JP2021113299A - Adhesive composition for heat-resistant adhesive sheet and heat-resistant adhesive sheet - Google Patents

Abstract

To provide: an adhesive composition which, even when heat-treated at a high temperature (for example, 260°C), can maintain good adhesivity to and detachability from an adherend, hardly stains the surface of the adherend when detached therefrom, and can form an adhesive layer which can suppress oxidation of the adherend; and a heat-resistant adhesive sheet.SOLUTION: Provided is an adhesive composition for a heat-resistant adhesive sheet, comprising: a (meth)acrylic copolymer containing a constitutional unit derived from N-methoxymethyl acrylamide, a constitutional unit derived from a monomer having a hydroxyl group, and a constitutional unit derived from a (meth)acrylic acid alkyl ester monomer, where a content of the constitutional unit derived from N-methoxymethyl acrylamide is in a range of 6 mass% to 30 mass% relative to the whole constitutional units; and a crosslinking agent. Also provided is an application thereof.SELECTED DRAWING: None

Description

The present invention relates to a pressure-resistant adhesive composition for a heat-resistant pressure-sensitive adhesive sheet and a heat-resistant pressure-sensitive adhesive sheet.

In the heat treatment step at the time of manufacturing the electronic member represented by the heat pressing step and the solder reflow step, a heat resistant adhesive sheet is used for the purpose of protecting the electronic member. The pressure-sensitive adhesive layer provided in the heat-resistant pressure-sensitive adhesive sheet is required to have a property that an excessive increase and an excessive decrease in adhesive strength due to heat treatment are unlikely to occur.
Conventionally, as a method for improving the heat resistance of a pressure-sensitive adhesive sheet, a method of using a copolymer containing a structural unit derived from a nitrogen-containing monomer as a raw material of a pressure-sensitive adhesive composition is known.

For example, Patent Document 1 describes a heat-resistant adhesive containing an acrylic resin (A) obtained by copolymerizing a copolymerization component [I] containing a (meth) acrylic acid ester-based monomer (a1) as a main component. A pressure-resistant pressure-sensitive adhesive film pressure-sensitive adhesive composition, which is a film pressure-sensitive adhesive composition and contains a (meth) acrylamide-based monomer (a2) having a specific structure as a copolymerization component [I], is disclosed.
Further, for example, Patent Document 2 describes an optical film with a pressure-sensitive adhesive in which a pressure-sensitive adhesive layer is formed on at least one surface of the optical film, and the pressure-sensitive adhesive layer has the specific structures (A) and (A-1). 80% to 96% by weight of (meth) acrylic acid ester, (A-2) 1% to 15% by weight of unsaturated monomer having one olefinic double bond and at least one aromatic ring in the molecule. %% by weight, (A-3) 0.1% by weight to 5% by weight of N-alkoxyalkyl (meth) acrylamide having a specific structure, and (A-4) 0.5% by weight of unsaturated monomer having a polar functional group. 100 parts by weight of acrylic resin, which is a copolymer obtained from a monomer mixture containing% to 5% by weight, (B) 0.3 to 12 parts by weight of an ionic compound having an organic cation, and (C) cross-linking. A pressure-sensitive adhesive composition containing 0.1 parts by weight to 5 parts by weight of an agent is disclosed.

Japanese Unexamined Patent Publication No. 2013-177568 Japanese Unexamined Patent Publication No. 2012-196953

In recent years, the heat-resistant adhesive sheet is required to be used at an extremely higher temperature than the conventional one, for example, 260 ° C. Usually, when the adhesive sheet is used in a high temperature environment, the adhesive strength of the adhesive layer increases, and a problem that it becomes difficult to peel off from the adherend tends to occur. Further, when the pressure-sensitive adhesive sheet is used in a high-temperature environment, the cohesive force of the pressure-sensitive adhesive layer is reduced, and when the pressure-sensitive adhesive layer is peeled off from the adherend, adhesive residue is generated on the surface of the adherend, which easily contaminates the adherend. .. Further, when the cohesive force of the pressure-sensitive adhesive layer is reduced, when the adherend is a copper foil, air enters between the pressure-sensitive adhesive sheet and the copper foil, which causes unintended peeling or oxidation of the copper foil. It may be discolored depending on.
Therefore, the pressure-sensitive adhesive composition used for the heat-resistant pressure-resistant adhesive sheet can maintain good adhesiveness and peelability to the adherend even when used in a high-temperature environment of, for example, 260 ° C., and can be peeled off. At this time, it is required to be able to form an adhesive layer that does not easily contaminate the surface of the adherend and can suppress the oxidation of the adherend.

