vinyl resin particles

Abstract

[Problem] To provide novel vinyl-based resin particles that have excellent dispersion stability and solvent resistance for organic solvents, suppress aggregate generation and gelation, and are capable of forming fine, uniform pores in a film of a thermosetting resin, etc. [Solution] Vinyl-based resin particles that are a polymer having a structural unit (A) derived from a vinyl-based monomer and a structural unit (b1) derived from a compound represented by general formula (I) different from the structural unit (A), to be used to make a thermosetting resin porous. [In the formula, m represents an integer of 1-3, R represents a polymerizable unsaturated group, AO represents a C2-4 alkyleneoxy group, n represents an integer of 0-100, X represents a hydrogen atom or an anionic hydrophilic group selected from the group consisting of -SO3M, -COOM, and -PO3M (in the formula, M represents an alkali metal atom, an alkaline earth metal atom, an ammonium group, or an organic ammonium group.).]

Description

[Technical Field]

[0001] The present invention relates to vinyl resin particles, and more particularly to vinyl resin particles for producing porous films used to make thermosetting resins and the like porous. [Background technology]

[0002] In recent years, research has been conducted on polyimide and / or polyamide-imide porous membranes for use as filters used as gas or liquid separation membranes, separators for lithium ion batteries, fuel cell electrolyte membranes, or low-dielectric-constant materials. For example, a known method for producing a porous polyimide film used for separator applications involves coating a substrate with a varnish in which fine particles such as silica particles are dispersed in a polymer solution of polyamic acid or polyimide, and then heating the coated film as necessary to obtain a polyimide film containing the fine particles. Subsequently, the fine particles such as silica particles in the polyimide film are removed using hydrofluoric acid to make the film porous (see Patent Document 1).

[0003] When forming a porous polyimide film by a method such as that described in Patent Document 1, it is desirable to use a varnish with a uniformly dispersed composition to form a coating film with a uniform thickness and composition. However, the hydrofluoric acid used in the manufacturing method described in Patent Document 1 is generally not easy to handle. For this reason, the use of hydrofluoric acid increases the manufacturing cost of porous polyimide films, and a method for manufacturing porous films without using hydrofluoric acid is desired. For example, it is possible to use other fine particles, such as organic fine particles, instead of the silica particles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5605566 Summary of the Invention [Problem to be solved by the invention]

[0005] However, organic fine particles are often prepared in an aqueous solvent and distributed as a water-containing fine particle dispersion. Therefore, when using organic fine particles, if a varnish containing a polyamic acid or polyimide is prepared using a water-containing fine particle dispersion, a varnish containing water is inevitably obtained. When the varnish contains water and fine particles, there is a problem that a mixture of non-uniform composition is likely to be formed that can cause poor formation of the coating film, such as poor compatibility between polyamic acid and the water-containing solvent, or the presence of the fine particles inhibiting the orientation of the polyamic acid molecules, resulting in clumps of polyamic acid encapsulating the fine particles, which can lead to the risk of causing a decrease in film strength.

[0006] To avoid these problems, it has been considered to produce a varnish that is substantially free of water using completely dried organic fine particles. However, dried organic fine particles have poor dispersion stability and solvent resistance in organic solvents that dissolve polyamic acid, and aggregates are generated, making it difficult to obtain a polyimide porous film with uniformly formed pores and good air permeability.

[0007] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide novel vinyl resin particles that have excellent dispersion stability and solvent resistance in organic solvents, are suppressed in the formation of aggregates and gelation, and are capable of forming uniform, fine pores in a film of a thermosetting resin or the like. [Means for solving the problem]

[0008] The present invention relates to the following [1] to [9]. [1] A structural unit (A1) derived from a monofunctional vinyl monomer and Structural units (A2) derived from polyfunctional vinyl monomers and A polymer having structural units (B) derived from a reactive emulsifier, Vinyl resin particles for producing a porous membrane, the proportion of the structural unit (A1) is 88 to 99 mass%, the proportion of the structural unit (A2) is 0.9 to 10 mass%, and the proportion of the structural unit (B) is 0.1 to 2 mass%; Vinyl resin particles for porous membrane production. [2] a structural unit (A) derived from a vinyl monomer; The polymer has a structural unit (b1) derived from a compound represented by the following general formula (I), which is different from the structural unit (A): Vinyl resin particles for porous membrane production. [ka] [In the formula, m represents an integer of 1 to 3; R represents a group represented by the following formula (i) or (ii): [ka] (wherein R1 represents a hydrogen atom or a methyl group), AO represents an alkyleneoxy group having 2 to 4 carbon atoms, and n represents an integer of 0 to 100. X represents a hydrogen atom or an anionic hydrophilic group selected from the group consisting of -SO3M, -COOM, and -PO3M (wherein M represents an alkali metal atom, an alkaline earth metal atom, an ammonium group, or an organic ammonium group). [3] The vinyl resin particles according to [2], wherein the proportion of the structural unit (b1) is 0.1% by mass to 2.0% by mass with respect to the total mass of the structural units of the polymer. [4] The vinyl resin particles according to [2] or [3], wherein the structural unit (A) derived from the vinyl monomer contains a structural unit (A1) derived from a monofunctional vinyl monomer and a structural unit (A2) derived from a polyfunctional vinyl monomer. [5] Vinyl resin particles according to any one of [1] to [4], wherein the median diameter of the resin particles is 0.05 μm to 2.0 μm. [6] The structural unit (A1) derived from a monofunctional vinyl monomer includes a structural unit (a1) derived from a monofunctional styrene monomer. [1], [4] or [5]. [7] The structural unit (A1) derived from a monofunctional vinyl monomer includes a structural unit (a2) derived from a monofunctional (meth)acrylic monomer. [1] and [4] to [6]. Vinyl resin particles according to any one of [1] and [4] to [6]. [8] the proportion of the polyfunctional vinyl monomer (A2) is 0.9% by mass to 10% by mass based on the total mass of the structural units of the polymer; [1] and [4] to [7], vinyl resin particles. [9] In an aqueous dispersion medium in the presence of a polymerization initiator, The method is characterized by emulsion polymerizing a vinyl monomer and a compound represented by the following general formula (I) which is different from the vinyl monomer: A method for producing an aqueous dispersion of vinyl-based resin particles. [ka] [In the formula, m represents an integer of 1 to 3; R represents a group represented by the following formula (i) or (ii): [ka] (wherein R1 represents a hydrogen atom or a methyl group), AO represents an alkyleneoxy group having 2 to 4 carbon atoms, and n represents an integer of 0 to 100. X represents a hydrogen atom or an anionic hydrophilic group selected from the group consisting of -SO3M, -COOM, and -PO3M (wherein M represents an alkali metal atom, an alkaline earth metal atom, an ammonium group, or an organic ammonium group). [Effects of the Invention]

[0009] The vinyl resin particles of the present invention can be mixed with an organic solvent that dissolves a thermosetting resin (e.g., polyamic acid, which is a precursor of a polyimide resin), and the generation of aggregates, gelation, and viscosity increase are suppressed, resulting in stable mixing. Furthermore, dissolution and shape change of the particles are suppressed even in the organic solvent, resulting in excellent solvent resistance. Therefore, when the vinyl resin particles of the present invention are used as a porosity-inducing agent for a thermosetting resin, dissolution or aggregation of the particles is unlikely to occur even when mixed with a thermosetting resin material, and uniform, fine pores can be easily formed in a film obtained from the resin material, making it possible to produce a porous body (porous film). [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 shows electron microscope photographs of resin particles after the solvent resistance test ((a) Example 1, (b) Example 2, (c) Example 3, and (d) Example 4). [Figure 2] FIG. 2 shows electron microscope photographs of resin particles after the solvent resistance test ((a) Comparative Example 1, (b) Comparative Example 2). [Figure 3] FIG. 3 shows SEM images of the porous membranes ((a) Example 5, (b) Example 6, (c) Example 7, and (d) Example 8). [Figure 4] FIG. 4 shows an SEM image of the porous membrane (Comparative Example 3). DETAILED DESCRIPTION OF THE INVENTION

[0011] [Vinyl resin particles] The present invention is directed to vinyl resin particles, which are polymers essentially having a structural unit (A) derived from a vinyl monomer and a structural unit (b1) derived from a compound represented by general formula (I) described below. That is, the vinyl resin particles (polymer) of the present invention can be a copolymer (copolymer) of a monomer component (mixture) containing a vinyl monomer and a compound represented by general formula (I), which constitute each of the structural units described above. The vinyl resin particles of the present invention can be suitably used as a porosifying agent for thermosetting resins, that is, as vinyl resin particles for producing porous membranes.

