KR102159055B1 - Adhesive composition, adhesive layer and adhesive sheet - Google Patents

Abstract

(Problem) In order to solve the problem in the conventional acrylic pressure-sensitive adhesive, it is to provide a pressure-sensitive adhesive composition in which crosslinking proceeds quickly without using a tin compound, and a pressure-sensitive adhesive layer and a pressure-sensitive adhesive sheet made of this.
(Solving means) 100 parts by mass of an acrylic polymer (A) containing a hydroxyl group and a carboxyl group, 0.1 parts by mass to 15 parts by mass of an isocyanate crosslinking agent (B), and 0.002 parts by mass to 0.5 parts by mass of an iron-based catalyst (C) , A pressure-sensitive adhesive composition comprising a compound (D) causing keto-enol tautomerism, and the mass ratio (D/C) of the compound (D) causing keto-enol tautomerism to the catalyst (C) having iron as an active center is A pressure-sensitive adhesive composition of 3 to 70.

Description

Adhesive composition, adhesive layer, and adhesive sheet {ADHESIVE COMPOSITION, ADHESIVE LAYER AND ADHESIVE SHEET}

The present invention relates to an adhesive composition, an adhesive layer, and an adhesive sheet. Specifically, it relates to an adhesive sheet with little performance change over time, and an adhesive composition and an adhesive layer used therein.

Adhesive sheets are used in various aspects such as fixing (bonding), conveying, protecting and decorating articles. As a representative example of such a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive layer formed using a pressure-sensitive adhesive composition (acrylic pressure-sensitive adhesive composition) containing an acrylic polymer as a base polymer is mentioned. As such an acrylic polymer, in general, a copolymer with a monomer containing an alkyl (meth)acrylate as a main component (main component) and containing an appropriate functional group is used. In particular, by using an acrylic polymer having a carboxyl group as a functional group, the adhesion to a polar adherend such as a metal plate or a resin plate is improved, and an appropriate cohesive force can be provided, so that it is used with a favorable reputation.

In addition, in the pressure-sensitive adhesive sheet, for example, an acrylic polymer having a functional group such as a hydroxyl group and a crosslinking agent that reacts with the functional group are mixed to obtain a pressure-sensitive adhesive composition, and the acrylic polymer is crosslinked with the crosslinking agent to form a pressure-sensitive adhesive layer. Since crosslinking is a chemical reaction, it proceeds with time, and it takes some time to stabilize. In addition, adhesive strength changes as the crosslinking proceeds. Therefore, it is necessary to complete the crosslinking reaction early. Therefore, for example, in a combination of an acrylic copolymer having a hydroxyl group and an isocyanate crosslinking agent, a metal catalyst such as a tin compound is used (see Patent Document 1). However, in recent years, from the viewpoint of environmental response, legal regulations or concerns have arisen in the use of specific metals.

Therefore, it has been studied to use a catalyst having iron as an active center as a metal catalyst replacing the tin compound (see Patent Document 2).

Japanese Published Patent Publication No. 2005-314513 Japanese Patent Publication No. 2011-001440

However, it was confirmed that when an acrylic polymer having a carboxyl group was used, the catalytic function of iron was deteriorated and the crosslinking reaction could not be completed quickly. In this way, if the crosslinking reaction is not completed immediately after production, for example, when an external pressure is applied to the pressure-sensitive adhesive sheet during manufacture or storage, problems such as deformation of the pressure-sensitive adhesive layer or mixing of scratches occur.

Therefore, an object of the present invention is to solve the problem of using an iron catalyst instead of a tin compound that has been conventionally used, in the case of a pressure-sensitive adhesive layer, a pressure-sensitive adhesive composition with less change in adhesive force due to rapid crosslinking and, It is to provide an adhesive layer and an adhesive sheet made of this.

The present inventors, as a result of earnestly examining in order to achieve the above object, in an adhesive composition for crosslinking an acrylic polymer having a hydroxyl group and a carboxyl group with an isocyanate crosslinking agent in the presence of an iron catalyst, causing keto-enol tautomerism By using the compound in combination with a specific amount, deactivation of the catalytic function of the iron catalyst due to the carboxyl group was prevented, and when the pressure-sensitive adhesive layer was used, it was found that the crosslinking reaction proceeds quickly, and the present invention was completed.

That is, in the present invention, 100 parts by mass of an acrylic polymer (A) having a hydroxyl group and a carboxyl group,

0.1 parts by mass to 15 parts by mass of an isocyanate crosslinking agent (B),

0.002 parts by mass to 0.5 parts by mass of a catalyst (C) having iron as an active center,

It is a pressure-sensitive adhesive composition containing a compound (D) causing keto-enol tautomerism,

There is provided a pressure-sensitive adhesive composition in which the mass ratio (D/C) of the compound (D) causing keto-enol tautomerism to the catalyst (C) having iron as an active center is 3 to 70.

In particular, in the pressure-sensitive adhesive composition of the present invention, the acrylic polymer (A) having a hydroxyl group and a carboxyl group is 65% by mass to 99.89% by mass of an alkyl (meth)acrylate having an alkyl group having 4 to 12 carbon atoms, and 0.1% by mass of a hydroxyl group-containing monomer. It is preferable to contain-25 mass% and 0.01 mass%-10 mass% of carboxyl group-containing monomers as a constituent component.

Further, in the pressure-sensitive adhesive composition of the present invention, it is preferable that the catalyst (C) having iron as an active center is an iron chelate compound, and that the compound (D) causing the keto-enol tautomerism is β-diketone. Suitable.

In addition, the present invention provides a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition.

Further, the present invention provides a pressure-sensitive adhesive sheet formed by forming the pressure-sensitive adhesive layer on a support.

When the pressure-sensitive adhesive composition of the present invention is used as a pressure-sensitive adhesive layer, a crosslinking reaction proceeds quickly. For this reason, after the pressure-sensitive adhesive sheet is formed, since the crosslinking proceeds rapidly, the properties are stabilized. For example, formation of a crosslinking process after aging, etc. becomes unnecessary, such as deformation due to external pressure to the pressure-sensitive adhesive sheet during manufacture or storage. It is possible to obtain an effect such as preventing the occurrence of scratches or the like.

