Photocurable sheet adhesive

Abstract

Provided is a photocurable sheet adhesive that contains an (A) component, a (B) component, and a (C) component, wherein at least one epoxy resin constituting the (B) component gives a cured product that has a glass transition temperature (Tg) of 25°C or lower. The photocurable sheet adhesive can be sufficiently cured by only irradiation with light. (A) component: A binder resin component composed of one or more binder resins. (B) component: An epoxy-based curable component composed of one or more epoxy resins. (C) component: A photocationic polymerization initiator.

Description

Technical Field

[0001] The present invention relates to a photocurable sheet-like adhesive that can be sufficiently cured only by light irradiation.

Background Art

[0002] Conventionally, epoxy resins have been used as curable components of curable adhesives. For example, Patent Document 1 describes a thermosetting sheet-like adhesive containing an epoxy resin, characterized in that the cured product of the thermosetting sheet-like adhesive satisfies specific requirements regarding the storage elastic modulus.

[0003] Generally, when a curable adhesive containing an epoxy resin cures, a three-dimensional crosslinked structure is formed inside the cured adhesive. Therefore, in a curable adhesive containing an epoxy resin, the molecular movement of the curable component may decrease during the curing reaction, and the curing reaction may not proceed sufficiently. If the curing reaction does not proceed sufficiently, there may be problems such as not obtaining a cured adhesive having the desired properties, or unreacted curable components remaining in the cured adhesive and eluting this curable component.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When using a thermosetting sheet-like adhesive as described in Patent Document 1, usually, the curing reaction is started by heating, and the curing reaction is allowed to proceed under high-temperature conditions as it is. Therefore, a state where the molecular movement of the curable component is active can be maintained for a long time.

[0006] On the one hand, the photocurable sheet-like adhesive can initiate the curing reaction only by light irradiation without heating. However, when using the photocurable sheet-like adhesive, if only the light irradiation treatment is performed and the heat treatment is not carried out, the above problems caused by the insufficient progress of the curing reaction are likely to occur.

[0007] The present invention has been made for the purpose of improving the curability of the photocurable sheet-like adhesive. That is, an object of the present invention is to provide a photocurable sheet-like adhesive that can be sufficiently cured only by light irradiation without performing heat treatment.

Means for Solving the Problems

[0008] In order to solve the above problems, the present inventors have intensively studied a photocurable sheet-like adhesive containing an epoxy resin. As a result, it has been found that a photocurable sheet-like adhesive that can be sufficiently cured only by light irradiation can be obtained by using an epoxy resin that gives a cured product having a glass transition temperature (Tg) of 25°C or lower, and the present invention has been completed. That is, according to the present invention, the photocurable sheet-like adhesives of the following [1] to [8] are provided. 〔1〕A photocurable sheet-like adhesive containing the following (A) component, (B) component, and (C) component, wherein at least one of the epoxy resins constituting the (B) component is an epoxy resin [epoxy resin (BL)] that gives a cured product having a glass transition temperature (Tg) of 25°C or lower. (A) component: A binder resin component composed of one or more binder resins (B) component: An epoxy-based curable component composed of one or more epoxy resins (C) component: A photo cationic polymerization initiator 〔2〕The photocurable sheet-like adhesive according to [1], wherein at least one of the binder resins constituting the (A) component is a phenoxy resin. 〔3〕The photocurable sheet-like adhesive according to [1] or [2], wherein at least one of the binder resins constituting the (A) component is a polyvinyl acetal resin. 〔4〕The photocurable sheet adhesive according to any one of 〔1〕to 〔3〕, wherein the content of the component (B) is 35 to 75% by mass based on the whole 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〕Regarding the cured product obtained by curing the photocurable sheet adhesive according to any one of 〔1〕to 〔6〕 under the following conditions using a high-pressure mercury lamp, the storage shear modulus (G’0) at 0°C and the storage shear modulus (G’ 100 ) when measured satisfy the following formula (I). The photocurable sheet adhesive.

[0009]

Equation

[0010] 〔Curing conditions of the photocurable sheet adhesive〕 Temperature: 23°C Illuminance when measured at a wavelength of 365 nm: 200 mW / cm 2 Integrated light quantity when measured at a wavelength of 365 nm: 1000 mJ / cm 2 〔8〕The photocurable sheet adhesive according to any one of 〔1〕to 〔7〕, which is used in the manufacture of an optical device.

Advantages of the Invention

[0011] According to the present invention, there is provided a photocurable sheet adhesive that can be sufficiently cured only by light irradiation without performing heat treatment.

Embodiments for Carrying Out the Invention

[0012] The photocurable sheet adhesive of the present invention is a photocurable sheet adhesive containing the above components (A), (B), and (C), wherein at least one of the epoxy resins constituting the component (B) is an epoxy resin that gives a cured product having a glass transition temperature (Tg) of 25°C or lower. The sheet adhesive refers to an adhesive formed into a sheet shape that shows non-fluidity at normal temperature (23°C, the same hereinafter). In the present invention, the photocurable sheet adhesive may be in the form of a strip or a long strip (band shape). In this specification, the "photocurable sheet adhesive" may be described as the "sheet adhesive".

