JP6943732B2 - Adhesive composition for protective film and protective film - Google Patents

Description

The present invention relates to an adhesive composition for a protective film and a protective film.

When processing or transporting articles such as metal plates, painted steel plates, and synthetic resin plates, a protective film is attached to the surface of the articles to prevent damage and stains on the articles. Such a protective film is peeled off and removed from the article (that is, the adherend) when the surface protection becomes unnecessary.
As the pressure-sensitive adhesive used for the protective film, for example, a monomer containing a hydroxyl group as a reactive functional group is contained as a copolymerization component in an amount of 0.1% by mass to 10% by mass, and the glass transition temperature (Tg) is high. Dimethyl having a polyoxyalkylene group of 0.01 parts by mass to 2.0 parts by mass with respect to 100 parts by mass of the acrylic copolymer (A) at -60 ° C to -40 ° C and 100 parts by mass of the acrylic copolymer (A). Processing process protection containing the silicon compound (B) and the cross-linking agent (C) having 0.1 to 1.5 equivalents of isocyanate groups with respect to the reactive functional groups in the acrylic copolymer (A). Adhesive compositions for films are known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2009-292959

By the way, the protective film is required to prevent slippage, dropout, etc. while surface protection is required. In order to secure such characteristics, a pressure-sensitive adhesive capable of forming a pressure-sensitive adhesive layer having a high cohesive force is generally used as the protective film.
However, when an article to which a protective film having a highly cohesive adhesive layer is attached is punched, the adhesive derived from the adhesive layer may adhere to the cutting blade in the form of powder. Such a phenomenon is called "powder dropping" and can be a serious problem especially in articles used in precision electronic devices.
Further, when the article to which the protective film is attached is heat-treated, the adhesive strength of the pressure-sensitive adhesive layer provided on the protective film can be increased. When the adhesive strength of the pressure-sensitive adhesive layer is excessively increased, contamination (for example, adhesive residue and cloudiness) due to a part of the pressure-sensitive adhesive derived from the pressure-sensitive adhesive layer remaining on the surface of the article after the protective film is peeled off and removed. May be confirmed.
Therefore, the adhesive used for the protective film is less likely to cause powder to fall off, and even when exposed to a high temperature environment, for example, a temperature environment of 80 ° C. or higher, the surface of the adherend is exposed at the time of peeling. It is required to be able to form an adhesive layer that is hard to contaminate.

Regarding the above points, it is said that the pressure-sensitive adhesive composition for a protective film described in Patent Document 1 can form a pressure-sensitive adhesive layer without adhesive residue and powder removal, but there is room for improvement in powder removal.

The problem to be solved by the present invention is adhesion for a protective film capable of forming an adhesive layer that is less likely to cause powder falling and that is less likely to contaminate the surface of the adherend at the time of peeling even when exposed to a high temperature environment. To provide an agent composition.
Further, the problem to be solved by the present invention is to provide a protective film provided with an adhesive layer which is less likely to cause powder falling and which is less likely to contaminate the surface of the adherend at the time of peeling even when exposed to a high temperature environment. To provide.

Specific means for solving the problem include the following aspects.
<1> Containing a structural unit derived from a fluorine-containing (meth) acrylic acid alkyl ester monomer of 6% by mass or more and 30% by mass or less with respect to all the structural units, and containing a carboxy group, a hydroxyl group, an amide group, and N. 0.1 for the (meth) acrylic polymer having at least one crosslinkable functional group selected from the group consisting of substituted amide groups and the crosslinkable functional group of the (meth) acrylic polymer. A pressure-sensitive adhesive composition for a protective film containing an equivalent amount or more and 0.8 equivalent amount or less of a cross-linking agent.
<2> The pressure-sensitive adhesive composition for a protective film according to <1>, wherein the (meth) acrylic polymer contains a structural unit derived from the monomer having a crosslinkable functional group.
<3> The pressure-sensitive adhesive composition for a protective film according to <1> or <2>, wherein the crosslinkable functional group is a hydroxyl group.
<4> The pressure-sensitive adhesive composition for a protective film according to <3>, wherein the hydroxyl value of the (meth) acrylic polymer is 3 mgKOH / g or more and less than 20 mgKOH / g.
<5> The above (meth) acrylic polymer further contains a structural unit derived from a (meth) acrylic acid alkyl ester monomer having a glass transition temperature of −60 ° C. or lower when used as a homopolymer <1. > The pressure-sensitive adhesive composition for a protective film according to any one of <4>.
<6> The pressure-sensitive adhesive composition for a protective film according to any one of <1> to <5>, wherein the weight average molecular weight of the (meth) acrylic polymer is 150,000 or more and 450,000 or less.
<7> The pressure-sensitive adhesive composition for a protective film according to any one of <1> to <6>, which is an isocyanate-based compound.
<8> The pressure-sensitive adhesive composition for a protective film according to any one of <1> to <7>, wherein the fluorine-containing (meth) acrylic acid alkyl ester monomer is a fluorine-containing methacrylic acid alkyl ester monomer. thing.
<9> A protective film comprising a base material and a pressure-sensitive adhesive layer provided on the base material and formed by the pressure-sensitive adhesive composition for a protective film according to any one of <1> to <8>. ..

According to the present invention, there is an adhesive composition for a protective film that is less likely to cause powder falling and can form an adhesive layer that is less likely to contaminate the surface of the adherend at the time of peeling even when exposed to a high temperature environment. Provided.
Further, according to the present invention, there is provided a protective film provided with an adhesive layer which is less likely to cause powder falling and which is less likely to contaminate the surface of the adherend at the time of peeling even when exposed to a high temperature environment.

Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be carried out with appropriate modifications within the scope of the object of the present invention.

The numerical range indicated by using "~" in the present specification means a range including the numerical values before and after "~" as the minimum value and the maximum value, respectively.
In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described stepwise. .. Further, in the numerical range described in the present specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.
In the present specification, a combination of two or more preferred embodiments is a more preferred embodiment.
In the present specification, the amount of each component means the total amount of a plurality of kinds of substances when a plurality of kinds of substances corresponding to each component are present, unless otherwise specified.

As used herein, the term "adhesive composition" means a liquid or paste-like substance after the (meth) acrylic polymer and the cross-linking agent are mixed and before the cross-linking reaction is completed.
As used herein, the term "adhesive layer" means a layer made of a substance after the cross-linking reaction in the pressure-sensitive adhesive composition is completed. The pressure-sensitive adhesive layer is, for example, a solid or gel-like layer.

In the present specification, the "(meth) acrylic polymer" is a polymer in which at least the main component of the monomers constituting the polymer is a monomer having a (meth) acryloyl group. Means. The monomer which is the main component here means the monomer having the largest content (mass%) among the monomers constituting the polymer. In some embodiments of the (meth) acrylic polymer of the present invention, the content of structural units derived from the monomer having a (meth) acryloyl group as the main component is 50% by mass or more of all the structural units.

In the present specification, "(meth) acrylic" is a term that includes both "acrylic" and "methacrylic", and "(meth) acrylate" is a term that includes both "acrylate" and "methacrylate". , "(Meta) acryloyl" is a term that includes both "acryloyl" and "methacrylic".

In the present specification, the "property that does not easily cause powder removal" may be referred to as "powder removal resistance", and the "property that does not easily contaminate the surface of the adherend at the time of peeling" may be referred to as "stain resistance".

[Adhesive composition for protective film]
The adhesive composition for a protective film of the present invention (hereinafter, appropriately referred to as “adhesive composition”) is a fluorine-containing (meth) acrylic acid alkyl ester of 6% by mass or more and 30% by mass or less based on all the constituent units. At least one crosslinkable functional group containing a structural unit derived from a monomer and selected from the group consisting of a carboxy group, a hydroxyl group, an amide group, and an N-substituted amide group (hereinafter, appropriately referred to as "specific crosslinkable functional group"). A (meth) acrylic polymer having (referred to as a group), and a cross-linking agent of 0.1 equivalent or more and 0.8 equivalent or less with respect to the cross-linking functional group of the (meth) acrylic polymer. including.
The pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer that does not easily cause powder to fall off and that does not easily contaminate the surface of the adherend during peeling even when exposed to a high temperature environment.
Although it is not clear why the pressure-sensitive adhesive composition of the present invention can exert such an effect, the present inventors speculate as follows. However, the following speculation does not limitly interpret the effect of the pressure-sensitive adhesive composition of the present invention, but is described as an example.

The protective film is required to prevent slippage, dropout, etc. while surface protection is required. Therefore, a pressure-sensitive adhesive capable of forming a pressure-sensitive adhesive layer having a high cohesive force is generally used for attaching the protective film to the adherend. However, when an article to which a protective film having a highly cohesive adhesive layer is attached is punched, the adhesive derived from the adhesive layer adheres to the cutting blade in the form of powder, so-called powder dropping may occur. ..
Further, when the article to which the protective film is attached is heat-treated, the adhesive strength of the pressure-sensitive adhesive layer provided on the protective film can be increased. When the adhesive strength of the pressure-sensitive adhesive layer is excessively increased, contamination (for example, adhesive residue and cloudiness) due to a part of the pressure-sensitive adhesive derived from the pressure-sensitive adhesive layer remaining on the surface of the article after the protective film is peeled off and removed. May be confirmed.
In order to suppress the powder falling as described above, it is conceivable to reduce the cohesive force of the pressure-sensitive adhesive layer to the extent that the protective film does not slip or fall off by lowering the cross-linking density of the pressure-sensitive adhesive layer. .. When the crosslink density of the pressure-sensitive adhesive layer is low, the pressure-sensitive adhesive layer is less likely to become hard and brittle, and thus it is considered that powder removal is less likely to occur. However, if the crosslink density of the pressure-sensitive adhesive layer is low, a so-called adhesive residue problem may occur. Therefore, it has been difficult to realize a pressure-sensitive adhesive composition having both powder removal resistance and stain resistance when exposed to a high temperature environment.

