Adhesive composition and adhesive sheet

Abstract

To provide an adhesive composition capable of forming an adhesive layer or the like that exhibits high adhesiveness to low-polarity adherends and also has excellent heat resistance, and an adhesive sheet using the same. The adhesive composition of the present invention comprises a (meth)acrylic polymer (A) that is a polymer comprising 51 to 99.9 mass% of a (meth)acrylic acid alkoxyalkyl ester and 0.1 to 15 mass% of a monomer component (a) containing a crosslinkable functional group-containing monomer, 10 to 50 mass parts of a tackifying resin (B) per 100 mass parts of the (meth)acrylic polymer (A).

Description

Technical Field

[0001] This invention relates to adhesive compositions and adhesive sheets. Background Technology

[0002] Materials used in automobiles and other applications are shifting from metallic materials to plastics. This is driven by the demand for lightweight automobiles and the development of higher strength plastic materials.

[0003] Plastic materials are generally low-polarity, and general-purpose materials such as polypropylene, polyethylene, and cyclic olefin resins are known to be difficult to bond. Therefore, adhesive sheets used in automotive applications and other applications are required to have good adhesion to difficult-to-bond, low-polarity substrates.

[0004] As a method for obtaining an adhesive that exhibits high adhesion to low-polarity adherends, Patent Document 1 discloses, for example, an acrylic adhesive composition comprising a nucleo-hydrogenated terpene phenol resin. Patent Document 2 discloses a resin composition comprising a (meth)acrylic polymer with a glass transition temperature below -40°C and a tackifying resin comprising 5 parts by weight or more and 40 parts by weight or less relative to 100 parts by weight of the (meth)acrylic polymer.

[0005] However, in recent years, applications such as automotive have demanded higher requirements, such as high adhesion regardless of the type of substrate being bonded. Existing technical documents Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2007-224258 Patent Document 2: Japanese Patent Application Publication No. 2019-119845 Summary of the Invention The technical problem that the invention aims to solve

[0007] The technical problem to be solved by the present invention is to provide an adhesive composition that can form an adhesive layer that exhibits high adhesion to low polarity adherends such as polypropylene, polyethylene, and cycloolefin resins and also has excellent heat resistance, as well as an adhesive sheet using the adhesive composition. means of solving technical problems

[0008] In view of the above, the inventors conducted in-depth research and found that the adhesive composition made by incorporating a high-hydroxyl-value tackifying resin into an acrylic polymer mainly composed of (meth)acrylate alkoxyalkyl esters exhibits high adhesion to low-polarity adherends, thus completing the present invention.

[0009] That is, the present invention relates to the following [1] to [7]. [1] An adhesive composition comprising a (meth)acrylic polymer (A), a tackifying resin (B), and a crosslinking agent (C), wherein the (meth)acrylic polymer (A) is a polymer comprising 51 to 99.9% by weight of an alkoxyalkyl ester of (meth)acrylic acid and 0.1 to 15% by weight of a monomeric component (a) containing a crosslinking functional group, and comprising 10 to 50 parts by weight of the tackifying resin (B) relative to 100 parts by weight of the (meth)acrylic polymer (A). [2] An adhesive composition as described in [1], wherein the (meth)acrylic polymer (A) is a polymer comprising 51 to 99.9% by mass of an alkoxyalkyl ester of (meth)acrylic acid, 0.1 to 15% by mass of a carboxyl-containing monomer and 0 to 5% by mass of a hydroxyl-containing monomer (a). [3] The adhesive composition as described in [1] or [2], wherein the haze of the adhesive layer with a thickness of 25 μm obtained from the adhesive composition is less than 5%. [4] The adhesive composition as described in any one of [1] to [3], wherein the contact angle between the surface of the adhesive layer obtained from the adhesive composition and the flowing paraffin is less than 40°. [5] An adhesive composition as described in any one of [1] to [4], wherein the acid value of the tackifying resin (B) is less than 5 mg KOH / g. [6] An adhesive composition as described in any one of [1] to [5], wherein the tackifying resin (B) is a resin having a phenolic backbone. [7] An adhesive sheet having an adhesive layer formed from any one of the adhesive compositions described in [1] to [6]. Invention Effects

[0010] According to the present invention, adhesive compositions capable of forming adhesive layers with excellent adhesion to low-polarity adherends such as polyolefins, and adhesive sheets having adhesive layers with excellent adhesion to low-polarity adherends can be provided. Detailed Implementation

[0011] The present invention will now be described in detail. In this specification, acrylic acid and methacrylic acid are collectively referred to as "(meth)acrylic acid", and acrylates and methacrylates are collectively referred to as "(meth)acrylates". In addition, polymerization and copolymerization are collectively referred to as "polymerization", and polymers and copolymers are collectively referred to as "polymers".

[0012] [Adhesive Composition] An adhesive composition of one aspect of the present invention comprises a specific (meth)acrylic polymer (A), a tackifying resin (B) with a hydroxyl value of 100 mg KOH / g or higher, and a crosslinking agent (C).

