Pressure-sensitive adhesive composition, pressure-sensitive adhesive layer and pressure-sensitive adhesive sheet made of the pressure-sensitive adhesive composition

Abstract

Provided are a pressure-sensitive adhesive layer that has adhesive strength to both high-polarity and low-polarity adherends, is excellent in heat resistance retention and coating film transparency, and is easily peelable (easy peelability) by irradiation with active energy rays or heating; a pressure-sensitive adhesive composition that can realize this and has storage stability; and a pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer. [Solution] A pressure-sensitive adhesive composition comprising an acrylic copolymer (A) having a specific weight-average molecular weight, an acrylic copolymer (B) having a specific weight-average molecular weight, and an acid catalyst (C), wherein the acrylic copolymer (B) is a copolymer of a monomer mixture containing a (meth)acrylic monomer (b1) having a carboxy group protected by a protecting group, the content of the (meth)acrylic monomer (b1) in 100 mass% of the monomer mixture being 5 to 95 mass%, and the content of the acrylic copolymer (B) relative to 100 mass parts of the acrylic copolymer (A) being 1 to 50 mass parts.

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive layer and a pressure-sensitive adhesive sheet each comprising the pressure-sensitive adhesive composition. [Background technology]

[0002] Because pressure-sensitive adhesive sheets having a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive are easy to handle, they are used in a wide range of fields, including label and medical applications. The substrates used for pressure-sensitive adhesive sheets vary widely depending on the application, and high-polarity substrates such as stainless steel (SUS) and polyester may be used, while low-polarity substrates such as polyolefin may be used. However, low-polarity substrates generally tend to be difficult to adhere to, and there is a demand for pressure-sensitive adhesives that can ensure adhesion to, for example, polyolefin-based resins. Furthermore, adhesives are used in applications where high-temperature environments are expected, such as marking films, window films, and automotive components, as well as in applications where visibility is required, such as optical displays. Therefore, they must have excellent heat-resistant adhesive strength and heat-resistant retention, and the transparency of the coating film must prevent peeling or slippage even in high-temperature environments.

[0003] In recent years, with the rise in awareness of recycling, efforts have been made to improve dismantling by making materials that have sufficient adhesive strength when in use but are easy to peel off when disposed of.

[0004] Patent Document 1 discloses a pressure-sensitive adhesive composition containing: a (meth)acrylic acid ester copolymer (A) having an active energy ray-reactive group in a side chain, the (meth)acrylic acid ester copolymer containing a (meth)acrylic acid alkyl ester having 1 to 12 carbon atoms in the alkyl group and a carboxy precursor group-containing monomer having a carboxy precursor group that releases a hydrocarbon gas upon heating and is converted to a carboxy group; an acid generator (B) that generates an acid upon at least one of irradiation with active energy rays and heating; and a photoinitiator (C). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 188819 Summary of the Invention [Problem to be solved by the invention]

[0006] While the pressure-sensitive adhesive composition described in Patent Document 1 exhibits sufficient adhesive strength to highly polar adherends, the inventors' investigations revealed that it did not exhibit sufficient adhesive strength to polypropylene resin (hereinafter also referred to as PP resin), which is a low-polarity adherend. Furthermore, dismantling requires a two-step process of irradiation with active energy rays and heating, and no reduction in adhesive strength effective for dismantling was confirmed in environments where irradiation with active energy rays is not possible. Furthermore, in the case of a pressure-sensitive adhesive whose adhesive properties are changed by irradiation with active energy rays or heating, thereby imparting easy dismantling properties, as in Patent Document 1, storage stability is required so that no changes occur except at the intended timing (when irradiated with active energy rays or when heated).

[0007] In other words, a pressure-sensitive adhesive layer that has adhesive strength to both high-polarity and low-polarity adherends, has excellent heat resistance retention and coating film transparency, and is easily peelable (easy peelability) by irradiation with active energy rays or heating, and a pressure-sensitive adhesive composition with storage stability that can realize this, and a pressure-sensitive adhesive sheet having such a pressure-sensitive adhesive layer have not yet been developed. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems, and as a result have completed the present invention. The pressure-sensitive adhesive composition according to the present invention, and the pressure-sensitive adhesive layer and pressure-sensitive adhesive sheet each comprising the pressure-sensitive adhesive composition have the following configurations [1] to [6].

[0009] [1] A pressure-sensitive adhesive composition comprising an acrylic copolymer (A), an acrylic copolymer (B), and an acid catalyst (C), wherein the weight-average molecular weight of the acrylic copolymer (A) is 300,000 or more, the weight-average molecular weight of the acrylic copolymer (B) is in the range of 5,000 to 200,000, the acrylic copolymer (B) is a copolymer of a monomer mixture containing a (meth)acrylic monomer (b1) having a carboxy group protected by a protecting group, the content of the (meth)acrylic monomer (b1) in 100% by mass of the monomer mixture is 5 to 95% by mass, and the content of the acrylic copolymer (B) per 100 parts by mass of the acrylic copolymer (A) is 1 to 50 parts by mass. [2] The pressure-sensitive adhesive composition according to [1], wherein the acrylic copolymer (A) is a copolymer of a monomer mixture containing a (meth)acrylic monomer (a1) having a hydroxy group, and the content of the (meth)acrylic monomer (a1) having a hydroxy group in 100% by mass of the monomer mixture is 0.1 to 30% by mass. [3] The pressure-sensitive adhesive composition according to [1] or [2], further comprising a curing agent (D). [4] The pressure-sensitive adhesive composition according to any one of [1] to [3], wherein the acid catalyst (C) comprises at least one of an acid generator that generates an acid upon irradiation with active energy rays or heating and an acid having an acid dissociation constant (Pka) of 1.0 or less, and the content of the acid catalyst (C) is 0.1 to 5 parts by mass per 100 parts by weight of the acrylic copolymer (A). [5] [1] [4] A pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition according to any one of [1] to [4]. [6] An adhesive sheet having the adhesive layer according to [5]. [Effects of the Invention]

[0010] The present invention makes it possible to provide a pressure-sensitive adhesive layer that has adhesive strength to both high-polarity and low-polarity adherends, has excellent heat resistance retention and coating film transparency, and is easily peelable (easy to peel) by irradiation with active energy rays or heating, as well as a pressure-sensitive adhesive composition with storage stability that can realize this, and a pressure-sensitive adhesive sheet having this pressure-sensitive adhesive layer. DETAILED DESCRIPTION OF THE INVENTION

[0011] The pressure-sensitive adhesive composition of the present invention, and the pressure-sensitive adhesive layer and pressure-sensitive adhesive sheet made of the pressure-sensitive adhesive composition will be described below, but the present invention is not limited thereto. In this specification, (meth)acrylic includes acrylic and methacrylic, and (meth)acryloyl group includes acryloyl group and methacryloyl group. Monomer is a monomer having an ethylenically unsaturated group. Furthermore, in this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the lower and upper limit values ​​of the range. Furthermore, "film" and "sheet" are not distinguished by thickness. In other words, in this specification, "sheet" includes thin film-like objects, and "film" includes thick sheet-like objects. Furthermore, both "sheet" and "film" include laminates. Furthermore, the term "adherend" refers to a counterpart to which the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is attached. Unless otherwise noted, the various components appearing in this specification may be used independently either alone or in combination of two or more.

[0012] The pressure-sensitive adhesive composition of the present invention contains an acrylic copolymer (A), an acrylic copolymer (B), and an acid catalyst (C). Each component will be described below.

[0013] <Acrylic copolymer (A)> The acrylic copolymer (A) is a copolymer having a weight-average molecular weight of 300,000 or more obtained by copolymerizing a mixture of acrylic monomers. There are no limitations on the (meth)acrylic monomers constituting the acrylic copolymer (A), but it is preferable that it contains a hydroxyl-containing (meth)acrylate monomer (a1) from the viewpoint of improving compatibility with the acrylic copolymer (B), and it is also preferable that it is an acrylic copolymer in which a carboxyl-containing (meth)acrylic monomer (a2) and an alkyl (meth)acrylate monomer (a3) ​​are copolymerized as appropriate.

