JP7709956B2 - Light-curing sheet adhesive - Google Patents

Description

The present invention relates to a photocurable sheet adhesive that can be sufficiently cured by exposure to light alone.

Traditionally, epoxy resins are used as the curable component of curable adhesives.
For example, Patent Document 1 describes a thermosetting sheet adhesive containing an epoxy resin, characterized in that the cured product of the thermosetting sheet adhesive satisfies specific requirements regarding the storage modulus.

Generally, when a curable adhesive containing an epoxy resin cures, a three-dimensional cross-linked structure is formed inside the cured adhesive. For this reason, in curable adhesives containing epoxy resins, the molecular motion of the curable components may decrease during the curing reaction, and the curing reaction may not proceed sufficiently. If the curing reaction does not proceed sufficiently, problems may occur such as not being able to obtain a cured adhesive product with the desired properties, or unreacted curable components remaining in the cured adhesive product and eluting the curable components.

JP 2017-110128 A

When using a thermosetting sheet adhesive such as that described in Patent Document 1, the curing reaction is usually initiated by heating and then allowed to proceed under high temperature conditions, so that the molecular motion of the curable components can be maintained in an active state for a long period of time.

On the other hand, photocurable sheet adhesives are capable of initiating a curing reaction by light irradiation alone, without the need for heating. However, if light irradiation is the only process performed when using photocurable sheet adhesives, and heating is not performed, the above-mentioned problems are likely to occur due to the curing reaction not progressing sufficiently.

The present invention has been made with the aim of improving the curing properties of photocurable sheet adhesives. In other words, the present invention aims to provide a photocurable sheet adhesive that can be sufficiently cured by only irradiating light without the need for heat treatment.

In order to solve the above problems, the present inventors have conducted extensive research into photocurable sheet adhesives containing epoxy resins, and have found that by using an epoxy resin that gives a cured product with a glass transition temperature (Tg) of 25° C. or lower, a photocurable sheet adhesive that can be sufficiently cured by light irradiation alone can be obtained, which has led to the completion of the present invention.
That is, according to the present invention, there are provided the following photocurable sheet adhesives [1] to [8].
[1] A photocurable sheet adhesive comprising the following components (A), (B), and (C), wherein at least one of the epoxy resins constituting component (B) is an epoxy resin [epoxy resin (BL)] that gives a cured product having a glass transition temperature (Tg) of 25°C or lower:
Component (A): Binder resin component composed of one or more binder resins Component (B): Epoxy-based curable component composed of one or more epoxy resins Component (C): Photocationic polymerization initiator [2] The photocurable sheet adhesive according to [1], wherein at least one of the binder resins constituting the component (A) is a phenoxy resin.
[3] The photocurable sheet adhesive according to [1] or [2], wherein at least one of the binder resins constituting the component (A) is a polyvinyl acetal resin.
[4] The photocurable sheet adhesive according to any one of [1] to [3], wherein the content of component (B) is 35 to 75 mass% based on the total mass of the photocurable sheet adhesive.
[5] The photocurable sheet adhesive according to any one of [1] to [4], wherein the epoxy resin (BL) is an epoxy resin having an oxyalkylene structure.
[6] The photocurable sheet adhesive according to any one of [1] to [5], wherein at least one of the epoxy resins constituting the component (B) is liquid at 23°C.
[7] A photocurable sheet adhesive according to any one of [1] to [6] above, wherein the photocurable sheet adhesive is cured under the following conditions using a high-pressure mercury lamp to obtain a cured product, and when the storage shear modulus at 0°C (G' ₀ ) and the storage shear modulus at 100°C (G' ₁₀₀ ) are measured, the cured product satisfies the following formula (I):

[Curing conditions for photocurable sheet adhesive]
Temperature: 23℃
Illuminance measured at a wavelength of 365 nm: 200 mW/ ^cm2
Accumulated light quantity measured at a wavelength of 365 nm: 1000 mJ/ ^cm2
[8] The photocurable sheet adhesive according to any one of [1] to [7], which is used in the manufacture of an optical device.

According to the present invention, a photocurable sheet adhesive is provided that can be sufficiently cured by only irradiating light without the need for heat treatment.

The photocurable sheet adhesive of the present invention is a photocurable sheet adhesive containing the above-mentioned components (A), (B), and (C), in which at least one of the epoxy resins constituting component (B) is an epoxy resin that gives a cured product having a glass transition temperature (Tg) of 25°C or lower.
The sheet-like adhesive refers to an adhesive formed into a sheet that exhibits no fluidity at room temperature (23° C., the same applies below). In the present invention, the photocurable sheet-like adhesive may be in the form of a strip or a long strip (strip).
In this specification, the "photocurable sheet adhesive" may be referred to as the "sheet adhesive".

[Component (A)]
The photocurable sheet adhesive of the present invention contains, as component (A), a binder resin component constituted of one or more binder resins. Component (A) is constituted only by a binder resin.
In the present invention, the term "binder resin component" means the binder resin when the photocurable sheet adhesive contains one type of binder resin, and means a mixture of two or more types of binder resins when the photocurable sheet adhesive contains two or more types of binder resins.
The term "binder resin" refers to a polymer component that imparts shape retention or flexibility to the photocurable sheet adhesive.

The photocurable sheet adhesive of the present invention contains component (A), which makes it easier for the adhesive to maintain a certain shape even in an uncured state.