[0013] (Meth)acrylic polymer (A) The (meth)acrylic polymer (A) included in the adhesive composition of the present invention is a polymer comprising 51 to 99.9% by mass of an alkoxyalkyl methacrylate and 0.1 to 15% by mass of a crosslinking functional group monomer (a). The monomer component (a) may consist solely of the alkoxyalkyl methacrylate and the crosslinking functional group monomer, or it may also contain other monomers. ·(meth)acrylate alkoxyalkyl ester The alkoxyalkyl group in (meth)acrylate typically has 2 to 18 carbon atoms, preferably 2 to 12, and more preferably 2 to 10. Examples of (meth)acrylate alkoxyalkyl esters include methoxymethyl methacrylate, 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, 3-methoxypropyl methacrylate, 3-ethoxypropyl methacrylate, 4-methoxybutyl methacrylate, and 4-ethoxybutyl methacrylate.

[0014] Alkoxyalkyl esters of (meth)acrylate can be used alone or in more than two types, but 2-methoxyethyl ester of (meth)acrylate is preferred. The amount of the (meth)acrylate alkoxyalkyl ester in all monomer components (a) is 51 to 99.9% by mass, preferably 71 to 99.9% by mass, and more preferably 81 to 98% by mass.

[0015] When the amount of (meth)acrylate alkoxyalkyl ester is within the above range, it exhibits sufficient adhesion to low-polarity substrates. • Monomers containing cross-linking functional groups As the monomer containing the crosslinking functional group, it is preferred to have at least one of a carboxyl group and a hydroxyl group as the crosslinking functional group, and more preferably at least one monomer selected from carboxyl-containing monomers and hydroxyl-containing monomers.

[0016] Examples of the carboxyl-containing monomers include (meth)acrylic acid, 2-carboxyethyl (meth)acrylic acid, 3-carboxypropyl (meth)acrylic acid, 4-carboxybutyl (meth)acrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, and maleic anhydride, with (meth)acrylic acid being preferred. One or more of the above-mentioned carboxyl-containing monomers may be used alone.

[0017] Examples of the hydroxyl-containing monomers mentioned above include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 1,4-cyclohexanediethanol mono(meth)acrylate, chloro-2-hydroxypropyl acrylate, diethylene glycol mono(meth)acrylate, and allyl alcohol, with 2-hydroxypropyl (meth)acrylate and hydroxybutyl (meth)acrylate being preferred. One or more of the above-mentioned hydroxyl-containing monomers may be used alone.

[0018] At least a portion of the carboxyl and hydroxyl groups from the monomer containing crosslinking functional groups become crosslinking points in the (meth)acrylic copolymer (A), and can form a crosslinked structure by reacting with the crosslinking agent (C) described later.

[0019] As the crosslinking functional group monomer, one type can be used alone, or two or more types can be used. The amount of the crosslinking functional group monomer in all monomer components (a) is 0.1 to 15% by mass, preferably 0.5 to 10% by mass, more preferably 1 to 5% by mass. In such an embodiment, a moderately formed crosslinked structure of the (meth)acrylic polymer (A) can yield an adhesive layer with moderate flexibility. Other monomers Other monomers that may be included in monomer component (a) may be monomers that copolymerize with the alkoxyalkyl methacrylate and the crosslinking functional group monomer, without particular limitation. Examples include alkyl methacrylate, alicyclic hydrocarbon methacrylate, nitrogen-containing monomer, epoxy-containing methacrylate, acetoacetyl methacrylate, aromatic monomer, methacryloyloxypropylmethoxysilane, vinyl acetate, vinyl chloride, and (meth)acrylonitrile.

[0020] Examples of the above-mentioned alkyl methacrylates include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, n-heptyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, n-nonyl methacrylate, isononyl methacrylate, n-decyl methacrylate, isodecyl methacrylate, lauryl methacrylate, stearyl methacrylate, and isostearyl methacrylate.

[0021] Examples of (meth)acrylates containing alicyclic hydrocarbon groups include cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and adamantane (meth)acrylate.

[0022] As examples of the aforementioned nitrogen-containing monomers, monomers having at least one functional group, either an amide group or an amino group, can be cited. Specific examples include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, acryloylmorpholine, N-vinylacetamide, diacetone(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, vinylpyrrolidone, hydroxymethyl(meth)acrylamide, methoxyethyl(meth)acrylamide, and other monomers containing an amide group.

[0023] Examples of the above-mentioned epoxy-containing (meth)acrylates include glycidyl (meth)acrylate. As an example of the above-mentioned acetoacetyl-containing (meth)acrylate, acetoacetoxyethyl (meth)acrylate can be cited.

[0024] Examples of the aforementioned aromatic ring-containing monomers include benzyl (meth)acrylate, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, styrene, methylstyrene, and vinyltoluene.

[0025] When the monomer component (a) also contains the other monomers, the content of the other monomers in 100% by mass of the monomer component (a) is generally less than 30% by mass, preferably 0.1 to 30% by mass, more preferably 0.2 to 25% by mass. As the other monomers, one or more may be used alone.

