JP7599803B2 - Epoxy resin composition - Google Patents

Description

The present invention relates to an epoxy resin composition. More specifically, the present invention relates to an epoxy resin composition containing a thiol compound.

Epoxy resin compositions have excellent adhesive strength, heat resistance, and electrical properties, and are therefore used as adhesives and sealants in fields such as electrical and electronic equipment parts and automotive parts. In recent years, there has been a demand for epoxy resin compositions that can be cured at low temperatures and in a short time in order to prevent deterioration of parts under high-temperature conditions and to improve productivity.

Thiol-based curing agents are known as curing agents for epoxy resin compositions that can be cured at low temperatures in a short time. For example, Patent Document 1 and Patent Document 2 describe compositions containing an epoxy resin and a thiol compound. Patent Document 1 describes a resin composition containing a compound that has four thiol groups in the compound and acts as a curing agent for epoxy resins that do not have ester bonds, an epoxy resin, a curing accelerator, and a silane coupling agent. Patent Document 1 describes that the thiol compound does not hydrolyze in a high-temperature and high-humidity environment, and is less likely to cause a decrease in adhesive strength. Patent Document 2 describes a resin composition containing an epoxy resin, an ester structure-containing polythiol compound, and a carbodiimide. It describes that the resin composition has excellent moisture resistance. In the compositions described in Patent Documents 3 and 4, a thiol-based curing agent is used as a curing agent, and a microcapsule-type curing agent is used as a curing accelerator, enabling short-time curing at low temperatures and storage stability.

However, conventional epoxy resin compositions containing thiol-based curing agents as described in these patent documents can be cured at low temperatures, but require a long time to cure, and therefore cannot be said to have sufficient curability. Furthermore, conventional epoxy resin compositions containing thiol-based curing agents can be cured at high temperatures in a short time from the viewpoint of improving productivity, but they are unsatisfactory in terms of handleability, as voids are generated in the cured product and the volatile components of the resin contaminate the substrate. Furthermore, conventional epoxy resin compositions containing thiol-based curing agents are unsatisfactory in terms of reliability, as the resulting cured product has a low Tg and insufficient heat resistance, and the adhesive strength is significantly reduced after storage under high temperature and high humidity conditions.

Patent No. 6534189 JP 2019-123825 A International Publication No. 2017/057019 JP 2021-38314 A

The present invention therefore aims to provide an epoxy resin composition that gives a cured product with excellent heat resistance and moisture resistance, has excellent low-temperature curing properties and short-time curing properties, and produces few volatile components during curing.

As a result of intensive research conducted by the present inventors to solve the above problems, they discovered that by blending a specific amount of a specific thiol compound having three or more thiol groups in one molecule in an epoxy resin composition containing an epoxy resin, a thiol compound, a silicone-modified epoxy resin, a microcapsule-type curing accelerator, and a reaction inhibitor, the resulting composition has excellent low-temperature curing properties and short-time curing properties, produces a small amount of volatile components during curing, and gives a cured product with excellent heat resistance and moisture resistance, which led to the completion of the present invention.

That is, the present invention provides the following epoxy resin compositions, etc.

[1]
An epoxy resin composition comprising the following components (A) to (E):
(A) 100 parts by mass of a non-silicone-modified epoxy resin having two or more epoxy groups in one molecule; (B) 100 parts by mass of a thiol compound having three or more thiol groups in one molecule; (C) 0.5 to 100 parts by mass of a silicone-modified epoxy resin; (D) 1.0 to 200 parts by mass of a microcapsule-type curing accelerator; (E) 0.05 to 10 parts by mass of a reaction inhibitor; provided that the amount of component (B) is such that the molar equivalent ratio of thiol groups in component (B) to the total molar equivalent of epoxy groups in components (A) and (C) is 0.1 to 1.0.

[2]
The epoxy resin composition according to [1], wherein the component (B) is a thiol compound having four or more thiol groups in one molecule.

[3]
The epoxy resin composition according to [1] or [2], wherein the molar equivalent ratio of thiol groups in component (B) per 1 molar equivalent of total epoxy groups in components (A) and (C) is 0.1 to 0.5.

[4]
The epoxy resin composition according to any one of items [1] to [3], wherein the component (D) is a microcapsule-type curing accelerator containing at least one selected from the group consisting of a phosphorus compound, a tertiary amine compound, an imidazole compound, a urea compound, and an amine adduct compound.

[5]
The epoxy resin composition according to any one of items [1] to [4], wherein the component (E) is a borate ester compound and/or a phosphite ester compound.

[6]
The epoxy resin composition according to any one of items [1] to [5], wherein the volume average particle size of component (D) is 0.1 to 10 μm.

The epoxy resin composition of the present invention has excellent low-temperature curing properties and short-time curing properties, produces few volatile components during curing, and gives a cured product with excellent heat resistance and moisture resistance. Therefore, the epoxy resin composition of the present invention is useful as an adhesive, a sealant, etc.

FIG. 1 is an example of a graph plotting the relationship between temperature and dimensions of a test piece measured for dimensional changes at temperatures between 25° C. and 300° C. in an example, and illustrates a method for determining the glass transition temperature.

The epoxy resin composition of the present invention comprises an epoxy resin, a thiol compound, a silicone-modified epoxy resin, a microcapsule-type curing accelerator, and a reaction inhibitor, and is characterized in that the thiol compound has three or more thiol groups in one molecule.
The present invention will be described in detail below.

(A) Non-Silicone-Modified Epoxy Resin (A) is the main component of the present invention, is not silicone-modified, has two or more epoxy groups in one molecule, and preferably has one or more aromatic rings in one molecule.

