Thermosetting acrylic resin composition and adhesive sheet or adhesive tape

Abstract

Provided is a thermosetting acrylic resin composition that has excellent adhesion and suppresses the occurrence of ultrafine bubbles when cured under heat and pressure. A thermosetting acrylic resin composition according to the present invention includes: an acrylic copolymer (A) that has a carboxyl group; and a phenol resin (B). When the acrylic copolymer (A) is an acrylic copolymer (A-1) that has a glass transition temperature of no higher than -35°C, the thermosetting acrylic resin composition includes a specific amount of an epoxy curing agent (C-1). The acrylic thermosetting resin composition includes a specific amount of a novolac phenol resin (B-1) or a self-crosslinking phenol resin (B-2) as the phenol resin (B). When the thermosetting acrylic resin composition includes the novolac phenol resin (B-1) as the phenol resin (B), the thermosetting acrylic resin composition also includes a specific amount of an amine curing agent (C-2).

Description

Thermosetting acrylic resin composition, and adhesive sheet or adhesive tape

[0001] The present invention relates to a thermosetting acrylic resin composition and an adhesive sheet or adhesive tape having an adhesive layer formed from this thermosetting acrylic resin composition.

[0002] Generally, thermosetting adhesive compositions that can be cured by heat treatment have been proposed for bonding electronic components and vehicle components. However, in recent years, electronic devices such as portable electronic information devices have become smaller and more powerful, and the electronic components mounted thereon have also tended to be miniaturized. Therefore, thermosetting adhesive compositions used for adhesively fixing miniaturized electronic components to flexible printed circuits (FPCs), coverlays, and metals have been developed to exhibit sufficient adhesive strength even in thin films and small areas.

[0003] For example, Patent Document 1 discloses a thermosetting adhesive composition characterized by containing 1 to 60 parts by weight of a phenolic resin and 1 to 25 parts by weight of hexamethylenetetramine per 100 parts by weight of a specific acrylic polymer.

[0004] Patent Document 2 discloses an adhesive composition containing an acrylic polymer containing two specific types of acrylic copolymers, a resol-type phenolic resin, and an epoxy resin.

[0005] JP 2010-065078 A JP 2007-009057 A

[0006] The thermosetting adhesive composition of Patent Document 1 contains a large amount of hexamethylenetetramine, which generates a large amount of ammonia gas as a by-product during the reaction, potentially resulting in the generation of bubbles. Furthermore, the large amount of hexamethylenetetramine added makes the reaction more likely to proceed, which could result in poor storage stability in high-temperature environments, such as in the summer when temperatures reach around 40°C.

[0007] The adhesive composition of Patent Document 2 has problems in that the acrylic copolymer containing epoxy groups is a special material that is not easy to obtain and is expensive, resulting in high production costs, and there are also few types available, limiting material options. Furthermore, since two types of acrylic copolymers with different monomer compositions are used, compatibility is expected to be low, and there is a possibility that an adhesive composition with the desired performance cannot be stably produced due to changes over time caused by phase separation.

[0008] The present inventors conducted extensive research into the performance requirements of thermosetting adhesive compositions and found that when a thin-film adhesive composition (adhesive layer) cures under heat and pressure, it overflows in extremely small amounts between the adherend and the substrate of the adhesive sheet or tape, generating ultrafine bubbles ranging from several microns to several tens of microns. Furthermore, these ultrafine bubbles are cavities formed where the adhesive composition has flowed out, and the amount of bubbles generated affects the degree of flow of the adhesive composition under heat and pressure (e.g., the ease of flow due to melting of the resin components) and the amount of gas generated (e.g., gases resulting from by-products such as ammonia and water). Furthermore, the present inventors discovered that in areas where a large amount of these ultrafine bubbles have formed, the adhesive area is reduced, leading to partial peeling of the adhesive sheet or tape, or the intrusion or leakage of water or chemicals, resulting in defective products.

[0009] An object of the present invention is to provide a thermosetting acrylic resin composition that suppresses the generation of ultrafine bubbles when cured under heat and pressure and that also has excellent adhesive properties, and to provide an adhesive sheet or adhesive tape that includes an adhesive layer formed using the same.

[0010] As a result of intensive research conducted by the present inventors in order to achieve the above-mentioned object, they have completed the present invention, which relates to a thermosetting acrylic resin composition containing an acrylic copolymer, a phenolic resin, and a curing agent, and an adhesive sheet or adhesive tape having an adhesive layer formed using the same.

[0011] That is, the present invention includes the following aspects: [1] A thermosetting acrylic resin composition comprising an acrylic copolymer (A) having a carboxy group and a phenolic resin (B), wherein when the acrylic copolymer (A) is an acrylic copolymer (A-1) having a glass transition temperature of −35° C. or less, the composition further comprises an epoxy curing agent (C-1), and the content of the epoxy curing agent (C-1) is 0.000002 parts by mass or more and 0.4 parts by mass or less per 100 parts by mass of the acrylic copolymer (A-1), when the phenolic resin (B) comprises a novolac phenolic resin (B-1), the content of the novolac phenolic resin (B-1) is 2 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the acrylic copolymer (A), and the composition further comprises an amine curing agent (C-2), and the content of the amine curing agent (C-2) is 0.002 parts by mass or more and 0.9 parts by mass or less per 100 parts by mass of the acrylic copolymer (A), A thermosetting acrylic resin composition, wherein the phenolic resin (B) does not contain the novolac phenol (B-1), but contains a self-crosslinking phenolic resin (B-2), and the content of the self-crosslinking phenolic resin (B-2) is 2 to 60 parts by mass per 100 parts by mass of the acrylic copolymer (A). [2] The thermosetting acrylic resin composition according to [1], wherein the acrylic copolymer (A) is an acrylic copolymer (A-1) having a glass transition temperature of -35°C or lower. [3] The thermosetting acrylic resin composition according to [1], wherein the acrylic copolymer (A) is an acrylic copolymer (A-2) having a glass transition temperature of higher than -35°C. [4] The thermosetting acrylic resin composition according to any one of [1] to [3], wherein the phenolic resin (B) contains a novolac phenolic resin (B-1). [5] The thermosetting acrylic resin composition according to any one of [1] to [4], wherein the phenolic resin (B) contains a self-crosslinking phenolic resin (B-2). [6] The thermosetting acrylic resin composition according to any one of [1] to [3], wherein the phenolic resin (B) does not contain the novolac phenolic resin (B-1) but contains a self-crosslinking phenolic resin (B-2).[7] The thermosetting acrylic resin composition according to [5], further comprising the amine curing agent, wherein the content of the amine curing agent is 0.002 parts by mass or more and 0.9 parts by mass or less per 100 parts by mass of the acrylic copolymer (A). [8] The thermosetting acrylic resin composition according to [6], further comprising the amine curing agent, wherein the content of the amine curing agent is 0.002 parts by mass or more and 0.9 parts by mass or less per 100 parts by mass of the acrylic copolymer (A). [9] The thermosetting acrylic resin composition according to any one of [1] to [8], further comprising a filler.