[0026] The weight-average molecular weight (Mw) of the (meth)acrylic acid polymer (A) via gel permeation chromatography (GPC) is typically between 300,000 and 1,500,000. In this form, an adhesive with excellent high-temperature durability can be obtained. Furthermore, the adhesive composition also exhibits excellent coatability.

[0027] (Manufacturing conditions for (meth)acrylic polymer (A)) The (meth)acrylic acid polymer (A) can be obtained by polymerizing the monomer component (a) using conventionally known polymerization methods such as solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization, but solution polymerization is preferred. The (meth)acrylic acid polymer (A) can be obtained as a polymer solution composed of the polymer and an organic solvent. Examples of organic solvents that can be used for polymerization include those described later.

[0028] For example, a polymerization solvent and monomer component (a) are added to a reaction vessel, a polymerization initiator is added under an inert gas atmosphere such as nitrogen, the reaction start temperature is set to 40-100°C, preferably 50-90°C, and the reaction system is usually maintained at 50-90°C, preferably 60-90°C, for 3-20 hours to obtain (meth)acrylic acid polymer (A).

[0029] Examples of polymerization initiators include peroxide-based polymerization initiators and azo-based initiators. Examples of peroxide-based polymerization initiators include: tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, benzoyl peroxide, lauroyl peroxide, hexanoyl peroxide, diisopropyl peroxide dicarbonate, di-2-ethylhexyl peroxide dicarbonate, tert-butyl peroxypentanoate, 2,2-bis(4,4-di-tert-butylperoxycyclohexyl)propane, 2,2-bis(4,4-di-tert-pentylperoxycyclohexyl)propane, 2,2-bis(4,4-di-tert-octylperoxycyclohexyl)propane, 2,2-bis(4,4-di-α-isopropylphenylperoxycyclohexyl)propane, 2,2-bis(4,4-di-tert-butylperoxycyclohexyl)butane, and 2,2-bis(4,4-di-tert-octylperoxycyclohexyl)butane.

[0030] Examples of azo initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylpentanitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(2,4-dimethylpentanitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carboxynitrile), 2-(carbamoylazo)isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylpentanitrile, and 2,2'-azobis(2- Azo compounds including aminodipropane dihydrochloride, 2,2'-azobis(N,N'-dimethylisobutylamidine), 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], 2,2'-azobis(isobutylamine) diacetate, 4,4'-azobis(4-cyanopentanoic acid), 2,2'-azobis(2-cyanopropanol), dimethyl-2,2'-azobis(2-methylpropionate), and 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide).

[0031] A single polymerization initiator or two or more can be used. Furthermore, there are no restrictions on adding polymerization initiators multiple times during polymerization. The polymerization initiator is typically used in an amount ranging from 0.001 to 5 parts by mass, preferably 0.005 to 3 parts by mass, relative to 100 parts by mass of the monomer component (a) forming the (meth)acrylic acid polymer (A). Additionally, polymerization initiators, chain transfer agents, polymerizable monomers, and polymerization solvents may be added as appropriate during the above polymerization reaction.

[0032] Examples of polymerization solvents used in solution polymerization include: aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, and n-octane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane, and cyclooctane; ethers such as diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, dibutyl ether, tetrahydrofuran, dioxane, anisole, phenethyl ether, and diphenyl ether; halogenated hydrocarbons such as chloroform, carbon tetrachloride, 1,2-dichloroethane, and chlorobenzene; esters such as ethyl acetate, propyl acetate, butyl acetate, and methyl propionate; ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, and cyclohexanone; amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; nitriles such as acetonitrile and benzonitrile; and sulfoxides such as dimethyl sulfoxide and sulfolane.

[0033] The polymerization solvent can be used alone or in combination with two or more solvents. Tackifying resin (B) The tackifying resin (B) contained in the adhesive composition of the present invention has a hydroxyl value of 100 mg KOH / g or higher.

[0034] The hydroxyl value of the tackifying resin (B) is preferably 100 mg KOH / g or higher, more preferably 110 mg KOH / g or higher. Furthermore, the hydroxyl value is preferably 300 mg KOH / g or lower, more preferably 250 mg KOH / g or lower. The hydroxyl value of the tackifying resin (B) can be determined by potentiometric titration. A hydroxyl value within the above range indicates good compatibility with the (meth)acrylic acid polymer (A) and results in high adhesion to low-polarity substrates in the resulting adhesive sheet. Furthermore, due to the excellent compatibility between the (meth)acrylic acid polymer (A) and the tackifying resin (B), the exudation of the tackifying resin (B) onto the adhesive layer surface can be suppressed after the adhesive sheet is manufactured.

[0035] The acid value of the tackifying resin (B) is not particularly limited, but is generally below 10 mg KOH / g, preferably below 5 mg KOH / g, more preferably below 3 mg KOH / g, and particularly preferably 0 to 1 mg KOH / g. The acid value of the tackifying resin (B) can be determined by potentiometric titration. An acid value within the above range indicates good compatibility with the (meth)acrylic acid polymer (A), and the resulting adhesive sheet exhibits excellent tack.