The epoxy resin may be any conventionally known epoxy resin as long as it has two or more, preferably three or more, epoxy groups in one molecule. However, it is an epoxy resin other than a silicone-modified epoxy resin. Examples of the epoxy resin of the component (A) include bisphenol type epoxy resins such as bisphenol A type epoxy resins, bisphenol F type epoxy resins, and bisphenol S type epoxy resins; novolac type epoxy resins such as phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A novolac type epoxy resins, and bisphenol F novolac type epoxy resins; dicyclopentadiene type epoxy resins; alicyclic epoxy resins such as 3,4-epoxycyclohexenylmethyl-3',4'-epoxycyclohexenecarboxylate; polyfunctional phenol type epoxy resins such as resorcinol type epoxy resins and resorcinol novolac type epoxy resins; stilbene type epoxy resins, triazine skeleton-containing epoxy resins, fluorene skeleton-containing epoxy resins, trisphenol alkane type epoxy resins, biphenyl type epoxy resins, xylylene type epoxy resins, biphenyl aralkyl type epoxy resins, naphthalene type epoxy resins, and diglycidyl ether compounds of polycyclic aromatics such as anthracene; and phosphorus-containing epoxy resins obtained by introducing a phosphorus compound into these. These can be used alone or in combination of two or more types.

Component (A) preferably has a viscosity at 25°C of 10 to 100,000 mPa·s, and more preferably 20 to 50,000 mPa·s. The viscosity is measured using a B-type viscometer in accordance with JIS K 7117-1:1999.

The amount of component (A) is preferably 4 to 60 mass% based on the total mass of the epoxy resin composition, more preferably 8 to 55 mass%, and even more preferably 12 to 50 mass%.

(B) Thiol compound having 3 or more thiol groups per molecule Component (B) is a polythiol compound that acts as a curing agent for epoxy resins, that is, it is a curing agent for the above-mentioned component (A) and the component (C) described below. Polythiol compounds have high low-temperature curing properties and cure epoxy resins at low temperatures in a short time. Component (B) is characterized by having 3 or more thiol groups per molecule, preferably 4 or more, more preferably 4 to 6 thiol groups per molecule. If the number of thiol groups per molecule is 2 or less, the glass transition temperature of the resulting cured product is low and the heat resistance and moisture resistance are poor, which is not preferable.

Examples of the polythiol compound include polythiol compounds such as aliphatic polythiol compounds, aromatic polythiol compounds, polythiol compounds having an ether bond, polythiol compounds having an ester bond, and mercaptoalkylglycoluril compounds.
Examples of polythiol compounds having an ester bond include trimethylolpropane tris(3-mercaptopropionate), tris-[(3-mercaptopropionyloxy)-ethyl]-isocyanurate, pentaerythritol tetrakis(3-mercaptopropionate), dipentaerythritol hexakis(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptobutyrate), and 1,3,5-tris(3-mercaptobutyryloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione.
Examples of the mercaptoalkyl glycoluril compound include 1,3,4,6-tetrakis(mercaptomethyl) glycoluril, 1,3,4,6-tetrakis(2-mercaptoethyl) glycoluril, 1,3,4,6-tetrakis(3-mercaptopropyl) glycoluril, 1,3,4,6-tetrakis(mercaptomethyl)-3a-methyl glycoluril, 1,3,4,6-tetrakis(2-mercaptoethyl)-3a-methyl glycoluril, 1,3,4,6-tetrakis(3-mercaptopropyl)-3a-methyl glycoluril, and 1,3,4,6-tetrakis(mercaptomethyl)-3a-methyl glycoluril. Examples of the mercaptopropyl ether uril include, but are not limited to, 1,3,4,6-tetrakis(2-mercaptoethyl)-3a,6a-dimethylglycoluril, 1,3,4,6-tetrakis(3-mercaptopropyl)-3a,6a-dimethylglycoluril, 1,3,4,6-tetrakis(mercaptomethyl)-3a,6a-diphenylglycoluril, 1,3,4,6-tetrakis(2-mercaptoethyl)-3a,6a-diphenylglycoluril, and 1,3,4,6-tetrakis(3-mercaptopropyl)-3a,6a-diphenylglycoluril.
These may be used alone or in combination of two or more.

The epoxy resin composition of the present invention is characterized in that the polythiol compound is contained in an amount such that the molar equivalent ratio of the thiol group in the polythiol compound is 0.1 to 1.0 relative to 1 molar equivalent of all epoxy groups in the (A) component and the (C) component described later. The molar equivalent ratio is preferably 0.1 to 0.8, more preferably 0.1 to 0.5, even more preferably 0.2 to 0.5, and particularly preferably 0.2 to 0.4. If the ratio is less than 0.1, the low-temperature curing property may be impaired, unreacted epoxy groups may remain, and the glass transition temperature may decrease or the adhesion may decrease. If the ratio exceeds 1.0, unreacted thiol groups may remain, and cracks may occur during reflow or temperature cycles.
In the present invention, the term "equivalent" refers to the molecular weight per functional group. The term "thiol equivalent" refers to the active hydrogen equivalent. The above-mentioned equivalent ratio (molar equivalent ratio) refers to the ratio of the thiol equivalent (active hydrogen equivalent) in the thiol compound (B) to one equivalent of epoxy contained in the components (A) and (C), and it is sufficient to blend an amount of the thiol compound (B) that contains thiol active hydrogen to provide an equivalent ratio of 0.1 to 1.0, preferably within the above-mentioned range.

(C) Silicone-modified epoxy resin The component (C) is a silicone-modified epoxy resin. The inclusion of the silicone-modified epoxy resin improves the curing property and moisture resistance reliability of the epoxy resin composition. The silicone-modified epoxy resin includes a copolymer obtained by reacting an alkenyl-group-containing epoxy resin with an organohydrogenpolysiloxane. Examples of the alkenyl-group-containing epoxy resin include those represented by the following formulas (1) to (3).

