JP7750237B2 - Curable resin composition, electrical/electronic component, and method for manufacturing electrical/electronic component - Google Patents

Description

The present invention relates to a curable resin composition, an electrical/electronic component, and a method for manufacturing an electrical/electronic component.

In electronic devices such as motors, coils, and electronic control units installed in automobiles, etc., a structure is required that can secure the components to prevent damage due to vibration and prevent the intrusion of water and corrosive gases in order to protect the wiring board and the electronic components mounted on that wiring board. In such cases, a structure is generally used in which the entire electronic component is sealed and secured in place using a material known as an encapsulant.

For example, Patent Document 1 discloses an encapsulating epoxy resin composition used to form an encapsulant that seals the gap between a wiring board and an electronic component. Patent Document 2 discloses an unsaturated polyester resin composition for molding electrical and electronic components, containing 7 to 15% by weight of a novolac vinyl ester resin, 2 to 5% by weight of a bis-unsaturated polyester resin, and 65 to 80% by weight of magnesium oxide.

JP 2014-148586 A Japanese Patent Application Laid-Open No. 2004-27019

However, epoxy resins have a problem in that their raw material cost is relatively high compared to other resins, making them difficult to use in large products. Furthermore, epoxy resin compositions have a high molding temperature of 170-180°C and a long curing time, leaving room for improvement in terms of reliability, productivity, and cost of electronic devices. The resin composition disclosed in Patent Document 2 also leaves room for further improvement in terms of adhesion to substrates.

The present invention has been made to solve the above-mentioned problems, and aims to provide a curable resin composition that produces a cured product with excellent adhesion to substrates, particularly poorly adhesive resin substrates. Furthermore, the present invention aims to provide an electrical/electronic component that uses a cured product with excellent adhesion as an encapsulant, and a method for producing the same.

The present invention includes the following aspects.
[1]
(A) curable resin,
(B) an ethylenically unsaturated monomer,
(C) an acidic surfactant,
(D) inorganic filler,
(E) a thermal polymerization initiator, and optionally a saturated polybasic acid;
The (A) curable resin contains at least a vinyl ester resin,
the mixture of the (A) curable resin, the (B) ethylenically unsaturated monomer, and the saturated polybasic acid has an acid value of 12 mgKOH/g or less;
the mixture of the (A) curable resin, the (B) ethylenically unsaturated monomer, the (C) acidic surfactant, and the saturated polybasic acid has an acid value of 10 mgKOH/g or more;
The (C) acidic surfactant is a low-volatile substance having an acid value of 20 mgKOH/g or more.
Curable resin composition.
[2]
The curable resin composition according to [1], wherein the acid value of the acidic surfactant (C) is 30 to 190 mg KOH/g.
[3]
The curable resin composition according to either [1] or [2], wherein the (C) acidic surfactant is a phosphate ester compound.
[4]
The curable resin composition according to any one of [1] to [3], wherein the (B) ethylenically unsaturated monomer is styrene.
[5]
per 100 parts by mass of the total of (A) the curable resin, (B) the ethylenically unsaturated monomer, and any saturated polybasic acid,
(A) 5 to 95 parts by mass of a curable resin,
(B) 5 to 95 parts by mass of an ethylenically unsaturated monomer,
(C) 0.1 to 10 parts by mass of an acidic surfactant,
(D) 200 to 700 parts by mass of an inorganic filler; and (E) 0.1 to 20 parts by mass of a thermal polymerization initiator.
[6]
The curable resin composition according to any one of [1] to [5], further comprising (F) glass fibers.
[7]
The curable resin composition according to any one of [1] to [6], further comprising (G) a low shrinkage agent.
[8]
An electric/electronic part comprising a cured product of the curable resin composition according to any one of [1] to [7].
[9]
A method for producing an electric/electronic component, comprising: a step of encapsulating components of the electric/electronic component with the curable resin composition according to any one of [1] to [7]; and a step of heat-curing the curable resin composition.

The present invention provides a curable resin composition that produces a cured product with excellent adhesion to substrates, particularly poorly adhesive resin substrates. Furthermore, it also provides a cured product with excellent adhesion obtained by curing the curable resin composition, an electrical/electronic component comprising the same, and a method for producing the same.

The following describes in detail an embodiment of the present invention. However, the present invention is not limited to the embodiment described below.

In this specification, "(meth)acrylic acid" means methacrylic acid or acrylic acid, and "(meth)acrylate" means acrylate or methacrylate.

"Ethylenically unsaturated bond" means a double bond formed between carbon atoms excluding carbon atoms forming an aromatic ring, and "ethylenically unsaturated monomer" means a monomer having an ethylenically unsaturated bond.

1. Curable Resin Composition The curable resin composition of one embodiment contains (A) a curable resin, (B) an ethylenically unsaturated monomer, (C) an acidic surfactant, (D) an inorganic filler, and (E) a thermal polymerization initiator.

If necessary, the curable resin composition may further contain at least one selected from the group consisting of saturated polybasic acids, (F) glass fibers, and (G) low-shrinkage agents.

[(A) Curable resin]
The (A) curable resin is not particularly limited as long as it is a curable resin commonly used in sealing material applications. For example, a resin having a functional group capable of forming a crosslinked structure when the curable resin composition is heat-cured is preferred. Specific examples of the (A) curable resin include (A-1) vinyl ester resin, (A-2) unsaturated polyester resin, (A-3) urethane (meth)acrylate resin, (A-4) diallyl phthalate resin, and (A-5) epoxy resin. From the viewpoints of material cost and moldability, the (A) curable resin preferably contains at least (A-1) vinyl ester resin. The (A) curable resin may be used alone or in combination of two or more types.

The content of (A-1) vinyl ester resin in (A) curable resin is preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. When the content of (A-1) vinyl ester resin is 75% by mass or more, the material costs of the curable resin composition can be reduced, and a cured product with better moldability and adhesion can be obtained. There is no particular upper limit to the content of (A-1) vinyl ester resin in (A) curable resin. For example, it may be 100% by mass, 97% by mass, or 95% by mass.

The content of (A) curable resin is preferably 5 to 95 parts by mass, more preferably 20 to 75 parts by mass, and even more preferably 30 to 50 parts by mass, per 100 parts by mass of the total of (A) curable resin, (B) ethylenically unsaturated monomer, and optional saturated polybasic acid.