Regarding the above points, the pressure-sensitive adhesive compositions described in Patent Document 1 and Patent Document 2 are not intended to be used at an extremely higher temperature such as 260 ° C. than before. Further, according to the study by the present inventors, the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive compositions described in Patent Document 1 and Patent Document 2 has a remarkable cohesive force when heat-treated at a high temperature of 260 ° C. It has been found that it is reduced and tends to leave adhesive residue on the surface of the adherend during peeling.

The problem to be solved by the present invention is that good adhesiveness and peelability to the adherend can be maintained even when heat-treated at a high temperature (for example, 260 ° C.), and the adherend can be peeled off. It is an object of the present invention to provide an adhesive composition for a heat-resistant pressure-sensitive adhesive sheet, which is less likely to contaminate the surface and can form a pressure-sensitive adhesive layer capable of suppressing oxidation of an adherend, and a heat-resistant pressure-sensitive adhesive sheet.

Specific means for solving the problem include the following aspects.
<1> Containing a structural unit derived from N-methoxymethylacrylamide, a structural unit derived from a monomer having a hydroxyl group, and a structural unit derived from a (meth) acrylic acid alkyl ester monomer, the above-mentioned N-methoxymethyl For heat-resistant adhesive sheets containing a (meth) acrylic copolymer in which the content of structural units derived from acrylamide is 6% by mass or more and 30% by mass or less with respect to all structural units, and a cross-linking agent. Adhesive composition.
<2> The ratio of the number of moles of crosslinkable functional groups in the crosslinker to the total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer is in the range of 0.1 or more and 1.0 or less. The pressure-resistant pressure-resistant adhesive sheet pressure-sensitive adhesive composition according to <1>.
<3> The description in <1> or <2>, wherein the content of the structural unit derived from the monomer having a hydroxyl group is in the range of 1.5% by mass or more and 20% by mass or less with respect to all the structural units. Adhesive composition for heat-resistant adhesive sheet.
<4> The ratio of the number of moles of crosslinkable functional groups in the crosslinker to the total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer is in the range of 0.3 or more and 0.5 or less. The pressure-resistant pressure-sensitive adhesive sheet pressure-sensitive adhesive composition according to any one of <1> to <3>.
<5> The heat-resistant pressure-sensitive adhesive sheet according to any one of <1> to <4>, wherein the alkyl group in the (meth) acrylic acid alkyl ester monomer has 4 or more and 12 or less carbon atoms. Adhesive composition.
<6> The (meth) acrylic acid alkyl ester monomer contains a (meth) acrylic acid alkyl ester monomer having a glass transition temperature of −20 ° C. or lower when used as a homopolymer <1> to <5> The pressure-sensitive adhesive composition for a heat-resistant pressure-sensitive adhesive sheet according to any one of.
<7> A heat-resistant pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed by the pressure-resistant pressure-sensitive pressure-sensitive adhesive sheet pressure-sensitive adhesive composition according to any one of <1> to <6>.

According to the present invention, even when heat-treated at a high temperature (for example, 260 ° C.), good adhesiveness and peelability to the adherend can be maintained, and the surface of the adherend is contaminated during peeling. Provided are an adhesive composition for a heat-resistant pressure-sensitive adhesive sheet, which is difficult and can form a pressure-sensitive adhesive layer capable of suppressing oxidation of an adherend, and a heat-resistant pressure-sensitive adhesive sheet.

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 a certain 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.

In the present specification, the "(meth) acrylic copolymer" means that the content of the structural unit derived from the monomer having a (meth) acryloyl group is the total structural unit [that is, the (meth) acrylic copolymer. It means a copolymer which is 50% by mass or more of [the total constituent unit of the polymer].

