JP7558864B2 - Adhesive composition and adhesive sheet - Google Patents

Description

The present disclosure relates to an adhesive composition and an adhesive sheet.

2. Description of the Related Art Conventionally, pressure-sensitive adhesives have been used to temporarily fix various members in the manufacturing process of electronic devices. Various pressure-sensitive adhesives used for temporary fixing have been reported so far.
For example, Patent Document 1 discloses an adhesive that is made of an adhesive that exhibits adhesion at temperatures equal to or higher than its melting point, and is characterized in that the adhesive strength retention rate of the adhesive, calculated from a certain formula, is 50% or more at a temperature of 150°C and 10% or less at temperatures below the melting point.

JP 2008-179744 A

In the manufacturing process of electronic devices, a component temporarily fixed to an adherend may be exposed to a high-temperature environment, and in some processes, the ambient temperature may reach approximately 150°C. For this reason, the adhesive used for temporary fixation is required to be able to form an adhesive layer that exhibits high adhesive strength so that the component does not peel off from the adherend or shift from its initial attachment position on the adherend, not only in a temperature environment of 25°C, but also in a high-temperature environment of, for example, 150°C.

Regarding the above points, the adhesive layer formed by the adhesive described in Patent Document 1 is said to exhibit high adhesive strength to the adherend in a high-temperature environment of 150°C. However, Patent Document 1 does not consider the adhesive strength at 25°C, which is a typical working temperature. Furthermore, according to the inventors' study, the adhesive layer formed by the adhesive described in Patent Document 1 does not have sufficient adhesive strength to the adherend in a temperature environment of 25°C, and may peel off or shift from the adherend during the temporary fixing stage, and there is room for improvement in the adhesive strength to the adherend in a temperature environment of 25°C.

An object of one embodiment of the present disclosure is to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer that exhibits high adhesive strength to an adherend in both temperature environments of 25°C and 150°C.
The problem to be solved by another embodiment of the present disclosure is to provide a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer that exhibits high adhesive strength to an adherend in both temperature environments of 25°C and 150°C.

Specific means for solving the problems include the following aspects.
<1> A (meth)acrylic copolymer including 20% by mass to 60% by mass of structural units derived from a monomer having a linear alkyl group having 16 or more carbon atoms, based on all structural units, and 15% by mass to 40% by mass of structural units derived from a monomer having a carboxy group, based on all structural units;
A cross-linking agent;
A pressure-sensitive adhesive composition comprising:
<2> The pressure-sensitive adhesive composition according to <1>, wherein the content of the crosslinking agent is 0.01 to 0.05 parts by mass based on 100 parts by mass of the (meth)acrylic copolymer.
<3> The pressure-sensitive adhesive composition according to <1> or <2>, wherein the crosslinking agent is an epoxy-based crosslinking agent.
<4> The pressure-sensitive adhesive composition according to any one of <1> to <3>, wherein the (meth)acrylic copolymer has a weight-average molecular weight of 100,000 to 300,000.
<5> The pressure-sensitive adhesive composition according to any one of <1> to <4>, wherein a ratio of the number of moles of crosslinkable functional groups in the crosslinking agent to the number of moles of carboxy groups in the (meth)acrylic copolymer is 0.00002 to 0.006.
<6> A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of <1> to <5>.

According to one embodiment of the present disclosure, there is provided a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer that exhibits high adhesive strength to an adherend in both temperature environments of 25°C and 150°C.
According to another embodiment of the present disclosure, there is provided a pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer that exhibits high adhesive strength to an adherend in both temperature environments of 25°C and 150°C.

The adhesive composition and adhesive sheet of the present disclosure are described in detail below. The following description of the requirements may be based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments, and can be modified as appropriate within the scope of the purpose of the present disclosure.

In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits, respectively.
In the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in the present disclosure. In addition, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

In the present disclosure, a combination of two or more preferred aspects is a more preferred aspect.
In the present disclosure, when the adhesive composition contains multiple substances corresponding to each component, the amount of each component in the adhesive composition means the total amount of the multiple substances present in the adhesive composition, unless otherwise specified.

In the present disclosure, the term "(meth)acrylic copolymer" refers to a copolymer in which the content of structural units derived from monomers having a (meth)acryloyl group is 50 mass% or more of all structural units (i.e., all structural units of the (meth)acrylic copolymer).
In the present disclosure, "(meth)acrylic monomer" means a monomer having a (meth)acryloyl group.

In this disclosure, "(meth)acrylic" is a term that encompasses both "acrylic" and "methacrylic", "(meth)acrylate" is a term that encompasses both "acrylate" and "methacrylate", and "(meth)acryloyl" is a term that encompasses both "acryloyl" and "methacryloyl".

In this disclosure, "n-" means normal, "i-" means iso, "s-" means secondary, and "t-" means tertiary.

In this disclosure, "adhesive" and "adhesive composition" are synonymous.

[Adhesive composition]
The pressure-sensitive adhesive composition of the present disclosure is a pressure-sensitive adhesive composition comprising a (meth)acrylic copolymer (hereinafter also referred to as a "specific (meth)acrylic copolymer") containing 20% by mass to 60% by mass of structural units derived from monomers having a linear alkyl group having 16 or more carbon atoms, relative to all structural units, and 15% by mass to 40% by mass of structural units derived from monomers having a carboxy group, relative to all structural units, and a crosslinking agent.
According to the pressure-sensitive adhesive composition of the present disclosure, a pressure-sensitive adhesive layer that exhibits high adhesive strength to an adherend can be formed in both temperature environments of 25°C and 150°C.
The reason why the pressure-sensitive adhesive composition of the present disclosure can exhibit such an effect is unclear, but the present inventors speculate as follows, however, the following speculation is not intended to limit the pressure-sensitive adhesive composition of the present disclosure, but is merely an example.

The pressure-sensitive adhesive composition of the present disclosure comprises a specific (meth)acrylic copolymer containing a structural unit derived from a monomer having a linear alkyl group having 16 or more carbon atoms and a structural unit derived from a monomer having a carboxy group, each in a specific range of ratio, and a crosslinking agent.
The adhesive composition of the present disclosure contains a specific (meth)acrylic copolymer containing a specific ratio or more of a structural unit derived from a monomer having a carboxyl group, and a crosslinking agent, so that the adhesive layer formed is considered to show high cohesive strength even in a high-temperature environment of 150°C. The adhesive composition of the present disclosure also contains a structural unit derived from a monomer having a linear alkyl group having 16 or more carbon atoms. A monomer having a linear alkyl group having 16 or more carbon atoms is a monomer called a crystalline monomer. A crystalline monomer exhibits fluidity at a temperature equal to or higher than its melting point, and crystallizes at a temperature lower than its melting point. The adhesive composition of the present disclosure contains a specific ratio or more of a structural unit derived from a monomer having a linear alkyl group having 16 or more carbon atoms in the specific (meth)acrylic copolymer, so that the adhesive layer formed is considered to show sufficient wettability to an adherend in a high-temperature environment of 150°C due to the fluidity of the crystalline monomer. Therefore, it is presumed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure exhibits high adhesive strength to the adherend in a high-temperature environment of 150°C due to the expression of high cohesive strength and sufficient wettability to the adherend.
In the pressure-sensitive adhesive composition of the present disclosure, the content of the structural unit derived from the monomer having a linear alkyl group having 16 or more carbon atoms in the specific (meth)acrylic copolymer is below a specific ratio, and the proportion of the crystalline monomer is not excessively large, so that the pressure-sensitive adhesive layer formed is unlikely to become rigid even in a temperature environment of 25° C. In addition, in the pressure-sensitive adhesive composition of the present disclosure, the content of the structural unit derived from the monomer having a carboxyl group in the specific (meth)acrylic copolymer is below a specific ratio, so that the pressure-sensitive adhesive layer formed is also unlikely to become rigid. Therefore, it is presumed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present disclosure exhibits high adhesion to the adherend in a temperature environment of 25° C.
From the above, it is presumed that the pressure-sensitive adhesive composition of the present disclosure can form a pressure-sensitive adhesive layer that exhibits high adhesive strength to an adherend in both temperature environments of 25°C and 150°C.