[0036] The softening point of the tackifying resin (B) can be appropriately selected according to the desired adhesive properties, without particular limitation, and is typically 90–180°C, preferably 95–170°C, and more preferably 100–160°C. A softening point within the above range allows the resulting adhesive composition to be suitable for applications requiring heat resistance, such as automotive applications.

[0037] The tackifying resin (B) only needs to have a hydroxyl value of 100 mg KOH / g or higher, and its structure is not particularly limited. Examples include resins with adhesive properties, resins with a phenolic backbone, hydroxyl-modified resins, and resins obtained from low molecular weight (meth)acrylic acid derivatives with high hydroxyl content. Among these, resins with a phenolic backbone are preferred because they are readily available, inexpensive, and economical. Examples of resins with a phenolic backbone used as the tackifying resin (B) include resins with a hydroxyl value of 100 mg KOH / g or higher and with a phenolic backbone in the main chain or side chain, such as phenolic resins, terpene phenolic resins, and resins with a phenolic backbone introduced through grafting modification.

[0038] Examples of the tackifying resin (B) include: YSPOLYSTER G125 (hydroxyl value 115 mg KOH / g, acid value 0 mg KOH / g, softening point 125℃), YS POLYSTER G150 (hydroxyl value 115 mg KOH / g, acid value 0 mg KOH / g, softening point 150℃), YS POLYSTER N125 (hydroxyl value 145 mg KOH / g, acid value 0 mg KOH / g, softening point 125℃), YS POLYSTER K125 (hydroxyl value 205 mg KOH / g, acid value 0 mg KOH / g, softening point 125℃), and YS POLYSTER K140 (hydroxyl value 200 mg KOH / g, acid value 0 mg KOH / g, softening point 140℃) manufactured by Yasuhara Chemical Co., Ltd. Other examples include HP-210 (hydroxyl value 240mgKOH / g, acid value 0mgKOH / g, softening point 100℃) manufactured by Fudo Co., Ltd.

[0039] The amount of tackifying resin (B) in the adhesive composition of the present invention is typically 10 to 50 parts by weight relative to 100 parts by weight of (meth)acrylic polymer (A), preferably 10 to 40 parts by weight, and more preferably 15 to 30 parts by weight. When the amount of tackifying resin (B) is within the above range, an adhesive sheet with excellent high-temperature properties can be obtained.

[0040] Crosslinking agent (C) As the crosslinking agent (C) included in the adhesive composition of the present invention, there are no particular limitations as long as it can crosslink the (meth)acrylic polymer (A). For example, isocyanate compound (C1), epoxy compound (C2), metal chelate (C3), and other crosslinking agents that react with the above-mentioned (meth)acrylic polymer (A) can be used as the crosslinking agent (C).

[0041] The crosslinking agent (C) can be used alone or in combination with two or more agents. (Isocyanate compound (C1)) As the isocyanate compound (C1), for example, an isocyanate compound having 2 or more isocyanate groups per molecule is generally used, preferably 2 to 8, more preferably 3 to 6. An isocyanate group number within the above range is preferred from the viewpoint of the efficiency of the crosslinking reaction between the (meth)acrylic polymer (A) and the isocyanate compound, as well as from the viewpoint of maintaining the flexibility of the adhesive layer.

[0042] Examples of diisocyanates with two isocyanate groups per molecule include aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates. Examples of aliphatic diisocyanates include ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, which have 4 to 30 carbon atoms. Examples of alicyclic diisocyanates include isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylene diisocyanate, hydrogenated toluene diisocyanate, hydrogenated diphenylmethane diisocyanate, and hydrogenated tetramethylxylene diisocyanate, which have 7 to 30 carbon atoms. Examples of aromatic diisocyanates include benzene diisocyanate, toluene diisocyanate, xylene diisocyanate, naphthalene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, and diphenylpropane diisocyanate, which have 8 to 30 carbon atoms.

[0043] Isocyanate compounds with three or more isocyanate groups in a single molecule can be categorized as aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates. Specific examples include 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, and 4,4',4”-triphenylmethane triisocyanate.

[0044] In addition, examples of isocyanate compounds include polymers (e.g., dimers or trimers, biuret esters, isocyanurate esters), derivatives (e.g., addition reaction products of polyols and diisocyanate crosslinking agents with two or more molecules) of the aforementioned isocyanate group, and polymers. Examples of low-molecular-weight polyols include trimethylolpropane, glycerol, pentaerythritol, and other ternary or higher alcohols; examples of high-molecular-weight polyols include polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, and polyisoprene polyols.

[0045] Examples of such isocyanate compounds include trimers of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, biuret or isocyanurate forms of hexamethylene diisocyanate or toluene diisocyanate, reaction products of trimethylolpropane with toluene diisocyanate or xylene diisocyanate (e.g., 3-molecular adducts of toluene diisocyanate or xylene diisocyanate), reaction products of trimethylolpropane with hexamethylene diisocyanate (e.g., 3-molecular adducts of hexamethylene diisocyanate), polyether polyisocyanates, and polyester polyisocyanates.