(Form for carrying out the invention)

Hereinafter, an embodiment of the present invention will be described in detail. The pressure-sensitive adhesive composition of the present invention comprises 100 parts by mass of an acrylic polymer (A) having a hydroxyl group and a carboxyl group,

0.1 parts by mass to 15 parts by mass of an isocyanate crosslinking agent (B),

0.002 parts by mass to 0.5 parts by mass of a catalyst (C) having iron as an active center,

It is a pressure-sensitive adhesive composition containing a compound (D) causing keto-enol tautomerism,

The mass ratio (D/C) of the compound (D) causing keto-enol tautomerism to the catalyst (C) having iron as the active center is 3 to 70.

(Acrylic polymer (A))

The pressure-sensitive adhesive composition of the present invention contains an acrylic polymer (A) having a hydroxyl group and a carboxyl group. The acrylic polymer (A) is an acrylic polymer having a functional group containing an active hydrogen such as a hydroxyl group or a carboxyl group capable of reacting with an isocyanate crosslinking agent (B) described later on a main chain or a side chain. Such an acrylic polymer (A) has at least an alkyl (meth)acrylate as a main component, and contains a hydroxyl group-containing monomer and a carboxyl group-containing monomer (hereinafter, both may be referred to as ``functional group-containing monomers'') as constituent components, and these It can be obtained by copolymerization of a monomer component composed of a monomer.

In the present invention, the (meth)acrylate alkyl ester, which is the main monomer constituting the acrylic polymer (A), is preferably an alkyl (meth)acrylate having an alkyl group having 4 to 12 carbon atoms. Specific examples thereof include, for example, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, amyl (meth) acrylate, isoamyl (meth) )Acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, Isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, and the like. In addition, in this specification, "(meth)acryl" is a concept including "acrylic" and "methacryl."

These alkyl (meth)acrylates having an alkyl group having 4 to 12 carbon atoms may be used alone or in combination, but the content ratio as a whole is preferably 65% by mass to 99.89% by mass, and 76% by mass in the monomer component. It is more preferable that it is mass%-99.48 mass %, and it is still more preferable that it is 80 mass%-91.97 mass %. If the content ratio of the alkyl (meth)acrylate is less than 65% by mass, the content of the functional group-containing monomer or other monomer described later increases, the glass transition temperature of the acrylic polymer increases, the fluidity decreases, and a sufficient adhesion area There are cases where it is impossible to fix the item because it cannot be obtained. Moreover, it may become difficult to adjust the degree of crosslinking (gel fraction). On the other hand, when the content of the (meth)acrylate alkyl ester exceeds 99.89% by mass, crosslinking formation is insufficient due to a decrease in the content ratio of the functional group-containing monomer, and the cohesive force of the pressure-sensitive adhesive composition may not be obtained.

In the present invention, the hydroxyl group-containing monomer is a monomer containing a hydroxyl group capable of reacting with a crosslinking agent such as an isocyanate compound. As a specific example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylic Rate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxy And hydroxyalkyl (meth)acrylates such as lauryl (meth)acrylate and [4-(hydroxymethyl)cyclohexyl]methylacrylate.

Also N-methylolacrylamide, N-methylolmethacrylamide, N-(2-hydroxyethyl)acrylamide, N-(2-hydroxyethyl)methacrylamide, N-(2-hydroxypropyl) Acrylamide, N-(2-hydroxypropyl)methacrylamide, N-(1-hydroxypropyl)acrylamide, N-(1-hydroxypropyl)methacrylamide, N-(3-hydroxypropyl) Acrylamide, N-(3-hydroxypropyl)methacrylamide, N-(2-hydroxybutyl)acrylamide, N-(2-hydroxybutyl)methacrylamide, N-(3-hydroxybutyl) N-hydroxyalkyl (meth) such as acrylamide, N-(3-hydroxybutyl)methacrylamide, N-(4-hydroxybutyl)acrylamide, and N-(4-hydroxybutyl)methacrylamide Acrylamide and the like.

Among these hydroxyl group-containing monomers, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferable in terms of their polymerizability and reactivity with a crosslinking agent, and in particular 4-hydroxybutylacryl The rate is preferred.

These hydroxyl group-containing monomers may be used alone or in combination, but the content ratio as a whole is preferably 0.1% by mass to 25% by mass (eg 1% by mass to 25% by mass) in the monomer component, and 5 It is more preferable that it is mass%-20 mass %, and it is still more preferable that it is 8 mass%-15 mass %. If the content ratio of the hydroxyl group-containing monomer is less than 0.1% by mass, crosslinking formation is insufficient, the cohesive force of the pressure-sensitive adhesive composition is not obtained, and the pressure-sensitive adhesive sheet is displaced when the article is fixed, or a paste residue is generated when the pressure-sensitive adhesive sheet is peeled off. There are cases. On the other hand, when the content ratio of the hydroxyl group-containing monomer exceeds 25% by mass, the cohesive force of the acrylic polymer increases, so that the fluidity decreases, a sufficient adhesion area cannot be obtained, and the article may not be fixed.

In the present invention, the carboxyl group-containing monomer is a carboxyl group-containing monomer. As a specific example, (meth)acrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc. are mentioned, for example. Among these carboxyl group-containing monomers, acrylic acid is preferable from the viewpoints of polymerization, cohesiveness, cost, and versatility.

These carboxyl group-containing monomers may be used alone or in combination, but the content ratio as a whole is preferably 0.01% by mass to 10% by mass, more preferably 0.02% by mass to 9% by mass, in the monomer component. It is more preferable that it is 0.03 mass%-8 mass %. When the content ratio of the carboxyl group-containing monomer is less than 0.01% by mass, the adhesive strength to the polar adherend may be insufficient. On the other hand, when the content ratio of the carboxyl group-containing monomer exceeds 10% by mass, the cohesive strength of the acrylic polymer increases, so that the fluidity decreases, and a sufficient bonding area cannot be obtained, and the article may not be fixed.

