alkenyl ethers, the average degree of polymerization of the polyoxyethylene skeleton (polyoxyethylene block) is preferably 24 or lower, more preferably 22 or lower, more preferably 20 or lower, more preferably 18 or lower, more preferably 17 or lower, more preferably 15 or lower, more preferably 13 or lower, and even more preferably 11 or lower. When the average degree of polymerization of the polyoxyethylene skeleton (average number of moles of ethylene oxide added) is within the above range, the interaction between the polyoxyethylene block of the polyoxyethylene alkenyl ether and the acylphosphine oxide-based photopolymerization initiator allows for better solubilization of the acylphosphine oxide-based photopolymerization initiator, and this state can be maintained more stably, resulting in a photocurable composition with superior storage stability.

[0095] While not particularly limited, polyoxyethylene oleyl ethers are preferred as polyoxyethylene alkenyl ethers.

[0096] This section describes polyoxyethylene sterol ethers. Polyoxyethylene sterol ethers are compounds obtained by addition polymerization of ethylene oxide to sterols, in which polyoxyethylene is added to the hydroxyl group of the sterol, forming an ether bond. The unsaturated double bonds contained in polyoxyethylene sterol ethers may be partially hydrogenated or fully hydrogenated.

[0097] Examples of sterols include cholesterol and phytosterols, which are preferred because they better solubilize acylphosphine oxide-based photopolymerization initiators and maintain that state more stably, and the photocurable composition has excellent storage stability. Polyoxyethylene phytosterol ethers are preferred.

[0098] Examples of phytosterols include β-sitosterol, stigmasterol, campesterol, and brassicasterol. A mixture of the above sterols is used as the phytosterol.

[0099] The polyoxyethylene phytosterol ether is preferably a mixture of a polyoxyethylene phytosterol ether having branched-chain saturated aliphatic hydrocarbon groups with 8 or more carbon atoms and a polyoxyethylene phytosterol ether having branched-chain unsaturated aliphatic hydrocarbon groups with 8 or more carbon atoms. This allows for better solubilization of acylphosphine oxide-based photopolymerization initiators and more stable maintenance of that state, resulting in a photocurable composition with superior storage stability.

[0100] The phytosterol components in polyoxyethylene phytosterol ether preferably include β-sitosterol, stigmasterol, and campesterol.

[0101] In the phytosterol components of polyoxyethylene phytosterol ether, the mass ratio of β-sitosterol content to stigmasterol content (β-sitosterol content / stigmasterol content) is preferably 0.5 or higher, more preferably 0.7 or higher, more preferably 1 or higher, and more preferably 1.5 or higher. In the phytosterol components of polyoxyethylene phytosterol ether, the mass ratio of β-sitosterol content to stigmasterol content (β-sitosterol content / stigmasterol content) is preferably 4 or less, more preferably 3.5 or less, more preferably 3 or less, and more preferably 2.5 or less. In polyoxyethylene phytosterol ether, when the mass ratio of β-sitosterol content to stigmasterol content (β-sitosterol content / stigmasterol content) is within the above range, the acylphosphine oxide-based photopolymerization initiator can be solubilized more effectively and its state can be maintained more stably, resulting in a photocurable composition with superior storage stability.

[0102] In the phytosterol components of polyoxyethylene phytosterol ether, the mass ratio of campesterol content to stigmasterol content (campesterol content / stigmasterol content) is preferably 0.1 or higher, more preferably 0.3 or higher, more preferably 0.5 or higher, and more preferably 0.7 or higher. In the phytosterol components of polyoxyethylene phytosterol ether, the mass ratio of campesterol content to stigmasterol content (campesterol content / stigmasterol content) is preferably 2 or less, more preferably 1.7 or less, more preferably 1.5 or less, and more preferably 1.3 or less. In polyoxyethylene phytosterol ether, when the mass ratio of β-sitosterol content to stigmasterol content (β-sitosterol content / stigmasterol content) is within the above range, the acylphosphine oxide-based photopolymerization initiator can be solubilized more effectively and its state can be maintained more stably, resulting in a photocurable composition with superior storage stability.