[0013] [Component (A)] The photocurable sheet adhesive of the present invention contains, as the component (A), a binder resin component composed of one or more binder resins. The component (A) is composed of only the binder resin. In the present invention, the "binder resin component" means the binder resin when the photocurable sheet adhesive contains one binder resin, and means a mixture thereof when the photocurable sheet adhesive contains two or more binder resins. The "binder resin" refers to a polymer component that gives shape retention or flexibility to the photocurable sheet adhesive.

[0014] By containing the component (A), the photocurable sheet adhesive of the present invention is likely to maintain a certain shape even in an uncured state.

[0015] The content of the component (A) is preferably 20 to 60% by mass, more preferably 25 to 53% by mass, and still more preferably 30 to 45% by mass with respect to the entire photocurable sheet adhesive. When the content of the component (A) is within the above range, it is easy to obtain a photocurable sheet adhesive having sufficient shape retention.

[0016] The weight average molecular weight (Mw) of the binder resin constituting component (A) is preferably from 10,000 to 300,000, more preferably from 30,000 to 200,000. The weight average molecular weight (Mw) of the binder resin can be determined as a standard polystyrene conversion value by performing gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

[0017] As the binder resin, those having a glass transition temperature (Tg) of 50°C or higher are preferred, and those having a glass transition temperature (Tg) of 80°C or higher are more preferred. When the content ratio of component (B) increases, the shape retention of the photocurable sheet adhesive may decrease. However, by containing a binder resin having a glass transition temperature (Tg) of 50°C or higher, this problem is less likely to occur. 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.

[0018] 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, styrene-butadiene-styrene block copolymers, and the like. The binder resin can be used alone or in combination of two or more.

[0019] Preferably, at least one of the binder resins is a phenoxy resin. The phenoxy resin is a polymer having a main chain of a polyaddition structure of an aromatic diol and an aromatic diglycidyl ether. The phenoxy resin generally corresponds to a high molecular weight epoxy resin and refers to those having a degree of polymerization of about 100 or more.

[0020] Some phenoxy resins have a high glass transition temperature (Tg), and such phenoxy resins are suitably used as binder resins.

[0021] The epoxy equivalent of the phenoxy resin is preferably 5,000 g / eq or more, more preferably 7,000 g / eq or more. The value of the epoxy equivalent can be measured in accordance with JIS K7236 (the same applies hereinafter).

[0022] 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, cyclopentadiene type phenoxy resin, and the like. These phenoxy resins can be used alone or in combination of two or more.

[0023] The phenoxy resin can be obtained by a method of reacting difunctional phenols with epihalohydrin to a high molecular weight, or by a method of polyaddition reaction of a difunctional epoxy resin and difunctional phenols. For example, the phenoxy resin can be obtained by reacting difunctional phenols with epihalohydrin in an inert solvent at a temperature of 40 to 120 °C in the presence of an alkali metal hydroxide. Also, the phenoxy resin can be obtained by subjecting a difunctional epoxy resin and difunctional phenols to a polyaddition reaction by heating in an organic solvent such as an amide solvent, an ether solvent, a ketone solvent, a lactone solvent, or an alcohol solvent having a boiling point of 120 °C or higher in the presence of a catalyst such as an alkali metal compound, an organic phosphorus compound, or a cyclic amine compound, with a reaction solid content concentration of 50% by weight or less at 50 to 200 °C.

[0024] The difunctional phenols are not particularly limited as long as they are compounds having two phenolic hydroxyl groups. For example, monocyclic difunctional 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 obtained by introducing a linear alkyl group, branched alkyl group, aryl group, methylol group, allyl group, cycloaliphatic group, halogen (such as tetrabromobisphenol A), nitro group, etc. into the aromatic ring of these phenol skeletons; polycyclic difunctional phenols obtained by introducing a linear alkyl group, branched alkyl group, allyl group, allyl group with a substituent, cycloaliphatic group, alkoxycarbonyl group, etc. into the carbon atom in the center of these bisphenol skeletons; and the like.

[0025] Examples of the epihalohydrin include epichlorohydrin, epibromohydrin, and epiiodohydrin.

[0026] In the present invention, commercially available products can also be used as the phenoxy resin. For example, product names: YX7200 (glass transition temperature (Tg): 150°C), YX6954 (phenoxy resin containing bisphenol acetophenone skeleton, glass transition temperature (Tg): 130°C) manufactured by Mitsubishi Chemical Corporation; product name: YP70 (glass transition temperature (Tg): 70°C) manufactured by Nippon Steel Chemical & Material Co., Ltd.; and the like.