[10] An adhesive sheet or adhesive tape comprising an adhesive layer formed from the thermosetting acrylic resin composition according to any one of [1] to [9].

[11] An adhesive sheet or adhesive tape comprising a substrate and an adhesive layer formed on at least one surface of the substrate from the thermosetting acrylic resin composition according to any one of [1] to [9].

[0012] According to the present invention, it is possible to provide a thermosetting acrylic resin composition that suppresses the generation of ultrafine bubbles when cured under heat and pressure and has excellent adhesive properties, and a thermal adhesive sheet or thermal adhesive tape that includes an adhesive layer formed using the same.

[0013] Fig. 1 is a schematic cross-sectional view showing one example of the layer structure of an adhesive sheet or adhesive tape according to the present invention. Fig. 2 is a schematic cross-sectional view showing another example of the layer structure of an adhesive sheet or adhesive tape according to the present invention. Fig. 3 is a schematic cross-sectional view for explaining a test method for evaluating the generation of ultrafine bubbles in the adhesive layer of an adhesive sheet or adhesive tape. Fig. 4 is a schematic plan view for explaining a test method for evaluating the generation of ultrafine bubbles in the adhesive layer of an adhesive sheet or adhesive tape. Fig. 5 is a digital microscope image of the results of an evaluation test for the generation of ultrafine bubbles in the adhesive layer of an adhesive sheet or adhesive tape (Comparative Example). Fig. 6 is a digital microscope image of the results of an evaluation test for the generation of ultrafine bubbles in the adhesive layer of an adhesive sheet or adhesive tape (Example).

[0014] Preferred embodiments of the present invention will now be described.

[0015] (Thermosetting Acrylic Resin Composition) The thermosetting acrylic resin composition of the present invention is a thermosetting acrylic resin composition containing an acrylic copolymer (A) having a carboxy group and a phenolic resin (B), wherein the acrylic copolymer (A) contains an acrylic copolymer (A-1) having a glass transition temperature (hereinafter referred to as "Tg") of -35°C or less or an acrylic copolymer (A-2) having a Tg higher than -35°C, and the phenolic resin (B) contains a novolac phenolic resin (B-1) or a self-crosslinking phenolic resin (B-2). Depending on the selection of the acrylic copolymers (A-1) and (A-2), the thermosetting acrylic resin composition of the present invention can include the following embodiments. Note that the thermosetting acrylic resin composition of the present invention may contain a novolac phenolic resin (B-1) and a self-crosslinking phenolic resin (B-2) as the phenolic resin (B), or may contain another thermosetting resin (D).

[0016] <Embodiment (a): Case in which the phenolic resin (B) contains a novolac-type phenolic resin (B-1)> The embodiment (a) can include the following embodiments (a1) and (a2). (a1) A thermosetting acrylic resin composition, wherein the acrylic copolymer (A) is an acrylic copolymer (A-1) having a Tg of −35° C. or less, further comprising an epoxy curing agent (C-1), the content of which is 0.000002 parts by mass or more and 0.4 parts by mass or less per 100 parts by mass of the acrylic copolymer (A-1), the phenolic resin (B) comprises a novolac phenolic resin (B-1), the content of which is 2 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the acrylic copolymer (A-1), and further comprising an amine curing agent (C-2), the content of which is 0.002 parts by mass or more and 0.9 parts by mass or less per 100 parts by mass of the acrylic copolymer (A).

[0017] (a2) A thermosetting acrylic resin composition in which the acrylic copolymer (A) is an acrylic copolymer (A-2) having a Tg higher than −35° C., the phenolic resin (B) contains a novolac phenolic resin (B-1) in an amount of 2 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the acrylic copolymer (A-2), and further contains an amine curing agent (C-2) in an amount of 0.002 parts by mass or more and 0.9 parts by mass or less per 100 parts by mass of the acrylic copolymer (A-2).

[0018] <Embodiment (b): Case in which the phenolic resin (B) does not contain the novolac phenol (B-1)> Embodiment (b) can include the following embodiments (b1) and (b2): (b1) A thermosetting acrylic resin composition in which the acrylic copolymer (A) is an acrylic copolymer (A-1) having a Tg of −35° C. or less, further comprising an epoxy curing agent (C-1) in an amount of 0.000002 parts by mass or more and 0.4 parts by mass or less per 100 parts by mass of the acrylic copolymer (A-1), and the phenolic resin (B) comprises a self-crosslinking phenolic resin (B-2) in an amount of 2 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the acrylic copolymer (A-1).

[0019] (b2) A thermosetting acrylic resin composition, wherein the acrylic copolymer (A) is an acrylic copolymer (A-2) having a Tg higher than −35° C., the phenolic resin (B) contains a self-crosslinking phenolic resin (B-2), and the content of the self-crosslinking phenolic resin (B-2) is 2 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the acrylic copolymer (A-2).

[0020] <Acrylic Copolymer (A)> The acrylic copolymer (A) used in the thermosetting acrylic resin composition of the present invention is a copolymer having a carboxy group. The term "acrylic" is a general term encompassing "acrylic" and "methacrylic," and the acrylic copolymer (A) is an acrylic copolymer and / or a methacrylic copolymer. The acid value of the acrylic copolymer (A) is preferably 0.1 mgKOH / g or more and 100 mgKOH / g or less, more preferably 1 mgKOH / g or more and 50 mgKOH / g or less, and even more preferably 4 mgKOH / g or more and 40 mgKOH / g or less. If the acrylic copolymer (A) does not have a carboxy group, the adhesive strength will not be sufficiently increased. By having the acid value of the acrylic copolymer within a predetermined range, it is possible to sufficiently suppress the generation of ultrafine bubbles and obtain sufficient adhesive strength. This acid value is the amount (mg) of KOH required to neutralize 1 g of the acrylic copolymer (A) and can be measured by a method in accordance with JIS K 0070:1992.

[0021] The Tg of the acrylic copolymer (A) is preferably in the range of -100°C or higher and 100°C or lower, and more preferably in the range of -80°C or higher and 20°C or lower. This Tg is a theoretical value, and is a value calculated based on the following FOX formula: 1 / Tg = W1 / Tg1 + W2 / Tg2 + W3 / Tg3 + ... + W i / Tg i Here, the subscripts 1, 2, 3, ... i represent the monomer components constituting the copolymer, and W i is the weight fraction of monomer component i, Tg i represents the Tg of a homopolymer of the monomer component i. The Tg of the homopolymer can be the value described in Polymer Handbook, 4th Edition, by J. Brand, published by Wiley in 1998.

[0022] When the acrylic copolymer (A) is an acrylic copolymer (A-1) having a Tg of −35° C. or less, ultrafine bubbles are likely to be generated, and by using an epoxy curing agent (C-1) in a predetermined content in combination, the generation of ultrafine bubbles can be sufficiently suppressed.