[0103] In the phytosterol components of polyoxyethylene phytosterol ether, the mass ratio of the β-sitosterol content to the campesterol content (β-sitosterol content / campesterol content) is preferably 0.5 or higher, more preferably 0.7 or higher, more preferably 1 or higher, and more preferably 1.5 or higher. In the phytosterol components of polyoxyethylene phytosterol ether, the mass ratio of the β-sitosterol content to the campesterol content (β-sitosterol content / campesterol content) is preferably 4 or less, more preferably 3.5 or less, more preferably 3 or less, and more preferably 2.5 or less. When the mass ratio of β-sitosterol content to campesterol content (β-sitosterol content / campesterol content) in the phytosterol component of polyoxyethylene phytosterol ether is within the above range, the acylphosphine oxide-based photopolymerization initiator can be solubilized more effectively and its state can be maintained more stably, resulting in a photocurable composition with superior storage stability.

[0104] The average degree of polymerization (number of moles of ethylene oxide added) of the polyoxyethylene skeleton (polyoxyethylene block) in polyoxyethylene sterol ether is preferably 2 or more, more preferably 4 or more, more preferably 6 or more, more preferably 7 or more, more preferably 8 or more, and more preferably 9 or more. The average degree of polymerization (number of moles of ethylene oxide added) of the polyoxyethylene skeleton (polyoxyethylene block) in polyoxyethylene sterol ether is preferably 50 or less, more preferably 45 or less, more preferably 42 or less, more preferably 40 or less, more preferably 38 or less, more preferably 36 or less, more preferably 34 or less, and more preferably 32 or less. When the average degree of polymerization (number of moles of ethylene oxide added) of the polyoxyethylene skeleton (polyoxyethylene block) in polyoxyethylene sterol ether is within the above range, the acylphosphine oxide-based photopolymerization initiator can be solubilized more effectively and its state can be maintained more stably, resulting in a photocurable composition with superior storage stability.

[0105] This section describes polyoxyethylene hydrogenated castor oil. Polyoxyethylene hydrogenated castor oil is a compound obtained by addition polymerization of ethylene oxide to hydrogenated castor oil. Castor oil is a triglyceride in which glycerin and fatty acids are esterified. The fatty acids include palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, and dihydroxystearic acid, in addition to silinoleic acid, which accounts for about 90%.

[0106] Polyoxyethylene hydrogenated castor oil is obtained by addition polymerization of ethylene oxide to hydrogenated castor oil and has a polyoxyethylene skeleton in its molecule. This allows for better solubilization of acylphosphine oxide-based photopolymerization initiators and more stable maintenance of that state, resulting in a photocurable composition with superior storage stability.

[0107] In polyoxyethylene hydrogenated castor oil, the average degree of polymerization of the polyoxyethylene skeleton (polyoxyethylene block) is preferably 60 or higher, more preferably 70 or higher, more preferably 80 or higher, and more preferably 90 or higher. In polyoxyethylene alkyl ethers, the average degree of polymerization of the polyoxyethylene skeleton (polyoxyethylene block) is preferably 150 or lower, more preferably 140 or lower, more preferably 130 or lower, more preferably 120 or lower, and more preferably 110 or lower. When the average degree of polymerization of the polyoxyethylene skeleton (polyoxyethylene block) (average number of moles of ethylene oxide added) is within the above range, the interaction between polyoxyethylene hydrogenated castor oil and the acylphosphine oxide-based photopolymerization initiator allows for better solubilization of the acylphosphine oxide-based photopolymerization initiator, and this state can be maintained more stably, resulting in a photocurable composition with superior storage stability.

[0108] This section describes sorbitan fatty acid esters. Sorbitan fatty acid esters are ester compounds of sorbitan and fatty acids. Sorbitan fatty acid esters may be monoesters, diesters, or triesters, but triesters are preferred.

[0109] The carbon number of the fatty acid used as a raw material for sorbitan fatty acid ester is preferably 10 or more, more preferably 12 or more, more preferably 14 or more, and more preferably 16 or more. The carbon number of the fatty acid used as a raw material for sorbitan fatty acid ester is preferably 26 or less, more preferably 24 or less, more preferably 22 or less, and more preferably 20 or less. When the carbon number of the fatty acid is within the above range, the acylphosphine oxide-based photopolymerization initiator can be solubilized more effectively and that state can be maintained more stably, resulting in a photocurable composition with superior storage stability.

