JP7481011B2 - Thermally cationic polymerizable resin composition - Google Patents

Description

The present invention relates to a thermally cationic polymerizable resin composition.

Cationically curable resins are widely used in fields such as paints, electrical and electronics, civil engineering and construction, and adhesives because the cured products have excellent properties such as mechanical strength, chemical resistance, electrical insulation, and adhesive properties.

In general, thermosetting resin compositions that utilize the radical redox mechanism (a combination of an iodonium salt-based photocationic polymerization initiator and an organic peroxide (thermal radical polymerization initiator)) can be cured at low temperatures, and even when only thermal curing is performed, they can exhibit physical properties equivalent to those when both UV curing and thermal curing are performed. As such compositions, Patent Documents 1 to 3 disclose thermal cationic polymerizable compositions that contain the above-mentioned radical redox mechanism and a cationic curable resin.

JP 2014-129473 A JP 2014-129474 A JP 2011-116977 A

However, the thermally cationic polymerizable compositions described in Patent Documents 1 to 3 utilize a mechanism of radical generation, and are therefore susceptible to oxygen inhibition, which can result in insufficient curing of the surface. This has raised concerns that insufficiently cured components may volatilize as outgassing during heat resistance tests, contaminating surrounding components, and other problems.

Therefore, the objective of the present invention is to provide a thermally cationic polymerizable resin composition that has excellent surface curing properties and reduced outgassing.

The inventors of the present invention have conducted extensive research in light of the above problems and have found that adding a thermal cationic initiator to a formulation that utilizes a radical redox mechanism can improve the curing properties of the resin surface and reduce the amount of outgassing. They have also found that adjusting the amount of thermal cationic initiator added can improve the surface curing properties while maintaining the glass transition temperature at a high temperature, thereby reducing the amount of outgassing.

The present invention relates to the following [1] to [4].
[1] (A) a cationically curable resin,
(B) iodonium salts of the formula Ar ¹ -I ⁺ -Ar ² ·X ^- , where Ar ¹ and Ar ² are independently substituted or unsubstituted aryl groups, and X ^- is an anion;
1. A thermal cationic polymerization resin composition comprising: (C) an organic peroxide; and (D) a thermal cationic polymerization initiator, wherein the content of the (D) component is 0.03 parts by weight or more and 1.50 parts by weight or less per 100 parts by weight of the (A) component.
[2] The thermally cationically polymerizable resin composition according to [1], wherein the component (D) is a sulfonium salt.
[3] The thermally cationically polymerizable resin composition according to _{[1] or [2} ], in which the anion of component (D) is SbF ₆ ^- , B(C ₆ F ₅ ) ₄ ^- , or [P(R _F ) _n F 6-n ] ^- (wherein R _F is independently a partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, and n is an integer of 0 to 5).
[4] The thermally cationically polymerizable resin composition according to any one of [1] to [3], wherein the component (A) is at least one selected from the group consisting of an epoxy resin and an oxetane resin.

The present invention provides a thermally cationic polymerizable resin composition that has excellent surface curing properties and reduced outgassing.

The following describes in detail the embodiments of the present invention.

[Thermal cationically polymerizable resin composition]
The thermal cationic polymerizable resin composition comprises (A) a cationic curable resin, (B) an iodonium salt represented by the formula: Ar ¹ -I ⁺ -Ar ^{2.X -} (wherein Ar ¹ and Ar ² are independently a substituted or unsubstituted aryl group, and X ^- is an anion), (C) an organic peroxide, and (D) a thermal cationic polymerization initiator, and the content of the component (D) is 0.03 parts by weight or more and 1.50 parts by weight or less per 100 parts by weight of the component (A).

The thermally cationic polymerizable resin composition has a content of component (D) of 0.03 parts by weight or more and 1.50 parts by weight or less, so that the glass transition temperature (Tg) can be maintained at a high temperature.

<(A) Cationic curable resin>
The cationic curable resin is not particularly limited as long as it has one or more cationic polymerizable groups in the molecule. Examples of the cationic polymerizable group include an epoxy group, an oxetanyl group, and a vinyl ether group. Specific examples of the cationic curable resin include an epoxy resin, an oxetane resin, a polystyrene compound, and a vinyl ether compound.

<Epoxy resin>
Epoxy resins can include aromatic, aliphatic and cycloaliphatic epoxy resins.