[0023] The acrylic copolymer (A) preferably contains at least units of (meth)acrylic acid alkyl ester (AI) and units of a carboxyl group-containing monomer (AII) as units derived from the monomers that form the acrylic copolymer (A), and may further contain units of other monomer components as necessary. Note that "(meth)acrylic" is a generic term that encompasses "acrylic" and "methacrylic."

[0024] Examples of the (meth)acrylic acid alkyl ester (AI) include ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, and tetradecyl (meth)acrylate. The alkyl group of the (meth)acrylic acid alkyl ester (AI) may be linear or branched. Among these, (meth)acrylic acid alkyl esters having an alkyl group with 2 to 14 carbon atoms are preferred, (meth)acrylic acid alkyl esters having 4 to 12 carbon atoms are more preferred, and n-butyl acrylate and 2-ethylhexyl acrylate are even more preferred. The above (meth)acrylic acid alkyl esters (AI) may be used alone or in combination of two or more.

[0025] The (meth)acrylic acid alkyl ester (AI) is preferably used as a main component for forming the acrylic copolymer (A). The content of units of the (meth)acrylic acid alkyl ester (AI) in the acrylic copolymer (A) is preferably 80% by mass or more, more preferably 85% by mass or more, and from the viewpoint of containing a sufficient amount of units of the carboxy group-containing monomer (AII), it is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 95% by mass or less.

[0026] The carboxyl group-containing monomer (AII) is not particularly limited as long as it is a monomer having a carboxyl group, and examples thereof include (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Acid anhydrides of these carboxyl group-containing monomers (e.g., acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride) can also be used as the carboxyl group-containing monomer. Among these, acrylic acid, methacrylic acid, and itaconic acid are preferred. The carboxyl group-containing monomer (AII) may be used alone or in combination of two or more.

[0027] By using an acrylic copolymer (A) containing units of a carboxyl group-containing monomer (AII) in combination with an epoxy curing agent (C-1), the adhesiveness and ease of melting of a thermosetting acrylic resin composition can be improved. Furthermore, when the Tg of the acrylic copolymer (A) is low (particularly when it is -35°C or lower), ultrafine bubbles are likely to be generated during curing under heat and pressure. However, the crosslinking reaction of the acrylic copolymer (A) with the epoxy curing agent (C-1) makes it difficult for the resin component to melt, making it possible to suppress the generation of ultrafine bubbles. The content of units of the carboxyl group-containing monomer (AII) in the acrylic copolymer (A) is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, in order to ensure a sufficient crosslinking reaction. There is no particular upper limit on the content, but it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. The content of the carboxyl group-containing monomer (AII) units in the acrylic copolymer (A) is preferably set so that the acrylic copolymer (A) has the above-mentioned acid value.

[0028] The acrylic copolymer (A) may contain units of other monomers (copolymerizable monomers) copolymerizable with the (meth)acrylic acid alkyl ester (AI) and the carboxyl group-containing monomer (AII) as long as the desired effects are not impaired. Examples of such copolymerizable monomers include (meth)acrylic acid C, such as methyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. 15-20Alkyl esters; non-aromatic ring-containing (meth)acrylic acid esters such as (meth)acrylic acid cycloalkyl esters and (meth)acrylic acid isobornyl esters; aromatic ring-containing (meth)acrylic acid esters such as (meth)acrylic acid aryl esters, (meth)acrylic acid aryloxyalkyl esters and (meth)acrylic acid arylalkyl esters; epoxy group-containing acrylic monomers such as glycidyl (meth)acrylate and methylglycidyl (meth)acrylate; vinyl ester monomers such as vinyl acetate and vinyl propionate; styrene-based monomers such as styrene and α-methylstyrene; hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxypropyl (meth)acrylate alkoxyalkyl (meth)acrylate monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; aminoalkyl (meth)acrylate monomers such as aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate and t-butylaminoethyl (meth)acrylate; (N-substituted) amide monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide and N-hydroxy(meth)acrylamide; olefin monomers such as ethylene, propylene, isoprene and butadiene; and vinyl ether monomers such as methyl vinyl ether.

[0029] Furthermore, as the copolymerizable monomer, polyfunctional monomers such as hexanediol di(meth)acrylate, butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, glycerin di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, and divinylbenzene can also be used.

[0030] The acrylic copolymer (A) can be prepared by, for example, a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a polymerization method using ultraviolet irradiation, or the like.

[0031] The polymerization initiator, chain transfer agent, solvent, etc. used in the polymerization of the acrylic copolymer (A) are not particularly limited.

[0032] As the polymerization initiator, any one that can be normally used in the production of a general acrylic copolymer can be used for the polymerization of the acrylic copolymer (A). Examples of the polymerization initiator used for the polymerization of the acrylic copolymer (A) include 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4,4-trimethylpentane), dimethylpentane, ... Examples of the polymerization initiator include azo-based polymerization initiators such as diethyl-2,2'-azobis(2-methylpropionate); and peroxide-based polymerization initiators such as benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-bis(t-butylperoxy)cyclododecane. These polymerization initiators can be used alone or in combination of two or more. The amount of the polymerization initiator used can be appropriately selected from the range of ordinary amounts used.

[0033] Any chain transfer agent that can be commonly used in the production of general acrylic copolymers can be used in the polymerization of the acrylic copolymer (A). Examples of chain transfer agents that can be used in the polymerization of the acrylic copolymer (A) include 2-mercaptoethanol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-ethylhexyl thioglycolate, 2,3-dimethylcapto-1-propanol, dodecanethiol, and α-methylstyrene dimer. The chain transfer agents can be used alone or in combination of two or more. The amount of the chain transfer agent used can be appropriately selected from the range of the amount typically used.

[0034] In solution polymerization, a solvent, a monomer, a polymerization initiator, and optionally a chain transfer agent are mixed, and the monomer is dissolved in the solvent. Polymerization can be carried out by stirring, heating, and / or irradiating with active energy rays such as ultraviolet light. Various common solvents can be used in solution polymerization. Examples of such solvents include organic solvents such as esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. The solvents can be used alone or in combination of two or more.

[0035] In emulsion polymerization, polymerization is usually carried out in a state where the monomer is dispersed in water in the presence of a surfactant (emulsifier). The polymerization reaction can be initiated at room temperature or under heat by adding a polymerization initiator (in the presence of a chain transfer agent, if necessary). The type and amount of surfactant used are not particularly limited. As the surfactant, known anionic surfactants, nonionic surfactants, cationic surfactants, etc. can be used. Anionic or nonionic surfactants are preferred, and surfactants having a reactive functional group (typically a radically polymerizable functional group) may also be used. The surfactants can be used alone or in combination of two or more.

[0036] In bulk polymerization, the monomers, a polymerization initiator, and, if necessary, a chain transfer agent are mixed together substantially without using a solvent, and the mixture is polymerized by self-heating or heating under stirring, and / or by irradiation with active energy rays such as ultraviolet rays.

