WO2024090459A1

WO2024090459A1 - Photocurable resin composition and optical adhesive

Info

Publication number: WO2024090459A1
Application number: PCT/JP2023/038441
Authority: WO
Inventors: 祐希河田
Original assignee: 積水フーラー株式会社
Priority date: 2022-10-27
Filing date: 2023-10-25
Publication date: 2024-05-02

Abstract

The present invention provides a photocurable resin composition that can maintain excellent adhesiveness even under high temperature and high humidity and that can be applied as a thin film when adhering adherends to each other. The photocurable resin composition of the present invention contains a (meth)acrylic polymerizable compound (A), a photopolymerization initiator (B), a silane coupling agent (C) having an SP value of less than 17.5, and a silane coupling agent (D) having an SP value of 17.5 or more and can therefore firmly adhere and integrate adherends to each other even under high temperature and high humidity.

Description

Photocurable resin composition and optical adhesive

The present invention relates to a photocurable resin composition and an optical adhesive.

　Photocurable resin compositions have traditionally been used to bond adherends such as glass and synthetic resins. In the bonding of lenses and prisms in the optical field, there is a demand for the thickness of the coating film of the photocurable resin composition to be as thin as a few micrometers.

In addition, in recent years, the use of optical lenses in in-vehicle applications has increased with the spread of autonomous driving and safe driving management systems, and there is a demand for reliable adhesiveness that is not compromised even in the high temperature and high humidity environment inside a vehicle.

As such a curable resin composition, Patent Document 1 discloses an adhesive composition for electronic components that contains a polymerizable compound (A) excluding a silane coupling agent (C) and/or a phosphate group-containing polymerizable monomer (D), a photopolymerization initiator (B), and a silane coupling agent (C) and/or a phosphate group-containing polymerizable monomer (D) represented by a specific structural formula.

JP 2007-153957 A

However, the adhesive composition for electronic components in Patent Document 1 has problems in that its adhesiveness decreases under high temperature and high humidity conditions, and its reliability is low under high temperature and high humidity conditions. Therefore, there is a demand for a curable resin composition that has excellent adhesiveness under high temperature and high humidity conditions.

The present invention provides a photocurable resin composition that can maintain excellent adhesion even under high temperature and high humidity conditions.

The photocurable resin composition of the present invention is characterized by containing a (meth)acrylic polymerizable compound (A), a photopolymerization initiator (B), a silane coupling agent (C) having an SP value of less than 17.5, and a silane coupling agent (D) having an SP value of 17.5 or more.

The optical adhesive of the present invention is characterized by containing the above-mentioned photocurable resin composition.

The photocurable resin composition of the present invention can firmly bond and integrate adherends together even under high temperature and humidity conditions.

FIG. 1 is a schematic side view showing a method for measuring adhesive strength. FIG. 2 is a schematic plan view showing a method for measuring the adhesive strength.

The photocurable resin composition of the present invention contains a (meth)acrylic polymerizable compound (A), a photopolymerization initiator (B), a silane coupling agent (C) having an SP value of less than 17.5, and a silane coupling agent (D) having an SP value of 17.5 or more.

[(Meth)acrylic polymerizable compound (A)]
The photocurable resin composition contains a (meth)acrylic polymerizable compound (A). The (meth)acrylic polymerizable compound (A) has a radically polymerizable unsaturated bond (e.g., an ethylenically unsaturated double bond) in the molecule.

The (meth)acrylic polymerizable compound (A) is not particularly limited, and examples thereof include monofunctional (meth)acrylates, polyfunctional (meth)acrylates, acrylic acid, and methacrylic acid. Note that (meth)acrylate means acrylate or methacrylate. The (meth)acrylic polymerizable compound (A) does not contain a silicon atom (Si) in the molecule. The (meth)acrylate refers to a compound having an acrylate structure (-COO-) that is generated by the reaction of a carboxy group (-COOH) and a hydroxyl group (-OH).

In the present invention, a (meth)acrylic polymerizable compound refers to a polymerizable compound having an acryloyl group [formula (4)] or a methacryloyl group [formula (5)] in the molecule. In formulas (4) and (5), *4 and *5 are bonds and represent single bonds.

The (meth)acrylic polymerizable compound (A) is preferably a monofunctional methacrylate or a polyfunctional methacrylate, since it can improve the adhesion between the produced polymer and the adherend under high temperature and high humidity conditions by reducing the cure shrinkage rate of the polymer obtained by curing the photocurable resin composition. The (meth)acrylic polymerizable compound (A) may be used alone or in combination of two or more kinds.

The (meth)acrylic polymerizable compound (A) preferably contains a monofunctional (meth)acrylate, since the adhesiveness of the cured product (polymer) of the photocurable resin composition to the adherend is improved. The (meth)acrylic polymerizable compound (A) preferably contains a monofunctional (meth)acrylate and a polyfunctional (meth)acrylate, since the adhesiveness of the cured product (polymer) of the photocurable resin composition under high temperature and high humidity is improved. The (meth)acrylic polymerizable compound (A) preferably contains a monofunctional (meth)acrylate, (meth)acrylic acid, and a polyfunctional (meth)acrylate, since the adhesiveness of the cured product (polymer) of the photocurable resin composition under high temperature and high humidity is improved. The monofunctional (meth)acrylate has only one radically polymerizable unsaturated bond (e.g., an ethylenically unsaturated double bond) in the molecule. The polyfunctional (meth)acrylate has multiple radically polymerizable unsaturated bonds (e.g., an ethylenically unsaturated double bond) in the molecule. (Meth)acrylic acid means acrylic acid or methacrylic acid.

The content of (meth)acrylate in the (meth)acrylic polymerizable compound (A) is preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, more preferably 80% by mass or more, and more preferably 85% by mass or more, since the adhesiveness of the cured product (polymer) of the photocurable resin composition under high temperature and high humidity conditions is improved. The content of (meth)acrylate in the (meth)acrylic polymerizable compound (A) is preferably 95% by mass or less, more preferably 93% by mass or less, and more preferably 90% by mass or less, since the adhesiveness of the cured product (polymer) of the photocurable resin composition to an adherend is improved.

The content of the monofunctional (meth)acrylate in the (meth)acrylic polymerizable compound (A) is preferably 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 65% by mass or more, and more preferably 70% by mass or more, since the adhesiveness of the cured product (polymer) of the photocurable resin composition to the adherend is improved. The content of the monofunctional (meth)acrylate in the (meth)acrylic polymerizable compound (A) is preferably 90% by mass or less, more preferably 85% by mass or less, and more preferably 80% by mass or less, since the adhesiveness of the cured product (polymer) of the photocurable resin composition under high temperature and high humidity conditions is improved.

The content of (meth)acrylic acid in the (meth)acrylic polymerizable compound (A) is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more, since the adhesiveness of the cured product (polymer) of the photocurable resin composition to the adherend is improved. The content of (meth)acrylic acid in the (meth)acrylic polymerizable compound (A) is preferably 20% by mass or less, and more preferably 15% by mass or less, since the adhesiveness of the cured product (polymer) of the photocurable resin composition under high temperature and high humidity conditions is improved.