The content of component (A) is preferably from 20 to 60 mass %, more preferably from 25 to 53 mass %, and even more preferably from 30 to 45 mass %, based on the total mass of the photocurable sheet adhesive.
When the content of component (A) is within the above range, a photocurable sheet adhesive having sufficient shape retention is easily obtained.

The weight average molecular weight (Mw) of the binder resin constituting component (A) is preferably 10,000 to 300,000, and more preferably 30,000 to 200,000.
The weight average molecular weight (Mw) of the binder resin can be determined as a value converted into standard polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

The binder resin preferably has a glass transition temperature (Tg) of 50° C. or higher, and more preferably 80° C. or higher.
If the content ratio of component (B) is increased, the shape retention of the photocurable sheet adhesive may decrease, but this problem is less likely to occur if a binder resin with a glass transition temperature (Tg) of 50°C or higher is contained.
There is no particular upper limit for the glass transition temperature (Tg) of the binder resin, but it is usually 200° C. or lower.
The glass transition temperature (Tg) of the binder resin can be measured in accordance with JIS K 7121 using a differential scanning calorimeter.

Examples of the binder resin include olefin resins, acrylic polymers, polyester resins, polyvinyl alcohol resins, polyvinyl acetal resins, polyvinyl chloride, phenoxy resins, polyamide resins, cellulose-based materials, polyvinyl ethers, polyimide resins, styrene-isoprene-styrene block copolymers, and styrene-butadiene-styrene block copolymers.
The binder resins may be used alone or in combination of two or more.

At least one of the binder resins is preferably a phenoxy resin.
Phenoxy resin is a polymer whose main chain has a polyaddition structure of aromatic diol and aromatic diglycidyl ether. Phenoxy resin generally corresponds to a high molecular weight epoxy resin and has a degree of polymerization of about 100 or more.

Some phenoxy resins have a high glass transition temperature (Tg), making them suitable for use as binder resins.

The epoxy equivalent of the phenoxy resin is preferably 5,000 g/eq or more, more preferably 7,000 g/eq or more. The epoxy equivalent value can be measured in accordance with JIS K7236 (the same applies below).

Examples of the phenoxy resin include bisphenol A type phenoxy resin, bisphenol F type phenoxy resin, bisphenol S type phenoxy resin, copolymer type phenoxy resin of bisphenol A type and bisphenol F type, bisphenol E type phenoxy resin, naphthalene type phenoxy resin, novolac type phenoxy resin, biphenyl type phenoxy resin, and cyclopentadiene type phenoxy resin.
These phenoxy resins may be used alone or in combination of two or more.

The phenoxy resin can be obtained by a method of reacting a difunctional phenol with an epihalohydrin to a high molecular weight, or by a method of subjecting a difunctional epoxy resin with a difunctional phenol to a polyaddition reaction.
For example, the phenoxy resin can be obtained by reacting a bifunctional phenol with an epihalohydrin in the presence of an alkali metal hydroxide in an inert solvent at a temperature of 40 to 120° C. The phenoxy resin can also be obtained by subjecting a bifunctional epoxy resin with a bifunctional phenol to a polyaddition reaction in the presence of a catalyst such as an alkali metal compound, an organic phosphorus compound, a cyclic amine compound, or the like in an organic solvent having a boiling point of 120° C. or higher, such as an amide solvent, an ether solvent, a ketone solvent, a lactone solvent, or an alcohol solvent, by heating to 50 to 200° C. at a reaction solids concentration of 50% by weight or less.

The bifunctional phenols are not particularly limited as long as they are compounds having two phenolic hydroxyl groups. For example, monocyclic bifunctional phenols such as hydroquinone, 2-bromohydroquinone, resorcinol, and catechol; bisphenols such as bisphenol A, bisphenol F, bisphenol AD, and bisphenol S; dihydroxybiphenyls such as 4,4'-dihydroxybiphenyl; dihydroxyphenyl ethers such as bis(4-hydroxyphenyl)ether; and those in which a linear alkyl group, a branched alkyl group, an aryl group, a methylol group, an allyl group, a cyclic aliphatic group, a halogen (such as tetrabromobisphenol A), or a nitro group has been introduced into the aromatic ring of the phenol skeleton; and polycyclic bifunctional phenols in which a linear alkyl group, a branched alkyl group, an allyl group, an allyl group with a substituent, a cyclic aliphatic group, or an alkoxycarbonyl group has been introduced into the carbon atom in the center of the bisphenol skeleton.

Examples of epihalohydrins include epichlorohydrin, epibromohydrin, and epiiodohydrin.

In addition, in the present invention, commercially available products can also be used as the phenoxy resin. Examples include Mitsubishi Chemical's product name: YX7200 (glass transition temperature (Tg): 150°C), YX6954 (bisphenolacetophenone skeleton-containing phenoxy resin, glass transition temperature (Tg): 130°C), and Nippon Steel Chemical & Material's product name: YP70 (glass transition temperature (Tg): 70°C).

At least one of the binder resins is preferably a polyvinyl acetal resin.
Polyvinyl acetal resin is a polymer obtained by an acetalization reaction between the hydroxyl groups of polyvinyl alcohol (or a partially saponified product of its ester; the same applies below) and an aldehyde.