[0012] In one aspect, the present invention is directed to vinyl resin particles, which are polymers having structural units (A1) derived from a monofunctional vinyl monomer described below, structural units (A2) derived from a polyfunctional vinyl monomer described below, and structural units (B) derived from a reactive emulsifier described below.

[0013] In this specification, the term "(meth)acrylic monomer" refers to both acrylic monomers and methacrylic monomers. For example, the term "(meth)acrylic acid alkyl ester" refers to both acrylic acid alkyl ester and methacrylic acid alkyl ester. In addition, in this specification, expressions such as "structural unit derived from a vinyl-based monomer," "structural unit derived from a monofunctional styrene-based monomer," "structural unit derived from a monofunctional (meth)acrylic monomer," and "structural unit derived from a polyfunctional vinyl-based monomer" refer to structural units formed when a vinyl-based monomer, a monofunctional styrene-based monomer, a monofunctional (meth)acrylic monomer, or a polyfunctional vinyl-based monomer is polymerized, respectively, and do not represent the monomers themselves.

[0014] [Structural unit (A) derived from vinyl monomer] The polymer that is the vinyl resin particle of the present invention has a structural unit (A) derived from a vinyl monomer, which is distinct from the structural unit (B) derived from a reactive emulsifier, which will be described later, and the structural unit (b1) derived from the compound represented by general formula (I). The structural unit (A) can include a structural unit (A1) derived from a monofunctional vinyl monomer and a structural unit (A2) derived from a polyfunctional vinyl monomer, and the structural unit (A1) derived from a monofunctional vinyl monomer can include a structural unit (a1) derived from a monofunctional styrene monomer or a structural unit (a2) derived from a monofunctional (meth)acrylic monomer. In a preferred embodiment, the structural unit (A) contains both a structural unit (A1) derived from a monofunctional vinyl monomer and a structural unit (A2) derived from a polyfunctional vinyl monomer.

[0015] [Structural unit (A1) derived from monofunctional vinyl monomer] <Structural Unit (a1) Derived from Monofunctional Styrenic Monomer> The structural unit (A1) derived from the monofunctional vinyl monomer may include a structural unit (a1) derived from a monofunctional styrene monomer. The structural units derived from the styrene-based monomer can contribute to the formation of uniform, spherical particles.

[0016] The structural unit (a1) is not limited to, but may be, for example, a structural unit represented by the following formula: [ka] In the above formula, R a1 represents an alkyl group having 1 to 10 carbon atoms, -S(O)2OM1, where M1 represents an alkali metal atom, a Group 2 metal atom, an ammonium group, or an organic ammonium group. Furthermore, p represents 0 or an integer of 1 to 5, and a plurality of R a1 may be the same or different.)

[0017] Examples of the monofunctional styrene-based monomer that constitutes the structural unit (a1) include styrene and its derivatives, such as styrene, α-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, and 2,4,6-trimethylstyrene; and styrene sulfonates, such as sodium styrene sulfonate and ammonium styrene sulfonate. Among these, styrene, α-methylstyrene, and sodium styrene sulfonate are preferred.

[0018] <Structural Unit (a2) Derived from Monofunctional (Meth)acrylic Monomer> The structural unit (A1) derived from the monofunctional vinyl monomer may contain a structural unit (a2) derived from a monofunctional (meth)acrylic monomer in addition to the structural unit (a1) derived from the monofunctional styrene monomer. The structural unit derived from the (meth)acrylic monomer, whether monofunctional or polyfunctional, has the property of being easily decomposed (depolymerized) as a monomer unit and having excellent thermal decomposition properties, and can lower the thermal decomposition temperature of the vinyl resin particles of the present invention.

[0019] The structural unit (a2) is not limited to, but may be, for example, a structural unit represented by the following formula: [ka] In the above formula, R a21 , R a22 , R a23 each independently represents a hydrogen atom or a methyl group, R a24 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.

[0020] Examples of the monofunctional (meth)acrylic monomer that constitutes the structural unit (a2) include (meth)acrylic acid 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, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, 3-methylbutyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, and lauryl (meth)acrylate. Among these, from the viewpoint of facilitating the production of resin particles with a uniform particle size, methyl (meth)acrylate and ethyl (meth)acrylate are preferred as the (meth)acrylic acid-based monomer, with methyl (meth)acrylate being particularly preferred.

[0021] [Structural unit (A2) derived from a polyfunctional vinyl monomer] Furthermore, the vinyl resin particles of the present invention may contain, as the structural unit (A), a structural unit (A2) derived from a polyfunctional vinyl monomer in addition to the structural unit (A1) derived from a monofunctional vinyl monomer. By including the structural unit (A2) derived from a polyfunctional vinyl monomer, the solvent resistance of the resulting vinyl resin particles can be improved, a decrease in the viscosity of the varnish composition (polyimide varnish) described below due to swelling of the vinyl resin particles can be suppressed, and vinyl resin particles having high compressive strength and a uniform particle size can be more easily obtained. Examples of the structural unit (A2) include a structural unit (a3) ​​derived from a polyfunctional (meth)acrylic monomer and a structural unit (a4) derived from a polyfunctional (poly)vinyl monomer.

[0022] Among the structural units (A2), examples of the structural unit (a3) ​​derived from a polyfunctional (meth)acrylic monomer include, but are not limited to, those having a partial structure represented by the following formula: [ka] In the above formula, R a21 , R a22 , R a23 each independently represents a hydrogen atom or a methyl group.

[0023] Specific examples of the polyfunctional (meth)acrylic monomer that constitutes the structural unit (a3) ​​include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, ethylene oxide-modified 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, and propylene oxide-modified neopentyl glycol di(meth)acrylate. Di(meth)acrylates of polyhydric alcohols having 1 to 10 carbon atoms, such as chol di(meth)acrylate and tripropylene glycol di(meth)acrylate; alkyl di(meth)acrylates having 2 to 4 carbon atoms and having 2 to 50 molar addition of alkylene oxide groups, such as polyethylene glycol di(meth)acrylate having 2 to 50 molar addition of ethylene oxide, polypropylene glycol di(meth)acrylate having 2 to 50 molar addition of propylene oxide, and tripropylene glycol di(meth)acrylate; ethoxy Tri(meth)acrylates of polyhydric alcohols having 1 to 10 carbon atoms, such as hydroxylated glycerin tri(meth)acrylate, propylene oxide-modified glycerol tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol monohydroxytri(meth)acrylate, and trimethylolpropane triethoxytri(meth)acrylate; pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, and the like. Examples of the polyhydric alcohol having 1 to 10 carbon atoms include, but are not limited to, tetra(meth)acrylates of polyhydric alcohols having 1 to 10 carbon atoms such as pentaerythritol penta(meth)acrylate and dipentaerythritol(monohydroxy)penta(meth)acrylate; penta(meth)acrylates of polyhydric alcohols having 1 to 10 carbon atoms such as pentaerythritol penta(meth)acrylate and dipentaerythritol(monohydroxy)penta(meth)acrylate; and hexa(meth)acrylates of polyhydric alcohols having 1 to 10 carbon atoms such as pentaerythritol hexa(meth)acrylate.

[0024] Specific examples of the polyfunctional (poly)vinyl monomer that constitutes the structural unit (a4) include polyfunctional aliphatic vinyl monomers such as isoprene and butadiene; polyfunctional alicyclic vinyl monomers such as cyclopentadiene and cyclohexadiene; polyfunctional aromatic vinyl monomers such as divinylbenzene, divinyltoluene and divinylnaphthalene; polyfunctional vinyl ester monomers such as divinyl adipate, divinyl maleate, divinyl phthalate and divinyl isophthalate; polyfunctional allyl ester monomers such as diallyl maleate, diallyl phthalate, diallyl isophthalate and diallyl adipate; divinyl ether, diethylene Polyfunctional vinyl ether monomers such as ethylene glycol divinyl ether and triethylene glycol divinyl ether; polyfunctional allyl ether monomers such as diallyl ether, diallyloxyethane and triallyloxyethane; polyfunctional vinyl ketone monomers such as divinyl ketone and diallyl ketone; polyfunctional nitrogen-containing vinyl monomers such as diallylamine, diallyl isocyanurate, diallyl cyanurate, methylene bis(meth)acrylamide and bismaleimide; polyfunctional silicon-containing vinyl monomers such as dimethyldivinylsilane, divinylmethylphenylsilane and diphenyldivinylsilane, but are not limited to these.