As used herein, the term "adhesive composition" means a liquid or paste-like substance before the cross-linking reaction is completed.
As used herein, the term "adhesive layer" means a film made of a substance (so-called crosslinked product of the pressure-sensitive adhesive composition) after the cross-linking reaction in the pressure-sensitive adhesive composition is completed.

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

[Adhesive composition for heat-resistant adhesive sheet]
The pressure-resistant pressure-sensitive adhesive sheet pressure-sensitive adhesive composition of the present invention (hereinafter, also simply referred to as “pressure-sensitive pressure-sensitive adhesive composition”) is a structural unit derived from N-methoxymethylacrylamide and a structural unit derived from a monomer having a hydroxyl group. , And the constituent units derived from the (meth) acrylic acid alkyl ester monomer, and the content of the constituent units derived from the above N-methoxymethyl acrylamide is 6% by mass or more and 30% by mass or less with respect to all the constituent units. (Meta) acrylic copolymer [hereinafter, also referred to as “specific (meth) acrylic copolymer”. ] And a cross-linking agent.
According to the pressure-sensitive adhesive composition of the present invention, good adhesiveness and peelability to the adherend can be maintained even when heat-treated at a high temperature (for example, 260 ° C.), and the adherend can be peeled off. It is possible to form an adhesive layer that does not easily contaminate the surface of the adherend and can suppress the oxidation of the adherend.
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 limit the interpretation of the pressure-sensitive adhesive composition of the present invention, but is described as an example.

The pressure-sensitive adhesive composition of the present invention has a relatively high polarity of N-methoxymethylacrylamide in addition to a structural unit derived from a monomer having a hydroxyl group and a structural unit derived from a (meth) acrylic acid alkyl ester monomer. Since it contains a (meth) acrylic copolymer containing a constituent unit derived from the above in an amount in a specific range and a cross-linking agent, the formed pressure-sensitive adhesive layer appropriately adheres to the adherend and is initially ( It is considered that good adhesiveness and peelability to the adherend are exhibited before the so-called heat treatment).

Usually, the heat-treated pressure-sensitive adhesive layer tends to have a problem that the adhesive strength increases and it becomes difficult to peel off from the adherend. In general, the reason why the adhesive strength of the pressure-sensitive adhesive layer is increased by heat treatment is that the pressure-sensitive adhesive layer becomes flexible in a high-temperature environment, so that it wets and spreads on the adherend, and the adhesive strength with the interface of the adherend increases. It is thought that this is the reason. The pressure-sensitive adhesive composition of the present invention contains N-, which undergoes a self-crosslinking reaction in a high temperature environment, in addition to a structural unit derived from a monomer having a hydroxyl group and a structural unit derived from a (meth) acrylic acid alkyl ester monomer. Since it contains a (meth) acrylic copolymer containing a structural unit derived from methoxymethyl acrylamide in a specific range, the pressure-sensitive adhesive layer formed is derived from the self-crosslinking reaction of N-methoxymethyl acrylamide during heat treatment. It is considered that the curing shrinkage occurs, and the excessive increase in adhesive strength due to the spread of wetness to the adherend is suppressed. Therefore, the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention can maintain good adhesiveness and peelability to an adherend even when heat-treated at a high temperature of, for example, 260 ° C. Conceivable.

Usually, the heat-treated pressure-sensitive adhesive layer has a reduced cohesive force, and when it is peeled off from the adherend, adhesive residue is likely to be generated on the surface of the adherend. The pressure-sensitive adhesive composition of the present invention has N-, which undergoes a self-crosslinking reaction in a high temperature environment, in addition to a structural unit derived from a monomer having a hydroxyl group and a structural unit derived from a (meth) acrylic acid alkyl ester monomer. Since it contains a (meth) acrylic copolymer containing a structural unit derived from methoxymethyl acrylamide in a specific range, the pressure-sensitive adhesive layer formed undergoes a self-crosslinking reaction of N-methoxymethyl acrylamide when heat-treated. Is advanced, and it is considered that the decrease in cohesive force is suppressed. Therefore, it is considered that the pressure-sensitive adhesive layer formed by 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 heat-treated at a high temperature of 260 ° C., for example. Be done.