On the other hand, the pressure-sensitive adhesive composition of the present invention is a (meth) acrylic polymer containing a structural unit derived from a fluorine-containing (meth) acrylic acid alkyl ester monomer in a specific amount with respect to all the structural units. Therefore, when the formed pressure-sensitive adhesive layer is exposed to a high temperature environment, it is considered that fluorine atoms can be appropriately localized near the surface of the pressure-sensitive adhesive layer (so-called near the interface with the adherend). Be done. It is considered that the pressure-sensitive adhesive layer in which fluorine atoms are appropriately localized in the vicinity of the surface is difficult to wet and spread on the adherend and exhibits appropriate peelability. Therefore, it is presumed that the pressure-sensitive adhesive composition of the present invention is unlikely to contaminate the surface of the adherend at the time of peeling even when exposed to a high temperature environment.
Further, when the pressure-sensitive adhesive layer exhibits appropriate peelability, it is not necessary to increase the content of the cross-linking agent and increase the cross-linking density of the pressure-sensitive adhesive layer in order to improve the stain resistance. That is, it is possible to reduce the crosslink density of the pressure-sensitive adhesive layer.
Since the pressure-sensitive adhesive composition of the present invention is designed so that the cross-linking density of the formed pressure-sensitive adhesive layer is relatively low, specifically, the equivalent of the cross-linking agent is contained in the (meth) acrylic polymer. Since it is 0.8 equivalent or less with respect to the specific crosslinkable functional group, it is presumed that it is unlikely to become hard and brittle and powder is unlikely to fall off. Further, in the pressure-sensitive adhesive composition of the present invention, the equivalent of the cross-linking agent is 0.1 equivalent or more with respect to the specific cross-linking functional group of the (meth) acrylic polymer, so that the pressure-sensitive adhesive layer formed is: It can exhibit a cohesive force to the adherend to the extent that it does not shift or fall off. Therefore, it is suitable as an adhesive composition used for a protective film.

Hereinafter, each component of the pressure-sensitive adhesive composition of the present invention will be described.

[Specific (meth) acrylic polymer]
The (meth) acrylic polymer (that is, the specific (meth) acrylic polymer) contained in the pressure-sensitive adhesive composition of the present invention contains 6% by mass or more and 30% by mass or less of fluorine (meth) with respect to all the constituent units. ) At least one crosslinkable functional group (i.e., specific) containing a structural unit derived from an acrylic acid alkyl ester monomer and selected from the group consisting of a carboxy group, a hydroxyl group, an amide group, and an N-substituted amide group. It has a crosslinkable functional group).

<Specific crosslinkable functional group>
The specific (meth) acrylic polymer has at least one crosslinkable functional group (that is, a specific crosslinkable functional group) selected from the group consisting of a carboxy group, a hydroxyl group, an amide group, and an N-substituted amide group.
The specific crosslinkable functional group of the specific (meth) acrylic polymer may be derived from a fluorine-containing (meth) acrylic acid alkyl ester monomer, and a single amount of the fluorine-containing (meth) acrylic acid alkyl ester. It may be derived from a monomer other than the body.
That is, in the specific (meth) acrylic polymer, when the fluorine-containing (meth) acrylic acid alkyl ester monomer has a crosslinkable functional group, the fluorine-containing (meth) acrylic acid alkyl having the crosslinkable functional group is used. By including a structural unit derived from the ester monomer, it may have a crosslinkable functional group, and when the fluorine-containing (meth) acrylic acid alkyl ester monomer does not have a crosslinkable functional group, Even if it has a crosslinkable functional group by containing a structural unit derived from a monomer other than the fluorine-containing (meth) acrylic acid alkyl ester monomer, for example, a monomer having a crosslinkable functional group described later. good.
A preferred embodiment is a mode in which the specific (meth) acrylic polymer has a crosslinkable functional group by containing a structural unit derived from a monomer having a crosslinkable functional group described later.

The specific crosslinkable functional group of the specific (meth) acrylic polymer preferably contains a hydroxyl group, and more preferably a hydroxyl group.
In general, a pressure-sensitive adhesive layer formed of a pressure-sensitive adhesive composition containing a (meth) acrylic polymer having a hydroxyl group can easily wet and spread on an adherend, and thus can exhibit good adhesive strength. However, on the other hand, when the pressure-sensitive adhesive layer is exposed to a high temperature environment, the surface of the adherend tends to be easily contaminated at the time of peeling. On the other hand, the pressure-sensitive adhesive composition of the present invention has good adhesive strength and excellent stain resistance when exposed to a high temperature environment even when the (meth) acrylic polymer contains a hydroxyl group. Can be compatible.

<Constituent unit derived from fluorine-containing (meth) acrylic acid alkyl ester monomer>
The specific (meth) acrylic polymer contains a structural unit derived from a fluorine-containing (meth) acrylic acid alkyl ester monomer.
In the present specification, the “constituent unit derived from the fluorine-containing (meth) acrylic acid alkyl ester monomer” refers to a structural unit formed by addition polymerization of the fluorine-containing (meth) acrylic acid alkyl ester monomer. means.

The type of the fluorine-containing (meth) acrylic acid alkyl ester monomer is not particularly limited.
The alkyl group of the fluorine-containing (meth) acrylic acid alkyl ester monomer may be linear, branched-chain, or cyclic. The number of carbon atoms of the alkyl group is preferably 1 to 18, and more preferably 1 to 12, for example, from the viewpoint of the adhesive force of the formed pressure-sensitive adhesive layer on the adherend and the adhesion to the substrate.
The number of fluorine atoms in the fluorine-containing (meth) acrylic acid alkyl ester monomer is not particularly limited, but for example, the adhesive strength of the pressure-sensitive adhesive layer to the adherend and the stain resistance when exposed to a high temperature environment. From the viewpoint, 1 to 8 are preferable, and 2 to 4 are more preferable.

The fluorine-containing (meth) acrylic acid alkyl ester monomer is preferably a fluorine-containing methacrylic acid alkyl ester monomer.
As described above, in the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention, when exposed to a high temperature environment, fluorine atoms are localized near the surface (so-called interface with an adherend). Tend to do. The pressure-sensitive adhesive layer in which fluorine atoms are localized near the surface is less likely to wet and spread on the adherend and exhibits appropriate peelability, so that the surface of the adherend is less likely to be contaminated during peeling.
According to the fluorine-containing methacrylic acid alkyl ester monomer, the fluorine atom tends to be localized near the surface of the pressure-sensitive adhesive layer as compared with the fluorine-containing acrylic acid alkyl ester monomer. It is less likely to contaminate the surface of the body.

Specific examples of the fluorine-containing (meth) acrylic acid alkyl ester monomer include (meth) acrylic acid 2,2,2-trifluoroethyl, (meth) acrylic acid β- (perfluorooctyl) ethyl, and (meth). Acrylic acid 2,2,3,3-tetrafluoropropyl, (meth) acrylic acid 2,2,3,4,5,4-hexafluorobutyl, (meth) acrylic acid 1H, 1H, 9H-perfluoro-1 -Nonyl, 1H, 1H, 11H-perfluoroundecyl (meth) acrylate, perfluorooctyl (meth) acrylate, trifluoromethyl (meth) acrylate, 3 [4 [1-trifluoro) (meth) acrylate Examples thereof include methyl-2 and 2-bis [bis (trifluoromethyl) fluoromethyl] ethynyloxy] benzooxy] 2-hydroxypropyl.
Among these, as the fluorine-containing (meth) acrylic acid alkyl ester monomer, 2,2,2-trifluoroethyl (meth) acrylic acid is preferable from the viewpoint of the adhesive force of the pressure-sensitive adhesive layer to the adherend. 2,2,2-trifluoroethyl methacrylate is more preferable.

As the fluorine-containing (meth) acrylic acid alkyl ester monomer, a commercially available product can be used.
Examples of commercially available fluorine-containing (meth) acrylic acid alkyl ester monomers are "Viscoat (registered trademark) 3F", "Viscoat (registered trademark) 3FM", and "Viscoat (registered)" of Osaka Organic Chemical Industry Co., Ltd. Examples thereof include "Viscoat (registered trademark) 8F", "Viscort (registered trademark) 8FM", and "Light Ester M-3F" of Kyoeisha Chemical Co., Ltd.

The specific (meth) acrylic polymer may contain only one type of structural unit derived from the fluorine-containing (meth) acrylic acid alkyl ester monomer, or may contain two or more types.