[0025] Among these, from the viewpoint of facilitating the production of resin particles with a uniform particle size, preferred polyfunctional vinyl monomers constituting the structural unit (A2) include ethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, divinylbenzene, divinyltoluene, etc. Furthermore, from the viewpoint of excellent polymerization stability and facilitating the production of resin particles with few aggregates, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and 1,3-butylene glycol di(meth)acrylate are mentioned, and among these, ethylene glycol di(meth)acrylate is preferred.

[0026] The structural unit (A2) derived from the polyfunctional vinyl monomer preferably accounts for 1% by mass to 10% by mass relative to the total mass of the structural unit (A).

[0027] <Structural units derived from other polymerizable monomers> The polymer that is the vinyl resin particle of the present invention may contain structural units derived from vinyl monomers (polymerizable monomers) other than the structural units (A1) [(a1), (a2)] and (A2) [(a3), (a4)], as long as the effects of the present invention are not impaired. That is, the vinyl resin particle of the present invention can be a copolymer of a monomer component (mixture) containing other polymerizable monomers.

[0028] For example, examples of other polymerizable monomers other than the monofunctional styrene-based monomers and the monofunctional (meth)acrylic monomers include, but are not limited to, monofunctional (meth)acrylonitrile-based monomers such as (meth)acrylonitrile; monofunctional heterocycle-containing vinyl-based monomers such as N-vinylimidazole and N-vinyl-2-pyrrolidone; monofunctional vinyl ester-based monomers such as vinyl acetate (vinyl acetate), isopropenyl acetate, vinyl propionate, and vinyl decanoate; monofunctional vinyl ether-based monomers such as ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, cyclohexyl vinyl ether, and ethylene glycol vinyl ether; other monofunctional vinyl compound-based monomers such as vinylcyclopentane, vinylcyclohexane, and ethylvinylbenzene; monofunctional (meth)acrylic acid-based monomers such as (meth)acrylic acid and itaconic acid; and monofunctional (meth)acrylamide-based monomers such as (meth)acrylamide and N,N-dimethyl(meth)acrylamide.

[0029] <Reactive emulsifier and structural unit (B) derived from a reactive emulsifier> The reactive emulsifier is not particularly limited as long as it is an emulsifier that is reactive with the above-mentioned monomer or its polymer, but examples thereof include those that have a radically polymerizable double bond, a hydrophilic functional group, and a hydrophobic group in their molecular structure and that have emulsifying, dispersing, and wetting functions similar to general emulsifiers.

[0030] Examples of the molecular structure having a radically polymerizable double bond include a 1-propenyl group, a 2-methyl-1-propenyl group, an allyl group, a methallyl group, a vinyl group, an acryloyl group, and a methacryloyl group.

[0031] Examples of hydrophilic functional groups in the molecular structure include anionic groups (-OSO3) such as sulfate, nitrate, phosphate, borate, and carboxyl groups. - , -NO3 - , -OPO3 - , -B(OH)4 - , -COO - etc.); cationic groups such as amino groups (-NH3 + etc.); polyoxyalkylene chains such as polyoxyethylene, polyoxymethylene, polyoxypropylene, etc.; hydroxy groups, etc.

[0032] Examples of the hydrophobic group in the molecular structure include an alkyl group, an alkenyl group, a phenyl group, an alkylphenyl group, a styrenated phenyl group, and a naphthyl group.

[0033] Reactive emulsifiers are classified into anionic emulsifiers, nonionic emulsifiers, cationic emulsifiers, amphoteric emulsifiers, etc. depending on the type of hydrophilic functional group contained in the molecular structure. The reactive emulsifier may have a molecular structure with a radically polymerizable double bond, a hydrophilic functional group, and a hydrophobic group each having a plurality of types of structure and functional group.

[0034] Among the above, the reactive emulsifier is preferably one having at least a polyoxyalkylene chain and a sulfate group as hydrophilic functional groups inside the molecular structure.

[0035] Trade names of such reactive emulsifiers that are generally available commercially include, but are not limited to, ADEKA REASOAP SR, ER, SE, NE, PP (ADEKA Corporation), AQUALON HS, BC, KH (Dai-ichi Kogyo Seiyaku Co., Ltd.), LATEMURU PD (Kao Corporation), ELEMINOL JS, RS (Sanyo Chemical Industries, Ltd.), and ANTOX MS (Nippon Nyukazai Co., Ltd.).

[0036] [Structural unit (b1) derived from the compound represented by general formula (I)] As described above, the polymer that is the vinyl resin particle of the present invention can have a structural unit (b1) derived from a compound represented by the following general formula (I). The compound represented by the following general formula (I) has a hydrophobic group and a hydrophilic group in the molecule, as well as a copolymerizable unsaturated group. Therefore, the compound represented by the following general formula (I) also functions as a reactive (copolymerizable) emulsifier (corresponding to the reactive emulsifier described above), and is expected to suppress or improve various problems that occur during conventional emulsion polymerization, such as polymerization instability and foaming during emulsion polymerization, and deterioration in the physical properties of the polymer obtained after polymerization. [ka] In the above general formula (I), m represents an integer of 1 to 3, and preferably represents 2 from the viewpoint of emulsifiability.

[0037] AO represents an alkyleneoxy group having 2 to 4 carbon atoms. Examples of the alkyleneoxy group having 2 to 4 carbon atoms include an ethyleneoxy group, a propyleneoxy group, and a butyleneoxy group. Among these, an ethyleneoxy group is preferred as AO. The ethyleneoxy group is more hydrophilic than other alkyleneoxy groups and can form a resin emulsion having a high-density hydration layer, thereby further improving the stability of resin particles in an aqueous dispersion medium. n represents the number of repeating alkyleneoxy units (i.e., the number of moles of alkyleneoxy groups added). n is an integer of 0 to 100, and from the viewpoint of the stability of the resin particles in an aqueous dispersion medium, n is preferably an integer of 5 to 50, and more preferably an integer of 5 to 30.

[0038] X represents a hydrogen atom or an anionic hydrophilic group selected from the group consisting of -SO3M, -COOM, and -PO3M (wherein M represents an alkali metal atom, an alkaline earth metal atom, an ammonium group, or an organic ammonium group). Examples of alkali metal atoms include sodium atoms and potassium atoms, and examples of alkaline earth metal atoms include calcium atoms and barium atoms. In consideration of emulsifiability, X is preferably a hydrogen atom, -SO3NH4, -SO3Na, or -SO3K, and more preferably -SO3NH4.

[0039] R represents a polymerizable unsaturated group, specifically a group represented by the following formula (i) or (ii), in which R1 represents a hydrogen atom or a methyl group. [ka]

[0040] Examples of the structural unit (b1) derived from the compound represented by the above general formula (I) include the following structures. [ka] In the above formula, m, R1, AO, n, and X are as defined above. [ka] In the above formula, m, R1, AO, n, and X are as defined above.

[0041] A preferred example of the compound represented by the general formula (I) is a compound represented by the following formula (I-1). [ka] In the above formula, m, AO, n, and X are as defined above.

[0042] Examples of the structural unit (b1) derived from the compound represented by the above formula (I-1) include the following structures. [ka] In the above formula, m, AO, n, and X are as defined above.

[0043] The compound represented by the general formula (I) can be a commercially available product, such as the Aqualon AR series (AR-10, AR-1025, AR-20, AR-2020) manufactured by Daiichi Kogyo Kagaku Co., Ltd.