[0110] The fatty acid may be an unsaturated fatty acid or a saturated fatty acid. The fatty acid is not particularly limited and examples include isostearic acid (16-methylheptadecanoic acid), decyltetradecanoic acid, isopalmitic acid (14-methylpentadecanoic acid, 2-hexyldecanoic acid), and oleic acid. Unsaturated fatty acids are preferred, and oleic acid is more preferred.

[0111] The sorbitan fatty acid ester is not particularly limited, and examples include sorbitan trioleate, sorbitan dioleate, sorbitan monooleate, sorbitan trilaurate, sorbitan dilaurate, and sorbitan monolaurate, with sorbitan oleate being preferred and sorbitan trioleate being more preferred.

[0112] In the photocurable composition, the content of the nonionic surfactant is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, more preferably 2 parts by mass or more, more preferably 2.5 parts by mass or more, more preferably 3 parts by mass or more, more preferably 3.5 parts by mass or more, and more preferably 4 parts by mass or more, per 100 parts by mass of the polymerizable compound. In the photocurable composition, the content of the nonionic surfactant is preferably 10 parts by mass or less, more preferably 9 parts by mass or less, more preferably 8 parts by mass or less, more preferably 7 parts by mass or less, more preferably 6 parts by mass or less, and more preferably 5.5 parts by mass or less, per 100 parts by mass of the polymerizable compound. When the content of the nonionic surfactant is within the above range, the interaction between the nonionic surfactant and the acylphosphine oxide-based photopolymerization initiator allows for better solubilization of the acylphosphine oxide-based photopolymerization initiator, and this state can be maintained more stably, resulting in a photocurable composition with superior storage stability.

[0113] The mass ratio of the nonionic surfactant content to the acylphosphine oxide-based photopolymerization initiator content (nonionic surfactant content / acylphosphine oxide-based photopolymerization initiator content) is preferably 15 or more, more preferably 20 or more, and even more preferably 25 or more. The mass ratio of the nonionic surfactant content to the acylphosphine oxide-based photopolymerization initiator content (nonionic surfactant content / acylphosphine oxide-based photopolymerization initiator content) is preferably 100 or less, more preferably 75 or less, and even more preferably 50 or less. When the mass ratio of the nonionic surfactant content to the acylphosphine oxide-based photopolymerization initiator content is 15 or more, the interaction between the nonionic surfactant and the acylphosphine oxide-based photopolymerization initiator allows for better solubilization of the acylphosphine oxide-based photopolymerization initiator, and this state can be maintained more stably, resulting in a photocurable composition with superior storage stability.

[0114] [Aqueous medium] The photocurable composition contains an aqueous medium. The aqueous medium should be capable of dissolving the acylphosphine oxide-based photopolymerization initiator, which has been solubilized by micelles formed by a nonionic surfactant, and the polymerizable compound.

[0115] Aqueous media contain water as an essential component. Examples of water include pure water such as ion-exchanged water, limit filtered water, reverse osmosis water, and distilled water, as well as ultrapure water.

[0116] The aqueous medium preferably contains a water-soluble organic solvent. The water-soluble organic solvent is miscible with water and, when mixed with water, dissolves in it to form a single phase. The water-soluble organic solvent is not particularly limited and may include, for example, polyhydric alcohols such as glycerin, alkanediols (e.g., 1,3-butanediol, 2,3-butanediol, 1,2,6-hexanetriol, trimethylolpropane, ethylene glycol, propylene glycol, etc.), and polyalkylene glycols (e.g., diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, polypropylene glycol); sugar alcohols; alkyl alcohols with 1 to 4 carbon atoms such as ethanol, methanol, butanol, propanol, isopropanol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono- Examples of glycol ethers include n-propyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol monoethyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol monoisopropyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol monoisopropyl ether, and tripropylene glycol monomethyl ether.