[0037] The weight average molecular weight (Mw) of the acrylic copolymer (A) is not particularly limited as long as the desired properties of the thermosetting acrylic resin composition of the present invention can be obtained. For example, an acrylic copolymer (A) having a weight average molecular weight of 100,000 to 1,400,000, preferably 200,000 to 1,300,000, can be used. The weight average molecular weight of the acrylic copolymer (A) can be controlled by the type and amount of polymerization initiator and chain transfer agent, the temperature and time during polymerization, the monomer concentration, the monomer supply rate, etc. The weight average molecular weight of the acrylic copolymer (A) can be measured by gel permeation chromatography (GPC) and can be obtained as a molecular weight converted to standard polystyrene.

[0038] <Phenolic Resin (B)> The thermosetting acrylic resin composition of the present invention contains a phenolic resin (B). The phenolic resin (B) is a curing component that contributes to the thermosetting properties of the thermosetting acrylic resin composition. The type of phenolic resin (B) is not particularly limited as long as it contains a novolac-type phenolic resin (B-1) that can undergo a curing reaction with an amine-based curing agent (C-2), or a self-crosslinking phenolic resin (B-2) that undergoes self-crosslinking and hardens upon heating. The crosslinking reaction of this phenolic resin (B) with the amine-based curing agent (C-2), or the self-crosslinking of the self-crosslinking phenolic resin (B-2), improves the adhesiveness, heat resistance, and other properties of the thermosetting acrylic resin composition.

[0039] Specific examples of the novolac-type phenolic resin (B-1) include phenol novolac resin, cresol novolac resin, t-butylphenol novolac resin, nonylphenol novolac resin, dicyclopentadiene cresol novolac resin, dicyclopentadiene phenol novolac resin, xylylene-modified phenol novolac resin, naphthol novolac resin, trisphenol novolac resin, tetrakisphenol novolac resin, bisphenol F novolac resin, bisphenol A novolac resin, and phenol-modified xylene resin. Specific examples of the self-crosslinking phenolic resin (B-2) include resole-type phenolic resins such as liquid resole-type phenolic resin, solid resole-type phenolic resin, dimethylene ether resole-type phenolic resin, and methylol resole-type phenolic resin. The resole-type phenolic resin used in the present invention is not particularly limited, and can be appropriately selected from conventionally known resole-type phenolic resins. For example, resol-type phenolic resins can be used, which are prepared by reacting phenols or derivatives thereof, such as phenol, para-cresol, xylenol, para-alkylphenol, para-phenylphenol, or resorcinol, with aldehydes (e.g., formaldehyde or acetaldehyde) in the presence of a basic catalyst (e.g., sodium hydroxide, potassium hydroxide, calcium hydroxide, etc.), followed by neutralization and / or reduced-pressure dehydration as needed. From the perspective of overall evaluation, novolac-type phenolic resins (B-1) are preferred as the phenolic resin (B). Furthermore, self-crosslinking phenolic resins (B-2) are preferred from the perspective of reactivity. By using (B-1) or (B-2), for example, when bonding FPCs together, both sufficient adhesive strength and suppression of ultrafine bubbles can be achieved. The phenolic resins (B) may be used alone or in combination of two or more.

[0040] The content of the phenolic resin (B) is 2 to 60 parts by mass per 100 parts by mass of the acrylic copolymer (A) from the viewpoint of improving properties such as thermosetting property, adhesive property, and heat resistance. If the content of the phenolic resin (B) is too low, a sufficient effect of addition cannot be obtained, and if the content of the phenolic resin (B) is too high, curing may proceed before adhesiveness is fully developed, and sufficient adhesive strength may not be obtained. The content of the phenolic resin (B) is within the above numerical range whether the novolac-type phenolic resin (B-1) is used alone, the self-crosslinking phenolic resin (B-2) is used alone, or (B-1) and (B-2) are used in combination.

[0041] <Epoxy-Based Curing Agent (C-1)> The epoxy-based curing agent (C-1) used in the present invention is a component that reacts with the carboxyl groups of the acrylic copolymer (A-1) to form a crosslinked structure, and includes compounds having two or more epoxy groups in the molecule. Specific examples include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane. Examples of commercially available products include E-5CM (product name) (1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) manufactured by Soken Chemical & Engineering Co., Ltd., E-5XM (product name) manufactured by Soken Chemical & Engineering Co., Ltd., TEDRAD-C (product name) manufactured by Mitsubishi Gas Chemical Company, Inc., and TEDRAD-X (product name) manufactured by Mitsubishi Gas Chemical Company, Inc.

[0042] The content of the epoxy curing agent (C-1) is from 0.000002 to 0.4 parts by mass, and preferably from 0.0000025 to 0.38 parts by mass, per 100 parts by mass of the acrylic copolymer (A-1) having a Tg of −35° C. or less. If the thermosetting acrylic resin composition does not contain the epoxy curing agent (C-1) or the content thereof is small, the crosslinking of the acrylic copolymer (A-1) does not occur sufficiently, and the resin component tends to melt easily, and therefore ultrafine bubbles tend to be easily generated during curing under heat and pressure. Conversely, if the content is too high, excessive crosslinking occurs, and the adhesive strength tends to decrease.

[0043] <Amine-based curing agent (C-2)> The amine-based curing agent (C-2) used in the present invention is a component that reacts with carboxy groups in the phenolic resin (B) and the acrylic copolymer (A) to form a crosslinked structure. Specific examples include chain aliphatic amines (e.g., diethylenetriamine, triethylenetetramine, hexamethylenediamine, N,N-dimethylpropylamine, benzyldimethylamine, 2-(dimethylamino)phenol, 2,4,6-tris(dimethylaminomethyl)phenol, m-xylenediamine, etc.), cyclic aliphatic amines (e.g., N-aminoethylpiperazine, bis(3-methyl-4-aminocyclohexyl)methane, bis(4-aminocyclohexyl)methane, menthenediamine, isophoronediamine, 1,3-bis(aminomethyl)cyclohexane, etc.), heterocyclic amines (e.g., hexamethylenetetramine, piperazine, N,N-dimethylpiperazine, triethylenediamine, melamine, guanamine, etc.), and aromatic amines (e.g., metaphenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, etc.). The amine curing agent (C-2) may be used alone or in combination of two or more. Among these, hexamethylenetetramine is preferred from the standpoint of adhesive reliability.

[0044] When the phenolic resin (B) is a novolac phenolic resin (B-1), the thermosetting acrylic resin composition of the present invention contains an amine-based curing agent (C-2). The content of the amine-based curing agent (C-2) is preferably less than 1 part by mass, more preferably 0.002 to 0.9 parts by mass, per 100 parts by mass of the acrylic copolymer (A). When the thermosetting acrylic resin composition does not contain the amine-based curing agent (C-2), or when the content is too low, crosslinking does not occur sufficiently, so the resin component tends to melt easily, and therefore ultrafine bubbles tend to be generated easily. Conversely, when the content is too high, crosslinking occurs excessively, so the adhesive strength tends to decrease. When the phenolic resin (B) is a self-crosslinking phenolic resin (B-2), the thermosetting acrylic resin composition of the present invention does not necessarily contain the amine-based curing agent (C-2), but may contain it. If it is contained to promote crosslinking, the content can be set within the above-mentioned range.