[0044] In the vinyl resin particles (polymer) of the present invention, from the viewpoint of copolymerizability during polymerization, when all structural units of the polymer are taken as 100 mass%, for example, the proportion of structural unit (A) can be 98.0 mass% to 99.9 mass%, and the proportion of structural unit (B) (e.g., structural unit (b1)) can be 0.1 mass% to 2.0 mass%. Furthermore, when all structural units of the vinyl resin particles (polymer) are taken as 100% by mass, the proportion of the structural unit (A1) can be 88 to 99% by mass, the proportion of the structural unit (A2) can be 0.9 to 10% by mass, and the proportion of the structural unit (B) can be 0.1 to 2% by mass. The proportion of the structural unit (B) may be interpreted as the proportion of the structural unit (b1), or as the total proportion of the structural unit (b1) and the structural units (B) other than the structural unit (b1).

[0045] In order to obtain resin particles having a uniform particle size and stable to solvents, etc., the proportion of structural units (a1) derived from monofunctional styrene-based monomers in the structural units (A) can be 10% by mass to 99% by mass, the proportion of structural units (a2) derived from monofunctional (meth)acrylic monomers can be 0% by mass to 80% by mass, the proportion of structural units (A2) derived from polyfunctional vinyl-based monomers can be 1% by mass to 10% by mass, and the proportion of structural units derived from other polymerizable monomers can be 0% by mass to 5% by mass (total of the above: 100% by mass).

[0046] [Method of manufacturing vinyl resin particles] The vinyl resin particles of the present invention can be obtained by emulsion polymerization of a monomer component containing the vinyl monomer and a reactive emulsifier (e.g., a compound represented by general formula (I)). Emulsion polymerization is preferred because it is easy to obtain particles with a small particle size. Examples of the vinyl monomer include the various monomers mentioned above [monofunctional vinyl monomers (monofunctional styrene monomers, monofunctional (meth)acrylic monomers), polyfunctional vinyl monomers (polyfunctional (meth)acrylic monomers, polyfunctional (poly)vinyl monomers), and other polymerizable monomers], and examples of the reactive emulsifier include the compounds mentioned above. A preferred embodiment of emulsion polymerization includes an emulsion polymerization step of subjecting a polymerization mixture containing the monomer components, a polymerization initiator, and, if desired, other additives (such as a surfactant, a protective colloid, a chain transfer agent, or a pH adjuster) to emulsion polymerization, and may optionally include an aging step of aging the reaction liquid obtained in the emulsion polymerization step.

[0047] The emulsion polymerization is usually carried out in an aqueous dispersion medium, which is not particularly limited and may be, for example, water or a mixture of water and an alcohol solvent. From the viewpoint of the stability (non-aggregation) of the vinyl resin particles formed after emulsion polymerization, water is preferred as the aqueous dispersion medium. The amount of the aqueous dispersion medium used can be appropriately set so that the content of the vinyl resin particles present in the system after emulsion polymerization is a desired ratio. For example, the content of the vinyl resin particles present in the system may be set to 1% by mass to 70% by mass, 10% by mass to 60% by mass, or 20% by mass to 50% by mass, and the amount of the aqueous dispersion medium used may be appropriately set.

[0048] The polymerization initiator used in the emulsion polymerization is not particularly limited, and known polymerization initiators can be used. Examples include azo compounds such as azobisisobutyronitrile, 2,2-azobis(2-methylbutyronitrile), 2,2-azobis(2,4-dimethylvaleronitrile), 2,2-azobis(2-diaminopropane) hydrochloride, 4,4-azobis(4-cyanovaleric acid), 2,2-azobis(2-methylpropionamidine), and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate; persulfates such as potassium persulfate and ammonium persulfate; and peroxides such as hydrogen peroxide, benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide, and ammonium peroxide, but are not limited to these examples. Among these, azo compounds and peroxides can also function as decomposition accelerators, that is, when vinyl resin particles are used as a porous material, they can have the function of accelerating thermal decomposition, and therefore can be preferably used. The amount of the polymerization initiator used is not particularly limited, but from the viewpoint of increasing the polymerization rate and reducing the amount of unreacted monomer remaining, it is, for example, 0.05 parts by mass or more, preferably 0.1 parts by mass or more, per 100 parts by mass of the monomer component, and from the viewpoint of polymerization stability, it can be, for example, 5 parts by mass or less.

[0049] In the present invention, the reactive emulsifier and the compound represented by the general formula (I) also function as emulsifiers, and can satisfactorily initiate and complete emulsion polymerization. However, a surfactant (emulsifier) ​​generally used in emulsion polymerization may also be used as an additive within a range that does not impair the effects of the present invention. As the surfactant, an anionic surfactant or a cationic surfactant and / or other nonionic surfactant may be used in combination. For example, anionic surfactants (anionic emulsifiers) include fatty acid soaps; rosin acid soaps; alkyl sulfates such as ammonium dodecyl sulfate and sodium dodecyl sulfate; alkyl sulfonates such as ammonium dodecyl sulfonate and sodium dodecyl sulfonate; alkylaryl sulfonates such as ammonium dodecyl benzene sulfonate, sodium dodecyl benzene sulfonate, and sodium dodecyl naphthalene sulfonate; polyoxyalkylene alkyl sulfates; polyoxyalkylene aryl sulfates; polyoxyalkylene alkylaryl sulfates; dialkyl sulfosuccinates; arylsulfonic acid-formalin condensates; and fatty acid salts such as ammonium laurate and sodium stearylate. Examples of cationic surfactants include stearyltrimethylammonium, cetyltrimethylammonium, and lauryltrimethylammonium. Examples of nonionic surfactants include polyoxyalkylene alkylphenyl ethers, polyoxyalkylene alkyl ethers, alkyl polyglucosides, polyglycerin alkyl ethers, polyoxyalkylene fatty acid esters, polyglycerin fatty acid esters, and total alkyl simple fatty acid esters. When a surfactant is used separately in the emulsion polymerization step, the amount used can be, for example, 0.05 parts by mass or more, 0.1 parts by mass or more, or 0.3 parts by mass or more relative to 100 parts by mass of the monomer component, and the upper limit can be, for example, 10 parts by mass, 8 parts by mass or less, or 5 parts by mass or less.

[0050] For the purpose of improving polymerization stability during emulsion polymerization, known protective colloids may be used in combination as other additives, such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, polyacrylic acid, and gum arabic.

[0051] Other additives such as known chain transfer agents and pH adjusters may also be used in combination. Examples of the chain transfer agent include octyl mercaptan, dodecyl mercaptan, mercaptoethanol, thioglycolic acid, allyl alcohol, isopropyl alcohol, and sodium hypophosphite. Examples of the pH adjuster include inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; organic acids such as citric acid, succinic acid, malic acid, and lactic acid; inorganic bases such as sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate; and organic bases such as alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, and isopropanol; aliphatic amines such as ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine, and triethylenetetramine; aromatic polyamines such as phenylenediamine and tolylenediamine; and heterocyclic polyamines such as piperazine and aminoethylpiperazine.

[0052] The amount (feed ratio) of each monomer in the monomer components subjected to emulsion polymerization can be appropriately set. For example, the ratio of the vinyl monomer can be 98.0% to 99.9% by mass, and the ratio of the reactive emulsifier (e.g., the compound represented by general formula (I)) can be 0.1% to 2.0% by mass, relative to the total amount of all monomers (total 100% by mass). Furthermore, for example, the proportion of monofunctional vinyl monomers can be 88% by mass to 99% by mass, the proportion of polyfunctional vinyl monomers can be 0.9% by mass to 10% by mass, and the proportion of the reactive emulsifier can be 0.1% by mass to 2% by mass, relative to the total amount of all monomers (total 100% by mass). Furthermore, in the vinyl-based monomers (total 100% by mass), the monofunctional styrene-based monomer can be 10% by mass to 99% by mass, the monofunctional (meth)acrylic monomer can be 0% by mass to 80% by mass, the polyfunctional vinyl-based monomer can be 1% by mass to 10% by mass, and the other polymerizable monomers can be 0% by mass to 5% by mass.

[0053] The emulsion polymerization may be carried out by a known emulsion polymerization method, such as a monomer dropping method, a pre-emulsion method, a batch polymerization method, etc. From the viewpoint of industrial productivity, it is preferable to adopt the pre-emulsion method, since it allows stable polymerization and produces a polymer (resin particles) with few aggregates.