In the present invention, other monomers other than the aforementioned (meth)acrylate alkyl ester having an alkyl group having 4 to 12 carbon atoms, a hydroxyl group-containing monomer, and a carboxyl group-containing monomer may be used as the monomer component. Examples of such other monomers include alkyl (meth)acrylates having an alkyl group other than 4 to 12 carbon atoms. Specific examples of the (meth)acrylic acid alkyl ester having an alkyl group other than 4 to 12 carbon atoms used in the present invention include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and iso Propyl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl ( Meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and the like.

Further, examples of other monomers that can be used in the present invention include cyclic (meth)acrylamides such as N-(meth)acryloylmorpholine and N-acryloylpyrrolidine;

(Meth)acrylamide, N-substituted (meth)acrylamide (e.g., N-alkyl (meth)acrylamide such as N-ethyl (meth)acrylamide, Nn-butyl (meth)acrylamide; N,N -Dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-diisopropyl (meth)acrylamide, N,N-di acyclic (meth)acrylamides such as (n-butyl)(meth)acrylamide and N,N-dialkyl(meth)acrylamide) such as N,N-di(t-butyl)(meth)acrylamide;

N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazine-2 N-vinyl cyclic amides such as -one and N-vinyl-3,5-morpholinedione;

Monomers having an amino group such as aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate;

Monomers having a maleimide skeleton, such as N-cyclohexylmaleimide and N-phenylmaleimide;

N-methyl itaconimide, N-ethyl itaconimide, N-butyl itaconimide, N-2-ethylhexyl itaconimide, N-lauryl itaconimide, N-cyclohexyl itacone Nitrogen atom-containing monomers, such as an itaconimide-type monomer, such as imide, etc. are mentioned.

Other examples of monomers that can be employed as other monomers include monomers having an epoxy group such as glycidyl (meth)acrylate and allyl glycidyl ether;

Monomers having an alkoxy group, such as methoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate;

Monomers having a cyano group such as acrylonitrile and methacrylonitrile;

Styrene-based monomers such as styrene and α-methylstyrene;

Α-olefins such as ethylene, propylene, isoprene, butadiene and isobutylene;

Monomers having an isocyanate group such as 2-methacryloyloxyethyl isocyanate;

Vinyl ester monomers such as vinyl acetate and vinyl propionate;

Vinyl ether monomers such as vinyl ether;

(Meth)acrylic acid esters having a heterocycle, such as tetrahydrofurfuryl (meth)acrylate;

Monomers having a halogen atom such as fluorine (meth)acrylate;

Monomers having an alkoxysilyl group, such as 3-methacryloxypropyltrimethoxysilane and vinyl trimethoxysilane;

Monomers having a siloxane bond, such as silicone (meth)acrylate;

(Meth)acrylates having an alicyclic hydrocarbon group, such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, bornyl (meth)acrylate, and isobornyl (meth)acrylate;

(Meth)acrylates having an aromatic hydrocarbon group, such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol (meth)acrylate; And the like.

In addition, as other monomers, for example, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene Glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, hexanediol di (meth) acrylate, pentaerythritol di (meth) acrylate, trimethylolpropane Tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, divinylbenzene, butyl di(meth) Polyfunctional monomers, such as acrylate and hexyl di (meth)acrylate, may be used.

These other monomers may be used alone or in combination, but the content ratio as a whole is preferably 33% by mass or less, more preferably 18% by mass or less, further preferably 10% by mass or less in the monomer component. Do. When the content ratio of other monomers exceeds 33% by mass, the content of the (meth)acrylate alkyl ester having an alkyl group having 4 to 12 carbon atoms decreases, the glass transition temperature of the acrylic polymer increases, and fluidity decreases, and sufficient adhesion. There are cases in which the area cannot be obtained and the article cannot be fixed.

The acrylic polymer (A) used in the present invention preferably has a weight average molecular weight of 100,000 to 3 million, more preferably 200,000 to 2 million, and still more preferably 300,000 to 1.5 million. If the weight average molecular weight is less than 100,000, the cohesive force of the pressure-sensitive adhesive layer tends to decrease, and the pressure-sensitive adhesive sheet may shift when the article is fixed, or a paste residue may be generated when the pressure-sensitive adhesive sheet is peeled off. On the other hand, when the weight average molecular weight exceeds 3 million, the cohesive force tends to decrease due to the effect of the binding of the polymer and the fluidity tends to decrease, and a sufficient adhesive area may not be obtained and the article may not be fixed. In the present invention, the weight average molecular weight of the acrylic polymer refers to a value in terms of standard polystyrene obtained by measuring by GPC (gel/permeation/chromatography).

In addition, the acrylic polymer (A) used in the present invention preferably has a glass transition temperature (Tg) of 0°C or less (usually -100°C or more), more preferably -10°C or less, and -20°C or less. It is more preferable. When the glass transition temperature is higher than 0°C, the cohesive force increases and the fluidity decreases, a sufficient bonding area cannot be obtained, and the article may not be fixed in some cases. In addition, the glass transition temperature of the acrylic polymer can be adjusted within the above range by appropriately changing the monomer component and composition ratio to be used. As for the glass transition temperature of the acrylic polymer in the present invention, a measurement method using a dynamic viscoelastic device or a calculated value by the formula of FOX can be used.

The polymerization method of the acrylic polymer used in the present invention is not particularly limited, and polymerization can be performed by known methods such as solution polymerization, emulsion polymerization, lump polymerization, and suspension polymerization. Further, the obtained copolymer may be any of a random copolymer and a block copolymer.

(Isocyanate crosslinking agent (B))

The pressure-sensitive adhesive composition of the present invention contains an isocyanate crosslinking agent (B). As the isocyanate crosslinking agent (B), for example, lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate, cyclopentylene diisocyanate, cyclohexylene diisocyanate, and alicyclic isocyanates such as isophorone diisocyanate, Aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylene diisocyanate, trimethylolpropane/tolylene diisocyanate trimer adduct (trade name CORONATE L), Japan Polyurethane Industry Co., Ltd.), trimethylolpropane/hexamethylene diisocyanate trimer adduct (trade name Coronate HL, Japan Polyurethane Industry Co., Ltd.), isocyanurate body of hexamethylene diisocyanate (brand name Coronate HX, Japan Polyurethane Isocyanate adducts, such as industrial company make), etc. are mentioned. These compounds may be used alone or in combination.