<(A-1) Vinyl ester resin>
(A-1) vinyl ester resins are generally compounds having a radically polymerizable unsaturated bond obtained by a ring-opening reaction between (a) an epoxy group in an epoxy compound having two or more epoxy groups and (b) a carboxy group in an unsaturated monobasic acid having a radically polymerizable unsaturated bond and a carboxy group. (A-1) vinyl ester resins are described, for example, in the Polyester Resin Handbook (published by The Nikkan Kogyo Shimbun, Ltd. in 1988).

(A-1) Vinyl ester resin may be used alone or in combination of two or more types. For ease of handling, (A-1) vinyl ester resin is generally diluted with (B) ethylenically unsaturated monomer before use. By using (A-1) vinyl ester resin, it is possible to reduce the material costs of the curable resin composition and obtain a cured product with excellent adhesion.

The number average molecular weight (Mn) of the vinyl ester resin (A-1) can be adjusted depending on the desired physical properties, but from the viewpoint of handling, it is preferably in the range of 500 to 5,000. In this specification, the "weight average molecular weight" and "number average molecular weight" refer to values measured using gel permeation chromatography (GPC) under the following conditions at room temperature (23°C) and determined using a standard polystyrene calibration curve.
Apparatus: Shodex (registered trademark) GPC-101 (Showa Denko K.K.)
Column: Shodex (registered trademark) LF-804 (Showa Denko K.K.)
Column temperature: 40°C
Sample: 0.2% by mass solution of sample in tetrahydrofuran Flow rate: 1 mL/min Eluent: tetrahydrofuran Detector: Shodex (registered trademark) RI-71S (Showa Denko K.K.)

((a) Epoxy Compound)
The (a) epoxy compound is not particularly limited as long as it is a compound having two or more epoxy groups. Preferably, it is at least one selected from the group consisting of bisphenol-type epoxy compounds and novolac phenol-type epoxy compounds, and more preferably a bisphenol-type epoxy compound. By using the (A-1) vinyl ester resin using the (a) epoxy compound as a raw material, the mechanical strength and corrosion resistance of the cured product are further improved.

Examples of bisphenol-type epoxy compounds include those obtained by reacting bisphenol compounds such as bisphenol A, bisphenol F, bisphenol S, and tetrabromobisphenol A with epichlorohydrin and/or methylepichlorohydrin; and those obtained by reacting a glycidyl etherified compound of one or more of the above bisphenol compounds with epichlorohydrin and/or methylepichlorohydrin as a condensate of one or more of the above bisphenol compounds. From the standpoint of durability, reaction products of bisphenol compounds with epichlorohydrin are preferred, and reaction products of bisphenol A with epichlorohydrin are more preferred.

Novolak phenol-type epoxy compounds include, for example, those obtained by reacting phenol novolak or cresol novolak with epichlorohydrin and/or methyl epichlorohydrin.

((b) Unsaturated monobasic acid)
The unsaturated monobasic acid (b) is not particularly limited as long as it is a monocarboxylic acid having an ethylenically unsaturated bond. Preferred are methacrylic acid, acrylic acid, crotonic acid, cinnamic acid, etc., more preferably acrylic acid or methacrylic acid, and even more preferably methacrylic acid from the viewpoint of the corrosion resistance of the cured product.

((A-1) Method for synthesizing vinyl ester resin)
The vinyl ester resin (A-1) can be synthesized by a known synthesis method, for example, by adding an unsaturated monobasic acid (b) to an esterification catalyst and an epoxy compound (a) in a reaction vessel capable of being heated and stirred, and reacting the components at a temperature of 70 to 150°C, preferably 80 to 140°C, and more preferably 90 to 130°C.

In addition, any unreacted (b) unsaturated monobasic acid remaining after synthesizing (A-1) vinyl ester resin is considered to be (B) ethylenically unsaturated monomer, as described below.

As an esterification catalyst, known catalysts such as tertiary amines such as triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, and diazabicyclooctane, triphenylphosphine, and diethylamine hydrochloride can be used.

The compounding ratio of the (a) epoxy compound and the (b) unsaturated monobasic acid is preferably such that the total number of carboxy groups in the (b) unsaturated monobasic acid is 0.3 to 1.2 moles per mole of the total number of epoxy groups in the (a) epoxy compound, more preferably 0.4 to 1.1 moles, and even more preferably 0.5 to 1.0 moles. When the total number of carboxy groups in the (b) unsaturated monobasic acid is 0.3 moles or more, a cured product with sufficient hardness can be obtained when the curable resin composition is cured. On the other hand, when the total number of carboxy groups in the (b) unsaturated monobasic acid is 1.2 moles or less, the amount of unreacted (b) unsaturated monobasic acid can be reduced during the synthesis of the (A-1) vinyl ester resin, thereby reducing the acid value of the mixture of the (A) component and the (B) component and resulting in a cured product with better adhesion.

After synthesizing the (A-1) vinyl ester resin, any unreacted (b) unsaturated monobasic acid is not removed and can be used as is as the (B) ethylenically unsaturated monomer in the curable resin composition. When the curable resin composition is heat-cured, the unreacted (b) unsaturated monobasic acid may volatilize or bleed out, affecting the adhesion of the cured product. Therefore, it is desirable to reduce the content of unreacted (b) unsaturated monobasic acid as much as possible. For example, the content of unreacted (b) unsaturated monobasic acid relative to the total amount of the (A-1) vinyl ester resin and unreacted (b) unsaturated monobasic acid is preferably 5% by mass or less, and more preferably 3% by mass or less.

<(A-2) Unsaturated Polyester Resin>
The unsaturated polyester resin (A-2) is a polycondensate of a polyhydric alcohol and an unsaturated polybasic acid, or a polycondensate of a polyhydric alcohol, an unsaturated polybasic acid, and a saturated polybasic acid, and is not particularly limited.

(A-2) Unsaturated polyester resins may be used alone or in combination of two or more. By using (A-2) unsaturated polyester resin, a cured product with excellent mechanical strength and heat resistance can be obtained.

In this disclosure, styrene monomers and the like contained in general unsaturated polyester resins are classified as (B) ethylenically unsaturated monomers.