The content of the polyfunctional (meth)acrylate in the (meth)acrylic polymerizable compound (A) is preferably 5% by mass or more, more preferably 10% by mass or more, and more preferably 15% by mass or more, since the adhesiveness of the cured product of the photocurable resin composition under high temperature and high humidity conditions is improved by imparting a cohesive force to the cured product of the photocurable resin composition. The content of the polyfunctional (meth)acrylate in the (meth)acrylic polymerizable compound (A) is preferably 70% by mass or less, more preferably 65% by mass or less, more preferably 60% by mass or less, more preferably 50% by mass or less, more preferably 40% by mass or less, more preferably 35% by mass or less, more preferably 30% by mass or less, and more preferably 25% by mass or less, since the adhesiveness of the cured product of the photocurable resin composition to the adherend is improved by imparting an appropriate crosslinking density to the cured product (polymer) of the photocurable resin composition.

The monofunctional (meth)acrylate is not particularly limited, and examples thereof include monofunctional alkyl (meth)acrylates, monofunctional (meth)acrylates having a saturated aliphatic ring structure, monofunctional (meth)acrylates having an aromatic ring, and monofunctional (meth)acrylates having a polar group. The monofunctional alkyl (meth)acrylates, monofunctional (meth)acrylates having a saturated aliphatic ring structure, and monofunctional (meth)acrylates having an aromatic ring do not have a polar group. Examples of the polar group include a carboxy group (-COOH), a hydroxyl group (-OH), a phosphonic acid group [-P(=O)(OH) ₂ ], a phosphoric acid group [-OP(=O)(OH) ₂ ], and a functional group represented by formula (6). In formula (6), *6 and *7 are bonds and represent single bonds.

Examples of monofunctional alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, lauryl (meth)methacrylate, and stearyl (meth)acrylate. The alkyl (meth)acrylates may be used alone or in combination of two or more.

In the present invention, an alkyl group refers to an atomic group remaining after removing one hydrogen atom from an aliphatic saturated hydrocarbon. The hydrogen of the alkyl group is not replaced by another atom or atomic group. The alkyl group may be either linear or branched.

Examples of monofunctional (meth)acrylates having a saturated aliphatic ring structure include isobornyl (meth)acrylate, norbornyl (meth)acrylate, tricyclononyl (meth)acrylate, tricyclodecyl (meth)acrylate, tetracyclodecyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, 3,5,5-trimethylcyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and adamantyl (meth)acrylate, with dicyclopentanyl (meth)acrylate and isobornyl (meth)acrylate being preferred. The (meth)acrylates having a saturated aliphatic ring structure may be used alone or in combination of two or more.

Examples of monofunctional (meth)acrylates having an aromatic ring include phenoxyalkyl acrylates such as phenoxyethyl acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate, dicyclopentenyl (meth)acrylate, etc., with phenoxyalkyl acrylates being preferred and phenoxyethyl acrylate being more preferred. The (meth)acrylates having an aromatic ring may be used alone or in combination of two or more kinds.

In the monofunctional (meth)acrylate having a polar group, examples of the polar group include a carboxy group (-COOH), a hydroxyl group (-OH), a phosphonic acid group [-P(=O)(OH) ₂ ], a phosphate group [-OP(=O)(OH) ₂ ], and a functional group represented by formula (6), of which a hydroxyl group, a phosphate group, and a functional group represented by formula (6) are preferred. In formula (6), *6 and *7 are bonds and represent single bonds.

Examples of monofunctional (meth)acrylates having a polar group include monofunctional alkyl (meth)acrylates in which the hydrogen of the alkyl group is replaced with a polar group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-hydroxybutyl (meth)acrylate; hydroxy monofunctional (meth)acrylates such as polyethylene glycol mono(meth)acrylate; and 2-(meth)acryloyloxyethyl acid phosphate, with 2-hydroxyethyl (meth)acrylate being preferred. The monofunctional (meth)acrylates having a polar group may be used alone or in combination of two or more. (Meth)acryloxy means acryloxy or methacryloxy.

The content of monofunctional alkyl (meth)acrylate in the (meth)acrylic polymerizable compound (A) is preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 55% by mass or more, more preferably 60% by mass or more, and more preferably 70% by mass or more, since the adhesiveness of the cured product (polymer) of the photocurable resin composition to the adherend is improved. The content of monofunctional alkyl (meth)acrylate in the (meth)acrylic polymerizable compound (A) is preferably 95% by mass or less, more preferably 90% by mass or less, and more preferably 85% by mass or less, since the adhesiveness of the cured product (polymer) of the photocurable resin composition under high temperature and high humidity conditions is improved.

In the (meth)acrylic polymerizable compound (A), the content of the monofunctional (meth)acrylate having a saturated aliphatic ring structure is preferably 20% by mass or more, more preferably 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 63% by mass or more, and more preferably 66% by mass or more. In the (meth)acrylic polymerizable compound (A), the content of the monofunctional (meth)acrylate having a saturated aliphatic ring structure is preferably 90% by mass or less, more preferably 85% by mass or less, and more preferably 80% by mass or less. When the content of the monofunctional (meth)acrylate having a saturated aliphatic ring structure is 20% by mass or more, the adhesiveness of the photocurable resin composition under high temperature and high humidity is improved by imparting cohesive force to the cured product (polymer) of the photocurable resin composition. When the content of the monofunctional (meth)acrylate having a saturated aliphatic ring structure is 90% by mass or less, the adhesiveness of the photocurable resin composition under high temperature and high humidity is improved.

In the (meth)acrylic polymerizable compound (A), the content of the monofunctional (meth)acrylate having a polar group is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and more preferably 0.3% by mass or more. In the (meth)acrylic polymerizable compound (A), the content of the monofunctional (meth)acrylate having a polar group is preferably 20% by mass or less, more preferably 15% by mass or less, more preferably 12% by mass or less, more preferably 10% by mass or less, more preferably 8% by mass or less, and more preferably 6% by mass or less. When the content of the monofunctional (meth)acrylate having a polar group is 0.1% by mass or more, the adhesion of the cured product of the photocurable resin composition to the adherend is improved due to the intermolecular force with the polar group present on the surface of the adherend. When the content of the monofunctional (meth)acrylate having a polar group is 20% by mass or less, the swelling of the cured product of the photocurable resin composition due to absorption of moisture is reduced, and the adhesion of the photocurable resin composition to the adherend under high temperature and high humidity is improved.

The polyfunctional (meth)acrylate is not particularly limited, but a bifunctional (meth)acrylate is preferred because it improves the adhesiveness of the cured product (polymer) of the photocurable resin composition under high temperature and high humidity conditions. The content of the bifunctional (meth)acrylate in the polyfunctional (meth)acrylate is preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, more preferably 95% by mass or more, more preferably 99% by mass or more, and more preferably 100% by mass.