In the present invention, the content of the isocyanate crosslinking agent (B) is 0.1 parts by mass to 15 parts by mass, preferably 1 part by mass to 13 parts by mass, and 2 parts by mass to 100 parts by mass of the acrylic polymer (A). It is more preferable that it is 9 mass parts, and it is still more preferable that it is 3 mass parts-6 mass parts. If the content of the isocyanate crosslinking agent (B) is less than 0.1 parts by mass based on 100 parts by mass of the acrylic polymer (A), the crosslinking formation is insufficient, and the cohesive force of the pressure-sensitive adhesive layer is not obtained. When it shifts or peels off an adhesive sheet, a paste residue may be generated. On the other hand, when the content of the isocyanate-based crosslinking agent (B) exceeds 15 parts by mass based on 100 parts by mass of the acrylic polymer (A), the crosslinking proceeds excessively and the cohesive force increases, so that the fluidity decreases, and a sufficient adhesion area cannot be obtained. In some cases, it may become impossible to fix the article.

In addition to the isocyanate-based crosslinking agent, the pressure-sensitive adhesive composition of the present invention may contain other crosslinking agents as necessary. As other crosslinking agents, for example, epoxy crosslinking agents, melamine resins, aziridine derivatives, and metal chelate compounds are used. These compounds may be used alone or in combination.

Examples of the epoxy crosslinking agent include N,N,N',N'-tetraglycidyl-m-xylenediamine (trade name TETRAD-X, manufactured by Mitsubishi Gas Chemical) or 1,3-bis (N,N -Diglycidylaminomethyl)cyclohexane (trade name TETRAD-C, manufactured by Mitsubishi Gas Chemical Corporation), and the like. These compounds may be used alone or in combination.

Examples of the melamine resin include hexamethylol melamine. Examples of the aziridine derivatives include commercially available products such as HDU (manufactured by Sogo Pharmaceuticals Corporation), brand names TAZM (manufactured by Sogo Pharmaceuticals Corporation), and trade names TAZO (manufactured by Sogos Chemicals Corporation). These compounds may be used alone or in combination.

Examples of the metal chelate compound include aluminum, titanium, nickel, zirconium and the like as a metal component, and acetylene, methyl acetoacetate, ethyl acetoacetate, ethyl lactate, and acetylacetone as a chelate component. These compounds may be used alone or in combination.

When these isocyanate-based crosslinking agents (B) are used in combination, the amount used is not particularly limited as long as the effect of the present invention is not impaired, but the total amount of the isocyanate-based crosslinking agent (B) is 100 parts by mass of the acrylic polymer (A). On the other hand, it is preferably 0.1 to 15 parts by mass, more preferably 1 to 13 parts by mass, still more preferably 2 to 9 parts by mass, and particularly preferably 3 to 6 parts by mass.

In the pressure-sensitive adhesive composition of the present invention, the gel fraction after crosslinking with a crosslinking agent is preferably 80% by mass or more, more preferably 85% by mass or more, and still more preferably 90% by mass or more (normally 98% by mass % Below). If the gel fraction is less than 80% by mass, the cohesive force of the pressure-sensitive adhesive layer becomes small, and the pressure-sensitive adhesive sheet is shifted when the article is fixed, or when the pressure-sensitive adhesive sheet is peeled off, there are cases where it is easy to generate a paste residue. On the other hand, when the gel fraction exceeds 98% by mass, the cohesive force of the acrylic polymer increases, so the fluidity decreases, a sufficient bonding area cannot be obtained, and the article may not be fixed in some cases.

The gel fraction in the present invention refers to the mass of the pressure-sensitive adhesive layer W1g (about 0.1 g) after immersing in ethyl acetate at about 25°C for 1 week, and then removing the pressure-sensitive adhesive layer from ethyl acetate and drying at 130°C for 2 hours. It is a value calculated as (W2/W1) x 100 (mass %) by measuring W2g.

(Catalyst with iron as the active center (C))

The pressure-sensitive adhesive composition of the present invention contains a catalyst (C) having iron as an active center (hereinafter, sometimes referred to as an iron catalyst (C)). As the iron catalyst (C), an iron chelate compound can be suitably used, and for example, it can be represented by the general formula Fe(X)(Y)(Z). The iron chelate compound is represented by any of Fe(X) ₃ , Fe(X) ₂ (Y) and Fe(X)(Y)(Z) by the combination of (X)(Y)(Z). In the iron chelate compound Fe(X)(Y)(Z), (X)(Y)(Z) is a ligand for Fe, respectively, for example, when X, Y or Z is a β-diketone, β -As a diketone, acetylacetone, hexane-2,4-dione, heptane-2,4-dione, heptane-3,5-dione, 5-methyl-hexane-2,4-dione, octane-2,4- Dione, 6-methylheptane-2,4-dione, 2,6-dimethylheptane-3,5-dione, nonane-2,4-dione, nonane-4,6-dione, 2,2,6,6- Tetramethylheptane-3,5-dione, tridecane-6,8-dione, 1-phenyl-butane-1,3-dione, hexafluoroacetylacetone, ascorbic acid, and the like.

When X, Y or Z is a β-ketoester, as β-ketoester, methyl acetoacetate, ethyl acetoacetate, acetoacetate-n-propyl, isopropyl acetoacetate, acetoacetate-n-butyl, acetoacetic acid-sec -Butyl, acetoacetic acid-tert-butyl, propionyl acetate methyl, propionyl ethyl acetate, propionyl acetate-n-propyl, propionyl acetate isopropyl, propionyl acetate-n-butyl, propionyl acetate-sec-butyl, Propionyl acetate-tert-butyl, benzyl acetoacetate, dimethyl malonate, diethyl malonate, and the like.