[0027] It is preferable that at least one of the binder resins is a polyvinyl acetal resin. The polyvinyl acetal resin is a polymer obtained by an acetalization reaction between the hydroxyl group of polyvinyl alcohol (or a partial saponified product of its ester. The same applies hereinafter) and an aldehyde.

[0028] In order to obtain a photocurable sheet-like adhesive that provides a cured product with better adhesive strength, it is preferable that the photocurable sheet-like adhesive contains a large amount of a curable component (component (B)). However, a photocurable sheet-like adhesive containing a large amount of component (B) tends to have a decrease in the uniformity of the components, and as a result, the transparency of the obtained cured product may decrease. By using a polyvinyl acetal resin as the binder resin, the uniformity of the components can be improved, and it becomes easier to obtain a photocurable sheet-like adhesive that provides a cured product with excellent transparency.

[0029] Also, when a phenoxy resin is used as the binder resin, such a decrease in the uniformity of the components may occur. However, when component (A) contains both a phenoxy resin and a polyvinyl acetal resin, the uniformity of the components of the adhesive for photocurable sheets becomes good.

[0030] Examples of the polyvinyl acetal resin include polyvinyl butyral obtained by reacting polyvinyl alcohol and butyraldehyde, polyvinyl formal obtained by reacting polyvinyl alcohol and formaldehyde, polyvinyl acetal acetal obtained by reacting polyvinyl alcohol and acetaldehyde, and the like. These polyvinyl acetal resins can be used alone or in combination of two or more.

[0031] The polyvinyl acetal resin can be synthesized by reacting polyvinyl alcohol and aldehyde in an appropriate solvent using an acid catalyst. Examples of the solvent to be used include water; alcohol solvents such as methyl alcohol and ethyl alcohol; mixed solvents composed of water and alcohol; aprotic polar solvents such as dimethyl sulfoxide; and the like.

[0032] Also, the polyvinyl acetal resin can be synthesized by adding an acid catalyst and 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 and p-toluenesulfonic acid; inorganic acids such as nitric acid, sulfuric acid, and hydrochloric acid.

[0033] [Component (B)] The photocurable sheet-like 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 "epoxy-based curable component" means the epoxy resin when the photocurable sheet-like adhesive contains one kind of epoxy resin, and means a mixture thereof when the photocurable sheet-like adhesive contains two or more kinds of epoxy resins. Even if it is a compound having an epoxy group, if it corresponds to the binder resin constituting component (A), it is not considered to constitute component (B).

[0034] By containing component (B), the photocurable sheet-like adhesive of the present invention functions as a curable sheet-like adhesive.

[0035] The content of component (B) is preferably 35 to 75% by mass, more preferably 45 to 70% by mass, and still more preferably 53 to 65% by mass with respect to the whole photocurable sheet-like adhesive. When the content of component (B) is within the above range, it is easy to obtain a photocurable sheet-like adhesive having sufficient curability.

[0036] The weight average molecular weight (Mw) of the epoxy resin constituting component (B) is preferably 100 to 5,000, more preferably 200 to 4,000. The weight average molecular weight (Mw) of the epoxy resin can be determined as a standard polystyrene conversion value by performing gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

[0037] 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-like adhesive containing an epoxy resin having an epoxy equivalent of 100 g / eq or more and 500 g / eq or less, a cured product excellent in adhesive strength can be obtained.

[0038] Examples of the epoxy resin include monofunctional epoxy resins and polyfunctional epoxy resins. Since a cured product with more excellent adhesive strength is easily obtained, polyfunctional epoxy resins are preferred as the epoxy resin. The "polyfunctional epoxy resin" means an epoxy resin having two or more epoxy groups in the molecule.

[0039] Examples of the polyfunctional epoxy resin include aliphatic epoxy compounds (excluding alicyclic epoxy compounds), aromatic epoxy compounds, alicyclic epoxy compounds, and the like.

[0040] Examples of the aliphatic epoxy compound include 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol tetraglycidyl ether, dipentaerythritol hexaglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and the like.

[0041] Examples of the aromatic epoxy compound include glycidyl ether compounds of bisphenol A, bisphenol F, or compounds obtained by further adding an alkylene oxide thereto, and epoxy novolak resins; polyglycidyl ether compounds of aromatic compounds having two or more phenolic hydroxyl groups such as resorcinol, hydroquinone, and catechol; glycidyl ether compounds of aromatic compounds having two or more alcoholic hydroxyl groups such as phenyldimethanol, phenyldiethanol, and phenyldibutanol; glycidyl esters of polybasic acid aromatic compounds having two or more carboxylic acids such as phthalic acid, terephthalic acid, and trimellitic acid; and the like.

[0042] Examples of the alicyclic epoxy compound include polyglycidyl ether compounds of polyhydric alcohols having at least one alicyclic structure such as dicyclopentadiene dimethanol diglycidyl ether and hydrogenated products of bisphenol A, and cycloalkene oxide compounds such as cyclohexene oxide and cyclopentene oxide-containing compounds obtained by epoxidizing cyclohexene- and cyclopentene ring-containing compounds with an oxidizing agent.