[0014] [(Meth)acrylic monomer (a1) having a hydroxy group] Examples of the (meth)acrylic monomer (a1) having a hydroxy group (hereinafter also referred to as monomer (a1)) include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and the like, and these can be used alone or in combination of two or more.

[0015] The content of monomer (a1) is preferably 0.1 to 30% by mass based on 100% by mass of the monomer mixture. It is more preferably 0.5 to 30% by mass, and even more preferably 1 to 30% by mass. By setting the content of monomer (a1) to 0.1% by mass or more, the cohesive strength of the pressure-sensitive adhesive composition is increased, making it possible to prevent lifting and peeling after leaving it in a high-temperature atmosphere. By setting the content of monomer (a1) to 30% by mass or less, it is possible to reduce the adhesion between the pressure-sensitive adhesive layer and the adherend by irradiation with active energy rays or heating at the desired timing, making it easier to peel.

[0016] [(Meth)acrylic monomer (a2) having a carboxy group] Examples of the (meth)acrylic monomer (a2) having a carboxy group (hereinafter also referred to as monomer (a2)) include acrylic acid, methacrylic acid, and monomers represented by the following formula: CH2=CR1-CO-O-(C2H4-COO-)nH Here, R1 represents hydrogen or a methyl group, and n represents an integer of 1 or more.

[0017] The content of the monomer (a2) is preferably 0.1 to 10 mass% based on 100 mass% of the monomer mixture constituting the acrylic copolymer (A). It is more preferably 0.1 to 8 mass%, and even more preferably 0.1 to 5 mass%. By having it be 0.1 to 10 mass%, the cohesive strength of the pressure-sensitive adhesive composition can be increased and storage stability can be ensured.

[0018] [Alkyl (meth)acrylate monomer (a3)] The alkyl (meth)acrylate monomer (a3) ​​may be a (meth)acrylic acid alkyl ester in which the alkyl group has a carbon number of 1 to 20. The alkyl group may be a linear or branched alkyl group, or may be a cyclic alkyl group such as an alicyclic alkyl group.

[0019] Examples of alkyl (meth)acrylate monomers having a linear or branched alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl acrylate, t-butyl acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, n-heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undeca(meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate.

[0020] Examples of alkyl (meth)acrylate monomers having an alicyclic alkyl group include alkyl (meth)acrylate monomers having a monocyclic aliphatic hydrocarbon ring, alkyl (meth)acrylate monomers having a bicyclic aliphatic hydrocarbon ring, and alkyl (meth)acrylate monomers having a tricyclic or higher aliphatic hydrocarbon ring. Examples of alkyl (meth)acrylate monomers having a monocyclic aliphatic hydrocarbon ring include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. Examples of (meth)acrylic acid alkyl esters having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth)acrylate. Examples of alkyl(meth)acrylate monomers having three or more aliphatic hydrocarbon rings include dicyclopentanyl(meth)acrylate, dicyclopentanyloxyethyl(meth)acrylate, tricyclopentanyl(meth)acrylate, 1-adamantyl(meth)acrylate, 2-methyl-2-adamantyl(meth)acrylate, and 2-ethyl-2-adamantyl(meth)acrylate.

[0021] The content of monomer (a3) ​​in 100% by mass of the monomer mixture is preferably 10 to 90% by mass, more preferably 15 to 85% by mass, and even more preferably 20 to 80% by mass. When the content is 10% by mass or more, the adhesive strength is excellent in high-temperature environments, and when the content is 90% by mass or less, the adhesive strength is high even at room temperature.

[0022] [Other monomers] The monomer mixture constituting the acrylic copolymer (A) may contain other monomers in addition to the monomers (a1) to (a3) ​​as optional components, provided that the effects of the present invention are not impaired. Examples include alkoxy (meth)acrylates such as 2-methoxyethyl acrylate, vinyl monomers such as vinyl acetate and styrene, and monomers having a glycidyl group such as glycidyl (meth)acrylate.

[0023] The content of other monomers is preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 9% by mass or less, particularly preferably 6% by mass or less, and most preferably 3% by mass or less, based on 100% by mass of the monomer mixture.

[0024] (Weight average molecular weight (Mw)) The weight-average molecular weight of the acrylic copolymer (A) is 300,000 or more. There is no particular upper limit as long as it is within the range that can be produced, but if an upper limit is to be imposed, it is preferably 1,800,000 or less. It is preferably 600,000 to 1,500,000, and more preferably 600,000 to 1,200,000. By keeping the weight-average molecular weight within the above range, it becomes easier to achieve both adhesion to each adherend and holding power. The weight-average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). Details will be described in the examples.

[0025] <Acrylic copolymer (B)> The acrylic copolymer (B) is a copolymer having a weight average molecular weight of 5,000 to 200,000 obtained by copolymerizing a monomer mixture containing a (meth)acrylic monomer (b1) having a carboxy group protected by a protecting group. Since the acrylic copolymer (B) contains a (meth)acrylic monomer (b1) in which the polar carboxy group is protected by a protecting group, the acrylic copolymer (B) tends to have a high affinity with adherends having low polarity. The monomer mixture constituting the acrylic copolymer (B) preferably further contains a (meth)acrylic monomer (b2) having an amino group or a hydroxy group. The inclusion of the (meth)acrylic monomer (b2) having an amino group or a hydroxy group improves the compatibility between the acrylic copolymer (B) and the acrylic copolymer (A), and facilitates the acrylic copolymer (B), which has a small weight-average molecular weight, to be appropriately localized on the outermost surface of the pressure-sensitive adhesive layer.

[0026] [(Meth)acrylic monomer (b1) having a carboxy group protected by a protecting group] A (meth)acrylic monomer (b1) (hereinafter also referred to as monomer (b1)) having a carboxy group protected by a protecting group is deprotected and converted to a carboxy group by the acid component of an acid generator that generates an acid upon irradiation with active energy rays or heating and / or an acid with an acid dissociation constant (PKa) of 1.0 or less. The generation of the carboxy group generates a hydrocarbon gas such as an alkylene or alkane, which reduces adhesion between the adherend and the pressure-sensitive adhesive layer, allowing for easy peeling. Furthermore, because the polar carboxy group is protected by a protecting group, affinity for low-polarity adherends can be enhanced.

[0027] Monomer (b1) is not particularly limited as long as it can be deprotected by an acid to form a carboxy group, but an ester group composed of an alkyl group having a secondary or tertiary carbon atom, which is prone to undergo olefin elimination by an acid, and a carboxy group can be preferably used. In addition, as a group other than the alkyl group having a secondary or tertiary carbon atom, a benzyl group, which is prone to elimination under mild conditions, can also be preferably used.

[0028] Examples of the monomer (b1) include sec-butyl(meth)acrylate, isopropyl(meth)acrylate, sec-hexyl(meth)acrylate, sec-octyl(meth)acrylate, sec-nonyl(meth)acrylate, sec-decyl(meth)acrylate, bornyl(meth)acrylate, isobornyl(meth)acrylate, cyclohexyl(meth)acrylate, tert-butyl(meth)acrylate, tert-hexyl(meth)acrylate, tert-octyl(meth)acrylate, Examples of suitable monomers include 2-methyl-2-adamantyl(meth)acrylate, tert-nonyl(meth)acrylate, tert-decyl(meth)acrylate, 2-methyl-2-adamantyl(meth)acrylate, 2-ethyl-2-adamantyl(meth)acrylate, and benzyl(meth)acrylate, and tert-butyl(meth)acrylate is preferred because it can be easily released with the acid catalyst (C), thereby making it easier to peel the pressure-sensitive adhesive sheet according to this embodiment from the adherend. Monomer (b1) may be used singly or in combination of two or more types.