In the present invention, an iron catalyst other than the iron chelate compound may be used, and for example, a compound of iron and an alkoxy group, a halogen atom, or an acyloxy group may be used. In the case of a compound of iron and an alkoxy group, as an alkoxy group, a methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, sec-butoxy group, tert-butoxy group, pentyloxy group, hexyloxy group Group, heptyloxy group, octyloxy group, 2-ethylhexyloxy group, phenoxy group, cyclohexyloxy group, benzyloxy group, 1-benzylnaphthyloxy group, and the like.

In the case of a compound of iron and a halogen atom, examples of the halogen atom include fluorine, chlorine, bromine, and iodine.

In the case of a compound of iron and an acyloxy group, as an acyloxy group, 2-ethylhexyl acid, octylic acid, naphthenic acid, resinic acid (abietic acid, neoabietic acid, d-pimaric acid, iso -d-Pimaric acid, porocarpic acid, gluconic acid, fumaric acid, citric acid, aspartic acid, α-ketoglutamic acid, malic acid, succinic acid, aliphatic organic acid or benzoic acid containing amino acids such as glycine and histidine as main components , Cinnamic acid, and aromatic fatty acids containing p-oxycinnamic acid as a main component), and the like.

In the present invention, among these catalysts (C) having an active center of iron, an iron chelate compound having β-diketone as a ligand is preferable from the viewpoint of reactivity and curability, and in particular, tris (acetylacetonate) iron is used. desirable. These iron catalysts (C) may be used alone or in combination of two or more.

In the present invention, the content of the catalyst (C) having iron as the active center is 0.002 parts by mass to 0.5 parts by mass, preferably 0.003 parts by mass to 0.3 parts by mass, based on 100 parts by mass of the acrylic polymer (A), It is more preferable that it is 0.004 mass parts-0.2 mass parts. If the content of the iron catalyst (C) is less than 0.002 parts by mass with respect to 100 parts by mass of the acrylic polymer (A), the curability is insufficient and the adhesive strength of the pressure-sensitive adhesive sheet immediately after production increases, and the glue residue is removed when the pressure-sensitive adhesive sheet is peeled off. It may become easy to occur, and there may be a case where the change in adhesive force over time increases. On the other hand, if the content of the iron catalyst (C) exceeds 0.5 parts by mass based on 100 parts by mass of the acrylic polymer (A), the keto-enol tautomerism required to prevent the deactivation of the iron catalyst (C) described later The required content of the resulting compound (D) increases, the compound (D) remains as a residue in the pressure-sensitive adhesive sheet, and the change in adhesive force over time may increase.

In the present invention, it is preferable to adjust the amount of the catalyst (C) containing iron as the active center according to the content of the isocyanate crosslinking agent (B). That is, with respect to the amount (mass) of the isocyanate crosslinking agent (B), the iron catalyst (C) is preferably blended in an amount of 0.05 mass% to 12.5 mass%, and blending in an amount of 0.075 mass% to 7.5 mass%. It is more preferable to do it. When the content of the iron catalyst (C) is less than 0.05% by mass with respect to the isocyanate crosslinking agent (B), the curability is insufficient, the adhesive strength of the pressure-sensitive adhesive sheet immediately after production becomes large, and when the pressure-sensitive adhesive sheet is peeled off, it becomes easy to generate a paste residue. In some cases, there are also cases where the change in adhesive strength over time increases. When the content of the iron catalyst (C) exceeds 12.5% by mass with respect to the isocyanate crosslinking agent (B), the compound (D) causing keto-enol tautomerism required to prevent deactivation of the iron catalyst (C) described later This required content increases, the compound (D) remains as a residue in the pressure-sensitive adhesive sheet, and the change in the adhesive strength over time may increase.

(Compound (D) causing keto-enol tautomerism)

The pressure-sensitive adhesive composition of the present invention contains a compound (D) that causes keto-enol tautomerism (hereinafter, sometimes referred to as a keto-enol tautomer compound (D)). Keto-enol tautomeric compound (D) is a compound that causes tautomerism between keto (ketone, aldehyde) and enol (see Figure 1), acts as a chelating agent with respect to the iron catalyst, and has a catalytic function by carboxyl groups. It is a compound that prevents the deactivation of That is, in the iron catalyst (C), if a carboxyl group is present, the catalytic function of the carboxyl group changes by changing the chemical structure of the iron catalyst (C), but if the compound (D) causing keto-enol tautomerism is present, It is thought that the deactivation of the compound (D), which causes keto-enol tautomerism rather than the carboxyl group, is preferentially coordinated in the vicinity of the iron catalyst (C), thereby blocking changes in the chemical structure of the iron catalyst (C):

(R ¹ , R ² , R ³ are substituents such as hydrogen, alkyl group, alkenyl group, and aryl group, and may contain a hetero atom or a halogen atom in the molecule).

Examples of the compound (D) causing keto-enol tautomerism include methyl acetoacetate, ethyl acetoacetate, acetoacetate-n-propyl, isopropyl acetoacetate, acetoacetate-n-butyl, acetoacetate-sec-butyl, Acetoacetic acid-t-butyl, propionyl methyl acetate, propionyl ethyl acetate, propionyl acetate-n-propyl, propionyl acetate isopropyl, propionyl acetate-n-butyl, propionyl acetate-sec-butyl, propionyl acetate β-ketoesters such as -tert-butyl, benzyl acetoacetate, dimethyl malonate, and diethyl malonate;

Acetylacetone, hexane-2,4-dione, heptane-2,4-dione, heptane-3,5-dione, 5-methyl-hexane-2,4-dione, octane-2,4-dione, 6-methyl Heptane-2,4-dione, 2,6-dimethylheptane-3,5-dione, nonane-2,4-dione, nonane-4,6-dione, 2,2,6,6-tetramethylheptane-3 Β-diketones such as ,5-dione, tridecane-6,8-dione, 1-phenyl-butane-1,3-dione, hexafluoroacetylacetone, and ascorbic acid;

Acid anhydrides such as acetic anhydride;

Ketones such as acetone, methyl ethyl ketone, methyl-n-butyl ketone, methyl isobutyl ketone, methyl-tert-butyl ketone, methylphenyl ketone, and cyclohexanone; And the like. Among these compounds, it is preferable to use β-diketones having a high effect of preventing deactivation of the catalytic function due to a carboxyl group, and among them, acetylacetone is more preferable.