[0046] From the viewpoint of preventing yellowing, xylene diisocyanate and hexamethylene diisocyanate crosslinking agents are preferred among isocyanate compounds; from the viewpoint of stress mitigation, toluene diisocyanate crosslinking agents are preferred. Examples of xylene diisocyanate crosslinking agents include xylene diisocyanate and its polymers, derivatives, and polymers; examples of hexamethylene diisocyanate crosslinking agents include hexamethylene diisocyanate and its polymers, derivatives, and polymers; examples of toluene diisocyanate crosslinking agents include toluene diisocyanate and its polymers, derivatives, and polymers.

[0047] (Epoxy compound (C2)) Examples of epoxy compounds (C2) include compounds with two or more epoxy groups in their molecules, such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylenediamine, and 1,3-bis(N,N'-diamine glycidylaminomethyl)cyclohexane.

[0048] (Metal chelate (C3)) As metal chelates (C3), examples include compounds formed by coordinating alkoxides, acetylacetone, ethyl acetoacetate, etc., onto polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium. Specific examples include aluminum isopropoxide, aluminum sec-butyrate, aluminum diisopropoxide of ethyl acetoacetate, aluminum triacetoacetate, and aluminum triacetylacetone.

[0049] The amount of crosslinking agent (C) in the adhesive composition is typically 0.01 to 10 parts by weight relative to 100 parts by weight of the (meth)acrylic acid polymer (A), preferably 0.02 to 5 parts by weight, and more preferably 0.03 to 2.5 parts by weight. In this configuration, a sufficiently and moderately crosslinked structure can be formed, resulting in an adhesive with high cohesion, an excellent balance of adhesive properties, and excellent durability.

[0050] Organic solvents (D) The adhesive composition of the present invention may further contain an organic solvent (D) for adjusting coatability. Examples of organic solvent (D) include those described in the manufacturing conditions of the (meth)acrylic polymer (A). Furthermore, the organic solvent used in manufacturing the (meth)acrylic polymer (A) may be the same as or different from the organic solvent (D) contained in the adhesive composition. One or more organic solvents may be used alone.

[0051] When the adhesive composition contains an organic solvent (D), it is typically 30 to 90% by mass, preferably 40 to 90% by mass, in 100% by mass of the adhesive composition. Additive (E) In addition to the components (A) to (D) described above, the adhesive composition of the present invention may also contain additives (E) without impairing the effects of the present invention.

[0052] Examples of additives (E) include tackifying resins other than the aforementioned tackifying resin (B), silane coupling agents, antistatic agents, antioxidants, light stabilizers, metal corrosion inhibitors, plasticizers, crosslinking accelerators, and reprocessing agents. One type of additive (E) may be used alone, or two or more may be used. The amount of additive (E) in the adhesive composition varies depending on the type of additive (E) and is not particularly limited, but is typically 0.01 to 10% by mass in 100% by mass of the adhesive composition, preferably 0.1 to 5% by mass.

[0053] (Adhesive composition) The adhesive composition of the present invention can be prepared, for example, by mixing the above-mentioned components using conventionally known methods. For example, the adhesive composition can be prepared by mixing a solution containing (meth)acrylic polymer (A), a tackifying resin (B), a crosslinking agent (C), and other components such as additives used as needed.

[0054] (Adhesive layer) The adhesive layer formed from the adhesive composition consisting of the (meth)acrylic polymer (A), the tackifying resin (B), and the crosslinking agent (C) has a haze of preferably 5.0% or less, more preferably 0.5% to 4.5%, and even more preferably 1.0% to 2.5% when the thickness is 25 μm. A haze within the above range indicates that the (meth)acrylic polymer (A) and the tackifying resin (B) are moderately compatible, exhibiting high adhesion of the resulting adhesive sheet to low-polarity substrates. Furthermore, in applications where transparency is not required, the adhesive composition may contain fillers, pigments, or other additives that impair transparency; however, the haze of the 25 μm thick adhesive layer formed from the (meth)acrylic polymer (A), the tackifying resin (B), and the crosslinking agent (C) is preferably within the above range.

[0055] Furthermore, the contact angle between the adhesive layer surface formed by the adhesive composition of the present invention and the flowing paraffin is preferably less than 40°, more preferably 10 to 35°. A contact angle within the above range indicates that a tackifying resin (B) is appropriately present on the surface of the adhesive layer in contact with the adherend.

[0056] The adhesive layer formed from the adhesive composition exhibits the above-mentioned properties, and therefore also exhibits high adhesion to low polarity substrates such as various polyolefins, such as polyethylene (PE), polypropylene (PP), and cyclic olefin resins (COP).

[0057] [Adhesive sheet] An adhesive sheet according to one embodiment of the present invention has an adhesive layer formed from the adhesive composition of one embodiment of the present invention described above, including sheet-like, strip-like, and other forms.