There are no particular restrictions on the polyhydric alcohol, as long as it is a compound containing two or more hydroxyl groups. Examples of polyhydric alcohols include alkylene glycols such as ethylene glycol, propylene glycol, butanediol, diethylene glycol, dipropylene glycol, triethylene glycol, pentanediol, hexanediol, neopentanediol, tetraethylene glycol, polyethylene glycol, 2-methyl-1,3-propanediol, 1,4-cyclohexanedimethanol, and hydrogenated bisphenol A; bisphenol A; alkylene oxide-modified bisphenol A such as ethylene oxide adduct of bisphenol A and propylene oxide adduct of bisphenol A; and glycerin. From the viewpoints of heat resistance and mechanical strength of the cured product and fluidity of the curable resin composition during molding, propylene glycol, dipropylene glycol, neopentanediol, hydrogenated bisphenol A, and bisphenol A are preferred, with propylene glycol being more preferred. Polyhydric alcohols may be used alone or in combination.

The unsaturated polybasic acid is not particularly limited as long as it is a compound having an ethylenically unsaturated bond and two or more carboxy groups, or an acid anhydride thereof, and known compounds can be used. Unsaturated polybasic acids having 4 to 6 carbon atoms or an acid anhydride thereof are particularly preferred, as they are less expensive and produce curable resin compositions with superior mechanical strength and heat resistance in the cured product. Examples of unsaturated polybasic acids include maleic acid, maleic anhydride, fumaric acid, citraconic acid, itaconic acid, and chloromaleic acid. Unsaturated polybasic acids selected from fumaric acid, maleic acid, maleic anhydride, and itaconic acid are more preferred. The unsaturated polybasic acids may be used alone or in combination.

Preferred combinations of polyhydric alcohols and unsaturated polybasic acids include, for example, a combination of fumaric acid and neopentanediol, a combination of maleic acid and dipropylene glycol, a combination of maleic anhydride and propylene glycol, a combination of fumaric acid and propylene glycol, and a combination of fumaric acid, hydrogenated bisphenol A, and propylene glycol. The combinations of fumaric acid and propylene glycol and fumaric acid, hydrogenated bisphenol A, and propylene glycol are preferred because they are lower cost and produce curable resin compositions with higher heat distortion temperatures, superior mechanical strength, and heat resistance.

The saturated polybasic acid is not particularly limited as long as it is a compound or anhydride thereof that does not have an ethylenically unsaturated bond and has two or more carboxy groups, and known compounds can be used. Examples of saturated polybasic acids include aromatic saturated polybasic acids or anhydrides thereof, such as phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, nitrophthalic acid, and halogenated phthalic anhydrides; aliphatic saturated polybasic acids, such as succinic acid, adipic acid, sebacic acid, oxalic acid, malonic acid, azelaic acid, and glutaric acid; and hexahydrophthalic anhydride. The saturated polybasic acids may be used alone or in combination.

The weight-average molecular weight (Mw) of the (A-2) unsaturated polyester resin is not particularly limited. The weight-average molecular weight of the (A-2) unsaturated polyester resin is preferably 2,000 to 25,000, more preferably 3,000 to 20,000, and even more preferably 3,500 to 10,000. If the weight-average molecular weight is 2,000 to 25,000, the moldability of the curable resin composition will be even better.

The degree of unsaturation of the (A-2) unsaturated polyester resin is preferably 50 to 100 mol%, more preferably 60 to 100 mol%, and even more preferably 70 to 100 mol%. When the degree of unsaturation is within the above range, the moldability of the curable resin composition containing the (A-2) unsaturated polyester resin is improved.

The degree of unsaturation of the (A-2) unsaturated polyester resin can be calculated by the following formula using the number of moles of the unsaturated polybasic acid and saturated polybasic acid used as raw materials.
Degree of unsaturation (mol %)={(number of moles of unsaturated polybasic acid×number of ethylenically unsaturated bonds per molecule of unsaturated polybasic acid)/(number of moles of unsaturated polybasic acid+number of moles of saturated polybasic acid)}×100

((A-2) Method for synthesizing unsaturated polyester resin)
The unsaturated polyester resin (A-2) can be synthesized by a known method using the above-mentioned raw materials. The various conditions for synthesizing the unsaturated polyester resin (A-2) are appropriately set depending on the raw materials used and their amounts.

Generally, the esterification reaction can be carried out in a stream of inert gas such as nitrogen gas at a temperature of 140°C to 230°C under pressure or reduced pressure. An esterification catalyst can be used in the esterification reaction, if necessary. Examples of esterification catalysts include well-known catalysts such as manganese acetate, dibutyltin oxide, stannous oxalate, zinc acetate, and cobalt acetate. The esterification catalysts can be used alone or in combination.

In addition, any unreacted unsaturated polybasic acid remaining after synthesizing (A-2) unsaturated polyester resin is considered to be (B) ethylenically unsaturated monomer, as described below.

In order to increase the molecular weight by improving the reaction rate and improve adhesion by reducing the acid value, it is preferable that the equivalent weight of the hydroxyl groups of the polyhydric alcohol be in the range of 0.9 to 1.2 relative to the total amount of carboxyl groups of the unsaturated polybasic acid and any saturated polybasic acid.

(A-2) After synthesizing the unsaturated polyester resin, any unreacted unsaturated polybasic acid and any saturated polybasic acid may be present in the curable resin composition without being removed.

<(A-3) Urethane (meth)acrylate resin>
As the (A-3) urethane (meth)acrylate resin, for example, a resin obtained by introducing (meth)acryloyl groups into the hydroxyl groups or isocyanato groups at both ends of a polyurethane obtained by reacting a polyhydric isocyanate with a polyhydric alcohol can be used.

As polyhydric alcohols, the compounds described above as raw materials for (A-2) unsaturated polyester resin can be used without any particular restrictions.

Examples of polyisocyanates include aliphatic polyisocyanates such as hexamethylene diisocyanate, lysine diisocyanate, lysine triisocyanate, and trimethylhexane diisocyanate; cyclic aliphatic polyisocyanates such as hydrogenated xylylene diisocyanate, isophorone diisocyanate, methylcyclohexane-2,4 (or 2,6)-diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,3-(isocyanatomethyl)cyclohexane; aromatic polyisocyanates such as tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, and triphenylmethane triisocyanate; and adducts, isocyanurates, and biurets of these polyisocyanates. Polyisocyanates may be used alone or in combination.