[0043] The epoxy resin can be used alone or in combination of two or more.

[0044] At least one of the epoxy resins constituting the 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. The glass transition temperature (Tg) of the cured product of the epoxy resin can be determined by performing differential scanning calorimetry. The "epoxy resin that gives a cured product having a glass transition temperature (Tg) of 25°C or lower" means a resin that gives a cured product having 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 formation conditions of this cured product are not particularly limited as long as a sufficiently cured cured product can be obtained. For example, as described in the examples, a cured product for measurement can be obtained using a thermal cationic polymerization initiator.

[0045] Even when the curing reaction of the epoxy resin (BL) has progressed and it has become a state where it constitutes a part of the cured product, it has sufficient molecular mobility. Therefore, by using the component (B) containing the epoxy resin (BL), it is possible to obtain a photocurable sheet-like adhesive that can be sufficiently cured only by light irradiation without performing heat treatment. Since this effect is more remarkable, the epoxy resin (BL) preferably gives a cured product having a glass transition temperature (Tg) of -5°C or lower, and more preferably gives a cured product having a glass transition temperature (Tg) of -20°C or lower.

[0046] Examples of the epoxy resin (BL) include epoxy resins having an oxyalkylene structure. Epoxy resins having an oxyalkylene structure tend to give cured products with a relatively low glass transition temperature (Tg), and thus are preferably used as the epoxy resin (BL).

[0047] 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 oxydecahydronaphthylene group, an oxynorbornanylene group, an oxyadamantanylene group, and the like.

[0048] The content of the epoxy resin (BL) constituting the component (B) (when there are two or more epoxy resins (BL), the total amount thereof) is usually 80 to 100% by mass, preferably 90 to 100% by mass, and more preferably 95 to 100% by mass with respect to the entire component (B). When the content of the epoxy resin (BL) is 80% by mass or more with respect to the entire component (B), it becomes easier to obtain a photocurable sheet-like adhesive that can be sufficiently cured only by light irradiation.

[0049] The content of the epoxy resin (BL) is preferably 35 to 75% by mass, more preferably 37 to 70% by mass, and still more preferably 40 to 65% by mass with respect to the entire photocurable sheet-like adhesive.

[0050] At least one of the epoxy resins constituting the component (B) is preferably liquid at 23°C. "Liquid at 23°C" means having fluidity at 23°C. The viscosity of this epoxy resin, measured at 23°C and 1.0 rpm using an E-type viscometer, is preferably 2 to 10000 mPa·s. By using an epoxy resin that is liquid at 23°C, a photocurable sheet-like adhesive with a low elastic modulus at normal temperature can be obtained. Such a photocurable sheet-like adhesive is excellent in adhesiveness under normal temperature and mild high-temperature conditions, so in the adhesion process, the operation of heating and softening the photocurable sheet-like adhesive can be omitted, or it can be adhered under relatively mild conditions of about 35 to 70°C.

[0051] When the photocurable sheet-like 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% by mass, more preferably 37 to 70% by mass, and still more preferably 40 to 65% by mass with respect to the entire photocurable sheet-like adhesive. When 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-like adhesive excellent in adhesiveness at normal temperature.

[0052] From the viewpoint of improving both the curability and adhesiveness of the photocurable sheet-like adhesive, it is preferable that the epoxy resin (BL) is liquid at 23°C.

[0053] [Component (C)] The photocurable sheet-like adhesive of the present invention contains a photo cationic polymerization initiator as the component (C). The photo cationic polymerization initiator is preferable because it can efficiently promote the polymerization reaction of the component (B) and improve the storage stability of the photocurable sheet-like adhesive as compared with other curing agents.

[0054] A photo cationic polymerization initiator is a compound that generates cationic species upon irradiation with ultraviolet rays and initiates the curing reaction of a cationically curable compound, and it consists of a cationic part that absorbs ultraviolet rays and an anionic part that serves as a source of acid.

[0055] Examples of the photo cationic polymerization initiator include sulfonium salt-based compounds, iodonium salt-based compounds, phosphonium salt-based compounds, ammonium salt-based compounds, diazonium salt-based compounds, selenium salt-based compounds, oxonium salt-based compounds, bromine salt-based compounds, and the like. Among these, sulfonium salt-based compounds are preferable because of their excellent compatibility with other components, and aromatic sulfonium salt-based compounds having an aromatic group are more preferable.