[0058] Examples of adhesive sheets include adhesive sheets formed solely of adhesive layers, double-sided adhesive sheets having a substrate and adhesive layers formed on both sides of the substrate, with at least one adhesive layer being an adhesive composition of the present invention, single-sided adhesive sheets having a substrate and an adhesive layer formed on one side of the substrate by an adhesive composition of the present invention, and adhesive sheets having substrates disposed on both sides of an adhesive layer formed by an adhesive composition of the present invention.

[0059] There are no particular limitations on the aforementioned substrates, and examples include plastic substrates, non-woven fabrics, woven fabrics, paper, metals, glass, ceramics, and foams. The thickness of the substrate varies depending on its application and is not particularly limited, but is typically 5–200 μm.

[0060] Examples of plastic substrates include polyethylene terephthalate, polyvinyl chloride, polyolefins, polypropylene, polymethyl methacrylate, polycarbonate, polyimide, and ABS.

[0061] The substrate can be a peel-treated substrate. In the case where the adhesive sheet is an adhesive sheet in which substrates are disposed on both sides of an adhesive layer formed by the adhesive composition of the present invention, at least one of the substrates is a peel-treated substrate, and the peel-treated substrate is removed when bonding with the adherend.

[0062] The thickness of the adhesive layer can be appropriately selected according to the application and other factors, and there is no particular limitation. However, from the point of view of maintaining adhesive performance, it is usually 5 to 200 μm, preferably 10 to 100 μm.

[0063] The adhesive layer can also be at least partially crosslinked during its manufacturing process by reacting the (meth)acrylic polymer (A) in the adhesive composition with the crosslinking agent (C). There are no particular limitations on the method for manufacturing the adhesive sheet, but the following method is an example: The adhesive composition is applied to a substrate. If the adhesive composition contains a solvent, it is dried at a temperature of typically 50–150°C, preferably 60–100°C, for typically 1–10 minutes, preferably 2–7 minutes to remove the solvent, forming a coating film. Next, another substrate is bonded to the surface of the coating film on the substrate-free side. Subsequently, it is cured at a temperature of typically 5–60°C, preferably 15–40°C, and typically 30–70% RH, preferably 40–70% RH, for typically more than 1 day, preferably 3–10 days, to manufacture the adhesive sheet. This curing process is also called ripening. Ripening under these conditions allows cross-linking to occur during the curing process, enabling efficient formation of cross-linked bodies.

[0064] As a coating method for the adhesive composition, coating and drying can be carried out by means of known methods such as spin coating, knife coating, roller coating, bar coating, doctor blade coating, mold coating, gravure coating, and doctor blade coating to achieve a specified thickness.

[0065] The adhesive sheet with an adhesive layer obtained from the adhesive composition also exhibits excellent adhesion to low-polarity substrates such as polyolefins, and has excellent high-temperature properties, making it suitable for various applications such as automotive applications. Example

[0066] The following describes one embodiment of the present invention based on specific examples, but the present invention is not limited to these examples. In the following description of examples, etc., unless otherwise specified, "parts" means "parts by mass".

[0067] ((Meth)acrylic polymer A) The method for determining the weight-average molecular weight (Mw) of (meth)acrylic acid polymer (A) is as follows.

[0068] The weight-average molecular weight (Mw) of the (meth)acrylic acid copolymer (A) was determined by gel permeation chromatography (GPC) under the following conditions using standard polystyrene.

[0069] • Measuring apparatus: HLC-8120GPC (manufactured by Tosoh Corporation) • GPC column composition: The following 5-column chromatographic column (all manufactured by Tosoh Corporation) (1) TSK-GEL HXL-H (protective column) (2) TSK-GEL G7000HXL (3) TSK-GEL GMHXL (4) TSK-GEL GMHXL (5) TSK-GEL G2500HXL • Sample concentration: Dilute with tetrahydrofuran to 1.0 mg / cm³ 3 • Mobile phase solvent: Tetrahydrofuran • Flow rate: 1.0 cm 3 / min Column temperature: 40℃ [Manufacturing Example 1] (Manufacturing of acrylic polymer (A-1)) In a flask equipped with a stirrer, nitrogen inlet tube, thermometer, and reflux condenser, 96.8 parts by mass of 2-methoxyethyl acrylate, 3 parts by mass of acrylic acid, 0.2 parts by mass of 2-hydroxyethyl acrylate, 37 parts by mass of toluene, and 24 parts by mass of ethyl acetate were added. The contents of the flask were heated to 85°C while nitrogen was introduced into the flask. Then, 0.1 parts by mass of azobisisobutyronitrile (AIBN), fully purged with nitrogen, were added to the flask with stirring. The temperature of the contents of the flask was maintained at 85–86°C for 4 hours of heating and cooling. After raising the temperature to 95°C, the mixture was refluxed twice. Finally, 19 parts by mass of toluene and 78 parts by mass of ethyl acetate were added to obtain a solution containing the acrylic polymer (A-1). The weight-average molecular weight (Mw) of the obtained acrylic polymer (A-1), determined by gel permeation chromatography (GPC), was 650,000.