Further, since the pressure-sensitive adhesive composition of the present invention contains a (meth) acrylic copolymer containing a structural unit derived from highly polar N-methoxymethyl acrylamide in a specific range, for example, the adherend may be. In the case of copper, the adhesiveness is improved, the floating of the pressure-sensitive adhesive layer from the adherend is suppressed, and the oxidation of copper due to oxygen mixed in the interface between the pressure-sensitive adhesive layer and the adherend is suppressed. It is thought that it can be done.
By the way, when the pressure-sensitive adhesive sheet is attached to the adherend, oxygen may be mixed between the pressure-sensitive adhesive layer and the adherend. When this mixed oxygen acts on the adherend, the adherend may be oxidized and spot-like traces may be generated. In particular, in the heat pressing process, which is one of the manufacturing processes of electronic members, the adhesive sheet bonded to the adherend is sandwiched between the upper and lower metal plates, so that the interface between the adherend and the adhesive layer becomes closed. , When oxygen is mixed, it is difficult for oxygen to be released to the outside. Therefore, spot-like traces (also referred to as “bubble traces”) due to oxygen remaining at the interface between the adherend and the pressure-sensitive adhesive layer are likely to occur. In particular, when the adherend is a copper foil, bubble traces tend to be more likely to occur. The pressure-sensitive adhesive composition of the present invention contains a constituent unit derived from N-methoxymethylacrylamide, which generates methanol that has a reducing action on copper oxide when thermally crosslinked, in an amount in a specific range (meth) acrylic. Since it contains a copolymer, it is considered that the appearance of bubble traces can be suppressed.

[Specific (meth) acrylic copolymer]
The pressure-sensitive adhesive composition of the present invention contains a structural unit derived from N-methoxymethylacrylamide, a structural unit derived from a monomer having a hydroxyl group, and a structural unit derived from a (meth) acrylic acid alkyl ester monomer. , The content of the structural unit derived from the above N-methoxymethylacrylamide is in the range of 6% by mass or more and 30% by mass or less with respect to all the structural units (that is, the specific (meth)]. Acrylic copolymer] is included.

<Constituent unit derived from N-methoxymethylacrylamide>
The specific (meth) acrylic copolymer (A) contains a structural unit derived from N-methoxymethylacrylamide.

As used herein, the term "constituent unit derived from N-methoxymethylacrylamide" means a structural unit formed by addition polymerization of N-methoxymethylacrylamide.

The content of the structural unit derived from N-methoxymethyl acrylamide in the specific (meth) acrylic copolymer is 6% by mass or more and 30% by mass or less with respect to all the structural units of the specific (meth) acrylic copolymer. It is preferably in the range of 8% by mass or more and 25% by mass or less, and more preferably in the range of 10% by mass or more and 20% by mass or less.
Formed when the content of structural units derived from N-methoxymethylacrylamide in the specific (meth) acrylic copolymer is 6% by mass or more with respect to all the structural units of the specific (meth) acrylic copolymer. Even when the pressure-sensitive adhesive layer is heat-treated at a high temperature, the pressure-sensitive adhesive layer tends to be less likely to contaminate the surface of the adherend at the time of peeling.
When the content of the structural unit derived from N-methoxymethyl acrylamide in the specific (meth) acrylic copolymer is 30% by mass or less with respect to all the structural units of the specific (meth) acrylic copolymer, it is formed. The pressure-sensitive adhesive layer to be coated tends to suppress the oxidation of the adherend even when it is heat-treated at a high temperature.

<Constituent unit derived from a monomer having a hydroxyl group>
The specific (meth) acrylic copolymer contains a structural unit derived from a monomer having a hydroxyl group. The hydroxyl group of the structural unit derived from the monomer having a hydroxyl group can form a crosslinked structure by a crosslinking reaction with a crosslinking agent described later.

In the present specification, the “constituent unit derived from a monomer having a hydroxyl group” means a structural unit formed by addition polymerization of a monomer having a hydroxyl group.