[Specific (meth)acrylic copolymer]
The pressure-sensitive adhesive composition of the present disclosure contains a (meth)acrylic copolymer [i.e., a specific (meth)acrylic copolymer] that contains 20% by mass to 60% by mass of structural units derived from a monomer having a linear alkyl group having 16 or more carbon atoms, relative to all structural units, and 15% by mass to 40% by mass of structural units derived from a monomer having a carboxy group, relative to all structural units.
The constituent units of the specific (meth)acrylic copolymer will be described below.

<Structural Unit Derived from a Monomer Having a Linear Alkyl Group Having 16 or More Carbon Atoms>
The specific (meth)acrylic copolymer contains 20% by mass to 60% by mass of structural units derived from a monomer having a linear alkyl group having 16 or more carbon atoms, based on the total amount of structural units.
In the present disclosure, a "structural unit derived from a monomer having a linear alkyl group having 16 or more carbon atoms" means a structural unit formed by addition polymerization of a monomer having a linear alkyl group having 16 or more carbon atoms.
In the present disclosure, the "monomer having a linear alkyl group having 16 or more carbon atoms" does not include a monomer that corresponds to a monomer having a carboxy group, which will be described later.

The type of monomer having a linear alkyl group having 16 or more carbon atoms is not particularly limited.
Examples of monomers having a linear alkyl group having 16 or more carbon atoms include monomers having at least one linear alkyl group having 16 or more carbon atoms and an ethylenically unsaturated group in one molecule.
The ethylenically unsaturated group is not particularly limited.
Specific examples of the ethylenically unsaturated group include a vinyl group, an allyl group, a vinylphenyl group, a (meth)acrylamide group, and a (meth)acryloyl group.
The ethylenically unsaturated group is preferably a (meth)acryloyl group, that is, the monomer having a linear alkyl group having 16 or more carbon atoms is preferably a (meth)acrylic acid alkyl ester monomer.

The monomer having a linear alkyl group having 16 or more carbon atoms is preferably an unsubstituted monomer.
The linear alkyl group has 16 or more carbon atoms, and preferably 18 or more carbon atoms.
The upper limit of the number of carbon atoms in the linear alkyl group is not particularly limited, but is preferably 22 or less from the viewpoint of production suitability, for example.

Specific examples of monomers having a linear alkyl group having 16 or more carbon atoms include hexadecyl (meth)acrylate, octadecyl (meth)acrylate (also known as stearyl (meth)acrylate), eicosyl (meth)acrylate, and docosyl (meth)acrylate (also known as behenyl (meth)acrylate).
As the monomer having a linear alkyl group having 16 or more carbon atoms, at least one selected from the group consisting of octadecyl (meth)acrylate [i.e., stearyl (meth)acrylate] and docosyl (meth)acrylate [i.e., behenyl (meth)acrylate] is preferable, and at least one selected from octadecyl methacrylate (i.e., stearyl methacrylate) and docosyl methacrylate (i.e., behenyl methacrylate) is more preferable.

The specific (meth)acrylic copolymer may contain only one type of structural unit derived from a monomer having a linear alkyl group having 16 or more carbon atoms, or may contain two or more types.

The content of the structural units derived from a monomer having a linear alkyl group having 16 or more carbon atoms in the specific (meth)acrylic copolymer is 20% by mass to 60% by mass based on the total structural units of the specific (meth)acrylic copolymer.
When the content of the constituent units derived from a monomer having a linear alkyl group having 16 or more carbon atoms in the specific (meth)acrylic copolymer is 20% by mass or more relative to the total constituent units of the specific (meth)acrylic copolymer, the adhesive layer shows a tendency to have high adhesive strength to an adherend in a high-temperature environment of 150° C. From this viewpoint, the content of the constituent units derived from a monomer having a linear alkyl group having 16 or more carbon atoms in the specific (meth)acrylic copolymer is 20% by mass or more, preferably 25% by mass or more, more preferably 30% by mass or more, and even more preferably 35% by mass or more relative to the total constituent units of the specific (meth)acrylic copolymer.
When the content of the constituent units derived from a monomer having a linear alkyl group having 16 or more carbon atoms in the specific (meth)acrylic copolymer is 60% by mass or less relative to the total constituent units of the specific (meth)acrylic copolymer, the adhesive layer shows a tendency to have high adhesive strength to an adherend in a temperature environment of 25° C. From this viewpoint, the content of the constituent units derived from a monomer having a linear alkyl group having 16 or more carbon atoms in the specific (meth)acrylic copolymer is 60% by mass or less, preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less relative to the total constituent units of the specific (meth)acrylic copolymer.

<Structural Unit Derived from Monomer Having a Carboxy Group>
The specific (meth)acrylic copolymer contains 15% by mass to 40% by mass of structural units derived from a monomer having a carboxy group, based on the total amount of structural units.
The carboxy group of the structural unit derived from a monomer having a carboxy group can contribute to crosslinking with a crosslinking agent described below.
In the present disclosure, a "structural unit derived from a monomer having a carboxy group" refers to a structural unit formed by addition polymerization of a monomer having a carboxy group.

The type of the monomer having a carboxy group is not particularly limited.
An example of a monomer having a carboxy group is a monomer having at least one carboxy group and an ethylenically unsaturated group in one molecule.
The ethylenically unsaturated group is not particularly limited.
Specific examples of the ethylenically unsaturated group include a vinyl group, an allyl group, a vinylphenyl group, a (meth)acrylamide group, and a (meth)acryloyl group.
The ethylenically unsaturated group is preferably a (meth)acryloyl group.

Specific examples of monomers having a carboxy group include acrylic acid, methacrylic acid, crotonic acid, maleic anhydride, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, ω-carboxy-polycaprolactone mono(meth)acrylate [e.g., ω-carboxy-polycaprolactone (n≈2) monoacrylate], succinic acid esters (e.g., 2-acryloyloxyethyl-succinic acid), vinyl formate, vinyl acetate, vinyl propionate, and vinyl neodecanoate.
The monomer having a carboxy group is preferably at least one selected from, for example, acrylic acid and methacrylic acid, and more preferably acrylic acid.

The specific (meth)acrylic copolymer may contain only one type of structural unit derived from a monomer having a carboxy group, or may contain two or more types.

The content of the structural units derived from the monomer having a carboxy group in the specific (meth)acrylic copolymer is 15% by mass to 40% by mass based on the total structural units of the specific (meth)acrylic copolymer.
When the content of the constituent units derived from the monomer having a carboxy group in the specific (meth)acrylic copolymer is 15% by mass or more relative to the total constituent units of the specific (meth)acrylic copolymer, the adhesive layer tends to have high adhesive strength to an adherend in a high-temperature environment of 150° C. From this viewpoint, the content of the constituent units derived from the monomer having a carboxy group in the specific (meth)acrylic copolymer is 15% by mass or more, preferably 18% by mass or more, and more preferably 20% by mass or more relative to the total constituent units of the specific (meth)acrylic copolymer.
When the content of the constituent units derived from the monomer having a carboxy group in the specific (meth)acrylic copolymer is 40% by mass or less relative to the total constituent units of the specific (meth)acrylic copolymer, the adhesive layer shows a tendency to have high adhesive strength to an adherend in a temperature environment of 25° C. From this viewpoint, the content of the constituent units derived from the monomer having a carboxy group in the specific (meth)acrylic copolymer is 40% by mass or less, preferably 35% by mass or more, and more preferably 30% by mass or more relative to the total constituent units of the specific (meth)acrylic copolymer.