Examples of polyfunctional (meth)acrylates include polyfunctional (meth)acrylates without polar groups such as 1,6-hexanediol (meth)acrylate, 1-((meth)acryloxy)-3-((meth)acryloxy)-2-propanol, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, and hydroxypivalic acid neopentyl glycol (meth)acrylic acid adduct, as well as polyfunctional (meth)acrylates with polar groups such as bis(2-(meth)acryloxyethyl) acid phosphate, pentaerythritol tri(meth)acrylate, and dipentaerythritol penta(meth)acrylate, with 1,6-hexanediol (meth)acrylate, triethylene glycol di(meth)acrylate, and bis(2-(meth)acryloxyethyl) acid phosphate being preferred. The polyfunctional (meth)acrylates may be used alone or in combination of two or more.

In the polyfunctional (meth)acrylate having a polar group, examples of the polar group include a carboxy group (-COOH), a hydroxyl group (-OH), a phosphonic acid group [-P(=O)(OH) ₂ ], a phosphate group [-OP(=O)(OH) ₂ ], and a functional group represented by formula (6), of which a hydroxyl group, a phosphate group, and a functional group represented by formula (6) are preferred. In formula (6), *6 and *7 are bonds and represent single bonds.

The polyfunctional (meth)acrylate preferably contains a (meth)acrylic oligomer having an acryloxy group [formula (1)] or a methacryloxy group [formula (2)] at both ends of the main chain. When the (meth)acrylic oligomer is contained, the cured product of the photocurable resin composition has excellent adhesiveness under high temperature and high humidity conditions. In the present invention, the main chain refers to the longest chain in the molecule. The length of the chain is determined based on the number of atoms that directly constitute the chain, and the greater the number of atoms, the longer the chain.

The main chain of the (meth)acrylic oligomer is not particularly limited, but a main chain containing at least one skeleton selected from the group consisting of a polyurethane skeleton, a polyisoprene skeleton, and a polybutadiene skeleton is preferred. The main chain of the (meth)acrylic oligomer preferably contains a polyurethane skeleton, since the cured product of the photocurable resin composition exhibits superior adhesiveness under high temperature and high humidity conditions.

The (meth)acrylic oligomer preferably contains a polyester skeleton, a polycarbonate skeleton or a polyether skeleton in the main chain, more preferably a polyester skeleton or a polycarbonate skeleton, and even more preferably a polyester skeleton, because the cured product of the photocurable resin composition exhibits superior adhesion under high temperature and high humidity conditions.

The (meth)acrylic oligomer preferably has a main chain that has a polyurethane skeleton and a polyester skeleton, or a polyurethane skeleton and a polycarbonate skeleton, because the cured product of the photocurable resin composition exhibits superior adhesive properties under high temperature and high humidity conditions. Note that a (meth)acrylic oligomer having a polyurethane skeleton and a polyester skeleton in the main chain is commercially available, for example, from Nippon Kayaku Co., Ltd. under the product name "UX-4101." A (meth)acrylic oligomer having a polyurethane skeleton and a polycarbonate skeleton in the main chain is commercially available, for example, from Negami Chemical Industries Co., Ltd. under the product name "UN-9000PEP."

The weight average molecular weight of the (meth)acrylic oligomer is preferably 1000 or more, more preferably 2000 or more, and more preferably 3000 or more. The weight average molecular weight of the (meth)acrylic oligomer is preferably 100,000 or less, more preferably 50,000 or less, more preferably 30,000 or less, more preferably 20,000 or less, more preferably 15,000 or less, more preferably 13,000 or less, more preferably 12,000 or less, more preferably 11,000 or less, more preferably 10,000 or less, and more preferably 8,000 or less. When the weight average molecular weight of the (meth)acrylic oligomer is 1000 or more, the cured product of the photocurable resin composition exhibits superior adhesiveness under high temperature and high humidity. When the weight average molecular weight of the (meth)acrylic oligomer is 100,000 or less, the cured product of the photocurable resin composition exhibits superior adhesiveness under high temperature and high humidity.

In the present invention, the weight average molecular weight of the (meth)acrylic oligomer refers to the polystyrene-equivalent value measured by GPC (gel permeation chromatography).

The weight average molecular weight of the (meth)acrylic oligomer can be measured, for example, using the following measuring device and measuring conditions.
Measurement device: Waters Corporation, product name "ACQUITY APC System"
Measurement conditions Column: Waters HSPgel(TM)HR MB-M
Mobile phase: tetrahydrofuran 0.5 mL/min Sample concentration: 1 mg/mL
Detector: RI detector Standard material: polystyrene (manufactured by Aldrich, molecular weight: 370 to 2,520,000)
SEC temperature: 40°C

A (meth)acrylic oligomer having a polyurethane skeleton and a polyester skeleton in the main chain and an acryloxy group [formula (1)] or a methacryloxy group [formula (2)] at both ends of the main chain can be produced, for example, as follows. Note that the production method shown below is only one example of a method for producing the (meth)acrylic oligomer, and (meth)acrylic oligomers produced by methods other than the production method shown below can also be used.

A diisocyanate and a polyester polyol are reacted in a general-purpose manner to produce a urethane oligomer having isocyanate groups at both ends and a polyurethane skeleton and a polyester skeleton in the main chain, and the hydroxyl groups of a (meth)acrylate having a hydroxyl group (e.g., 2-hydroxyethyl (meth)acrylate, hydroxymethyl (meth)acrylate, etc.) are reacted with the isocyanate groups at both ends of the urethane oligomer to produce the compound.

The diisocyanate is not particularly limited, and examples thereof include aromatic diisocyanates, aliphatic diisocyanates, and alicyclic diisocyanates.

Aromatic diisocyanates include diphenylmethane diisocyanate, toluene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, 1,3-bis(1-isocyanato-1-methylethyl)benzene, 1,4-bis(1-isocyanato-1-methylethyl)benzene, ω,ω'-diisocyanato-1,4-diethylbenzene, and urethane prepolymers with isocyanate groups at both ends.

Examples of aliphatic diisocyanates include hexamethylene diisocyanate, tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl-pentane-1,5-diisocyanate, lysine diisocyanate, and trioxyethylene diisocyanate.

Examples of alicyclic diisocyanates include isophorone diisocyanate, cyclohexyl diisocyanate, hydrogenated diphenylmethane diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tetramethylxylene diisocyanate.

Examples of polyester polyols include ester reaction products of low molecular weight diols with a molecular weight of 60 to 300 and dicarboxylic acids or their reactive derivatives, which have hydroxyl groups at both ends of the main chain.

Low molecular weight diols having a molecular weight of 60 to 300 are not particularly limited, and examples include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, butanediol, 1,6-hexanediol, 2-methyl-1,8-octanediol, nonanediol, cyclohexanedimethanol, neopentyl glycol, and 3-methyl-1,5-pentanediol.

The dicarboxylic acid is not particularly limited, and examples thereof include adipic acid, sebacic acid, succinic acid, maleic acid, phthalic acid, hexahydrophthalic acid, terephthalic acid, and other dicarboxylic acids or their anhydrides.