[0056] As sulfonium salt compounds, there are triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium tetrakis(pentafluorophenyl)borate, 4,4'-bis[diphenylsulfonio]diphenyl sulfide - bishexafluorophosphate, 4,4'-bis[di(β-hydroxyethoxy)phenylsulfonio]diphenyl sulfide - bishexafluoroantimonate, 7-[di(p-tolyl)sulfonio]-2-isopropylthioxanthone hexafluorophosphate, 7-[di(p-tolyl)sulfonio]-2-isopropylthioxanthone hexafluoroantimonate, 7-[di(p-tolyl)sulfonio]-2-isopropyltetrakis(pentafluorophenyl)borate, phenylcarbonyl-4'-diphenylsulfonio-diphenyl sulfide - hexafluorophosphate, phenylcarbonyl-4'-diphenylsulfonio-diphenyl sulfide - hexafluoroantimonate, 4-tert-butylphenylcarbonyl-4'-diphenylsulfonio-diphenyl sulfide - hexafluorophosphate, 4-tert-butylphenylcarbonyl-4'-diphenylsulfonio-diphenyl sulfide - hexafluoroantimonate, 4-tert-butylphenylcarbonyl-4'-diphenylsulfonio-diphenyl sulfide - tetrakis(pentafluorophenyl)borate, 4-(phenylthio)phenyl diphenylsulfonium hexafluoroantimonate, 4-(phenylthio)phenyl diphenylsulfonium hexafluorophosphate, 4-{4-(2-chlorobenzoyl)phenylthio}phenyl bis(4-fluorophenyl)sulfonium hexafluoroantimonate, a halide of thiophenyldiphenylsulfonium hexafluoroantimonate, 4,4',4''-tri(β-hydroxyethoxyphenyl)sulfonium hexafluoroantimonate, 4,4'-Bis[diphenylsulfonio]diphenyl sulfide-bis(hexafluoroantimonate), diphenyl[4-(phenylthio)phenyl]sulfonium trifluorotris(pentafluoroethyl)phosphate, tris[4-(4-acetylphenylsulfanyl)phenyl]sulfonium tris[(trifluoromethyl)sulfonyl]methanide, salts such as those in which the cationic part is 4-(phenylthio)phenyl diphenylsulfonium and the anionic part is a phosphorus-based anion with fluorine and a perfluoroalkyl group added, etc. may be mentioned.,

[0057] Examples of iodonium salt-based compounds include diphenyliodonium tetrakis(pentafluorophenyl)borate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, di(4-nonylphenyl)iodonium hexafluorophosphate, (tricumyl)iodonium tetrakis(pentafluorophenyl)borate, etc.

[0058] Examples of phosphonium salt-based compounds include tri-n-butyl(2,5-dihydroxyphenyl)phosphonium bromide, hexadecyltributylphosphonium chloride, etc.

[0059] Examples of ammonium salt-based compounds include benzyltrimethylammonium chloride, phenyltributylammonium chloride, benzyltrimethylammonium bromide, etc.

[0060] The photo cationic polymerization initiator can be used alone or in combination of two or more kinds. When the photocurable sheet-like adhesive contains a photo cationic polymerization initiator, the content of the photo cationic polymerization initiator is preferably 0.1 to 5% by mass, more preferably 0.5 to 4% by mass, based on the total amount of the photocurable sheet-like adhesive.

[0061] 〔Other components〕 The photocurable sheet-like 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 can be used alone or in combination of two or more. When the sheet-like adhesive of the present invention contains these additives, the content can be appropriately determined according to the purpose.

[0062] 〔Layer structure of photocurable sheet-like adhesive〕 The thickness of the photocurable sheet-like adhesive of the present invention is usually 1 to 50 μm, preferably 1 to 40 μm, more preferably 2 to 30 μm. The thickness of the photocurable sheet-like adhesive can be measured in accordance with JIS K 7130 (1999) using a known thickness gauge. When the photocurable sheet-like adhesive has a release film described later, the thickness of the photocurable sheet-like adhesive is the thickness excluding the thickness of the release film.

[0063] From the viewpoint of protection from the external environment, the photocurable sheet-like adhesive of the present invention preferably has a release film on at least one surface, and may have release films on both surfaces.

[0064] Note that the photocurable sheet-like adhesive of the present invention having a release film on at least one surface represents the state before use. When using the photocurable sheet-like adhesive of the present invention, usually, the release film is peeled off and removed. When the photocurable sheet-like adhesive has release films on both surfaces, usually, the release film with a lower peeling force is peeled off and removed first.

[0065] 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 preferred.

[0066] When the release film has a release agent layer, examples of the release agent include rubber-based elastomers such as silicone resin, olefin resin, isoprene resin, and butadiene resin, long-chain alkyl resin, alkyd resin, fluorine-based resin, etc.

[0067] The thickness of the release film is usually 10 to 300 μm, preferably 10 to 200 μm, more preferably 15 to 100 μm.

[0068] 〔Method for producing photocurable sheet-like adhesive〕 The method for producing the photocurable sheet-like adhesive of the present invention is not particularly limited. For example, it can be produced using the casting method.

