WO2024157960A1 - Curable resin composition and method for producing same - Google Patents

Abstract

The present disclosure provides a curable resin composition which has a low viscosity and good fluidability before heating, effectively becomes highly viscous by heating, and provides a (semi)cured article having low tackiness. The curable resin composition comprises 50 to 95% by mass of a curable compound (A) and 50 to 5% by mass of acrylic resin microparticles (B), in which the acrylic resin microparticles (B) satisfy 0 < D50 ≤ 1.0 and 0 < [(D90-D10)/D50] ≤ 1.0, and the viscosity (ηx) of the curable resin composition measured under the conditions of 25°C and a shear rate of 10 sec^-1, the viscosity (ηy) of the curable resin composition measured under the conditions of 25°C and a shear rate of 3000 sec^-1, and the viscosity (ηz) of the curable resin composition measured after the heating of the curable resin composition at 120°C and measured under the conditions of 25°C and a shear rate of 10 sec^-1 satisfy 0 <ηy[Pa·s] ≤ 10 and ηz/ηx ≥ 3.

Description

Curable resin composition and method for producing same

This disclosure relates to a curable resin composition and a method for producing the same.

Curable (resin) compositions that contain curable compounds such as monomers, oligomers, prepolymers, and curable resins, have fluidity before heating, and can be solidified by heating are widely used as materials for resin molded bodies such as cast plates, adhesives, cured coatings, and fiber-resin composites such as fiber-reinforced plastics (FRP) and prepregs. In such applications, the curable (resin) composition preferably has low viscosity during operations such as casting before heating, coating on an adherend or substrate, and impregnation into a fiber substrate, and the (semi-)cured product obtained by heating the curable (resin) composition preferably has low stickiness (tackiness).
In this specification, the term "semi-cured" is a general term for semi-cured and fully cured.

In response to the above demands, there has been proposed a curable resin composition containing a viscosity switching agent (also called a pregelling agent) that can dissolve or swell in the curable compound by heating.
Patent Document 1 discloses a curable resin composition containing an epoxy resin and acrylic resin fine particles that dissolve or swell in the epoxy resin at high temperatures and have a particle size of 1.0 μm or less at 25° C. (Claim 1).
Patent Document 2 discloses a curable resin composition containing an epoxy resin, a curing agent, and a pregelling agent such as acrylic resin fine particles (claims 1 to 3).

Japanese Patent Application Publication No. 10-237196 International Publication No. 2016/002777

In the techniques disclosed in Patent Documents 1 and 2, the fluidity before heating may be insufficient or unstable, and the increase in viscosity after heating may be ineffective.
Patent Documents 1 and 2 also do not consider curable compounds other than epoxy resins. Depending on the combination of the curable compound and the fine particles, the pot life after the preparation of the curable resin composition may be short, and before heating, the fine particles may dissolve in the curable compound, causing the viscosity to increase. In this case, the fluidity before heating and/or the viscosity increase after heating may be insufficient.

The objective of this disclosure is to provide a curable resin composition that has low viscosity and good fluidity during operations such as casting, coating, and impregnation before heating, and that effectively increases viscosity when heated to give a (semi-)cured product with low tackiness, and a method for producing the same.

The present disclosure provides the following curable resin compositions [1] to [9] and methods for producing the same.
[1] A curable resin composition comprising 50 to 95% by mass of a curable compound (A) and 50 to 5% by mass of acrylic resin fine particles (B),
The acrylic resin fine particles (B) have a cumulative 10% particle diameter D10 [μm], a cumulative 50% particle diameter D50 [μm], and a cumulative 90% particle diameter D90 [μm] in a volume-based cumulative particle diameter distribution that satisfy 0<D50≦1.0 and 0<[(D90−D10)/D50]≦1.0,
a viscosity of the curable resin composition measured under conditions of 25°C and a shear rate of 10 sec ^-1 is ηx, a viscosity of the curable resin composition measured under conditions of 25°C and a shear rate of 3000 sec ^-1 is ηy, and the curable resin composition is heated from 25°C to 120°C at a heating rate of 5°C/min and then cooled from 120°C to 25°C at a heating rate of 5°C/min, and then the viscosity of the curable resin composition measured under conditions of 25°C and a shear rate of 10 sec ^-1 is ηz, wherein at least ηy of ηx and ηy is more than 0 Pa s and 10 Pa s or less, and ηz/ηx is 3 or more.

[2] The curable resin composition according to [1], wherein D50 is 0.1 μm or more and (D90-D10)/D50 is 0.1 or more.
[3] The curable resin composition according to [1] or [2], wherein ηz/ηx is 20,000 or less.
[4] The curable resin composition according to any one of [1] to [3], wherein the acrylic resin fine particles (B) contain one or more methacrylic resins (M).
[5] The curable resin composition according to [4], wherein the content of the methacrylic acid ester unit in the acrylic resin fine particles (B) is 90 to 100 mass%.
[6] The curable resin composition according to [5], wherein the content of methyl methacrylate in the acrylic resin fine particles (B) is 90 to 100 mass%.
[7] The curable resin composition according to any one of [1] to [6], wherein the acrylic resin fine particles (B) have a glass transition temperature of 100° C. or higher.
[8] The curable resin composition according to any one of [1] to [7], wherein the curable compound (A) contains one or more curable compounds selected from the group consisting of a (meth)acryloyl group-containing monomer, a (meth)acryloyl group-containing oligomer, and an epoxy resin.

[9] A method for producing a curable resin composition comprising 50 to 95% by mass of a curable compound (A) and 50 to 5% by mass of acrylic resin fine particles (B),
the viscosity of the curable resin composition measured under conditions of 25° C. and a shear rate of 10 sec ^-1 is ηx, the viscosity of the curable resin composition measured under conditions of 25° C. and a shear rate of 3000 sec ^-1 is ηy, and the curable resin composition is heated from 25° C. to 120° C. at a temperature increase rate of 5° C./min, and then cooled from 120° C. to 25° C. at a temperature decrease rate of 5° C./min, and then the viscosity of the curable resin composition measured under conditions of 25° C. and a shear rate of 10 sec ^-1 is ηz, of ηx and ηy, at least ηy is more than 0 Pa s and 10 Pa s or less, and ηz/ηx is 3 or more;
a step (S1) of preparing acrylic resin microparticles (B) having a cumulative 10% particle diameter D10 [μm], a cumulative 50% particle diameter D50 [μm], and a cumulative 90% particle diameter D90 [μm] in a volume-based cumulative particle diameter distribution that satisfy 0<D50≦1.0 and 0<[(D90-D10)/D50]≦1.0;
A method for producing a curable resin composition, comprising: a step (S2) of mixing the curable compound (A) and the acrylic resin fine particles (B).

According to the present disclosure, it is possible to provide a curable resin composition that has low viscosity and good fluidity during operations such as casting, coating, and impregnation before heating, and that effectively increases viscosity when heated to give a (semi-)cured product with low tackiness, and a method for producing the same.

[Curable resin composition]
The curable resin composition of the present disclosure contains one or more types of curable compounds (A) and one or more types of acrylic resin fine particles (B).
The curable resin composition of the present disclosure is a thermosetting resin composition that can be cured by heating or irradiation with active energy rays, and is preferably cured by heating. Examples of active energy rays include ultraviolet rays and electron beams.

The content of the curable compound (A) in the curable resin composition of the present disclosure (the total amount when multiple types are used) is 50 to 95 mass%. The lower limit is preferably 55 mass%, more preferably 60 mass%. The upper limit is preferably 90 mass%, more preferably 85 mass%.
The content of the acrylic resin fine particles (B) in the curable resin composition of the present disclosure (the total amount when multiple types are used) is 50 to 5 mass%. The upper limit is preferably 45 mass%, more preferably 40 mass%. The lower limit is preferably 10 mass%, more preferably 15 mass%.