In the (meth)acrylate polymerizable compound (A), the content of the (meth)acrylic oligomer having a polyurethane skeleton and a polyester skeleton in the main chain and an acryloxy group [formula (1)] or a methacryloxy group [formula (2)] at both ends of the main chain is preferably 10% by mass or more, more preferably 15% by mass or more, more preferably 18% by mass or more, more preferably 20% by mass or more, and more preferably 30% by mass or more. In the (meth)acrylate polymerizable compound (A), the content of the (meth)acrylic oligomer having a polyurethane skeleton and a polyester skeleton in the main chain and an acryloxy group [formula (1)] or a methacryloxy group [formula (2)] at both ends of the main chain is preferably 70% by mass or less, more preferably 60% by mass or less, and more preferably 50% by mass or less. When the content of the (meth)acrylic oligomer is 10% by mass or more, the cured product of the photocurable resin composition exhibits better adhesion under high temperature and high humidity conditions. When the (meth)acrylic oligomer content is 70% by mass or less, the cured product of the photocurable resin composition exhibits superior adhesion under high temperature and high humidity conditions.

In the (meth)acrylic polymerizable compound (A), the content of the polyfunctional (meth)acrylate not having a polar group is preferably 5% by mass or more, more preferably 10% by mass or more, more preferably 15% by mass or more, and more preferably 17% by mass or more. In the (meth)acrylic polymerizable compound (A), the content of the polyfunctional (meth)acrylate not having a polar group is preferably 70% by mass or less, more preferably 60% by mass or less, more preferably 50% by mass or less, more preferably 40% by mass or less, more preferably 35% by mass or less, more preferably 30% by mass or less, more preferably 27% by mass or less, and more preferably 25% by mass or less. When the content of the polyfunctional (meth)acrylate not having a polar group is 5% by mass or more, the adhesiveness of the cured product (polymer) of the photocurable resin composition under high temperature and high humidity is improved. When the content of the polyfunctional (meth)acrylate is 70% by mass or less, the adhesiveness of the photocurable resin composition to the adherend under high temperature and high humidity is improved.

In the (meth)acrylic polymerizable compound (A), the content of the polyfunctional (meth)acrylate having a polar group is preferably 0.1 mass% or more, more preferably 0.2 mass% or more, and more preferably 0.3 mass% or more. In the (meth)acrylic polymerizable compound (A), the content of the polyfunctional (meth)acrylate having a polar group is preferably 5 mass% or less, more preferably 4 mass% or less, and more preferably 3 mass% or less. When the content of the polyfunctional (meth)acrylate having a polar group is 0.1 mass% or more, the adhesion of the photocurable resin composition to the adherend is improved. When the content of the polyfunctional (meth)acrylate having a polar group is 5 mass% or less, the coatability of the photocurable resin composition is improved.

In the above polyfunctional (meth)acrylate, examples of the polar group include a carboxy group (-COOH), a hydroxyl group (-OH), a phosphonic acid group [-P(=O)(OH) ₂ ], a phosphoric acid group [-OP(=O)(OH) ₂ ], and a functional group represented by formula (6). In formula (6), *6 and *7 are bonds and represent single bonds.

[Photopolymerization initiator (B)]
The photocurable resin composition contains a photopolymerization initiator (B). The photopolymerization initiator generates radicals when irradiated with radiation, and radically polymerizes the (meth)acrylic polymerizable compound (A) contained in the photocurable resin composition.

The photopolymerization initiator (B) is not particularly limited as long as it can radically polymerize the (meth)acrylic polymerizable compound (A) contained in the photocurable resin composition. As the photopolymerization initiator, for example, an α-hydroxyketone-based photopolymerization initiator, an acylphosphine oxide-based photopolymerization initiator, a thioxanthone-based photopolymerization initiator, or a triazine-based photopolymerization initiator is preferable, and an α-hydroxyketone-based photopolymerization initiator is preferable because it has excellent compatibility with the (meth)acrylic polymerizable compound (A) and has excellent curing properties of the photocurable resin composition. The photopolymerization initiator (B) may be used alone or in combination of two or more kinds.

α-Hydroxyketone photopolymerization initiators are not particularly limited, and examples include 1-hydroxycyclohexyl phenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one, and 2-hydroxy-2-methyl-1-phenyl-propan-1-one.

Examples of acylphosphine oxide photopolymerization initiators include 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

An example of a thioxanthone-based photopolymerization initiator is 2,4-diethylthioxanthone.

Examples of triazine-based photopolymerization initiators include 2-[2-(furan-2-yl)vinyl]-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-[2-(5-methylfuran-2-yl)vinyl]-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-[(4-methoxyphenyl)vinyl]-4,6-bis(trichloromethyl)-1,3,5-triazine, and 2-[(3,4-dimethoxyphenyl)vinyl]-4,6-bis(trichloromethyl)-1,3,5-triazine.

In the photocurable resin composition, the content of the photopolymerization initiator is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and more preferably 0.3 parts by mass or more, per 100 parts by mass of the (meth)acrylic polymerizable compound (A) contained in the photocurable resin composition. In the photocurable resin composition, the content of the photopolymerization initiator is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, and more preferably 2.0 parts by mass or less, per 100 parts by mass of the (meth)acrylic polymerizable compound (A) contained in the photocurable resin composition. When the content of the photopolymerization initiator is 0.1 parts by mass or more, the photocurability of the photocurable resin composition is improved. When the content of the photopolymerization initiator is 5.0 parts by mass or less, the molecular weight of the cured product (polymer) of the photocurable resin composition is increased to improve the cohesive force, and the adhesiveness of the cured product of the photocurable resin composition to the adherend is improved.

[Silane coupling agents (C) and (D)]
The photocurable resin composition contains a silane coupling agent (C) having an SP value of less than 17.5 (hereinafter, sometimes simply referred to as "silane coupling agent (C)") and a silane coupling agent (D) having an SP value of 17.5 or more (hereinafter, sometimes simply referred to as "silane coupling agent (D)").

Silane coupling agents have a structure in which a hydrolyzable group is bonded to a silicon atom. The hydrolyzable group is not particularly limited, and examples thereof include a hydrogen atom, an alkoxy group, an acyloxy group, a ketoximate group, an aminooxy group, a mercapto group, and an alkenyloxy group. Since this improves the adhesion of the cured product of the photocurable resin composition to an adherend, an alkoxy group is preferred, and a methoxy group and an ethoxy group are more preferred.

The photocurable resin composition contains a silane coupling agent (C) with an SP value of less than 17.5 and a silane coupling agent (D) with an SP value of 17.5 or more. Depending on the adherend (e.g., glass, synthetic resin, etc.) to be bonded using the photocurable resin composition, either the silane coupling agent (C) or (D) acts preferentially on the adherend, while the other silane coupling agent acts preferentially on the polymer produced by polymerizing the (meth)acrylic polymerizable compound (A). As a result, the adhesive and the adherend can be firmly bonded via the two types of silane coupling agents (C) and (D), and as a result, the adherend is firmly bonded by the adhesive.

The SP values of silane coupling agents (C) and (D) are values calculated using the Fedors formula shown below.