[0070] [Manufacturing Examples 2-8] Except for changing the type of monomer supplied for polymerization and the composition (parts by mass) of the feed as shown in Table 1, a solution containing acrylic polymers (A-2) to (A-6), (A'-7) or (A'-8) was obtained in the same manner as in Manufacturing Example 1.

[0071] Furthermore, in Manufacturing Example 2, the 37 parts by mass of toluene and 24 parts by mass of ethyl acetate added at the start of polymerization in Manufacturing Example 1 were replaced with 24 parts by mass of toluene and 37 parts by mass of ethyl acetate for the reaction. Additionally, in Manufacturing Example 3, the 37 parts by mass of toluene and 24 parts by mass of ethyl acetate added at the start of polymerization in Manufacturing Example 1 were replaced with 47 parts by mass of toluene and 14 parts by mass of ethyl acetate for the reaction.

[0072] The weight-average molecular weight (Mw) of each acrylic polymer obtained by gel permeation chromatography (GPC) is shown in Table 1.

[0073] Table 1 MEA: 2-Methoxyethyl Acrylate AA: Acrylic acid 2-HEA: 2-Hydroxyethyl Acrylate BA: n-Butyl acrylate (Tackifying Resin B) In the following examples and comparative examples, the following resins were used as tackifying resins.

[0074] Table 2 G-125: YS POLYSTER G125; terpene phenol resin (manufactured by Yasuhara Chemical Co., Ltd.) N-125: YS POLYSTER N125; terpene phenol resin (manufactured by Yasuhara Chemical Co., Ltd.) K-125: YS POLYSTER K125; terpene phenol resin (manufactured by Yasuhara Chemical Co., Ltd.) HP-120: HP-120; Phenolic modified xylene resin (manufactured by Fukudo Co., Ltd.) T-130: YS POLYSTER130; terpene phenol resin (manufactured by Yasuhara Chemical Co., Ltd.) KE-359: PINECRYSTAL KE-359; hydrogenated rosin ester resin (manufactured by Arakawa Chemical Industry Co., Ltd.) In addition, the physical properties of the tackifying resin were determined using the following methods.

[0075] <Softening point> The softening point is determined by the softening point test method (ring and ball method) specified in JIS K 2207.

[0076] <Hydroxy value> The hydroxyl value is determined by potentiometric titration according to JIS K0070, using the number of mg of potassium hydroxide required to neutralize the acetic acid bound to the hydroxyl group when 1g of tackifying resin is acetylated.

[0077] <Acid Value> The acid value was determined by potentiometric titration according to JIS K0070, which yielded the amount of potassium hydroxide (mg) required to neutralize 1g of tackifying resin.

[0078] <Determination of Contact Angle of Flowing Paraffin> A solution of tackifying resin was prepared by adding 20 parts by weight of tackifying resin and 30 parts by weight of ethyl acetate to a container. Next, a plastic plate was immersed in the prepared tackifying resin solution and dried at 80°C for 5 minutes. Approximately 1 μl of flowing paraffin (manufactured by Junsei Chemicals Co., Ltd.) was placed on the surface of the formed tackifying resin film. The contact angle of the flowing paraffin was measured in atmosphere using a KYOWA CONTACT-ANGLE METER CA-D type (manufactured by Kyowa Interface Science Co., Ltd.), with the average value of n=10 as the measured value. The measurement conditions followed JIS R3257.

[0079] [Example 1] (Preparation of the adhesive composition) In the acrylic polymer (A-1) solution obtained in Manufacturing Example 1 (equivalent to 100 parts by mass of solid component (acrylic polymer), 20 parts by mass of tackifying resin (B-1) and 0.045 parts by mass of epoxy crosslinking agent E-5XM (manufactured by Soken Chemical Co., Ltd.) were added, and the mixture was stirred with a glass rod for 5 minutes to obtain adhesive composition (1).

[0080] (Manufacturing of adhesive sheets) On a 25 μm thick polyethylene terephthalate (PET) film, the obtained adhesive composition is degassed and then coated with a doctor blade until the dried thickness reaches 25 μm. The solvent is removed by drying at 80°C for 3 minutes to form a coating film as the adhesive layer.

[0081] The peeled PET film is laminated onto the surface of the adhesive layer opposite to the PET film. Then, it is left to cure at 23°C / 50%RH for 7 days to produce an adhesive sheet with an adhesive layer of 25μm thickness.

[0082] (Physical property evaluation) The physical properties of the obtained adhesive sheet were measured and evaluated as follows. The results are shown in Table 3.

[0083] <Adhesion Strength Evaluation> The adhesive sheet was cut into 25mm × 100mm dimensions to obtain test pieces. The peeled PET film of the test pieces was removed, and the exposed adhesive layer was adhered to PP (polypropylene), PE (polyethylene), and COP (cyclic olefin resin) boards, respectively, serving as the substrates. After three round-trip pressings with a 2kg roller, the pieces were placed at 23℃ / 50% RH for 20 minutes. Then, the adhesive force (N / 25mm) was measured by stretching the end of the test piece along a 180° direction at a speed of 300mm / min on each substrate.