When introducing a (meth)acryloyl group, for example, a method can be used in which a terminal isocyanato group is reacted with a hydroxyl group-containing (meth)acrylic compound, or a method can be used in which a terminal hydroxyl group is reacted with an isocyanato group-containing (meth)acrylic compound such as 2-(meth)acryloyloxyethyl isocyanate, 2-(meth)acryloyloxypropyl isocyanate, or 1,1-bis(acryloyloxymethyl)ethyl isocyanate. Examples of hydroxyl group-containing (meth)acrylic compounds include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, caprolactone-modified hydroxyalkyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, tris(hydroxyethyl)isocyanuric acid di(meth)acrylate, pentaerythritol tri(meth)acrylate, glycerin mono(meth)acrylate, and hydroxyethyl acrylamide, with 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, caprolactone-modified hydroxyalkyl (meth)acrylate, and hydroxyethyl acrylamide being preferred. The isocyanato group-containing (meth)acrylic compounds and hydroxyl group-containing (meth)acrylic compounds may each be used alone or in combination of two or more.

In addition, any unreacted hydroxyl group-containing (meth)acrylic compound or unreacted isocyanato group-containing (meth)acrylic compound remaining after synthesizing (A-3) urethane (meth)acrylate resin is considered to be (B) ethylenically unsaturated monomer, as described below.

<(A-4) Diallyl Phthalate Resin>
The diallyl phthalate resin (A-4) is an oligomer obtained by an esterification reaction between diallyl phthalate and a polyhydric alcohol, and any conventionally known diallyl phthalate resin can be used without particular limitation. The diallyl phthalate resin (A-4) may be used alone or in combination of two or more kinds.

In addition, after synthesizing (A-4) diallyl phthalate resin, any unreacted diallyl phthalate may remain in the curable resin composition without being removed.

<(A-5) Epoxy Resin>
As the epoxy resin (A-5), the compounds described in the section (a) Epoxy Compounds can be used. The epoxy resin (A-5) may be used alone or in combination of two or more kinds.

[(B) Ethylenically unsaturated monomer]
The (B) ethylenically unsaturated monomer is not particularly limited as long as it is a monomer having an ethylenically unsaturated bond and does not fall under the category of (C) acidic surfactant, which will be described later. The (B) ethylenically unsaturated monomer may be used alone or in combination of two or more. From the viewpoint of reducing the acid value of the mixture of component (A), component (B), and any saturated polybasic acid, a compound having no carboxy group is preferred.

Specific examples include vinyl compounds such as styrene, vinyltoluene, t-butylstyrene, methoxystyrene, divinylbenzene, vinylnaphthalene, and acenaphthylene; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, furfuryl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and phenyl (meth) Examples of (meth)acrylates include acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, allyl (meth)acrylate, isobornyl (meth)acrylate, acetoacetoxyethyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecanol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate. From the viewpoint of copolymerizability with component (A), vinyl compounds are preferred, and one or more selected from styrene, vinyltoluene, t-butylstyrene, and methoxystyrene are more preferred, with styrene being even more preferred.

The content of the (B) ethylenically unsaturated monomer is preferably 5 to 95 parts by mass, more preferably 25 to 80 parts by mass, and even more preferably 50 to 70 parts by mass, per 100 parts by mass of the total of the (A) curable resin, the (B) ethylenically unsaturated monomer, and the optional saturated polybasic acid. When the content of the (B) ethylenically unsaturated monomer is 5 parts by mass or more, the viscosity of the curable resin composition can be adjusted within an appropriate range, and good moldability is achieved. When the content of the (B) ethylenically unsaturated monomer is 95 parts by mass or less, the mechanical strength of the cured product is good.

The acid value of the mixture of (A) the curable resin, (B) the ethylenically unsaturated monomer, and any saturated polybasic acid is 12 mgKOH/g or less, preferably 11 mgKOH/g or less, and more preferably 10.5 mgKOH/g or less. The lower limit of the acid value of the mixture is not particularly limited, but may be, for example, 1 mgKOH/g or more, 3 mgKOH/g or more, or 5 mgKOH/g or more. The saturated polybasic acid may be unreacted saturated polybasic acid that remains when synthesizing (A) the curable resin. When the acid value of the mixture is 12 mgKOH/g or less, the adhesion of the cured product is good.

When the content of unreacted monomers during the synthesis of the (A) curable resin, for example, unreacted (b) unsaturated monobasic acid during the synthesis of the (A-1) vinyl ester resin, or unreacted unsaturated polybasic acid and saturated polybasic acid during the synthesis of the (A-2) unsaturated polyester resin, is high, the acid value of the mixture increases due to these unreacted monomers. When a curable resin composition containing such a mixture is heat-cured, the unreacted monomers volatilize or bleed out, which is thought to affect adhesion. Therefore, the acid value of the mixture can be used as an indicator of the adhesion of the cured product of the curable resin composition.

In this disclosure, the acid value is a value measured in accordance with JIS K0070:1992 and is measured using the following procedure.

Approximately 2 g of sample is accurately weighed into a 100 mL Erlenmeyer flask using a precision balance, and 10 mL of a 1:1 (by weight) ethanol/diethyl ether mixed solvent is added and dissolved. Furthermore, 1 to 3 drops of phenolphthalein ethanol solution are added to the container as an indicator, and the sample is thoroughly stirred until it becomes homogeneous. This is then titrated with 0.1 M potassium hydroxide ethanol solution, and the neutralization endpoint is determined when the indicator's pale red color persists for 30 seconds. The value obtained from the results using the following calculation formula (1) is the acid value of the mixture.
Acid value (mgKOH/g) = [B x f x 5.661]/S... (1)
In addition, B, f, and S in the calculation formula (1) are as follows.
B: Amount of 0.1 M potassium hydroxide ethanol solution used (mL)
f: Factor of 0.1 M potassium hydroxide ethanol solution (correction for variations due to reagent lots)
S: Amount of sample collected (g)

[(C) Acidic Surfactant]
The (C) acidic surfactant is not particularly limited as long as it is a low-volatile substance having a surface-active effect and an acid value of 20 mgKOH/g or more, and is a compound that is excellent in compatibility with the (A) curable resin and the (B) ethylenically unsaturated monomer, and in dispersibility of the (D) inorganic filler and the optional component (F) glass fiber, which will be described later. When a compound corresponds to both a saturated polybasic acid and a (C) acidic surfactant, the compound is classified as a (C) acidic surfactant.