Here, ΣΔE is the sum of the cohesive energies of the atomic groups of the silane coupling agent (J/mol), and ΣΔV is the sum of the molecular volumes of the atomic groups of the silane coupling agent (cm ³ /mol).

The SP value of a silane coupling agent is calculated based on the sum of the cohesive energies and the sum of the molecular volumes of each atomic group, as described above. The sum of the cohesive energies and the sum of the molecular volumes of each atomic group were proposed by Fedors, and the SP value of a silane coupling agent can be calculated based on the proposed values. For example, the SP value of a silane coupling agent tends to be low if it has a radically polymerizable functional group in the molecule.

The radically polymerizable functional group may be any functional group capable of radically polymerizing with the (meth)acrylic polymerizable compound (A), but vinyl groups, acryloxy groups, and methacryloxy groups are preferred.

An acryloxy group is a monovalent atomic group represented by formula (1), and a methacryloxy group is a monovalent atomic group represented by formula (2). In formulas (1) and (2), *1 and *2 are bonds and represent single bonds.

First, a silane coupling agent (C) having an SP value of less than 17.5 will be described. The silane coupling agent (C) having an SP value of less than 17.5 is not particularly limited, and examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, (3-acryloxypropyl)trimethoxysilane, (3-methacryloxypropyl)trimethoxysilane, (3-methacryloxypropyl)triethoxysilane, (3-methacryloxyoctyl)trimethoxysilane, (3-mercaptopropyl)trimethoxysilane, etc., with alkoxysilane being preferred, trialkoxysilane being more preferred, trimethoxysilane and triethoxysilane being more preferred, and vinyltriethoxysilane, (3-acryloxypropyl)trimethoxysilane, and (3-methacryloxypropyl)trimethoxysilane being preferred.

The SP value of the silane coupling agent (C) is less than 17.5, preferably 17.3 or less, and more preferably 17.2 or less. The SP value of the silane coupling agent (C) is preferably 15 or more, more preferably 15.3 or more, and more preferably 15.5 or more.

Silane coupling agents (C) having an SP value of less than 17.5 preferably have a radical polymerizable functional group in the molecule. Silane coupling agents (C) having an SP value of less than 17.5 are preferably alkoxysilanes having a radical polymerizable functional group in the molecule (preferably vinyl, acryloxy, methacryloxy), more preferably trialkoxysilanes having a radical polymerizable functional group in the molecule (preferably vinyl, acryloxy, methacryloxy), more preferably trimethoxysilanes having a radical polymerizable functional group in the molecule (preferably vinyl, acryloxy, methacryloxy), and more preferably triethoxysilanes having a radical polymerizable functional group in the molecule (preferably vinyl, acryloxy, methacryloxy). Silane coupling agents (C) having an SP value of less than 17.5 are preferably vinylalkoxysilanes, methacryloxyalkylalkoxysilanes, and acryloxyalkylalkoxysilanes, more preferably vinyltrialkoxysilanes, methacryloxyalkyltrialkoxysilanes, and more preferably acryloxyalkyltrialkoxysilanes. The alkoxy group contained in the silane coupling agent (C) having an SP value of less than 17.5 is preferably a methoxy group, an ethoxy group, a propoxy group, or a butoxy group, and more preferably a methoxy group or an ethoxy group. When the silane coupling agent (C) having an SP value of less than 17.5 has a radical polymerizable functional group in the molecule, the silane coupling agent (C) is dispersed and incorporated into the polymer generated by polymerization of the (meth)acrylic polymerizable compound (A) in the radical polymerization reaction of the (meth)acrylic polymerizable compound (A) during the curing of the photocurable resin composition. Therefore, the cured product of the photocurable resin composition exhibits uniform adhesion to the adherend as a whole, and the cured product (polymer) of the photocurable resin composition exhibits excellent adhesion to the adherend under high temperature and high humidity.

And because the silane coupling agent (C) is incorporated into the polymer, the silane coupling agent (C) is not excessively unevenly distributed on the adherend, and is maintained in an appropriately dispersed state in the cured product (polymer) of the photocurable resin composition for a long period of time. Therefore, the cured product of the photocurable resin composition can maintain overall uniform adhesion to the adherend under high temperature and high humidity conditions for a long period of time, and the cured product of the photocurable resin composition can maintain excellent adhesion to the adherend under high temperature and high humidity conditions for a long period of time.

The silane coupling agent (C) preferably has a methacryloxy group or an acryloxy group as the radically polymerizable functional group, and more preferably has a methacryloxy group. When the silane coupling agent (C) has a (meth)acryloxy group as the radically polymerizable functional group, it is incorporated in a more well-dispersed state into the cured product (polymer) of the photocurable resin composition in the copolymerization reaction with the (meth)acrylic polymerizable compound (A), and the cured product of the photocurable resin composition exhibits more uniform overall adhesion to the adherend under high temperature and high humidity conditions, and the cured product (polymer) of the photocurable resin composition exhibits even better adhesion to the adherend under high temperature and high humidity conditions.

Next, a silane coupling agent (D) having an SP value of 17.5 or more will be described. The silane coupling agent (D) having an SP value of 17.5 or more is not particularly limited, and examples thereof include (3-glycidyloxypropyl)triethoxysilane, (3-glycidyloxypropyl)trimethoxysilane, (3-glycidyloxyoctyl)trimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, and 3-isocyanatepropyltriethoxysilane. Since the adhesiveness of the cured product of the photocurable resin composition to the adherend under high temperature and high humidity conditions is improved, (3-glycidyloxypropyl)triethoxysilane and (3-glycidyloxypropyl)trimethoxysilane are preferred.

The SP value of the silane coupling agent (D) is 17.5 or more, preferably 17.55 or more, and more preferably 17.6 or more. The SP value of the silane coupling agent (D) is preferably 20 or less, more preferably 19.5 or less, more preferably 19 or less, more preferably 18 or less, more preferably 17.9 or less, and more preferably 17.8 or less.

Silane coupling agents (D) with an SP value of 17.5 or more preferably have an epoxy group, and more preferably have a glycidyl group, since they improve the adhesion of the cured product of the photocurable resin composition to an adherend under high temperature and high humidity conditions without impairing the photocurability of the photocurable resin composition.

When the silane coupling agent (D) having an SP value of 17.5 or more has a glycidyl group, the silane coupling agent (D) preferably has a structure in which an alkyl group is bonded to a silicon atom and the hydrogen bonded to the carbon atom of the alkyl group is replaced with a glycidyloxy group (glycidyloxyalkylsilane), preferably has a structure in which an alkyl group and an alkoxy group (preferably a methoxy group or an ethoxy group) are bonded to a silicon atom and the hydrogen bonded to the carbon atom of the alkyl group is replaced with a glycidyloxy group (glycidyloxyalkylalkoxysilane), and preferably has a structure in which one alkyl group and three alkoxy groups (preferably a methoxy group or an ethoxy group) are bonded to a silicon atom and the hydrogen bonded to the carbon atom of the alkyl group is replaced with a glycidyloxy group (glycidyloxyalkyltrialkoxysilane). The number of carbon atoms in the alkyl group is preferably 1 to 12, more preferably 2 to 10. When the number of carbon atoms in the alkyl group is within the above range, the cured product of the photocurable resin composition has excellent adhesion to the adherend under high temperature and high humidity conditions.