<Constituent units derived from other monomers>
The specific (meth)acrylic copolymer may contain a constituent unit derived from a monomer that does not fall into either the category of a monomer having a linear alkyl group having 16 or more carbon atoms or a monomer having a carboxy group (so-called other monomer).
In the present disclosure, the term "structural units derived from other monomers" refers to structural units formed by addition polymerization of other monomers.
Examples of the other monomers include (meth)acrylic acid alkyl ester monomers that do not fall into the category of monomers having a linear alkyl group with 16 or more carbon atoms or monomers having a carboxy group (so-called other (meth)acrylic acid alkyl ester monomers). The constituent units derived from the other (meth)acrylic acid alkyl ester monomers can contribute to adjusting the adhesive strength of the pressure-sensitive adhesive layer.

The other (meth)acrylic acid alkyl ester monomer is preferably an unsubstituted (meth)acrylic acid alkyl ester monomer.
The alkyl group of the other (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic.
The alkyl group preferably has 1 to 15 carbon atoms, more preferably has 3 to 12 carbon atoms, and further preferably has 4 to 10 carbon atoms.
Specific examples of other (meth)acrylic acid alkyl ester monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate [also known as lauryl (meth)acrylate], cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate.
As the other (meth)acrylic acid alkyl ester monomer, for example, n-butyl acrylate is preferable.

Other monomers include, for example, (meth)acrylates having a hydroxyl group, such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate; (meth)acrylates having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; alkoxyalkyl (meth)acrylates, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; aromatic monovinyls, such as styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and vinyltoluene; vinyl cyanides, such as acrylonitrile and methacrylonitrile; and vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate. Other examples include various derivatives of these monomers.

When the specific (meth)acrylic copolymer contains a constituent unit derived from another monomer, it may contain only one type of constituent unit derived from the other monomer, or it may contain two or more types of constituent units derived from the other monomer.

When the specific (meth)acrylic copolymer contains structural units derived from other monomers, the content of the structural units derived from other monomers in the specific (meth)acrylic copolymer is not particularly limited and can be set appropriately according to the purpose within a range that does not impair the effects of the pressure-sensitive adhesive composition of the present disclosure.

<<Weight average molecular weight of specific (meth)acrylic copolymer>>
The weight average molecular weight (also referred to as "Mw") of the specific (meth)acrylic copolymer is not particularly limited, but is, for example, preferably 50,000 to 500,000, more preferably 50,000 to 400,000, even more preferably 100,000 to 400,000, and particularly preferably 100,000 to 300,000.
When the weight average molecular weight of the specific (meth)acrylic copolymer is 50,000 or more, the structure of the specific (meth)acrylic copolymer is better maintained, and therefore the adhesive strength of the pressure-sensitive adhesive layer to an adherend in a high-temperature environment of 150°C tends to be higher.
When the weight average molecular weight of the specific (meth)acrylic copolymer is 500,000 or less, the adhesive strength of the pressure-sensitive adhesive layer to an adherend in a temperature environment of 25° C. tends to be higher. This is thought to be because the pressure-sensitive adhesive layer formed is less likely to become hard.

The weight average molecular weight of the specific (meth)acrylic copolymer is a value measured by the following method, specifically, according to the following (1) to (3).
(1) A solution of the specific (meth)acrylic copolymer is applied to a release paper and dried at 100° C. for 1 minute to obtain a film of the specific (meth)acrylic copolymer.
(2) Using the film-like specific (meth)acrylic copolymer obtained in (1) above and tetrahydrofuran, a sample solution having a solid content concentration of 0.2% by mass is obtained. Note that the "solid content concentration" here means the mass ratio of the specific (meth)acrylic copolymer in the sample solution.
(3) The weight average molecular weight of the specific (meth)acrylic copolymer is measured in terms of standard polystyrene using gel permeation chromatography (GPC) under the following conditions.

～Conditions～
Measuring device: High-speed GPC [Model: HLC-8220 GPC, manufactured by Tosoh Corporation]
Detector: differential refractometer (RI) [installed in HLC-8220, manufactured by Tosoh Corporation]
Column: 4 TSKgel GMH _XL (manufactured by Tosoh Corporation) Column temperature: 40°C
Eluent: Tetrahydrofuran Injection amount of sample solution: 100 μL
Flow rate: 0.8mL/min

The weight average molecular weight of the specific (meth)acrylic copolymer can be adjusted to the desired value by adjusting the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, etc.

<<Content of specific (meth)acrylic copolymer>>
The content of the specific (meth)acrylic copolymer in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited, but for example, it is preferably 75% by mass to 99.999% by mass, more preferably 80% by mass to 99.99% by mass, and even more preferably 85% by mass to 99.97% by mass, relative to the total solid content in the pressure-sensitive adhesive composition.
In the present disclosure, the "total solid content in the PSA composition" means the total mass of the PSA composition when the PSA composition does not contain a solvent, and means the mass of the residue remaining after removing the solvent from the PSA composition when the PSA composition contains a solvent.
In this disclosure, "solvent" means water and organic solvents.

[Method for producing specific (meth)acrylic copolymer]
The method for producing the specific (meth)acrylic copolymer is not particularly limited.
The specific (meth)acrylic copolymer can be produced by polymerizing the above-mentioned monomers by a known polymerization method typified by, for example, a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, or a bulk polymerization method.
As a polymerization method, a solution polymerization method is preferred in that the processing steps are relatively simple and can be carried out in a short time when preparing the pressure-sensitive adhesive composition of the present disclosure after production.

In the solution polymerization method, a predetermined organic solvent, monomer, polymerization initiator, and optionally used chain transfer agent are generally charged into a polymerization tank, and the mixture is heated and reacted for several hours with stirring, for example, at the reflux temperature of the organic solvent. In this case, at least a portion of the organic solvent, monomer, polymerization initiator, and optionally used chain transfer agent may be added successively. The reaction may also be carried out in a nitrogen gas flow.

Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds, aliphatic hydrocarbon compounds, alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, and alcohol compounds.
More specifically, examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds such as benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic or alicyclic hydrocarbon compounds such as n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and turpentine oil; ester compounds such as ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; acetone, methyl ethyl acetate, and the like. Examples of the alcohol compounds include ketones, methyl-i-butyl ketone, isophorone, cyclohexanone, and methylcyclohexanone; glycol ether compounds, such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether; and alcohol compounds, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t-butyl alcohol.

When producing the specific (meth)acrylic copolymer, it is preferable to use an organic solvent that is unlikely to cause chain transfer during the polymerization reaction of aromatic hydrocarbon compounds, ester compounds, ketone compounds, etc., and in particular, it is preferable to use ethyl acetate from the viewpoints of the solubility of the specific (meth)acrylic copolymer and the ease of the polymerization reaction.

During the polymerization reaction, only one type of organic solvent may be used, or two or more types may be used.

Examples of the polymerization initiator include organic peroxides and azo compounds that are used in ordinary solution polymerization methods.
Specific examples of organic peroxides include t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-amylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-octylperoxycyclohexyl)propane, 2,2-bis(4,4-di-α-cumylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)butane, and 2,2-bis(4,4-di-t-octylperoxycyclohexyl)butane.
Specific examples of azo compounds include 2,2'-azobisisobutyronitrile [AIBN], 2,2'-azobis(2,4-dimethylvaleronitrile) [ABVN], 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), and 2,2'-azobis(isobutyrate)dimethyl.
In producing the specific (meth)acrylic copolymer, it is preferable to use a polymerization initiator that does not cause a graft reaction during the polymerization reaction, and it is particularly preferable to use an azo compound.