In order to obtain a photocurable sheet adhesive that gives a cured product with superior adhesive strength, the photocurable sheet adhesive preferably contains a large amount of the curable component (component (B)). However, photocurable sheet adhesives that contain a large amount of component (B) tend to have reduced component uniformity, which may result in reduced transparency of the obtained cured product.
By using a polyvinyl acetal resin as the binder resin, the uniformity of the components can be improved, making it easier to obtain a photocurable sheet-like adhesive that gives a cured product with excellent transparency.

In addition, when phenoxy resin is used as the binder resin, a decrease in the uniformity of such components may occur, but when component (A) contains both phenoxy resin and polyvinyl acetal resin, the uniformity of the components of the adhesive for photocurable sheets is good.

Examples of the polyvinyl acetal resin include polyvinyl butyral obtained by reacting polyvinyl alcohol with butylaldehyde, polyvinyl formal obtained by reacting polyvinyl alcohol with formaldehyde, and polyvinyl acetoacetal obtained by reacting polyvinyl alcohol with acetaldehyde.
These polyvinyl acetal resins may be used alone or in combination of two or more.

Polyvinyl acetal resin can be synthesized by reacting polyvinyl alcohol with an aldehyde in a suitable solvent using an acid catalyst. Examples of the solvent that can be used include water, alcoholic solvents such as methyl alcohol and ethyl alcohol, mixed solvents of water and alcohol, and aprotic polar solvents such as dimethyl sulfoxide.

Alternatively, the polyvinyl acetal resin can be synthesized by adding an acid catalyst and an aldehyde to a polyvinyl acetate solution and reacting them.
The acid catalyst to be used is not particularly limited, and examples thereof include organic acids such as acetic acid, paratoluenesulfonic acid, etc.; and inorganic acids such as nitric acid, sulfuric acid, etc.

[(B) component]
The photocurable sheet adhesive of the present invention contains, as component (B), an epoxy-based curable component composed of one or more epoxy resins. Component (B) is composed only of an epoxy resin.
In the present invention, the term "epoxy-based curable component" means an epoxy resin when the photocurable sheet adhesive contains one type of epoxy resin, and means a mixture of two or more types of epoxy resins when the photocurable sheet adhesive contains two or more types of epoxy resins.
In addition, even if a compound has an epoxy group, if it corresponds to the binder resin constituting component (A), it is not considered to constitute component (B).

The photocurable sheet adhesive of the present invention contains component (B) and thereby functions as a curable sheet adhesive.

The content of component (B) is preferably 35 to 75 mass %, more preferably 45 to 70 mass %, and even more preferably 53 to 65 mass %, based on the total mass of the photocurable sheet adhesive.
When the content of component (B) is within the above range, a photocurable sheet adhesive having sufficient curability is easily obtained.

The weight average molecular weight (Mw) of the epoxy resin constituting component (B) is preferably 100 to 5,000, and more preferably 200 to 4,000.
The weight average molecular weight (Mw) of the epoxy resin can be determined in terms of standard polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

The epoxy equivalent of the epoxy resin is preferably 100 g/eq or more and 500 g/eq or less, more preferably 115 g/eq or more and 450 g/eq or less. By curing a photocurable sheet adhesive containing an epoxy resin having an epoxy equivalent of 100 g/eq or more and 500 g/eq or less, a cured product with excellent adhesive strength can be obtained.

The epoxy resin may be a monofunctional epoxy resin or a polyfunctional epoxy resin.
As the epoxy resin, a multifunctional epoxy resin is preferred because it is easy to obtain a cured product having superior adhesive strength.
The term "multifunctional epoxy resin" means an epoxy resin having two or more epoxy groups in the molecule.

Examples of polyfunctional epoxy resins include aliphatic epoxy compounds (excluding alicyclic epoxy compounds), aromatic epoxy compounds, alicyclic epoxy compounds, etc.

Examples of aliphatic epoxy compounds include 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, triglycidyl ether of glycerin, triglycidyl ether of trimethylolpropane, tetraglycidyl ether of sorbitol, hexaglycidyl ether of dipentaerythritol, diglycidyl ether of polyethylene glycol, and diglycidyl ether of polypropylene glycol.

Examples of aromatic epoxy compounds include glycidyl ethers of bisphenol A, bisphenol F, or compounds obtained by further adding alkylene oxide to these compounds, and epoxy novolac resins; polyglycidyl ethers of aromatic compounds having two or more phenolic hydroxyl groups, such as resorcinol, hydroquinone, and catechol; glycidyl ethers of aromatic compounds having two or more alcoholic hydroxyl groups, such as phenyldimethanol, phenyldiethanol, and phenyldibutanol; glycidyl esters of polybasic aromatic compounds having two or more carboxylic acids, such as phthalic acid, terephthalic acid, and trimellitic acid; and the like.

Examples of alicyclic epoxy compounds include polyglycidyl ethers of polyhydric alcohols having at least one alicyclic structure, such as dicyclopentadiene dimethanol diglycidyl ether and hydrogenated bisphenol A, and cycloalkene oxide compounds such as cyclohexene oxide and cyclopentene oxide-containing compounds obtained by epoxidizing cyclohexene or cyclopentene ring-containing compounds with an oxidizing agent.

Epoxy resins can be used alone or in combination of two or more types.