The glycidyloxy group has the following structure (3). *3 is a bond and means a single bond.

The silane coupling agent (D) having an SP value of 17.5 or more preferably does not have a radically polymerizable functional group in the molecule. If the silane coupling agent (D) does not have a radically polymerizable functional group in the molecule, the silane coupling agent (D) is not incorporated into the polymer generated by radical polymerization of the (meth)acrylic polymerizable compound (A) in the radical polymerization reaction during the curing of the photocurable resin composition, and exists in a free state in the cured product (polymer) of the photocurable resin composition. Therefore, the silane coupling agent (D) can move in the cured product of the photocurable resin composition as necessary to improve its effect on the adherend, thereby improving the adhesion of the cured product of the photocurable resin composition to the adherend under high temperature and high humidity conditions.

In the case of silane coupling agents (C) and (D), if the silane coupling agent (C) with an SP value of less than 17.5 has a radically polymerizable functional group in the molecule, while the silane coupling agent (D) with an SP value of 17.5 or more does not have a radically polymerizable functional group in the molecule, the silane coupling agent (C) with an SP value of less than 17.5 can be incorporated into the cured product (polymer) of the photocurable resin composition, and the silane coupling agent (C) can be appropriately dispersed in the cured product of the photocurable resin composition, while the silane coupling agent (D) with an SP value of 17.5 or more can be present in a free state in the cured product of the photocurable resin composition.

Thus, the silane coupling agent (C) is incorporated into the polymer and restricted from excessive movement, while the silane coupling agent (D) is allowed to exist mobile in the polymer of the photocurable resin composition, and while preventing the silane coupling agents (C) and (D) from being excessively unevenly distributed, the silane coupling agents (C) and (D) move appropriately depending on the adherend, allowing the silane coupling agent to act uniformly on the adherend, and the cured product of the photocurable resin composition exhibits excellent adhesion to the adherend under high temperature and high humidity conditions.

If a silane coupling agent (C) with an SP value of less than 17.5 has a radically polymerizable functional group in its molecule, while a silane coupling agent (D) with an SP value of 17.5 or more does not have a radically polymerizable functional group in its molecule, when the adherend is glass, the silane coupling agent (D) with a high SP value that is in a free state in the cured product of the photocurable resin composition can act effectively on the glass because glass has a high SP value, and the photocurable resin composition can exhibit excellent adhesion to glass, particularly under high temperature and high humidity conditions.

The content of the silane coupling agent (C) in the photocurable resin composition is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, more preferably 2 parts by mass or more, and more preferably 3 parts by mass or more, per 100 parts by mass of the (meth)acrylic polymerizable compound (A). The content of the silane coupling agent (C) in the photocurable resin composition is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and more preferably 6 parts by mass or less, per 100 parts by mass of the (meth)acrylic polymerizable compound (A). When the content of the silane coupling agent (C) is 0.5 parts by mass or more, it can be uniformly dispersed throughout the cured product of the photocurable resin composition or at the interface with the adherend, and the cured product of the photocurable resin composition exhibits excellent adhesion to the adherend under high temperature and high humidity. When the content of the silane coupling agent (C) is 10 parts by mass or less, the cohesive force of the cured product (polymer) of the photocurable resin composition can be improved, and the adhesion to the adherend can be improved.

The content of the silane coupling agent (D) in the photocurable resin composition is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and more preferably 0.5 parts by mass or more, per 100 parts by mass of the (meth)acrylic polymerizable compound. The content of the silane coupling agent (D) in the photocurable resin composition is preferably 7 parts by mass or less, more preferably 6 parts by mass or less, more preferably 5 parts by mass or less, and more preferably 4 parts by mass or less, per 100 parts by mass of the (meth)acrylic polymerizable compound. When the content of the silane coupling agent (D) is 0.1 parts by mass or more, the cured product of the photocurable resin composition exhibits excellent adhesion to the adherend under high temperature and high humidity. When the content of the silane coupling agent (D) is 7 parts by mass or less, the cohesive force of the cured product (polymer) of the photocurable resin composition can be improved, and the adhesion to the adherend can be improved.

The total content of the silane coupling agents (C) and (D) in the photocurable resin composition is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and more preferably 3 parts by mass or more, per 100 parts by mass of the (meth)acrylic polymerizable compound (A). The total content of the silane coupling agents (C) and (D) in the photocurable resin composition is more preferably 15 parts by mass or less, more preferably 12 parts by mass or less, more preferably 10 parts by mass or less, and more preferably 8 parts by mass or less, per 100 parts by mass of the (meth)acrylic polymerizable compound (A). When the total content of the silane coupling agents (C) and (D) is 1 part by mass or more, the adhesion of the cured product of the photocurable resin composition to the adherend under high temperature and high humidity conditions is improved. When the total content of the silane coupling agents (C) and (D) is 15 parts by mass or less, the cohesive force of the cured product (polymer) of the photocurable resin composition can be improved, and the adhesion to the adherend can be improved.

In the photocurable resin composition, the mass ratio of the content of silane coupling agent (C) having an SP value of less than 17.5 to the content of silane coupling agent (D) having an SP value of 17.5 or more [silane coupling agent (C) having an SP value of less than 17.5/silane coupling agent (D) having an SP value of 17.5 or more] (hereinafter sometimes referred to as the "silane coupling agent ratio") is preferably 0.5 or more, more preferably 1 or more, more preferably 2 or more, more preferably 2.3 or more, more preferably 3 or more, and more preferably 4 or more. In the photocurable resin composition, the mass ratio of the content of the silane coupling agent (C) having an SP value of less than 17.5 to the content of the silane coupling agent (D) having an SP value of 17.5 or more [silane coupling agent (C) having an SP value of less than 17.5 / silane coupling agent (D) having an SP value of 17.5 or more] is preferably 25 or less, more preferably 24 or less, more preferably 20 or less, more preferably 17 or less, more preferably 13 or less, more preferably 11 or less, more preferably 10 or less, more preferably 9 or less, and more preferably 7 or less. When the silane coupling agent ratio is 0.5 or more, the adhesion of the cured product of the photocurable resin composition to the adherend under high temperature and high humidity is improved. When the silane coupling agent ratio is 25 or less, the adhesion of the cured product of the photocurable resin composition to the adherend under high temperature and high humidity is improved.

[Additive]
The photocurable resin composition may contain a thixotropic agent, an adhesion-imparting resin, a plasticizer, a non-thermally expandable fine particle, a dye, a pigment, a flame retardant, a surfactant, and the like, within the range that does not impair the physical properties of the composition.

[Photocurable resin composition]
The method for producing the photocurable resin composition is not particularly limited, and the photocurable resin composition can be produced, for example, by uniformly mixing the (meth)acrylic polymerizable compound (A), the photopolymerization initiator (B), the silane coupling agent (C) and the silane coupling agent (D), and additives contained as necessary, in a general manner, preferably under reduced pressure.