In the curable resin composition of the present disclosure, the acrylic resin fine particles (B) dispersed in the curable resin composition can impart thixotropy to the curable resin composition at room temperature before heating. Due to this action, the curable resin composition of the present disclosure can have low viscosity at least in the high shear rate range, and can have low viscosity and good fluidity at least during operations in which the curable resin composition is subjected to high shear force, such as casting, coating on an adherend or substrate, and impregnation into a fiber substrate.
The acrylic resin fine particles (B) dispersed in the curable resin composition can effectively increase the viscosity of the curable resin composition of the present disclosure by quickly absorbing the curable compound (A) or dissolving or swelling in the curable compound (A) after heating.
If the content of the curable compound (A) is equal to or more than the lower limit, the curable resin composition before heating can have low viscosity and good fluidity at least in the high shear rate range, and the increase in viscosity before heating can be suppressed. If the content of the acrylic resin fine particles (B) is equal to or more than the lower limit, the increase in viscosity after heating is effective, and a (semi-)cured product having low tackiness can be obtained.

Depending on the combination of the curable compound and the microparticles, after the curable resin composition is prepared and before heating, dissolution of the microparticles into the curable compound may progress, resulting in an increase in the initial viscosity before heating and/or a decrease in the rate of increase in viscosity after heating.

The viscosity of the curable resin composition measured under conditions of 25°C and a shear rate of 10 sec ^-1 (also referred to as initial viscosity) is ηx, the viscosity of the curable resin composition measured under conditions of 25°C and a shear rate of 3000 sec ^-1 (also referred to as viscosity in the high shear rate range) is ^ηy , and the viscosity of the curable resin composition measured under conditions of 25°C to 120°C at a heating rate of 5°C/min, followed by cooling from 120°C to 25°C at a cooling rate of 5°C/min (also referred to as viscosity after heating to 120°C) is ηz.

In the curable resin composition of the present disclosure, at least ηy of ηx and ηy is more than 0 Pa·s and 10 Pa·s or less. The upper limit is preferably 8 Pa·s, more preferably 7 Pa·s, particularly preferably 5 Pa·s, and most preferably 4 Pa·s. It is preferable that both ηx and ηy satisfy the above conditions. Since the curable resin composition of the present disclosure has a low viscosity of 10 Pa·s or less at least in the high shear rate range, it can have low viscosity and good fluidity at least during operations such as casting, coating, and impregnation in which high shear force is applied to the curable resin composition.
The curable resin composition of the present disclosure has ηz/ηx of 3 or more. In this case, the increase in viscosity after heating is effective, and a (semi-)cured product having low tackiness can be effectively obtained. The lower limit is preferably 10, more preferably 20, particularly preferably 30, and most preferably 40. The upper limit is not particularly limited, and is, for example, 20,000.
In the curable resin composition of the present disclosure, the combination and compounding ratio of the curable compound (A) and the acrylic resin fine particles (B) are designed so that, of ηx and ηy, at least ηy is more than 0 Pa·s and 10 Pa·s or less, and ηz/ηx is 3 or more.

(Curable compound (A))
As the curable compound (A), a known compound having one or more polymerizable unsaturated bonds and/or one or more polymerizable functional groups in the molecule can be used. The polymerizable functional group is, for example, Examples of the curable compound (A) include an epoxy group, an oxetane group, and an acid anhydride group. The form of the curable compound (A) includes a monomer, an oligomer, a prepolymer, and a curable resin. One or more curable compounds (A) may be selected within ranges that provide suitable properties such as viscosity and curing rate of the composition.

Compounds having a polymerizable unsaturated bond include monofunctional vinyl monomers having only one polymerizable alkenyl group in one molecule; polyfunctional vinyl monomers having two or more polymerizable alkenyl groups in one molecule; monofunctional or polyfunctional oligomers, etc.

Examples of monofunctional vinyl monomers include unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, and itaconic acid; (meth)acryloyl group-containing monomers such as (meth)acrylic acid esters; (meth)acrylamide; cyanide vinyl monomers such as (meth)acrylonitrile; (meth)acrylic acid metal salts; aromatic vinyl monomers such as styrene (St), 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, 4-tert-butylstyrene, α-methylstyrene, and 4-methyl-α-methylstyrene; other vinyl monomers such as vinyl chloride and vinyl acetate. From the viewpoint of the fluidity of the curable resin composition before heating, (meth)acryloyl group-containing monomers are preferred.
In this specification, (meth)acrylic is a general term for acrylic and methacrylic, and the same applies to (meth)acrylic acid, (meth)acrylonitrile, etc.

Examples of methacrylic acid esters include alkyl methacrylates such as methyl methacrylate (MMA), ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, and dodecyl methacrylate; cycloalkyl methacrylates such as 1-methylcyclopentyl methacrylate, cyclohexyl methacrylate, cycloheptyl methacrylate, cyclooctyl methacrylate, and tricyclo[5.2.1.0 ^2,6 ]dec-8-yl methacrylate; aryl methacrylates such as phenyl methacrylate; and aralkyl methacrylates such as benzyl methacrylate.

Acrylic acid esters include methyl acrylate (MA), ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, dodecyl acrylate, stearyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, cyclohexyl acrylate, 2-methoxyethyl acrylate, 3-methoxybutyl acrylate, trifluoromethyl acrylate, trifluoroethyl acrylate, pentafluoroethyl acrylate, glycidyl acrylate, allyl acrylate, phenyl acrylate, toluyl acrylate, benzyl acrylate, isobornyl acrylate, and 3-dimethylaminoethyl acrylate.

Examples of polyfunctional vinyl monomers include reaction products of polyols and (meth)acrylic acid; and urethane (meth)acrylates obtained by adding one or more hydroxyl group-containing (meth)acrylate compounds to a compound having a terminal isocyanate group in the molecule.

Reaction products of polyols and (meth)acrylic acid include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, trimethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, tetramethylene glycol di(meth)acrylate, 1,2-butanediol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, and 1,4-butanediol. Di(meth)acrylate, 1,5-pentanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,2-hexylene glycol di(meth)acrylate di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,7-heptanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 2-hydroxy-1,3 dimethacryloxypropane, cyclohexanediol di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, hydrogenated bisphenol A di(meth)acrylate, hydrogenated bisphenol Bisphenol F di(meth)acrylate, hydrogenated bisphenol AF di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dioxane glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene diacrylate, glycerin tri(meth)acrylate, diglycerin tri(meth)acrylate, 1,2,6-hexanetriol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate acrylate, 1,2,5-pentanetriol tri(meth)acrylate, trishydroxymethylaminomethane tri(meth)acrylate, 3-(2-hydroxyethoxy)-1,2-propanediol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tris(2-(meth)acryloyloxyethyl)isocyanurate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

Examples of compounds having a terminal isocyanate group in the molecule, which are raw materials for urethane (meth)acrylates, include isophorone diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, norbornane diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane (cis-, trans-mixture), and nurate-type trimers thereof.
Examples of hydroxyl group-containing (meth)acrylate compounds that are raw materials for urethane (meth)acrylates include hydroxyethyl (meth)acrylate, glycerin di(meth)acrylate, trimethylolpropane di(meth)acrylate, pentaerythritol tri(meth)acrylate, ditrimethylolpropane tri(meth)acrylate, and dipentaerythritol penta(meth)acrylate.

Examples of monofunctional or polyfunctional oligomers include oligomers of (meth)acrylic acid ester monomers, (meth)acrylates obtained using oligomer-type polyhydroxy compounds, epoxy (meth)acrylates obtained using oligomer-type epoxy compounds, urethane (meth)acrylate-based oligomers, and (meth)acrylic oligomers such as polybutadiene (meth)acrylate (including hydrogenated polybutadiene (meth)acrylate). The weight average molecular weight (Mw) of the oligomer is not particularly limited and can be, for example, 400 to 150,000, 500 to 100,000, 1,000 to 50,000, or 10,000 to 50,000.