The content of the compound (D) causing keto-enol tautomerism is contained so that the mass ratio (D/C) of the keto-enol tautomer compound (D) to the catalyst (C) having iron as the active center is 3 to 70. And, it is preferable to contain so that it may become 10 to 70, it is more preferable to contain so that it may become 20 to 60, and it is more preferable to contain so that it may become 40 to 55. When the content ratio of the keto-enol tautomer compound (D) and the iron catalyst (C) exceeds 70, the keto-enol tautomer compound (D) is excessively contained in the iron catalyst (C), and the keto- Since the enol tautomeric compound (D) causes a negative reaction with the isocyanate-based crosslinking agent (B) in the blending solution, isocyanate groups that can react with hydroxyl groups during curing decrease, and sufficient curability cannot be obtained. On the other hand, if the content ratio of the keto-enol tautomer compound (D) and the iron catalyst (C) is less than 3, the keto-enol tautomer compound (D) is excessively contained with respect to the iron catalyst (C), and carboxyl Deactivation of the catalytic function due to the group cannot be prevented, resulting in insufficient curing.

When the compound (D) causing keto-enol tautomerism is contained so that the mass ratio (D/C) of the keto-enol tautomer compound (D) to the catalyst (C) having the iron as the active center is 3 to 70 Although it is good, in that case, it is preferable to mix|blend 0.15 to 35 mass parts with respect to 100 mass parts of acrylic polymer (A), and it is more preferable to contain 0.2 to 20 mass parts. When the content of the keto-enol tautomeric compound (D) exceeds 35 parts by mass based on 100 parts by mass of the acrylic polymer (A), the compound (D) remains as a residue in the pressure-sensitive adhesive sheet, and the change in adhesive strength over time May increase. On the other hand, if the content of the keto-enol tautomer compound (D) is less than 0.15 parts by mass based on 100 parts by mass of the acrylic polymer (A), deactivation of the catalytic function by the carboxyl group cannot be prevented, and curing becomes insufficient. There is.

In addition, the pressure-sensitive adhesive composition of the present invention may contain other known additives, for example, powders such as colorants and pigments, surfactants, plasticizers, tackifiers, low molecular weight polymers, surface lubricants, leveling agents, oxidation agents. An inhibitor, a corrosion inhibitor, a light stabilizer, an ultraviolet absorber, a polymerization inhibitor, a silane coupling agent, an inorganic or organic filler, a metal powder, a particle shape, a foil shape, and the like can be appropriately added depending on the application.

(Adhesive layer)

The adhesive layer of the present invention is formed by crosslinking the above adhesive composition. In addition, the adhesive sheet of the present invention is formed by forming such an adhesive layer on a support. At this time, the crosslinking of the pressure-sensitive adhesive composition is generally performed after application of the pressure-sensitive adhesive composition, but it is also possible to transfer the pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition after crosslinking to a support.

In the pressure-sensitive adhesive layer of the present invention, the gel fraction after crosslinking with a crosslinking agent is preferably 80% by mass or more, more preferably 85% by mass or more, and still more preferably 90% by mass or more (usually 98% by mass % Below). If the gel fraction is less than 80% by mass, the cohesive force of the pressure-sensitive adhesive layer becomes small, and the pressure-sensitive adhesive sheet is shifted when the article is fixed, or when the pressure-sensitive adhesive sheet is peeled off, there are cases where it is easy to generate a paste residue. On the other hand, when the gel fraction exceeds 98% by mass, the cohesive force of the acrylic polymer increases, so the fluidity decreases, a sufficient bonding area cannot be obtained, and the article may not be fixed in some cases.

The method of forming the pressure-sensitive adhesive layer is not particularly described, but it is produced by, for example, applying the pressure-sensitive adhesive composition to a support and drying and removing a polymerization solvent to form a pressure-sensitive adhesive layer on the support. Thereafter, curing may be performed for the purpose of adjusting the component migration of the pressure-sensitive adhesive layer or adjusting the crosslinking reaction. In particular, in order to advance the crosslinking reaction, it can be heated at 100 to 140°C for about 15 seconds to 2 minutes. In addition, when the pressure-sensitive adhesive composition is applied on a support to prepare a pressure-sensitive adhesive layer, one or more solvents other than the polymerization solvent may be newly added to the pressure-sensitive adhesive composition so that it can be uniformly applied on the support.

In addition, as a method for forming the pressure-sensitive adhesive layer of the present invention, a known method used for producing an adhesive sheet is used. Specifically, for example, roll coating, gravure coating, reverse coating, roll brush, spray coating, air knife coating, and the like can be mentioned.

The thickness of the pressure-sensitive adhesive layer of the present invention can be appropriately determined depending on the application, but is usually about 1 µm to 1000 µm, and preferably about 5 µm to 500 µm.

(Adhesive sheet)

The pressure-sensitive adhesive sheet of the present invention is formed by forming the pressure-sensitive adhesive layer on a support. The pressure-sensitive adhesive sheet of the present invention may be formed in a rolled form, or may be formed in a laminated form. That is, the pressure-sensitive adhesive sheet of the present invention can have any shape such as a sheet shape, a tape shape, and a film shape. Also, depending on the purpose of use, cutting or punching may be performed in an appropriate shape.

The support is not particularly limited as long as it can be formed in a sheet shape or a film shape. For example, polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer Polymer, ethylene-1-butene copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, polyolefin film such as ethylene-vinyl alcohol copolymer, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, etc. Polyester film, polyacrylate film, polystyrene film, nylon 6, nylon 6,6, polyamide film such as partially aromatic polyamide, polyvinyl chloride film, polyvinylidene chloride film, polycarbonate film, polyfluoroethylene A film, a polyimide film, a polyvinyl alcohol film, etc. are mentioned.

The thickness of the support in the present invention is usually 5 µm to 200 µm, preferably about 10 µm to 100 µm.

In the support, if necessary, release and antifouling treatment with a silicone-based, fluorine-based, long-chain alkyl-based or fatty acid amide-based release agent, silica powder, etc., acid treatment, alkali treatment, primer treatment, Corona treatment, plasma treatment, UV treatment, or other anti-static treatment, such as coating type, kneading type, and vapor deposition type, may be performed.