[0029] The content of monomer (b1) is 5 to 95% by mass in 100% by mass of the monomer mixture. It is preferably 10 to 95% by mass, and more preferably 15 to 95% by mass. By making the content of monomer (b1) 5% by mass or more, hydrocarbon-based gas is efficiently generated from the pressure-sensitive adhesive layer, making it possible to more easily peel the pressure-sensitive adhesive sheet according to this embodiment from an adherend. By making the content of monomer (b1) 95% by mass or less, it becomes easier to ensure sufficient contents of other monomers, making it easier to achieve the desired adhesive strength in the pressure-sensitive adhesive sheet according to this embodiment.

[0030] [(Meth)acrylic monomer (b2) having an amino group or a hydroxy group] The (meth)acrylic monomer (b2) having an amino group or a hydroxy group (hereinafter also referred to as monomer (b2)) is not particularly limited as long as it is a (meth)acrylic monomer having an amino group or a hydroxy group in the molecule. Examples of the monomer (b2) include N,N-dialkylaminoalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and N,N-diethylaminoethyl (meth)acrylate, and these can be used alone or in combination of two or more.

[0031] The content of monomer (b2) is preferably 0.1 to 20% by mass based on 100% by mass of the monomer mixture, more preferably 0.2 to 20% by mass, and even more preferably 0.5 to 20% by mass. By making the content of monomer (b2) 0.1% by mass or more, compatibility with the acrylic copolymer (A) is improved, and by making the content of monomer (b2) 20% by mass or less, the acrylic copolymer (B) can be appropriately localized on the outermost surface of the pressure-sensitive adhesive layer.

[0032] [(Meth)acrylic monomer (b3) having an aliphatic or aromatic hydrocarbon group] The (meth)acrylic monomer (b3) having an aliphatic or aromatic hydrocarbon group (hereinafter also referred to as monomer (b3)) includes a (meth)acrylic monomer having a linear or branched alkyl group and a (meth)acrylic monomer containing an aromatic hydrocarbon group. The number of carbon atoms in the linear or branched alkyl group is preferably 1 to 20 from the viewpoint of the balance between adhesive strength and cohesive strength. However, if a compound is both a monomer (b1) and a monomer (b3), it is classified as a monomer (b1).

[0033] Examples of (meth)acrylic monomers having a linear or branched alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, n-heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undeca(meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate. Examples of aromatic hydrocarbon group-containing (meth)acrylic monomers include benzyl (meth)acrylate, naphthyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxybutyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, 2-(1-naphthyloxy)ethyl (meth)acrylate, 2-(2-naphthyloxy)ethyl (meth)acrylate, 6-(1-naphthyloxy)hexyl (meth)acrylate, 6-(2-naphthyloxy)hexyl (meth)acrylate, 8-(1-naphthyloxy)octyl (meth)acrylate, and 8-(2-naphthyloxy)octyl (meth)acrylate.

[0034] The monomer (b3) is an optional component, and the total content of the monomer (b1) and the monomer (b3) in 100% by mass of the monomer mixture constituting the (meth)acrylic copolymer (B) is preferably 50 to 99.9% by mass, more preferably 60 to 99.9% by mass, and even more preferably 80 to 99.9% by mass. When the total content of monomer (b1) and monomer (b3) is within the above range, the heat resistance of the acrylic copolymer (B) can be imparted, and the content of other monomers can be easily ensured to be sufficient, making it easier to achieve the desired adhesive strength in the pressure-sensitive adhesive sheet according to this embodiment.

[0035] [Other (meth)acrylic monomers (b4)] The other monomer (b4) (hereinafter also referred to as monomer (b4)) refers to a (meth)acrylic monomer other than the monomer (b1), the monomer (b2), and the monomer (b3). The monomer mixture constituting the acrylic copolymer (B) may contain the monomer (b4) as needed, but the content thereof is preferably 30% by mass or less in 100% by mass of the monomer mixture.

[0036] (Weight average molecular weight (Mw)) The weight-average molecular weight (Mw) of the acrylic copolymer (B) is in the range of 5,000 to 200,000, preferably in the range of 5,000 to 150,000, and more preferably in the range of 10,000 to 100,000. When the weight-average molecular weight (Mw) of the acrylic copolymer (B) is 5,000 or more, the pressure-sensitive adhesive composition can exhibit appropriate cohesive strength. Furthermore, when the weight-average molecular weight (Mw) is 5,000 or more, the compatibility between the acrylic copolymer (B) and the acrylic copolymer (A) tends not to be excessive, and therefore, when the pressure-sensitive adhesive layer is formed, the acrylic copolymer (B) is appropriately localized on the surface of the pressure-sensitive adhesive layer. When the acrylic copolymer (B) is appropriately localized on the surface of the pressure-sensitive adhesive layer, the wettability with the adherend is improved, allowing the pressure-sensitive adhesive layer to adhere to the adherend with high adhesive strength, and therefore the pressure-sensitive adhesive layer can exhibit high initial adhesive strength. Furthermore, when the weight average molecular weight (Mw) of the acrylic copolymer (B) is 200,000 or less, the cohesive strength of the pressure-sensitive adhesive composition does not become excessively high, and hydrocarbon gas is efficiently generated from the pressure-sensitive adhesive layer, making it possible to more easily peel the pressure-sensitive adhesive sheet according to this embodiment from the adherend.

[0037] The weight average molecular weight (Mw) of the acrylic copolymer (B) can be adjusted to a desired value by adjusting the reaction temperature, reaction time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, and the like.

[0038] (Production of acrylic copolymer (A) and acrylic copolymer (B)) The acrylic copolymer (A) and the acrylic copolymer (B) can be produced by polymerizing the above-mentioned monomer mixture. The polymerization can be carried out by known polymerization methods such as solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization, but solution polymerization is preferred. Solvents used in solution polymerization are preferably, for example, acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, and cyclohexanone. The polymerization temperature is preferably a boiling point reaction at 60 to 120°C. The polymerization time is preferably about 5 to 12 hours.

[0039] The polymerization initiator used for the polymerization is preferably a radical polymerization initiator, and the radical polymerization initiator is generally a peroxide or an azo compound. Examples of peroxides include dialkyl peroxides such as di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, and 2,5-di(t-butylperoxy)hexyne-3; Peroxyesters such as t-butyl peroxybenzoate, t-butyl peroxyacetate, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; ketone peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; Peroxyketals such as 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and n-butyl-4,4-bis(t-butylperoxy)valerate; Hydroperoxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, and 2,5-dimethylcyclohexane-2,5-dihydroperoxide; diacyl peroxides such as benzoyl peroxide, decanoyl peroxide, lauroyl peroxide, and 2,4-dichlorobenzoyl peroxide; Examples include peroxydicarbonates such as bis(t-butylcyclohexyl) peroxydicarbonate.

[0040] Examples of the azo compound include 2,2'-azobisbutyronitrile such as 2,2'-azobisisobutyronitrile (abbreviation: AIBN) and 2,2'-azobis(2-methylbutyronitrile); 2,2'-azobisvaleronitriles such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile); 2,2'-azobispropionitriles such as 2,2'-azobis(2-hydroxymethylpropionitrile); Examples include 1,1'-azobis-1-alkanenitriles such as 1,1'-azobis(cyclohexane-1-carbonitrile).

[0041] The polymerization initiator is preferably used in an amount of 0.01 to 10 parts by mass, more preferably 0.1 to 2 parts by mass, based on 100 parts by mass of the monomer mixture.