Curable resins include epoxy resins, phenolic resins, maleimide compounds, cyanate resins, isocyanate resins, benzoxazine resins, oxetane resins, amino resins, unsaturated polyester resins, allyl resins, dicyclopentadiene resins, silicone resins, triazine resins, and melamine resins. Among these, epoxy resins are preferred for applications such as prepregs, from the standpoint of moldability and electrical insulation.

As the epoxy resin, a known compound having two or more epoxy groups in the molecule can be used. Examples include unmodified epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, bisphenol E type epoxy resin, naphthalene type epoxy resin, biphenyl type epoxy resin, dicyclopentadiene type epoxy resin, phenol novolac type epoxy resin, alicyclic epoxy resin, and glycidylamine type epoxy resin. Among them, bisphenol A type epoxy resin, bisphenol F type epoxy resin, and alicyclic epoxy resin are preferred because they have excellent heat resistance of the cured product and are relatively inexpensive.

The epoxy resin may be a modified epoxy resin such as urethane modified epoxy resin, rubber modified epoxy resin, or chelate modified epoxy resin; or a copolymer of the above unmodified epoxy resin with other polymers such as polyether modified epoxy resin or silicone modified epoxy resin.

As the epoxy resin, an epoxy resin in which a part of the above-mentioned non-modified epoxy resin is substituted with one or more reactive diluents having an epoxy group may be used. Examples of reactive diluents include polyalkylene glycol diglycidyl ethers such as polyethylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether; glycol diglycidyl ethers such as neopentyl glycol diglycidyl ether and 1,4-butanediol diglycidyl ether; diglycidyl esters of aliphatic polybasic acids such as adipic acid diglycidyl ester and maleic acid diglycidyl ester; glycidyl ethers of dihydric or higher polyhydric aliphatic alcohols such as trimethylolpropane triglycidyl ether and trimethylolethane triglycidyl ether; monoglycidyl compounds such as resorcinol glycidyl ether, t-butylphenyl glycidyl ether, and allyl glycidyl ether; and monoalicyclic epoxy compounds such as 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

The epoxy equivalent of the epoxy resin is not particularly limited, and is preferably 80 to 2000 g/eq. The "epoxy equivalent" is the mass of a resin containing one equivalent of an epoxy group, and can be measured in accordance with JIS K7236.
The epoxy resin can be produced by a known method, such as a method of reacting a polyhydric alcohol or a polyhydric phenol with an excess amount of epihalohydrin in the presence of a base.

When the curable compound (A) contains an epoxy resin, the curable compound (A) may be a combination of an epoxy resin and a curable compound known as a curing agent for epoxy resins, such as an acid anhydride.
Examples of the acid anhydride include maleic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methylnadic anhydride.

The curable compound (A) preferably contains one or more curable compounds selected from the group consisting of (meth)acryloyl group-containing monomers, (meth)acryloyl group-containing oligomers, and epoxy resins.

(Acrylic Resin Fine Particles (B))
The curable resin composition of the present disclosure contains one or more types of acrylic resin fine particles (B).
The acrylic resin fine particles (B) have a volume-based cumulative particle size distribution in which, calculated from the smaller particle size, the particle size D10 at which the cumulative frequency is 10%, the particle size D50 (also referred to as the median size) at which the cumulative frequency is 50%, and the particle size D90 at which the cumulative frequency is 90% satisfy the following conditions:

D50 is more than 0 μm and 1.0 μm or less. The upper limit is preferably 0.8 μm, more preferably 0.7 μm, particularly preferably 0.5 μm, and most preferably 0.3 μm. The lower limit is preferably 0.05 μm, more preferably 0.1 μm, and particularly preferably 0.15 μm. If D50 is within the above range, the curable resin composition of the present disclosure has good fluidity before heating and good viscosity increase effect after heating.
(D90-D10)/D50 (also referred to as span value) is more than 0 and not more than 1.0. The upper limit is preferably 0.9, more preferably 0.7, and particularly preferably 0.5. The lower limit is preferably 0.1, more preferably 0.2, and particularly preferably 0.3. The smaller the span value, the smaller the variation in particle size, which is preferable. If the span value exceeds 1.0, the variation in particle size is large, and the flow state of the curable resin composition of the present disclosure before heating becomes unstable, and there is a risk that the desired action and effect cannot be stably obtained. If the span value is within the above range, the flowability of the curable resin composition before heating and the viscosity increase effect after heating are suitable.

In the curable resin composition of the present disclosure, the acrylic resin fine particles (B) may be partially dissolved or swollen. Unless otherwise specified in this specification, the D10, D50, and D90 of the acrylic resin fine particles (B) are the D10, D50, and D90 of the acrylic resin fine particles (B) alone before being mixed with the curable compound (A).
The D10, D50, and D90 of the acrylic resin fine particles (B) can be determined by a method of measuring a latex or aqueous dispersion containing the acrylic resin fine particles (B) by a light scattering method using a laser diffraction/scattering type particle size distribution measuring device or the like, or by a method of measuring from an electron microscope image of the acrylic resin fine particles (B). For specific measuring methods, please refer to the section [Examples] below.

The glass transition temperature (Tg) of the acrylic resin fine particles (B) is preferably 100° C. or higher. The lower limit is more preferably 105° C., particularly preferably 110° C., and most preferably 115° C. The upper limit is, for example, 125° C.
In this specification, unless otherwise specified, the "glass transition temperature (Tg)" is a value measured in accordance with JIS K7121: 2012. For specific measurement methods, see the section [Examples] below.

The acrylic resin fine particles (B) are fine particles containing one or more kinds of acrylic resins. The acrylic resin is a homopolymer or copolymer containing one or more kinds of (meth)acrylic acid ester units. The acrylic resin fine particles (B) may be acrylic single-layer structure fine particles having a uniform composition as a whole, or may be acrylic multilayer structure fine particles having 2 to 4 layers made of acrylic resins having different compositions.
The acrylic resin fine particles (B) preferably contain one or more methacrylic resins (M). The content of the methacrylic resins (M) in the acrylic resin fine particles (B) (the total amount in the case of a plurality of types) is preferably 90% by mass or more, more preferably 95% by mass or more, particularly preferably 98% by mass or more, and may be 100% by mass.

Examples of methacrylic acid esters include alkyl methacrylates such as methyl methacrylate (MMA), ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, and dodecyl methacrylate; cycloalkyl methacrylates such as 1-methylcyclopentyl methacrylate, cyclohexyl methacrylate, cycloheptyl methacrylate, cyclooctyl methacrylate, and tricyclo[5.2.1.0 ^2,6 ]dec-8-yl methacrylate; aryl methacrylates such as phenyl methacrylate; and aralkyl methacrylates such as benzyl methacrylate. Among these, from the viewpoint of viscosity control of the curable resin composition, MMA, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, etc. are preferred, and MMA, etc. is more preferred.
The content of the methacrylic acid ester units in the acrylic resin microparticles (B) (the total amount in the case of multiple types) is preferably 90% by mass or more, more preferably 95% by mass or more, particularly preferably 98% by mass or more, and most preferably 99.5% by mass or more, and may be 100% by mass.
The content of MMA units in the acrylic resin fine particles (B) is preferably 90% by mass or more, more preferably 95% by mass or more, particularly preferably 98% by mass or more, and most preferably 99.5% by mass or more, and may be 100% by mass.

The methacrylic resin (M) may contain one or more types of monomer units other than the methacrylic acid ester units. The content of the other monomer units in the methacrylic resin (M) (the total amount if multiple types) is preferably 10% by mass or less, more preferably 5% by mass or less, particularly preferably 2% by mass or less, and most preferably 0.5% by mass or less.

The methacrylic resin (M) may contain one or more acrylate units as other monomer units. Examples of the acrylate units include methyl acrylate (MA), ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, dodecyl acrylate, stearyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, cyclohexyl acrylate, 2-methoxyethyl acrylate, 3-methoxybutyl acrylate, trifluoromethyl acrylate, trifluoroethyl acrylate, pentafluoroethyl acrylate, glycidyl acrylate, allyl acrylate, phenyl acrylate, toluyl acrylate, benzyl acrylate, isobornyl acrylate, and 3-dimethylaminoethyl acrylate. Among these, from the viewpoint of availability, MA, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, and tert-butyl acrylate are preferred, MA and ethyl acrylate are more preferred, and MA is particularly preferred.