[0069] The method for producing the photocurable sheet-like adhesive by the casting method is to coat the release film with the adhesive composition as a raw material using a known method and dry the obtained coating film to obtain a photocurable sheet-like adhesive with a release film.

[0070] The adhesive composition contains the above components (A), (B), and (C), and other components as required. The adhesive composition may further contain a solvent. As solvents, there may be mentioned 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; alicyclic hydrocarbon solvents such as cyclopentane, cyclohexane and methylcyclohexane; and the like. These solvents can be used singly or in combination of two or more. When the adhesive composition contains a solvent, the content of the solvent can be appropriately determined in consideration of coatability and the like. The adhesive composition can be prepared by appropriately mixing and stirring the respective components according to a conventional method.

[0071] The release film used in the production of the photocurable sheet-like adhesive functions as a support in the production process of the photocurable sheet-like adhesive, and functions as the release film of the above-described photocurable sheet-like adhesive until the photocurable sheet-like adhesive is used.

[0072] Examples of the method for coating the adhesive composition include spin coating method, spray coating method, bar coating method, knife coating method, roll coating method, blade coating method, die coating method, gravure coating method and the like.

[0073] Examples of the method for drying the coating film of the adhesive composition include conventionally known drying methods such as hot air drying, hot roll drying, and infrared irradiation. As the conditions for drying the coating film, for example, it is 80 to 150 ° C for 30 seconds to 5 minutes.

[0074] 〔Properties of the photocurable sheet-like adhesive〕 When curing the photocurable sheet-like adhesive of the present invention, ultraviolet rays are usually irradiated. 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, and metal halide lamps. Also, as the wavelength of the ultraviolet light to be irradiated, a wavelength range of 190 to 380 nm can be used. The type, irradiation amount, irradiation time, etc. of the ultraviolet light can be appropriately determined according to the constituent components of the sheet-like adhesive to be irradiated and the content of each constituent component. The irradiation illuminance is 20 to 1000 mW / cm 2 , and the light quantity of 50 to 3000 mJ / cm 2 is preferably in the range.

[0075] Regarding the cured product obtained by curing the photocurable sheet-like adhesive of the present invention using a high pressure mercury lamp under the following conditions, the storage shear modulus (G’0) at 0°C and the storage shear modulus (G’ 100 ) when measured are preferably those that satisfy the following formula (I).

[0076] [Number]

[0077] [Curing conditions of the photocurable sheet-like adhesive] Temperature: 23°C Illuminance when measured at a wavelength of 365 nm: 200 mW / cm 2 Integrated light quantity when measured at a wavelength of 365 nm: 1000 mJ / cm 2

[0078] Generally, the storage elastic modulus of the cured product is high under low temperature conditions and low under high temperature conditions. Also, in a cured product where the curable adhesive is sufficiently cured and contains almost no unreacted curable components, the difference between the measured value under low temperature conditions and the measured value under high temperature conditions tends to be small. On the other hand, a cured product in which the curable adhesive is not sufficiently cured and contains a large amount of unreacted curable components tends to flow under high temperature conditions (that is, the value of the storage elastic modulus tends to be quite low), and the difference between the measured value under low temperature conditions and the measured value under high temperature conditions tends to be large.

[0079] Therefore, based on the value of (G’0 / G’ 100 ), it is possible to determine whether a three-dimensional crosslinked structure has been sufficiently formed in the cured product (whether the curing reaction has sufficiently proceeded). For example, since the photocurable sheet-like adhesive of the present invention contains an epoxy resin (BL) as at least one of the components (B), the curing reaction can proceed sufficiently only by light irradiation without performing heat treatment. For such a photocurable sheet-like adhesive, the value of G’0 / G’ 100 is usually less than 100, preferably 50 or less, 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.

[0080] The value of G’0 is preferably 50 MPa or less, more preferably 15 MPa or less. A photocurable sheet-like adhesive having a G’0 value of 50 MPa or less is suitably used as an adhesive for flexible devices. There is no particular lower limit for the value of G’0, but it is usually 0.1 MPa or more.

[0081] The value of the above G’ 100 is preferably 0.1 MPa or more, more preferably 0.2 MPa or more. A photocurable sheet-like adhesive having a G’ value of 0.1 MPa or more is suitably used as an adhesive for devices that require heat resistance. There is no particular upper limit for the value of G’ 100 , but it is usually less than 50 MPa. 100

[0082] As described above, the photocurable sheet-like adhesive of the present invention can be sufficiently cured only by light irradiation. Therefore, by using the photocurable sheet-like adhesive of the present invention as a forming material for adhesive members in various devices, it is possible to suppress the occurrence of defective products due to heat load and the occurrence of defective products due to insufficient progress of the curing reaction.

[0083] 〔Use of the photocurable sheet-like adhesive〕 The photocurable sheet adhesive of the present invention is suitably used in manufacturing optical devices including light-emitting elements, light-receiving elements, display elements, and the like. Examples of the optical device include an organic EL display, organic EL lighting, a liquid crystal display, a solar cell, and electronic paper.