The content (ratio) of the structural unit derived from the fluorine-containing (meth) acrylic acid alkyl ester monomer in the specific (meth) acrylic polymer constitutes all the structural units (that is, the specific (meth) acrylic polymer. It is 6% by mass or more and 30% by mass or less, preferably 8% by mass or more and 28% by mass or less, and more preferably 10% by mass or more and 25% by mass or less.
When the content of the constituent units derived from the fluorine-containing (meth) acrylic acid alkyl ester monomer in the specific (meth) acrylic polymer is 6% by mass or more with respect to all the constituent units, the pressure-sensitive adhesive layer is heated to a high temperature. When exposed to the environment, fluorine atoms can be appropriately localized near the surface of the pressure-sensitive adhesive layer (so-called near the interface with the adherend). The pressure-sensitive adhesive layer in which fluorine atoms are appropriately localized in the vicinity of the surface is less likely to wet and spread on the adherend and exhibits appropriate peelability, so that the surface of the adherend is less likely to be contaminated during peeling.
Further, when the pressure-sensitive adhesive layer exhibits appropriate peelability, it is not necessary to increase the content of the cross-linking agent and increase the cross-linking density of the pressure-sensitive adhesive layer in order to improve the stain resistance. That is, when the content of the structural unit derived from the fluorine-containing (meth) acrylic acid alkyl ester monomer in the specific (meth) acrylic polymer is 6% by mass or more with respect to all the structural units, the pressure-sensitive adhesive layer Since it is possible to reduce the crosslink density of the adhesive layer and prevent the adhesive layer from becoming hard and brittle, it is possible to form an adhesive layer in which powder is less likely to fall off.
Further, when the content of the structural unit derived from the fluorine-containing (meth) acrylic acid alkyl ester monomer in the specific (meth) acrylic polymer is 30% by mass or less with respect to all the structural units, it is under a high temperature environment. The surface of the adherend from which the pressure-sensitive adhesive layer exposed to the above has been peeled off is less likely to cause fogging due to the fluorine-containing (meth) acrylic acid alkyl ester monomer.

<Constituent unit derived from a monomer having a crosslinkable functional group>
The specific (meth) acrylic polymer is a single having at least one crosslinkable functional group (that is, a specific crosslinkable functional group) selected from the group consisting of a carboxy group, a hydroxyl group, an amide group, and an N-substituted amide group. It is preferable to include a structural unit derived from a polymer.
As used herein, the "constituent unit derived from a monomer having a crosslinkable functional group" means a structural unit formed by addition polymerization of a monomer having a crosslinkable functional group.

The type of monomer having a carboxy group is not particularly limited.
Specific examples of the monomer having a carboxy group include (meth) acrylic acid, crotonic acid, maleic anhydride, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, and ω-carboxy-polycaprolactone (n≈2) mono. Examples include (meth) acrylate.
Among these, acrylic acid is preferable as the monomer having a carboxy group, for example, from the viewpoint of reactivity with a cross-linking agent and cross-linking density.

The type of monomer having a hydroxyl group is not particularly limited.
Specific examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 6-. Hydroxyhexyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, 3-methyl-3-hydroxybutyl (meth) acrylate, 1,1-dimethyl-3-hydroxybutyl (meth) acrylate ) Acrylate, 1,3-dimethyl-3-hydroxybutyl (meth) acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth) acrylate, 2-ethyl-3-hydroxyhexyl (meth) acrylate, glycerin mono Examples thereof include (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, and poly (ethylene glycol-propylene glycol) mono (meth) acrylate.
Among these, as the monomer having a hydroxyl group, for example, at least one selected from 4-hydroxybutyl acrylate (4HBA) and 2-hydroxyethyl acrylate (2HEA) from the viewpoint of reactivity with a cross-linking agent and cross-linking density. Seeds are preferred.

The type of monomer having an amide group or an N-substituted amide group is not particularly limited.
Specific examples of the monomer having an amide group or an N-substituted amide group include acrylamide, methacrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-methoxymethyl (meth) acrylamide, and N. Examples thereof include -ethoxymethyl (meth) acrylamide, N-propoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-t-butyl acrylamide, N-octyl acrylamide, and diacetone acrylamide.

When the specific (meth) acrylic polymer contains a structural unit derived from a monomer having a specific crosslinkable functional group, the specific crosslinkable functional group is preferably a hydroxyl group.
As described above, in general, the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition containing the (meth) acrylic polymer having a hydroxyl group can easily wet and spread on the adherend, and thus can exhibit good adhesive strength. However, on the other hand, the pressure-sensitive adhesive layer becomes hard and brittle when exposed to a high temperature environment, and tends to contaminate the surface of the adherend at the time of peeling. On the other hand, the pressure-sensitive adhesive composition of the present invention has good adhesive strength and excellent stain resistance when exposed to a high temperature environment even when the (meth) acrylic polymer contains a hydroxyl group. Can be compatible.

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

When the specific (meth) acrylic polymer contains a structural unit derived from a monomer having a specific crosslinkable functional group, it is derived from the monomer having a specific crosslinkable functional group in the specific (meth) acrylic polymer. The content rate (ratio) of the structural units is preferably 1% by mass or more and 10% by mass or less, preferably 2% by mass or more, with respect to all the structural units (that is, all the structural units constituting the specific (meth) acrylic polymer). 8% by mass or less is more preferable, and 3% by mass or more and 6% by mass or less is further preferable.
When the content of the structural unit derived from the monomer having the specific crosslinkable functional group in the specific (meth) acrylic polymer is 1% by mass or more with respect to all the structural units, the cohesive force of the pressure-sensitive adhesive layer becomes strong. For further improvement, the stain resistance when exposed to a high temperature environment can be further improved, and the adhesive layer can be attached to the adherend with higher adhesive strength.
When the content of the structural unit derived from the monomer having the specific crosslinkable functional group in the specific (meth) acrylic polymer is 10% by mass or less with respect to all the structural units, the crosslink density of the pressure-sensitive adhesive layer becomes high. Since the pressure-sensitive adhesive layer is not excessively high and the adhesive layer is less likely to become hard and brittle, powder falling tends to be less likely to occur. Further, since the wettability of the pressure-sensitive adhesive layer is further improved, the pressure-sensitive adhesive layer can be attached to the adherend with higher adhesive strength.

(Constituent unit derived from (meth) acrylic acid alkyl ester monomer)
The specific (meth) acrylic polymer is different from the structural unit derived from the fluorine-containing (meth) acrylic acid alkyl ester monomer and the monomer having a specific crosslinkable functional group, and is different from the (meth) acrylic acid alkyl ester simple substance. It is preferable to further contain a structural unit derived from a polymer (hereinafter, simply referred to as “(meth) acrylic acid alkyl ester monomer”).
The structural unit derived from the (meth) acrylic acid alkyl ester monomer contributes to the adjustment of the adhesive strength of the pressure-sensitive adhesive layer.

In the present specification, the “constituent unit derived from the (meth) acrylic acid alkyl ester monomer” means a structural unit formed by addition polymerization of the (meth) acrylic acid alkyl ester monomer.

When the specific (meth) acrylic polymer further contains a structural unit derived from the (meth) acrylic acid alkyl ester monomer, the (meth) acrylic acid alkyl ester monomer is an unsubstituted (meth) acrylic acid. Alkyl ester monomers are preferable, and the types thereof are not particularly limited.
The alkyl group of the (meth) acrylic acid alkyl ester monomer may be linear, branched or cyclic.
The carbon number of the alkyl group is preferably in the range of 1 to 18, more preferably in the range of 1 to 12, from the viewpoint of the adhesive force of the formed pressure-sensitive adhesive layer to the adherend and the adhesion to the substrate. ..

Specific examples of the (meth) acrylic acid alkyl ester monomer include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, and 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, Examples thereof include n-decyl (meth) acrylate, n-dodecyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, and isobornyl (meth) acrylate.
Among these, as the (meth) acrylic acid alkyl ester monomer, a monomer having a glass transition temperature of −60 ° C. or lower when used as a homopolymer is preferable. The "glass transition temperature when a homopolymer is used" will be described later, and thus the description thereof will be omitted here.
When the specific (meth) acrylic polymer further contains a structural unit derived from a monomer having a glass transition temperature of -60 ° C or lower when used as a homopolymer, it is resistant to contamination when exposed to a high temperature environment. A pressure-sensitive adhesive layer having better properties can be formed.

Further, as the (meth) acrylic acid alkyl ester monomer, for example, 2-ethylhexyl acrylate (2EHA), n-butyl acrylate (n-BA), from the viewpoint that the adhesive strength of the pressure-sensitive adhesive layer can be easily adjusted. And at least one selected from the group consisting of i-octyl acrylate (i-OA) are preferred, for example, 2-ethylhexyl acrylate (2EHA) and i- from the viewpoint of stain resistance when exposed to a high temperature environment. At least one selected from octyl acrylate (i-OA) is more preferred.

When the specific (meth) acrylic polymer further contains a structural unit derived from the (meth) acrylic acid alkyl ester monomer, the specific (meth) acrylic polymer becomes the (meth) acrylic acid alkyl ester monomer. Only one type of constituent unit may be contained, or two or more types may be contained.

When the specific (meth) acrylic polymer contains a structural unit derived from the (meth) acrylic acid alkyl ester monomer, it is derived from the (meth) acrylic acid alkyl ester monomer in the specific (meth) acrylic polymer. The content rate (ratio) of the constituent units is, for example, relative to all the constituent units (that is, all the constituent units constituting the specific (meth) acrylic polymer) from the viewpoint that the adhesive strength of the pressure-sensitive adhesive layer can be easily adjusted. Therefore, 50% by mass or more is preferable, 65% by mass or more is more preferable, and 75% by mass or more is further preferable.
The upper limit of the content (ratio) of the structural unit derived from the (meth) acrylic acid alkyl ester monomer in the specific (meth) acrylic polymer is not particularly limited, and is, for example, 90 mass with respect to all the structural units. % Or less is preferable.

<Other building blocks>
The specific (meth) acrylic polymer is a specific structural unit derived from the fluorine-containing (meth) acrylic acid alkyl ester monomer and an arbitrary structural unit within the range in which the effect of the present invention is exhibited. It may contain a structural unit (so-called other structural unit) other than the structural unit derived from the monomer having a crosslinkable functional group and the structural unit derived from the (meth) acrylic acid alkyl ester monomer.