In the above formulas (1) to (3), ^R1 is a glycidyl group (2,3-epoxypropyl group), X is independently a hydrogen atom or a bromine atom, n is a number of 0 or more, preferably a number of 0 to 50, more preferably a number of 1 to 20. m is an integer of 0 or more, preferably a number of 1 to 5, more preferably 1.

The organohydrogenpolysiloxane may be a compound represented by the following average composition formula (4).
H _a (R ² ) _b SiO _(4-ab)/2 (4)

In the above formula (4), R ² is independently a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, a hydroxy group, an alkoxy group having 1 to 10 carbon atoms, or an alkenyloxy group having 2 to 10 carbon atoms. Examples of the monovalent hydrocarbon group include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, and decyl, aryl groups such as phenyl and tolyl, and aralkyl groups such as benzyl and phenylethyl, as well as halogen-substituted monovalent hydrocarbon groups in which some or all of the hydrogen atoms of these hydrocarbon groups are substituted with halogen atoms or the like. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, and an n-hexyloxy group. Examples of the alkenyloxy group include a vinyloxy group, a propenoxy group, and an isopropenoxy group.

In the above formula (4), a and b are numbers that satisfy 0.001≦a≦1, 1≦b≦3, and 1<a+b≦4, and preferably 0.01≦a≦0.1, 1.8≦b≦2, and 1.85≦a+b≦2.1.

The organohydrogenpolysiloxane represented by the above formula (4) desirably has 1 to 1,000 silicon atoms in one molecule, preferably 2 to 400, and more preferably 5 to 200. Examples of such organohydrogenpolysiloxanes include compounds represented by formula (5).

In the above formula (5), ^R2 is the same as above, and is preferably a methyl group or a phenyl group. p is a number from 0 to 1,000, and preferably a number from 3 to 400, and q is a number from 0 to 20, and preferably a number from 0 to 5, and more preferably q=0. Furthermore, p+q is a number that satisfies 1<p+q≦1,000, preferably 2<p+q<400, and even more preferably 5<p+q<200.

Examples of such organohydrogenpolysiloxanes include compounds represented by the following formula:

The organohydrogenpolysiloxane preferably has a weight average molecular weight of 100 to 100,000, more preferably 500 to 20,000. When the weight average molecular weight of the organohydrogenpolysiloxane is within the above range, depending on the structure or weight average molecular weight of the alkenyl group-containing epoxy resin reacted with the organohydrogenpolysiloxane, a uniform structure in which the organohydrogenpolysiloxane is uniformly dispersed in the matrix or a sea-island structure in which the organohydrogenpolysiloxane forms fine layer separations in the matrix appears.

When the weight average molecular weight of the organohydrogenpolysiloxane is relatively small, particularly between 100 and 10,000, a uniform structure is formed. When the weight average molecular weight of the organohydrogenpolysiloxane is relatively large, particularly between 10,000 and 100,000, a sea-island structure is formed. Either the uniform structure or the sea-island structure can be selected depending on the application. When the weight average molecular weight of the organohydrogenpolysiloxane is less than 100, the resulting cured product is undesirably rigid and brittle. When the weight average molecular weight of the organohydrogenpolysiloxane is more than 100,000, the sea-island structure becomes large, undesirably generating localized stress in the resulting cured product.

In this specification, the weight average molecular weight is a weight average molecular weight measured by gel permeation chromatography (GPC) using polystyrene as a standard substance, and is a value measured under the following conditions.
[GPC measurement conditions]
Developing solvent: tetrahydrofuran Flow rate: 0.6 mL/min
Column: TSK Guard column Super H-L
TSKgel SuperH4000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH3000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH2000 (6.0mm I.D. x 15cm x 2)
(Both manufactured by Tosoh Corporation)
Column temperature: 40°C
Sample injection volume: 20 μL (sample concentration: 0.5% by mass in tetrahydrofuran solution)
Detector: Differential Refractometer (RI)

The method of reacting the alkenyl group-containing epoxy resin with the organohydrogenpolysiloxane can be a known method, for example, a method of adding the alkenyl group-containing epoxy resin with the organohydrogenpolysiloxane in the presence of a platinum catalyst. In this way, a silicone-modified epoxy resin can be obtained. It is preferable to copolymerize the organohydrogenpolysiloxane in an amount such that the organohydrogenpolysiloxane has 0.1 to 1 mole of SiH groups per mole of alkenyl groups in the alkenyl group-containing epoxy resin.

The amount of silicone-modified epoxy resin (C) in the composition of the present invention is 0.5 to 100 parts by mass, preferably 1 to 80 parts by mass, and more preferably 2 to 60 parts by mass, per 100 parts by mass of component (A).

(D) Microcapsule-type curing accelerator The (D) component is a microcapsule-type curing accelerator, which accelerates the reaction between the epoxy resin (A) and (C) components and the thiol compound (B). The curing accelerator (catalyst) used as an active ingredient in the core material (core particle) of this microcapsule preferably has a reaction temperature (i.e., a temperature at which catalytic action is expressed) of 50°C or higher so as to exhibit storage stability and fast curing at a low temperature of a certain temperature or higher. Examples of such curing accelerators include phosphorus compounds, tertiary amine compounds, imidazole compounds, urea compounds, and amine adduct compounds.

Examples of the phosphorus compounds include triorganophosphine compounds such as tributylphosphine, triphenylphosphine, tri(methylphenyl)phosphine, tri(nonylphenyl)phosphine, tri(methoxyphenyl)phosphine, diphenyltolylphosphine, triphenylphosphine, and triphenylborane; and quaternary phosphonium salts such as tetraphenylphosphonium and tetraphenylborate. Among these, triphenylphosphine and tri(methylphenyl)phosphine are preferred.