Examples

[0084] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples at all.

[0085] 〔Compounds used in Examples or Comparative Examples〕 · Binder resin (A1): Phenoxy resin [manufactured by Mitsubishi Chemical Corporation, trade name: YX7200B35, glass transition temperature (Tg): 150°C, Mw: 30,000] · Binder resin (A2): Polyvinyl acetal resin [manufactured by Sekisui Chemical Co., Ltd., trade name: Esrec KS-5Z, glass transition temperature (Tg): 113°C, Mw: 130,000] · Binder resin (A3): Polyvinyl acetal resin [manufactured by Sekisui Chemical Co., Ltd., trade name: Esrec 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., trade name: YP70, glass transition temperature (Tg): 70°C, Mw: 55,000] · Binder resin (A5): Phenoxy resin [manufactured by Mitsubishi Chemical Corporation, trade 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, trade name: YX7400, epoxy equivalent: 440 g / eq, glass transition temperature (Tg) of cured product: -69°C] · Epoxy resin (BL2): Epoxy resin having an oxyalkylene group (liquid at 23°C) [manufactured by ADEKA Corporation, trade name: ED-506, epoxy equivalent: 300 g / eq, glass transition temperature (Tg) of cured product: -50.7°C] · Epoxy resin (B1): Hydrogenated bisphenol A type epoxy resin (liquid at 23°C) [manufactured by Mitsubishi Chemical Corporation, trade 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, trade name: Celoxide 2021P, epoxy equivalent: 128 - 145 g / eq, glass transition temperature (Tg) of cured product: 94.5°C] · Cationic polymerization initiator (C1): Photo - cationic polymerization initiator, 4 - (phenylthio)phenyl diphenylsulfonium hexafluorophosphate [manufactured by San Apro Limited, trade name: CPI - 100P]

[0086] Note that the glass transition temperature (Tg) of the cured product of the epoxy resin constituting the component (B) was measured by the following method. (Preparation of measurement sample) To 100 parts by mass of each epoxy resin, 0.5 part by mass of a thermal cationic polymerization initiator [manufactured by Sanshin Chemical Industry Co., Ltd., trade name: SI - B3A] was added. The obtained mixture was poured into a polytetrafluoroethylene mold with a thickness of 1 mm and a size of 20 mm × 20 mm, and heated at 100°C for 60 minutes to cure, obtaining a cured product (measurement sample). (Differential scanning calorimetry) Using a differential scanning calorimeter [manufactured by TA Instruments, product name: DSCQ2000], differential scanning calorimetry was performed by the following method, and then the glass transition temperature was determined. That is, the above - mentioned measurement sample was crushed, 5 mg was taken, put into an aluminum pan, covered with a lid and sealed, held at 120°C for 5 minutes once, and then cooled. Thereafter, measurement was carried out at a heating rate of 10°C / min from - 100°C to + 120°C. The temperature at the intersection of the straight line obtained by extending the baseline on the low - temperature side of the obtained curve to the high - temperature side and the tangent line drawn at the point where the curvature of the stepped change part of the glass transition is maximized was defined as the glass transition temperature (Tg).

[0087] [Example 1] 100 parts by mass of a binder resin (A1) (in terms of the active ingredient excluding the solvent; the same applies hereinafter), 100 parts by mass of an epoxy resin (BL1), and 4.0 parts by mass of a cationic polymerization initiator (C1) were diluted with methyl ethyl ketone to prepare a resin composition (1) having an active ingredient concentration of 40% by mass. This resin composition (1) was applied onto the release-treated surface of a release film (manufactured by Lintec Corporation, trade name: SP-PET752150), and the obtained coating film was dried at 100°C for 2 minutes to form a sheet-like adhesive having a thickness of 5 μm. Onto this sheet-like adhesive, the release-treated surface of another release film (manufactured by Lintec Corporation, trade name: SP-PET381031) was laminated to produce a sheet-like adhesive (1) with a release film.

[0088] [Examples 2 to 8, Comparative Examples 1 to 2] Sheet-like adhesives (2) to (10) with release films were produced in the same manner as in Example 1, except that the components described in Table 1 were used as the components constituting the sheet-like adhesive.

[0089] The following tests were conducted on the sheet-like adhesives (1) to (10) with release films obtained in Examples 1 to 8 and Comparative Examples 1 to 2. The results are shown in Table 1.