During the polymerization reaction, only one type of polymerization initiator may be used, or two or more types may be used.

The amount of polymerization initiator used is not particularly limited and can be set appropriately depending on, for example, the molecular weight of the desired specific (meth)acrylic copolymer.

In producing the specific (meth)acrylic copolymer, a chain transfer agent may be used, if necessary.
Examples of the chain transfer agent include cyanoacetic acid, alkyl ester compounds of cyanoacetic acid having 1 to 8 carbon atoms, bromoacetic acid, alkyl ester compounds of bromoacetic acid having 1 to 8 carbon atoms, aromatic compounds such as α-methylstyrene, anthracene, phenanthrene, fluorene, and 9-phenylfluorene, aromatic nitro compounds such as p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and p-nitrotoluene, benzoquinone derivatives such as benzoquinone and 2,3,5,6-tetramethyl-p-benzoquinone, borane derivatives such as tributylborane, carbon tetrabromide, ... Examples of the halogenated hydrocarbon compounds include carbon chloride, 1,1,2,2-tetrabromoethane, tribromoethylene, trichloroethylene, bromotrichloromethane, tribromomethane, and 3-chloro-1-propene, aldehyde compounds such as chloral and furaldehyde, alkyl mercaptan compounds having 1 to 18 carbon atoms, aromatic mercaptan compounds such as thiophenol and toluene mercaptan, mercaptoacetic acid, alkyl ester compounds of mercaptoacetic acid having 1 to 10 carbon atoms, hydroxyalkyl mercaptan compounds having 1 to 12 carbon atoms, and terpene compounds such as pinene and terpinolene.

When a chain transfer agent is used in the production of the specific (meth)acrylic copolymer, the amount of the chain transfer agent used is not particularly limited and can be set appropriately depending on, for example, the molecular weight of the target specific (meth)acrylic copolymer.

The polymerization temperature is not particularly limited and can be set appropriately depending on, for example, the molecular weight of the desired specific (meth)acrylic copolymer.

[Crosslinking Agent]
The pressure-sensitive adhesive composition of the present disclosure contains a crosslinking agent.
The type of crosslinking agent is not particularly limited.
Examples of the crosslinking agent include an epoxy-based crosslinking agent, an isocyanate-based crosslinking agent, a metal chelate-based crosslinking agent, and an aziridine-based crosslinking agent.
The crosslinking agent is preferably at least one type of crosslinking agent selected from the group consisting of, for example, epoxy-based crosslinking agents, isocyanate-based crosslinking agents, and metal chelate-based crosslinking agents, and more preferably an epoxy-based crosslinking agent.

In this disclosure, "epoxy-based crosslinking agent" refers to a compound having two or more epoxy groups in one molecule (so-called bifunctional or higher epoxy compound). Also, "isocyanate-based crosslinking agent" refers to a compound having two or more isocyanate groups in one molecule (so-called polyisocyanate compound). Also, "metal chelate-based crosslinking agent" refers to a metal chelate compound that functions as a crosslinking agent. Also, "aziridine-based crosslinking agent" refers to a compound having two or more aziridine groups in one molecule (so-called bifunctional or higher aziridine compound).

The type of the epoxy crosslinking agent is not particularly limited.
Specific examples of epoxy crosslinking agents include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polytetramethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol di ... Examples of such glycidyl ethers include glycerol polyglycidyl ether, resorcinol diglycidyl ether, 2,2-dibromoneopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, tris(glycidyl)isocyanurate, tris(glycidoxyethyl)isocyanurate, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-1,3-benzenedi(methanamine).

As the epoxy crosslinking agent, a commercially available product can be used.
Examples of commercially available epoxy crosslinking agents include "TETRAD (registered trademark)-X" and "TETRAD (registered trademark)-C" (both manufactured by Mitsubishi Gas Chemical Company, Inc.), and "Denacol (registered trademark) EX-201" and "Denacol (registered trademark) EX-931" (both manufactured by Nagase ChemteX Corporation).

The type of the isocyanate-based crosslinking agent is not particularly limited.
Examples of the isocyanate crosslinking agent include aromatic polyisocyanate compounds such as xylylene diisocyanate (XDI), diphenylmethane diisocyanate, triphenylmethane triisocyanate, and tolylene diisocyanate (TDI); aliphatic polyisocyanate compounds or alicyclic polyisocyanate compounds such as hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate (PDI), isophorone diisocyanate, and hydrogenated aromatic polyisocyanate compounds.
Further, examples of the isocyanate-based crosslinking agent include dimers, trimers, and pentamers of the above polyisocyanate compounds, adducts of the above polyisocyanate compounds with polyol compounds such as trimethylolpropane, and biuret products of the above polyisocyanate compounds.

As the isocyanate-based crosslinking agent, a commercially available product can be used.
Examples of commercially available isocyanate crosslinking agents include "Coronate (registered trademark) HX", "Coronate (registered trademark) HL-S", "Coronate (registered trademark) L", "Coronate (registered trademark) L-45E", "Coronate (registered trademark) 2031", "Coronate (registered trademark) 2037", "Coronate (registered trademark) 2234", "Coronate (registered trademark) 2785", "Aquanate (registered trademark) 200", and "Aquanate (registered trademark) 210" (all manufactured by Tosoh Corporation), "Sumidur (registered trademark) N3300", "Desmodur (registered trademark) N3400", and "Sumidur (registered trademark) N75" (all manufactured by Sumika Covestro Urethane Co., Ltd.), "Duranate (registered trademark) E-405-80T", "Duranate (registered trademark) AE700-100", "Duranate (registered trademark) Examples of such polyurethane foams include "Duranate (registered trademark) 24A-100" and "Duranate (registered trademark) TSE-100" (all manufactured by Asahi Kasei Corporation), as well as "Takenate (registered trademark) D-110N", "Takenate (registered trademark) D-120N", "Takenate (registered trademark) M-631N", "MT-Olestar (registered trademark) NP1200", and "STABIO (registered trademark) XD-340N" (all manufactured by Mitsui Chemicals, Inc.).

The type of the metal chelate crosslinking agent is not particularly limited.
Examples of metal chelate crosslinking agents include aluminum chelate compounds, titanium chelate compounds, zirconium chelate compounds, and cobalt chelate compounds.
As the metal chelate crosslinking agent, an aluminum chelate compound is preferred.
Specific examples of aluminum chelate compounds include aluminum monoacetylacetonate bis(ethylacetoacetate), aluminum tris(ethylacetoacetate), and aluminum tris(acetylacetonate).

As the metal chelate crosslinking agent, a commercially available product can be used.
Examples of commercially available metal chelate crosslinking agents include Aluminum Chelate A [trade name, aluminum tris(acetylacetonate), manufactured by Kawaken Fine Chemicals Co., Ltd.], Aluminum Chelate D [trade name, aluminum monoacetylacetonate bis(ethylacetoacetate), manufactured by Kawaken Fine Chemicals Co., Ltd.], and ALCH-TR [trade name, aluminum tris(ethylacetoacetate), manufactured by Kawaken Fine Chemicals Co., Ltd.].

The adhesive composition of the present disclosure may contain only one type of crosslinking agent, or may contain two or more types.