The photocurable resin composition has as its essential components a (meth)acrylic polymerizable compound (A), a photopolymerization initiator (B), a silane coupling agent (C) with an SP value of less than 17.5, and a silane coupling agent (D) with an SP value of 17.5 or more. Since there is no need to include components that cause an increase in the viscosity of the photocurable resin composition, the viscosity can be kept low, the photocurable resin composition can be applied to the surface of the adherend in a thin film thickness, and the adherend can be bonded and integrated with the thin cured product of the photocurable resin composition.

Furthermore, since the photocurable resin composition can be applied to the surface of the adherend in a thin film thickness, the coating of the photocurable resin composition can be irradiated with radiation sufficiently to the inside, allowing the photoradical polymerization reaction to proceed smoothly and sufficiently, producing a cured product with excellent adhesion even under high temperature and high humidity conditions.

The viscosity of the photocurable resin composition at 25°C is preferably 1 mPa·s or more, more preferably 2 mPa·s or more, and more preferably 3 mPa·s or more. The viscosity of the photocurable resin composition at 25°C is preferably 5000 mPa·s or less, more preferably 4000 mPa·s or less, more preferably 3000 mPa·s or less, more preferably 1000 mPa·s or less, more preferably 900 mPa·s or less, more preferably 800 mPa·s or less, more preferably 700 mPa·s or less, more preferably 600 mPa·s or less, more preferably 500 mPa·s or less, more preferably 400 mPa·s or less, more preferably 300 mPa·s or less, more preferably 200 mPa·s or less, more preferably 100 mPa·s or less, and more preferably 50 mPa·s or less. When the viscosity of the photocurable resin composition at 25°C is 1 mPa·s or more, the adhesiveness of the cured product of the photocurable resin composition to the adherend is improved. When the viscosity of the photocurable resin composition at 25°C is 5000 mPa·s or less, the applicability of the photocurable resin composition to the surface of the adherend is improved.

The viscosity of the photocurable resin composition is measured in accordance with JIS K6833 using a B-type viscometer and a low viscosity measurement spindle (a spindle capable of measuring 20 mPa·s or less) at 25°C and 50% relative humidity at a rotation speed of 50 rpm. The low viscosity measurement spindle may be, for example, a commercially available spindle under the product name "ULA" from Eiko Seiki Co., Ltd.

[Method for bonding adherends using photocurable resin composition]
The photocurable resin composition is used to bond and integrate adherends. The adherend is not particularly limited, and examples thereof include thin-layer glass, optical glass, prisms, lenses, silicon wafers, semiconductor mounting parts, and synthetic resin molded products (e.g., synthetic resin sheets, etc.). The photocurable resin composition can be suitably used as an optical adhesive for bonding and integrating optical adherends. The photocurable resin composition can be suitably used, in particular, for bonding and integrating optical adherends such as thin-layer glass, optical glass, prisms, and lenses. The adherends may be of the same type or different types.

The procedure for bonding and integrating adherends using a photocurable resin composition will now be described. First, the adherends are laminated together with the photocurable resin composition between the opposing surfaces of the adherends to produce a laminate (lamination process). Three or more adherends may also be laminated together with the photocurable resin composition between the opposing surfaces of the adherends to produce a laminate.

In the lamination process, when producing a laminate, the photocurable resin composition can be applied in a thin film thickness, making it possible to reduce the overall thickness of the laminate and to miniaturize the finished product obtained using the photocurable resin composition.

The photocurable resin composition is a one-liquid type, so there is no need for the complicated process of mixing two liquids to create a laminate, and the laminate can be easily manufactured.

Then, the entire laminate obtained is irradiated with radiation from the stacking direction of the laminate, curing the photocurable resin composition interposed between the opposing surfaces of the adherends that make up the laminate to produce a cured product (polymer) (curing process). This cured product can bond and integrate the adherends together.

The photocurable resin composition can be applied to the surface of the adherend in a thin film thickness, so the photocurable resin composition applied to the surface of the adherend can be cured sufficiently and reliably to develop excellent adhesion.

The peak wavelength of the radiation is preferably 500 nm or less, since this provides excellent curing properties for the photocurable resin composition. The radiation is irradiated in the stacking direction (thickness direction) of the laminate, and the radiation is preferably light with a wavelength of 320 nm or more. By using radiation with a wavelength of 320 nm or more, it is possible to largely prevent the radiation from being absorbed by the optical glass, and even if multiple photocurable resin composition layers are present, it is possible to allow the radiation to sufficiently penetrate all of the photocurable resin composition layers. The photopolymerization initiator (B) contained in the photocurable resin composition effectively absorbs the radiation, allowing the radical polymerization of the (meth)acrylic polymerizable compound (A) and, if necessary, the silane coupling agent contained in the photocurable resin composition to proceed smoothly.

Furthermore, even if multiple layers of photocurable resin composition are present, it is not necessary to irradiate the laminate with radiation for each layer of the photocurable resin composition. After the laminate is produced, radiation can be irradiated to the entire thickness of the laminate in the stacking direction, so that all of the photocurable resin composition constituting the laminate can be irradiated with radiation and reliably cured in a short period of time, and the adherends can be bonded together.

The cured product of the photocurable resin composition that bonds and integrates the adherends maintains excellent adhesion even under high temperature and humidity conditions, so the bonded and integrated state of the adherends can be reliably maintained even in harsh environments such as the interior of an automobile.

The present invention will be described in more detail below using examples, but the present invention is not limited thereto. Specific numerical values of the blending ratio (content ratio), physical property values, parameters, etc. used in the following description can be replaced with the upper limit values (numerical values defined as "equal to or less than") or lower limit values (numerical values defined as "equal to or greater than") of the corresponding blending ratio (content ratio), physical property values, parameters, etc. described in "Means for solving the problem."

The following compounds were used in the examples and comparative examples.

[(Meth)acrylic polymerizable compound (A)]
[Monofunctional (meth)acrylic polymerizable compound]
Methacrylic acid (monofunctional (meth)acrylate having an aromatic ring)
Phenoxyethyl acrylate (monofunctional (meth)acrylate having a saturated aliphatic ring structure)
・Dicyclopentanyl methacrylate ・Isobornyl acrylate

[Polyfunctional (meth)acrylic polymerizable compound]
(Polyfunctional (meth)acrylate having no polar group)
1,6-Hexanediol dimethacrylate Polyfunctional acrylic oligomer 1 (manufactured by Nippon Kayaku Co., Ltd., product name "UX-4101", having a polyurethane skeleton and a polyester skeleton in the main chain, having acryloxy groups [formula (1)] at both ends of the main chain, having no polar groups in the molecule, weight average molecular weight: 6500)
- Multifunctional acrylic oligomer 2 (manufactured by Daicel Allnex Corporation, product name "EBECRYL8411", having a polyurethane skeleton and a polyester skeleton in the main chain, having acryloxy groups [formula (1)] at both ends of the main chain, having no polar groups in the molecule, weight average molecular weight: 12,000)
(Polyfunctional (meth)acrylate having a polar group)
Bis(2-methacryloxyethyl) acid phosphate (manufactured by Kyoeisha Chemical Co., Ltd., product name "Light Ester P-2M")