[0054] In the emulsion polymerization, the method of adding the above-mentioned monomer components, polymerization initiator, and other additives is not particularly limited and may be appropriately determined. For example, in the case of emulsion polymerization by the pre-emulsion method, a vinyl monomer is first emulsified in a reactive emulsifier (e.g., a compound represented by general formula (I)) and an aqueous dispersion medium such as water to obtain a pre-emulsion, and the obtained pre-emulsion is then dropped into a reaction vessel, and a polymerization initiator is added as appropriate to allow the emulsion polymerization reaction to proceed. Alternatively, emulsion polymerization may be initiated using a portion of the polymerization mixture, and then the remaining polymerization mixture is added dropwise. Alternatively, emulsion polymerization may be initiated in advance using a mixture containing a portion of the total amount of the monomer components and a portion of the polymerization initiator (and other additives), and then the remaining monomer components and polymerization initiator (and other additives) are added dropwise, either separately or in combination.

[0055] Furthermore, the emulsion polymerization step may be repeated two or more times, i.e., for example, in an embodiment including a first emulsion polymerization step and a second emulsion polymerization step, where a core portion is formed in the first emulsion polymerization step and a shell portion is formed on the surface of the core portion in the subsequent second emulsion polymerization step, thereby forming core-shell type resin particles. In this case, the second emulsion polymerization step may be performed multiple times, and when the second emulsion polymerization step is performed a second time, resin particles are obtained in which a new shell portion is formed on the surface of the shell portion formed in the first second emulsion polymerization step. When the process includes a first emulsion polymerization step and a second emulsion polymerization step, the composition of the monomer components used in each step can be different, or the monomer components used in each step can be a single monomer. That is, different monomers (one type) can be used in the first emulsion polymerization step and the second emulsion polymerization step, or a mixture of monomers and one monomer can be used, or a mixture of different monomers can be used in each step. When a mixture of the same type of monomers is used, a mixture with different monomer mixing ratios can be used. For example, the first emulsion polymerization step can use a mixture containing a monofunctional styrene-based monomer among monofunctional vinyl monomers, a polyfunctional vinyl monomer, and a reactive emulsifier (e.g., a compound represented by general formula (I)), and the subsequent second emulsion polymerization step can use a mixture containing a monofunctional styrene-based monomer among monofunctional vinyl monomers, a monofunctional (meth)acrylic monomer, a polyfunctional vinyl monomer, and a reactive emulsifier (e.g., a compound represented by general formula (I)).

[0056] The polymerization temperature in the emulsion polymerization may be appropriately set depending on the polymerization initiator used, etc., and may be, for example, 30° C. to 90° C., or 50° C. to 80° C. The polymerization time may be appropriately set depending on the reaction rate determined from the charged amount of the monomer component and the remaining amount in the reaction liquid, and is usually 1 hour to 12 hours, for example, about 2 hours to 8 hours.

[0057] Next, the aging step is carried out after the emulsion polymerization step for the purpose of reducing unreacted monomers or stabilizing the dispersion containing polymer particles (vinyl resin particles) obtained by emulsion polymerization. The aging temperature in the aging step can be, for example, 50°C to 90°C, or can be, for example, 70°C to 85°C. By setting the aging temperature within the above range, it is expected that the amount of unreacted monomer mixture can be reduced while suppressing particle aggregation. The aging time can be appropriately set depending on the reaction rate calculated from the total amount of charged monomer components and the remaining amount of monomer components in the reaction solution, and is usually 1 hour to 12 hours, preferably 2 hours to 8 hours.

[0058] In the aging step, a surfactant may be added as needed for the purpose of, for example, making it easier to suppress aggregation of polymer particles during aging. As the surfactant used in the aging step, it is preferable to use the surfactants listed in the emulsion polymerization step, and anionic surfactants or nonionic surfactants can also be used. The amount of surfactant used in the aging step can be, for example, 0.05 parts by mass or more, 0.1 parts by mass or more, or 0.3 parts by mass or more, relative to 100 parts by mass of the total amount of the monomer components subjected to the emulsion polymerization step, and can be, for example, 10 parts by mass or less, 8 parts by mass or less, or 5 parts by mass.

[0059] After the emulsion polymerization step (and optionally the aging step), the vinyl resin particles of the present invention can be obtained in the form of a dispersion (also referred to as a dispersion liquid) containing the formed polymer in an aqueous dispersion medium. The content of vinyl resin particles (polymer) in the aqueous dispersion medium is not particularly limited, but can be, for example, 10 to 80% by mass, 20 to 70% by mass, or 30 to 60% by mass.

[0060] The present invention also relates to a method for producing an aqueous dispersion of vinyl resin particles, which includes a step of emulsion-polymerizing vinyl monomers, including monofunctional vinyl monomers and polyfunctional vinyl monomers, and a reactive emulsifier, such as a compound represented by the general formula (I) that is different from the vinyl monomers, in an aqueous dispersion medium in the presence of a polymerization initiator.

[0061] [Vinyl resin particle size] The vinyl resin particles of the present invention have a median diameter D 50 It is preferable that the particles are 0.05 μm to 2.0 μm in size. The median diameter in the present invention can be a value of 50% volume diameter based on volume measured by dynamic light scattering. Generally, as the particle size decreases, particle aggregation tends to occur, particularly during polymerization, but the vinyl resin particles of the present invention exhibit an excellent aggregation-inhibiting effect in their dispersion, so the particle size of the vinyl resin particles can be set to a relatively small range. By setting the median size within the above range, when the vinyl resin particles are used as a porous material for a thermosetting resin, fine pores can be formed in the resin. However, if the median diameter is less than 0.2 μm, the particle size may be too small to contribute to the formation of sufficient pores, and if it exceeds 1.5 μm, there is a risk of reducing the mechanical strength of the thermosetting resin to be pore-formed.

[0062] [Thermal decomposition temperature of vinyl resin particles] The vinyl resin particles of the present invention preferably have a thermal decomposition temperature under atmospheric pressure that is lower than the thermal decomposition temperature of the thermosetting resin described below. In this specification, the thermal decomposition temperature means the temperature at which weight loss due to thermal decomposition of a sample begins when measured using a thermogravimetry analyzer (TGA) under conditions conforming to JIS K7120 (thermogravimetric measurement method for plastics). Although it depends on the type of thermosetting resin to be used, the thermal decomposition temperature of the vinyl resin particles of the present invention in a nitrogen atmosphere is, for example, 340 to 440°C, and preferably 370 to 410°C.

[0063] [Vinyl resin particles and their dispersions] The vinyl resin particles are obtained in the form of a dispersion (dispersion liquid) dispersed in an aqueous dispersion medium through the above-mentioned emulsion polymerization process, and can be used as a dispersion in various solvents depending on the application of the resin particles. For example, the aqueous dispersion medium in the dispersion dispersed in the above-mentioned aqueous dispersion medium can be replaced with a solvent, and the resin particles can be used in the form of a dispersion dispersed in an organic solvent (organic solvent dispersion). Alternatively, the aqueous dispersion medium or the organic solvent may be removed from the dispersion to obtain vinyl resin particles (powder), which can be used. Methods for removing the aqueous dispersion medium or the organic solvent include freeze drying, hot air drying, spray drying, and the like. Furthermore, the resulting resin particles (powder) can be dispersed again in an aqueous dispersion medium or an organic solvent and used as an aqueous solvent dispersion or an organic solvent dispersion.

[0064] Examples of the organic solvent include lower alcohols such as methanol, ethanol, and isopropanol; linear amides such as N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc); cyclic amides such as N-methyl-2-pyrrolidone (NMP); ethers such as γ-butyrolactone (GBL); glycols such as ethyl cellosolve and ethylene glycol, and acetonitrile. This substitution can be carried out by a conventional method such as distillation or ultrafiltration. The content of the vinyl resin particles in the organic solvent dispersion can be appropriately set depending on the application, and can be, for example, 1% to 70% by mass, 10% to 60% by mass, or 20% to 50% by mass relative to the total mass of the organic solvent dispersion. If the proportion of the resin particles in the organic solvent dispersion is less than 1% by mass, it is not economical, and if it is more than 70% by mass, the dispersion will not be stable and aggregation or sedimentation of the resin particles may occur, and handling may be impaired when mixed with a thermosetting resin described below. The viscosity of the organic solvent dispersion can be set to about 0.6 mPa·s to 100 mPa·s at 20°C, for example. The dispersion may further comprise other compounds such as surfactants.