[0042] <Acid catalyst (C)> The acid catalyst (C) used in the present invention contains at least one of an acid generator that generates an acid upon irradiation with active energy rays or heating and an acid having an acid dissociation constant (Pka) of 1.0 or less. Examples of the acid catalyst (C) having an acid dissociation constant (Pka) of 1.0 or less that can be used include organic acids such as aromatic sulfonic acids such as p-toluenesulfonic acid and benzenesulfonic acid, and aliphatic sulfonic acids, inorganic acids such as hydrochloric acid and sulfuric acid, and hydrates thereof.

[0043] Acid generators that generate an acid upon irradiation with active energy rays or heating include, for example, photoacid generators that generate an acid capable of initiating cationic polymerization upon irradiation with energy rays such as ultraviolet rays, and thermal acid generators that generate an acid upon heating, etc. Among these, photoacid generators are preferably used because they can suitably disintegrate a pressure-sensitive adhesive layer by two types of external stimuli, namely, light and heat, while not easily decomposing or disintegrating when stored as a pressure-sensitive adhesive composition or when used as a pressure-sensitive adhesive tape to fix an article, and can maintain stable storage stability and adhesive properties.

[0044] Examples of the photoacid generator include N-hydroxynaphthalimide trifluoromethanesulfonate ester, N-hydroxynaphthalimide methanesulfonate ester, N-hydroxynaphthalimide benzenesulfonate ester, N-hydroxynaphthalimide triflate, bis(cyclohexylsulfonyl)diazomethane, bis(tert-butylsulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane, triphenylsulfonium trifluoromethanesulfonate, diphenyl-4-methylphenylsulfonium trifluoromethanesulfonate, diphenyl-2,4,6-trimethylphenylsulfonium-p-toluenesulfonate, bis(dodecylphenyl)iodonium hexafluoroantimonate, bis(tert-butylphenyl)iodonium hexafluorophosphate, bis(tert-butylphenyl)iodonium trifluoromethanesulfonate, triphenylsulfonium trifluoromethanesulfonate, and biphenyliodonium. trifluoromethanesulfonate, phenyl-(3-hydroxypentadecylphenyl)iodonium hexafluoroantimonate, phenyl-(3-hydroxypentadecylphenyl)iodonium hexafluoroantimonate, and the like can be used.

[0045] These photoacid generators may be appropriately selected depending on the intended use. For example, since the thermal decomposition temperature of these acid generators may decrease when mixed with a pressure-sensitive adhesive, it is preferable to use an acid generator such as N-hydroxynaphthalimide trifluoromethanesulfonic acid ester or bis(cyclohexylsulfonyl)diazomethane, which has a thermal decomposition temperature of about 150°C or higher when used alone, in order to prevent acid from being generated by the influence of heat during storage, etc., and the resulting degradation of the pressure-sensitive adhesive composition.

[0046] Among photoacid generators, photoacid generators that generate gas upon heating, such as bis(cyclohexylsulfonyl)diazomethane, are preferred because they can easily achieve particularly high dismantling properties due to the generation of acid by light and the generation of gas by heating.Photoacid generators that do not easily generate gas even when heated to about 100°C, such as N-hydroxynaphthalimide trifluoromethanesulfonic acid ester, are preferred because they can provide a pressure-sensitive adhesive layer with high thermal stability.

[0047] Furthermore, among photoacid generators, photoacid generators having a light-absorbing structure such as a benzene ring or naphthalene ring structure in the skeleton are preferred because they can achieve favorable dismantling properties with a short light irradiation time or a small content, which makes it easy to reduce production costs and dismantling costs.On the other hand, photoacid generators not having such a light-absorbing structure can be preferably used when stability against light irradiation is required.

[0048] Furthermore, as the thermal acid generator, a sulfonium salt, a benzothiazonium salt, an ammonium salt, or a phosphonium salt can be used. For example, 4-acetoxyphenyldimethylsulfonium hexafluoroarsenate, benzyl-4-hydroxyphenylmethylsulfonium hexafluoroantimonate, 4-acetoxyphenylbenzylmethylsulfonium hexafluoroantimonate, dibenzyl-4-hydroxyphenylsulfonium hexafluoroantimonate, 4-acetoxyphenylbenzylsulfonium hexafluoroantimonate, 3-benzylbenzothiazolium hexafluoroantimonate, and the like can be used.

[0049] The content of the acid catalyst (C) in the pressure-sensitive adhesive composition according to this embodiment is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass, per 100 parts by mass of the acrylic copolymer (A). When the content of the acid catalyst (C) is 0.1 part by mass or more, acid can be effectively generated in the resulting pressure-sensitive adhesive layer, thereby enabling the acrylic copolymer (B) to effectively generate a hydrocarbon gas, thereby making it easier to peel the pressure-sensitive adhesive sheet from the adherend. Furthermore, when the content of the acid catalyst (C) is 5 parts by mass or less, the stability of the pressure-sensitive adhesive sheet formed by forming a coating film using the pressure-sensitive adhesive composition according to this embodiment can be more easily maintained.

[0050] <Curing agent (D)> The curing agent (D) reacts with the functional groups in the acrylic copolymer (A) and / or the acrylic copolymer (B) by heat or the like to form bonds.

[0051] As the curing agent (D), one or more curing agents can be appropriately selected from known curing agents such as epoxy-based curing agents, isocyanate-based curing agents, oxazoline-based curing agents, aziridine-based curing agents, carbodiimide-based curing agents, metal chelate-based curing agents, and melamine-based curing agents, taking into consideration the reactivity with the functional groups of the acrylic copolymer in the pressure-sensitive adhesive composition. From the viewpoint of substrate adhesion, it is preferable to include an isocyanate-based curing agent, and it is more preferable to use an isocyanate-based curing agent and an epoxy-based curing agent in combination.

[0052] The isocyanate curing agent is an isocyanate having two or more isocyanate groups. Examples of preferred isocyanates include aromatic polyisocyanates, aliphatic polyisocyanates, araliphatic polyisocyanates, alicyclic polyisocyanates, and their biuret, nurate, and adduct forms. From the viewpoint of yellowing resistance, aliphatic polyisocyanates, alicyclic polyisocyanates, and their biuret, nurate, and adduct forms are more preferred. The amount of the isocyanate curing agent is preferably 0.1 to 5 parts by mass, more preferably 0.1 to 2 parts by mass, per 100 parts by mass of the acrylic copolymer (A).

[0053] The biuret compound is a self-condensation product having a biuret bond formed by self-condensation of an isocyanate monomer, such as a biuret compound of hexamethylene diisocyanate.

[0054] The nurate derivative is a trimer of an isocyanate monomer, such as a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, or a trimer of tolylene diisocyanate.

[0055] The adduct is a bifunctional or higher isocyanate compound obtained by reacting an isocyanate monomer with a bifunctional or higher low-molecular-weight active hydrogen-containing compound. Examples of the adduct include a compound obtained by reacting trimethylolpropane with hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane with tolylene diisocyanate, a compound obtained by reacting trimethylolpropane with xylylene diisocyanate, a compound obtained by reacting trimethylolpropane with isophorone diisocyanate, and a compound obtained by reacting 1,6-hexanediol with hexamethylene diisocyanate.

[0056] The isocyanate compound is preferably a trifunctional isocyanate compound from the viewpoint of forming a sufficient crosslinked structure. The isocyanate compound is more preferably an adduct or nurate, which is a reaction product of an isocyanate monomer and a trifunctional low-molecular-weight active hydrogen-containing compound. The isocyanate compound is preferably a trimethylolpropane adduct of hexamethylene diisocyanate, a nurate of hexamethylene diisocyanate, a trimethylolpropane adduct of tolylene diisocyanate, a nurate of tolylene diisocyanate, a trimethylolpropane adduct of isophorone diisocyanate, or a nurate of isophorone diisocyanate, and more preferably a trimethylolpropane adduct of hexamethylene diisocyanate, a trimethylolpropane adduct of tolylene diisocyanate, or a trimethylolpropane adduct of isophorone diisocyanate.