Examples of aromatic epoxy compounds include bisphenol A type epoxy resins (DIC's EPICLON 850, 850-S, EXA-850CRP, EXA-8067, etc.), bisphenol F type epoxy resins (DIC's EPICLON 830-S, EXA-830LVP, etc.), bisphenol AD type epoxy resins, bisphenol S type epoxy resins, naphthalene type epoxy resins (DIC's EPICLON HP-4032D, HP-7200H, etc.), phenol novolac type epoxy resins (DIC's EPICLON N-740, N-770, etc.), cresol novolac type epoxy resins (DIC's EPICLON N-660, N-670, N-655-EXP-S, etc.), and multifunctional epoxy resins. Examples of polyfunctional epoxy compounds include glycidyl ethers of tetra(hydroxyphenyl)alkanes, glycidyl ethers of tetrahydroxybenzophenones, and epoxidized polyvinylphenols.

Examples of aliphatic epoxy resins include polyglycidyl ethers of polyhydric alcohols or their alkylene oxide adducts. Specific examples of aliphatic epoxy compounds include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerin diglycidyl ether, trimethylolpropane triglycidyl ether (Epolite 100MF manufactured by Kyoeisha Chemical Co., Ltd.), polyethylene glycol diglycidyl ether, and 1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct of 2,2-bis(hydroxymethyl)-1-butanol (EHPE3150 manufactured by Daicel Corporation).

Aliphatic epoxy resins are resins having a structure in which an epoxy group is formed by two carbon atoms and an oxygen atom that form an alicyclic structure, and do not include aliphatic epoxy resins in which an epoxy group is bonded to one carbon atom that forms an alicyclic structure. Examples of alicyclic epoxy compounds include cyclohexane-based, cyclohexyl methyl ester-based, cyclohexyl methyl ether-based, spiro-based, and tricyclodecane-based epoxy compounds. Specific examples of alicyclic epoxy compounds include (3,3',4,4'-diepoxy)bicyclohexyl (Celloxide 8010 manufactured by Daicel Corporation, etc.), 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (Celloxide 2021P manufactured by Daicel Corporation, etc.), 1,2:8,9-diepoxylimonene, and 1,2-epoxy-4-vinylcyclohexane.

<Oxetane resin>
Specific examples of oxetane resins include 3-ethyl-3-hydroxymethyloxetane (oxetane alcohol) (OXT-101 manufactured by Toagosei Co., Ltd., etc.), 2-ethylhexyloxetane (OXT-212 manufactured by Toagosei Co., Ltd., etc.), xylylene bisoxetane (XDO, OXT-121 manufactured by Toagosei Co., Ltd., etc.), 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane (OXT-221 manufactured by Toagosei Co., Ltd., etc.), oxetanyl silsesquioxetane (OXT-191 manufactured by Toagosei Co., Ltd., etc.), phenol novolak oxetane (PHOX manufactured by Toagosei Co., Ltd., etc.), and 3-ethyl-3-phenoxymethyloxetane (POX, OXT-211 manufactured by Toagosei Co., Ltd., etc.).

<Vinyl ether compounds>
Specific examples of the vinyl ether compound include hydroxybutyl vinyl ether (such as HBVE manufactured by ISP), vinyl ether of 1,4-cyclohexanedimethanol (such as CHVE manufactured by ISP), triethylene glycol divinyl ether (such as DVE-3 manufactured by ISP), dodecyl vinyl ether (such as DDVE manufactured by ISP), and cyclohexyl vinyl ether (such as CVE manufactured by ISP).

<Preferred cationic curable resin>
The component (A) is preferably at least one selected from the group consisting of epoxy resins and oxetane resins.
The component (A) may be one type or a combination of two or more types.