At least one of the epoxy resins constituting component (B) is an epoxy resin that gives a cured product having a glass transition temperature (Tg) of 25° C. or lower [epoxy resin (BL)].
The glass transition temperature (Tg) of the cured epoxy resin can be determined by differential scanning calorimetry.
"Epoxy resins that give cured products with a glass transition temperature (Tg) of 25° C. or lower" are those that give cured products with a glass transition temperature (Tg) of 25° C. or lower when cured alone or in the presence of a curing agent or the like. The conditions for forming the cured product are not particularly limited as long as a sufficiently cured product is obtained. For example, as described in the examples, a thermal cationic polymerization initiator can be used to obtain a cured product for measurement.

The epoxy resin (BL) has sufficient molecular mobility even when the curing reaction progresses and the epoxy resin (BL) becomes part of the cured product. Therefore, by using the (B) component containing the epoxy resin (BL), it is possible to obtain a photocurable sheet adhesive that can be sufficiently cured by only light irradiation without heat treatment. Since this effect is more pronounced, it is preferable that the epoxy resin (BL) is one that gives a cured product with a glass transition temperature (Tg) of -5°C or lower, and more preferably one that gives a cured product with a glass transition temperature (Tg) of -20°C or lower.

Epoxy resins (BL) include epoxy resins having an oxyalkylene structure. Epoxy resins having an oxyalkylene structure tend to give cured products with relatively low glass transition temperatures (Tg), and are therefore preferably used as epoxy resins (BL).

Examples of the oxyalkylene structure include an oxymethylene group, an oxyethylene group, an oxypropylene group, an oxytrimethylene group, an oxybutylene group, an oxypentylene group, an oxyhexylene group, an oxyheptylene group, an oxyoctylene group, an oxynonylene group, an oxydecylene group, an oxyundecylene group, an oxydodecylene group, an oxytridecylene group, an oxytetradecylene group, an oxypentadecylene group, an oxycyclopropylene group, an oxycyclobutylene group, an oxycyclopentylene group, an oxycyclohexylene group, an oxydecahydronaphthalene group, an oxynorbornanylene group, and an oxyadamantanylene group.

The content of the epoxy resin (BL) constituting the component (B) (when two or more types of epoxy resins (BL) are used, the total amount of these resins) is usually 80 to 100 mass%, preferably 90 to 100 mass%, and more preferably 95 to 100 mass%, based on the entire component (B).
When the content of the epoxy resin (BL) is 80 mass % or more based on the entire component (B), it becomes easier to obtain a photocurable sheet adhesive that can be sufficiently cured by light irradiation alone.

The content of epoxy resin (BL) is preferably 35 to 75 mass% of the entire photocurable sheet adhesive, more preferably 37 to 70 mass%, and even more preferably 40 to 65 mass%.

At least one of the epoxy resins constituting component (B) is preferably a liquid at 23°C.
"Liquid at 23° C." means that it has fluidity at 23° C. It is preferable that the viscosity of this epoxy resin, measured at 23° C. and 1.0 rpm using an E-type viscometer, is 2 to 10,000 mPa·s.
A photocurable sheet adhesive having a low elastic modulus at room temperature can be obtained by using an epoxy resin that is liquid at 23° C. Such a photocurable sheet adhesive has excellent application properties at room temperature and at mild high temperature conditions, so that it is possible to omit the step of heating the photocurable sheet adhesive to soften it during the application process, or to apply the adhesive under relatively mild conditions of about 35 to 70° C.

When the photocurable sheet adhesive of the present invention contains an epoxy resin that is liquid at 23°C, the content of the epoxy resin that is liquid at 23°C is preferably 35 to 75 mass% based on the total mass of the photocurable sheet adhesive, more preferably 37 to 70 mass%, and even more preferably 40 to 65 mass%.
By ensuring that the content of the epoxy resin (B) that is liquid at 23° C. is within the above range, it becomes easier to obtain a photocurable sheet adhesive that has excellent application properties at room temperature.

From the viewpoint of improving both the curing properties and the application properties of the photocurable sheet adhesive, it is preferable that the epoxy resin (BL) is liquid at 23°C.

[(C) component]
The photocurable sheet adhesive of the present invention contains a photocationic polymerization initiator as component (C).
The cationic photopolymerization initiator is preferred because it efficiently advances the polymerization reaction of the component (B) and can improve the storage stability of the photocurable sheet adhesive compared to other curing agents.

A photocationic polymerization initiator is a compound that generates cationic species when irradiated with ultraviolet light, initiating the curing reaction of a cationic curable compound. It consists of a cationic portion that absorbs ultraviolet light and an anionic portion that serves as a source of acid generation.

Examples of photocationic polymerization initiators include sulfonium salt compounds, iodonium salt compounds, phosphonium salt compounds, ammonium salt compounds, diazonium salt compounds, selenium salt compounds, oxonium salt compounds, and bromine salt compounds. Among these, sulfonium salt compounds are preferred because of their excellent compatibility with other components, and aromatic sulfonium salt compounds having an aromatic group are more preferred.