[0057] Examples of epoxy curing agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, tetraglycidyl-3,3'-diaminodiphenyl sulfone, tetraglycidyldiaminodiphenylmethane, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidylaminophenylmethane (all of which are examples of tetrafunctional epoxy compounds), glycerin diglycidyl ether, 1,6-hexanediol diglycidyl ether, etc., and one or more of these can be selected as appropriate. The amount of epoxy curing agent is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and most preferably 0.5 to 2 parts by mass, per 100 parts by mass of the acrylic copolymer (A).

[0058] The oxazoline-based curing agent has two or more oxazoline groups in the molecule and may be a low molecular weight compound or a polymer. Examples of the low molecular weight oxazoline-based curing agent include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2,2'-bis-(2-oxazoline), 2,2'-methylene-bis-(2-oxazoline), 2,2'-ethylene-bis-(2-oxazoline), 2,2'-trimethylene-bis-(2-oxazoline), and 2,2'-tetramethylene-bis-(2-oxazoline). Examples of oxazoline-based curing agents for polymers include 2,2'-hexamethylene-bis-(2-oxazoline), 2,2'-octamethylene-bis-(2-oxazoline), 2,2'-ethylene-bis-(4,4'-dimethyl-2-oxazoline), 2,2'-p-phenylene-bis-(2-oxazoline), 2,2'-m-phenylene-bis-(2-oxazoline), 2,2'-m-phenylene-bis-(4,4'-dimethyl-2-oxazoline), 2,2'-(1,3-phenylene)-bis-(2-oxazoline), bis-(2-oxazolinylcyclohexane) sulfide, and bis-(2-oxazolinylnorbornane) sulfide. Examples of oxazoline-based curing agents for polymers include polymers that contain an addition-polymerizable oxazoline as an essential component. Examples of the addition-polymerizable oxazoline include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, etc. The amount of the oxazoline-based curing agent is preferably 0.1 to 10 parts by mass per 100 parts by mass of the acrylic copolymer (A).

[0059] Examples of the aziridine curing agent include N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxite), tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane, etc. The amount of the aziridine curing agent is preferably 0.1 to 2 parts by mass per 100 parts by mass of the acrylic copolymer (A).

[0060] The carbodiimide curing agent is preferably a high-molecular-weight polycarbodiimide produced by a decarboxylation condensation reaction of a diisocyanate compound in the presence of a carbodiimidization catalyst. Commercially available high-molecular-weight polycarbodiimides are preferably the Carbodilite series from Nisshinbo Industries. Among these, Carbodilite V-03, 07, and 09 are preferred due to their excellent compatibility with organic solvents. The amount of the carbodiimide curing agent is preferably 0.1 to 10 parts by mass per 100 parts by mass of the acrylic copolymer (A).

[0061] The metal chelate curing agent is preferably a coordination compound of a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, or zirconium with acetylacetone or ethyl acetoacetate. Examples of metal chelates include aluminum ethyl acetoacetate diisopropylate, aluminum trisacetylacetonate, aluminum bisethyl acetoacetate monoacetylacetonate, and aluminum alkyl acetoacetate diisopropylate. The amount of the metal chelate curing agent is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and most preferably 0.5 to 2 parts by mass, per 100 parts by mass of the acrylic copolymer (A).

[0062] Typical examples of the melamine-based curing agent include fully alkyl-etherified melamine resins, methylol group-type melamine resins, imino group-type melamine resins partially containing imino groups, etc. The amount of the melamine-based curing agent is preferably 0.1 to 10 parts by mass per 100 parts by mass of the acrylic copolymer (A).

[0063] <Adhesive composition> The pressure-sensitive adhesive composition of the present invention contains an acrylic copolymer (A), an acrylic copolymer (B), and an acid catalyst (C), and optionally further contains a curing agent (D), and the content of the acrylic copolymer (B) relative to 100 parts by mass of the acrylic copolymer (A) is 1 to 50 parts by mass. By containing an acrylic copolymer (A) and an acrylic copolymer (B) that has a lower weight-average molecular weight than the acrylic copolymer (A) and has a high affinity for low-polarity adherends, the acrylic copolymer (B) can be appropriately localized on the outermost surface (the surface that contacts the adherend) of the adhesive layer while maintaining transparency when the adhesive layer is formed. Furthermore, the interaction between the acrylic copolymers (A) and (B) allows the acrylic copolymer (B) to maintain its localization even in high-temperature environments, resulting in exceptional effects such as excellent adhesion to low-polarity adherends, heat-resistant adhesion, and heat-resistant retention, as well as excellent coating film transparency and processability that does not cause poor appearance during processing. When the content of the acrylic copolymer (B) relative to 100 parts by mass of the acrylic copolymer (A) is 1 part by mass or more, the acrylic copolymer (B) is appropriately localized on the surface of the pressure-sensitive adhesive layer during heating. When the acrylic copolymer (B) is appropriately localized on the surface of the pressure-sensitive adhesive layer, hydrocarbon gas is easily released, thereby making it easier to peel the pressure-sensitive adhesive sheet according to this embodiment from an adherend. Furthermore, when the content of the acrylic copolymer (B) relative to 100 parts by mass of the acrylic copolymer (A) is 50 parts by mass or less, the acrylic copolymers (A) and (B) maintain appropriate compatibility, thereby preventing, for example, a decrease in adhesive strength due to poor compatibility. Therefore, the pressure-sensitive adhesive layer can exhibit high adhesive strength over time. The content of the acrylic copolymer (B) relative to 100 parts by mass of the acrylic copolymer (A) is preferably 5 to 40 parts by mass, more preferably 5 to 30 parts by mass.

[0064] (tackifying resin) The pressure-sensitive adhesive composition of the present invention may further contain a tackifying resin. Examples of tackifying resins include aliphatic petroleum resins, aromatic petroleum resins, synthetic hydrocarbon resins, terpene resins, rosin resins (rosin, polymerized rosin, hydrogenated rosin, and their esters with glycerin, pentaerythritol, etc., resin acid dimers, etc.), acrylic resins, etc. Among these, rosin resins, terpene resins, and synthetic hydrocarbon resins are preferred, and synthetic hydrocarbon resins are more preferred, from the viewpoints of adhesiveness, suppression of foaming, lifting, and peeling when left in a high-temperature environment or a high-temperature, high-humidity environment, ability to be attached to curved surfaces, and constant-load peel resistance.

[0065] Examples of aliphatic petroleum resins include Quinton B170 manufactured by Zeon Corporation; examples of aromatic petroleum resins include Nippon Oil Neopolymer L-90 manufactured by JXTG; examples of aliphatic / aromatic petroleum resins include FTR6100 manufactured by Mitsui Chemicals, Inc.; and examples of rosin derivatives include Sylvatac RE85 manufactured by Arizona Chemical Company and Super Ester A-75 manufactured by Arakawa Chemical Industries, Ltd.

[0066] Examples of synthetic hydrocarbon resins include aliphatic petroleum resins, aromatic petroleum resins, aliphatic / aromatic petroleum resins, hydrogenated petroleum resins, coumarone-indene resins, and phenol resins.

[0067] Examples of terpene resins include α-pinene resins, β-pinene resins, dipentene resins, aromatic modified terpene resins, hydrogenated terpene resins, terpene phenol resins, acid modified terpene resins, styrenated terpene resins, and styrene-aliphatic hydrocarbon copolymer resins.

[0068] Examples of rosin-based resins include rosin ester, polymerized rosin, hydrogenated rosin, disproportionated rosin, maleic acid-modified rosin, fumaric acid-modified rosin, rosin phenolic resin, and natural rosin.