In this disclosure, a low-volatile substance is a substance that has a weight retention rate of 90% or more when heated at 150°C for 60 minutes in an atmospheric environment. The molecular weight or weight-average molecular weight of the low-volatile substance is, for example, 500 or more, 1,000 or more, or 1,500 or more. There is no particular upper limit for the molecular weight or weight-average molecular weight of the low-volatile substance, but it may be, for example, 7,000 or less, 6,000 or less, or 5,000 or less.

As the (C) acidic surfactant, those generally known as dispersants or plasticizers for resin compositions can be suitably used. Low-volatility oligomers are preferred, and low-volatility oligomers having constituent components containing monomer units such as ethylene units, styrene units, ester units, ether units, and urethane units, and acid groups such as carboxy groups, sulfo groups, and phospho groups are more preferred. Phosphate ester compounds or carboxylic acid ester compounds are even more preferred, and phosphate ester compounds containing a long-chain polyester structure are even more preferred.

In order to improve the adhesion of the cured product, it is effective to improve the wettability of the curable resin composition with the substrate (adherend). For this reason, it is considered important that the curable resin composition have an acid value above a certain value. The use of a (C) acidic surfactant with an acid value of 20 mg KOH/g or more improves the adhesion of the cured product. Furthermore, to prevent the evaporation or bleed-out of the (C) acidic surfactant from affecting the adhesion of the cured product when the curable resin composition is heated and cured, a low-volatility (C) acidic surfactant is used.

Suitable examples of the phosphate ester compounds include those described in JP-A-61-194091, JP-A-3-112992, JP-A-2007-527896, and JP-A-2014-520127. Specific examples include phosphate triester compounds of methyl ester of 12-hydroxystearic acid polyester, and ester compounds of polyethylene glycol monomethyl ether and malic acid ester compounds with tetraphosphoric acid.

(C) Commercially available acidic surfactants can also be used, such as those manufactured by BYK Additives & Instruments under the product names BYK W-9010, BYK W-9011, BYK P-9051, BYK P-9050, BYK P-9060, BYK P-9065, BYK P-9080, and BYK P-9085. From the viewpoint of adhesion of the cured product, BYK W-9010 and BYK P-9051 are preferred.

The acid value of (C) the acidic surfactant is 20 mgKOH/g or more, preferably 30 to 190 mgKOH/g, more preferably 100 to 180 mgKOH/g, and even more preferably 120 to 160 mgKOH/g. If the acid value is less than 20 mgKOH/g, it is necessary to increase the amount of (C) the acidic surfactant to ensure the acid value of the curable resin composition, which can have a negative impact on the properties of the cured product, such as adhesion.

The content of (C) acidic surfactant is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 9 parts by mass, and even more preferably 1 to 8 parts by mass, per 100 parts by mass of the total of (A) curable resin, (B) ethylenically unsaturated monomer, and optional saturated polybasic acid. When the content of (C) acidic surfactant is 0.1 part by mass or more, the curable resin composition has a sufficient acid value, and a cured product with good adhesion can be obtained. When the content of (C) acidic surfactant is 10 parts by mass or less, there is no adverse effect on the properties of the cured product.

The acid value of the mixture of (A) curable resin, (B) ethylenically unsaturated monomer, (C) acidic surfactant, and any saturated polybasic acid is 10 mgKOH/g or more, preferably 10 to 30 mgKOH/g, and more preferably 11 to 20 mgKOH/g. When the acid value of the mixture is 10 mgKOH/g or more, the wettability of the curable resin composition to the adherend is improved, making it possible to obtain a cured product with sufficient adhesion.

[(D) Inorganic filler]
As the inorganic filler (D), a particulate material known in the technical field of the present invention can be used. By using the inorganic filler (D), it is possible to reduce the molding shrinkage rate of the molded article, adjust the viscosity of the curable resin composition to improve workability, or improve the strength of the molded article.

(D) Examples of inorganic fillers include calcium carbonate, silica, aluminum oxide, aluminum hydroxide, barium sulfate, calcium sulfate, calcium hydroxide, calcium oxide, magnesium oxide, magnesium hydroxide, wollastonite, clay, kaolin, mica, gypsum, silicic anhydride, and glass powder. Calcium carbonate, aluminum oxide, and aluminum hydroxide are preferred because they are inexpensive. (D) Inorganic fillers may be used alone or in combination of two or more.

The average particle size of the (D) inorganic filler is preferably 1 to 100 μm, more preferably 1 to 60 μm, and even more preferably 1 to 50 μm. If the average particle size of the (D) inorganic filler is 1 μm or more, particle aggregation can be suppressed. On the other hand, if the average particle size of the (D) inorganic filler is 100 μm or less, the moldability of the curable resin composition is good.

In this specification, "average particle size" refers to the 50% particle size (D50) in the volume-based cumulative particle size distribution measured using a laser diffraction/scattering particle size distribution analyzer (Microtrac Bell Co., Ltd., FRA).

(D) The shape of the inorganic filler is not particularly limited. Examples include approximately spherical, ellipsoidal, scaly, amorphous, etc.

The amount of (D) inorganic filler is preferably 200 to 700 parts by mass, and more preferably 300 to 600 parts by mass, per 100 parts by mass of the total of (A) curable resin, (B) ethylenically unsaturated monomer, and optional saturated polybasic acid. If the amount of (D) inorganic filler is 200 parts by mass or more, the mechanical properties of the cured product will be better. If the amount of (D) inorganic filler is 700 parts by mass or less, the (D) inorganic filler will be more uniformly dispersed in the curable resin composition, allowing for the production of a homogeneous molded product.

[(E) Thermal polymerization initiator]
The thermal polymerization initiator (E) is not particularly limited as long as it is a polymerization initiator that generates radicals upon heating, and examples thereof include peroxides such as diacyl peroxides, peroxyesters, hydroperoxides, dialkyl peroxides, ketone peroxides, peroxyketals, alkyl peresters, and percarbonates.

Of these peroxides, the following are preferred as the (E) thermal polymerization initiator: 1,1-di-t-hexylperoxycyclohexane, t-hexylperoxyisopropyl monocarbonate, t-butylperoxyoctoate, t-butylperoxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, t-amylperoxy-2-ethylhexanoate, benzoyl peroxide, 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, t-butylperoxyisopropyl carbonate, t-butylperoxybenzoate, dicumyl peroxide, and di-t-butyl peroxide. The (E) thermal polymerization initiators may be used alone or in combination of two or more.