The type of monomer constituting the other structural unit is not particularly limited.
Examples of the monomer constituting the other structural unit include (meth) acrylate having a cyclic group represented by benzyl (meth) acrylate and phenoxyethyl (meth) acrylate, methoxyethyl (meth) acrylate, and ethoxyethyl. Alkoxyalkyl (meth) acrylate represented by (meth) acrylate, styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and aromatic monovinyl represented by vinyltoluene, acrylonitrile and methacryl. Examples thereof include vinyl cyanide typified by lonitrile, and vinyl esters typified by vinyl acrylate, vinyl acetate, vinyl propionate, and vinyl versatic acid. In addition, various derivatives of these monomers can be mentioned.

(Hydroxyl value of specific (meth) acrylic polymer)
When the specific (meth) acrylic polymer has a hydroxyl group as a specific crosslinkable functional group, the hydroxyl value of the specific (meth) acrylic polymer is preferably 3 mgKOH / g or more and less than 20 mgKOH / g, and 7 mgKOH / g or more and 18 mgKOH / g. It is more preferably g or less, and further preferably 10 mgKOH / g or more and 16 mgKOH / g or less.
When the hydroxyl value of the specific (meth) acrylic polymer is 3 mgKOH / g or more, the adhesive force of the pressure-sensitive adhesive layer formed due to the specific (meth) acrylic polymer having a hydroxyl group as a specific crosslinkable functional group. There is a tendency for the improvement effect of
When the hydroxyl value of the specific (meth) acrylic polymer is less than 20 mgKOH / g, the adhesive layer formed has a low crosslink density and does not have a very high cohesive force. As a result, the brittleness of the pressure-sensitive adhesive layer is further improved, so that powder removal tends to be less likely to occur.

The hydroxyl value of the specific (meth) acrylic polymer is calculated by the following formula. In the following calculation formula, 56.1 is the molecular weight of KOH.
Hydroxy group value (mgKOH / g)
= {(A1 / 100) ÷ A2} × 56.1 × 1000 × A3
A1: Ratio (unit: mass%) of the monomer having a hydroxyl group in all the monomers used for producing a specific (meth) acrylic polymer.
A2: Molecular weight of the monomer having a hydroxyl group used for producing a specific (meth) acrylic polymer A3: Monomer having a hydroxyl group The number of hydroxyl groups contained in one molecule

When there are two or more types of monomers having a hydroxyl group used in the production of a specific (meth) acrylic polymer, the hydroxyl value of each monomer is calculated according to the above formula, and then the hydroxyl value is calculated. The obtained values are totaled to obtain the hydroxyl value.

-Weight average molecular weight of specific (meth) acrylic polymer-
The weight average molecular weight (Mw) of the specific (meth) acrylic polymer is preferably 150,000 or more and 450,000 or less, preferably 150,000 or more and 400,000 or less, and more preferably 150,000 or more and 350,000 or less.
When the weight average molecular weight (Mw) of the specific (meth) acrylic polymer is 150,000 or more, the pressure-sensitive adhesive layer can exhibit more sufficient cohesive force, so that even when exposed to a high temperature environment, it will be peeled off. It tends to be less likely to contaminate the surface of the adherend.
When the weight average molecular weight (Mw) of the specific (meth) acrylic polymer is 450,000 or less, the adhesion of the pressure-sensitive adhesive layer to the substrate can be further improved, so that the adhesive layer can be peeled off even when exposed to a high temperature environment. At this time, the surface of the adherend tends to be less likely to be contaminated. Generally, in the pressure-sensitive adhesive composition used for a protective film exposed to a high temperature environment, a (meth) acrylic polymer having a high molecular weight is used from the viewpoint of improving heat resistance. On the other hand, in the pressure-sensitive adhesive composition of the present invention, even if the weight average molecular weight (Mw) of the (meth) acrylic polymer is relatively low (that is, even if it is 450,000 or less), it is exposed to a high temperature environment. Excellent stain resistance when it is used.
The weight average molecular weight (Mw) of the specific (meth) acrylic polymer is desired by adjusting the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, and the like. Can be a value.

The weight average molecular weight (Mw) of the specific (meth) acrylic polymer is a value measured by the following method. Specifically, the measurement is performed according to the following (1) to (3).
(1) A solution of the specific (meth) acrylic polymer is applied to a release paper and dried at 100 ° C. for 1 minute to obtain a film-like specific (meth) acrylic polymer.
(2) A sample solution having a solid content concentration of 0.2% by mass is obtained by using the film-shaped specific (meth) acrylic polymer obtained in (1) above and tetrahydrofuran.
(3) Using gel permeation chromatography (GPC), the weight average molecular weight (Mw) of the specific (meth) acrylic polymer is measured as a standard polystyrene-equivalent value under the following conditions.

~conditions~
Measuring device: High-speed GPC (Model number: HLC-8220 GPC, Tosoh Corporation)
Detector: Differential refractometer (RI) (embedded in HLC-8220, Tosoh Corporation)
Column: 4 TSK-GEL GMHXL (Tosoh Corporation) connected in series Column temperature: 40 ° C
Eluent: tetrahydrofuran Sample concentration: 0.2% by mass
Injection volume: 100 μL
Flow rate: 0.6 mL / min

(Glass transition temperature of specific (meth) acrylic polymer)
The glass transition temperature (Tg) of the specific (meth) acrylic polymer is not particularly limited.
The glass transition temperature (Tg) of the specific (meth) acrylic polymer is, for example, preferably −30 ° C. or lower, more preferably −70 ° C. or higher and −40 ° C. or lower, and further preferably −60 ° C. or higher and −50 ° C. or lower.
When the glass transition temperature (Tg) of the specific (meth) acrylic polymer is −30 ° C. or lower, a pressure-sensitive adhesive layer having better wettability to the adherend can be formed.

The glass transition temperature (Tg) of the specific (meth) acrylic polymer is a value obtained by converting the absolute temperature (K) calculated from the following formula 1 into the Celsius temperature (° C.).
1 / Tg = m1 / Tg1 + m2 / Tg2 + ... + m (k-1) / Tg (k-1) + mk / Tgk (Equation 1)

In the formula 1, Tg1, Tg2, ..., Tg (k-1), and Tgk are the absolute temperatures (K) when each monomer constituting the specific (meth) acrylic polymer is used as a homopolymer. ) Represents the glass transition temperature (Tg). m1, m2, ..., M (k-1), and mk represent the mole fractions of each monomer constituting the specific (meth) acrylic polymer, and m1 + m2 + ... + m (k-). 1) + mk = 1.
The absolute temperature (K) can be converted to the Celsius temperature (° C) by subtracting 273 from the absolute temperature (K), and the Celsius temperature (° C) can be converted to the absolute temperature (K) by adding 273 to the Celsius temperature (° C). Can be converted to.

The "glass transition temperature (Tg) when made into a homopolymer" is the glass transition temperature (Tg) represented by the absolute temperature (K) of the homopolymer produced by polymerizing the monomer alone. say.
The glass transition temperature (Tg) of the homopolymer was measured using a differential scanning calorimetry device (DSC) (model number: EXSTAR6000, Seiko Instruments Co., Ltd.) in a nitrogen stream, a measurement sample of 10 mg, and a temperature rise rate of 10 ° C./min. The turning point of the obtained DSC curve was taken as the glass transition temperature (Tg) of the homopolymer.

The "glass transition temperature (Tg) represented by the Celsius temperature (° C.) when made into a homopolymer" of a typical monomer is -76 ° C for 2-ethylhexyl acrylate (2EHA) and 2-ethylhexyl methacrylate (2-ethylhexyl methacrylate). 2EHMA) is -10 ° C, n-butyl acrylate (n-BA) is -57 ° C, n-butyl methacrylate is 21 ° C, t-butyl acrylate (t-BA) is 41 ° C, t-butyl methacrylate is 107 ° C, Methyl acrylate (MA) at 5 ° C, methyl methacrylate (MMA) at 103 ° C, isobonyl methacrylate (IBMX) at 155 ° C, ethyl acrylate (EA) at -27 ° C, methacrylic acid at 185 ° C, 4-hydroxybutyl acrylate ( 4HBA) is -39 ° C, 2-hydroxyethyl acrylate (2HEA) is -15 ° C, 2-hydroxyethyl methacrylate (2HEMA) is 55 ° C, acrylic acid (AA) is 163 ° C, isooctyl acrylate (i-OA) is −75 ° C., dimethylaminoethyl methacrylate (DM) at 18 ° C., trifluoroethyl methacrylate at 72 ° C., and trifluoroethyl acrylate at −5 ° C.

The glass transition temperature (Tg) of the specific (meth) acrylic polymer can be appropriately adjusted by using, for example, monomers having different glass transition temperatures (Tg) when they are homopolymers.

[Method for producing specific (meth) acrylic polymer]
The method for producing the specific (meth) acrylic polymer is not particularly limited.
The specific (meth) acrylic polymer can be produced by polymerizing a monomer by a known polymerization method typified by, for example, solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization.
Among these, as a polymerization method, for example, in preparing a pressure-sensitive adhesive composition after production, solution polymerization is preferable because the treatment step is relatively simple and can be performed in a short time.

In solution polymerization, generally, a predetermined organic solvent, a monomer, a polymerization initiator, and a chain transfer agent used as needed are charged in a polymerization tank, and the mixture is stirred in a nitrogen stream or at the reflux temperature of the organic solvent. While heating for several hours. In this case, at least a part of the organic solvent, the monomer, the polymerization initiator and / or the chain transfer agent may be added sequentially.

Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, alcohol compounds and the like.
At the time of the polymerization reaction, only one of these organic solvents may be used, or two or more of these organic solvents may be mixed and used.