The pressure-sensitive adhesive sheet of the present invention can, if necessary, bond a release film (separator) for the purpose of protecting the pressure-sensitive adhesive layer surface. Although paper or plastic film is used as a material constituting the release film, a plastic film is suitably used from the viewpoint of excellent surface smoothness. The film is not particularly limited as long as it is a film capable of protecting the pressure-sensitive adhesive layer, and examples thereof include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride. A copolymer film, a polyethylene terephthalate film, a polybutylene terephthalate film, a polyurethane film, an ethylene-vinyl acetate copolymer film, etc. are mentioned.

The thickness of the release film is usually 5 µm to 200 µm, preferably about 10 µm to 100 µm. In the release film, if necessary, release and antifouling treatment with a silicone-based, fluorine-based, long-chain alkyl-based or fatty acid amide-based release agent, silica powder, etc., or antistatic treatment such as coating type, kneading type, vapor deposition type, etc. You may.

(Example)

Hereinafter, examples and the like specifically showing the configuration and effects of the present invention will be described, but the present invention is not limited thereto. In addition, the evaluation items in Examples etc. were measured as follows.

<Measurement of weight average molecular weight of acrylic polymer>

The weight average molecular weight of the produced acrylic polymer was measured by GPC (gel transmission chromatography).

Device: HLC-8220GPC, manufactured by Tosoh Corporation

column:

Sample column: TSKguardcolumn Super HZ-H (1 piece) + TSKgel Super HZM-H (2 pieces) manufactured by Tosoh Corporation

Reference column: Tosoh Corporation, TSKgel Super H-RC (1 pc.)

Flow: 0.6ml/min

Injection volume: 10 μL

Column temperature: 40°C

Eluent: THF

Injection sample concentration: 0.2% by mass

Detector: differential refractometer

In addition, the weight average molecular weight was calculated in terms of polystyrene.

<Production of the adhesive sheet for evaluation>

On a polyethylene terephthalate (PET) film (38 μm in thickness), the pressure-sensitive adhesive composition solutions of Examples and Comparative Examples described later were applied, and dried at 130° C. for 30 seconds to remove the solvent to form a pressure-sensitive adhesive layer (thickness 25 μm). . Then, it covered with the release film surface-treated with a release agent, and left to stand at room temperature (23 degreeC) for 1 hour, and the adhesive sheet for evaluation immediately after production was obtained. Further, this PSA sheet was stored for 4 days under conditions of room temperature (23°C) and 50% RH to obtain a PSA sheet for evaluation after aging.

<Measurement of adhesive force>

Each prepared adhesive sheet for evaluation is cut into a size of 20 mm in width and 100 mm in length, rubbed 10 reciprocations with a clean waste impregnated with isopropyl alcohol, and washed with a clean acrylic plate. It was press-bonded by the method, and it was set as the sample for adhesive force evaluation. After allowing this evaluation sample to stand for 30 minutes in a measuring environment of 23°C and 50% RH, high-speed adhesive strength [N/20 mm] was measured under conditions of a tensile speed of 30 m/min and a peel angle of 180° using a high-speed peel tester. . Further, the low-speed adhesive strength [N/20 mm] was measured under the conditions of a tensile speed of 0.3 m/min and a peel angle of 180°.

In the present invention, the progress of crosslinking was evaluated based on the rate of change between the adhesive force of the pressure-sensitive adhesive sheet immediately after production and the adhesive force of the pressure-sensitive adhesive sheet after aging. That is, the rate of change in this evaluation is a value obtained by dividing the adhesive force of the adhesive sheet after aging by the adhesive force of the adhesive sheet immediately after production (that is, the rate of change = the adhesive force of the adhesive sheet after aging / the adhesive force of the adhesive sheet immediately after production), and the rate of change is If it is 0.60 or more, it is judged that the change in adhesive force is small, and it is judged that crosslinking has sufficiently advanced immediately after production. In addition, high-speed adhesion is a criterion for the difficulty of peeling when peeling the adhesive sheet, while low-speed adhesion is a criterion for determining whether or not the article is fixed. need.

[Preparation of acrylic polymer (1)]

In a 4-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, cooler, and dropping lot, 100 parts by mass of 2-ethylhexyl acrylate (2EHA) and 10 parts by mass of 4-hydroxybutyl acrylate (4HBA) as monomer components , 0.06 parts by mass of acrylic acid (AA), 0.2 parts by mass of azobisisobutyronitrile and 356 parts by mass of ethyl acetate were added as polymerization initiators, and nitrogen gas was introduced while gently stirring, and the temperature of the liquid in the flask was around 60°C. And the polymerization reaction was carried out for about 3 hours to prepare an acrylic polymer solution. The weight average molecular weight of the obtained acrylic polymer (1) was 610,000, and the glass transition temperature calculated from the formula of FOX was -67°C.

[Preparation of acrylic polymer (2)]

As the monomer component, except using 100 parts by mass of 2-ethylhexyl acrylate (2EHA), 10 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 5 parts by mass of acrylic acid (AA), in the same manner as in the preparation of the acrylic polymer (1). , An acrylic polymer solution was prepared. The weight average molecular weight of the obtained acrylic polymer (2) was 630,000, and the glass transition temperature calculated from the formula of FOX was -63°C.

[Preparation of acrylic polymer (3)]

As the monomer component, except using 100 parts by mass of 2-ethylhexyl acrylate (2EHA), 10 parts by mass of 2-hydroxyethyl acrylate (HEA), and 0.06 parts by mass of acrylic acid (AA), in the same manner as in the preparation of the acrylic polymer (1). , An acrylic polymer solution was prepared. The weight average molecular weight of the obtained acrylic polymer (3) was 610,000, and the glass transition temperature calculated from the formula of FOX was -66°C.