Sulfonium salt compounds include triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium tetrakis(pentafluorophenyl)borate, 4,4'-bis[diphenylsulfonio]diphenylsulfide-bishexafluorophosphate, 4,4'-bis[di(β-hydroxyethoxy)phenylsulfonio]diphenylsulfide-bishexafluoroantimonate, 7-[di(p-toluyl)sulfonio]-2-isopropylthioxanthone hexafluorophosphate, 7-[di(p-toluyl)sulfonio]-2-isopropylthioxanthone hexafluorophosphate, -isopropylthioxanthone hexafluoroantimonate, 7-[di(p-toluyl)sulfonio]-2-isopropyltetrakis(pentafluorophenyl)borate, phenylcarbonyl-4'-diphenylsulfonio-diphenylsulfide-hexafluorophosphate, phenylcarbonyl-4'-diphenylsulfonio-diphenylsulfide-hexafluoroantimonate, 4-tert-butylphenylcarbonyl-4'-diphenylsulfonio-diphenylsulfide-hexafluorophosphate, 4-tert-butylphenylcarbonyl-4'-diphenylsulfonio-diphenylsulfide 4-(4-(2-chlorobenzoyl)phenylthio)phenylbis(4-fluorophenyl)sulfonium hexafluoroantimonate, 4,4',4''-tetrakis(pentafluorophenyl)borate, 4-(phenylthio)phenyldiphenylsulfonium hexafluoroantimonate, 4-(phenylthio)phenyldiphenylsulfonium hexafluorophosphate, 4-{4-(2-chlorobenzoyl)phenylthio}phenylbis(4-fluorophenyl)sulfonium hexafluoroantimonate, thiophenyldiphenylsulfonium hexafluoroantimonate halide, 4,4',4''-tetrakis(pentafluorophenyl)borate, tris(β-hydroxyethoxyphenyl)sulfonium hexafluoroantimonate, 4,4'-bis[diphenylsulfonio]diphenylsulfide-bishexafluoroantimonate, diphenyl[4-(phenylthio)phenyl]sulfonium trifluorotrispentafluoroethylphosphate, tris[4-(4-acetylphenylsulfanyl)phenyl]sulfonium tris[(trifluoromethyl)sulfonyl]methanide, salts in which the cation moiety is 4-(phenylthio)phenyldiphenylsulfonium and the anion moiety is a phosphorus-based anion to which fluorine and a perfluoroalkyl group are added, and the like.

Examples of iodonium salt compounds include diphenyliodonium tetrakis(pentafluorophenyl)borate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, di(4-nonylphenyl)iodonium hexafluorophosphate, (tricumyl)iodonium tetrakis(pentafluorophenyl)borate, etc.

Examples of phosphonium salt compounds include tri-n-butyl(2,5-dihydroxyphenyl)phosphonium bromide and hexadecyltributylphosphonium chloride.

Examples of ammonium salt compounds include benzyltrimethylammonium chloride, phenyltributylammonium chloride, and benzyltrimethylammonium bromide.

The cationic photopolymerization initiators can be used alone or in combination of two or more.
When the photocurable sheet adhesive contains a photocationic polymerization initiator, the content of the photocationic polymerization initiator is preferably 0.1 to 5 mass %, more preferably 0.5 to 4 mass %, based on the total mass of the photocurable sheet adhesive.

[Other ingredients]
The photocurable sheet adhesive of the present invention may contain other components as long as the effects of the present invention are not impaired.
Examples of other components include additives such as silane coupling agents, ultraviolet absorbers, antistatic agents, light stabilizers, antioxidants, resin stabilizers, fillers, pigments, extenders, and softeners.
These may be used alone or in combination of two or more.
When the sheet adhesive of the present invention contains these additives, the content thereof can be appropriately determined depending on the purpose.

[Layer structure of photocurable sheet adhesive]
The thickness of the photocurable sheet adhesive of the present invention is usually 1 to 50 μm, preferably 1 to 40 μm, and more preferably 2 to 30 μm.
The thickness of the photocurable sheet adhesive can be measured using a known thickness meter in accordance with JIS K 7130 (1999). In addition, when the photocurable sheet adhesive has a release film as described below, the thickness of the photocurable sheet adhesive does not include the thickness of the release film.

From the standpoint of protection from the external environment, it is preferable that the photocurable sheet adhesive of the present invention has a release film on at least one side, and it may have a release film on both sides.

Note that the photocurable sheet adhesive of the present invention having a release film on at least one side represents the state before use, and when using the photocurable sheet adhesive of the present invention, the release film is usually peeled off and removed. When the photocurable sheet adhesive has release films on both sides, the release film with the lower release strength is usually peeled off and removed first.

As the release film, a resin film can usually be used.
Examples of the resin component of the resin film include polyimide, polyamide, polyamideimide, polyphenylene ether, polyether ketone, polyether ether ketone, polyolefin, polyester, polycarbonate, polysulfone, polyether sulfone, polyphenylene sulfide, polyarylate, acrylic resin, cycloolefin polymer, aromatic polymer, polyurethane polymer, etc. Among these, polyester resin is preferable.

When the release film has a release agent layer, examples of the release agent include rubber-based elastomers such as silicone-based resins, olefin-based resins, isoprene-based resins, butadiene-based resins, long-chain alkyl-based resins, alkyd-based resins, fluorine-based resins, etc.

The thickness of the release film is usually 10 to 300 μm, preferably 10 to 200 μm, and more preferably 15 to 100 μm.

[Method for producing photocurable sheet adhesive]
The method for producing the photocurable sheet adhesive of the present invention is not particularly limited, and it can be produced, for example, by a casting method.