[0117] As the water-soluble organic solvent, polyhydric alcohols are preferred, glycerin, alkanediols, and polyalkylene glycols are more preferred, glycerin and polyalkylene glycols are even more preferred, and glycerin and polyethylene glycols are even more preferred. When the aqueous medium contains a polyhydric alcohol, the polar groups derived from the multiple hydroxyl groups contained in the polyhydric alcohol and the nonpolar groups derived from the carbon chains can further stabilize the solubilization of the acylphosphine oxide-based photopolymerization initiator by micelles of the nonionic surfactant. The solubilized state of the acylphosphine oxide-based photopolymerization initiator can be maintained more stably, and the photocurable composition has better storage stability.

[0118] The degree of polymerization of the polyalkylene glycol is preferably 2 or higher, and more preferably 4 or higher. The degree of polymerization of the polyalkylene glycol is preferably 30 or lower, and more preferably 15 or lower. When the degree of polymerization of the polyalkylene glycol is within the above range, the solubilization of the acylphosphine oxide-based photopolymerization initiator by the micelles of the nonionic surfactant can be maintained more stably, and the photocurable composition has better storage stability.

[0119] The water content in the aqueous medium is preferably 1% by mass or more, more preferably 10% by mass or more, more preferably 15% by mass or more, and more preferably 20% by mass or more. The water content in the aqueous medium is preferably 99% by mass or less, more preferably 80% by mass or less, more preferably 70% by mass or less, more preferably 60% by mass or less, more preferably 50% by mass or less, more preferably 40% by mass or less, and more preferably 30% by mass or less.

[0120] The content of the water-soluble organic solvent in the aqueous medium is preferably 1% by mass or more, more preferably 20% by mass or more, more preferably 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, and more preferably 70% by mass or more. The content of the water-soluble organic solvent in the aqueous medium is preferably 99% by mass or less, more preferably 90% by mass or less, more preferably 85% by mass or less, and more preferably 80% by mass or less.

[0121] [Photocurable composition] Photocurable compositions can be produced by mixing a polymerizable compound, an acylphosphine oxide-based photopolymerization initiator, a nonionic surfactant, and an aqueous medium in a known manner. If the nonionic surfactant is in paste or solid form before mixing, it is preferable to heat the nonionic surfactant to make it liquid before mixing it with the other compounds.

[0122] The photocurable composition may contain additives such as thickeners, electrolytes, conductive fillers, preservatives, antibacterial agents, disinfectants, rust inhibitors, antioxidants, stabilizers, fragrances, colorants, defoamers, UV absorbers, chelating compounds, metal oxides, moisturizing agents, conductivity modifiers, hardness modifiers, and thermal polymerization initiators, to the extent that they do not impair its physical properties.

[0123] Photocurable compositions can be polymerized and cured by irradiation with active light such as ultraviolet light or visible light, thereby producing a polymer. At the same time, they can incorporate an aqueous medium into this polymer to form a hydrogel, which is a swollen structure.

[0124] As described above, the photocurable composition exhibits suppressed precipitation of acylphosphine oxide-based photopolymerization initiators during storage before curing, and the acylphosphine oxide-based photopolymerization initiators are stably dissolved in the aqueous medium. Therefore, the photocurable composition can be uniformly and effectively cured by active light irradiated onto it.

[0125] In the photocurable composition, the polymerizable compound decreases over time as polymerization progresses, while the polymer is generated and increases. However, due to the action of micelles of the nonionic surfactant, the acylphosphine oxide-based photopolymerization initiator remains solubilized in the aqueous medium, suppressing the precipitation of the acylphosphine oxide-based photopolymerization initiator throughout the entire polymerization process. Therefore, the photocurable composition can uniformly polymerize the polymerizable compound to produce a homogeneous hydrogel. Furthermore, the resulting hydrogel does not exhibit the cloudiness caused by the precipitation of the acylphosphine oxide-based photopolymerization initiator and has an excellent transparent or translucent appearance.

[0126] The photocurable composition can be suitably used as a gel material for 3D printers. The photocurable composition can also be suitably used in 3D printers employing vat polymerization.