The amount of (E) thermal polymerization initiator is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, and even more preferably 1 to 5 parts by mass, per 100 parts by mass of the total of (A) curable resin, (B) ethylenically unsaturated monomer, and optional saturated polybasic acid. When the amount of (E) thermal polymerization initiator is 0.1 parts by mass or more, the curing reaction during molding of the curable resin composition proceeds uniformly, resulting in good physical properties and appearance of the cured product. When the amount of (E) thermal polymerization initiator is 20 parts by mass or less, the storage stability of the curable resin composition is good and handling is improved.

[(F) Glass fiber]
The curable resin composition may contain (F) glass fiber as needed. The (F) glass fiber is not particularly limited as long as it is a fibrous material having an aspect ratio of 3 or more. Specific examples include chopped strand glass.

The fiber length of (F) the glass fiber is preferably 20 mm or less, more preferably 10 mm or less, and even more preferably 5 mm or less. When the fiber length is 20 mm or less, the moldability of the curable resin composition is good, and the appearance of the cured product is good. The fiber length is preferably 0.1 mm or more, more preferably 0.5 mm or more, and even more preferably 1 mm or more. When the fiber length is 0.1 mm or more, the strength of the cured product is good. The average fiber diameter of (F) the glass fiber is preferably 3 to 100 μm, and more preferably 5 to 30 μm.

When (F) glass fiber is used, its content is preferably 1 to 300 parts by mass, more preferably 5 to 100 parts by mass, and even more preferably 10 to 50 parts by mass, per 100 parts by mass of the total of (A) curable resin, (B) ethylenically unsaturated monomer, and optional saturated polybasic acid. If the (F) glass fiber content is 1 part by mass or more, the mechanical properties of the molded article obtained from the curable resin composition will be better. If the (F) glass fiber content is 300 parts by mass or less, the (F) glass fiber will be more uniformly dispersed in the curable resin composition, allowing for the production of a homogeneous molded article.

[(G) Low-shrinkage agent]
The curable resin composition may contain a (G) low shrinkage agent, if necessary. The (G) low shrinkage agent is not particularly limited, and any agent known in the technical field of the present invention can be used. Thermoplastic resins are preferred as the (G) low shrinkage agent. Examples of the (G) low shrinkage agent include polystyrene, polyethylene, polymethyl methacrylate, polyvinyl acetate, saturated polyester, polycaprolactone, and styrene-butadiene rubber. The (G) low shrinkage agent may be used alone or in combination of two or more.

The content of (G) low shrinkage agent is preferably 10 to 80 parts by mass, and more preferably 15 to 30 parts by mass, per 100 parts by mass of the total of (A) curable resin, (B) ethylenically unsaturated monomer, and optional saturated polybasic acid. If the content of (G) low shrinkage agent is 10 parts by mass or more, the shrinkage rate of the cured product will be small, and the desired dimensional accuracy can be achieved in the molded product. If the content of (G) low shrinkage agent is 80 parts by mass or less, the mechanical properties of the cured product will be better.

[Other additives]
In addition to the above components, the curable resin composition may contain components known in the technical field of the present invention, such as viscosity modifiers such as thickeners, colorants, polymerization inhibitors, and viscosity reducers, and molding aids such as mold release agents, within a range that does not impair the effects of the present invention.

The thickener is a compound other than (D) the inorganic filler that exhibits a thickening effect, such as an isocyanate compound. Thickeners may be used alone or in combination with two or more other types. The amount of thickener added can be adjusted appropriately depending on the handleability, fluidity, etc. required for the curable resin composition.

Colorants are used when coloring the cured product. Various dyes, inorganic pigments, or organic pigments can be used as colorants. Colorants may be used alone or in combination. The amount of colorant added can be adjusted appropriately depending on the desired degree of coloration of the cured product.

Examples of polymerization inhibitors include hydroquinone, trimethylhydroquinone, p-benzoquinone, naphthoquinone, t-butylhydroquinone, catechol, p-t-butylcatechol, and 2,6-di-t-butyl-4-methylphenol. Polymerization inhibitors may be used alone or in combination. The amount of polymerization inhibitor added can be adjusted appropriately depending on the storage environment and period of the curable resin composition, curing conditions, etc.

2. Method for Producing Curable Resin Composition The curable resin composition can be produced by mixing (A) a curable resin, (B) an ethylenically unsaturated monomer, (C) an acidic surfactant, (D) an inorganic filler, (E) a thermal polymerization initiator, and, as necessary, optional components such as (F) glass fiber, (G) a shrinkage reducing agent, and other additives other than (C) the acidic surfactant, or a combination of two or more of these optional components. The curable resin composition may contain a saturated polybasic acid, and the saturated polybasic acid may be derived during the production of the (A) curable resin.

An example of a mixing method is kneading. There are no particular restrictions on the kneading method, and examples include kneading using a kneader, disperser, planetary mixer, etc. The kneading temperature is preferably 5°C to 50°C, and more preferably 10°C to 40°C.

There are no particular restrictions on the order in which the components are mixed when producing a curable resin composition. For example, mixing (A) the curable resin and some or all of the (B) ethylenically unsaturated monomer before mixing the other components is preferred, as this makes it easier to obtain a curable resin composition in which the components are sufficiently dispersed or uniformly mixed. At least a portion of the (B) ethylenically unsaturated monomer may be premixed with the (A) curable resin so that it acts as a solvent, dispersion medium, etc.

When using (F) glass fiber, one mixing method involves preparing glass fiber with a predetermined fiber length distribution in advance and mixing the (F) glass fiber into a composition containing components other than the (F) glass fiber. This method allows for fine adjustment of the fiber length distribution of the (F) glass fiber. Another method involves preparing a curable resin composition containing the (F) glass fiber, and then breaking the (F) glass fiber through kneading to achieve the desired fiber length distribution. The fiber length distribution of the (F) glass fiber can be controlled by conditions such as the type and amount of other components to be kneaded, the type of mixer, the mixing speed, the mixing temperature, and the mixing time. This method is simple because it does not require prior breaking of the (F) glass fiber.

3. Method for Producing a Cured Product The curable resin composition can be cured by heating as needed. The conditions for curing the curable resin composition can be appropriately set depending on the materials used. An example of preferred conditions is a temperature of 120 to 180°C, more preferably 120 to 160°C, and a curing time of 1 to 30 minutes.