The methacrylic resin (M) may contain one or more other monofunctional monomer units other than (meth)acrylic acid ester units as other monomer units. Examples of other monofunctional monomers include unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, and itaconic acid; (meth)acrylamide; vinyl cyanide monomers such as (meth)acrylonitrile; metal salts of (meth)acrylic acid; aromatic vinyl monomers such as styrene (St), 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, 4-tert-butylstyrene, α-methylstyrene, and 4-methyl-α-methylstyrene; acid anhydrides such as maleic anhydride; and other vinyl monomers such as vinyl chloride and vinyl acetate.

The methacrylic resin (M) may contain one or more polyfunctional monomer units as other monomer units. Examples of polyfunctional monomers include ethylene glycol dimethacrylate, propylene glycol dimethacrylate, triethylene glycol dimethacrylate, hexanediol dimethacrylate (HDDMA), ethylene glycol diacrylate, propylene glycol diacrylate, triethylene glycol diacrylate, allyl methacrylate, and triallyl isocyanurate.
The content of polyfunctional monomer units in the methacrylic resin (M) (the total amount when multiple types are present) is preferably 5 mass% or less, more preferably 3 mass% or less, particularly preferably 2 mass% or less, and most preferably 1 mass% or less.

The acetone insoluble content of the acrylic resin fine particles (B) is not particularly limited and can be 0 to 100% by mass. Since the viscosity increase after heating of the curable resin composition of the present disclosure is effective, it is preferably 0 to 1% by mass, more preferably 0 to 0.5% by mass.
The acrylic resin fine particles (B) containing only one or more methacrylic resins (M) that do not contain polyfunctional monomer units and do not have a crosslinked structure as a constituent resin may have an acetone insoluble content of 0 to 1 mass %.
The acrylic resin fine particles (B) containing the methacrylic resin (M) which contains a polyfunctional monomer unit and has a crosslinked structure may have an acetone insoluble content of 95 to 100% by mass.
The acetone insoluble content of the acrylic resin fine particles (B) can be measured by the method described in the section [Examples] below.

The polymerization method for the acrylic resin fine particles (B) is not particularly limited, and examples thereof include emulsion polymerization, suspension emulsion polymerization, solution polymerization, and combinations thereof, with emulsion polymerization being preferred.
An example of the production method using emulsion polymerization will be described below.
A monomer liquid containing one or more monomers including a (meth)acrylic acid ester monomer, a polymerization initiator, an emulsifier, and, if necessary, a chain transfer agent, etc., is prepared, and one or more stages of emulsion polymerization are carried out to obtain a latex containing single-layer or multi-layer acrylic resin fine particles (B). The D50 and (D90-D10)/D50 of the acrylic resin fine particles (B) can be controlled within a preferred range by adjusting the polymerization conditions, such as the type and amount of the polymerization initiator, the type and amount of the emulsifier, and the type and amount of the chain transfer agent.

The polymerization initiator is not particularly limited, and examples thereof include water-soluble inorganic initiators such as potassium persulfate and ammonium persulfate, redox initiators using such inorganic initiators in combination with sulfites or thiosulfates, etc., and redox initiators using an organic peroxide in combination with ferrous salts or sodium sulfoxylate, etc. The polymerization initiator may be added all at once at the start of polymerization, or may be added in portions at the start of polymerization and during polymerization, taking into consideration the reaction rate, etc.
The type, amount and addition timing of the polymerization initiator can be designed so that the D50 and (D90-D10)/D50 of the acrylic resin fine particles (B) fall within the desired range.

The emulsifier is not particularly limited, and examples thereof include anionic emulsifiers such as long-chain alkyl sulfonates, alkyl sulfosuccinate salts, and alkylbenzene sulfonates; nonionic emulsifiers such as polyoxyethylene alkyl ethers and polyoxyethylene nonyl phenyl ether; and nonionic/anionic emulsifiers such as polyoxyethylene nonyl phenyl ether sulfates such as sodium polyoxyethylene nonyl phenyl ether sulfate, polyoxyethylene alkyl ether sulfates such as sodium polyoxyethylene alkyl ether sulfate, and alkyl ether carboxylates such as sodium polyoxyethylene tridecyl ether acetate.
The type and amount of the emulsifier can be designed so that the D50 and (D90-D10)/D50 of the acrylic resin fine particles (B) are within the desired range.

　Chain transfer agents can be used to adjust the molecular weight. There are no particular limitations on the chain transfer agent, and examples include alkyl mercaptans such as n-octyl mercaptan (nOM), n-dodecyl mercaptan, t-dodecyl mercaptan, and n-hexadecyl mercaptan; xanthogen disulfides such as dimethyl xanthogen disulfide and diethyl xanthogen disulfide; thiuram disulfides such as tetrathiuram disulfide; and halogenated hydrocarbons such as carbon tetrachloride and ethylene bromide. The type and amount of the chain transfer agent can be appropriately designed within a range in which the desired molecular weight can be obtained. The amount of the chain transfer agent is designed according to the type and amount of the polymerization initiator, and is preferably 0.05 to 2 parts by mass, more preferably 0.08 to 1 part by mass, per 100 parts by mass of monomer (total amount in the case of multiple types).

By changing the polymerization conditions such as the composition of the monomer liquid and the number of layers, multiple types of latexes of acrylic resin microparticles (B) with different volume-based cumulative particle size distributions can be prepared, and these can be mixed to obtain a latex of acrylic resin microparticles (B) with D50 and (D90-D10)/D50 within the desired range.

The acrylic resin fine particles (B) can be collected from the latex by coagulating the latex, for example by freeze coagulation, salting-out coagulation, or acid precipitation coagulation.
In the case of the freeze coagulation method, the obtained latex is cooled to freeze-aggregate, and the aggregates are then melted, taken out, and dried to obtain powdery acrylic resin fine particles (B).

In the salting-out coagulation method and the acid precipitation coagulation method, a coagulant is added to the obtained latex to coagulate it, and the obtained slurry is washed, dehydrated, and dried to obtain powdered acrylic resin fine particles (B). The coagulant used in these methods may be any agent capable of coagulating or coagulating the latex, and examples of such agents include aqueous solutions containing inorganic acids, organic acids, or salts thereof. The washing and dehydration of the slurry can be performed using a filter press, a belt press, a Ginner type centrifuge, a screw decanter type centrifuge, or the like. From the viewpoints of productivity and washing efficiency, a screw decanter type centrifuge, or the like, is preferred. The number of washing and dehydration is preferably 2 to 3 times.

Since the dispersibility of the acrylic resin fine particles (B) in the curable resin composition of the present disclosure is good, the water content of the powdery acrylic resin fine particles (B) obtained after drying is preferably 0.2 mass% or less, and more preferably 0.1 mass% or less.
The raw material form of the acrylic resin fine particles (B) at the time of mixing with the curable compound (A) is not particularly limited, and may be a powder, latex, or aqueous dispersion.

(Optional ingredients)
The curable resin composition of the present disclosure may contain one or more optional components as necessary. The optional components include polymerization initiators, curing aids, and cocatalysts; curing agents; curing accelerators; antioxidants; release agents such as silicone oils, natural waxes, and synthetic waxes; inorganic fine particles such as glass, crystalline silica, fused silica, calcium silicate, and alumina; fibers such as glass fibers and carbon fibers; flame retardants such as antimony trioxide; halogen trapping agents such as hydrotalcite and rare earth oxides; pigments such as carbon black and red iron oxide, and colorants such as dyes; silane coupling agents; defoamers; rheology adjusters; liquid media such as water and organic solvents.