Examples of the tertiary amine compounds include amine compounds having an alkyl group or an aralkyl group as a substituent bonded to a nitrogen atom, such as triethylamine, benzyldimethylamine, benzyltrimethylamine, and α-methylbenzyldimethylamine; cycloamidine compounds such as 1,8-diazabicyclo[5.4.0]undecene-7 and 1,4-diazabicyclo[2.2.2]octane, and their phenol salts, octylate salts, and oleate salts, as well as salts or complex salts of quaternary boron compounds with their organic acids. Among these, 1,8-diazabicyclo[5.4.0]undecene-7 and 1,4-diazabicyclo[2.2.2]octane are preferred.

Examples of the imidazole compounds include 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2,4-dimethylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 1,2-diethylimidazole, 2-phenyl-4-methylimidazole, 2,4,5-triphenylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-benzyl-2-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-allyl-4,5-diphenylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. Of these, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-ethylimidazole, 1,2-dimethylimidazole, 1,2-diethylimidazole, 2,4-dimethylimidazole, and 2-phenyl-4-methylimidazole are preferred.

Examples of the urea compounds include N,N-dimethyl-N'-phenylurea, N,N-dimethyl-N'-(3,4-dichlorophenyl)urea, 4,4'-methylenebis(phenyldimethylurea), aromatic dimethylurea compounds, aliphatic dimethylurea compounds, toluenebisdimethylurea, dimethylaminocarboxylaminomethyltrimethylcyclohexyldimethylurea, etc. Among these, aromatic dimethylurea compounds and aliphatic dimethylurea compounds are preferred.

The above-mentioned amine adduct compound may, for example, be a compound having an amino group obtained by reacting at least one compound selected from the group consisting of a carboxylic acid compound, a phenol compound, an isocyanate compound, and an epoxy resin with an amine compound.

Examples of carboxylic acid compounds include succinic acid, adipic acid, sebacic acid, phthalic acid, and dimer acid.

Examples of phenolic compounds include monophenols such as carbolic acid, cresol, xylenol, carvacrol, motil, and naphthol, and polyphenols such as catechol, resorcinol, hydroquinone, bisphenol A, bisphenol F, pyrogallol, and phloroglucin.

Examples of isocyanate compounds include ethylene diisocyanate, propylene diisocyanate, butylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, 4-4'-dicyclohexylmethane diisocyanate, norbornane diisocyanate, 1,4-isocyanatocyclohexane, 1,3-bis(isocyanatomethyl)-cyclohexane, 1,3-bis(2-isocyanatopropyl-2-yl)-cyclohexane, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylene diisocyanate, and 1,5-naphthalene diisocyanate.

Examples of epoxy compounds include butyl glycidyl ether, hexyl glycidyl ether, phenyl glycidyl ether, allyl glycidyl ether, para-tert-butylphenyl glycidyl ether, paraxylyl glycidyl ether, bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin, novolac type epoxy resins such as phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolac type epoxy resin, and bisphenol F novolac type epoxy resin, dicyclopentadiene type epoxy resin, 3,4-epoxy resin, Examples of epoxy resins include alicyclic epoxy resins such as 3',4'-epoxycyclohexenylmethyl-3',4'-epoxycyclohexenecarboxylate, polyfunctional phenolic epoxy resins such as resorcinol-type epoxy resins and resorcinol novolac-type epoxy resins, stilbene-type epoxy resins, triazine-skeleton-containing epoxy resins, fluorene-skeleton-containing epoxy resins, triphenolalkane-type epoxy resins, biphenyl-type epoxy resins, xylylene-type epoxy resins, biphenylaralkyl-type epoxy resins, naphthalene-type epoxy resins, and diglycidyl ether compounds of polycyclic aromatics such as anthracene, as well as phosphorus-containing epoxy resins in which a phosphorus compound has been introduced into these.

Examples of amine compounds include methylamine, ethylamine, propylamine, butylamine, ethylenediamine, 1,2-propanediamine, tetramethyleneamine, 1,5-diaminopentane, hexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, 2,2,4-triethylhexamethyldiamine, 1,2-diaminopropane, diethylenetriamine, triethylenetetramine, tetraethylenepentane, cyclohexylamine, isophoronediamine, 1,3-bisaminomethylcyclohexane, aminoethylpiperazine, diethylaminopropylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, dimethanolamine, diethanolamine, dipropanolamine, dicyclohexylamine, and piperazine.

Among these, amine adduct compounds obtained by reacting an isocyanate resin or an epoxy resin with an amine compound are preferred.

These curing accelerators can be used alone or in combination of two or more.

The shell material for microencapsulating the curing accelerator must have a melting point of 50 to 90°C in order to maintain storage stability and ensure fast curing. The shell material is not particularly limited as long as it has such a melting point, and all known materials can be used, such as (meth)acrylic monomers, such as alkyl esters with 1 to 8 carbon atoms, such as acrylic acid esters, itaconic acid esters, and crotonic acid esters; alkyl esters in which the alkyl group has a substituent such as an allyl group; monofunctional monomers such as styrene, α-methylstyrene, acrylonitrile, methacrylonitrile, and vinyl acetate; and polymers obtained by (co)polymerizing one or more monomers selected from polyfunctional monomers such as ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, divinylbenzene, bisphenol A di(meth)acrylate, and methylene bis(meth)acrylamide. Among these, polymers of (meth)acrylate monomers are preferred.

The microcapsule-type hardening accelerator of component (D) is a microcapsule that contains a hardening accelerator such as an imidazole compound or a tertiary amine compound as a core component in such a shell material, and can be manufactured by the following methods (a) to (c), but is not limited thereto.