[0045] <Other Thermosetting Resins (D)> The thermosetting acrylic resin composition of the present invention may contain a thermosetting resin (D) other than the acrylic copolymer (A) and the phenolic resin (B). The thermosetting resin (D) may be a thermosetting resin that can undergo a curing reaction with the amine-based curing agent (C-2), or a self-crosslinking thermosetting resin that undergoes self-crosslinking and hardens upon heating, and the type is not particularly limited. The curing reaction of this thermosetting resin (D) with the amine-based curing agent (C-2), or the self-crosslinking of the thermosetting resin (D) in the case of a self-crosslinking type, forms a crosslinked structure, thereby improving properties such as adhesion and heat resistance. Examples of such thermosetting resins include epoxy resins, urea resins, cyanate resins, maleimide resins, acetal resins, phenol aralkyl resins, poly-p-vinylphenol resins, and polyoxystyrenes such as polyparaoxystyrene.

[0046] <Filler (E)> The thermosetting acrylic resin composition of the present invention may further contain a filler (E). By containing the filler (E), the thermosetting acrylic resin composition can easily adjust its physical properties such as elastic modulus, dimensional stability, yield strength, and elongation at break. Typical examples of the filler (E) include inorganic fillers and organic fillers. Typical shapes of the filler include spherical, acicular, and flake shapes. One type of filler selected from these may be contained, or two or more types of fillers may be contained.

[0047] Examples of constituent materials for inorganic fillers include crystalline silica, amorphous silica, wollastonite, talc, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, calcium oxide, magnesium oxide, aluminum oxide, aluminum nitride, aluminum borate whiskers, and boron nitride. Other constituent materials for inorganic fillers include, for example, elemental metals such as aluminum, gold, silver, copper, and nickel, as well as alloys, amorphous carbon, and graphite. On the other hand, examples of constituent materials for organic fillers include polymethyl methacrylate (PMMA), polyimide, polyamideimide, polyetheretherketone, polyetherimide, and polyesterimide.

[0048] <Bio-based Carbon Content> From the viewpoint of conserving petroleum resources and reducing carbon dioxide emissions, the thermosetting acrylic resin composition of the present invention preferably has a biologically-derived carbon content (bio-based carbon content) of 20% by mass or more, more preferably 25% by mass or more, and even more preferably 50% by mass or more. The upper limit of this content is 100% by mass. While biologically-derived carbon contains a certain proportion of the radioactive isotope (C14), petroleum-derived carbon contains almost no C14. Therefore, the biologically-derived carbon content can be calculated by measuring the concentration of C14 contained in the thermosetting acrylic resin composition. Specifically, it can be measured in accordance with ASTM D6866-20 or ISO International Standard ISO16620-2.

[0049] (Adhesive Sheet or Adhesive Tape) An adhesive sheet or adhesive tape according to an embodiment of the present invention is provided with an adhesive layer formed from the thermosetting acrylic resin composition according to the above-described embodiment. As an adhesive tape or one embodiment of the adhesive tape, it can be provided as a so-called "baseless type" consisting only of an adhesive layer. A baseless type adhesive sheet or adhesive tape can be formed, for example, by applying a thermosetting acrylic resin composition to a support such as release paper, followed by drying. Furthermore, the adhesive layer can also be provided with a release liner, as described below. In this embodiment, when the adhesive layer has two main surfaces, the release liner is arranged so as to contact one or both of the two main surfaces.

[0050] Furthermore, the adhesive sheet or adhesive tape of the embodiment of the present invention can also be configured in such a manner that an adhesive layer formed from the thermosetting acrylic resin composition of the above embodiment is provided on at least one surface of the substrate.

[0051] The adhesive layer formed from the thermosetting acrylic resin composition may be formed on only one surface of the substrate, or may be formed on both surfaces of the substrate. The adhesive layer may be formed in direct contact with the substrate, or an easy-adhesion treatment layer may be provided between the substrate and the adhesive layer. The easy-adhesion treatment layer can be formed by performing an easy-adhesion treatment on the surface on which the adhesive layer is to be provided. Examples of easy-adhesion treatments include primer treatment, corona treatment, etching treatment, plasma treatment, sandblasting treatment, etc., and one or more of these treatments may be performed in combination.

[0052] The adhesive layer can be formed by coating a layer-forming composition material containing a thermosetting acrylic resin composition and a solvent on a substrate, and then evaporating the solvent by heating, or by further causing a crosslinking reaction in the coating layer. To form the coating layer, a common coating device such as a roll coater, die coater, or lip coater can be used. When heating after coating, the solvent in the layer-forming material can be removed along with the crosslinking reaction by heating. The adhesive layer can also be provided on the substrate by transfer. In this case, lamination using a heated roll is preferred to improve adhesion between the substrate and the adhesive layer.

[0053] The thickness of the adhesive layer after drying can be set, for example, to 200 μm or less, preferably 1 μm or more and 150 μm or less, more preferably 1.5 μm or more and 100 μm or less. The planar size of the adhesive sheet and adhesive tape can be set appropriately depending on the planar size of the substrate used during production, or they can be cut to the desired size after production and can be made into a roll. In this specification, a wide sheet-like material (and its roll) is referred to as an adhesive sheet, and a long, narrow tape-like material (and its roll) is referred to as an adhesive tape.

[0054] FIG. 1 shows a schematic cross-sectional view of a single-sided adhesive sheet or tape having an adhesive layer 12 provided on one side of a substrate 11. FIG. 2 shows a schematic cross-sectional view of a double-sided adhesive sheet or tape having adhesive layers 22, 23 provided on both sides of a substrate 21. In the single-sided adhesive sheet or tape, the substrate 11 may have a laminated structure, and the layer on the surface 11B side (the outermost layer) is preferably a resin layer. In the single-sided adhesive sheet or tape, the surface 11A of the substrate 11 may be subjected to a surface treatment such as a corona discharge treatment, or may be provided with a primer layer such as an adhesion-enhancing treatment layer, as necessary. By performing the adhesion-enhancing treatment, the adhesive layer 12 can have improved adhesion to the substrate 11. If necessary, surface 11B of substrate 11 may be treated with a release agent, for example, provided with a release layer, thereby preventing the adhesive composition of adhesive layer 12 from adhering to surface 11B of substrate 11 when the single-sided adhesive sheet or single-sided adhesive tape is wound into a roll, and maintaining ease of unwinding (pulling out). A release liner, as described below, can be provided on the surface of adhesive layer 12 (the surface opposite to the substrate 11 side).

[0055] In the double-sided adhesive sheet or double-sided adhesive tape shown in Figure 2, both surfaces (21A and 21B) or either one of the surfaces of the substrate 21 may be subjected to an adhesion-facilitating treatment, for example, a surface treatment such as corona discharge treatment, or an undercoat layer such as an adhesion-facilitating treatment layer may be provided. By performing the adhesion-facilitating treatment, the adhesion between the adhesive layer 22 or adhesive layer 23 and the substrate 21 can be improved. A release liner, as described below, may be provided on the surface of the adhesive layer 22 and / or adhesive layer 23 (the surface opposite the substrate 21 side).