The method for producing a photocurable sheet adhesive by casting involves applying the raw adhesive composition to a release film using a known method, and then drying the resulting coating to obtain a photocurable sheet adhesive with a release film.

The adhesive composition contains the above-mentioned components (A), (B), and (C), and, if necessary, other components.
The adhesive composition may further contain a solvent.
Examples of the solvent include aromatic hydrocarbon solvents such as benzene and toluene; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as n-pentane, n-hexane and n-heptane; and alicyclic hydrocarbon solvents such as cyclopentane, cyclohexane and methylcyclohexane.
These solvents may be used alone or in combination of two or more.
When the adhesive composition contains a solvent, the content of the solvent can be appropriately determined taking into consideration the coatability and the like.
The adhesive composition can be prepared by appropriately mixing and stirring the respective components according to a conventional method.

The release film used in the production of the photocurable sheet adhesive functions as a support during the production process of the photocurable sheet adhesive, and also functions as a release film for the above-mentioned photocurable sheet adhesive until the photocurable sheet adhesive is used.

Methods for applying the adhesive composition include, for example, spin coating, spray coating, bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

Methods for drying the coating of the adhesive composition include conventionally known drying methods such as hot air drying, heated roll drying, and infrared irradiation.
The coating film is dried, for example, at 80 to 150° C. for 30 seconds to 5 minutes.

[Characteristics of photocurable sheet adhesive]
When the photocurable sheet adhesive of the present invention is cured, it is usually irradiated with ultraviolet light.
Specific examples of the ultraviolet light source include light sources such as ultra-high pressure mercury lamps, high pressure mercury lamps, low pressure mercury lamps, carbon arc lamps, black light fluorescent lamps, metal halide lamps, etc. The wavelength of the ultraviolet light to be irradiated may be in the wavelength range of 190 to 380 nm.
The type, dose, and duration of irradiation of ultraviolet light can be appropriately determined depending on the components of the sheet adhesive to be irradiated and the content of each component.
The irradiation illuminance is preferably about 20 to 1000 mW/cm ² , and the light quantity is preferably about 50 to 3000 mJ/cm ² .

The photocurable sheet adhesive of the present invention is preferably one that satisfies the following formula (I) when the storage shear modulus at 0°C ( _G'0 ) and the storage shear modulus at 100°C ( _G'100 ) of the cured product obtained by curing under the following conditions using a high-pressure mercury lamp are measured:

[Curing conditions for photocurable sheet adhesive]
Temperature: 23℃
Illuminance measured at a wavelength of 365 nm: 200 mW/ ^cm2
Accumulated light quantity measured at a wavelength of 365 nm: 1000 mJ/ ^cm2

Typically, the storage modulus of a cured material is high under low temperature conditions and low under high temperature conditions. Also, in cured materials where the curable adhesive is sufficiently cured and contains almost no unreacted curable components, the difference between the measured values under low temperature conditions and the measured values under high temperature conditions tends to be small. On the other hand, in cured materials where the curable adhesive is not sufficiently cured and contains a large amount of unreacted curable components, they tend to become fluid under high temperature conditions (i.e., the storage modulus value tends to be quite low), and the difference between the measured values under low temperature conditions and the measured values under high temperature conditions tends to be large.

Therefore, it is possible to judge whether a three-dimensional crosslinked structure has been sufficiently formed in the cured product (whether the curing reaction has progressed sufficiently) based on the value of (G' ₀ /G' ₁₀₀ ).
For example, since the photocurable sheet adhesive of the present invention contains an epoxy resin (BL) as at least one of the components (B), the curing reaction can proceed sufficiently by light irradiation alone without heat treatment. The value of _G'0 / _G'100 of such a photocurable sheet adhesive is usually less than 100, preferably 50 or less, and more preferably 15 or less. There is no particular lower limit for the value of _G'0 / _G'100 , but it is usually more than 1.0.

The value of _G'0 is preferably 50 MPa or less, more preferably 15 MPa or less. A photocurable sheet adhesive having a G'0 value of 50 MPa or less is suitable for use as an adhesive for flexible devices. There is no particular lower limit _{for G'0 ,} but it is usually 0.1 MPa or more.

The _G'100 value is preferably 0.1 MPa or more, more preferably 0.2 MPa or more. A photocurable sheet adhesive having a _G'100 value of 0.1 MPa or more is suitable for use as an adhesive for devices requiring heat resistance. There is no particular upper limit for _G'100 , but it is usually less than 50 MPa.

As described above, the photocurable sheet adhesive of the present invention can be sufficiently cured by irradiation with light alone.
Therefore, by using the photocurable sheet adhesive of the present invention as a material for forming adhesive members in various devices, it is possible to prevent the occurrence of defective products due to thermal load or defective products due to insufficient progress of the curing reaction.

[Uses of photocurable sheet adhesives]
The photocurable sheet adhesive of the present invention is suitably used in producing optical devices including a light emitting element, a light receiving element, a display element, and the like.
Examples of optical devices include organic EL displays, organic EL lighting, liquid crystal displays, solar cells, and electronic paper.