[Preparation of acrylic polymer (4)]

As the monomer component, except using 100 parts by mass of 2-ethylhexyl acrylate (2EHA), 10 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 2 parts by mass of acrylic acid (AA), in the same manner as in the preparation of the acrylic polymer (1). , An acrylic polymer solution was prepared. The weight average molecular weight of the obtained acrylic polymer (4) was 620,000, and the glass transition temperature calculated from the formula of FOX was -65°C.

[Preparation of acrylic polymer (5)]

An acrylic polymer solution was prepared in the same manner as in the preparation of the acrylic polymer (1), except that 100 parts by mass of 2-ethylhexyl acrylate (2EHA) and 0.06 parts by mass of acrylic acid (AA) were used as the monomer component. The weight average molecular weight of the obtained acrylic polymer (5) was 400,000, and the glass transition temperature calculated from the formula of FOX was -70°C.

(Example 1)

[Production of adhesive sheet using adhesive composition]

With respect to 100 parts by mass (solid content) of the acrylic polymer (1), 4 parts by mass of trimethylolpropane/tolylenediisocyanate trimer adduct (manufactured by Japan Polyurethane Industrial Co., Ltd., brand name ``Coronate L'') as a crosslinking agent, tris as an iron catalyst (Acetylacetonate) iron (manufactured by Nippon Chemical Industries, trade name ``Nacem ferric'') 0.005 parts by mass, as a compound causing keto-enol tautomerism, 0.25 parts by mass of acetylacetone (AcAc) was added, and toluene After dilution so that the solid content concentration became 29 mass %, it stirred and obtained the adhesive composition. Using this, a pressure-sensitive adhesive sheet for evaluation was produced according to the production method.

(Examples 2 to 6, Comparative Examples 1 to 4)

By the formulation shown in Table 1, an adhesive composition was prepared in the same procedure as in Example 1, and an adhesive sheet for evaluation was created.

In addition, in the table, "C/L" in a crosslinking agent is a trimer adduct of trimethylolpropane/tolylene diisocyanate (manufactured by Japan Polyurethane Industries, brand name "Coronate L"), and "C/HX" is hexa The isocyanurate body of methylene diisocyanate (manufactured by Japan Polyurethane Industrial Co., Ltd., brand name ``Coronate HX''), and ``OL-1'' in the catalyst, dioctyl tin dilaurate (manufactured by Tokyo Fine Chemical, brand name) "EMBILIZER OL-1") is shown.

In the pressure-sensitive adhesive compositions of Examples 1 to 6, the rate of change in the pressure-sensitive adhesive force of the pressure-sensitive adhesive sheet immediately after production and the pressure-sensitive adhesive force of the pressure-sensitive adhesive sheet after aging was 0.60 or more, and it was confirmed that stable adhesive strength can be obtained immediately after production. That is, with respect to the acrylic polymer having a carboxyl group, isocyanate crosslinking was almost completed immediately after production, and it was confirmed that the catalytic function of the iron catalyst was not deactivated. In addition, in the examples, in Example 2, stick slip was observed when peeling off both high-speed adhesive strength and low-speed adhesive force. Stick slip is a vibration phenomenon that occurs on the peeling surface, and is not preferable in some cases because there is a case where damage may be caused to the adherend, or a paste residue may be partially generated on the adherend.

On the other hand, in the pressure-sensitive adhesive composition of Comparative Example 1 not containing the compound (D) causing keto-enol tautomerism, the catalytic function of the iron catalyst was deactivated by the carboxyl group in the acrylic polymer, and the crosslinking reaction was not completed immediately after preparation. Therefore, it was confirmed that crosslinking proceeded due to aging, and the adhesive force after aging was significantly changed compared to immediately after production. In addition, since the pressure-sensitive adhesive compositions of Comparative Examples 2 and 3 did not have a hydroxyl group in the acrylic polymer, crosslinking did not proceed and the cohesive strength was insufficient, and it was confirmed that cohesive failure was performed in the measurement of the adhesive strength. In addition, in Comparative Example 4 using a tin-based catalyst, since the catalytic activity was lower than that of the iron catalyst, the crosslinking reaction was not completed immediately after production, and the crosslinking proceeded by aging, and the adhesive strength after aging was significantly changed compared to immediately after production. It was confirmed that they were doing.

Although the present invention has been described in detail with reference to specific embodiments, it is obvious to those skilled in the art that various changes and modifications can be added without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2013-126193 filed on June 15, 2013, the content of which is incorporated herein by reference.

Claims (8)

100 parts by mass of an acrylic polymer (A) having a hydroxyl group and a carboxyl group,
0.1 parts by mass to 15 parts by mass of an isocyanate crosslinking agent (B),
0.002 parts by mass to 0.5 parts by mass of a catalyst (C) having iron as an active center,
It is a pressure-sensitive adhesive composition comprising a compound (D) causing keto-enol tautomerism,
The pressure-sensitive adhesive composition in which the mass ratio (D/C) of the compound (D) causing keto-enol tautomerism to the catalyst (C) having iron as an active center is 3 to 70. The method of claim 1,
The acrylic polymer (A) having a hydroxyl group and a carboxyl group contains 65 mass% to 99.89 mass% of an alkyl (meth)acrylate having an alkyl group having 4 to 12 carbon atoms, 0.1 mass% to 25 mass% of a hydroxyl group-containing monomer, and a carboxyl group A pressure-sensitive adhesive composition comprising 0.01% by mass to 10% by mass of a monomer as a constituent component. The method of claim 1,
The pressure-sensitive adhesive composition wherein the catalyst (C) having iron as an active center is an iron chelate compound. The method of claim 1,
The said keto-enol tautomerism compound (D) is at least one kind selected from β-ketoesters, β-diketones, acid anhydrides and ketones. The method of claim 4,
The pressure-sensitive adhesive composition wherein the compound (D) causing the keto-enol tautomerism is β-diketone. The method of claim 1,
The pressure-sensitive adhesive composition wherein the content of the compound (D) causing the keto-enol tautomerism is 0.15 to 35 parts by mass based on 100 parts by mass of the acrylic polymer (A). An adhesive layer obtained by crosslinking the adhesive composition according to any one of claims 1 to 6. A pressure-sensitive adhesive sheet formed by forming the pressure-sensitive adhesive layer according to claim 7 on a support.