(a) A method in which a shell material and core particles of a microcapsule-type hardening accelerator are dissolved or dispersed in a solvent that is a dispersion medium, and then the solubility of the shell material in the dispersion medium is reduced to precipitate the shell on the surface of the core particles of the microcapsule-type hardening accelerator.

(b) A method in which core particles of a microcapsule-type hardening accelerator are dispersed in a dispersion medium, and the above-mentioned shell material is added to the dispersion medium to precipitate on the core particles of the microcapsule-type hardening accelerator.

(c) A method in which the above shell material is added to a dispersion medium, and the surface of the core particles of the microcapsule-type hardening accelerator is used as a reaction site to form a shell there.

The dispersion medium used in the above production methods (a) to (c) includes solvents, resins, and the like.
Examples of the solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, n-butyl acetate, propylene glycol monomethyl ethyl ether acetate, benzene, toluene, xylene, cyclohexane, methanol, ethanol, isopropanol, n-butanol, butyl carbitol, and water.
Examples of the resins include epoxy resins, phenolic resins, maleimide resins, cyanate ester resins, and silicone resins.
Among these, aromatic hydrocarbons such as toluene and alcohols such as n-butanol are preferred as dispersion media with good dispersibility.

The microcapsule-type curing accelerator obtained by this method preferably has an average particle size of 0.1 to 10 μm, and more preferably 1 to 5 μm. If the average particle size is too small, the specific surface area becomes large, and there is a risk that the viscosity of the epoxy resin composition will increase when mixed. If the average particle size exceeds 10 μm, the dispersion in the epoxy resin composition will become non-uniform, which may cause a decrease in reliability. The average particle size is the volume average particle size measured by laser diffraction.

The amount of component (D) is 1.0 to 200 parts by mass, and more preferably 5 to 150 parts by mass, per 100 parts by mass of the epoxy resin (A) described above. If the amount of component (D) is 1.0 to 200 parts by mass, there is no risk of the heat resistance and moisture resistance of the cured product of the composition becoming unbalanced, or the curing speed during molding becoming very slow or fast.

(E) Reaction Inhibitor The (E) reaction inhibitor is added for the purpose of improving storage stability, and is not particularly limited and any known one can be used. Examples of the reaction inhibitor include boric acid ester compounds, aluminum chelate compounds, phosphorous acid ester compounds, organic acids, etc. Among them, boric acid ester compounds and phosphorous acid ester compounds are preferred.

Examples of borate ester compounds include trimethyl borate, triethyl borate, tri-n-propyl borate, triisopropyl borate, tri-n-butyl borate, tripentyl borate, triallyl borate, trihexyl borate, tricyclohexyl borate, trioctyl borate, trinonyl borate, tridecyl borate, tridodecyl borate, trihexadecyl borate, trioctadecyl borate, tris(2-ethylhexyloxy)borane, bis(1,4,7,10-tetraoxaundecyl)(1,4,7,10,13-pentaoxatetradecyl)(1,4,7-trioxaundecyl)borane, tribenzyl borate, triphenyl borate, tri-o-tolyl borate, tri-m-tolyl borate, and triethanolamine borate. Among these, triisopropyl borate is preferred.

Examples of aluminum chelate compounds include triethyl aluminate, tripropyl aluminate, triisopropyl aluminate, tributyl aluminate, and trioctyl aluminate.

Examples of phosphite ester compounds include phosphorous acid, monomethyl phosphite, dimethyl phosphite, monoethyl phosphite, diethyl phosphite, monobutyl phosphite, dibutyl phosphite, monolauryl phosphite, dilauryl phosphite, monooleyl phosphite, dioleyl phosphite, monophenyl phosphite, diphenyl phosphite, mononaphthyl phosphite, dinaphthyl phosphite, di-o-tolyl phosphite, di-m-tolyl phosphite, di-p-tolyl phosphite, di-p-chlorophenyl phosphite, di-p-bromophenyl phosphite, and di-p-fluorophenyl phosphite. Of these, phosphorous acid is preferred. These reaction inhibitors can be used alone or in combination of two or more.

The amount of component (E) is 0.05 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, and even more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the epoxy resin (A) described above. If the amount of component (E) is 0.05 to 10 parts by mass, the reaction suppression effect is sufficient, and there is no risk of a decrease in Tg or bending strength due to insufficient curing.

The epoxy resin composition of the present invention can be obtained by blending the above-mentioned components (A) to (E) in the prescribed amounts, but other additives can be added as necessary within the range that does not impair the object and effect of the present invention. Such additives include inorganic fillers, flame retardants, ion trapping agents, antioxidants, adhesion promoters, stress reducing agents, colorants, coupling agents, etc.

The inorganic filler is added for the purpose of reducing the thermal expansion coefficient of the epoxy resin composition and improving the moisture resistance reliability. The inorganic filler is preferably spherical. In this specification, "spherical" refers to particles having an aspect ratio of 2.0 or less, preferably 1.5 or less. By using spherical particles of the inorganic filler, the viscosity of the epoxy resin composition can be further reduced, and an epoxy resin that is liquid at 25°C can be suitably provided.

Examples of inorganic fillers include silicas such as fused silica, crystalline silica, and cristobalite; metal oxides such as aluminum oxide, titanium oxide, and magnesium oxide; and nitrides such as silicon nitride, aluminum nitride, and boron nitride. Among these, silicas are preferably used, taking into consideration the availability of materials and the stability of quality. The average particle size of these inorganic fillers is preferably 0.01 to 50 μm, more preferably 0.05 to 30 μm, and can be selected according to the application. The average particle size may be the volume average particle size measured, for example, by laser diffraction. The type of inorganic filler can be one type alone or two or more types in combination.