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

[Compounds used in the Examples and Comparative Examples]
Binder resin (A1): Phenoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: YX7200B35, glass transition temperature (Tg): 150° C., Mw: 30,000)
Binder resin (A2): Polyvinyl acetal resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC KS-5Z, glass transition temperature (Tg): 113°C, Mw: 130,000)
Binder resin (A3): Polyvinyl acetal resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BX-25Z, glass transition temperature (Tg): 86°C, degree of polymerization: 2,300)
Binder resin (A4): Phenoxy resin (manufactured by Nippon Steel Chemical & Material Co., Ltd., product name: YP70, glass transition temperature (Tg): 70° C., Mw: 55,000)
Binder resin (A5): Phenoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: YX7180BH40, glass transition temperature (Tg): 15° C., Mw: 40,000)
Epoxy resin (BL1): Epoxy resin having an oxyalkylene group (liquid at 23°C) (manufactured by Mitsubishi Chemical Corporation, product name: YX7400, epoxy equivalent: 440 g/eq, glass transition temperature (Tg) of the cured product: -69°C)
Epoxy resin (BL2): Epoxy resin having an oxyalkylene group (liquid at 23°C) (manufactured by ADEKA Corporation, product name: ED-506, epoxy equivalent: 300 g/eq, glass transition temperature (Tg) of the cured product: -50.7°C)
Epoxy resin (B1): Hydrogenated bisphenol A type epoxy resin (liquid at 23°C) (manufactured by Mitsubishi Chemical Corporation, product name: YX8000, epoxy equivalent: 205 g/eq, glass transition temperature (Tg) of cured product: 96.4°C)
Epoxy resin (B2): Epoxy resin (liquid at 23°C) (manufactured by Daicel Corporation, product name: CELLOXIDE 2021P, epoxy equivalent: 128 to 145 g/eq, glass transition temperature (Tg) of cured product: 94.5°C)
Cationic polymerization initiator (C1): Photocationic polymerization initiator, 4-(phenylthio)phenyldiphenylsulfonium hexafluorophosphate (manufactured by San-Apro Co., Ltd., product name: CPI-100P)

The glass transition temperature (Tg) of the cured product of the epoxy resin constituting component (B) was measured by the following method.
(Preparation of measurement samples)
To 100 parts by mass of each epoxy resin, 0.5 parts by mass of a thermal cationic polymerization initiator (manufactured by Sanshin Chemical Industry Co., Ltd., product name: SI-B3A) was added. The resulting mixture was poured into a polytetrafluoroethylene mold having a thickness of 1 mm and a size of 20 mm x 20 mm, and cured by heating at 100°C for 60 minutes to obtain a cured product (measurement sample).
(Differential Scanning Calorimetry)
Differential scanning calorimetry was carried out using a differential scanning calorimeter (manufactured by TA Instruments, product name: DSCQ2000) according to the following method, and then the glass transition temperature was determined.
That is, the above measurement sample was crushed, 5 mg was taken, placed in an aluminum pan, sealed with a lid, held at 120° C. for 5 minutes, and then cooled. Then, the temperature was increased from −100° C. to +120° C. at a rate of 10° C./min.
The glass transition temperature (Tg) was determined as the temperature at the intersection of a straight line extending from the low-temperature side baseline of the obtained curve to the high-temperature side and a tangent drawn at the point where the gradient of the curve in the stepwise change portion of the glass transition is maximum.

Example 1
100 parts by mass of binder resin (A1) (calculated as active ingredient excluding solvent, the same applies hereinafter), 100 parts by mass of epoxy resin (BL1), and 4.0 parts by mass of cationic polymerization initiator (C1) were diluted with methyl ethyl ketone to prepare a resin composition (1) having an active ingredient concentration of 40 mass%.
This resin composition (1) was coated on the release-treated surface of a release film (manufactured by Lintec Corporation, product name: SP-PET752150), and the resulting coating was dried at 100° C. for 2 minutes to form a sheet adhesive having a thickness of 5 μm. The release-treated surface of another release film (manufactured by Lintec Corporation, product name: SP-PET381031) was attached to the sheet adhesive to produce a sheet adhesive with release film (1).

[Examples 2 to 8, Comparative Examples 1 and 2]
Sheet adhesives (2) to (10) with release films were prepared in the same manner as in Example 1, except that the components constituting the sheet adhesive were those shown in Table 1.

The following tests were carried out on the sheet adhesives (1) to (10) with release films obtained in Examples 1 to 8 and Comparative Examples 1 and 2. The results are shown in Table 1.

[Storage shear modulus (G') of cured sheet adhesive]
The storage shear modulus (G') of the cured sheet adhesive was measured by a torsional shear method in accordance with JIS K7244-6 using a viscoelasticity measuring device (product name: MCR302, manufactured by Anton Paar).
The details of the measurement method are shown below.
(Preparation of measurement samples)
After peeling off the release sheet from the sheet-like adhesive with release film obtained in the Examples and Comparative Examples, the sheet-like adhesive was stacked to obtain a laminate with a thickness of 0.5 mm. The obtained laminate of sheet-like adhesives was irradiated with UV light to cure the laminate made of the sheet-like adhesive. After UV irradiation, the laminate was left to stand at 23°C for 24 hours to obtain a cured product of the sheet-like adhesive (laminate).
The UV irradiation was performed using a high pressure mercury lamp manufactured by iGraphics Co., Ltd., under irradiation conditions of an illuminance of 200 mW/cm ² and an integrated light quantity of 1000 mJ/cm ² when measured at a temperature of 23° C. and a wavelength of 365 nm. The actinometer used was “UVPF-A1” manufactured by iGraphics Co., Ltd.
The cured sheet adhesive (laminate) was punched out into a cylindrical body with a diameter of 8 mm (height of 0.5 mm) and used as a measurement sample.
(Measurement of storage shear modulus (G'))
The storage shear modulus (G') of the obtained measurement sample was measured under the conditions of a frequency of 1 Hz, a test start temperature of -20°C, a test end temperature of +150°C, and a heating rate of 3°C/min. The values at 0°C and 100°C are shown in Table 1.