<(B) Iodonium Salt Represented by Formula: Ar ¹ -I ⁺ -Ar ² ·X ^- >
The component (B) is an iodonium salt (hereinafter, also simply referred to as "iodonium salt") represented by the formula: Ar ¹ -I ⁺ -Ar ^{2.X -} (wherein Ar ¹ and Ar ² are independently substituted or unsubstituted aryl groups, and X ^- is an anion). Here, the "aryl group" refers to an aromatic hydrocarbon group having 6 to 18 carbon atoms, preferably a phenyl group or a naphthyl group. The aryl group may be unsubstituted or substituted with one or more optional substituents, and such substituents may include a linear or branched alkyl group having 1 to 18 carbon atoms, a linear or branched alkoxy group having 1 to 18 carbon atoms, a linear or branched alkoxycarbonyl group having 2 to 18 carbon atoms, a linear or branched acyloxy group having 2 to 18 carbon atoms, a halogen atom, a cyano group, a nitro group, a hydroxyl group, and the like. The "anion" may be any monovalent counter anion, but is preferably a non-antimony anion, and particularly preferably BF ₄ ^- , AsF ₆ ^- , or B(C ₆ F ₅ ) ₄ ^- , or [P(R _F ) _n F _6-n ] ^- , [C(R _F SO ₂ ) ₃ ] ^- , or [N(R _F SO ₂ ) ₂ ] ^- (wherein R _F is independently a partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, and n is an integer from 0 to 5).

Specific examples of the component (B) include diphenyliodonium hexafluoroarsenate, di(4-chlorophenyl)iodonium hexafluoroarsenate, di(4-bromophenyl)iodonium hexafluoroarsenate, phenyl(4-methoxyphenyl)iodonium hexafluoroarsenate, 4-methylphenyl-4-(1-methylethyl)phenyliodonium hexafluorophosphate, 4-methylphenyl-4-(1-methylethyl)phenyliodonium tri(pentafluoroethyl)trifluorophosphate (e.g., IK-1 manufactured by San-Apro Co., Ltd.), 4-methylphenyl-4-(1-methylethyl)phenyliodonium tetrakis(pentafluorophenyl)borate (e.g., PI-2074 manufactured by Rhodia Co., Ltd.), 4-methylphenyl-4-(2-methylpropyl)phenyliodonium hexafluorophosphate (e.g., IRGACURE (registered trademark) 250 manufactured by BASF Co., Ltd.), bis(C Examples of iodonium salts include _10-14 -alkylphenyl)iodonium hexafluorophosphate (e.g., WPI-113 manufactured by Wako Pure Chemical Industries, Ltd.), 4-methylphenyl-4-(1-methylethyl)phenyliodonium hexafluoroantimonate (e.g., WPI-116 manufactured by Wako Pure Chemical Industries, Ltd.), etc. Such iodonium salts are commercially available from reagent suppliers as, for example, cationic initiators, and can be easily obtained.

Component (B) may be one type or a combination of two or more types.

<(C) Organic Peroxide>
The organic peroxide (C) is a compound containing a peroxy group (-O-O-). The organic peroxide is a radical source. The radicals generated from the organic peroxide reductively decompose the iodonium salt of the component (B) to generate an acid without the use of light, thereby promoting cationic polymerization. Examples of the organic peroxide include diacyl peroxides, hydroperoxides, dialkyl peroxides, peroxyketals, peroxyesters, and peroxycarbonates.

Specific examples of component (C) include diacyl peroxides such as dilauroyl peroxide, dibenzoyl peroxide, and bis-3,5,5-trimethylhexanoyl peroxide; hydroperoxides such as 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide (e.g., Kayacumene H manufactured by Kayaku Aguzo Co., Ltd.), and t-butyl hydroperoxide; dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 1,3-bis(t dialkyl peroxides such as 2,5-dimethyl-2,5-di(t-butylperoxypropyl)benzene, t-butylcumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3; peroxyketals such as 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 1,1-di-t-butylperoxycyclohexane, and 2,2-di-t-butylperoxybutane; 1,1,3,3-tetramethylbutylperoxyneodecanoate, α-cumyl peroxy neodecanoate, t-butyl peroxy neodecanoate, t-butyl peroxy neoheptanoate, t-butyl peroxy pivalate, 1,1,3,3-tetramethylbutyl peroxy 2-ethylhexanoate, t-amyl peroxy 2-ethylhexanoate, t-butyl peroxy 2-ethylhexanoate, di-t-butyl peroxy hexahydroterephthalate, t-amyl peroxy 3,5,5-trimethylhexanoate, t-butyl peroxy Examples of organic peroxides include peroxyesters such as acetate, t-butyl peroxybenzoate, t-hexyl peroxybenzoate, and t-amyl peroxybenzoate; and peroxycarbonates such as di-2-ethylhexyl peroxydicarbonate, diisopropyl peroxydicarbonate, t-butyl peroxyisopropyl carbonate, t-butylperoxy 2-ethylhexyl carbonate, and 1,6-bis(t-butylperoxycarbonyloxy)hexane. These organic peroxides are commercially available from reagent suppliers and can be easily obtained.