More specifically, examples of the organic solvent used in the polymerization reaction include benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, and hydrocarbons. And aromatic hydrocarbons represented by aromatic naphtha, n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and fat represented by terepine oil. Ethers typified by system or alicyclic hydrocarbons, ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate. Classes, acetone, methyl ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, and ketones typified by methylcyclohexanone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether. , And glycol ethers typified by diethylene glycol monobutyl ether, as well as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t-. Examples thereof include alcohols typified by butyl alcohol.

In the production of the specific (meth) acrylic polymer, it is preferable to use an organic solvent that does not easily cause chain transfer during the polymerization reaction of esters, ketones, etc., and in particular, the solubility of the specific (meth) acrylic polymer. From the viewpoint of ease of polymerization reaction and the like, it is preferable to use ethyl acetate, toluene or the like.

Examples of the polymerization initiator include organic peroxides and azo compounds used in ordinary solution polymerization.
Examples of the organic peroxide include t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propylperoxydicarbonate, and di-2-ethylhexylperoxydi. Carbonate, t-butylperoxypivalate, 2,2-bis (4,5-di-t-butylperoxycyclohexyl) propane, 2,2-bis (4,5-di-t-amylperoxycyclohexyl) propane, 2,2-bis (4,5-di-t-octylperoxycyclohexyl) propane, 2,2-bis (4,54-di-α-cumylperoxycyclohexyl) propane, 2,2-bis (4,4) Examples include -di-t-butylperoxycyclohexyl) butane and 2,2-bis (4,5-di-t-octylperoxycyclohexyl) butane.
Examples of the azo compound include 2,2'-azobisisobutynitrile (AIBN), 2,2'-azobis (2,4-dimethylvaleronitrile) (ABVN), and 2,2'-azobis (4-methoxy-). 2,4-Dimethylvaleronitrile), 1,1'-azobis (cyclohexane-1-carbonitrile), and 2,2'-azobis (isobutyric acid) dimethyl.

In the production of the specific (meth) acrylic polymer, it is preferable to use a polymerization initiator that does not cause a graft reaction during the polymerization reaction, and in particular, it is preferable to use an azobis-based polymerization initiator.

The amount of the polymerization initiator used is not particularly limited, and is appropriately set according to the molecular weight of the target specific (meth) acrylic polymer.

In the production of the specific (meth) acrylic polymer, a chain transfer agent may be used, if necessary, as long as the object and effect of the present invention are not impaired.
Examples of the chain transfer agent include cyanoacetic acid, alkyl esters having 1 to 8 carbon atoms of cyanoacetic acid, bromoacetic acid, alkyl esters having 1 to 8 carbon atoms of bromoacetic acid, α-methylstyrene, anthracene, phenanthrene, and fluorene. , And aromatic compounds typified by 9-phenylfluorene, p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and aromatic nitro compounds typified by p-nitrotoluene, Benzoquinone and benzoquinone derivatives typified by 2,3,5,6-tetramethyl-p-benzoquinone, borane derivatives typified by tributylborane, carbon tetrabromide, carbon tetrachloride, 1,1,2,2- Tetrabromoethane, tribromoethylene, trichloroethylene, bromotrichloromethane, tribromomethane, halogenated hydrocarbons typified by 3-chloro-1-propene, aldehydes typified by chloral and furaldehyde, carbon number 1 to 1 18 alkyl mercaptans, aromatic mercaptans typified by thiophenols and toluene mercaptans, mercaptoacetic acid, alkyl esters of mercaptoacetic acid having 1 to 10 carbon atoms, hydroxyalkyl mercaptans having 1 to 12 carbon atoms, and binen. And terpenes represented by turpinolene.

When a chain transfer agent is used in the production of the specific (meth) acrylic polymer, the amount of the chain transfer agent used is not particularly limited, and is appropriately suitable according to the molecular weight of the target specific (meth) acrylic polymer. Set.

The polymerization temperature is not particularly limited and is appropriately set according to the molecular weight of the target specific (meth) acrylic polymer.

<Crosslinking agent>
The pressure-sensitive adhesive composition of the present invention is at least one selected from the group consisting of a specific crosslinkable functional group (that is, a carboxy group, a hydroxyl group, an amide group, and an N-substituted amide group) possessed by the specific (meth) acrylic polymer. (Crosslinkable functional group) contains a cross-linking agent of 0.1 equivalent or more and 0.8 equivalent or less.
A crosslinked structure is formed by the reaction of the specific crosslinkable functional group of the specific (meth) acrylic polymer with the crosslinking agent.

The cross-linking agent is not particularly limited, and known ones can be used.
Examples of the cross-linking agent include isocyanate-based compounds, epoxy-based compounds, and metal chelate-based compounds.
In the present specification, the "isocyanate compound" means a compound having an isocyanate group, and the "epoxide compound" means a compound having an epoxy group.
Among these, as the cross-linking agent, at least one selected from isocyanate compounds and epoxy compounds is preferable, and at least one selected from isocyanate compounds is more preferable.
When the cross-linking agent is an isocyanate compound, the adhesion of the pressure-sensitive adhesive layer to the substrate tends to be further improved.
The pressure-sensitive adhesive composition of the present invention may contain only one type of cross-linking agent, or may contain two or more types of cross-linking agents.

Examples of the isocyanate-based compound include xylylene diisocyanate (XDI), diphenylmethane diisocyanate, triphenylmethane triisocyanate, aromatic polyisocyanate compound typified by tolylene diisocyanate (TDI), hexamethylene diisocyanate (HMDI), isophorone diisocyanate, and the above. Chain or cyclic aliphatic polyisocyanate compounds typified by hydrogenated additives of aromatic polyisocyanate compounds, biuret, dimer, trimeric or pentameric of these polyisocyanate compounds, these polyisocyanate compounds. And an adduct with a polyol compound such as trimethylolpropane.

Among these, isocyanate compounds include tolylene diisocyanate, dimer of tolylene diisocyanate, adduct of tolylene diisocyanate and polyol, isocyanurate which is trimeric or pentameric of tolylene diisocyanate, and tri. A tolylene diisocyanate compound derived from various tolylene diisocyanates such as a biuret form of a range isocyanate is preferable.
Further, as the isocyanate compound, at least one selected from tolylene diisocyanate and an adduct of tolylene diisocyanate and polyol from the viewpoint of reactivity with a specific crosslinkable functional group and compatibility with a specific polymer. Is preferable, and at least one selected from tolylene diisocyanate and an adduct compound of tolylene diisocyanate and trimethyl propane is particularly preferable from the viewpoint of suppressing gelation at the time of crosslinking and reactivity.

As the isocyanate compound, a commercially available product can be used.
Commercially available isocyanate-based compounds include "Coronate (registered trademark) HX", "Coronate (registered trademark) HL-S", "Coronate (registered trademark) L", and "Coronate (registered trademark) L" of Toso Co., Ltd. -45E ”,“ Coronate® 2031 ”,“ Coronate® 2030 ”,“ Coronate® 2234 ”,“ Coronate® 2785 ”,“ Aquanate® 200 ”, And "Aquanate (registered trademark) 210", "Sumijuru (registered trademark) N3300", "Death Module (registered trademark) N3400", and "Sumijuru (registered trademark) N-" of Sumika Cobestro Urethane Co., Ltd. 75, Asahi Kasei Co., Ltd.'s "Duranate (registered trademark) E-405-80T", "Duranate (registered trademark) 24A-100", "Duranate (registered trademark) TSE-100", and Mitsui Takeda Chemical Co., Ltd. Trademarks of "Takenate (registered trademark) D-110N", "Takenate (registered trademark) D-120N", "Takenate (registered trademark) M-631N" and "MT-Orester (registered trademark) NP1200" Any of those commercially available can be preferably used.

Examples of the epoxy compound 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 polyglycidyl ether, resorcin diglycidyl ether, 2,2-dibromoneo Pentyl glycol diglycidyl ether, trimethyl propantriglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, diglycidyl adipate, diglycidyl phthalate, tris (glycidyl) isocyanurate, tris (glycidoxyethyl) Examples thereof include isocyanurate, 1,3-bis (N, N-glycidyl aminomethyl) cyclohexane, N, N, N', N'-tetraglycidyl-1,3-benzenedi (methaneamine) and the like.

Among these, as the epoxy compound, 1,3-bis (N, N-glycidylaminomethyl) cyclohexane is preferable from the viewpoint of cohesive force.

As the epoxy compound, a commercially available product can be used.
As commercially available epoxy compounds, those commercially available under the trade names of "TETRAD-X" and "TETRAD-C" of Mitsubishi Gas Chemical Company, Inc. can be preferably used.

The equivalent of the cross-linking agent is 0.1 equivalent or more and 0.8 equivalent or less, and 0.2 equivalent or more and 0.7 equivalent or less with respect to 1 equivalent of the specific cross-linking functional group possessed by the specific (meth) acrylic polymer. Is preferable, and 0.3 equivalents or more and 0.6 equivalents or less are more preferable.
When the content of the cross-linking agent is 0.1 equivalent or more with respect to the specific cross-linking functional group of the specific (meth) acrylic polymer, the pressure-sensitive adhesive layer having an appropriate cohesive force that can be used for a protective film. Can be formed.
Further, when the content of the cross-linking agent is 0.8 equivalent or less with respect to the specific cross-linking functional group of the specific (meth) acrylic polymer, the cross-linking density becomes low and the pressure-sensitive adhesive layer becomes hard and brittle. It is possible to form an adhesive layer in which powder is less likely to fall off.