4. Method for Producing Molded Article A molded article containing a cured product of the curable resin composition can be produced by molding the curable resin composition into a desired shape and curing it. The molding and curing methods are not particularly limited, and methods commonly used in the technical field of the present invention, such as compression molding, transfer molding, and injection molding, can be used.

For example, there are methods in which the mold is opened and the curable resin composition is poured into the mold and cured; or methods in which the curable resin composition is injected into a closed mold through a hole in the mold, such as a sprue, while the mold is under reduced pressure or while pressure is applied from the outside, as in injection molding. The conditions for curing the curable resin composition in the mold can be set appropriately depending on the material used. One preferred condition is a temperature of 120 to 180°C, more preferably 120 to 160°C, and a curing time of 1 to 30 minutes.

In one embodiment, an electrical/electronic component is provided that comprises a cured product of the curable resin composition. The electrical/electronic component can be produced, for example, by encapsulating the components of the electrical/electronic component with the curable resin composition and then heat-curing the curable resin composition. The components of the electrical/electronic component can be encapsulated, for example, by injecting the curable resin composition into a housing that contains the components.

From the standpoint of adhesion, the curable resin composition is suitable for use with polyphenylene sulfide (PPS) substrates, polybutylene terephthalate (PBT) substrates, epoxy glass substrates, and copper substrates. The curable resin composition can provide excellent adhesion, particularly to poorly adhesive resin substrates such as PPS substrates. By using the curable resin composition, it is possible to omit the surface treatment process using primers, plasma, etc., which is typically performed on poorly adhesive resin substrates such as PPS substrates.

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

(A) An example of the synthesis of a curable resin is shown below.

[Synthesis Example 1] (A-1) Synthesis of Vinyl Ester Resin A 1 L four-neck flask equipped with a thermometer, stirrer, gas inlet, and reflux condenser was charged with 478.9 g of bisphenol A epoxy resin Araldite (registered trademark) AER-2603 (Asahi Kasei E-Materials Corporation) having an epoxy equivalent of 188.0 and 73.1 g of methacrylic acid in which 0.35 g of methylhydroquinone had been dissolved, and the mixture was heated with stirring. When the temperature reached 100-110°C, 146.2 g of methacrylic acid in which 1.4 g of 2,4,6-tris(dimethylaminomethyl)phenol (Seikuol (registered trademark) TDMP, Seiko Chemical Co., Ltd.) had been dissolved was added dropwise over 30 minutes, and the mixture was allowed to react at 130°C. When the acid value reached 30 mgKOH/g or less, the mixture was cooled, and 389 g of styrene and 0.1 g of hydroquinone were added to synthesize a bisphenol A vinyl ester resin containing 47% by mass of styrene.

[Synthesis Example 2] (A-2) Synthesis of Unsaturated Polyester Resin 0.93 kg (9.5 mol) of maleic anhydride, 0.07 kg (0.5 mol) of phthalic anhydride, and 0.76 kg (10 mol) of propylene glycol were charged into a four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet, and a reflux condenser. The temperature was raised to 200°C while heating and stirring under a nitrogen gas flow to carry out an esterification reaction, yielding an unsaturated polyester resin. Thereafter, styrene monomer was added in an amount of 30% by mass relative to the total of the unsaturated polyester resin and the styrene monomer, yielding a mixture of unsaturated polyester resin and styrene. The resulting unsaturated polyester resin had an unsaturation degree of 95 mol% and a weight average molecular weight of 8,000.

The "weight average molecular weight" and "number average molecular weight" were measured at room temperature (23°C) using gel permeation chromatography (GPC) under the following conditions, and the values were determined using a standard polystyrene calibration curve.
Apparatus: Shodex (registered trademark) GPC-101 (Showa Denko K.K.)
Column: Shodex (registered trademark) LF-804 (Showa Denko K.K.)
Column temperature: 40°C
Sample: 0.2% by mass solution of sample in tetrahydrofuran Flow rate: 1 mL/min Eluent: tetrahydrofuran Detector: Shodex (registered trademark) RI-71S (Showa Denko K.K.)

Other ingredients used were as follows:

(B) Ethylenically unsaturated monomer:
- Styrene (Idemitsu Kosan Co., Ltd.)

(C) Acidic surfactant:
BYK W-9010 (phosphate ester dispersant, acid value 129 mg KOH/g, 150°C, 60-minute weight retention rate 99% or more, BYK)
BYK P-9051 (polyester dispersant, acid value 157 mg KOH/g, 150°C, 60-minute weight retention rate 99% or more, BYK)

(D) Inorganic filler:
Softon 1200 (calcium carbonate, average particle size 1.80 μm, Bihoku Funka Kogyo Co., Ltd.)

(E) Thermal polymerization initiator:
Luperox 575 (t-amylperoxy-2-ethylhexanoate, Arkema Yoshitomi Co., Ltd.)

(F) Glass fiber:
ECS-03B173/P9 (fiber diameter 13 μm, fiber length 3 mm, Nippon Electric Glass Co., Ltd.)

(G) Low shrinkage agent:
・Taketron (polyethylene powder, Takehara Chemical Industry Co., Ltd.)

(C') Other additives other than (C) acidic surfactant:
Stearic acid (acid value 197 mg KOH/g, 150°C, 60-minute weight retention rate 89%, NOF Corporation)
Lucant HC-100 (co-oligomer of ethylene and α-olefin, no acid value, Mitsui Chemicals, Inc.)
Dipropylene glycol (no acid value, boiling point 232°C, Dow Chemical)
HS-9817SSK (a mixture of 70% saturated polyester and 30% styrene by mass, acid value 11.5 mg KOH/g, manufactured by Choko Materials Industry Co., Ltd.)

The acid values of (C) acidic surfactants and (C') other additives other than (C) acidic surfactants are shown in Table 1.

Example 1
(Preparation of curable resin composition)
(A) 100 parts by mass of the styrene-diluted bisphenol A vinyl ester resin synthesized in Synthesis Example 1 as a curable resin (containing 52 parts by mass of bisphenol A vinyl ester resin, 47 parts by mass of styrene, and 1 part by mass of unreacted methacrylic acid), (B) 40 parts by mass of styrene as an ethylenically unsaturated monomer, (C) 4 parts by mass of BYK W-9010 as an acidic surfactant, (D) 560 parts by mass of Softon 1200 as an inorganic filler, and (E) 2 parts by mass of Luperox 575 as a thermal polymerization initiator were charged into a twin-arm kneader and kneaded for 15 minutes at 30°C to prepare a curable resin composition.