Component (C) may be one type or a combination of two or more types.

<(D) Thermal Cationic Polymerization Initiator>
The thermal cationic polymerization initiator (D) is a component that serves as a cation generating source when cationic polymerization is carried out by heating. The thermal cationic polymerization initiator may be an onium salt composed of a cationic portion and an anionic portion, the cationic portion being an aromatic sulfonium, aromatic diazonium, aromatic ammonium, thianthrhenium, thioxanthonium, or (2,4-cyclopentadiene-1-yl)[(1-methylethylbenzene]-Fe cation, and the anionic portion being SbF ₆ ^- , BF ₄ ^- , PF ₆ ^- , B(C ₆ F ₅ ) ₄ ^- , [P(R _F ) _n F _6-n ] ^- (wherein R _F is independently a moiety or a fully fluorinated alkyl group having 1 to 6 carbon atoms, and n is an integer of 0 to 5), or [BX ₄ ] ^- (wherein X is a phenyl group substituted with at least two or more fluorine atoms or trifluoromethyl groups). The thermal cationic polymerization initiator is preferably a sulfonium salt. The anion of the thermal cationic polymerization initiator may be SbF ₆ ^- , B(C ₆ F ₅ ) ₄ ⁻ , or [P(R _F ) _n F _6-n ] ⁻ (wherein R _F is independently a partially or fully fluorinated alkyl group having 1 to 6 carbon atoms and n is an integer from 0 to 5).

Commercially available products of component (D) include TA-60, TA-60B, TA-100, and TA-120 manufactured by San-Apro Co., Ltd.; Adeka Opton CP-77 and Adeka Opton CP-66 manufactured by ADEKA Corporation; CI-2639 and CI-2624 manufactured by Nippon Soda Co., Ltd.; CXC-1612 and CXC-1738 manufactured by King Industries Co., Ltd.; and San-Aid SI-45, San-Aid SI-60, San-Aid SI-80, San-Aid SI-100, San-Aid SI-110, San-Aid SI-B3, San-Aid SI-B3A, and San-Aid SI-B4 manufactured by Sanshin Chemical Industry Co., Ltd.

Component (D) may be one type or a combination of two or more types.

<(E) Other Components>
The thermal cationic polymerizable resin composition may contain other components according to the purpose, as long as the effects of the present invention are not impaired. Examples of other components include photosensitizers, fillers, coupling agents (particularly silane coupling agents), pot life stabilizers, polymerization inhibitors, solvents, reinforcing agents, colorants, stabilizers, extenders, viscosity regulators, tackifiers, flame retardants, UV absorbers, antioxidants, discoloration inhibitors, antibacterial agents, antifungal agents, antiaging agents, antistatic agents, plasticizers, lubricants, smoothing agents, foaming agents, and release agents.

<Photosensitizer>
The photosensitizer is a component for increasing sensitivity to light. Examples of the photosensitizer include thioxanthone derivatives, carbonyl compounds, organic sulfur compounds, persulfides, redox compounds, azo and diazo compounds, halogen compounds, photoreducible dyes, and the like, with thioxanthone derivatives being preferred. Specific examples of the thioxanthone derivatives include isopropylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, thioxanthone ammonium salt, and the like, with 2,4-diethylthioxanthone being preferred.
The photosensitizer may be one type or a combination of two or more types.

<Filling agent>
The filler is not particularly limited, and examples thereof include known inorganic fillers and organic fillers.

Inorganic fillers include calcium carbonate, magnesium carbonate, barium sulfate, magnesium sulfate, aluminum silicate, titanium oxide, alumina, zinc oxide, silicon dioxide (precipitated silica, fumed silica, etc.), kaolin, talc, glass beads, sericite activated clay, aluminum hydroxide, asbestos powder, copper oxide, copper hydroxide, iron oxide, lead oxide, magnesium oxide, tin oxide, carbon, mica, smectite, carbon black, bentonite, aluminum nitride, and silicon nitride. From the viewpoint of adhesion, the inorganic fillers are preferably silicon dioxide, glass beads, and talc, and talc is particularly preferred.