For example, when the cross-linking agent is an isocyanate-based compound, the content of the cross-linking agent is such that the isocyanate group contained in the isocyanate-based compound is 0. The amount is 1 molar equivalent or more and 0.8 molar equivalent or less.
Further, for example, when the cross-linking agent is an epoxy-based compound, the content of the cross-linking agent is such that the epoxy group contained in the epoxy-based compound is based on the total of the specific cross-linking functional groups contained in the specific (meth) acrylic polymer. The amount is 0.1 molar equivalent or more and 0.8 molar equivalent or less.
When the cross-linking agent is a metal chelate compound, the equivalent amount of the cross-linking agent can be calculated by appropriately referring to the description in paragraph [0090] of JP-A-2017-132862.

<Crosslink catalyst>
The pressure-sensitive adhesive composition of the present invention may contain a cross-linking catalyst.
The cross-linking catalyst is not particularly limited, and known ones can be used.
Examples of the cross-linking catalyst include organometallic compounds represented by dioctyltin dilaurate and 1,3-diacetoxytetrabutylstanoxane, and tertiary amine compounds represented by triethylenediamine and N-methylmorpholine. Can be mentioned.

<Organic solvent>
The pressure-sensitive adhesive composition of the present invention may contain an organic solvent, for example, from the viewpoint of improving coatability.
Examples of the organic solvent include the same organic solvents as those used in the polymerization reaction of the (meth) acrylic polymer described above.

The content of the organic solvent in the pressure-sensitive adhesive composition of the present invention is not particularly limited.
When the pressure-sensitive adhesive composition of the present invention contains an organic solvent, the content of the organic solvent is, for example, 10 parts by mass with respect to 100 parts by mass of the above-mentioned (meth) acrylic polymer from the viewpoint of improving coatability. More than 50 parts by mass is preferable.

<Other ingredients>
The pressure-sensitive adhesive composition of the present invention may contain components other than the above-mentioned components (so-called other components), if necessary, as long as the effects of the present invention are not impaired.
Other components include polymers other than specific (meth) acrylic polymers, tackifiers, antioxidants, colorants (eg dyes and pigments), light stabilizers (eg UV absorbers), antistatic agents. Examples include various additives such as agents.

[Protective film]
The protective film of the present invention includes a base material and a pressure-sensitive adhesive layer provided on the base material and formed by the above-mentioned pressure-sensitive adhesive composition of the present invention. That is, in the protective film of the present invention, a base material and a pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention are laminated.
Generally, a protective film is attached to the surface of an article to protect the surface of the article from being contaminated or damaged, and when the article is processed, the protective film is attached to the article. As it is, it is subjected to each process such as punching, inspection, transportation, and assembly, and if necessary, it is heat-treated and peeled off from the article when surface protection is no longer necessary.
Since the protective film of the present invention includes the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention, for example, even when it is subjected to punching processing, the pressure-sensitive adhesive derived from the pressure-sensitive adhesive layer is applied to the cutting blade. Adheses in the form of powder, so-called powder falling is unlikely to occur, and even when exposed to a high temperature environment such as heat treatment, the surface of the article (that is, the adherend) is contaminated during peeling. It's hard to do.

The base material in the protective film of the present invention is not particularly limited as long as an adhesive layer can be formed on the base material.
Examples of the base material include vinyl chloride resin, acrylic resin, polyolefin resin, ABS resin, polycarbonate resin, polyimide resin, acetate resin, polyether sulfone resin, polyamide resin, and fluorine resin. Examples thereof include a base material containing a resin such as a polyester resin.
Among these, as the base material, a base material containing a polyester resin is preferable from the viewpoint of surface protection performance, and a base material containing polyethylene terephthalate is particularly preferable from the viewpoint of practicality.

The substrate in the protective film of the present invention may contain various additives such as plasticizers, colorants (for example, dyes and pigments), heat stabilizers, light stabilizers, fillers, antistatic agents, flame retardants and the like. good.
Further, the base material may be partially or wholly patterned.

The thickness of the base material is generally 500 μm or less, preferably 300 μm or less, and more preferably 200 μm or less.
The lower limit of the thickness of the base material is, for example, preferably 5 μm or more, more preferably 10 μm or more, from the viewpoint of the strength of the protective film.

An antistatic layer may be provided on one side or both sides of the base material. Further, the surface of the base material on the side where the pressure-sensitive adhesive layer is provided may be surface-treated by a corona treatment machine or a plasma treatment machine from the viewpoint of improving the adhesion to the pressure-sensitive adhesive layer.

The method for forming the pressure-sensitive adhesive layer is not particularly limited, and a commonly used method can be adopted.
As a method of forming the pressure-sensitive adhesive layer on the base material, for example, the following method can be adopted.
The pressure-sensitive adhesive composition of the present invention is applied on a substrate as it is or diluted with a solvent if necessary to form a coating film on the substrate. Next, the formed coating film is dried to remove the solvent, and then cured to form an adhesive layer on the substrate.
The surface of the exposed pressure-sensitive adhesive layer 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 surface of the pressure-sensitive adhesive layer. Can be mentioned. Examples of the resin film include a polyester film typified by a polyethylene terephthalate film. Examples of the stripping agent include fluororesins, paraffin waxes, silicones, long-chain alkyl group compounds and the like.
The release film protects the surface of the pressure-sensitive adhesive layer until the protective film is put into practical use, and is peeled off at the time of use.

As another method for forming the pressure-sensitive adhesive layer on the substrate, for example, the following method can be adopted.
The pressure-sensitive adhesive composition of the present invention is applied as it is or, if necessary, diluted with a solvent on a release film such as a paper or a resin film that has been easily peeled with a release agent. , A coating film is formed on the release film. Then, the formed coating film is dried to remove the solvent. Next, the surface of the release film on which the pressure-sensitive adhesive layer is formed is brought into contact with the base material and pressed, and the pressure-sensitive adhesive layer is transferred to the base material to form the pressure-sensitive adhesive layer on the base material. Then, curing is performed.

The method of applying the pressure-sensitive adhesive composition on the base material or the release film is not particularly limited, and a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, a spray coater, etc. are used. Known methods to be used can be mentioned.
The amount of the pressure-sensitive adhesive composition applied onto the base material or the release film is appropriately set according to the thickness of the pressure-sensitive adhesive layer to be formed.

The method for drying the coating film formed on the base material or the release film is not particularly limited, and examples thereof 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 according to the thickness of the pressure-sensitive adhesive layer to be formed, the amount of the organic solvent in the pressure-sensitive adhesive composition, and the like.

The curing conditions are not particularly limited, and for example, the curing is carried out in an environment of 23 ° C. and 50% RH for 1 to 10 days.

The thickness of the pressure-sensitive adhesive layer can be appropriately set according to the adhesive strength required for the protective film, the type of the adherend, the surface roughness of the adherend, and the like.
The thickness of the pressure-sensitive adhesive layer is generally 1 μm or more and 100 μm or less, preferably 5 μm or more and 75 μm or less, and more preferably 10 μm or more and 50 μm or less.

Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

[Manufacture of (meth) acrylic polymer]
[Manufacturing Example 1]
In a reactor equipped with a stirrer, a reflux cooler, a sequential dropping device, and a thermometer, 2-ethylhexyl acrylate (2EHA; other monomer, Tg when made into a homopolymer: -76 ° C.) 92. 4 parts by mass, 2,2,2-trifluoroethyl methacrylate (trade name: light ester M-3F, fluorine-containing (meth) acrylic acid alkyl ester monomer, Tg when used as a homopolymer: 72 ° C. , Kyoeisha Chemical Co., Ltd. 24 parts by mass and 4-hydroxybutyl acrylate (4HBA; monomer having crosslinkable functional group (hydroxyl), Tg when made into a homopolymer: -39 ° C) 3.6 mass After charging the parts and 75 parts by mass of ethyl acetate (EAc), 0.04 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added as a polymerization initiator. After the addition of AIBN, the contents of the reactor were heated and kept at reflux temperature (88 ° C.) for 15 minutes.
Then, in this reactor, 61.6 parts by mass of 2EHA, 16 parts by mass of 2,2,2-trifluoroethyl methacrylate, 2.4 parts by mass of 4HBA, and 15 parts by mass of EAc were further added. And the mixture A consisting of 0.023 parts by mass of AIBN was sequentially added dropwise over 90 minutes. After dropping the mixture A, the temperature of the contents in the reactor was further maintained at 88 ° C. for 30 minutes, and then 25 parts by mass of EAc and 0.23 parts by mass of t-butylperoxypivalate (polymerization initiator) were added. The mixture B composed of the above was sequentially added dropwise over 70 minutes. After dropping the mixture B, the temperature of the contents in the reactor was further maintained at 88 ° C. for 90 minutes, diluted with EAc and toluene to a solid content of 35% by mass, cooled, and (meth) acrylic weight. A coalesced solution was obtained.
The "solid content" in the solution of the (meth) acrylic polymer means the amount of residue obtained by removing volatile components such as a solvent from the solution of the (meth) acrylic polymer (hereinafter, the same applies).

Monomer composition (unit: mass%) of (meth) acrylic polymer, weight average molecular weight (Mw, unit: 10,000 ( ^{denoted as "× 10 4} " in Table 1)), hydroxyl value (unit: mgKOH) / G), glass transition temperature (Tg, unit: ° C.), and solid content (unit: mass%) are shown in Table 1.
The weight average molecular weight (Mw) is measured by the method described above.
The hydroxyl value and the glass transition temperature (Tg) are calculated by the method described above.