[0056] The substrate is not particularly limited as long as it functions as a support for the adhesive layer, but films, nonwoven fabrics, foams, cloths, paper, and combinations thereof commonly used in adhesive films or adhesive tapes can be used. Among these, films that are easy to obtain uniform thickness are preferred, and resin films that have the heat resistance required in the usage environment are particularly preferred. Specific examples include polyimide-based resins such as polyimide (PI) and polyamideimide (PAI), polyamide-based resins such as polyamide (PA) and polyetheramide, polyetherketone-based resins such as polyetherketone and polyetheretherketone (PEEK), polyester-based resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyphenylene sulfide (PPS), polyethersulfone (PES), and fluororesins (e.g., polytetrafluoroethylene (PTFE), ethylene-polytetrafluoroethylene copolymer (ETFE), and perfluoroalkoxyalkane (PFA)). These films can be used as a single layer or a laminate film of two or more layers. The laminated film may include one or more combinations of layers made of different materials. As the heat-resistant resin film, a polyimide film is particularly preferred because of its excellent dimensional stability at high temperatures.

[0057] The thickness of the substrate is not particularly limited, but is preferably from 1 μm to 200 μm, more preferably from 2 μm to 150 μm, and particularly preferably from 2.5 μm to 125 μm.

[0058] The surface of the substrate on which the adhesive layer is to be formed may be subjected to an adhesion-facilitating treatment, if necessary. Examples of adhesion-facilitating treatments include primer treatment, corona treatment, etching treatment, plasma treatment, sandblasting treatment, etc. One or a combination of two or more of these treatments may be used.

[0059] The substrate may be subjected to a surface treatment such as antistatic treatment if necessary. Examples of the antistatic treatment include treatment with an antistatic agent such as a cationic surfactant, an anionic surfactant, or a nonionic surfactant. Furthermore, the substrate may be subjected to a coloring treatment such as printing or kneading if necessary.

[0060] The substrate preferably has a biological carbon content (bio-based carbon content) of 25% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, with the upper limit being 100% by mass.

[0061] When the adhesive layer is formed on only one side of the substrate and no release liner is provided, it is preferable that at least the outermost layer on the side of the substrate opposite the side on which the adhesive layer is provided is made of a resin material. Furthermore, it is preferable that the surface of the substrate or the surface of the outermost layer (the side on which the adhesive layer is not provided) is treated with a release agent. By applying a release agent treatment, the adhesive sheet wound into a roll can be easily peeled and used. During production, the adhesive sheet formed by applying the adhesive composition to the substrate is rolled up, and then the adhesive sheet can be peeled (rewound), processed, and then rewound again. Preferred release agents include acrylic resins, fluorine-based resins, alkyd-based resins, mixtures of alkyl resins and amino resins, polyvinyl carbamate-based resins, and silicone-based release agents.

[0062] (Release Liner) As the release liner, ordinary release paper, release film, etc. can be used. The release liner functions as a protective material for the adhesive layer and is peeled off when adhering to the adherend. As the release liner, a substrate having a release layer, for example, a resin film (e.g., PET film), paper, cloth, etc., surface-treated with a release agent such as a silicone-based, long-chain alkyl-based, or fluorine-based, can be used. In addition, a low-adhesion film made of a non-polar polymer such as a fluorine-based resin (e.g., polytetrafluoroethylene) or an olefin-based resin (e.g., polyethylene, polypropylene, etc.) can also be used.

[0063] (Method for producing adhesive sheet or adhesive tape) The method for producing the adhesive sheet or adhesive tape of the present invention is not particularly limited, but they can be produced by forming an adhesive layer on at least one surface of a substrate. The adhesive layer can be formed by a general method, such as a coating method in which the adhesive is directly applied to the substrate as described below, or a transfer method in which an adhesive layer is formed on the surface of a release liner and the adhesive layer side of the release liner on which the adhesive layer has been formed is then laminated to the substrate.

[0064] The adhesive layer can be formed by coating the surface of a substrate (or a release liner) with an adhesive composition containing the aforementioned predetermined components. A solvent may be added to adjust the viscosity of the adhesive composition during coating. Specific examples of solvents include aromatic solvents such as toluene and xylene; aliphatic solvents such as hexane, octane, and isoparaffin; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone; ester solvents such as ethyl acetate and isobutyl acetate; and ether solvents such as diisopropyl ether and 1,4-dioxane. Mixing methods used in preparing the adhesive composition include mechanical kneading dispersion and solvent dispersion. Apparatuses that can be used for this dispersion include mixers / kneaders, ball mills, planetary mixers, paint conditioners, and three-roll mills. Two or more of these apparatuses may also be used in combination. Methods for coating the adhesive composition onto the surface of a substrate (or a release liner) include, for example, methods using a roll coater or reverse coater. By using the above-mentioned coating method, the adhesive composition can be coated onto the surface of the substrate (or release liner) in one or more layers, and by heating as necessary, an adhesive layer can be formed on the surface of the substrate (or release liner).

[0065] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0066] The constituent materials of the prepared curable acrylic resin compositions are as follows: (Acrylic copolymer (A)) (A-1) Toray Coatex Co., Ltd., product name: R-2000 (containing carboxyl groups) (A-2) Toray Coatex Co., Ltd., product name: R-6000 (not containing carboxyl groups) (A-2) Toray Coatex Co., Ltd., product name: R-9000 (containing carboxyl groups) (A-2) Nagase ChemteX Corporation, product name: SG-70L (containing carboxyl groups) (A-2) Nagase ChemteX Corporation, product name: WS-023 (containing carboxyl groups) (A-2) Nagase ChemteX Corporation, product name: SG-708-6 (containing carboxyl groups) (Phenol resin (B)) (B-1) Arakawa Chemical Industries, Ltd., product name: Tamanol 759 (novolac type) (B-2) AICA Kogyo Co., Ltd., product name: CKM-908 (resol type), CKS-3898 (resol type) (Epoxy-based curing agent (C-1)) Soken Chemical & Engineering Co., Ltd., product name: E-5CM (1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) (Amine-based curing agent (C-2)) Ouchi Shinko Chemical Industry Co., Ltd., product name: Noccela H (hexamethylenetetramine)

[0067] <Preparation of Thermosetting Acrylic Resin Composition and Adhesive Sheet> As shown in Tables 1 and 2, 100 parts by mass of the solid content of the acrylic copolymer (A) (A-1 or A-2) was mixed with a phenolic resin (B) (B-1 or B-2), an epoxy-based curing agent (C-1), an amine-based curing agent (C-2), and ethyl acetate (dilution solvent) in a predetermined content ratio (by mass) to obtain a thermosetting acrylic resin composition.

[0068] This thermosetting acrylic resin composition was coated onto a PET release liner. The coating was then heated at 100°C to evaporate the solvent or to induce a crosslinking reaction in the coating layer, forming an adhesive layer. A PET release liner was attached to the adhesive layer, and the crosslinking reaction was accelerated at 40°C for 3 days, yielding the desired adhesive layer (thickness: 15 μm).