Organic fillers include acrylic particles, polymethyl methacrylate, polystyrene (polystyrene beads), copolymers obtained by copolymerizing the monomers constituting these (i.e., methyl methacrylate or styrene) with other monomers, polyethylene particles, polysiloxane resin particles, polyamide particles, polyester microparticles, polyurethane microparticles, and rubber microparticles (acrylic rubber particles, isoprene rubber particles). The organic filler may have a core-shell structure. From the viewpoint of adhesion, the organic filler is preferably rubber microparticles, and particularly preferably rubber microparticles having a core-shell structure.

When the filler is an organic filler, the weight average molecular weight of the organic filler is not particularly limited, but is preferably 50,000 to 4,000,000, and particularly preferably 300,000 to 3,000,000.

The average particle size of the filler is not particularly limited, but is preferably 0.01 μm or more and less than 10 μm, and particularly preferably 1 μm to 5 μm. The average particle size of the filler can be measured using a laser diffraction particle size distribution measuring device.

The filler may be a component that functions as a thixotropic agent. The thixotropic agent is a component that imparts coating properties and the like to the first sealing composition. An example of a filler that functions as a thixotropic agent is fumed silica. The fumed silica may be surface-treated. Examples of surface treatment agents for inorganic thixotropic agents include monoalkyltrialkoxysilane, dimethyldichlorosilane, polydimethylsiloxane, and hexamethyldisilazane. Surface-treated or untreated fumed silica may be a commercially available product.
The fillers may be used alone or in combination of two or more.

<Silane coupling agent>
Examples of the silane coupling agent include a silane compound having one or more reactive functional groups selected from the group consisting of epoxy group, alkenyl group (e.g., vinyl group), (meth)acrylic group, primary or secondary amino group, mercapto group, isocyanato group, ureido group and halogen atom, or an alkyl group substituted with said group, and one or more alkoxy groups, and may have an unsubstituted alkyl group.The reactive functional group may be bonded to the silicon atom of the silane compound as the alkyl group substituted with said reactive functional group.

Specific examples of the silane coupling agent include silane compounds having an epoxy group and an alkoxy group, and which may have an alkyl group, such as 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane; silane compounds having an alkenyl group and an alkoxy group, and which may have an alkyl group, such as vinyltrimethoxysilane and p-styryltrimethoxysilane; silane compounds having a (meth)acrylic group and an alkoxy group, and which may have an alkyl group, such as 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane; N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(a [0043] Examples of such silane compounds include silane compounds having a primary or secondary amino group and an alkoxy group, and optionally having an alkyl group, such as N-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, and N-phenyl-3-aminopropyltrimethoxysilane; and silane compounds having one or more groups selected from the group consisting of a mercapto group, an isocyanato group, a ureido group, and a halogen atom, and one or more alkoxy groups, and optionally having an alkyl group, such as 3-ureidopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, and 3-isocyanatopropyltriethoxysilane.
The silane coupling agent may be used alone or in combination of two or more kinds.

<Other components (E)>
The polymerization inhibitor includes hydroquinone, paramethoxyphenol, dibutylhydroxytoluene, and the like.
Examples of the pot life stabilizer include an SI auxiliary (4-hydroxyphenyldimethylsulfonium methylsulfite) and a hindered phenol-based antioxidant.
Components other than those mentioned above can be appropriately selected from known components.

The (E) component may be one or a combination of two or more. For example, the (E) component may be a combination of one or more inorganic fillers and one or more photosensitizers.

<Method of preparing the composition>
The thermally cationically polymerizable resin composition can be produced by mixing the components. When the components (B) to (E) are solids, they may be dissolved in a solvent to improve compatibility with the components (particularly the component (A)) and then used to produce the cationically polymerizable resin composition.

[Curing method]
The thermally cationic polymerizable resin composition can be cured by applying heat. The thermally cationic polymerizable resin composition may be temporarily cured (temporarily fixed) by irradiating with energy rays such as ultraviolet rays, and then permanently cured (mainly fixed) by applying heat. When the thermally cationic polymerizable resin composition is temporarily cured by irradiating with energy rays, the thermally cationic polymerizable resin composition may contain a photosensitizer.