The type of monomer having a hydroxyl group is not particularly limited.
Specific examples of the monomer having a hydroxyl group include 2-hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-. Hydroxybutyl (meth) acrylate, 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, 1,3-dimethyl-3-hydroxybutyl (meth) acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth) acrylate, 2-ethyl-3-3 Examples thereof include hydroxyhexyl (meth) acrylate and N-hydroxyethyl (meth) acrylamide.
As the monomer having a hydroxyl group, for example, hydroxyalkyl (meth) acrylate is preferable from the viewpoint of good copolymerizability with the (meth) acrylic acid alkyl ester monomer.
Further, as the monomer having a hydroxyl group, for example, from the viewpoint of good compatibility with the (meth) acrylic acid alkyl ester monomer, a hydroxyalkyl having a hydroxyalkyl group having 1 to 5 carbon atoms. (Meta) acrylate is preferable, hydroxyalkyl (meth) acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms is more preferable, and a group consisting of 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, and 2-hydroxyethyl acrylate. At least one selected from the above is more preferable.

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

The content of the structural unit derived from the monomer having a hydroxyl group in the specific (meth) acrylic copolymer is 1% by mass or more and 25% by mass with respect to all the structural units of the specific (meth) acrylic copolymer. It is preferably in the following range, more preferably in the range of 1.5% by mass or more and 20% by mass or less, further preferably in the range of 5% by mass or more and 15% by mass or less, and 5% by mass or more and 10%. It is particularly preferably in the range of mass% or less.
When the content of the structural unit derived from the monomer having a hydroxyl group in the specific (meth) acrylic copolymer is 1% by mass or more with respect to all the structural units of the specific (meth) acrylic copolymer, Since the adhesive layer to be formed has a more appropriate cohesive force, it is easier to maintain good adhesiveness and peelability to the adherend even when heat-treated at a high temperature, and at the time of peeling. It tends to be less likely to contaminate the surface of the adherend.
When the content of the structural unit derived from the monomer having a hydroxyl group in the specific (meth) acrylic copolymer is 25% by mass or less with respect to all the structural units of the specific (meth) acrylic copolymer, The formed pressure-sensitive adhesive layer tends to better suppress the oxidation of the adherend even when it is heat-treated at a high temperature.

<Constituent unit derived from (meth) acrylic acid alkyl ester monomer>
The specific (meth) acrylic copolymer contains a structural unit derived from the (meth) acrylic acid alkyl ester monomer.
The structural unit derived from the (meth) acrylic acid alkyl ester monomer contributes to the adjustment of adhesive strength.

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.
The "(meth) acrylic acid alkyl ester monomer" in the present specification does not include a (meth) acrylic acid alkyl ester monomer having at least one of a hydroxyl group and a carboxy group.

The type of (meth) acrylic acid alkyl ester monomer is not particularly limited.
As the (meth) acrylic acid alkyl ester monomer, an unsubstituted (meth) acrylic acid alkyl ester monomer is preferable.
The alkyl group of the (meth) acrylic acid alkyl ester monomer may be linear, branched or cyclic.
From the viewpoint of adhesive strength, for example, the number of carbon atoms of the alkyl group is preferably in the range of 1 or more and 18 or less, more preferably in the range of 1 or more and 12 or less, and preferably in the range of 4 or more and 12 or less. More preferred.
In particular, when the number of carbon atoms of the alkyl group is in the range of 4 or more and 12 or less, the formed pressure-sensitive adhesive layer has a more appropriate cohesive force. Good adhesiveness and peelability are more likely to be maintained, and the surface of the adherend is less likely to be contaminated during peeling.

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.

The (meth) acrylic acid alkyl ester monomer preferably contains, for example, a (meth) acrylic acid alkyl ester monomer having a glass transition temperature of −20 ° C. or lower when used as a homopolymer, and is a homopolymer. It is more preferable to contain a (meth) acrylic acid alkyl ester monomer in which the glass transition temperature is in the range of −80 ° C. or higher and −20 ° C. or lower, and the glass transition temperature when made into a homopolymer is −80. It is more preferable to contain a (meth) acrylic acid alkyl ester monomer in the range of ° C. or higher and −50 ° C. or lower, and the glass transition temperature when made into a homopolymer is in the range of −80 ° C. or higher and −55 ° C. or lower. It is particularly preferable to contain a (meth) acrylic acid alkyl ester monomer.
When the (meth) acrylic acid alkyl ester monomer contains a (meth) acrylic acid alkyl ester monomer having a glass transition temperature of −20 ° C. or lower when used as a homopolymer, it is subjected to heat treatment at a high temperature. Since the increase in the adhesive strength of the pressure-sensitive adhesive layer is further suppressed, good adhesiveness and peelability of the pressure-sensitive adhesive layer to the adherend tend to be more easily maintained even after heat treatment at a high temperature.