[0127] Liquid-level polymerization methods include free-level and restricted-level methods, and photocurable compositions can be suitably used in either method. In the free-level method, the photocurable composition is stored in the liquid tank of a 3D printer, and an active light is irradiated onto the liquid surface of the photocurable composition in the liquid tank to polymerize and cure the photocurable composition, while gradually moving the generated cured material away from the active light. At the same time, the photocurable composition between the generated cured material and the liquid surface is sequentially polymerized and cured, and the resulting layers are sequentially stacked on top of the previously generated cured material to produce a molded body of any shape. In the restricted-level method, an active light is irradiated onto the photocurable composition from the bottom of the liquid tank where the photocurable composition is stored, polymerizing and curing the photocurable composition, while gradually moving the generated cured material away from the active light. At the same time, the photocurable composition between the generated cured material and the bottom of the liquid tank is sequentially polymerized and cured, and the resulting layers are sequentially stacked on top of the previously generated cured material to produce a molded body of any shape.

[0128] As described above, the photocurable composition does not produce cloudiness due to the precipitation of acylphosphine oxide-based photopolymerization initiators during storage before use and during the 3D printing process from the start to the end of polymerization. Therefore, by irradiating the photocurable composition with active light, the photocurable composition can be easily cured at the desired location, producing a cured product with high precision, and a hydrogel molded body with the desired three-dimensional structure and excellent appearance can be easily produced.

[0129] The above describes the case where a photocurable composition is used as a gel material for a 3D printer. However, by supplying the photocurable composition into a mold having the desired shape and curing it with active light, a hydrogel molded body with the desired shape and excellent appearance can also be easily produced.

[0130] Hydrogel molded articles, which are cured products produced from photocurable compositions, can take on various desired forms, including planar forms such as sheets and lines, as well as three-dimensional forms. Hydrogel molded articles produced from photocurable compositions can be used as sensor materials, bearings and interlayers that come into contact with metal, bandages and packs that come into contact with the human body, and seedbeds, as well as for medical applications such as model organs, implant materials, scaffold materials for regenerative medicine, artificial skin, artificial joints, artificial muscles, artificial blood vessels, artificial cartilage, artificial organs, prosthetic arms and legs, and cell culture sheets. [Examples]

[0131] The present invention will be described more specifically below with reference to examples, but the present invention is not limited thereto. Specific numerical values ​​such as blending ratios (content percentages), physical properties, and parameters used in the following description may be replaced with the corresponding upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to") of the blending ratios (content percentages), physical properties, and parameters described in the "Means for Solving the Problems" and "Modes for Carrying Out the Invention" sections.

[0132] [Polymerizable compound] (Monofunctional monomer) • N-(2-hydroxyethyl)acrylamide (HEAA) (Polyfunctional monomers) • Polyglycerin-based acrylate (manufactured by Sakamoto Pharmaceutical Co., Ltd., product name "SYntech SA-TE60," containing multiple acryloyl groups in the molecule. It also contains a glycerin skeleton and a polyoxyalkylene skeleton. Formula 3)

[0133] [Acylphosphine oxide-based photopolymerization initiators] • Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO, manufactured by IGM Resin BV, trade name "Omnirad819", particle size: 0.5~500μm)

[0134] [Alkylphenone-based photopolymerization initiators] • 2-Hydroxy-2-methylpropiophenone (manufactured by IGM Resin BV, trade name "Omnirad1173")

[0135] [Nonionic surfactants] (Polyglycerol fatty acid ester (ester compound of polyglycerol and fatty acid)) • Polyglyceryl-10 triisostearate (manufactured by Nippon Emulsion Co., Ltd., product name "EMALEX TISG-10", branched alkyl group: isostearyl group (number of carbon atoms: 18), average degree of polymerization of polyglycerin: 10) • Polyglyceryl-10 monoisostearate (manufactured by Sakamoto Pharmaceutical Co., Ltd., product name "S-Face 10G-IS", branched alkyl group: isostearyl group (number of carbon atoms: 18), average degree of polymerization of polyglycerin: 10)