[0065] [Thermosetting resin] The vinyl resin particles of the present invention are suitable for use in making thermosetting resins porous. That is, the present invention can provide a porosity-inducing material made from the vinyl resin particles. Examples of thermosetting resins include polyimide resins and diallyl phthalate resins. Among these, polyimide resins are a suitable example of the thermosetting resins that can be made porous by the vinyl resin particles of the present invention. By using the vinyl resin particles of the present invention as a porosity-inducing material for polyimide resins, uniform pores can be formed in the polyimide resin film.

[0066] [Method for making thermosetting resin porous (method for manufacturing porous body)] There are no particular limitations on the method for making a thermosetting resin porous (method for producing a porous body) using the vinyl resin particles of the present invention. For example, when a polyimide resin is used as the thermosetting resin, a varnish composition containing a polyamic acid (a polyimide precursor), the vinyl resin particles of the present invention, and a solvent is first applied to a substrate to form a coating film (coating film formation step), and the coating film is then dried, i.e., the solvent is removed from the coating film, to form a coating film (precursor film for a polyimide porous film) containing the polyimide precursor and the vinyl resin particles (precursor film for a polyimide porous film). Subsequently, the coating film (precursor film for a polyimide porous film) is baked to convert the polyimide precursor to polyimide and remove (thermally decompose) the vinyl resin particles (removal step for removing the vinyl resin particles), thereby obtaining a porous polyimide film. The removal step (baking step) for removing the vinyl resin particles can be carried out at a temperature that converts the polyimide precursor to polyimide and decomposes and eliminates the vinyl resin particles. Before removing the vinyl resin particles, the coating (precursor film of the polyimide porous film) may be peeled off from the substrate (peeling step), and this unbaked film may be baked (removal step for removing the vinyl resin particles). Specific examples of methods for making thermosetting resin porous will be described below, but the method is not limited to the following methods.

[0067] <Coating film formation process> This step is a step of forming a coating film by applying a varnish composition containing a polyamic acid, which is a polyimide precursor, the vinyl resin particles of the present invention, and a solvent onto a substrate. Examples of the substrate include a PET film, a SUS substrate, and a glass substrate.

[0068] <<Varnish Composition>> As the polyamic acid, any product obtained by polymerizing any tetracarboxylic dianhydride and diamine can be used without any particular limitation. The tetracarboxylic dianhydride and diamine can be appropriately selected from compounds conventionally used as raw materials for synthesizing polyamic acids. The tetracarboxylic dianhydride may be an aromatic tetracarboxylic dianhydride or an aliphatic tetracarboxylic dianhydride, and the diamine may be an aromatic diamine or an aliphatic diamine. The method for producing the polyamic acid is not particularly limited, and a known method such as reacting a tetracarboxylic dianhydride component with a diamine component in a solvent can be used. In this case, the amounts of tetracarboxylic dianhydride and diamine used (charged amounts) are not particularly limited, but the ratio of diamine to 1 mole of tetracarboxylic dianhydride can be, for example, 0.50 moles to 1.50 moles. When the synthesis of the polyamic acid is carried out in a solvent described below, the reaction solution of the polyamic acid can be used as it is as a polyamic acid-containing liquid for preparing the varnish composition.

[0069] The solvent used in the varnish composition may be water, an organic solvent, or a combination thereof. The organic solvent used in the varnish composition is preferably a compound that is neutral or weakly basic in water, from the viewpoint of avoiding hydrolysis of the polyamic acid. Suitable examples of the organic solvent include the various organic solvents mentioned above in connection with the organic solvent dispersion of resin particles.

[0070] A dispersant may be added to the varnish composition to uniformly disperse the vinyl resin particles. When a dispersant is used, it can be used in an amount of, for example, 0.01% by mass to 5% by mass based on the fine particles.

[0071] The varnish composition can be produced by mixing the various components described above in predetermined amounts, and the specific procedure is not particularly limited. The varnish composition can contain vinyl resin particles and polyamic acid so that when it is made into a polyamic acid-particle composite film (precursor film) described below, the ratio of vinyl resin particles to polyamic acid is, for example, 0.5 to 4.0 (mass ratio). Alternatively, when it is made into the composite film, it can contain these components so that the volume ratio of vinyl resin particles to polyamic acid is, for example, 1.0 to 5.0. The solids concentration of the varnish composition is not particularly limited, but may be, for example, 1% by mass or more, 5% by mass or more, or 10% by mass or more, with the upper limit being, for example, 60% by mass or less, for example, 30% by mass or less. Note that the solids concentration here means the concentration of components other than the solvent, and even liquid components are included in the weight as solids. The viscosity of the varnish composition is not particularly limited as long as it can form a coating film of the desired thickness. For example, the viscosity of the varnish composition can be set to 300 cP or more and 20,000 cP or less.

[0072] <Precursor film formation process> This step is a step of removing the solvent from the coating film obtained in the previous step to form a precursor film of the polyimide porous film. To remove the solvent from the coating film, the varnish composition described above is applied to a substrate to form a coating film, and then the coating film is dried at a temperature of 0°C or higher and 100°C or lower under normal pressure or in vacuum, preferably at a temperature of 10°C or higher and 100°C or lower under normal pressure.

[0073] The precursor film may be formed directly on the substrate, or may be formed on an underlayer film different from the precursor film formed on the substrate. Furthermore, after forming a precursor film using the varnish composition, an upper layer film different from the precursor film may be formed on top of the precursor film. In this specification, both the mode in which an underlayer film is provided on the substrate and the mode in which an upper layer film is provided on the precursor film are included in the precursor film forming step.

[0074] Peeling process After the precursor film forming step, a peeling step of peeling the precursor film from the substrate may be included before the vinyl resin particle removing step described below. When this step is included, the substrate is not required to have heat resistance capable of withstanding the temperature at which the precursor film is baked.

[0075] <Step of Removing Vinyl Resin Particles (Baking Step)> This step involves thermally decomposing and removing the vinyl resin particles of the present invention simultaneously with imidizing the precursor film of the polyimide porous film by baking or the like, or during or after the imidization. This step allows for the formation of uniform, fine pores in the polyimide resin film to obtain a polyimide porous film. In this step, the vinyl resin particles may be removed while the polyamic acid is being imidized, or after the polyamic acid is being imidized.

[0076] The method for imidizing the polyamic acid is not particularly limited. The imidization may be either thermal imidization or chemical imidization. For chemical imidization, a method such as immersing a precursor film containing the polyamic acid in acetic anhydride or a mixed solvent of acetic anhydride and isoquinoline can be used. Among the above imidization methods, baking, which is thermal imidization, is preferred because it does not require removal of the imidizing agent by washing, etc. Baking related to thermal imidization will be described below.

[0077] The baking temperature varies depending on the structure of the polyamic acid, but is preferably 120°C or higher and 500°C or lower, more preferably 150°C or higher and 450°C or lower, and even more preferably 300°C or higher and 450°C or lower. The baking conditions may include, for example, a method in which the temperature is raised from room temperature to about 400°C to 450°C over about 3 hours, and then maintained at that temperature for about 2 to 30 minutes, or a dry-thermal imidization method including a continuous or stepwise temperature-raising operation in which the temperature is raised from room temperature to 400°C to 450°C in increments of, for example, 50°C (each step is maintained for about 20 minutes), and finally maintained at 400°C to 450°C for about 2 to 30 minutes. When a precursor film is formed on a substrate, and the precursor film or a laminated film including the precursor film is peeled off from the substrate and then subjected to a firing process, a method can be adopted in which the ends of the precursor film or the laminated film are fixed to a SUS mold or the like to prevent deformation due to firing.

[0078] The thickness of the polyimide porous film obtained after baking can be determined by measuring the thickness at multiple locations using, for example, a micrometer and averaging the measured thickness. The preferred average thickness varies depending on the application of the polyimide porous film. For example, when used as a separator, the thickness is preferably 5 μm to 500 μm, more preferably 10 μm to 100 μm, and even more preferably 15 μm to 30 μm. When used as a filter, the thickness is preferably 5 μm to 500 μm, more preferably 10 μm to 300 μm, and even more preferably 20 μm to 150 μm.