[0069] The amount of the tackifier resin is preferably 1 to 30 parts by mass, more preferably 1 to 25 parts by mass, and most preferably 1 to 20 parts by mass, per 100 parts by mass of the acrylic copolymer (A). An amount of 1 part by mass or more makes it easier to ensure adhesion, ability to be attached to curved surfaces, and constant-load peel resistance, while an amount of 30 parts by mass or less makes it easier to prevent yellowing when left in a high-temperature environment or outdoors for a long period of time, and to prevent peeling and yellowing due to light.

[0070] The softening point of the tackifier resin is preferably 90 to 160°C, more preferably 90 to 140°C, and most preferably 90 to 135°C. By setting the softening point to 90°C or higher, it becomes easier to ensure holding power when left in a high-temperature environment or a high-temperature, high-humidity environment. By setting the softening point to 160°C or lower, it becomes easier to ensure adhesion to polyolefin-based adherends such as polypropylene, and it becomes easier to prevent peeling of the PSA sheet due to light when exposed outdoors for long periods of time. The softening point of the tackifier resin was measured in accordance with JIS K 6863. Specifically, after filling a ring base with the tackifier resin, a ball (specified in JIS B1501: steel ball / diameter 9.53 mm / mass 3.5±0.05 g) was placed on it, and the temperature at which the ball dropped at a heating rate of 5°C / °C using an automatic bulb-type softening point tester ASP-KG4 (manufactured by Meitex Co., Ltd.) was taken as the melting point.

[0071] <Adhesive layer> The pressure-sensitive adhesive layer of the present invention comprises the pressure-sensitive adhesive composition of the present invention.

[0072] When applying the pressure-sensitive adhesive composition, the viscosity can be adjusted by adding an appropriate liquid medium. Specific examples include hydrocarbon solvents such as toluene, xylene, hexane, and heptane; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as acetone and methyl ethyl ketone; halogenated hydrocarbon solvents such as dichloromethane and chloroform; ether solvents such as diethyl ether, methoxytoluene, and dioxane, and other hydrocarbon solvents. However, water and alcohols must be used carefully because they may inhibit the reaction between the acrylic copolymer (A) and the isocyanate curing agent.

[0073] The coating method is not particularly limited, and examples thereof include various coating methods using a Mayer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, spin coater, etc. The drying and curing method is also not particularly limited, and examples thereof include hot air drying, infrared rays, reduced pressure methods, and methods using active energy rays, but hot air or steam heating at 60 to 180°C is preferred from the viewpoint of outgassing resistance.

[0074] The thickness of the adhesive layer is preferably 2 to 1000 μm, more preferably 5 to 500 μm, still more preferably 10 to 100 μm, and most preferably 20 to 50 μm. The adhesive layer may be in the form of a single layer or a laminate of two or more layers.

[0075] The gel fraction of the pressure-sensitive adhesive layer is preferably 20 to 80% by mass, more preferably 25 to 70% by mass, and even more preferably 30 to 70% by mass. A gel fraction of 20% by mass or more improves the cohesive strength of the pressure-sensitive adhesive composition, resulting in a strong pressure-sensitive adhesive layer, making it easier to ensure stress relaxation properties and suppressing lifting and peeling in high-temperature environments. A gel fraction of 70% by mass or less makes it easier to obtain a flexible pressure-sensitive adhesive layer and ensure adhesion to low-polarity adherends. Generally, the gel fraction of a polymer is equal to the degree of crosslinking, and the more crosslinked portions in the polymer, the higher the gel fraction. The gel fraction (the amount of crosslinked structure introduced) can be adjusted to a desired range by the method for introducing the crosslinked structure, the type and amount of the crosslinking agent, etc.

[0076] The pressure-sensitive adhesive layer of the present invention comprises Ga It is preferable that the adhesive strength to the lath board satisfies the following (1) and (2). (1) The adhesive strength of the adhesive layer before heating or exposure to active energy rays is 10 N / 25 mm or more (2) The adhesive strength of the adhesive layer after heating or exposure to active energy rays is 1N / 25mm or less The method for measuring adhesive strength will be described in detail in the Examples.

[0077] <Adhesive sheet> The pressure-sensitive adhesive sheet comprises a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition of the present invention.

[0078] The pressure-sensitive adhesive sheet of the present invention preferably has a configuration in which a release film is attached to at least one surface of the pressure-sensitive adhesive layer, specifically, a configuration in which release films are formed on both surfaces of the pressure-sensitive adhesive layer, or a configuration in which a release film is formed on one surface of the pressure-sensitive adhesive layer and a PET substrate is provided on the other surface of the pressure-sensitive adhesive, and the pressure-sensitive adhesive layer is formed from the pressure-sensitive adhesive composition of the present invention.

[0079] Examples of the substrate include plastic films such as polyester (polyethylene terephthalate, polyethylene naphthalate), polycarbonate, polymethyl methacrylate, polyethylene, polypropylene, cyclic olefin, polyvinyl chloride, polyurethane, polyamide, and ethylene-vinyl acetate copolymer; inorganic materials such as glass plates; nonwoven fabrics; and paper.

[0080] <Release film> The release film is not particularly limited, but a transparent plastic substrate can be suitably used. Examples of materials for the transparent plastic substrate include polyesters such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), and plastic materials such as polycarbonate, triacetyl cellulose, polysulfone, polyarylate, and polycycloolefin. The plastic materials can be used alone or in combination of two or more.

[0081] Among the transparent plastic substrates described above, a transparent plastic substrate having excellent heat resistance, i.e., a transparent plastic substrate that is suppressed or prevented from deforming under severe conditions such as high temperature, high temperature and high humidity, etc. PET films or sheets are particularly suitable as the transparent plastic substrate.

[0082] The thickness of the transparent plastic substrate is not particularly limited, and is, for example, preferably from 10 to 200 μm, more preferably from 25 to 150 μm.

[0083] <Method of manufacturing adhesive sheets> A method for producing a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made from the pressure-sensitive adhesive composition will now be described. However, conventionally known methods can be used as appropriate, and the present invention is not limited to the following production method. For example, when using a pressure-sensitive adhesive composition prepared by dissolving in a solvent, the pressure-sensitive adhesive composition diluted with a solvent is coated onto a sheet having a surface layer formed thereon by knife coating, bar coating, blade coating, doctor coating, roll coating, cast coating, or the like to form a coating film. The sheet can then be heated and dried as needed to form a pressure-sensitive adhesive layer on the sheet. On the other hand, when using a pressure-sensitive adhesive composition prepared by a kneading method using heat, the pressure-sensitive adhesive layer can be formed on the sheet using a hot-melt coater, which can soften the pressure-sensitive adhesive composition by preheating. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made from the pressure-sensitive adhesive composition has appropriate adhesive strength at room temperature (e.g., 25°C), excellent adhesiveness at high temperatures (e.g., 100 to 150°C), and can maintain these properties for long periods of time at high temperatures (e.g., 80°C for 7 days). [Example]

[0084] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass." The blending amounts in the tables are in parts by mass, and amounts other than the solvent are calculated as non-volatile contents. Blank spaces in the tables indicate that no blending was performed. The method for measuring the weight average molecular weight of the acrylic copolymer is as follows.

[0085] (Measurement of weight average molecular weight) The weight-average molecular weight (Mw) was measured by gel permeation chromatography (GPC). The instrument used was a GPC instrument manufactured by Shimadzu Corporation: an LC-GPC system "Prominence." The columns used were TSKgel α-M manufactured by Tosoh Corporation, with two columns connected in series. N,N-dimethylformamide (DMF) was used as the eluent, and measurements were carried out at 40°C. Mw was determined by conversion using polystyrene with a known Mw as the standard substance.

[0086] (Viscosity measurement) The acrylic copolymer (A) and the acrylic copolymer (B) were mixed at an arbitrary weight ratio, and the viscosity was measured using a Brookfield viscometer (rotor: 3, rotation speed: 12 rpm, measurement time: 1 minute, unit: mPa·s) at 25°C.