[0136] (Polyoxyethylene polyoxypropylene alkyl ether) • Polyoxyethylene polyoxypropylene decyltetradecyl ether 1 (manufactured by Nikko Chemicals Co., Ltd., product name "NIKKOL PEN4612", branched alkyl group: decyltetradecyl group (number of carbon atoms: 24), average degree of polymerization of polyoxyethylene: 12, average degree of polymerization of polyoxypropylene: 6)

[0137] • Polyoxyethylene polyoxypropylene cetyl ether (manufactured by Nikko Chemicals Co., Ltd., product name "NIKKOL SG-C420", linear alkyl group: cetyl group (number of carbon atoms: 16), average degree of polymerization of polyoxyethylene: 20, average degree of polymerization of polyoxypropylene: 4)

[0138] • Polyoxyethylene polyoxypropylene decyltetradecyl ether 2 (manufactured by Nikko Chemicals Co., Ltd., product name "NIKKOL SG-DTD620", branched alkyl group: decyltetradecyl group (number of carbon atoms: 24), average degree of polymerization of polyoxyethylene: 20, average degree of polymerization of polyoxypropylene: 6)

[0139] • Polyoxyethylene polyoxypropylene decyltetradecyl ether 3 (manufactured by Nikko Chemicals Co., Ltd., product name "NIKKOL SG-DTD630", branched alkyl group: decyltetradecyl group (number of carbon atoms: 24), average degree of polymerization of polyoxyethylene: 30, average degree of polymerization of polyoxypropylene: 6)

[0140] • Polyoxyethylene polyoxypropylene decyltetradecyl ether 4 (manufactured by NOF Corporation, product name "Solbure GS-01", branched alkyl group: decyltetradecyl group (number of carbon atoms: 24), average degree of polymerization of polyoxyethylene: 24, average degree of polymerization of polyoxypropylene: 13)

[0141] (Polyoxyethylene phytosterol ether) • Polyoxyethylene phytosterol ether 1 (manufactured by Nikko Chemicals Co., Ltd., product name "NIKKOL BPS-10", average degree of polymerization of polyoxyethylene: 10, a mixture of polyoxyethylene phytosterol ether having branched-chain saturated aliphatic hydrocarbon groups with 8 or more carbon atoms and polyoxyethylene phytosterol ether having branched-chain unsaturated aliphatic hydrocarbon groups with 8 or more carbon atoms, mass ratio of phytosterol content (β-sitosterol:stigmasterol:campesterol) = 2:1:1) • Polyoxyethylene phytosterol ether 2 (manufactured by Nikko Chemicals Co., Ltd., product name "NIKKOL BPS-20", average degree of polymerization of polyoxyethylene: 20, a mixture of polyoxyethylene phytosterol ether having branched-chain saturated aliphatic hydrocarbon groups with 8 or more carbon atoms and polyoxyethylene phytosterol ether having branched-chain unsaturated aliphatic hydrocarbon groups with 8 or more carbon atoms, mass ratio of phytosterol content (β-sitosterol:stigmasterol:campesterol) = 2:1:1) • Polyoxyethylene phytosterol ether 3 (manufactured by Nikko Chemicals Co., Ltd., product name "NIKKOL BPS-30", average degree of polymerization of polyoxyethylene: 30, a mixture of polyoxyethylene phytosterol ether having branched-chain saturated aliphatic hydrocarbon groups with 8 or more carbon atoms and polyoxyethylene phytosterol ether having branched-chain unsaturated aliphatic hydrocarbon groups with 8 or more carbon atoms, mass ratio of phytosterol content (β-sitosterol:stigmasterol:campesterol) = 2:1:1)

[0142] (Polyoxyethylene hydrogenated castor oil) • Polyoxyethylene hydrogenated castor oil (manufactured by Nippon Emulsion Co., Ltd., product name "EMALEX HCO-100", average degree of polymerization of polyoxyethylene: 100)

[0143] (Polyoxyethylene alkyl ether) • Polyoxyethylene isostearyl ether 1 (manufactured by Nippon Emulsion Co., Ltd., product name "EMALEX 1810", branched alkyl group: isostearyl group (number of carbon atoms: 18), average degree of polymerization of polyoxyethylene: 10)