<Content of ingredients>
The content of each component in the thermally cationic polymerizable resin composition is preferably as follows.
The total content of the epoxy resin and oxetane resin in component (A) is preferably 60 to 100 parts by weight, and particularly preferably 80 to 100 parts by weight, per 100 parts by weight of component (A).
The total content of the oxetane resins in the component (A) is preferably 5 to 50 parts by weight, and particularly preferably 10 to 40 parts by weight, per 100 parts by weight of the epoxy resin.
The total content of the alicyclic epoxy resin and aromatic epoxy resin in component (A) is preferably 60 to 100 parts by weight, and particularly preferably 80 to 100 parts by weight, per 100 parts by weight of the epoxy resins in component (A).
From the viewpoint of thermal curing speed, the content of the component (B) is preferably 0.1 to 10.0 parts by weight, and particularly preferably 0.5 to 5.0 parts by weight, per 100 parts by weight of the component (A).
From the viewpoint of thermal curing speed, the content of the component (C) is preferably 1.0 to 10.0 parts by weight, and particularly preferably 1.5 to 5.0 parts by weight, per 100 parts by weight of the component (A).
The content of the (D) component is 0.03 to 1.50 parts by weight per 100 parts by weight of the (A) component. If the content of the (D) component is less than 0.03 parts by weight per 100 parts by weight of the (A) component, the surface curing property tends to be poor and the amount of outgassing tends to increase, whereas if the content of the (D) component is more than 1.50 parts by weight, the glass transition temperature tends to be low and the amount of outgassing tends to increase.
The total amount of components (A) to (D) is preferably 20 to 100 parts by weight, more preferably 30 to 100 parts by weight, and particularly preferably 40 to 100 parts by weight, based on the total amount of the thermally cationic polymerizable resin composition. The remainder is component (E).

[Application]
The thermally cationic polymerizable resin composition can be used for fixing optical components (e.g., backlight unit assembly of a display device, optical pickup assembly), camera module assembly, lens module assembly, optical communication module assembly, hard disk assembly, and protection of electronic components (e.g., molding).

The following examples are presented to clarify specific embodiments of the present invention, but the present invention is not limited to the examples shown here.

Each composition of the examples and comparative examples was produced using the following raw materials.
1. Component (A): Cationic curable resin (1) Epoxy resin Cresol novolac type epoxy resin (EPICLON N-655-EXP-S, manufactured by DIC Corporation)
Bisphenol A type epoxy resin (DIC Corporation, EPICLON EXA-850CRP)
Bisphenol F type epoxy resin (DIC Corporation, EPICLON EXA-830LVP)
Alicyclic epoxy resin: (3,3',4,4'-diepoxy)bicyclohexyl (manufactured by Daicel Corporation, Celloxide 8010)
Alicyclic epoxy resin: 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (manufactured by Daicel Corporation, Celloxide 2021P)
(2) Oxetane resin 3-ethyl-3-phenoxymethyloxetane (manufactured by Toagosei Co., Ltd., OXT-211 (POX))
Xylylene bisoxetane (manufactured by Toagosei Co., Ltd., OXT-121 (XDO))
Oxetanylsilsesquioxetane (manufactured by Toagosei Co., Ltd., OXT-191)

2. Component (B): Iodonium salt 4-methylphenyl-4-(1-methylethyl)phenyliodonium tetrakis(pentafluorophenyl)borate (manufactured by Solvay (Rhodia) Co., Ltd., PI-2074).

3. Component (C): organic peroxide 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate (Perocta O, manufactured by NOF Corporation).

4. Component (D): Thermal cationic polymerization initiator 4-hydroxyphenyl-methyl-benzylsulfonium tris(pentafluoroethyl)trifluorophosphate (TA-100, manufactured by San-Apro Co., Ltd.).

5. (E) Component: Other components Photosensitizer: 2,4-diethylthioxanthone (manufactured by Nippon Kayaku Co., Ltd., DETX-s)
Filler: Silica (AGC Si-Tech, NP-100)
Filler (thixotropic agent): Fumed silica (manufactured by Nippon Aerosil Co., Ltd., NKC130)
Solvent: 4-butyrolactone (Kanto Chemical)
Pot life stabilizer: 4-hydroxyphenyldimethylsulfonium methylsulfite (manufactured by Sanshin Chemical Industry Co., Ltd., SI auxiliary)
Polymerization inhibitor): dibutylhydroxytoluene (Kanto Chemical Co., Ltd., BHT)
Coupling agent: 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., KBM403)
Some solid sensitizers, initiators, additives, etc., are difficult to dissolve in the resin, so they were dissolved in 4-butyrolactone beforehand and then mixed with the resin.