In order to strengthen the bond strength between the resin component and the inorganic filler, it is preferable that the inorganic filler is surface-treated in advance with a coupling agent such as a silane coupling agent or a titanate coupling agent. Examples of such coupling agents include epoxy silanes such as γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, N-β(aminoethyl)-γ-aminopropyltrimethoxysilane, reaction products of imidazole and γ-glycidoxypropyltrimethoxysilane, amino silanes such as γ-aminopropyltriethoxysilane and N-phenyl-γ-aminopropyltrimethoxysilane, and mercapto silanes such as γ-mercaptopropyltrimethoxysilane and γ-(thiiranylmethoxy)propyltrimethoxysilane. The amount of the coupling agent used in the surface treatment and the surface treatment method are not particularly limited. The coupling agent may be added separately to the composition of the present invention as component (F).

The content of the inorganic filler in the composition of the present invention is preferably 20 to 1,200 parts by mass, more preferably 50 to 1,000 parts by mass, and even more preferably 100 to 800 parts by mass, per 100 parts by mass of the total of (A) to (E) above.

The flame retardant is added for the purpose of imparting flame retardancy, and any known flame retardant can be used without any particular limitation. Examples of the flame retardant include phosphazene compounds, silicone compounds, zinc molybdate-supported talc, zinc molybdate-supported zinc oxide, aluminum hydroxide, magnesium hydroxide, and molybdenum oxide.

The ion trapping agent is added to capture ion impurities contained in the resin composition and to prevent thermal and moisture degradation, and any known ion trapping agent can be used without any particular limitation. Examples of ion trapping agents include hydrotalcites, bismuth hydroxide compounds, and rare earth oxides.

The amounts of the above other components will vary depending on the application of the epoxy resin composition of the present invention, but typically the total amount should be 5% by mass or less of the entire composition.

Method for Producing Epoxy Resin Composition The method for producing the epoxy resin composition of the present invention is not particularly limited.
For example, a composition may be obtained by mixing, stirring, dissolving and/or dispersing (A) a non-silicone-modified epoxy resin, (B) a thiol compound, (C) a silicone-modified epoxy resin, (D) a microcapsule-type curing accelerator and (E) a reaction inhibitor, simultaneously or separately, while optionally carrying out a heat treatment. Depending on the application, at least one of other additives such as an inorganic filler, a flame retardant, an ion trapping agent and a coupling agent may be added to and mixed with a mixture of components (A) to (E) to obtain the epoxy resin composition of the present invention.

The epoxy resin composition of the present invention is preferably liquid at 25°C. The viscosity of the composition is preferably 1 to 650 Pa·s, more preferably 5 to 500 Pa·s, at 25°C. The viscosity is measured using an E-type viscometer in accordance with JIS Z 8803:2011.

There are no particular limitations on the method for producing the composition, and on the equipment used for mixing, stirring, and dispersing. For example, a mortar and pestle machine equipped with a stirring and heating device, a two-roll mill, a three-roll mill, a ball mill, a planetary mixer, or a mass colloider may be used, and these devices may be used in appropriate combination. There are no particular limitations on the curing conditions for the epoxy resin composition, but it may be heated, for example, at a temperature in the range of 60 to 200°C, preferably 80 to 180°C, for 30 minutes to 10 hours, preferably 1 to 5 hours. The epoxy resin composition of the present invention can be cured at a low temperature in a short time. Therefore, it can be cured well even at a temperature in the range of 70°C to 130°C for about 10 minutes to 2 hours.

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

The components used in the examples and comparative examples are as follows.
(A) Non-silicone-modified epoxy resin (A1) Epoxy resin: mixture of bisphenol A type epoxy resin and bisphenol F type epoxy resin (ZX1059, viscosity at 25°C 1,900 to 2,600 mPa·s: manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.)
(A2) Epoxy resin: naphthalene type epoxy resin (HP4032D, viscosity at 25°C: 25 Pa·s: manufactured by DIC Corporation)

(B) Thiol compound (B1) Thiol compound: 1,3,4,6-tetrakis(2-mercaptoethyl)glycoluril (TS-G, manufactured by Shikoku Chemical Industry Co., Ltd.)
(B2) Thiol compound: 1,3,4,6-tetrakis(3-mercaptopropyl)glycoluril (C3TS-G, manufactured by Shikoku Chemical Industry Co., Ltd.)
(B3) Thiol compound: pentaerythritol tetrakis(3-mercaptobutyrate) (Karends MT PE1, manufactured by Showa Denko K.K.)
(B4) Thiol compound: 1,3,5-tris(3-mercaptobutyryloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (Karens MT NR1, manufactured by Showa Denko K.K.)
(B5) Comparative thiol compound: tetraethylene glycol bis(3-mercaptopropionate) (EGMP-4, manufactured by SC Organic Chemicals)

で表されるアリルグリシジルエーテルで変性されたフェノールノボラック樹脂（フェノール当量１２５、アリル当量１，１００）２００ｇ、クロロメチルオキシラン８００ｇ、セチルトリメチルアンモニウムブロマイド０．６ｇをそれぞれ入れて加熱し、温度１１０℃で３時間撹拌混合した。これを冷却して温度７０℃とし、１６０ｍｍＨｇに減圧してから、この中に水酸化ナトリウムの５０％水溶液１２８ｇを共沸脱水しながら３時間かけて滴下した。得られた内容物を減圧して溶剤を留去し、次いでメチルイソブチルケトン３００ｇとアセトン３００ｇの混合溶剤にて溶解させた後、水洗し、これを減圧下で溶剤留去して下記式（７）

で表されるアリル基含有のエポキシ樹脂（アリル当量１５９０、エポキシ当量１９０）を得た。このエポキシ樹脂とメチルイソブチルケトン１７０ｇ、トルエン３３０ｇ、２質量％の白金濃度の２－エチルヘキサノール変性塩化白金酸溶液０．０７ｇを入れ、１時間の共沸脱水を行ない、還流温度にて下記式（８）