[0069] Next, one of the PET release liners on both sides of the adhesive layer was peeled off and removed, and a polyimide film (manufactured by Toray DuPont, product name: Kapton (registered trademark) 100H) was laminated at a temperature of 100°C using a desktop laminator to the side of the adhesive layer from which the PET release liner had been peeled off, to obtain an adhesive sheet with an adhesive layer provided on one side of the polyimide film.

[0070] <Measurement and Evaluation of Adhesive Strength> The obtained adhesive sheet was cut into a width of 20 mm and a length of 125 mm to prepare a sample for evaluation. The PET release liner was then peeled off and the sample was attached to a copper plate (manufactured by Paltec Co., Ltd., product name: C1100P) with a thickness of 0.7 mm, a width of 50 mm, and a length of 125 mm. Next, assuming the heat pressing that occurs during actual use of the adhesive sheet, a stainless steel (SUS304) plate with a thickness of 2.0 mm, a width of 50 mm, and a length of 125 mm was placed on top of the adhesive sheet, and a 2 kg weight was placed on the stainless steel plate. The adhesive sheet was then heated and cured for 1 hour in a dryer set to 180 ° C. After cooling at 23 ° C. for 1 hour or more, the force (adhesive strength) required to peel the adhesive sheet from the copper plate was measured using a tensile tester (manufactured by Toyo Seiki Seisakusho Co., Ltd., product name: Strograph E-L) under conditions of a peel speed of 300 mm / min and a peel angle of 180 ° C.

[0071] The adhesive strength after heat curing was evaluated according to the following criteria. The results are shown in Table 1. A: Maximum adhesive strength of 10 N / 20 mm or more (very good) B: Maximum adhesive strength of 6 N / 20 mm or more and less than 10 N / 20 mm (good) C: Maximum adhesive strength of less than 6 N / 20 mm (poor)

[0072] <Evaluation Test for Ultrafine Bubble Generation in Adhesive Layer> The prepared adhesive sheet was cut into 10 mm squares and bonded to a glass plate (manufactured by AGC, product name: float glass plate) with a thickness of 2.0 mm, a width of 50 mm, and a length of 125 mm to prepare a test specimen. As shown in FIG. 3, the prepared test specimen was subjected to pressure for 90 seconds using a heated press at an operating temperature of 130°C, so that the entire test specimen was subjected to a pressure of 2.0 MPa. During this pressure application, in order to apply pressure uniformly to the test specimen, a silicone rubber sheet (manufactured by Irumagawa Rubber Co., Ltd., product name: IS-825, hardness 50°) cut into 10 mm squares with a thickness of 2 mm was placed on top of the test specimen, and the entire test specimen was then subjected to pressure from above. In FIG. 3, reference numeral 30 denotes the glass plate, reference numeral 31 denotes the substrate (polyimide film), and reference numeral 32 denotes the adhesive layer (thermosetting acrylic resin composition).

[0073] Next, after cooling at 23°C for at least 1 hour, the maximum lengths (L1, L2, L3, L4) and maximum widths (W1, W2, W3, W4) of the ultrafine bubbles observed at approximately the center of each of the four sides of the test piece were measured using a digital microscope (Keyence Corporation, product name: VHX-8000). Figure 4 shows a schematic plan view of the test piece used for this measurement. In Figure 4, reference numeral 30 denotes the glass plate, reference numeral 31 denotes the substrate (polyimide film), and reference numeral 32 denotes the adhesive layer (thermosetting acrylic resin composition). The lengths of the ultrafine bubbles having the longest length observed in each of the first to fourth observation sections are designated L1, L2, L3, and L4, respectively, and the widths of the ultrafine bubbles having the widest width observed in each of the first to fourth observation sections are designated W1, W2, W3, and W4, respectively. The lengths (L1, L2, L3, L4) are the lengths from the edge (boundary line) of the substrate in the direction perpendicular to the edge (length of the bubbles on the substrate side). The widths (W1, W2, W3, W4) are the lengths along the edge (boundary line) of the substrate. Taking into account the variation in the generation of ultrafine bubbles, the ranges of the first to fourth observation areas were each observed at 200x magnification within a range of approximately 10-20% of the edge length of the substrate (including the center of the edge), taking into account the variation in the generation of ultrafine bubbles. The area index (S), which is an index of the amount of ultrafine bubbles generated, was calculated from the measured values ​​(unit: μm) of these lengths (L1, L2, L3, L4) and widths (W1, W2, W3, W4) according to the following formula, and evaluation was performed based on the calculated results. The results are shown in Tables 1 and 2. S = L total × W total L total =L1+L2+L3+L4 W total = W1 + W2 + W3 + W4

[0074] The evaluation of the amount of generated ultrafine bubbles was carried out based on the area index (S) according to the following criteria: A: S is 10,000 μm ２ Less than (very good) B: S is 10,000 μm ２ More than 15000 μm ２ Less than (good) C: S is 15,000 μm ２ or more (defect)

[0075] Figures 5 and 6 show digital microscope images of the evaluation test results for the generation of ultrafine bubbles. Figure 5 shows the evaluation test results for Comparative Example 4, which does not have the configuration of the present invention, and Figure 6 shows the evaluation test results for Example 2, which is according to the present invention. Both images are enlarged images of the vicinity of the edge (boundary) of the substrate (polyimide film) of the adhesive sheet. As is clear from Figure 5, in the Comparative Example, which does not have the configuration of the present invention, a large number of ultrafine bubbles are generated near the edge (boundary) of the substrate (polyimide film) of the adhesive sheet (i.e., near the outer peripheral edge of the adhesive sheet). On the other hand, as is clear from Figure 6, it can be seen that the generation of ultrafine bubbles is suppressed in the Examples according to the present invention.

[0076] The overall evaluation of the adhesive sheet performance (adhesive strength and generation of ultrafine bubbles) was judged according to the following criteria: A: All A ratings (very good). B: Some B ratings and no C ratings (good). C: At least one C rating, defective product.

[0077]

[0078]

[0079] As is clear from a comparison of Examples 1 and 2 with Comparative Example 1, it is found that if the epoxy curing agent (C-1) is not contained, ultrafine bubbles are likely to be generated, and that the generation of ultrafine bubbles can be suppressed by containing the epoxy curing agent (C-1). As is clear from a comparison of Examples 1 and 2 with Comparative Example 2, it is found that if the content of the epoxy curing agent (C-1) is too high, the adhesive strength decreases, and that sufficient adhesive strength can be obtained by containing a predetermined amount of the epoxy curing agent (C-1).

[0080] As is clear from a comparison of Examples 1 and 2 with Comparative Example 7, if the acrylic copolymer (A) does not have a carboxy group (if the acid value is 0), ultrafine bubbles are likely to be generated and the adhesive strength does not increase sufficiently. However, it is found that by using an acrylic copolymer (A) having a carboxy group, the generation of ultrafine bubbles can be suppressed and sufficient adhesive strength can be obtained.