The cured products of the sheet adhesives (laminates) obtained in Comparative Examples 1 and 2 had storage shear moduli that were too high, and therefore slippage occurred and measurement was not possible using the torsional shear method described above.
Therefore, for the cured products of the sheet-like adhesives (laminates) obtained in Comparative Examples 1 and 2, the storage modulus (E') was measured in accordance with JIS K7244-4 (1999) using a dynamic viscoelasticity measuring device (DMAQ800, manufactured by TA Instruments), and the storage shear modulus (G') was calculated from the approximation formula "E' = 3G'".
The details of the method for measuring the storage modulus (E') are shown below.
(Preparation of measurement samples)
A cured sheet-like adhesive (laminate) was obtained in the same manner as above, and the cured sheet-like adhesive (laminate) was then cut into a size of 30 mm length and 5 mm width to serve as a measurement sample.
(Measurement of storage modulus (E'))
Using the obtained measurement sample, the storage modulus (E') was measured under conditions of a frequency of 1 Hz, a test start temperature of -20°C, a test end temperature of 150°C, and a temperature rise rate of 3°C/min.

[Reference example 1]
After the sheet adhesive obtained in Comparative Example 2 was irradiated with ultraviolet light, instead of being left to stand at 23° C. for 24 hours, it was subjected to a heat treatment at 150° C. for 2 hours.
As a result, _G'0 was 4,000 MPa, _G'100 was 500 MPa, and _G'0 / _G'100 was 8.

The following can be seen from Table 1.
The sheet adhesives (1) to (8) obtained in Examples 1 to 8 contain an epoxy resin (BL) and have a G′ ₀ /G′ ₁₀₀ value of less than 100.
Thus, the sheet adhesives (1) to (8) obtained in Examples 1 to 8 are sheet adhesives that can be sufficiently cured by light irradiation alone.
On the other hand, in the sheet adhesives (9) and (10) obtained in Comparative Examples 1 and 2, the values of G' ₀ /G' ₁₀₀ are very large.
Comparing Reference Example 1 and Comparative Example 2, it is presumed that the curing reaction did not proceed sufficiently in Comparative Example 2 because no heat treatment was performed, resulting in a large decrease in the _G'100 value, and _therefore the G'0/ _G'100 value in Comparative Example 2 being large.

Claims (8)

A photocurable sheet adhesive comprising the following components (A), (B), and (C):
At least one of the binder resins constituting the component (A) is a phenoxy resin,
A photocurable sheet adhesive , wherein at least one of the epoxy resins constituting component (B) is an epoxy resin [epoxy resin (BL)] that gives a cured product having a glass transition temperature (Tg) of 25°C or lower .
Component (A): Binder resin component composed of one or more binder resins
Component (B): an epoxy-based curable component composed of one or more epoxy resins
Component (C): Photocationic polymerization initiator A photocurable sheet adhesive comprising the following components (A), (B), and (C):
At least one of the binder resins constituting the component (A) is a polyvinyl acetal resin,
A photocurable sheet adhesive , wherein at least one of the epoxy resins constituting component (B) is an epoxy resin [epoxy resin (BL)] that gives a cured product having a glass transition temperature (Tg) of 25°C or lower .
Component (A): Binder resin component composed of one or more binder resins
Component (B): an epoxy-based curable component composed of one or more epoxy resins
Component (C): Photocationic polymerization initiator 2. The photocurable sheet adhesive according to claim 1 , wherein at least one of the binder resins constituting the component (A) is a polyvinyl acetal resin. The photocurable sheet adhesive according to any one of claims 1 to 3, wherein the content of component (B) is 35 to 75 mass% based on the total amount of the photocurable sheet adhesive. The photocurable sheet adhesive according to any one of claims 1 to 4, wherein the epoxy resin (BL) is an epoxy resin having an oxyalkylene structure. The photocurable sheet adhesive according to any one of claims 1 to 5, wherein at least one of the epoxy resins constituting component (B) is liquid at 23°C. A photocurable sheet adhesive according to any one of claims 1 to 6, wherein the photocurable sheet adhesive is cured under the following conditions using a high-pressure mercury lamp to obtain a cured product, and when the storage shear modulus at 0°C (G' ₀ ) and the storage shear modulus at 100°C (G' ₁₀₀ ) are measured, the cured product satisfies the following formula (I):
[Curing conditions for photocurable sheet adhesive]
Temperature: 23℃
Illuminance measured at a wavelength of 365 nm: 200 mW/ ^cm2
Accumulated light quantity measured at a wavelength of 365 nm: 1000 mJ/ ^cm2 The photocurable sheet adhesive according to any one of claims 1 to 7, which is used in the manufacture of optical devices.