Specifically, the hydroxyl value of the (meth) acrylic polymer obtained in Production Example 1 was calculated as follows. The value obtained was rounded to the second decimal place. The content of 4HBA in the (meth) acrylic polymer is 3% by mass, and the molecular weight of 4HBA is 144.17. The number of hydroxyl groups contained in one molecule of 4HBA is 1.
Hydroxy group value (mgKOH / g) of the (meth) acrylic polymer obtained in Production Example 1 = {(3/100) ÷ 144.17} × 56.1 × 1000 × 1 = 11.66 ... 11.7

[Production Examples 2 to 9, and Production Example 11]
In Production Examples 2 to 9, and Production Example 11, the monomer composition in Production Example 1 is changed as shown in Table 1, and the amount of the solvent, the amount of the polymerization initiator, and the like are adjusted in the table. As shown in 1, a solution of the (meth) acrylic polymer was prepared by the same method as in Production Example 1 except that the weight average molecular weight (Mw) of the (meth) acrylic polymer was adjusted.
Monomer composition (unit: mass%) of (meth) acrylic polymer, weight average molecular weight (Mw, unit: 10,000 ( ^{denoted as "× 10 4} " in Table 1)), hydroxyl value (unit: mgKOH) / G), glass transition temperature (Tg, unit: ° C.), and solid content (unit: mass%) are shown in Table 1.
The weight average molecular weight (Mw) is measured by the method described above.
The hydroxyl value and the glass transition temperature (Tg) are calculated by the method described above.

[Manufacturing Example 10]
In Production Example 10, the monomer composition in Production Example 1 was changed as shown in Table 1, and the amount of the solvent, the amount of the polymerization initiator, and the like were adjusted, as shown in Table 1, (meth). A solution of the (meth) acrylic polymer was prepared by the same method as in Production Example 1 except that the weight average molecular weight (Mw) of the acrylic polymer was adjusted.
Monomer composition (unit: mass%) of (meth) acrylic polymer, weight average molecular weight (Mw, unit: 10,000 ( ^{denoted as "× 10 4} " in Table 1)), acid value (unit: mgKOH) / G), glass transition temperature (Tg, unit: ° C.), and solid content (unit: mass%) are shown in Table 1.
The weight average molecular weight (Mw) is measured by the method described above.
The glass transition temperature (Tg) is calculated by the method described above.

The acid value of the (meth) acrylic polymer was calculated by the following formula. In the following calculation formula, 56.1 is the molecular weight of KOH.
Acid value (mgKOH / g) = {(B1 / 100) ÷ B2} x 56.1 x 1000 x B3
B1: Percentage of monomers having a carboxy group in all the monomers used in the production of (meth) acrylic polymers (unit: mass%)
B2: Molecular weight of the monomer having a carboxy group used in the production of the (meth) acrylic polymer B3: Number of carboxy groups contained in one molecule of the monomer having a carboxy group

Specifically, the acid value of the (meth) acrylic polymer obtained in Production Example 10 was calculated as follows. The obtained value was rounded off to the second decimal place.
Acid value (mgKOH / g) of the (meth) acrylic polymer obtained in Production Example 10 = {(2/100) ÷ 72} × 56.1 × 1000 × 1 = 15.57 ・ ・ ・ ≈15. 6

[Production Example 12 and Production Example 13]
In Production Example 12 and Production Example 13, the weight average molecular weight (Mw) of the (meth) acrylic polymer is as shown in Table 1 by adjusting the amount of the solvent, the amount of the polymerization initiator, etc. in Production Example 1. A solution of the (meth) acrylic polymer was prepared by the same method as in Production Example 1 except that the above was adjusted.
Monomer composition (unit: mass%) of (meth) acrylic polymer, weight average molecular weight (Mw, unit: 10,000 ( ^{denoted as "× 10 4} " in Table 1)), hydroxyl value (unit: mgKOH) / G), glass transition temperature (Tg, unit: ° C.), and solid content (unit: mass%) are shown in Table 1.
The weight average molecular weight (Mw) is measured by the method described above.
The hydroxyl value and the glass transition temperature (Tg) are calculated by the method described above.

In Table 1, "4HBA" represents "4-hydroxybutyl acrylate", "2HEA" represents "2-hydroxyethyl acrylate", "AA" represents "acrylic acid", and "2EHA" represents "2-". "Ethylhexyl acrylate" is represented, "n-BA" is represented by "n-butyl acrylate", and "i-OA" is represented by "isooctyl acrylate".
"2,2,2-trifluoroethyl acrylic acid" in Table 1 is Viscoat (registered trademark) 3F (trade name; fluorine-containing (meth) acrylic acid alkyl ester monomer) of Osaka Organic Chemical Industry Co., Ltd. Tg: −5 ° C. when used as a homopolymer).
The glass transition temperature (Tg) described for each monomer in Table 1 is the glass transition temperature (Tg) when the monomer is used as a homopolymer, which is measured by the method described above.
In Table 1, "-" means that the corresponding monomer is not used.

[Manufacturing of adhesive composition]
[Example 1]
100 parts by mass (solid content conversion value) of the (meth) acrylic polymer solution (solid content: 35% by mass) prepared in Production Example 1 and an isocyanate-based compound as a cross-linking agent (trade name: Sumijour (registered trademark)). ) N3300, HMDI (hexamethylene diisocyanate), solid content: 100% by mass, Sumika Cobestrourethane Co., Ltd. 0.7 parts by mass (to the hydroxyl group which is a crosslinkable functional group of the above (meth) acrylic polymer On the other hand, HMDI has 0.5 molar equivalent of isocyanate groups) and a cross-linking catalyst (trade name: Adecaster (registered trademark) OT-1, dioctyltin dilaurate, solid content: 100% by mass, Co., Ltd. (Made by ADEKA) diluted 300-fold with acetylacetone was mixed with 2.1 parts by mass and sufficiently stirred to obtain the pressure-sensitive adhesive composition of Example 1. Details of the composition of the pressure-sensitive adhesive composition are shown in Table 2.

[Examples 2 to 11]
In Examples 2 to 11, the same operation as in Example 1 was carried out except that the type of the (meth) acrylic polymer in Example 1 was changed to that shown in Table 2, and the pressure-sensitive adhesive composition was prepared. Obtained.

[Example 12 and 13]
In Examples 12 and 13, the same operations as in Example 1 were carried out except that the type of the cross-linking agent in Example 1 was changed to that shown in Table 2, to obtain a pressure-sensitive adhesive composition.

[Example 14]
In Example 14, the same operation as in Example 1 was carried out except that the type of the (meth) acrylic polymer and the type of the cross-linking agent in Example 1 were changed to those shown in Table 2, and the pressure-sensitive adhesive composition was carried out. Got The amount of the cross-linking agent used in Example 14 was such that the epoxy group contained in the epoxy-based compound was 0. The amount was set to 5 molar equivalents.

[Example 15 and Example 16]
In Examples 15 and 16, the same operations as in Example 1 were carried out except that the amount of the cross-linking agent in Example 1 was changed to that shown in Table 2, to obtain a pressure-sensitive adhesive composition.

[Comparative Example 1 and Comparative Example 2]
In Comparative Example 1 and Comparative Example 2, the same operations as in Example 1 were carried out except that the type of the (meth) acrylic polymer in Example 1 was changed to that shown in Table 2, and the pressure-sensitive adhesive composition was prepared. Obtained.

[Comparative Example 3 and Comparative Example 4]
In Comparative Example 3 and Comparative Example 4, the same operation as in Example 1 was carried out except that the blending amount of the cross-linking agent in Example 1 was changed to the amount shown in Table 2, to obtain a pressure-sensitive adhesive composition.

[evaluation]
[Preparation of protective film for evaluation]
Using the pressure-sensitive adhesive composition obtained above, a protective film for evaluation was prepared as follows.
Polyethylene terephthalate (PET) film as a base material (trade name: Toyobo Ester (registered trademark) film E5001, thickness: 50 μm, using a gravure coater on Toyobo Co., Ltd., the thickness after drying is 20 μm. The pressure-sensitive adhesive composition was applied as described above to form a coating film. Next, the coating film formed on the PET film was dried at 100 ° C. for 1 minute using a hot air circulation type dryer. Next, the exposed surface of the dried coating film that does not come into contact with the PET film and the release film that was easily peeled off with a silicone-based release treatment agent (trade name: Film Vina (registered trademark) 100E, Fujimori Kogyo Co., Ltd.) The peeled surface of No. 1 was pressure-bonded with a pressure nip roll. Then, it was cured for 168 hours in an environment of 23 ° C. and 50% RH to prepare a protective film for evaluation (base material / adhesive layer / release film).

1. 1. Measurement of Adhesive Strength Before Heating The evaluation protective film prepared above was cut to a size of 25 mm × 150 mm using a cutter blade, and one evaluation protective film piece was prepared.
The peeling film of the prepared protective film piece for evaluation is peeled off, and the surface of the pressure-sensitive adhesive layer exposed by the peeling is referred to as a stainless steel plate (trade name: SUS304 (BA), Paltek Corporation) (hereinafter, appropriately referred to as "SUS plate"). After laminating and laminating on the surface of (referred to as), a 2 kg roller was reciprocated once and crimped to prepare a test piece (SUS plate / adhesive layer / base material). Next, the prepared test piece was left to stand for 30 minutes in an environment with an atmospheric temperature of 23 ° C. and 50% RH.
For the test piece after being left to stand, the adhesive strength (unit: N / 25 mm) when the protective film for evaluation (base material / adhesive layer) is peeled 180 ° in the long side (150 mm) direction from the SUS plate is used as a measuring device. , A & D Co., Ltd.'s single column type material tester (model number: STA-1225) was used to measure at an ambient temperature of 23 ° C. and a peeling speed of 300 mm / min in an environment of 50% RH. The adhesive strength before heating was evaluated according to the following evaluation criteria. The results are shown in Table 2.
If the evaluation result is "A", "B", or "C", it is judged that there is no practical problem.