[0081] As is clear from a comparison between Examples 3 and 4 and Comparative Example 3, when the content of phenolic resin (B) is low, ultrafine bubbles are likely to be generated, and when a sufficient amount of phenolic resin (B) is contained, the generation of ultrafine bubbles can be suppressed. As is clear from a comparison between Examples 3 and 4 and Comparative Example 5, when the content of phenolic resin (B) is too high, the adhesive strength decreases, and when a predetermined amount of phenolic resin (B) is contained, sufficient adhesive strength can be obtained.

[0082] As is clear from comparing Example 5 with Comparative Examples 4 and 6, when the phenolic resin (B) is a novolac phenolic resin (B-1), if the content of the amine curing agent (C-2) is too low or zero, ultrafine bubbles are likely to be generated. It can be seen that the generation of ultrafine bubbles can be suppressed by containing a sufficient amount of the amine curing agent (C-2). As is clear from comparing Example 5 with Comparative Examples 8 and 9, even if the content of the amine curing agent (C-2) is high, ultrafine bubbles are likely to be generated if the epoxy curing agent (C-1) is not contained. It can be seen that the generation of ultrafine bubbles can be effectively suppressed by containing a predetermined amount of the amine curing agent (C-2) and the epoxy curing agent (C-1). Furthermore, as is clear from comparing Comparative Example 1 with Comparative Examples 8 and 9, it can be seen that if the content of the amine curing agent (C-2) is too high, the adhesive strength tends to decrease.

[0083] As is clear from a comparison of Examples 6, 7, 8, and 9 with Comparative Example 1, when the acrylic copolymer (A) is an acrylic copolymer (A-1) having a Tg of -35°C or less, it is found that ultrafine bubbles are likely to be generated if the epoxy curing agent (C-1) is not contained. In this case, it is found that the generation of ultrafine bubbles can be suppressed by including a predetermined amount of the epoxy curing agent (C-1) as in Examples 1 and 2. On the other hand, when an acrylic copolymer (A-2) having a Tg higher than -35°C is used as in Examples 6, 7, 8, and 9, it is found that the generation of ultrafine bubbles can be suppressed even without the inclusion of the epoxy curing agent (C-1).

[0084] As in Examples 10 and 11, when the phenolic resin (B) is a self-crosslinking phenolic resin (B-2) (resol type), it is possible to suppress the generation of ultrafine bubbles and obtain sufficient adhesive strength without containing an amine-based curing agent (C-2). Comparing Examples 10 and 11 with Comparative Example 10, it is clear that even when the phenolic resin (B) is a self-crosslinking phenolic resin (B-2) (resol type), when the acrylic copolymer (A) is an acrylic copolymer (A-1) having a Tg of -35°C or less, ultrafine bubbles are likely to be generated if the epoxy-based curing agent (C-1) is not contained, and it is found that the generation of ultrafine bubbles can be suppressed by containing the epoxy-based curing agent (C-1). As is clear from a comparison between Examples 10 and 11 and Comparative Example 11, even when the phenolic resin (B) is a self-crosslinking phenolic resin (B-2) (resol type), if the content of the phenolic resin (B) is small, ultrafine bubbles are likely to be generated, and it can be seen that the generation of ultrafine bubbles can be suppressed by containing a sufficient amount of the phenolic resin (B).

[0085] The thermosetting acrylic resin composition of the present invention and the adhesive sheet and adhesive tape using the same are capable of suppressing the generation of ultrafine bubbles while maintaining excellent adhesive properties when cured under heat and pressure. Therefore, they are useful in a variety of applications where such properties are required. For example, they are useful in applications such as portable electronic devices, including smartphones, tablets, car navigation systems, cameras, audiovisual equipment, game consoles, and information devices, as well as in vehicle applications. Specifically, they are extremely useful, for example, in applications such as joining FPCs within electronic devices. Furthermore, in vehicle applications, they can be used, for example, to fasten automotive mechanical components, automotive exterior components, or automotive interior components.

[0086] REFERENCE SIGNS LIST 11 Substrate 12 Adhesive layer 21 Substrate 22 Adhesive layer 23 Adhesive layer 30 Glass plate 31 Substrate (polyimide film) 32 Adhesive layer (thermosetting acrylic resin composition)

Claims

1. A thermosetting acrylic resin composition comprising an acrylic copolymer (A) having a carboxy group and a phenolic resin (B), wherein when the acrylic copolymer (A) is an acrylic copolymer (A-1) having a glass transition temperature of -35°C or lower, the composition further comprises an epoxy curing agent (C-1), and the content of the epoxy curing agent (C-1) is 0.000002 parts by mass or more and 0.4 parts by mass or less per 100 parts by mass of the acrylic copolymer (A-1); when the phenolic resin (B) comprises a novolac phenolic resin (B-1), the content of the novolac phenolic resin (B-1) is 2 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the acrylic copolymer (A); and the composition further comprises an amine curing agent (C-2), and the content of the amine curing agent (C-2) is 0.002 parts by mass or more and 0.9 parts by mass or less per 100 parts by mass of the acrylic copolymer (A); When the phenol resin (B) does not contain the novolac-type phenol (B-1), it contains a self-crosslinking phenol resin (B-2), and the content of the self-crosslinking phenol resin (B-2) is 2 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the acrylic copolymer (A).

2. The thermosetting acrylic resin composition according to claim 1, wherein the acrylic copolymer (A) is an acrylic copolymer (A-1) having a glass transition temperature of -35°C or lower.

3. The thermosetting acrylic resin composition according to claim 1, wherein the acrylic copolymer (A) is an acrylic copolymer (A-2) having a glass transition temperature higher than -35°C.

4. The thermosetting acrylic resin composition according to claim 1, wherein the phenolic resin (B) comprises a novolac-type phenolic resin (B-1).

5. The thermosetting acrylic resin composition according to claim 1, wherein the phenolic resin (B) comprises a self-crosslinking phenolic resin (B-2).

6. The thermosetting acrylic resin composition according to claim 1, wherein the phenol resin (B) does not contain the novolac-type phenol (B-1) and contains a self-crosslinking phenol resin (B-2).

7. The thermosetting acrylic resin composition according to claim 5, further comprising the amine curing agent (C-2), the content of which is 0.002 parts by mass or more and 0.9 parts by mass or less per 100 parts by mass of the acrylic copolymer (A).

8. The thermosetting acrylic resin composition according to claim 6, further comprising the amine curing agent (C-2), the content of which is 0.002 parts by mass or more and 0.9 parts by mass or less per 100 parts by mass of the acrylic copolymer (A).

9. The thermosetting acrylic resin composition according to claim 1, further comprising a filler.

10. An adhesive sheet or tape comprising an adhesive layer formed from the thermosetting acrylic resin composition according to any one of claims 1 to 9.

11. An adhesive sheet or tape comprising a substrate and an adhesive layer formed on at least one surface of the substrate from the thermosetting acrylic resin composition according to any one of claims 1 to 9.

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