[0084] <Determination of Contact Angle of Flowing Paraffin> Peel off the peel-off PET film from one side of the obtained adhesive sheet. Place approximately 1 μl of flowing paraffin (purely chemically prepared) onto the exposed adhesive layer surface. Measure the contact angle of the flowing paraffin under atmospheric conditions using a KYOWACONTACT-ANGLE METER CA-D type instrument manufactured by Kyowa Interface Science Co., Ltd., and use the average value of n=10 as the measured value. The measurement conditions were in accordance with JIS R3257.

[0085] <Haze Measurement> On a PET film that has undergone peeling treatment, the adhesive composition obtained in the Examples and Comparative Examples is degassed, coated with a doctor blade to a thickness of 25 μm after drying, and dried at 80°C for 3 minutes to remove the solvent, forming a coating film that becomes the adhesive layer.

[0086] The peeled PET film is laminated onto the surface of the adhesive layer opposite to the side of the peeled PET film. Then, it is left to cure at 23°C / 50%RH for 7 days.

[0087] Peel off the peeling PET film from one side of the resulting adhesive sheet, and bond the exposed adhesive layer to the glass plate (manufactured by AGC Fabritech Co., Ltd., FL soda glass, 1.1 mm thick, haze value: 0.1%).

[0088] Then, the remaining PET film after the peeling process is removed, and the haze value of the test piece with only the adhesive layer on the glass plate is measured using a haze meter (model HM-150, manufactured by Murakami Color Technology Research Institute). The haze value of the test piece minus the haze value of the glass plate alone (0.1) is the haze value of the adhesive layer (%).

[0089] [Examples 2-11, Comparative Examples 1-7] Except for changing the types and amounts of acrylic polymer and tackifying resin as shown in Tables 3 and 4, the process was carried out in the same manner as in Example 1 to obtain the adhesive composition and adhesive sheet.

[0090] The resulting adhesive sheet was evaluated for its physical properties using the same method as in Example 1. The results are shown in Tables 3 and 4.

[0091] Table 3

[0092] Table 4 As shown in Tables 3 and 4, the adhesive sheets obtained by the adhesive compositions described in Examples 1 to 11 exhibit good adhesion to any of the substrates made of low-polarity and difficult-to-bond polyethylene, polypropylene, and polyolefin resins.

[0093] Furthermore, the adhesive layers obtained from the adhesive compositions described in Examples 1-11 exhibit low haze, good compatibility between the (meth)acrylic polymer (A) and the tackifying resin (B), and are suitable for applications requiring transparency. Moreover, the contact angles between the adhesive layers obtained from the adhesive compositions described in Examples 1-8 and the flowing paraffin are all less than 40°, indicating that the tackifying resin component is sufficiently present on the surface of the adhesive layer, resulting in high adhesive strength. Industrial utilization potential

[0094] The adhesive composition of the present invention is suitable for use as an adhesive layer for forming adhesive sheets. The adhesive sheets of the present invention are suitable as adhesive sheets for automotive interior and exterior materials or various structures, particularly suitable for use in bonding difficult-to-bond substrates such as those used in automobiles, and for applications requiring heat resistance.

Claims

1. An adhesive composition comprising a (meth)acrylic polymer (A), a tackifying resin (B), and a crosslinking agent (C), wherein the (meth)acrylic polymer (A) is a polymer comprising 70-99.9% by weight of an alkoxyalkyl ester of (meth)acrylic acid and 0.1-15% by weight of a monomeric component (a) containing a crosslinking functional group, wherein the (meth)acrylic polymer (A) has a weight-average molecular weight (Mw) of 300,000 to 1,000,000, wherein the tackifying resin (B) has a hydroxyl value of 100 mg KOH / g or higher and 300 mg KOH / g or lower, wherein the tackifying resin (B) has an acid value of 10 mg KOH / g or lower, and wherein 10-50 parts by weight of the tackifying resin (B) are contained relative to 100 parts by weight of the (meth)acrylic polymer (A).

2. The adhesive composition of claim 1, wherein, The (meth)acrylic acid polymer (A) is a polymer comprising 70-99.9% by mass of alkoxyalkyl esters of (meth)acrylic acid, 0.1-15% by mass of carboxyl-containing monomers and 0-5% by mass of hydroxyl-containing monomers (a).

3. The adhesive composition according to claim 1 or 2, wherein, The adhesive layer with a thickness of 25 μm obtained from the adhesive composition has a haze of less than 5%.

4. The adhesive composition according to claim 1 or 2, wherein, The contact angle between the surface of the adhesive layer obtained from the adhesive composition and the flowing paraffin is less than 40°.

5. The adhesive composition according to claim 1 or 2, wherein, The acid value of the tackifying resin (B) is less than 5 mg KOH / g.

6. The adhesive composition of claim 1 or 2, wherein, The tackifying resin (B) is a resin with a phenolic skeleton.

7. An adhesive sheet having an adhesive layer formed from the adhesive composition of any one of claims 1 to 6.

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