The content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited, but for example, it is preferably 0.001 parts by mass to 1 part by mass, more preferably 0.005 parts by mass to 0.5 parts by mass, even more preferably 0.01 parts by mass to 0.1 parts by mass, and particularly preferably 0.01 parts by mass to 0.05 parts by mass, relative to 100 parts by mass of the specific (meth)acrylic copolymer.
When the content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is 0.001 part by mass or more relative to 100 parts by mass of the specific (meth)acrylic copolymer, the pressure-sensitive adhesive layer tends to have higher adhesive strength to an adherend in a high-temperature environment of 150°C.
When the content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is 1 part by mass or less relative to 100 parts by mass of the specific (meth)acrylic copolymer, the pressure-sensitive adhesive layer tends to have higher adhesive strength to an adherend in a temperature environment of 25° C. The reason for this is believed to be that the pressure-sensitive adhesive layer formed is less likely to become hard.

<<Ratio of the number of moles of crosslinkable functional groups in a crosslinking agent to the number of moles of carboxyl groups in a specific (meth)acrylic copolymer>>
The ratio of the number of moles of crosslinkable functional groups in the crosslinking agent to the number of moles of carboxy groups in the specific (meth)acrylic copolymer [i.e., the number of moles of crosslinkable functional groups in the crosslinking agent/the number of moles of carboxy groups in the specific (meth)acrylic copolymer] is not particularly limited, but is, for example, preferably 0.00001 to 0.1, more preferably 0.00002 to 0.01, even more preferably 0.00002 to 0.006, and particularly preferably 0.0003 to 0.0016.
When the ratio of the number of moles of crosslinkable functional groups in the crosslinking agent to the number of moles of carboxy groups in the specific (meth)acrylic copolymer is 0.00001 or more, the adhesive strength of the pressure-sensitive adhesive layer to an adherend in a high-temperature environment of 150°C tends to be higher.
When the ratio of the number of moles of crosslinkable functional groups in the crosslinking agent to the number of moles of carboxy groups in the specific (meth)acrylic copolymer is 0.1 or less, the adhesive strength of the pressure-sensitive adhesive layer to an adherend in a temperature environment of 25°C tends to be higher.

In this disclosure, the term "crosslinkable functional group in the crosslinking agent" refers to a functional group possessed by the crosslinking agent that is capable of undergoing a crosslinking reaction with a carboxy group in the specific (meth)acrylic copolymer. For example, when the crosslinking agent is an isocyanate-based crosslinking agent, this refers to an isocyanate group, and when the crosslinking agent is an epoxy crosslinking agent, this refers to an epoxy group.

In this disclosure, the number of moles of crosslinkable functional groups means the total number of moles of all crosslinkable functional groups when there are multiple crosslinkable functional groups.

The ratio of the number of moles of crosslinkable functional groups in the crosslinking agent to the number of moles of carboxy groups in the specific (meth)acrylic copolymer [i.e., the number of moles of crosslinkable functional groups in the crosslinking agent/the number of moles of carboxy groups in the specific (meth)acrylic copolymer] can be calculated using the following formulas (1) to (3).

Molar number of crosslinkable functional groups in the crosslinking agent (unit: mmol)
= [content of crosslinkable functional group in crosslinking agent (unit: mass%)/solid content concentration of crosslinking agent (unit: mass%)×mixture amount of crosslinking agent [amount as solid content] (unit: g)]/chemical formula weight of crosslinkable functional group (unit: g/mol)×1000 (1)

Number of moles of carboxyl groups in a specific (meth)acrylic copolymer [unit: mmol]
= [Content of structural units derived from monomers having a carboxy group in specific (meth)acrylic copolymer (unit: mass%)/100×mixture amount of specific (meth)acrylic copolymer [amount as solid content] (unit: g)/molecular weight of structural units derived from monomers having a carboxy group (unit: g/mol)×number of carboxy groups in structural units derived from monomers having a carboxy group (valence)×1000] ... (2)

Ratio of the number of moles of crosslinkable functional groups in the crosslinking agent to the number of moles of carboxyl groups in the specific (meth)acrylic copolymer = Value obtained by calculation formula (1) / Value obtained by calculation formula (2) ... (3)

In addition, when the crosslinking agent is a metal chelate crosslinking agent, for example, a carboxy group contained in the specific (meth)acrylic copolymer forms a coordinate bond with a central metal in a metal chelate compound that is a metal chelate crosslinking agent, and therefore, by replacing the valence of the central metal with the number of functional groups, the number of moles of the crosslinkable functional groups in the crosslinking agent used for calculating the ratio of the number of moles of the crosslinkable functional groups in the crosslinking agent to the number of moles of the carboxy groups in the specific (meth)acrylic copolymer can be obtained.
For example, since the valence of the central metal in an aluminum chelate compound, which is a metal chelate crosslinking agent, is 3, the aluminum chelate compound can be calculated by replacing it with one having 3 moles of functional groups per mole.

When the crosslinking agent is a metal chelate crosslinking agent, the molar number of crosslinkable functional groups in the crosslinking agent is calculated by the following formula (4): When the crosslinking agent is a metal chelate crosslinking agent, the ratio of the molar number of crosslinkable functional groups in the crosslinking agent to the molar number of carboxy groups in the specific (meth)acrylic copolymer can be calculated by replacing the value calculated by formula (1) in the above formula (3) with the value calculated by formula (4) below.
Molar number of crosslinkable functional groups in the crosslinking agent (unit: mmol)
=A×B/C×1000...(4)
A = metal valence of metal chelate crosslinking agent B = amount of metal chelate crosslinking agent blended [amount as solid content] (unit: g)
C = molecular weight of metal chelate crosslinker (unit: g/mol)

[Organic Solvent]
The pressure-sensitive adhesive composition of the present disclosure may contain an organic solvent.
When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, the coatability can be improved.
As the organic solvent, for example, the same organic solvent as that used in the polymerization reaction of the specific (meth)acrylic copolymer can be used.

When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, it may contain only one type of organic solvent, or may contain two or more types of organic solvent.

When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, the content of the organic solvent is not particularly limited and can be set appropriately depending on the purpose.

[Other ingredients]
The pressure-sensitive adhesive composition of the present disclosure may contain components other than the components described above (so-called other components) as necessary, provided that the effects of the composition are not impaired.
Examples of other components include various additives such as polymers other than the specific (meth)acrylic copolymer, crosslinking catalysts, tackifiers, antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., ultraviolet absorbers), and antistatic agents.

When the pressure-sensitive adhesive composition of the present disclosure contains other components, the content of the other components can be set appropriately within a range that does not impair the effect of the pressure-sensitive adhesive composition of the present disclosure.

<Applications>
The application of the pressure-sensitive adhesive composition of the present disclosure is not particularly limited.
The pressure-sensitive adhesive composition of the present disclosure can form a pressure-sensitive adhesive layer that exhibits high adhesive strength to an adherend not only in a temperature environment of 25°C but also in a high-temperature environment of 150°C. Therefore, the pressure-sensitive adhesive composition is suitable as a pressure-sensitive adhesive composition for temporary fixation used in situations exposed to high-temperature environments, for example, in the manufacturing process of electronic devices.

[Adhesive sheet]
The pressure-sensitive adhesive sheet of the present disclosure includes a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure.
The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present disclosure exhibits high adhesive strength to an adherend in both temperature environments of 25° C. and 150° C. For this reason, the pressure-sensitive adhesive sheet of the present disclosure is not easily peeled off from an adherend and is not easily displaced from its initial attachment position on an adherend not only in a temperature environment of 25° C. but also in a high-temperature environment of 150° C.

The thickness of the pressure-sensitive adhesive layer provided in the pressure-sensitive adhesive sheet of the present disclosure is not particularly limited.
The thickness of the pressure-sensitive adhesive layer is generally 1 μm to 100 μm, preferably 3 μm to 50 μm, and more preferably 5 μm to 30 μm.