[Photopolymerization initiator (B)]
・1-Hydroxycyclohexyl phenyl ketone

[Silane coupling agent (C)]
Vinyltriethoxysilane (SP value: 15.88, radical polymerizable functional group: vinyl group)
(3-methacryloxypropyl)trimethoxysilane (SP value: 17.05, radical polymerizable functional group: methacryloxy group)
(3-acryloxypropyl)trimethoxysilane (SP value: 17.28, radical polymerizable functional group: methacryloxy group)
Hexyltrimethoxysilane (SP value: 15.88, radical polymerizable functional group: none)

[Silane coupling agent (D)]
(3-glycidyloxypropyl)triethoxysilane (SP value: 17.71, radical polymerizable functional group: none, has a glycidyl group)
(8-glycidyloxyoctyl)trimethoxysilane (SP value: 17.65, radical polymerizable functional group: none, has a glycidyl group)

(Examples 1 to 20, Comparative Examples 1 to 3)
The (meth)acrylic polymerizable compound (A), the silane coupling agent (C) and the silane coupling agent (D) in the amounts shown in Tables 1 to 3 were each supplied into a reaction vessel and mixed uniformly to prepare a mixed solution.

Next, a predetermined amount of photopolymerization initiator (B) shown in Tables 1 to 3 was added to the mixed liquid and mixed until the photopolymerization initiator (B) was completely dissolved in the mixed liquid to obtain a photocurable resin composition.

The viscosity of the obtained photocurable resin composition before curing at 25°C was measured as described above, and the results are shown in Tables 1 to 3.

The photocurable resin composition obtained was measured for initial adhesive strength and high temperature/high humidity adhesive strength, as well as the fracture morphology under the measurement conditions for initial adhesive strength and adhesive strength at high temperature/high humidity, as described below, and the results are shown in Tables 1 to 3.

[Initial adhesive strength]
Two

rectangular glass plates

1 and 2, each having a length of 50 mm, a width of 25 mm, and a thickness of 5 mm, were prepared. The entire surfaces of the two glass plates were washed with ethanol and dried.

As shown in Figures 1 and 2, one glass sheet 1 was placed on a horizontal mounting surface 3, and the edge of the long side of the other glass sheet 2 was placed on the edge of the long side of the glass sheet 1. The overlap width between the edges of the two

glass sheets

1 and 2 was 12.5 mm. A photocurable resin composition 5 was interposed between the edges of the long sides of the two

glass sheets

1 and 2, and the photocurable resin composition 5 was filled over the entire lateral length between the opposing surfaces of the edges of the long sides of the two

glass sheets

1 and 2. The photocurable resin composition 5 was 25 mm long x 12.5 mm wide x 0.01 mm thick. A supporting glass sheet 4 was placed in the gap between the overlapping glass sheet on the upper side and the mounting surface, and the upper glass sheet 2 was supported by the supporting glass sheet 4.

The photocurable resin composition 5 interposed between the overlapping portion of the two

glass plates

1 and 2 was irradiated with ultraviolet light having a peak wavelength of 360 nm at an illuminance of 2 mW/ ^cm2 for 10 minutes using an ultraviolet lamp (manufactured by Toshiba Lighting & Technology Corporation, product name "FL20S-BL") to cure the photocurable resin composition 5, thereby producing a cured body in which the two glass plates were laminated and integrated via the cured product of the photocurable resin composition. The ultraviolet lamp was disposed vertically above the overlapping portion of the two glass plates and at a height of 80 mm from the placement surface.

The obtained hardened body was subjected to a three-point bending test using a bench-top precision universal testing machine (Shimadzu Corporation, product name "Autograph AGS-100NX") to press the overlapping portion of the two glass sheets at a pressing speed of 10 mm/min, and the maximum strength obtained was taken as the measured strength (N), and the adhesive strength was calculated based on the following formula. The ambient environment during the measurement of the measured strength was 25°C and the relative humidity was 50%.

Initial adhesive strength (MPa)
= measured strength (N) / [0.025 (m) × 0.0125 (m) × 10 ^-6 ]

[High temperature and high humidity adhesive strength]
A cured product was prepared in the same manner as for the initial adhesive strength. The cured product was left for 48 hours in a high-temperature and high-humidity atmosphere of 120° C., 0.1 MPa and 100% relative humidity.

The hardened product that had been left in the high temperature and high humidity atmosphere for 48 hours was removed and left in an atmosphere of 25°C and 50% relative humidity for 24 hours. After that, the high temperature and high humidity adhesive strength of the obtained hardened product was measured in the same manner as the initial adhesive strength.

The adhesive strength retention rate (%) was calculated based on the following formula and is shown in Tables 1 to 3.
Adhesive strength maintenance rate (%) = 100 x high temperature and high humidity adhesive strength / initial adhesive strength

[Peeling Form]
After measuring the initial adhesive strength and the high-temperature, high-humidity adhesive strength, the cured product was visually observed at the portion where the two glass plates were laminated together via the cured product of the photocurable resin composition, and was evaluated based on the following criteria.
Material failure: The glass plate was broken.
Interfacial fracture: fracture occurred at the interface between the glass plate and the cured product of the photocurable resin composition.

The photocurable resin composition of the present invention can firmly bond and integrate adherends together even under high temperature and high humidity conditions, making it suitable for use in bonding and integrating adherends together in harsh environments such as the interior of an automobile.

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority based on Japanese Patent Application No. 2022-171960 filed on October 27, 2022, and Japanese Patent Application No. 2023-101972 filed on June 21, 2023, the disclosures of which are incorporated herein by reference in their entireties.

Reference Signs List 1 Glass plate 2 Glass plate 3 Placing surface 4 Support glass plate 5 Photocurable resin composition

Claims

A photocurable resin composition comprising (A) a (meth)acrylic polymerizable compound, (B) a photopolymerization initiator, (C) a silane coupling agent having an SP value of less than 17.5, and (D) a silane coupling agent having an SP value of 17.5 or more.
The photocurable resin composition according to claim 1, characterized in that the mass ratio of the content of the silane coupling agent (C) with an SP value of less than 17.5 to the content of the silane coupling agent (D) with an SP value of 17.5 or more [silane coupling agent (C) with an SP value of less than 17.5/silane coupling agent (D) with an SP value of 17.5 or more] is 0.5 to 25.
The photocurable resin composition according to claim 1 or 2, characterized in that the silane coupling agent (C) having an SP value of less than 17.5 has a radically polymerizable functional group in the molecule.
The photocurable resin composition according to claim 1 or 2, characterized in that the silane coupling agent (D) having an SP value of 17.5 or more has an epoxy group.
The photocurable resin composition according to claim 1 or 2, characterized in that the silane coupling agent (D) having an SP value of 17.5 or more has a glycidyl group.
The photocurable resin composition according to claim 1 or 2, characterized in that the viscosity at 25°C is 1 to 5000 mPa·s.
An optical adhesive comprising the photocurable resin composition according to claim 1 or 2.