で表されるオルガノポリシロキサン１３３ｇ（重量平均分子量８０００）を滴下時間３０分にて滴下した。更に、同一温度で４時間撹拌して反応させた後、得られた内容物を水洗し、溶剤を減圧下で留去したところ黄白色不透明固体の共重合体が得られた。エポキシ当量は２８０であり、ＡＳＴＭ Ｄ４２８７に従い、コーン／プレート粘度計を用いて測定した１５０℃でのＩＣＩ溶融粘度は８００ｍＰａ・ｓであり、ケイ素含有量３１質量％であった。 (C) Silicone-modified epoxy resin A 1-liter four-neck flask equipped with a reflux condenser, a thermometer, a stirrer, and a dropping funnel was charged with a mixture of the following formula (6):

200 g of phenol novolak resin (phenol equivalent 125, allyl equivalent 1,100) modified with allyl glycidyl ether represented by the formula (I), 800 g of chloromethyloxirane, and 0.6 g of cetyltrimethylammonium bromide were added and heated, and stirred and mixed at a temperature of 110° C. for 3 hours. The mixture was cooled to a temperature of 70° C. and reduced in pressure to 160 mmHg, and then 128 g of a 50% aqueous solution of sodium hydroxide was added dropwise thereto over a period of 3 hours while azeotropically dehydrating. The resulting contents were reduced in pressure to distill off the solvent, and then dissolved in a mixed solvent of 300 g of methyl isobutyl ketone and 300 g of acetone, washed with water, and the solvent was removed under reduced pressure to obtain a product represented by the following formula (7):

This epoxy resin was mixed with 170 g of methyl isobutyl ketone, 330 g of toluene, and 0.07 g of a 2-ethylhexanol-modified chloroplatinic acid solution having a platinum concentration of 2% by mass, and subjected to azeotropic dehydration for 1 hour. The mixture was heated at reflux temperature to obtain an allyl group-containing epoxy resin represented by the following formula (8):

133 g of organopolysiloxane (weight average molecular weight 8000) represented by the formula was added dropwise over a drop time of 30 minutes. After stirring and reacting for 4 hours at the same temperature, the resulting content was washed with water and the solvent was distilled off under reduced pressure to obtain a yellowish white opaque solid copolymer. The epoxy equivalent was 280, and the ICI melt viscosity at 150°C measured using a cone/plate viscometer according to ASTM D4287 was 800 mPa·s, and the silicon content was 31 mass%.

(D) Microcapsule-type hardening accelerator (D1) Tertiary amine-based microcapsule-type hardening accelerator (HX5945HP, average particle size 2 μm, manufactured by Asahi Kasei Corporation)
(D2) Imidazole-based microcapsule type curing accelerator (HX9322HP, average particle size 2 μm, manufactured by Asahi Kasei Corporation)
(D3) Imidazole-based microcapsule type curing accelerator (HX3941HP, average particle size 5 μm, manufactured by Asahi Kasei Corporation)

Comparative Example Curing Accelerator (Non-Microcapsule Type Curing Accelerator)
(D4) 2-phenyl-4-methyl-5-hydroxymethylimidazole (2P4MHZ-PW, manufactured by Shikoku Chemical Industries, Ltd.)
(D5) Amine-epoxy adduct-based latent curing catalyst (product name: Fujicure FXR-1081, manufactured by T&K Toka Corporation)

(E) Reaction inhibitor (E1) Triisopropyl borate (manufactured by Tokyo Chemical Industry Co., Ltd.)
(E2) Phosphorous acid (Tokyo Chemical Industry Co., Ltd.)

(F) Other Additives (F1) Silane coupling agent: γ-glycidoxypropyltrimethoxysilane (KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.)

The above components were mixed in the amounts (parts by mass) shown in Tables 1 and 2 to obtain epoxy resin compositions. Each composition and the cured product obtained by curing each composition were evaluated for viscosity, storage stability, adhesion, glass transition temperature (Tg), heat resistance, moisture resistance, and drop resistance using the methods shown below. The results are shown in Tables 1 and 2. The "molar equivalent ratio" in Tables 1 and 2 refers to the ratio of the thiol equivalent (active hydrogen equivalent) in component (B) to the epoxy equivalent in components (A) and (C), and means molar equivalent.

(1) Viscosity Measurement All of the epoxy resin compositions obtained in Examples 1 to 17 and Comparative Examples 1 to 7 were liquid at 25° C. In accordance with JIS Z 8803:2011, the viscosity was measured 2 minutes after setting the sample using an E-type viscometer at a measurement temperature of 25° C. (initial viscosity).

(2) Confirmation of storage stability Each epoxy resin composition was kept at 25° C. for 24 hours and then the viscosity was measured in the same manner as described above. The rate of change (%) of the viscosity after 24 hours relative to the initial viscosity was calculated to evaluate the storage stability.

(3) Adhesive strength after low-temperature curing Each epoxy resin composition of the examples and comparative examples was poured into a mold to obtain a truncated cone-shaped test piece with an upper diameter of 2 mm, a lower diameter of 5 mm, and a height of 3 mm. The test piece was placed on an aluminum plate and cured at 80° C. for 10 minutes. After curing, the test piece was cooled to room temperature and the shear adhesive strength was measured.

(4) Adhesive strength after high-temperature curing Each epoxy resin composition of the Examples and Comparative Examples was poured into a mold to obtain a truncated cone-shaped test piece with an upper diameter of 2 mm, a lower diameter of 5 mm, and a height of 3 mm. The test piece was placed on an aluminum plate and cured at 180° C. for 10 seconds. After curing, the test piece was cooled to room temperature and the shear adhesive strength was measured.