-Evaluation criteria-
A: 0.1N / 25mm or more and less than 0.5N / 25mm B: 0.5N / 25mm or more and less than 2.0N / 25mm, or 0.05N / 25mm or more and less than 0.1N / 25mm C: 2.0N / 25mm or more Less than 5.0N / 25mm, or 0.01N / 25mm or more and less than 0.05N / 25mm D: 5.0N / 25mm or more, or less than 0.01N / 25mm

2. Powder drop resistance The evaluation protective film produced above was cut to a size of 25 mm × 150 mm using a cutter blade, and one evaluation protective film piece was prepared.
Peel off the release film of the prepared protective film piece for evaluation, scratch the surface of the adhesive layer exposed by the peeling with a nail 5 times, and check whether the adhesive film forming the adhesive layer peels off in powder form. In addition to confirmation, when the film was peeled off, the number of scratches until the film was peeled off was measured, and the powder removal resistance was evaluated according to the following evaluation criteria. The results are shown in Table 2.
If the evaluation result is "A", "B", or "C", it is judged that there is no practical problem.

-Evaluation criteria-
A: The adhesive film forming the adhesive layer does not peel off in powder form.
B: The adhesive film forming the adhesive layer is scratched and peeled off in powder form at the fifth time.
C: The adhesive film forming the adhesive layer is scratched and peeled off in powder form at the third to fourth times.
D: The adhesive film forming the adhesive layer is scratched and peeled off in powder form in the first and second times.

3. 3. Measurement of Adhesive Strength After Heating The evaluation protective film prepared above was cut to a size of 25 mm × 150 mm using a cutter blade, and one evaluation protective film piece was prepared.
The peeling film of the prepared protective film piece for evaluation is peeled off, and the surface of the pressure-sensitive adhesive layer exposed by the peeling is referred to as a stainless steel plate (trade name: SUS304 (BA), Paltek Corporation) (hereinafter, appropriately referred to as "SUS plate"). After laminating and laminating on the surface of (referred to as), a 2 kg roller was reciprocated once and crimped to prepare a test piece (SUS plate / adhesive layer / base material). Next, the prepared test piece was put into a dryer whose temperature was adjusted to 100 ° C. for 168 hours, and then left to stand for 24 hours in an environment with an atmospheric temperature of 23 ° C. and 50% RH.
For the test piece after being left to stand, the adhesive strength (unit: N / 25 mm) when the protective film for evaluation (base material / adhesive layer) is peeled 180 ° in the long side (150 mm) direction from the SUS plate is used as a measuring device. , A & D Co., Ltd.'s single column type material tester (model number: STA-1225) was used to measure at an ambient temperature of 23 ° C. and a peeling speed of 300 mm / min in an environment of 50% RH. The adhesive strength after heating was evaluated according to the following evaluation criteria. The results are shown in Table 2.
If the evaluation result is "A", "B", or "C", it is judged that there is no practical problem.

-Evaluation criteria-
A: 0.1N / 25mm or more and less than 5.0N / 25mm B: 5.0N / 25mm or more and less than 7.0N / 25mm, or 0.05N / 25mm or more and less than 0.1N / 25mm C: 7.0N / 25mm or more Less than 10.0N / 25mm, or 0.01N / 25mm or more and less than 0.05N / 25mm D: 10.0N / 25mm or more, or less than 0.01N / 25mm

4. Stain resistance The evaluation protective film produced above was cut to a size of 25 mm × 150 mm using a cutter blade, and one evaluation protective film piece was prepared.
The peeling film of the prepared protective film piece for evaluation is peeled off, and the surface of the pressure-sensitive adhesive layer exposed by the peeling is referred to as a stainless steel plate (trade name: SUS304 (BA), Paltek Corporation) (hereinafter, appropriately referred to as "SUS plate"). After laminating and laminating on the surface of (referred to as), a 2 kg roller was reciprocated once and crimped to prepare a test piece (SUS plate / adhesive layer / base material). Next, the prepared test piece was put into a dryer whose temperature was adjusted to 100 ° C. for 168 hours, and then left to stand for 24 hours in an environment with an atmospheric temperature of 23 ° C. and 50% RH.
For the test piece after being left to stand, a single column type material tester (model number: STA-1225) of A & D Co., Ltd. was used, and the peeling speed was 300 mm / min in an environment of an atmospheric temperature of 23 ° C. and 50% RH. Under the conditions, the evaluation protective film (base material / adhesive layer) was peeled from the SUS plate by 180 ° in the long side (150 mm) direction. After peeling, the surface of the SUS plate was visually observed, and the stain resistance was evaluated according to the following evaluation criteria. The results are shown in Table 2.
If the evaluation result is "A", "B", or "C", it is judged that there is no practical problem because the surface of the adherend is less likely to be contaminated during peeling even when exposed to a high temperature environment. ..

-Evaluation criteria-
A: Neither adhesive residue nor cloudiness is confirmed.
B: No adhesive residue is confirmed, but light cloudiness is confirmed only on the edge of the bonded surface.
C: Adhesive residue is confirmed only on the edge portion of the bonded surface, and / or light cloudiness is confirmed on the entire bonded surface.
D: Adhesive residue is confirmed on the entire bonded surface, or deep cloudiness is confirmed on the entire bonded surface.

Details of each cross-linking agent shown in Table 2 are as shown below.
HMDI: Sumijule (registered trademark) N3300 (trade name, hexamethylene diisocyanate, solid content: 100% by mass, Sumika Cobestrourethane Co., Ltd.)
TDI: Coronate (registered trademark) L-45E (trade name, adduct of toluene diisocyanate (TDI) and trimethylolpropane, solid content: 45% by mass, Tosoh Corporation)
XDI (Xylylene diisocyanate): Takenate (registered trademark) D-110N (trade name, adduct of xylylene diisocyanate (XDI) and trimethylolpropane, solid content: 75% by mass, Mitsui Chemicals, Inc.)
Epoxy compound: TETRAD-X (trade name, N, N, N', N', -tetraglycidyl-m-xylylenediamine, solid content: 100% by mass, Mitsubishi Gas Chemical Company, Inc.)

As shown in Table 2, the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive compositions of Examples 1 to 16 is less likely to cause powder to fall off, and is subject to peeling even when exposed to a high temperature environment. It was found that the surface of the body was not easily contaminated. Further, it was found that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive compositions of Examples 1 to 16 exhibited an appropriate adhesive strength before and after heating.

On the other hand, the pressure-sensitive adhesive of Comparative Example 1 in which the content of the constituent units derived from the fluorine-containing (meth) acrylic acid alkyl ester monomer in the (meth) acrylic polymer is less than 6% by mass with respect to all the constituent units. In the pressure-sensitive adhesive layer formed by the composition, adhesive residue was confirmed on the entire surface to be bonded, and it was found that the surface of the adherend was easily contaminated.
According to the pressure-sensitive adhesive composition of Comparative Example 2, the content of the constituent units derived from the fluorine-containing (meth) acrylic acid alkyl ester monomer in the (meth) acrylic polymer exceeds 30% by mass with respect to all the constituent units. In the formed pressure-sensitive adhesive layer, deep cloudiness was confirmed on the entire surface to be bonded, and it was found that the surface of the adherend was easily contaminated.
The pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 3 in which the content of the cross-linking agent is less than 0.1 equivalent with respect to the cross-linking functional group of the (meth) acrylic polymer is formed on the bonded surface. Adhesive residue was confirmed on the whole, and it was found that the surface of the adherend was easily contaminated.
The pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 4 in which the content of the cross-linking agent exceeds 0.8 equivalents with respect to the cross-linking functional group of the (meth) acrylic polymer forms a pressure-sensitive adhesive layer. It was found that the film of the adhesive to be used was scratched and peeled off in the form of powder at the first scratch, and the powder was likely to fall off.

Claims (7)

A structural unit derived from a fluorine-containing (meth) acrylic acid alkyl ester monomer of 6% by mass or more and 30% by mass or less with respect to all the structural units, and
A monomer having at least one crosslinkable functional group selected from the group consisting of a carboxy group, a hydroxyl group, an amide group, and an N-substituted amide group, which is 1% by mass or more and 10% by mass or less based on all the constituent units. Derived constituent units and
In a (meth) acrylic acid alkyl ester monomer different from the fluorine-containing (meth) acrylic acid alkyl ester monomer and the monomer having a crosslinkable functional group in an amount of 50% by mass or more based on all the constituent units. Derived constituent units and
(Meta) acrylic polymer , including
A cross-linking agent of 0.1 equivalent or more and 0.8 equivalent or less with respect to the cross-linking functional group of the (meth) acrylic polymer.
Including
A pressure-sensitive adhesive composition for a protective film in which the fluorine-containing (meth) acrylic acid alkyl ester monomer is 2,2,2-trifluoroethyl methacrylate. The pressure-sensitive adhesive composition for a protective film according to claim 1, wherein the crosslinkable functional group is a hydroxyl group. The pressure-sensitive adhesive composition for a protective film according to claim 2 , wherein the (meth) acrylic polymer has a hydroxyl value of 3 mgKOH / g or more and less than 20 mgKOH / g. The protection according to any one of claims 1 to 3 , wherein the (meth) acrylic acid alkyl ester monomer is a monomer having a glass transition temperature of −60 ° C. or lower when used as a homopolymer. Adhesive composition for film. The pressure-sensitive adhesive composition for a protective film according to any one of claims 1 to 4 , wherein the (meth) acrylic polymer has a weight average molecular weight of 150,000 or more and 450,000 or less. The pressure-sensitive adhesive composition for a protective film according to any one of claims 1 to 5 , wherein the cross-linking agent is an isocyanate compound. A protective film comprising a base material and a pressure-sensitive adhesive layer provided on the base material and formed by the pressure-sensitive adhesive composition for a protective film according to any one of claims 1 to 6.