Examples 1 to 13, Comparative Examples 1 to 7
[Preparation conditions]
A thermally cationically polymerizable resin composition was prepared by mixing the components based on the formulation shown in Table 1 and stirring the mixture with a stirrer at room temperature (25±3° C.; the same applies below) until the mixture became transparent.

[Evaluation conditions]
Surface curability The resin was applied to a slide glass in a thickness of 50 μm and thermally cured for 60 minutes on a hot plate heated to 100° C. After cooling at room temperature for 10 minutes, the surface curability was confirmed by touching with a finger.
○: Cured, ×: Surface uncured (sticky, tacky)

Amount of outgassing 15±2 mg of resin was applied to a 100 μl aluminum pan and thermally cured for 60 minutes on a hot plate heated to 100° C. After cooling at room temperature for 10 minutes, the resin was weighed (initial weight) using a precision balance (Mettler Toledo, XP2U). The resin was then heated for 15 hours in a hot air oven (Espec, LC113) at 150° C. After cooling at room temperature for 60 minutes, the resin was weighed (weight after heating) using a precision balance. The weight change rate (%) was calculated using the following formula and used as the amount of outgassing.

Glass transition temperature (Tg) and storage modulus The resin was cast into a mold having a length of 50 mm, a width of 10 mm, and a thickness of 0.5 mm, and heat cured for 60 minutes in a hot air oven (LC113, manufactured by Espec Corp.) at 100°C to prepare a cured product test piece. The obtained cured product test piece was measured with a dynamic viscoelasticity measuring device (DMA, DMS6100, manufactured by Seiko Instruments Inc.) while increasing the temperature at a frequency of 1.0 Hz. The peak top temperature in the loss tangent tan δ of the obtained result was taken as Tg.
A test piece of the cured product was prepared under the same conditions as for Tg, and measurements were performed using a dynamic viscoelasticity measuring device (DMA, manufactured by Seiko Instruments Inc., DMS6100). From the results obtained, the value of the storage modulus at 25° C. was extracted.

The results are summarized in the table below.

The thermally cationically polymerizable resin compositions of Examples 1 to 13 were excellent in surface curing properties and had reduced outgassing amounts.
In particular, a comparison of Examples 1 to 5 shows that the amount of outgassing was further reduced when the content of component (D) was within the preferred range relative to 100 parts by weight of component (A). The same can be said when comparing Examples 7 to 11.
Furthermore, comparison of Examples 1 to 5 with Examples 7 to 11, and Example 6 with Example 12 revealed that even when the thermally cationically polymerizable resin composition further contained the component (E), the surface curing property was excellent and the amount of outgassing was reduced.
Comparative Examples 1 to 6 did not contain the (D) component or contained less than 0.03 parts by weight of the (D) component relative to 100 parts by weight of the (A) component, and therefore had poor surface curability. In particular, Comparative Examples 4 to 6 had a large amount of outgassing. Comparative Example 7 had a large amount of outgassing because the content of the (D) component was more than 1.50 parts by weight relative to 100 parts by weight of the (A) component. Furthermore, a comparison between Examples 1 to 5 and Comparative Examples 1 to 3 showed that, when the composition other than the (D) component was almost the same, the content of the (D) component was within a predetermined range relative to 100 parts by weight of the (A) component, and thus the surface curability was excellent and the amount of outgassing was reduced. The same can be said by comparing Examples 7 to 11 with Comparative Examples 4 to 6.

Claims (3)

(A) a cationically curable resin,
(B) iodonium salts of the formula Ar ¹ -I ⁺ -Ar ² ·X ^- , where Ar ¹ and Ar ² are independently substituted or unsubstituted aryl groups, and X ^- is an anion;
1. A thermal cationically polymerizable resin composition comprising: (C) an organic peroxide; and (D) a thermal cationic polymerization initiator, wherein the content of the component (D) is 0.05 part by weight or more and 0.40 part by weight or less per 100 parts by weight of the component (A), and the component (D) is a sulfonium salt . 2. The thermally cationically polymerizable resin composition according to claim 1, wherein the anion of component (D) is SbF ₆ ^- , B(C ₆ F ₅ ) ₄ ^- , or [P(R ^F ) _n F _6-n ] ^- (wherein R ^F is independently a partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, and n is an integer of 0 to 5). 3. The thermally cationic polymerizable resin composition according to claim 1 , wherein the component (A) is at least one selected from the group consisting of epoxy resins and oxetane resins.