[0087] <Production Example of Acrylic Copolymer (A)> (Acrylic copolymer (A-1)) Using a reactor equipped with a stirrer, reflux condenser, nitrogen inlet, thermometer, and dropping tube, 0.1 parts of 2-hydroxyethyl acrylate as monomer (a1), 0.1 parts of acrylic acid as monomer (a2), 20 parts of 2-ethylhexyl acrylate (2EHA) as monomer (a3), 79.8 parts of butyl acrylate (BA), 0.02 parts of 2,2-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 110 parts of ethyl acetate as a solvent were charged into a reaction vessel and polymerized at 70 °C for 5 hours under a nitrogen atmosphere. The viscosity was adjusted appropriately by adding ethyl acetate during polymerization. After the reaction was completed, the mixture was cooled and diluted with ethyl acetate to obtain an acrylic copolymer solution (A-1) with a non-volatile content of 40.0 ± 0.5%. The weight average molecular weight of the resulting acrylic copolymer was 1.5 million.

[0088] (Acrylic copolymers (A-2 to A-31, A'-1)) Acrylic copolymers (A-2 to A-31, A'-1) were synthesized in the same manner as for the production of acrylic copolymer (A-1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Tables 1 and 2. The weight-average molecular weights of the obtained acrylic copolymers are also shown in the tables.

[0089] [Table 1]

[0090] [Table 2]

[0091] Details of each monomer listed in Tables 1 and 2 are as follows: "HEA": 2-hydroxyethyl acrylate "HPA": 2-hydroxypropyl acrylate "HBA": 4-hydroxybutyl (meth)acrylate "AA": acrylic acid "2EHA": 2-ethylhexyl acrylate "BA": Butyl acrylate "MA": methyl acrylate

[0092] <Production Example of Acrylic Copolymer (B)> (Acrylic copolymer (B-1)) Using a reactor equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping tube, 85 parts of tert-butyl methacrylate (TBMA) as monomer (b1), 2 parts of 2-hydroxyethyl methacrylate (HEMA) as monomer (b2), 13 parts of methyl methacrylate (MMA) as monomer (b3), 0.02 parts of 2,2-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 150 parts of methyl ethyl ketone as a solvent were charged into a reaction vessel, and polymerized at 70 ° C. for 5 hours under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled and diluted with ethyl acetate to obtain an acrylic copolymer solution (B-1) with a non-volatile content of 40.0 ± 0.5%. The weight average molecular weight (Mw) of the obtained acrylic copolymer was 15,000.

[0093] (Acrylic Copolymers (B-2 to B-19, B'-1 to B'-4)) Acrylic copolymers (B-2 to A-19, B'-1 to B'-4) were synthesized in the same manner as for the acrylic copolymer (B-1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Tables 3 and 4 and the amount of solvent was adjusted appropriately. The weight-average molecular weights of the obtained acrylic copolymers are also shown in the tables.

[0094] [Table 3]

[0095] [Table 4]

[0096] Details of each monomer listed in Tables 3 and 4 are as follows: "TBMA": tert-butyl methacrylate "IBXA": Isobornyl acrylate "HEMA": 2-hydroxyethyl methacrylate "DAM": 2-(dimethylamino)ethyl methacrylate "MMA": Methyl methacrylate

[0097] Example 1 A pressure-sensitive adhesive composition was obtained by blending 100 parts of the acrylic copolymer (A-1), 20 parts of the acrylic copolymer (B-1), 1 part of "TA-100" as the acid catalyst (C), and 0.1 part of "Coronate L" (manufactured by Tosoh Corporation, trimethylolpropane-modified toluene diisocyanate) as the curing agent (C), and diluting the mixture with ethyl acetate to a non-volatile content of 35.0±0.5%. The obtained adhesive composition was applied to a 38 μm thick polyethylene terephthalate release sheet (Cerapeel MF, manufactured by Toray Advanced Film Co., Ltd.) using a comma coater so that the dried thickness would be 50 μm, and the coated sheet was dried at 100° C. for 2 minutes to obtain an adhesive sheet. Next, one side of a 100 μm thick polyethylene terephthalate film (hereinafter referred to as PET film, product name: A-4300, manufactured by Toyobo Co., Ltd.) was bonded to the adhesive surface of this adhesive sheet to prepare a laminate consisting of "release sheet / adhesive layer / PET film." The resulting laminate was then aged for 1 week under conditions of a temperature of 25° C. and a relative humidity of 55%, to obtain a test laminate.

[0098] <Examples 2 to 65 and Comparative Examples 1 to 7> As shown in Tables 5 and 6, pressure-sensitive adhesive compositions and test laminates were obtained in the same manner as in Example 1, except that the types and amounts of the acrylic copolymer, acid catalyst, and curing agent were changed. The materials used in the examples and comparative examples are listed below.

[0099] <Acid catalyst (C)> "TA-100": San-Apro Co., Ltd., thermally decomposable sulfonium salt "CPI-200K": Photodegradable sulfonium salt manufactured by San-Apro Co., Ltd. "TSA": Toluenesulfonic acid monohydrate (Pka=-2.8), manufactured by Kishida Chemical Co., Ltd. "Phosphoric acid": Phosphoric acid (Pka = 2.15), manufactured by Kishida Chemical Co., Ltd.

[0100] <Curing agent (D)> "Coronate L": Tosoh Corporation, trimethylolpropane-modified toluene diisocyanate "TETRAD-X": N,N,N',N'-tetraglycidyl-m-xylenediamine manufactured by Mitsubishi Gas Chemical Company, Inc.

[0101] <Storage stability of coating liquid> 100 parts of acrylic copolymer (A-1) were blended with 20 parts of acrylic copolymer (B-1) and 1 part of "TA-100" as an acid catalyst (C). The mixture was diluted with ethyl acetate to a nonvolatile content of 35.0±0.5% to obtain a coating liquid for evaluating storage stability, which had the composition of Example 1 but did not contain a curing agent (D). Similarly, coating liquids for evaluating storage stability, which had the compositions of Examples 2 to 65 and Comparative Examples 1 to 7 but did not contain a curing agent (D), were obtained. The resulting coating liquids were stored in a 50°C oven for one month. After one month, they were removed from the oven and measured using a viscometer (manufactured by Toki Sangyo Co., Ltd., device name: B-type viscometer viscosity) in a 23°C-50% RH environment. The viscosity change rate before and after aging ((viscosity after aging at 50°C - viscosity before aging at 50°C) / viscosity before aging at 50°C) was calculated and evaluated according to the following criteria. The evaluation results are shown in Tables 5 and 6. ◎: Viscosity change rate is less than 5% (excellent) ○: Viscosity change rate is 5% or more but less than 10% (good) △: Viscosity change rate is 10% or more but less than 30% (fairly good) ▲: Viscosity change rate is 30% or more but less than 50% (usable) ×: Viscosity change rate is 50% or more (unusable)

[0102] Using the obtained test laminate, the adhesive strength to alkali glass (hereinafter referred to as Glass) manufactured by Central Glass Co., Ltd. was measured before and after heat treatment by the following method. The results are shown in Tables 7 and 8.

[0103] <Glass adhesive strength before treatment> The test laminate obtained above was cut into a size of 25 mm wide x 100 mm long. The release sheet was peeled off, and the adhesive layer was attached to the top surface of the glass under an atmosphere of 23°C and 50% relative humidity (hereinafter referred to as 23°C-50%RH). The adhesive layer was then pressed with a roll according to JIS Z-0237 to obtain a sample for measuring glass adhesion strength. The top surface of the glass to which the adhesive layer was attached was wiped with absorbent cotton moistened with ethanol and left for at least 30 minutes. After 24 hours, the adhesive strength (peel angle 180°, peel speed 300 mm / min; unit N / 25 mm width) was measured using a universal tensile tester (permanent adhesive strength).