When the curable compound (A) includes a compound having a polymerizable unsaturated bond, the curable resin composition of the present disclosure may include a radical polymerization initiator as necessary, and further include a curing aid, a curing accelerator, a cocatalyst, and the like as necessary.
Examples of the radical polymerization initiator include organic peroxides such as benzoyl peroxide, cumene hydroperoxide, dicumyl peroxide, lauroyl peroxide, di-t-butyl peroxide, t-butyl hydroperoxide, methyl ethyl ketone peroxide, t-butyl peroxybenzoate, t-butyl peroxy-2-ethylhexanoate, and t-butyl peroxyoctanoate; and azo compounds such as azobisisobutyronitrile.

The curing aid is an additive that acts as a catalyst for the decomposition reaction (radical generation reaction) of the radical polymerization initiator, and examples thereof include metal salts of naphthenic acid and octenic acid (cobalt salts, tin salts, lead salts, etc.). From the viewpoints of toughness and appearance, cobalt naphthenate is preferred. When a curing accelerator is added, it is preferable to add 0.1 to 1 part by mass of the curing aid per 100 parts by mass of the curable compound (A) immediately before the curing reaction in order to suppress a rapid curing reaction.

The co-catalyst is an additive that causes radical generation at low temperatures, and examples of such co-catalysts include amine compounds such as N,N-dimethylaniline, triethylamine, and triethanolamine. From the viewpoint of efficient reaction, N,N-dimethylaniline is preferred. The amount of the co-catalyst added is preferably 0.01 to 0.5 parts by mass per 100 parts by mass of the curable compound (A), or 1 to 15 parts by mass per 100 parts by mass of the radical polymerization initiator.

When the curable compound (A) contains an epoxy resin, the curable resin composition of the present disclosure may contain a known cationic polymerization initiator as necessary.

When the curable compound (A) contains an epoxy resin, the curable resin composition of the present disclosure may contain a known curing agent and/or curing accelerator for epoxy resins (excluding the curable compound), as necessary. Examples of the curing agent and/or curing accelerator include amine compounds, phenolic compounds (such as novolac resins), mercaptans, Lewis acid amine complexes, onium salts, and imidazoles.

Any known antioxidant can be used, and from the viewpoint of antioxidant performance, phenol-based antioxidants, thioether-based antioxidants, and phosphite-based antioxidants are preferred, with phenol-based antioxidants and thioether-based antioxidants being more preferred.

Phenol-based antioxidants include dibutylhydroxytoluene, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-butylidenebis(6-tert-butyl-m-cresol), 3-(3,5-di-tert-butyl-4-hydroxyphenyl)stearyl propionate, pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylenebis(oxyethylene)]. Among these, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)stearyl propionate and pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] are preferred.

Thioether antioxidants include dilauryl-3,3'-thiodipropionate, ditridecyl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, laurylstearyl-3,3'-thiodipropionate, pentaerythritol tetrakis (3-laurylthiopropionate), bis[2-methyl Examples of the bis[3-(dodecylthio)propionic acid]2,2-bis[[3-(dodecylthio)-1-oxopropyloxy]methyl]-1,3-propanediyl) are 1,1'-thiobis(2-naphthol)(bis[3-(dodecylthio)propionic acid]2,2-bis[[3-(dodecylthio)-1-oxopropyloxy]methyl]-1,3-propanediyl) and the like. Among these, bis[3-(dodecylthio)propionic acid]2,2-bis[[3-(dodecylthio)-1-oxopropyloxy]methyl]-1,3-propanediyl) and the like are preferred.

Phosphite-based antioxidants include triphenyl phosphite, trisnonylphenyl phosphite, tris(2,4-di-tert-butylphenyl)phosphite, tridecyl phosphite, trioctyl phosphite, trioctadecyl phosphite, didecyl monophenyl phosphite, dioctyl monophenyl phosphite, diisopropyl monophenyl phosphite, monobutyl diphenyl phosphite, monodecyl diphenyl phosphite, monooctyl diphenyl phosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite, 2,2-methylenebis(4,6-di-tert-butylphenyl)octyl phosphite, bis(nonylphenyl)pentaerythritol diphosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, distearyl pentaerythritol diphosphite, etc. Among these, trisnonylphenyl phosphite, triphenyl phosphite, tris(2,4-di-tert-butylphenyl)phosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, and bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite are preferred, with tris(2,4-di-tert-butylphenyl)phosphite being more preferred.

The content of the antioxidant is preferably 0.0001 to 10 parts by mass relative to 100 parts by mass of the curable resin composition of the present disclosure, from the viewpoint of the heat coloration resistance and surface appearance of the (semi-)cured product. The lower limit is more preferably 0.001 parts by mass, and particularly preferably 0.01 parts by mass. The upper limit is more preferably 6 parts by mass, and particularly preferably 3 parts by mass or less.

[Method for producing curable resin composition]
The method for producing the curable resin composition of the present disclosure includes the steps of:
a step (S1) of preparing acrylic resin microparticles (B) having a cumulative 10% particle diameter D10 [μm], a cumulative 50% particle diameter D50 [μm], and a cumulative 90% particle diameter D90 [μm] in a volume-based cumulative particle diameter distribution that satisfy 0<D50≦1.0 and 0<[(D90-D10)/D50]≦1.0;
The method may include a step (S2) of mixing the curable compound (A) and the acrylic resin fine particles (B).

(Step (S1))
The acrylic resin fine particles (B) can be prepared in the form of a powder, a latex, or an aqueous dispersion.
The acrylic resin fine particles (B) can be polymerized by a known method. Since the polymerization method has been described above, the description thereof will be omitted here.

(Step (S2))
In the step (S2), one or more types of curable compounds (A), one or more types of acrylic resin fine particles (B), and, if necessary, one or more types of optional components, can be mixed all at once or in portions.
The acrylic resin fine particles (B) can be blended in the form of a powder, latex, or aqueous dispersion. If necessary, one or more known organic solvents may be added.
Examples of the mixer include a mechanical stirrer, a planetary mixer, a rotation/revolution mixer, a mixing roll such as a three-roll mixer, a kneader, etc. Among them, a three-roll mixer is preferred from the viewpoint of efficiently applying a shear force required for dispersing the acrylic resin fine particles (B).

(Step (S3))
When the curable resin composition obtained after step (S2) (mixing step) contains a liquid medium such as water and an organic solvent, a step (S3) of removing the liquid medium may be carried out after step (S2) to obtain a curable resin composition of the present disclosure that does not contain the liquid medium.

As described above, the present disclosure can provide a curable resin composition that has low viscosity and good fluidity during operations such as casting, coating, and impregnation before heating, and that effectively increases viscosity when heated to give a (semi-)cured product with low tackiness, as well as a method for producing the same.

[Application]
The curable resin composition of the present disclosure is suitable as a material for molded articles, adhesives, cured coatings, and the like.
The molded body may be a planar object having a single layer structure or a laminate structure such as a film, a sheet, and a plate; any three-dimensional structure, etc. The molded body may be a laminate or a composite body including a layer or a member made of a cured product of the curable resin composition of the present disclosure and a layer or a member made of other resins or various materials other than resins. Generally, the terms "film", "sheet", or "plate" are used for thin film molded bodies depending on the thickness, but there is no clear definition of these terms, and there is no clear distinction between them.
Examples of the composite include a fiber resin composite containing a fiber base material and a (semi-)cured product of the curable resin composition of the present disclosure, and examples thereof include fiber reinforced composite plastics (FRPs) such as carbon fiber reinforced composite plastics (CFRPs) and prepregs, etc. Prepregs are materials obtained by impregnating a fiber base material made of reinforcing fibers or the like with a curable resin composition and (semi-)curing it, and are suitable as intermediate materials for FRPs, etc.
Applications of molded articles (including composites) comprising a cured product of the curable resin composition of the present disclosure include components for aircraft, automobiles, sporting goods, wind turbines, pressure vessels, and the like.
The cured coating can be formed on various substrates such as displays, such as liquid crystal displays and touch panel displays that combine a liquid crystal display with a touch panel, or protective plates thereof, and can function as a scratch-resistant layer (hard coat layer) or a low-reflectivity layer for improving visibility.