[0079] The polyimide porous film thus obtained is an opaque film or a porous film colored yellow or brown. Regardless of the film thickness, the polyimide porous film is a porous film in which interconnected spherical pores are distributed throughout the film, and the front and back surfaces are interconnected. [Example]

[0080] The present invention will be described below with reference to examples. However, the present invention is not limited to these examples and comparative examples. The vinyl resin particles were tested using the following methods.

[0081] <Median diameter> For a dispersion in which resin particles are dispersed in water (aqueous resin particle dispersion), a volume-based particle size distribution was obtained using a dynamic light scattering (DLS) particle size distribution analyzer Nanotrac (registered trademark) Wave II (trade name, manufactured by Microtrac-Bell Co., Ltd.), and the median diameter (D50) in the particle size distribution was calculated.

[0082] <Mixed stability test> The resin particle aqueous dispersion was dried in a hot air convection dryer at 105°C, and 1 g of the resulting resin particle powder and 5 g of N,N-dimethylacetamide were weighed into a sample bottle and dispersed in an ultrasonic cleaner for 30 minutes. The state of the resulting resin particle dispersion (organic solvent dispersion) was visually inspected, and the mixing stability of the resin particles with the organic solvent was evaluated according to the following criteria. [Evaluation criteria] ○: No gelation and fluidity is maintained (good) △: Not gelled, but has lost fluidity (normal) ×: Gelling or resin particles dissolved (poor)

[0083] <Solvent resistance test> The resin particle dispersion (organic solvent dispersion) prepared in the above <Mixing Stability Test> was dried by air blowing at room temperature. The dried product was observed under an electron microscope to check the particle shape and whether or not the particles were fused together (dissolved), and the solvent resistance of the resin particles was evaluated according to the following evaluation criteria. [Evaluation criteria] ○: The particles maintain their spherical shape and are not fused together (good). △: Either the particle shape has changed or the particles have fused together (normal). ×: Both particle shape change and fusion between particles occurred (poor).

[0084] <Thermal decomposition temperature> The resin particle aqueous dispersion was dried in a hot air convection dryer at 105°C, and 10 mg of the resulting resin particle powder was heated from 25°C to 600°C using a differential thermobalance ThermoplusEVO2 (registered trademark) TG8121 (trade name, manufactured by Rigaku Corporation) under JIS-compliant conditions, using alumina as a reference, a nitrogen flow rate of 100 ml / min, and a heating rate of 10°C / min. The thermal decomposition onset temperature was read from the obtained TG curve and was defined as the thermal decomposition temperature of the vinyl resin particles.

[0085] [Preparation of vinyl resin particles] Example 1 383.0 g of ion-exchanged water was placed in a 1.0 L glass vessel equipped with a stirrer, thermometer, temperature controller, condenser, and dropping device, and nitrogen gas was introduced while stirring to replace the atmosphere. The vessel was then heated with a mantle heater and the temperature was controlled at 72±2°C to form a polymerization vessel. A 1.0 L glass vessel equipped with a stirrer was charged with 122.4 g of ion-exchanged water, 12.8 g of polyoxyethylene styrenated propenyl phenyl ether sulfate ester ammonium salt (Aqualon AR-1025 (25% aqueous solution) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as a compound represented by general formula (I) (reactive emulsifier), 378.6 g of styrene (styrene monomer manufactured by Asahi Kasei Corporation) as a monofunctional monomer, and 22.2 g of ethylene glycol dimethacrylate (Acryester ED manufactured by Mitsubishi Chemical Corporation) as a polyfunctional monomer, and the mixture was stirred to obtain a monomer emulsion in which styrene and ethylene glycol dimethacrylate were emulsified in ion-exchanged water. In a 0.1 L glass vessel equipped with a stirrer, 48.6 g of ion-exchanged water and 3.1 g of 2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate (VA-057, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were placed and dissolved with stirring to obtain an aqueous polymerization initiator solution. 26.8 g of the prepared monomer emulsion and 5.0 g of the prepared aqueous polymerization initiator solution were placed in the polymerization vessel, and initial polymerization was carried out for 120 minutes. After carrying out the initial polymerization for 120 minutes, the remaining monomer emulsion and the polymerization initiator aqueous solution were each pumped into the polymerization vessel over 240 minutes using a pump to carry out dropwise polymerization. After the dropwise addition was completed, the liquid supply lines were washed with 9.0 g of ion-exchanged water. After the polymerization reaction was continued for 120 minutes, the mixture was cooled to 40° C. to obtain an aqueous dispersion of a crosslinked polymer (aqueous dispersion of resin particles) with a solid content of 40%.

[0086] Example 2 Polymerization was carried out in the same manner as in Example 1, except that 374.2 g of styrene and 4.4 g of methyl methacrylate were used instead of 378.6 g of styrene, and trimethylolpropane trimethacrylate was used instead of ethylene glycol dimethacrylate, to obtain an aqueous dispersion of a crosslinked polymer (aqueous dispersion of resin particles) with a solid content of 40%.

[0087] Example 3 Polymerization was carried out in the same manner as in Example 1, except that 388.8 g of styrene was used instead of 378.6 g of styrene in Example 1, and 12.0 g of a divinylbenzene mixture (DVB570 manufactured by Nippon Steel Chemical & Material Co., Ltd., containing 57% divinylbenzene and 43% ethylvinylbenzene) (divinylbenzene: 6.84 g, ethylvinylbenzene: 5.16 g) was used instead of 22.2 g of ethylene glycol dimethacrylate, to obtain a crosslinked polymer aqueous dispersion (resin particle aqueous dispersion) with a solid content of 40%.

[0088] Example 4 Polymerization was carried out in the same manner as in Example 1, except that 364.7 g of styrene and 4.0 g of methyl methacrylate were used instead of 378.6 g of styrene, and 32.1 g of 1,3-butylene glycol dimethacrylate was used instead of 22.2 g of ethylene glycol dimethacrylate, to obtain an aqueous dispersion of a crosslinked polymer (aqueous dispersion of resin particles) with a solid content of 40%.

[0089] Comparative Example 1 A 1.0 L glass vessel equipped with a stirrer, thermometer, temperature controller, condenser, and dropping device was charged with 343.3 g of ion-exchanged water, and nitrogen gas was introduced while stirring to replace the atmosphere. After the nitrogen replacement, 0.6 g of a 40% aqueous solution of triethanolamine lauryl sulfate (Alscope LS-40T, manufactured by Toho Chemical Industry Co., Ltd.) was added as an emulsifier, heated with a mantle heater, and the temperature was controlled at 72±2°C to prepare a polymerization vessel. A 1.0 L glass vessel equipped with a stirrer was charged with 169.7 g of ion-exchanged water, 3.5 g of a 40% aqueous solution of triethanolamine lauryl sulfate as an emulsifier, 364.9 g of styrene as monofunctional monomers, and 11.1 g of 2-hydroxyethyl methacrylate (Acryester HO, manufactured by Mitsubishi Chemical Corporation), and the contents were stirred to obtain a monomer emulsion in which styrene and 2-hydroxyethyl methacrylate were emulsified in ion-exchanged water. In a 0.1 L glass vessel equipped with a stirrer, 49.1 g of ion-exchanged water and 3.2 g of 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate as a polymerization initiator were placed and dissolved by stirring to obtain an aqueous polymerization initiator solution. 28.4 g of the prepared monomer emulsion and 4.5 g of the prepared aqueous polymerization initiator solution were placed in the polymerization vessel, and initial polymerization was carried out for 120 minutes. After carrying out the initial polymerization for 120 minutes, the remaining monomer emulsion and the remaining aqueous polymerization initiator solution were each transferred to the polymerization vessel over 300 minutes using a liquid transfer pump, and dropwise polymerization was carried out. After the polymerization reaction was continued for 120 minutes, the mixture was cooled to 40° C. to obtain a non-crosslinked polymer aqueous dispersion (aqueous resin particle dispersion) with a solid content of 40%.