[0104] <Adhesive force of Glass after treatment> A sample for measuring the adhesive force of Glass was prepared in the same manner as above. After 24 hours, heat treatment or ultraviolet treatment was performed, and the adhesive force of Glass after treatment was measured. Specifically, for Examples 1, 3, 4, 6 to 15, 17, 18, 20 to 23, 26, 27, 29 to 65, and Comparative Examples 1 to 7, they were left standing in an environment of 150 °C for 1 hour. After taking out the adherend, after 24 hours, the adhesive force after heat treatment (peel angle 180°, peel speed 300 mm / min; unit N / 25 mm width) was measured with a universal tensile testing machine. For Examples 2, 5, 16, 19, 24, 25, and 28, a Toshiba Rikagaku mercury lamp "SHL-100UVQ-2" (75W) was used as the light source, the distance between the light source and the sample was set to 10 cm, and the sample was irradiated after more than 15 minutes had elapsed since the lamp was lit. The adhesive force after ultraviolet treatment (peel angle 180°, peel speed 300 mm / min; unit N / 25 mm width) was measured with a universal tensile testing machine.

[0105] ≪Evaluation of the test laminate≫ The adhesive force of the obtained test laminate to high-polarity and low-polarity adherends, the rigid body peel test (easy peelability), the heat resistance retention, and the transparency were evaluated by the following methods. The results are shown in Tables 7 and 8.

[0106] <Adhesive force of Glass (adhesive force to high-polarity adherend)> Regarding the measurement results (permanent adhesive force) of the adhesive force of Glass before treatment measured above, evaluation was performed according to the following evaluation criteria. [Evaluation criteria] ◎: Adhesive force is 15.0 N / 25 mm or more. (Excellent) 〇: Adhesive force is 10.0 N / 25 mm or more and less than 15.0 N / 25 mm. (Good) △: Adhesive force is 5.0 N / 25 mm or more and less than 10.0 N / 25 mm. (Somewhat good) ▲: Adhesive force is 3.0 N / 25 mm or more and less than 5.0 N / 25 mm. (Usable) ×: Adhesive force is less than 3.0 N / 25 mm. (Unusable)

[0107] <PP Adhesive Force (Adhesive Force to Low-Polarity Substrate)> The test laminate obtained above was cut into a size of 25 mm in width × 100 mm in length. The release sheet was peeled off, and the adhesive layer was attached to polypropylene (PP) in an atmosphere of 23°C and 50% relative humidity (hereinafter 23°C - 50%RH), and crimped with a roll according to JIS Z-0237. After crimping, it was held in an autoclave under the conditions of 50°C and 5 atm for 20 minutes to make each member adhere tightly to obtain a measurement sample. After 24 hours, the adhesive force (peeling angle 180°, peeling speed 300 mm / min; unit N / 25 mm width) was measured with a universal tensile testing machine (permanent adhesive force). The numerical values of the permanent adhesive force were evaluated according to the following criteria. [Evaluation Criteria] ◎: Adhesive force is 10.0 N / 25 mm or more. (Excellent) 〇: Adhesive force is 5.0 N / 25 mm or more and less than 10.0 N / 25 mm. (Good) △: Adhesive force is 3.0 N / 25 mm or more and less than 5.0 N / 25 mm. (Fairly Good) ▲: Adhesive force is 1 N / 25 mm or more and less than 3.0 N / 25 mm. (Usable) ×: Adhesive force is less than 1 N / 25 mm. (Unusable)

[0108] <Rigid Body Peeling Test (Easy Peeling Property)> The non-carrier adhesive sheet obtained above was cut into a size of 25 mm in width × 100 mm in length. The release sheet was peeled off, and after the adhesive layer was attached to Glass in an atmosphere of 50% relative humidity (hereinafter 23°C - 50%RH), the other release sheet was peeled off and attached to Glass, and crimped with a roll according to JIS Z-0237. After crimping, it was held in an autoclave under the conditions of 50°C and 5 atm for 20 minutes to make each member adhere tightly to obtain a measurement sample. After 24 hours, it was left standing in an environment of 150°C for 1 hour, and after taking out the adherend, the peeling between Glass and the adhesive layer (rigid body peeling test) was performed. The state of the rigid body peeling was evaluated according to the following criteria. [Evaluation Criteria] ◎: Peeling is possible. (Excellent) 〇: If a 1 cm cut is made with a cutter or the like to create a starting point, peeling is possible. (Good) △: Make a 3cm cut with a cutter or similar tool and peel off the film if you create an opening. (Fairly good) ▲: Make a 5cm cut with a cutter or similar tool to create an opening and peel it off. (Can be used) ×: Impossible to peel (cannot be used)

[0109] <Heat-resistance holding power> The resulting test laminate was prepared in a size of 25 mm wide x 150 mm long. The release sheet was peeled off, and the exposed adhesive layer was polished. This was then attached to a 25 mm wide x 25 mm wide section of the bottom edge of a 30 mm wide x 150 mm long stainless steel plate. After pressing it back and forth with a 2 kg roll once, a 1 kg load was applied to the bottom edge of the test laminate in an 80°C atmosphere and left for 70,000 seconds to measure the holding strength (in accordance with JIS Z0237:2000). Evaluation was performed by measuring the distance the top edge of the test laminate's adhesive surface shifted downward from its original position, and the results were evaluated according to the following criteria. [Evaluation criteria] ◎: The deviation length is less than 1 mm: (Excellent) 〇: The deviation length is 1mm or more but less than 3mm: (Good) △: Misalignment length is 3mm or more and less than 5mm: (fairly good) ▲: Misalignment length is 5mm or more but less than 10mm: (Can be used) ×: The length of deviation is 10mm or more or the product has fallen off (cannot be used).

[0110] <Transparency (appearance of coating film)> The obtained test laminate was visually inspected and evaluated based on the following evaluation criteria. ◎: The entire coating is transparent: (Good) 〇: Part of the coating is slightly cloudy: (fairly good) △: The entire coating is slightly cloudy (usable) ×: The entire coating is cloudy (unusable)

[0111] [Table 5]

[0112] [Table 6]

[0113] Table 7

[0114] Table 8

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic copolymer (A), an acrylic copolymer (B), and an acid catalyst (C), The acrylic copolymer (A) has a weight average molecular weight of 300,000 or more, The weight average molecular weight of the acrylic copolymer (B) is in the range of 5,000 to 200,000, the acrylic copolymer (B) is a copolymer of a monomer mixture containing a (meth)acrylic monomer (b1) having a carboxy group protected by a protecting group, the protecting group is an ester group composed of an alkyl group having a secondary or tertiary carbon atom and a carboxy group, the content of the (meth)acrylic monomer (b1) in 100% by mass of the monomer mixture is 5 to 95% by mass, The pressure-sensitive adhesive composition has a content of the acrylic copolymer (B) of 1 to 50 parts by mass relative to 100 parts by mass of the acrylic copolymer (A).

2. The acrylic copolymer (A) is a copolymer of a monomer mixture containing a (meth)acrylic monomer (a1) having a hydroxy group, The pressure-sensitive adhesive composition according to claim 1, wherein the content of the (meth)acrylic monomer (a1) having a hydroxy group in 100% by mass of the monomer mixture is 0.1 to 30% by mass.

3. The pressure-sensitive adhesive composition according to claim 1 , further comprising a curing agent (D).

4. the acid catalyst (C) contains at least one of an acid generator that generates an acid upon irradiation with active energy rays or heating and an acid having an acid dissociation constant (Pka) of 1.0 or less; 4. The pressure-sensitive adhesive composition according to claim 1, wherein the content of the acid catalyst (C) is 0.1 to 5 parts by mass based on 100 parts by weight of the acrylic copolymer (A).

5. An adhesive layer comprising the adhesive composition described in claim 4.

6. A pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer according to claim 5 .

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