[0090] [Storage Shear Modulus (G’) of the Cured Product of the Sheet-like Adhesive] The storage shear modulus (G’) of the cured product of the sheet-like adhesive was measured by the torsional shear method using a viscoelasticity measuring device (manufactured by Anton paar, product name: MCR302) in accordance with JIS K7244-6. Details of the measurement method are shown below. (Preparation of Measurement Sample) After peeling off the release sheet from the sheet-like adhesives with release films obtained in the examples and comparative examples, the sheet-like adhesives were stacked to obtain a laminate with a thickness of 0.5 mm. The obtained laminate of the sheet-like adhesives was irradiated with UV to cure the laminate composed of the sheet-like adhesives. After UV irradiation, it was allowed to stand at 23°C for 24 hours to obtain a cured product of the sheet-like adhesive (laminate). Note that the UV irradiation was measured using a high-pressure mercury lamp manufactured by Eye Graphics Co., Ltd. under the conditions of a temperature of 23°C and a wavelength of 365 nm, with an illuminance of 200 mW / cm 2 and an integrated light quantity of 1000 mJ / cm 2 . The light meter used was "UVPF-A1" manufactured by Eye Graphics Co., Ltd. The cured product of the sheet-like adhesive (laminate) was punched out into a cylinder (height 0.5 mm) with a diameter of 8 mm, and this was used as the measurement sample. (Measurement of storage shear modulus (G')) Using the obtained measurement sample, the storage shear modulus (G') 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.

[0091] Note that for the cured products of the sheet-like adhesives (laminates) obtained in Comparative Examples 1 and 2, since the storage shear modulus was too high, slippage occurred in the above torsional shear method and measurement could not be performed. Therefore, for the cured products of the sheet-like adhesives (laminates) obtained in Comparative Examples 1 and 2, in accordance with JIS K7244-4 (1999), the storage modulus (E') was measured using a dynamic viscoelasticity measuring device (DMA Q800 manufactured by TA Instruments), and the storage shear modulus (G') was calculated from the approximate formula "E' = 3G'". The details of the measurement method of the storage modulus (E') are shown below. (Preparation of measurement sample) After obtaining the cured product of the sheet-like adhesive (laminate) by the same method as above, the cured product of the sheet-like adhesive (laminate) was processed into a size of 30 mm in length and 5 mm in width, and this was used as the measurement sample. (Measurement of storage modulus (E')) Using the obtained measurement sample, the storage modulus (E') 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.

[0092] [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 4000MPa, G' 100 is 500MPa, and G'0 / G' 100 was 8.

[0093] [Table 1]

[0094] The following can be seen from Table 1: The sheet adhesives (1) to (8) obtained in Examples 1 to 8 contained an epoxy resin (BL), and G'0 / G' 100 The value of is 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, G'0 / G' 100 The value of is very large. Comparing Reference Example 1 and Comparative Example 2, the curing reaction did not proceed sufficiently in Comparative Example 2 because the heat treatment was not performed, and G' 100 The value of G'0 / G' in Comparative Example 2 was significantly decreased. 100 It is assumed that the value of has increased.

Claims

1. A photocurable sheet-like adhesive containing the following components (A), (B), and (C), wherein at least one of the binder resins constituting the component (A) is a phenoxy resin, at least one of the epoxy resins constituting the 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. A photocurable sheet-like adhesive. (A) component: A binder resin component composed of one or more binder resins (B) component: An epoxy-based curable component composed of one or more epoxy resins (C) component: A photo cationic polymerization initiator

2. A photocurable sheet-like adhesive containing the following components (A), (B), and (C), wherein at least one of the binder resins constituting the component (A) is a polyvinyl acetal resin, at least one of the epoxy resins constituting the 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. A photocurable sheet-like adhesive. (A) component: A binder resin component composed of one or more binder resins (B) component: An epoxy-based curable component composed of one or more epoxy resins (C) component: A photo cationic polymerization initiator

3. The photocurable sheet-like adhesive according to claim 1, wherein at least one of the binder resins constituting the component (A) is a polyvinyl acetal resin.

4. The photocurable sheet-like adhesive according to any one of claims 1 to 3, wherein the content of the component (B) is 35 to 75% by mass based on the total amount of the photocurable sheet-like adhesive.

5. The photocurable sheet-like adhesive according to any one of claims 1 to 4, wherein the epoxy resin (BL) is an epoxy resin having an oxyalkylene structure.

6. The photocurable sheet-like adhesive according to any one of claims 1 to 5, wherein at least one of the epoxy resins constituting the component (B) is in a liquid state at 23°C.

7. For the cured product obtained by curing the photocurable sheet-like adhesive according to any one of claims 1 to 6 under the following conditions using a high-pressure mercury lamp, the storage shear modulus (G') at 0 °C ０ ), and the storage shear modulus (G') at 100 °C １００ ), a photocurable sheet-like adhesive that satisfies the following formula (I). 【Number 1】 [Curing conditions of the photocurable sheet-like adhesive] Temperature: 23°C Illuminance when measured at a wavelength of 365 nm: 200 mW / cm ２ Integrated light quantity measured at a wavelength of 365 nm: 1000 mJ / cm ２

8. The photocurable sheet-like adhesive according to any one of claims 1 to 7, which is used in the manufacture of an optical device.

Images