In the present disclosure, the "thickness of the pressure-sensitive adhesive layer" means the average thickness of the pressure-sensitive adhesive layer.
The average thickness of the pressure-sensitive adhesive layer is a value measured by the following method.
The arithmetic mean value of the thicknesses of the pressure-sensitive adhesive layer measured at 10 randomly selected points in the thickness direction of the pressure-sensitive adhesive layer is calculated, and the obtained value is regarded as the average thickness of the pressure-sensitive adhesive layer. The thickness of the pressure-sensitive adhesive layer is measured using a film thickness meter.

The pressure-sensitive adhesive sheet of the present disclosure may be a substrate-free pressure-sensitive adhesive sheet that does not have a substrate, or a substrate-containing pressure-sensitive adhesive sheet that has a pressure-sensitive adhesive layer on one or both sides of a substrate.
When the adhesive sheet of the present disclosure is a substrate-free adhesive sheet that does not have a substrate, or when it is a substrate-containing adhesive sheet that has an adhesive layer on one side of a substrate, the exposed surface of the adhesive layer in the adhesive sheet of the present disclosure may be protected by a release film.

The release film is not particularly limited as long as it can be easily peeled off from the pressure-sensitive adhesive layer.
The release film may be, for example, a resin film having one or both sides subjected to a surface treatment with a release agent (so-called easy release treatment).
An example of the resin film is a polyester film, typically a polyethylene terephthalate (PET) film.
Examples of the release agent include silicone-based release agents (eg, silicone), wax-based release agents (eg, paraffin wax), and fluorine-based release agents (eg, fluorine-based resins).
The release film protects the surface of the pressure-sensitive adhesive layer until the pressure-sensitive adhesive sheet is put to practical use, and is peeled off at the time of use.

When the pressure-sensitive adhesive sheet of the present disclosure includes a substrate, the substrate is not particularly limited as long as a pressure-sensitive adhesive layer can be formed on the substrate.
Examples of the substrate include films containing resins such as polyolefin resins (e.g., polyethylene (PE) and polypropylene (PP)), polyester resins (e.g., polyethylene terephthalate (PET)), acetate resins (e.g., triacetyl cellulose resin), polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, acrylic resins, vinyl chloride resins, ABS (Acrylonitrile Butadiene Styrene) resins, and fluorine-based resins.

The surface of the substrate on which the adhesive layer is provided may be subjected to a surface treatment such as corona discharge treatment or plasma discharge treatment (so-called adhesion-enhancing treatment) in order to improve adhesion between the substrate and the adhesive layer.

The substrate may contain various additives, such as plasticizers, colorants (eg, dyes and pigments), heat stabilizers, light stabilizers, antistatic agents, flame retardants, antioxidants, and the like.
The substrate may be partially or entirely patterned.

The thickness of the substrate is not particularly limited, but is generally 10 μm to 500 μm, preferably 10 μm to 300 μm, more preferably 10 μm to 200 μm, and even more preferably 10 μm to 100 μm.

"Substrate thickness" in this disclosure means the average thickness of the substrate.
The average thickness of the substrate is a value measured by a method conforming to the above-mentioned method for measuring the average thickness of the pressure-sensitive adhesive layer.

[Method of producing adhesive sheet]
The method for producing the pressure-sensitive adhesive sheet of the present disclosure is not particularly limited.
The pressure-sensitive adhesive sheet of the present disclosure can be produced by known methods.
The pressure-sensitive adhesive sheet of the present disclosure can be produced, for example, by the following method.
In the case of a substrate-free type adhesive sheet, first, the adhesive composition of the present disclosure is applied to the easy-release treated surface of a release film to form a coating film on the release film.Then, the formed coating film is dried to form an adhesive film on the release film.Then, the exposed surface of the formed adhesive film is laminated and stuck to the easy-release treated surface of a separately prepared release film, and then cured to produce a substrate-free type adhesive sheet having a laminated structure of release film/adhesive layer/release film.

In the case of a substrate-type adhesive sheet, first, the adhesive composition of the present disclosure is applied to the easy-to-adhere surface of the substrate to form a coating film on the substrate. The formed coating film is then dried to form an adhesive film on the substrate. Next, the exposed surface of the formed adhesive film is laminated to the easy-to-release treated surface of a release film, and then cured to produce a substrate-type adhesive sheet having a laminated structure of release film/adhesive layer/substrate.

As another method, for example, the following method can be mentioned.
The adhesive composition of the present disclosure is applied to the easy-release treated surface of a release film to form a coating film on the release film.Then, the formed coating film is dried to form an adhesive film on the release film.Then, the exposed surface of the formed adhesive film is laminated on the easy-adhesion treated surface of the substrate, and then cured to produce a substrate-type adhesive sheet having a laminated structure of substrate/adhesive layer/release film.

The method for applying the pressure-sensitive adhesive composition is not particularly limited.
Examples of methods for applying the pressure-sensitive adhesive composition include known methods using a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, knife coater, spray coater, bar coater, applicator, and the like.
The amount of the pressure-sensitive adhesive composition to be applied is not particularly limited, and is appropriately set depending on, for example, the thickness of the pressure-sensitive adhesive layer to be formed.

The method for drying the coating film is not particularly limited.
Examples of methods for drying the coating film include natural drying, heat drying, hot air drying, and vacuum drying.
The drying temperature and drying time of the coating film are not particularly limited, and are appropriately set depending on the thickness of the coating film, the amount of the organic solvent in the coating film, and the like.
An example of the drying conditions is drying using a hot air dryer at 70° C. to 120° C. for 30 to 180 seconds.

Curing is carried out, for example, for 4 to 7 days in an environment with an ambient temperature of 20°C to 35°C and a relative humidity of 45% to 55% (i.e., 45% RH to 55% RH).

The adhesive composition and the like of the present disclosure will be explained in more detail below with reference to examples. The present disclosure is not limited to the following examples as long as they do not exceed the gist of the disclosure.

[Production of (meth)acrylic copolymer]
[Production Example A-1]
In a reaction vessel equipped with a stirrer and a thermometer, 130 parts by mass of ethyl acetate (organic solvent for polymerization), 40 parts by mass of stearyl methacrylate [STMA; monomer having a linear alkyl group with 16 or more carbon atoms], 25 parts by mass of acrylic acid [AA; monomer having a carboxy group], 35 parts by mass of n-butyl acrylate [n-BA; other monomer], and 0.125 parts by mass of 2,2'-azobisisobutyronitrile [AIBN; polymerization initiator] were mixed to obtain a mixture. Next, the temperature of the mixture in the reaction vessel was raised to the reflux temperature, and then the mixture was stirred while maintaining the temperature and polymerized for 6 hours to obtain a polymerization reaction product. The obtained polymerization reaction product was diluted with ethyl acetate so that the solid content concentration was 40% by mass, and a solution of (meth)acrylic copolymer A-1 was obtained.

The term "solid content concentration" used herein means the mass ratio of the (meth)acrylic copolymer A-1 in the solution of the (meth)acrylic copolymer A-1.
The same applies to each of the solutions of the following (meth)acrylic copolymers A-2 to A-17.

[Production Examples A-2 to A-13, A-16, and A-17]
In Production Examples A-2 to A-13, A-16, and A-17, the same operation as in Production Example A-1 was carried out except that the monomer composition of the (meth)acrylic copolymer was changed to the monomer composition shown in Table 1, and solutions of (meth)acrylic copolymers A-2 to A-13, A-16, and A-17 having a solid content concentration of 40 mass% were obtained.

[Production Examples A-14 and A-15]
In Production Examples A-14 and A-15, the same operation as in Production Example A-1 was performed except that the weight average molecular weight of the (meth)acrylic copolymer was adjusted to the weight average molecular weight shown in Table 1 by adjusting at least one of the amount of the organic solvent used and the amount of the polymerization initiator used, to obtain solutions of (meth)acrylic copolymers A-14 and A-15 having a solid content concentration of 40 mass%.