Examples and comparative examples according to the present invention will be described.
[Evaluation items and evaluation methods]
The evaluation items and evaluation methods are as follows.

(D50 (median diameter), (D90-D10)/D50)
The latex or aqueous dispersion of the acrylic resin fine particles (B) or the comparative resin fine particles was used as a sample, and the volume-based cumulative particle size distribution was measured by a light scattering method using a laser diffraction/scattering type particle size distribution measuring device "LA-950V2" manufactured by Horiba, Ltd. From the obtained particle size distribution, the particle size at which the cumulative frequency is 10% (cumulative 10% particle size) D10, the particle size at which the cumulative frequency is 50% (cumulative 50% particle size) D50 (median size), and the particle size at which the cumulative frequency is 90% (cumulative 90% particle size) D90 were calculated from the particle size distribution obtained, starting from the smaller particle size. The value of (D90-D10)/D50 was obtained.

(Acetone insolubles)
2 g of the acrylic resin particles (B) or the comparative resin particles was added to 50 mL of acetone and stirred and mixed at 23 ° C. for 24 hours. The entire amount of the obtained liquid was centrifuged using a Hitachi centrifuge "CR20GIII" (rotor: R20A2) at a rotation speed of 20,000 rpm, a temperature of 0 ° C., and for 90 minutes. The supernatant was collected, and after acetone was evaporated, it was vacuum dried at 50 ° C. for 8 hours to obtain a residue (acetone soluble content). In addition, the sediment from the above-mentioned centrifugation was collected and vacuum dried at 50 ° C. for 8 hours to obtain a residue (acetone insoluble content). The mass of the acetone insoluble content and the mass of the acetone soluble content were measured, and the ratio of the acetone insoluble content was calculated based on the following formula.
[Acetone insolubles (mass%)] = {[mass of acetone insolubles] / ([mass of acetone solubles] + [mass of acetone insolubles])} × 100

(Weight average molecular weight (Mw))
The weight average molecular weight (Mw) of the acrylic resin particles (B) or the comparative resin particles was determined by GPC (gel permeation chromatography). The separation column used was a series connection of "TSKguardcolumn Super HZ-H", "TSKgel HZM-M" and "TSKgel Super HZ4000" manufactured by Tosoh Corporation. The detector used was a differential refractive index detector (RI detector A sample solution was prepared by dissolving 4 mg of the resin to be measured in 5 ml of tetrahydrofuran. The temperature of the column oven was set to 40° C. Tetrahydrofuran was used as the eluent, and the eluent flow rate was set to 0.35 ml/min. Then, 20 μl of the sample solution was injected into the device and the chromatogram was measured. Ten standard polymethyl methacrylate (PMMA) samples with molecular weights ranging from 400 to 5,000,000 were measured by GPC, and a calibration curve showing the relationship between retention time and molecular weight was created. The Mw of the resin to be measured was determined.

(Glass Transition Temperature (Tg))
The glass transition temperature (Tg) of the acrylic resin microparticles (B) or the comparative resin microparticles was measured using a differential scanning calorimeter (Shimadzu Corporation's "DSC-60 Plus") in accordance with JIS K7121:2012. 10 mg of powder of the resin microparticles was placed in an aluminum pan and set in the above-mentioned device. After nitrogen replacement for 30 minutes or more, the temperature was once raised from room temperature (20 to 25 ° C) to 200 ° C at a rate of 20 ° C / min in a nitrogen flow of 10 ml / min, held for 5 minutes, and cooled to 30 ° C (primary scan). Next, the temperature was raised to 180 ° C at a rate of 10 ° C / min (secondary scan), and the DSC curve was measured. The midpoint glass transition temperature obtained from the DSC curve obtained by the secondary scan was taken as the glass transition temperature (Tg).

(Viscosity (ηx), (ηy), (ηz))
The initial viscosity (ηx), viscosity in the high shear rate range (ηy), and viscosity after heating at 120° C. (ηz) of the curable resin composition were measured using a rheometer (TA Instruments'"AR2000"). The gap between a pair of upper and lower parallel plates each having a diameter of 8 mm was set to 200 μm, and the curable resin composition was filled into the gap and held at 25° C. for 30 seconds, after which the viscosity was measured under the following conditions.
The viscosity was measured at 25°C and a shear rate of 10 sec ^-1 , and this viscosity value was taken as the initial viscosity (ηx). The viscosity was measured at 25°C and a shear rate of 3000 sec ^-1 , and this viscosity value was taken as the initial viscosity (ηx). The viscosity in the high shear region (ηy) was measured. The temperature was increased from 25° C. to 120° C. at a rate of 5° C./min while rotating a pair of upper and lower parallel plates at a shear rate of 10 sec ^- 1. After the temperature was lowered to 25° C. at a rate of 5° C./min, the viscosity was measured under conditions of 25° C. and a shear rate of 10 sec ⁻¹ , and this viscosity value was taken as the viscosity (ηz) after heating to 120° C. ηx was calculated.

[material]
The materials used are as follows:
(Curable compound (A))
(A-1): Isobornyl acrylate, "Light Acrylate IB-XA" manufactured by Kyoeisha Chemical Co., Ltd.
(A-2): Tricyclodecane dimethanol diacrylate, "NK Ester A-DCP" manufactured by Shin-Nakamura Chemical Co., Ltd.
(A-3): Ethoxylated bisphenol A dimethacrylate, "NK Ester BPE-80N" manufactured by Shin-Nakamura Chemical Co., Ltd.
(A-4): Trimethylolpropane triacrylate, "NK Ester A-TMPT" manufactured by Shin-Nakamura Chemical Co., Ltd.
(A-5): 2-hydroxy-1,3-dimethacryloxypropane, "NK Ester 701" manufactured by Shin-Nakamura Chemical Co., Ltd.
(A-6): Bisphenol A type epoxy resin, "jER828" manufactured by Mitsubishi Chemical Corporation;
(A-7): Bisphenol F type epoxy resin, "EPICLON EXA-830LVP" manufactured by DIC Corporation;
(A-8): Alicyclic epoxy resin, "Celloxide 2021P" manufactured by Daicel Corporation;
(A-9): Methylhexahydrophthalic anhydride, a curing agent for epoxy resins, “HN-5500” manufactured by Showa Denko Materials Co., Ltd.

[Production Example 1] (Production of acrylic resin fine particles (B-1))
In a nitrogen atmosphere, 150 parts by mass of distilled water, 0.03 parts by mass of an emulsifier ("Nikkol ECT-3NEX" manufactured by Nikko Chemicals Co., Ltd.), and 0.1 parts by mass of sodium carbonate were placed in a polymerization vessel equipped with a stirring blade, a cooling tube, and a dropping funnel, and the mixture was heated to 80 ° C. to dissolve uniformly. Next, 3.3 parts by mass of a 3% aqueous solution of potassium peroxodisulfate was added at the same temperature, and then a mixture consisting of 50 parts by mass of methyl methacrylate (MMA), 0.22 parts by mass of n-octyl mercaptan (nOM), and 0.25 parts by mass of a surfactant ("Nikkol ECT-3NEX" manufactured by Nikko Chemicals Co., Ltd.) was dropped from the dropping funnel over 60 minutes to form a first layer. After the dropwise addition, the reaction was continued for another 30 minutes at 80 ° C., and it was confirmed by gas chromatography that 99% or more of each monomer was consumed.

Next, a mixture consisting of 50 parts by mass of MMA, 0.22 parts by mass of nOM, and 0.25 parts by mass of a surfactant (Nikkol ECT-3NEX manufactured by Nikko Chemicals Co., Ltd.) was added dropwise to the obtained copolymer latex from a dropping funnel over a period of 60 minutes to form a second layer. After completion of the dropping, the reaction was continued for another 30 minutes at 80° C., and the polymerization was terminated when it was confirmed by gas chromatography that 99% or more of each monomer had been consumed.
In this production example, since the monomer compositions in the first and second emulsion polymerization stages were the same, the boundary between the first and second layers is not necessarily clear.
The particle size distribution of the particles in the obtained latex was measured. D50 (median diameter) was 0.20 μm, and (D90-D10)/D50 was 0.40.