[0090] Comparative Example 2 Polymerization was carried out in the same manner as in Example 1, except that 8.0 g of triethanolamine lauryl sulfate (40% aqueous solution) was used instead of 12.8 g of polyoxyethylene styrenated propenyl phenyl ether sulfate ester ammonium salt (25% aqueous solution) in Example 1, and the amounts of styrene and ethylene glycol dimethacrylate were changed to 392.8 g and 8.0 g, respectively, to obtain a crosslinked polymer aqueous dispersion (resin particle aqueous dispersion) with a solid content of 40%.

[0091] For each of the resin particle aqueous dispersions obtained in Examples 1 to 4 and Comparative Examples 1 and 2, the median diameter of the resin particles, the mixing stability of the resin particles with an organic solvent, the solvent resistance of the resin particles, and the thermal decomposition temperature of the resin particles were measured and evaluated according to the procedures of the test methods described above. The results are shown in Table 1. Electron microscope photographs obtained in the solvent resistance test are shown in Figure 1 ((a): Example 1, (b): Example 2, (c): Example 3, (d): Example 4) and Figure 2 ((a): Comparative Example 1, (b): Comparative Example 2).

[0092] [Table 1]

[0093] [Test example] Manufacturing of porous membrane The crosslinked polymer aqueous dispersions (resin particle aqueous dispersions) obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were used to prepare porous membranes.

[0094] <Example 5: Production of polyimide porous film (1)> <Preparation of Varnish Composition> The crosslinked polymer aqueous dispersion (resin particle dispersion) of Example 1 was spray-dried using a spray dryer ADL-311S-A (manufactured by Yamato Scientific Co., Ltd.) to obtain powdery vinyl resin particles. 10.7 parts by mass of the obtained powder vinyl resin particles and 43.0 parts by mass of N,N-dimethylacetamide (DMAc) were stirred and mixed to prepare a DMAc dispersion, to which 46.3 parts by mass of polyamic acid (20% by mass solution of polyamic acid prepared from PMDA: pyromellitic dianhydride and ODA: 4,4-diaminodiphenyl ether in N,N-dimethylacetamide) was added, and the mixture was dispersed using a three-roll mill to obtain a varnish composition with a uniform composition.

[0095] <Production of Porous Polyimide Film> The varnish composition was applied to a polyethylene terephthalate film and then dried at 90°C for 5 minutes to obtain a precursor film of a polyimide porous film. The precursor film obtained was peeled off from the polyethylene terephthalate film and then baked in a baking oven at 420°C for 5 minutes to thermally decompose the vinyl resin particles and imidize the polyamic acid, thereby obtaining the polyimide porous film of Example 5.

[0096] <Examples 6 to 8 and Comparative Examples 3 and 4: Production of Porous Polyimide Film (2)> Powdered vinyl resin particles were prepared in the same manner as in Example 5, except that the crosslinked polymer aqueous dispersions of Examples 2 to 4 or Comparative Examples 1 and 2 shown in Table 2 were used instead of the aqueous dispersion of Example 1 as the crosslinked polymer aqueous dispersion (resin particle aqueous dispersion). Vinyl resin particles were then prepared in powder form, and varnish compositions were prepared from the powder particles. Polyimide porous films of Examples 6 to 8 or Comparative Examples 3 and 4 were then obtained from the varnish compositions.

[0097] <Evaluation of porous membranes> The following evaluations were carried out on the polyimide porous films of Examples 5 to 8 and Comparative Examples 3 and 4. The obtained results are shown in Table 2. [Stress and elongation at break] Each porous membrane was cut into a strip of 3 cm x 3 mm to obtain a sample. The stress at break (MPa; tensile strength) and elongation at break (% GL) of this sample were evaluated using EZ Test (manufactured by Shimadzu Corporation). [Air permeability] Each porous membrane was cut into a 5 cm × 5 cm sample for measuring air permeability. The time required for 100 ml of air to pass through the sample was measured using a Gurley densometer (manufactured by Toyo Seiki Seisakusho, Ltd.) in accordance with JIS P 8117. The air permeability can be, for example, within 250 seconds or within 200 seconds. Since a lower value is preferable, no lower limit is specifically set, but considering the ease of handling of the porous membrane sample, it can be set to, for example, 30 seconds or more. If the Gurley air permeability is within 250 seconds, the porous membrane exhibits sufficiently high ion permeability and can be judged to be applicable as a separator for a lithium-ion battery.

[0098] [Table 2]

[0099] <SEM image observation of porous membrane> The surfaces (film side and air side of the substrate) of the porous polyimide films of Examples 5 to 8 and Comparative Example 3 were observed with a scanning electron microscope (SEM). The obtained SEM images of the air surface side are shown in FIG. 3 ((a) Example 5, (b) Example 6, (c) Example 7, (d) Example 8) and FIG. 4 (Comparative Example 3), respectively. As shown in Figure 3, it was confirmed that spherical pores of uniform size were formed with a roughly uniform distribution in the polyimide porous membrane of the example. The diameter of the pores was measured using a length measurement tool of an SEM, and it was confirmed that pores of a size equivalent to the median diameter of the resin particles in the resin particle dispersion used to produce the porous membrane were formed. On the other hand, as shown in Fig. 4, it was confirmed that spherical pores of non-uniform size were formed in a non-uniform distribution in the polyimide porous membrane of Comparative Example 3. Furthermore, as a result of measuring the diameter of the pores using a length measuring tool of an SEM, it was confirmed that pores having a diameter larger than the median diameter of the resin particles in the resin particle dispersion of Comparative Example 1 used to produce the porous membrane were scattered.

[0100] As shown in Table 2 and FIGS. 3 and 4, the vinyl resin particles according to the present invention have high air permeability and can be used to produce a polyimide porous film having uniform spherical pores with a diameter equivalent to the median diameter of the particles, and are useful as a porosity-making material for thermosetting resins.

Claims

1. a structural unit (A1) derived from a monofunctional vinyl monomer; A structural unit (A2) derived from a polyfunctional vinyl monomer; A polymer having a structural unit (B) derived from a reactive emulsifier, Vinyl resin particles, the proportion of the structural unit (A1) is 88 to 99 mass%, the proportion of the structural unit (A2) is 0.9 to 10 mass%, and the proportion of the structural unit (B) is 0.1 to 2 mass%, A polyimide resin porosifying material consisting of vinyl resin particles for producing a polyimide porous membrane.

2. A structural unit (A) derived from a vinyl monomer; a polymer having a structural unit (b1) derived from a compound represented by the following general formula (I), which is different from the structural unit (A): Vinyl resin particles for porous membrane production. 【Chemical 1】 [In the formula, m represents an integer of 1 to 3; R represents a group represented by the following formula (i) or (ii): 【Chemistry 2】 (In the formula, R １ represents a hydrogen atom or a methyl group), AO represents an alkyleneoxy group having 2 to 4 carbon atoms, and n represents an integer of 0 to 100. X is -SO ３ M, -COOM and -PO ３ M (wherein M represents an alkali metal atom, an alkaline earth metal atom, an ammonium group, or an organic ammonium group).

3. 3. The vinyl resin particles according to claim 2, wherein the proportion of the structural unit (b1) is 0.1% by mass to 2.0% by mass based on the total mass of the structural units of the polymer.

4. 4. The vinyl resin particle according to claim 2, wherein the structural unit (A) derived from the vinyl monomer comprises a structural unit (A1) derived from a monofunctional vinyl monomer and a structural unit (A2) derived from a polyfunctional vinyl monomer.

5. The porous material according to claim 1, or the vinyl resin particles according to any one of claims 2 to 4, wherein the median diameter of the resin particles is 0.05 μm to 2.0 μm.

6. The structural unit (A1) derived from a monofunctional vinyl monomer includes a structural unit (a1) derived from a monofunctional styrene monomer. The porous material according to claim 1 or 5, or the vinyl resin particles according to claim 4 or 5.

7. The structural unit (A1) derived from a monofunctional vinyl monomer includes a structural unit (a2) derived from a monofunctional (meth)acrylic monomer. The porous material according to claim 1, claim 5 or claim 6, or the vinyl resin particles according to any one of claims 4 to 6.

8. the proportion of the polyfunctional vinyl monomer (A2) is 0.9% by mass to 10% by mass based on the total mass of the structural units of the polymer; The porous material according to claim 1 or any one of claims 5 to 7, or the vinyl resin particles according to claim 4 to 7.

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