The monomer compositions (unit: mass%) of (meth)acrylic copolymers A-1 to A-17 and the weight average molecular weights (Mw) of (meth)acrylic copolymers A-1 to A-17 are shown in Table 1.

The weight average molecular weights of (meth)acrylic copolymers A-1 to A-17 were measured using the same method as for measuring the weight average molecular weight of the specific (meth)acrylic copolymers described above.

Of the (meth)acrylic copolymers A-1 to A-17 obtained above, (meth)acrylic copolymers A-1 to A-7 and A-13 to A-15 correspond to the specific (meth)acrylic copolymers in this disclosure.

Details of each monomer listed in Table 1 are as follows.
<Monomer Having a Linear Alkyl Group Having 16 or More Carbon Atoms>
"STMA": stearyl methacrylate [number of carbon atoms in alkyl group: 18]
"VMA": behenyl methacrylate [number of carbon atoms in alkyl group: 22]
"STA": stearyl acrylate [number of carbon atoms in alkyl group: 18]
<Monomer having a carboxy group>
"AA": acrylic acid "MAA": methacrylic acid

<Other monomers>
<<Monomers with hydroxyl groups>>
"2HEA": 2-hydroxyethyl acrylate
<<Monomers having a linear alkyl group with less than 16 carbon atoms>>
"n-BA": n-butyl acrylate (number of carbon atoms in the alkyl group: 4)
"LA": Lauryl acrylate [number of carbon atoms in alkyl group: 12]
<<Monomers having branched alkyl groups with 16 or more carbon atoms>>
"2DTMA": 2-decyltetradecanyl methacrylate

In Table 1, a "-" in the monomer composition column means that the monomer in that column is not used.

[Preparation of Pressure-Sensitive Adhesive Composition]
Example 1
100 parts by mass (solid content equivalent) of the solution of (meth)acrylic copolymer A-1 and 0.01 parts by mass (solid content equivalent) of a crosslinking agent [product name: TETRAD (registered trademark)-X, solid content concentration: 100% by mass, epoxy crosslinking agent, manufactured by Mitsubishi Gas Chemical Company, Inc.] were thoroughly mixed to obtain a pressure-sensitive adhesive composition of Example 1.
In the obtained pressure-sensitive adhesive composition, the ratio of the number of moles of crosslinkable functional groups in the crosslinking agent to the number of moles of carboxy groups in the (meth)acrylic copolymer [i.e., the number of moles of crosslinkable functional groups in the crosslinking agent/the number of moles of carboxy groups in the (meth)acrylic copolymer] was 0.0003.

The ratio of the number of moles of crosslinkable functional groups in the crosslinking agent to the number of moles of carboxy groups in (meth)acrylic copolymer A-1 was calculated in the same manner as the ratio of the number of moles of crosslinkable functional groups in the crosslinking agent to the number of moles of carboxy groups in a specific (meth)acrylic copolymer. Specifically, it was calculated as follows. Note that TETRAD (registered trademark)-X, an epoxy crosslinking agent, has a solids concentration of 100% by mass and an epoxy group content of 47.8% by mass. The chemical formula weight of the epoxy group is 43. The molecular weight of the constituent unit derived from acrylic acid, a monomer having a carboxy group, is 72.

Formula (1)
Molar number of crosslinkable functional groups in the crosslinking agent (unit: mmol)
= Content of crosslinkable functional group in crosslinking agent (unit: mass%)/Solid content concentration of crosslinking agent (unit: mass%)×Amount of crosslinking agent (amount as solid content) (unit: g)/Chemical formula weight of crosslinkable functional group (unit: g/mol)×1000
=47.8 (mass%)/100 (mass%) x 0.01 (g)/43 (g/mol) x 1000 = 0.1111...≒0.111

Formula (2)
Molar number of carboxy groups in (meth)acrylic copolymer A-1 [unit: mmol]
= [Content of structural units derived from monomers having a carboxy group in (meth)acrylic copolymer A-1 (unit: mass %)/100×amount of (meth)acrylic copolymer A-1 [amount as solid content] (unit: g)/molecular weight of structural units derived from monomers having a carboxy group (unit: g/mol)×number of carboxy groups in structural units derived from monomers having a carboxy group (valence)×1000]
= [25 (mass%)/100 x 100 (g)/72 (g/mol) x 1 x 1000] = 347.22...≒347.2

Formula (3)
The ratio of the number of moles of crosslinkable functional groups in the crosslinking agent to the number of moles of carboxy groups in the (meth)acrylic copolymer A-1 [i.e., the number of moles of crosslinkable functional groups in the crosslinking agent/the number of moles of carboxy groups in the (meth)acrylic copolymer A-1]
= Value obtained using formula (1) / Value obtained using formula (2) = 0.111/347.2 = 0.00031 ... ≒ 0.0003

[Examples 2 to 17]
The same procedure as in Example 1 was carried out except that the composition of the adhesive composition in Example 1 was changed to the composition shown in Table 2, to obtain each of the adhesive compositions of Examples 2 to 17.

Comparative Examples 1 to 7
The same procedure as in Example 1 was carried out except that the composition of the adhesive composition in Example 1 was changed to the composition shown in Table 3, to obtain each of the adhesive compositions of Comparative Examples 1 to 7.

The compositions of the pressure-sensitive adhesive compositions of Examples 1 to 17 and Comparative Examples 1 to 7, and the ratio of the number of moles of crosslinkable functional groups in the crosslinking agent to the number of moles of carboxy groups in the (meth)acrylic copolymer [i.e., the number of moles of crosslinkable functional groups in the crosslinking agent/the number of moles of carboxy groups in the (meth)acrylic copolymer] are shown in Tables 2 and 3.
The molecular weight of the constituent unit derived from methacrylic acid, which is a monomer having a carboxyl group, used in calculating the ratio of the number of moles of the crosslinkable functional group in the crosslinking agent to the number of moles of the carboxy group in the (meth)acrylic copolymer is 86.

[Preparation of Pressure-Sensitive Adhesive Sheet for Evaluation]
The adhesive composition prepared above was applied to one side of a polyimide film (trade name: Kapton (registered trademark) 100H, manufactured by Toray DuPont Co., Ltd.) as a substrate so that the thickness after drying was 10 μm, forming a coating film. Next, the formed coating film was dried using a hot air circulation dryer under drying conditions of a drying temperature of 100 ° C. and a drying time of 1 minute, forming an adhesive film on the polyimide film. Next, the surface on which the adhesive film was exposed was laminated and attached to the easy-to-release treated surface of a release film (trade name: Film Vina (registered trademark) 100E-0010 No. 23, thickness: 100 μm, manufactured by Fujimori Kogyo Co., Ltd.) that had been easily peeled with a silicone-based release treatment agent, and then aged for 168 hours in an environment of an atmospheric temperature of 25 ° C. and 50% RH to allow the crosslinking reaction to proceed, thereby preparing an evaluation adhesive sheet. The evaluation adhesive sheet prepared has a laminated structure of a substrate (polyimide film) / adhesive layer / release film.