[0144] • Polyoxyethylene isostearyl ether 2 (manufactured by Nippon Emulsion Co., Ltd., product name "EMALEX 1815", branched alkyl group: isostearyl group (number of carbon atoms: 18), average degree of polymerization of polyoxyethylene: 15)

[0145] • Polyoxyethylene isostearyl ether 3 (manufactured by Nippon Emulsion Co., Ltd., product name "EMALEX 1825", branched alkyl group: isostearyl group (number of carbon atoms: 18), average degree of polymerization of polyoxyethylene: 25)

[0146] (Polyoxyethylene alkenyl ether) • Polyoxyethylene oleyl ether (manufactured by Kao Corporation, product name "Emulgen 409PV", linear aliphatic hydrocarbon: oleyl group (unsaturated double bond: 1), average degree of polymerization of polyoxyethylene: 9)

[0147] (Sucrose fatty acid ester) • Sucrose stearate (manufactured by Mitsubishi Chemical Corporation, product name "S-1170")

[0148] [Aqueous medium] • Ion-exchanged water • Glycerin (manufactured by NOF Corporation, product name "Concentrated Glycerin")

[0149] (Examples 1-15, Comparative Examples 1 and 2) A photocurable composition was prepared by uniformly mixing the predetermined amounts of polymerizable compounds, acylphosphine oxide-based photopolymerization initiators, alkylphenone-based photopolymerization initiators, nonionic surfactants, and aqueous media shown in Table 1. For compounds that were solid at the time of mixing, the solid compounds were heated to their melting points to become liquid before being mixed with the other compounds.

[0150] The photocurable compositions obtained in Examples 1-15 were exposed to ultraviolet light with an integrated light intensity of 6000 mJ / cm². 2 By irradiating and curing the material in such a manner, a hydrogel molded body was obtained as a cured product.

[0151] The storage stability of the obtained photocurable compositions was measured according to the following procedure, and the results are shown in Table 1.

[0152] (Storage stability) 10 mL of the photocurable composition was placed in a 10 mL glass bottle with a lid and left to stand for 14 days in an atmosphere of 20°C.

[0153] On the 7th and 14th days from the start of the test, the bottom of the glass bottle was visually inspected and evaluated based on the following criteria.

[0154] A...No precipitation of acylphosphine oxide-based photopolymerization initiators was observed. B...Precipitation of acylphosphine oxide-based photopolymerization initiators was observed.

[0155] [Table 1]

Claims

1. Polymerizable compounds and Acylphosphine oxide-based photopolymerization initiators, A nonionic surfactant having a polyoxyalkylene skeleton, a branched aliphatic hydrocarbon group with 8 or more carbon atoms, or a sorbitan skeleton within the molecule, A photocurable composition characterized by containing an aqueous medium.

2. The photocurable composition according to claim 1, characterized in that the nonionic surfactant has a polyoxyalkylene skeleton and a branched aliphatic hydrocarbon group having 8 or more carbon atoms in its molecule.

3. The photocurable composition according to claim 1 or 2, characterized in that the mass ratio of the content of the nonionic surfactant to the content of the acylphosphine oxide-based photopolymerization initiator (content of nonionic surfactant / content of acylphosphine oxide-based photopolymerization initiator) is 15 or more.

4. The photocurable composition according to claim 1, characterized in that the above nonionic surfactant comprises at least one nonionic surfactant selected from the group consisting of polyoxyethylene alkyl ether, polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene hydrogenated castor oil, ester compounds of polyglycerin and a fatty acid having a branched aliphatic hydrocarbon group having 8 or more carbon atoms, polyoxyethylene sterol ether, and polyoxyethylene alkenyl ether.

5. The photocurable composition according to claim 1, characterized in that it contains 20 to 50% by mass of the polymerizable compound.

6. The photocurable composition according to claim 1 or 2, characterized in that the aqueous medium comprises water and glycerin or polyethylene glycol.

7. A molded article characterized by containing a cured product of the photocurable composition of claim 1.

8. The molded article according to claim 7, characterized in that it is a hydrogel.

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