The obtained latex was cooled at -30°C for 24 hours to freeze and aggregate, and then the aggregates were melted and removed. They were dried under reduced pressure at 80°C for one day to obtain powdered acrylic resin microparticles (B-1). The acetone insoluble content was 0%, the weight average molecular weight (Mw) was 71,000, and the glass transition temperature (Tg) was 120°C. The particle structure and physical properties are shown in Table 1.

[Production Example 2] (Production of acrylic resin fine particles (B-2))
In a nitrogen atmosphere, 150 parts by mass of distilled water, 0.03 parts by mass of an emulsifier ("Nikkol ECT-3NEX" manufactured by Nikko Chemicals Co., Ltd.), and 0.1 parts by mass of sodium carbonate were placed in a polymerization vessel equipped with a stirring blade, a cooling tube, and a dropping funnel, and were heated to 80° C. to dissolve uniformly. Next, 3.3 parts by mass of a 3% aqueous solution of potassium peroxodisulfate was added at the same temperature, and then a mixture consisting of 45 parts by mass of methyl methacrylate (MMA), 5 parts by mass of methyl acrylate (MA), 0.5 parts by mass of hexanediol dimethacrylate (HDDMA), 0.22 parts by mass of n-octyl mercaptan (nOM), and 0.25 parts by mass of a surfactant ("Nikkol ECT-3NEX" manufactured by Nikko Chemicals Co., Ltd.) was dropped from the dropping funnel over 60 minutes to form a first layer. After the dropwise addition was completed, the reaction was continued at 80° C. for an additional 30 minutes, and it was confirmed by gas chromatography that 99% or more of each monomer had been consumed.

Next, a mixture consisting of 45 parts by mass of MMA, 5 parts by mass of MA, 0.5 parts by mass of HDDMA, 0.22 parts by mass of nOM, and 0.25 parts by mass of a surfactant ("Nikkol ECT-3NEX" manufactured by Nikko Chemicals Co., Ltd.) was added dropwise to the obtained copolymer latex from a dropping funnel over 60 minutes to form a second layer. After completion of the dropping, the reaction was continued for another 30 minutes at 80°C, and the polymerization was terminated when it was confirmed by gas chromatography that 99% or more of each monomer had been consumed.
In this production example, since the compositions of the monomer mixtures in the first and second emulsion polymerization stages were the same, the boundary between the first and second layers is not necessarily clear.
The particle size distribution of the particles in the obtained latex was measured. D50 (median diameter) was 0.22 μm, and (D90-D10)/D50 was 0.36.

The obtained latex was cooled at -30°C for 24 hours to freeze and aggregate, and then the aggregates were melted and removed. They were dried under reduced pressure at 80°C for one day to obtain powdered acrylic resin microparticles (B-2). The acetone insoluble content was 100%. Since these acrylic resin microparticles have a crosslinked structure, they are insoluble in THF, and the weight average molecular weight (Mw) was unmeasurable. The glass transition temperature (Tg) was 103°C. The particle structure and physical properties are shown in Table 1.

[Production Example 3] (Production of acrylic resin fine particles (BC-3))
A mixture consisting of 100 parts by mass of methyl methacrylate (MMA), 0.29 parts by mass of n-octyl mercaptan (nOM), and 0.10 parts by mass of a peroxide radical polymerization initiator (NOF Corp.'s "Perocta O") and 200 parts by mass of distilled water were charged into a polymerization vessel equipped with a stirring blade, a cooling tube, and a dropping funnel under a nitrogen atmosphere. The mixture was stirred and mixed at a rotation speed of 150 rpm to form a suspension, and a polymerization reaction was carried out at 75°C for 3 hours. The polymerization was terminated when it was confirmed by gas chromatography that 99% or more of each monomer had been consumed. Particles were separated from the resulting suspension by centrifugal dehydration and washed with water.
The washed particles were redispersed in water, and the particle size distribution of the particles in the resulting aqueous dispersion was measured to find that D50 (median diameter) was 423 μm and (D90−D10)/D50 was 1.42.
The particles after washing were dried at 80° C. for 1 day to obtain bead-like acrylic resin particles (BC-3). The weight average molecular weight (Mw) was 85,000 and the glass transition temperature (Tg) was 120° C. The particle structure and physical properties are shown in Table 1.

[Production Example 4] (Production of acrylic resin fine particles (BC-4))
In a nitrogen atmosphere, 150 parts by mass of distilled water, 0.01 parts by mass of an emulsifier ("Nikkol ECT-3NEX" manufactured by Nikko Chemicals Co., Ltd.), and 0.1 parts by mass of sodium carbonate were placed in a polymerization vessel equipped with a stirring blade, a cooling tube, and a dropping funnel, and were heated to 80 ° C. to dissolve uniformly. Next, 3.3 parts by mass of a 3% aqueous solution of potassium peroxodisulfate was added at the same temperature, and then a mixture consisting of 50 parts by mass of methyl methacrylate (MMA) and 0.22 parts by mass of n-octyl mercaptan (nOM) was dropped from the dropping funnel over 60 minutes to form a first layer. After completion of the dropping, the reaction was continued for another 30 minutes at 80 ° C., and it was confirmed by gas chromatography that 99% or more of each monomer was consumed.

Next, a mixture consisting of 50 parts by mass of MMA, 0.22 parts by mass of nOM, and 0.25 parts by mass of a surfactant (Nikkol ECT-3NEX manufactured by Nikko Chemicals Co., Ltd.) was added dropwise to the obtained copolymer latex from a dropping funnel over a period of 60 minutes to form a second layer. After completion of the dropping, the reaction was continued for another 30 minutes at 80° C., and the polymerization was terminated when it was confirmed by gas chromatography that 99% or more of each monomer had been consumed.
In this production example, since the monomer compositions in the first and second emulsion polymerization stages were the same, the boundary between the first and second layers is not necessarily clear.
The obtained latex is referred to as "latex of particles (ii)". The particle size distribution of the particles in the obtained latex was measured. D50 (median diameter) was 0.90 μm.

The latex obtained in Production Example 1 is referred to as "latex of particle (i)". 25 parts by mass of latex of particle (ii) was added to 100 parts by mass of latex of particle (i) and mixed. The particle size distribution of the particles in the obtained mixed latex was measured. D50 (median diameter) was 0.21 μm, and (D90-D10)/D50 was 3.51.
The obtained latex was cooled at -30°C for 24 hours to freeze and aggregate, and then the aggregate was melted and taken out. It was dried under reduced pressure at 80°C for 1 day to obtain powdered acrylic resin fine particles (BC-4). The acetone insoluble content was 0%, the weight average molecular weight (Mw) was 70,000, and the glass transition temperature (Tg) was 120°C. The particle structure and physical properties are shown in Table 1.

[Production Example 5] (Production of aromatic vinyl resin fine particles (SC-1))
In a nitrogen atmosphere, 150 parts by mass of distilled water, 1.3 parts by mass of an emulsifier ("Neopelex G-15" manufactured by Kao Corporation), and 1.0 parts by mass of a dispersant ("Poise 520" manufactured by Kao Corporation) were placed in a polymerization vessel equipped with a stirring blade, a cooling tube, and a dropping funnel, and were heated to 80°C to dissolve uniformly. Next, at the same temperature, 3.3 parts by mass of a 3% aqueous solution of potassium peroxodisulfate was added, and then a mixture consisting of 50 parts by mass of styrene (St), 0.22 parts by mass of n-octyl mercaptan (nOM), and 0.25 parts by mass of a surfactant ("Adekacol CS-141E" manufactured by ADEKA Corporation) was dropped from the dropping funnel over 60 minutes to form a first layer. After completion of the dropping, the reaction was continued for another 30 minutes at 80°C, and it was confirmed by gas chromatography that 99% or more of each monomer was consumed.