[Measurement and Evaluation]
The adhesive sheet for evaluation prepared above was cut into a size of 25 mm × 150 mm to prepare an adhesive sheet piece for evaluation. In addition, a glass plate (product name: soda lime glass (ordinary glass), thickness: 1.8 mm, manufactured by Kawamura Kyuzo Shoten Co., Ltd.) was prepared as an adherend.
The release film was peeled off from the adhesive sheet piece for evaluation, and the surface of the adhesive layer exposed by peeling was laminated on one side of a glass plate, and then a 2 kg roller was moved back and forth once to press and bond the two pieces together to prepare a test piece. The prepared test piece has a laminated structure of adherend (glass plate)/adhesive sheet piece for evaluation [adhesive layer/substrate (polyimide film)]. Next, the prepared test piece was left to stand for 30 minutes in an environment with an atmospheric temperature of 25°C and 50% RH. For the test piece after standing, the adhesive strength (unit: N/25 mm) when the adhesive sheet piece for evaluation (configuration: adhesive layer/polyimide film) was peeled off 180° in the long side (150 mm) direction from the glass plate was measured using a Tensilon universal material testing machine (model number: RTF-1350) manufactured by A&D Co., Ltd. as a measuring device, under the condition of a peel speed of 300 mm/min. Then, evaluation was performed according to the following evaluation criteria. The results are shown in Tables 2 and 3.
In the following evaluation criteria, "A", "B", and "C" are at levels that are acceptable for practical use, with "A" being the most preferable.

-Evaluation criteria-
A: The adhesive strength is 1.0 N/25 mm or more.
B: The adhesive strength is 0.5 N/25 mm or more and less than 1.0 N/25 mm.
C: The adhesive strength is 0.3 N/25 mm or more and less than 0.5 N/25 mm.
D: The adhesive strength is less than 0.3 N/25 mm.

The adhesive sheet for evaluation prepared above was cut into a size of 25 mm × 150 mm to prepare an adhesive sheet piece for evaluation. In addition, a glass plate (product name: soda lime glass (ordinary glass), thickness: 1.8 mm, manufactured by Kawamura Kyuzo Shoten Co., Ltd.) was prepared as an adherend.
The release film was peeled off from the adhesive sheet piece for evaluation, and the surface of the adhesive layer exposed by peeling was laminated on one side of a glass plate, and then a 2 kg roller was moved back and forth once to press and bond the two pieces together to prepare a test piece. The prepared test piece has a laminated structure of adherend (glass plate)/adhesive sheet piece for evaluation [adhesive layer/substrate (polyimide film)]. Next, the prepared test piece was left to stand for 30 minutes in an environment with an atmospheric temperature of 150°C. For the test piece after standing, the adhesive strength (unit: N/25 mm) when the adhesive sheet piece for evaluation (configuration: adhesive layer/polyimide film) was peeled off 180° in the long side (150 mm) direction from the glass plate in an environment with an atmospheric temperature of 150°C was measured using a Tensilon universal material testing machine (model number: RTF-1350) manufactured by A&D Co., Ltd. as a measuring device, under the condition of a peel speed of 300 mm/min. Then, evaluation was performed according to the following evaluation criteria. The results are shown in Tables 2 and 3.
In the following evaluation criteria, "A", "B", and "C" are at levels that are acceptable for practical use, with "A" being the most preferable.

-Evaluation criteria-
A: The adhesive strength is 8.0 N/25 mm or more.
B: The adhesive strength is 5.0 N/25 mm or more and less than 8.0 N/25 mm.
C: The adhesive strength is 2.0 N/25 mm or more and less than 5.0 N/25 mm.
D: The adhesive strength is less than 2.0 N/25 mm.

Details of the crosslinking agents described in Table 2 and/or Table 3 are as follows.
<Epoxy-based crosslinking agent>
"TETRAD-X" (product name, chemical name: N,N,N',N'-tetraglycidyl-1,3-benzenedi(methaneamine), epoxy group content: 47.8% by mass, solid content: 100% by mass, manufactured by Mitsubishi Gas Chemical Company, Inc.)
"Denacol EX-201" (product name, chemical name: resorcinol diglycidyl ether, epoxy group content: 38.7% by mass, solid content: 100% by mass, manufactured by Nagase ChemteX Corporation)
<Isocyanate-based crosslinking agent>
"Coronate L-45E" (trade name, tolylene diisocyanate compound (adduct of tolylene diisocyanate (TDI) and trimethylolpropane (TMP)), isocyanate group content: 7.9% by mass, solid content: 45% by mass, manufactured by Tosoh Corporation)
<Metal chelate crosslinking agent>
"Aluminum Chelate A" (trade name, chemical name: aluminum tris(acetylacetonate), molecular weight: 324, manufactured by Kawaken Fine Chemicals Co., Ltd.)
The above-mentioned "TETRAD", "Denacol", and "Coronate" are all registered trademarks.

In Tables 2 and 3, the values shown in the "blended amount" column are all values calculated as solid content.
In Table 3, "-" in the column "Number of moles of crosslinkable functional groups in crosslinking agent/number of moles of carboxy groups in (meth)acrylic copolymer" means that there is no corresponding item in that column.

As shown in Table 2, it was confirmed that the adhesive layers formed from the adhesive compositions of Examples 1 to 17 exhibited high adhesive strength to the adherend in both temperature environments of 25°C and 150°C.

On the other hand, as shown in Table 3, it was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 1, in which the content of structural units derived from monomers having a carboxy group in the (meth)acrylic copolymer was less than 15 mass% relative to the total structural units, did not exhibit high adhesive strength in a high-temperature environment of 150°C.
It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 2, in which the content of structural units derived from monomers having a carboxy group in the (meth)acrylic copolymer exceeds 40 mass% relative to all structural units, does not exhibit high adhesive strength in a temperature environment of 25°C.
It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 3, in which the (meth)acrylic copolymer contains a constituent unit derived from a monomer having a hydroxyl group instead of a constituent unit derived from a monomer having a carboxy group, does not exhibit high adhesive strength in a high-temperature environment of 150°C.
It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 4, in which the content of structural units derived from monomers having a linear alkyl group having 16 or more carbon atoms in the (meth)acrylic copolymer is less than 20 mass% relative to all structural units, does not exhibit high adhesive strength in a high-temperature environment of 150°C.
It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 5, in which the content of structural units derived from monomers having a linear alkyl group having 16 or more carbon atoms in the (meth)acrylic copolymer exceeded 60 mass% with respect to all structural units, did not exhibit high adhesive strength in a temperature environment of 25°C.
It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 6, in which the (meth)acrylic copolymer contains a constituent unit derived from a monomer having a linear alkyl group having less than 16 carbon atoms instead of a constituent unit derived from a monomer having a linear alkyl group having 16 or more carbon atoms, does not exhibit high adhesive strength in a high-temperature environment of 150°C.
It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 7, in which the (meth)acrylic copolymer contains a structural unit derived from a monomer having a branched alkyl group having 16 or more carbon atoms instead of a structural unit derived from a monomer having a linear alkyl group having 16 or more carbon atoms, does not exhibit high adhesive strength in a high-temperature environment of 150°C.

Claims (6)

a (meth)acrylic copolymer containing 20% by mass to 60% by mass of structural units derived from a monomer having a linear alkyl group having 16 or more carbon atoms, based on all structural units, and 15% by mass to 40% by mass of structural units derived from a monomer having a carboxy group, based on all structural units;
A cross-linking agent;
A pressure-sensitive adhesive composition comprising: The pressure-sensitive adhesive composition according to claim 1, wherein the content of the crosslinking agent is 0.01 to 0.05 parts by mass per 100 parts by mass of the (meth)acrylic copolymer. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the crosslinking agent is an epoxy-based crosslinking agent. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the weight-average molecular weight of the (meth)acrylic copolymer is 100,000 to 300,000. The pressure-sensitive adhesive composition according to any one of claims 1 to 4, wherein the ratio of the number of moles of crosslinkable functional groups in the crosslinking agent to the number of moles of carboxy groups in the (meth)acrylic copolymer is 0.00002 to 0.006. An adhesive sheet having an adhesive layer formed from the adhesive composition according to any one of claims 1 to 5.