(Preparation of cured product)
The prepared curable resin composition was used to mold a molded product (cured product) in a transfer molding machine (model MF-070, Press Machinery Co., Ltd.) under conditions of a mold temperature of 140°C, a molding pressure of 15 kgf/cm ² , and a curing time of 180 seconds, to obtain a molded product (cured product) in the shape of a pudding cup (diameter on the substrate side: 5 mm, height: 3 mm) on a PPS (polyphenylene sulfide) substrate.

(Evaluation of Adhesion of Cured Product to Substrate)
A lateral load was applied to the obtained molded article at a constant rate of 2 mm/min using a die shear tester (Daisi Co., Ltd.), and the strength at which shear failure occurred was measured five times at 25°C, and the average value was taken as the adhesion strength. The results are shown in Table 2.

<Examples 2 to 4, Comparative Examples 1 to 7>
Curable resin compositions were prepared in the same manner as in Example 1, except that the types and compositions of raw materials were changed as shown in Table 2. The parts by mass in Synthesis Example 2 refer to the total parts by mass of the (A) curable resin and unreacted saturated polybasic acid. The styrene used to dilute the (A) curable resin was excluded from the blending amount of component (A) and added to the blending amount of the (B) ethylenically unsaturated monomer. Next, cured products were prepared in the same manner as in Example 1, and adhesion evaluations were performed. The results are shown in Table 2.

Example 5
(A) 100 parts by mass of the styrene-diluted bisphenol A vinyl ester resin synthesized in Synthesis Example 1 as the curable resin, (B) 40 parts by mass of styrene as the ethylenically unsaturated monomer, (C) 4 parts by mass of BYK W-9010 and 4 parts by mass of BYK P-9051 as acidic surfactants, (D) 560 parts by mass of Softon 1200 as the inorganic filler, (E) 2 parts by mass of Luperox 575 as a thermal polymerization initiator, and (G) 30 parts by mass of Taketron as a low-shrinkage agent were added to a twin-arm kneader and kneaded for 15 minutes at 30°C. Next, 40 parts by mass of ESC03B173/P9 as (F) glass fiber were added and kneaded for an additional 10 minutes at 30°C to prepare a curable resin composition. Using the obtained curable resin composition, a cured product was prepared in the same manner as in Example 1, and adhesion evaluation was performed. The results are shown in Table 2.

The results shown in Table 2 indicate that the molded articles of Examples 1 to 5 have high adhesion to PPS substrates. It is believed that by adjusting the acid value of (C) the acidic surfactant and the acid value of the mixture of (A) the curable resin, (B) the ethylenically unsaturated monomer, (C) the acidic surfactant, and any saturated polybasic acid within the specified range, wettability to the substrate is improved, resulting in high adhesion.

On the other hand, Comparative Examples 1 to 5, which did not use (C) an acidic surfactant, had poor adhesion. This is thought to be because the acid values of the other additives were low, so they could not be expected to improve wettability to the substrate, or because the other additives volatilized due to the mold temperature and heat generated during curing, or bled out onto the surface of the molded product, resulting in insufficient adhesion.

Comparative Examples 6 and 7, in which the acid value of the mixture of (A) curable resin, (B) ethylenically unsaturated monomer, and any saturated polybasic acid exceeded 12 mgKOH/g, also exhibited poor adhesion. This is thought to be because a large amount of unreacted monomer was present during the synthesis of (A) curable resin, and this unreacted monomer volatilized or bled out, affecting adhesion. In Comparative Example 6, the molded product peeled off from the substrate immediately after molding without the application of external force, making it impossible to evaluate adhesion.

The present invention provides a curable resin composition that yields a cured product with excellent adhesion to substrates, particularly poorly adhesive resin substrates. It also provides an electrical/electronic component that uses the cured product with excellent adhesion as an encapsulant, as well as a method for producing the same. The curable resin composition is preferably used for encapsulating and fixing wiring boards and electronic components mounted on the wiring boards, which are used in electronic devices such as motors, coils, connectors, and electronic control units installed in automobiles.

Claims (9)

(A) curable resin,
(B) an ethylenically unsaturated monomer,
(C) an acidic surfactant,
(D) inorganic filler,
(E) a thermal polymerization initiator, and optionally a saturated polybasic acid;
the (A) curable resin contains at least a vinyl ester resin, and the content of the (A-1) vinyl ester resin in the (A) curable resin is 75 mass% or more;
the content of the (A) curable resin is 30 to 50 parts by mass relative to 100 parts by mass in total of the (A) curable resin, the (B) ethylenically unsaturated monomer, and the optional saturated polybasic acid,
the mixture of the (A) curable resin, the (B) ethylenically unsaturated monomer, and the saturated polybasic acid has an acid value of 12 mgKOH/g or less;
the mixture of the (A) curable resin, the (B) ethylenically unsaturated monomer, the (C) acidic surfactant, and the saturated polybasic acid has an acid value of 10 mgKOH/g or more;
the (C) acidic surfactant is a low-volatile substance having an acid value of 20 mg KOH/g or more,
The (D) inorganic filler is a particulate material .
Curable resin composition. The curable resin composition according to claim 1, wherein the acid value of the acidic surfactant (C) is 30 to 190 mg KOH/g. The curable resin composition according to claim 1 or 2, wherein the (C) acidic surfactant is a phosphate ester compound. The curable resin composition according to any one of claims 1 to 3, wherein the (B) ethylenically unsaturated monomer is styrene. per 100 parts by mass of the total of (A) the curable resin, (B) the ethylenically unsaturated monomer, and any saturated polybasic acid ,
( B) 5 to 95 parts by mass of an ethylenically unsaturated monomer,
(C) 0.1 to 10 parts by mass of an acidic surfactant,
The curable resin composition according to any one of claims 1 to 4, comprising: (D) 200 to 700 parts by mass of an inorganic filler; and (E) 0.1 to 20 parts by mass of a thermal polymerization initiator. The curable resin composition according to any one of claims 1 to 5, further comprising (F) glass fibers. The curable resin composition according to any one of claims 1 to 6, further comprising (G) a low-profile agent. An electric/electronic component comprising a cured product of the curable resin composition according to any one of claims 1 to 7. A method for producing an electrical/electronic component, comprising the steps of encapsulating components of the electrical/electronic component with the curable resin composition according to any one of claims 1 to 7, and heat-curing the curable resin composition.