Then, a mixture consisting of 50 parts by mass of styrene (St), 0.22 parts by mass of n-octyl mercaptan (nOM), and 0.25 parts by mass of a surfactant (ADEKA Corp.'s "ADEKACOL CS-141E") was added dropwise from a dropping funnel to the obtained copolymer latex over a period of 60 minutes to form a second layer. After the addition was completed, the reaction was continued for another 30 minutes at 80°C, and the polymerization was terminated when it was confirmed by gas chromatography that at least 99% of each monomer had been consumed. The particle size distribution of the particles in the obtained latex was measured. The D50 (median diameter) was 0.20 μm, and the particle size distribution was 0.40.

The obtained latex was cooled at -30°C for 24 hours to freeze and aggregate, and then the aggregates were melted and removed. They were dried under reduced pressure at 80°C for one day to obtain powdered aromatic vinyl resin microparticles (SC-1). The weight-average molecular weight (Mw) was 76,000 and the glass transition temperature (Tg) was 102°C. The particle structure and physical properties are shown in Table 1.

[Example (E1)]
95 parts by mass of the curable compound (A-1) and 5 parts by mass of the acrylic resin fine particles (B-1) were mixed twice (2-pass treatment) at 25°C under the condition of a roll gap of 10 μm using a three-roll mill (EXAKT 50I manufactured by EXAKT) to obtain a curable resin composition (X-1). The blending composition and evaluation results are shown in Table 2.

[Examples (E2) to (E11), Comparative Examples (EC1) to (EC5)]
Curable resin compositions (X-1) to (X-11) and (XC-1) to (XC-5) were obtained in the same manner as in Example (E1), except that the blending composition was changed as shown in Table 2 or Table 3. The evaluation results are shown in Tables 2 and 3. The curable resin composition (XC-3) obtained in Comparative Example (EC3) was solid at room temperature, and viscosity measurement with a rheometer was impossible. The curable resin composition (XC-4) obtained in Comparative Example (EC4) had unstable viscosity measurements with a rheometer, and viscosity measurement was impossible.

[Summary of results]
In Examples (E1) to (E11), a curable resin composition was prepared containing 50 to 95% by mass of a curable compound (A) and 50 to 5% by mass of an acrylic resin fine particle (B) satisfying 0<D50≦1.0 and (D90-D10)/D50≦1.0. The initial viscosity (ηx) and the viscosity (ηy) in the high shear rate range of the obtained curable resin compositions were at least 10 Pa·s or less. The obtained curable resin compositions had at least a sufficiently low ηy, and had a relatively low viscosity and good fluidity during operations such as casting, coating, and impregnation in which high shear force is applied to the curable resin composition. The curable resin compositions obtained in these Examples all had an ηz/ηx of 3 or more (40 or more), and the viscosity effectively increased after heating, allowing a (semi-)cured product having low tackiness to be obtained.

In the curable resin composition obtained in Comparative Example (EC1) using the aromatic vinyl resin fine particles (DC) for comparison, after the preparation of the curable resin composition, before heating, the resin fine particles were dissolved in the curable compound. Therefore, the obtained curable resin composition had a ηz/ηx ratio of less than 3, and the viscosity increase after heating was poor.
The curable resin composition obtained in Comparative Example (EC2) had a poor combination of the curable compound (A) and the acrylic resin fine particles (B), and after the preparation of the curable resin composition, the resin fine particles were dissolved in the curable compound before heating. Therefore, the obtained curable resin composition had high initial viscosity (ηx) and high shear rate viscosity (ηy), and had poor flowability.
The curable resin composition obtained in Comparative Example (EC3) in which the content of the curable compound (A) was less than 50 mass% was solid at room temperature (20 to 25° C.) and had poor fluidity before heating.

The curable resin composition obtained in Comparative Example (EC4) using the comparative acrylic resin microparticles (BC) had an unstable flow state before heating due to the particle size and particle size distribution of the acrylic resin microparticles.
The curable resin composition obtained in Comparative Example (EC5) using the acrylic resin microparticles for Comparative Example (BC-4) had high initial viscosity (ηx) and viscosity in the high shear rate range (ηy) due to the particle size distribution of the acrylic resin microparticles, and had poor fluidity.

The present invention is not limited to the above-mentioned embodiments and examples, and design changes are possible as long as they do not deviate from the spirit of the present invention.

This application claims priority based on Japanese Patent Application No. 2023-008660, filed on January 24, 2023, the entire disclosure of which is incorporated herein by reference.

Claims (9)

A curable resin composition comprising 50 to 95% by mass of a curable compound (A) and 50 to 5% by mass of acrylic resin fine particles (B),
The acrylic resin fine particles (B) have a cumulative 10% particle diameter D10 [μm], a cumulative 50% particle diameter D50 [μm], and a cumulative 90% particle diameter D90 [μm] in a volume-based cumulative particle diameter distribution that satisfy 0<D50≦1.0 and 0<[(D90−D10)/D50]≦1.0,
a viscosity of the curable resin composition measured under conditions of 25°C and a shear rate of 10 sec ^-1 is ηx, a viscosity of the curable resin composition measured under conditions of 25°C and a shear rate of 3000 sec ^-1 is ηy, and the curable resin composition is heated from 25°C to 120°C at a heating rate of 5°C/min and then cooled from 120°C to 25°C at a heating rate of 5°C/min, and then the viscosity of the curable resin composition measured under conditions of 25°C and a shear rate of 10 sec ^-1 is ηz, wherein at least ηy of ηx and ηy is more than 0 Pa s and 10 Pa s or less, and ηz/ηx is 3 or more. The curable resin composition according to claim 1, in which D50 is 0.1 μm or more and (D90-D10)/D50 is 0.1 or more. The curable resin composition according to claim 1, in which ηz/ηx is 20,000 or less. The curable resin composition according to claim 1, wherein the acrylic resin fine particles (B) contain one or more methacrylic resins (M). The curable resin composition according to claim 4, wherein the content of methacrylic acid ester units in the acrylic resin fine particles (B) is 90 to 100 mass %. The curable resin composition according to claim 5, wherein the content of methyl methacrylate in the acrylic resin fine particles (B) is 90 to 100 mass %. The curable resin composition according to claim 1, wherein the glass transition temperature of the acrylic resin fine particles (B) is 100°C or higher. The curable resin composition according to claim 1, wherein the curable compound (A) comprises one or more curable compounds selected from the group consisting of (meth)acryloyl group-containing monomers, (meth)acryloyl group-containing oligomers, and epoxy resins. A method for producing a curable resin composition comprising 50 to 95% by mass of a curable compound (A) and 50 to 5% by mass of acrylic resin fine particles (B), comprising the steps of:
the viscosity of the curable resin composition measured under conditions of 25° C. and a shear rate of 10 sec ^-1 is ηx, the viscosity of the curable resin composition measured under conditions of 25° C. and a shear rate of 3000 sec ^-1 is ηy, and the curable resin composition is heated from 25° C. to 120° C. at a temperature increase rate of 5° C./min, and then cooled from 120° C. to 25° C. at a temperature decrease rate of 5° C./min, and then the viscosity of the curable resin composition measured under conditions of 25° C. and a shear rate of 10 sec ^-1 is ηz, of ηx and ηy, at least ηy is more than 0 Pa s and 10 Pa s or less, and ηz/ηx is 3 or more;
a step (S1) of preparing acrylic resin microparticles (B) having a cumulative 10% particle diameter D10 [μm], a cumulative 50% particle diameter D50 [μm], and a cumulative 90% particle diameter D90 [μm] in a volume-based cumulative particle diameter distribution that satisfy 0<D50≦1.0 and 0<[(D90-D10)/D50]≦1.0;
A method for producing a curable resin composition, comprising: a step (S2) of mixing the curable compound (A) and the acrylic resin fine particles (B).