Preparation of Cured Product Samples Each of the epoxy resin compositions of the Examples and Comparative Examples was heat-cured at 80° C. for 1 hour and then at 120° C. for 1 hour, and molded to obtain a cured product.

(5) Measurement of glass transition temperature (Tg) The cured products obtained above were processed into test pieces of 5 x 5 x 15 mm, and the test pieces were then set in a thermal dilatometer TMA8140C (manufactured by Rigaku Corporation). The heating program was set to a heating rate of 5°C/min, and a constant load of 19.6 mN was applied, after which the dimensional change of the test pieces was measured between 25°C and 300°C. The relationship between the dimensional change and temperature was plotted on a graph (an example of the graph is shown in Figure 1). From the graph of dimensional change and temperature obtained in this way, the glass transition temperatures in the examples and comparative examples were determined by the method for determining glass transition temperature described below.

Method for determining glass transition temperature (Tg) As shown in Figure 1, any two temperatures at which a tangent to the dimensional change-temperature curve is obtained below the inflection point temperature are designated as _T1 and _T2 , and any two temperatures at which a similar tangent is obtained above the inflection point temperature are designated as _T1 ' and _T2 '. The dimensional changes at _T1 and _T2 are designated as _D1 and _D2 , respectively, and the intersection of a straight line connecting point ( _T1 , _D1 ) and point ( _T2 , _D2 ) with a straight line connecting point ( _T1 ', D1 _' ) and point ( _T2 ', _{D2 '} ), with the dimensional changes at _T1 ' and T2' designated as _D1 ' and _D2 ', respectively, was designated as the glass transition temperature ( _Tg ).

(6) Heat resistance (adhesive strength retention after storage at 150°C)
Each epoxy resin composition of the Examples and Comparative Examples was poured into a mold to obtain a truncated cone-shaped test piece with an upper diameter of 2 mm, a lower diameter of 5 mm, and a height of 3 mm. The test piece was placed on an aluminum plate and cured by heating at 80°C for 1 hour and then at 120°C for 1 hour. After curing, the obtained test piece was cooled to room temperature and the shear adhesive strength was measured, and the measurement result was used as the initial value. The obtained test piece was stored in an oven at 150°C for 150 hours, and then cooled to room temperature and the shear adhesive strength was measured. More specifically, the adhesive strength retention after storage at 150°C was calculated using the following formula.

(7) Moisture resistance (adhesive strength retention rate after PCT storage)
Each epoxy resin composition of the Examples and Comparative Examples was poured into a mold to obtain a test piece in the shape of a truncated cone with an upper diameter of 2 mm, a lower diameter of 5 mm, and a height of 3 mm. The test piece was placed on an aluminum plate and cured by heating at 80°C for 1 hour and then at 120°C for 1 hour. After curing, the obtained test piece was cooled to room temperature and the shear adhesive strength was measured, and the measurement result was used as the initial value. The obtained test piece was stored in a PCT (121°C/humidity 100%/2 atm) for 96 hours, and then cooled to room temperature and the shear adhesive strength was measured. More specifically, the adhesive strength retention after PCT storage was calculated by the following formula.

(8) Drop Resistance Test Each epoxy resin composition of the Examples and Comparative Examples was applied onto a copper substrate, a copper block of 10 mm x 10 mm x 10 mm thick was placed on the applied surface, and the test piece was heated at 80°C for 1 hour and then at 120°C for 1 hour to be cured. After curing, the obtained test piece was cooled to room temperature. The obtained test piece was dropped from a height of 100 cm. The drop was repeated 10 times, and the number of drops until the copper block peeled off from the copper substrate was recorded.

Claims (6)

An epoxy resin composition comprising the following components (A) to (E):
(A) 100 parts by mass of a non-silicone-modified epoxy resin having two or more epoxy groups in one molecule; (B) 3 or more thiol groups in one molecule; (C) 0.5 to 100 parts by mass of a silicone-modified epoxy resin; (D) 1.0 to 200 parts by mass of a microcapsule-type curing accelerator; (E) 0.05 to 10 parts by mass of a reaction inhibitor; provided that the amount of component (B) is an amount such that the molar equivalent ratio of the thiol groups in component (B) to the total molar equivalent of the epoxy groups in components (A) and (C) is 0.1 to 1.0, and the silicone-modified epoxy resin (C) is a copolymer obtained by reacting one or more alkenyl group-containing epoxy resins represented by formulas (1) to (3) with an organohydrogenpolysiloxane represented by formula (5).

(In formulas (1) to (3), R ¹ is a glycidyl group (2,3-epoxypropyl group), X is independently a hydrogen atom or a bromine atom, n is a number from 0 to 50, and m is a number from 1 to 5.)

(In formula (5), R2 ^is independently a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, a hydroxy group, an alkoxy group having 1 to 10 carbon atoms, or an alkenyloxy group having 2 to 10 carbon atoms, p is a number from 0 to 1,000, q is a number from 0 to 20, and p+q is a number that satisfies 1<p+q≦1,000.) The epoxy resin composition according to claim 1, wherein component (B) is a thiol compound having four or more thiol groups in one molecule. The epoxy resin composition according to claim 1 or 2, in which the molar equivalent ratio of thiol groups in component (B) to the total molar equivalent of epoxy groups in components (A) and (C) is 0.1 to 0.5. The epoxy resin composition according to any one of claims 1 to 3, wherein component (D) is a microcapsule-type curing accelerator containing at least one selected from the group consisting of phosphorus compounds, tertiary amine compounds, imidazole compounds, urea compounds, and amine adduct compounds. The epoxy resin composition according to any one of claims 1 to 4, wherein component (E) is a borate ester compound and/or a phosphite ester compound. 6. The epoxy resin composition according to claim 1, wherein the volume average particle size of component (D) is 0.1 to 10 μm.

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