The (meth) acrylic acid alkyl ester monomer having a glass transition temperature of −20 ° C. or lower when used as a homopolymer is 2-ethylhexyl acrylate (glass transition temperature when used as a homopolymer: −76 ° C., Examples thereof include n-butyl acrylate (glass transition temperature when made into a homopolymer: −57 ° C.), i-octyl acrylate (glass transition temperature when made into a homopolymer: −75 ° C.), and the like.

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

The content of the structural unit derived from the (meth) acrylic acid alkyl ester monomer in the specific (meth) acrylic copolymer is not particularly limited, but for example, all the structural units of the specific (meth) acrylic copolymer. On the other hand, it is preferably 50% by mass or more, more preferably 50% by mass or more and 93% by mass or less, and further preferably 69% by mass or more and 92.5% by mass or less. It is particularly preferably in the range of 74% by mass or more and 90% by mass or less.
Here, the content of the structural unit derived from the (meth) acrylic acid alkyl ester monomer in the specific (meth) acrylic copolymer is 50 with respect to all the structural units of the specific (meth) acrylic copolymer. The mass% or more means that the structural unit derived from the (meth) acrylic acid alkyl ester monomer is contained as the main component of the structural unit constituting the specific (meth) acrylic copolymer. do.

<Constituent unit derived from a monomer having a carboxy group>
The specific (meth) acrylic copolymer may contain a structural unit derived from a monomer having a carboxy group. The carboxy group of the structural unit derived from the monomer having a carboxy group can form a crosslinked structure by a crosslinking reaction with a crosslinking agent described later.

As used herein, the "constituent unit derived from a monomer having a carboxy group" means a structural unit formed by addition polymerization of a monomer having a carboxy group.

The type of monomer having a carboxy group is not particularly limited.
Specific examples of the monomer having a carboxy group include acrylic acid, methacrylic acid, crotonic acid, maleic anhydride, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, and ω-carboxy-polycaprolactone mono (meth) acrylate [ For example, ω-carboxy-polycaprolactone (n≈2) monoacrylate], succinic acid ester (for example, 2-acryloyloxyethyl-succinic acid) and the like can be mentioned.

When the specific (meth) acrylic copolymer contains a structural unit derived from a monomer having a carboxy group, it may contain only one structural unit derived from the monomer having a carboxy group. It may contain more than seeds.

The content of the structural unit derived from the monomer having a carboxy group in the specific (meth) acrylic copolymer is not particularly limited.
The specific (meth) acrylic copolymer does not contain a structural unit derived from a monomer having a carboxy group, or the content of the structural unit derived from a monomer having a carboxy group is specific (meth). ) With respect to all the structural units of the acrylic copolymer, it is preferably in the range of more than 0% by mass and 10% by mass or less, and it does not contain a structural unit derived from a monomer having a carboxy group, or it does not contain a structural unit. , The content of the structural unit derived from the monomer having a carboxy group is in the range of more than 0% by mass and 5% by mass or less with respect to all the structural units of the specific (meth) acrylic copolymer. Is more preferable, and it is further preferable that it does not contain a structural unit derived from a monomer having a carboxy group.

<Other building blocks>
The specific (meth) acrylic copolymer may contain a structural unit (so-called other structural unit) other than the above-mentioned structural unit as long as the effect of the present invention is exhibited.

Examples of the monomer constituting the other structural unit include (meth) acrylate having an aromatic ring 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 acrylonitrile, 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.

When the specific (meth) acrylic copolymer contains other structural units, it may contain only one type of other structural units, or may contain two or more types of other structural units.

When the specific (meth) acrylic copolymer contains other structural units, the content of the other structural units in the specific (meth) acrylic copolymer is not particularly limited and can be appropriately set according to the purpose. ..

<< Glass transition temperature of specific (meth) acrylic copolymer >>
The glass transition temperature (also referred to as “Tg”) of the specific (meth) acrylic copolymer is preferably −20 ° C. or lower, more preferably −80 ° C. or higher and −20 ° C. or lower. It is more preferably in the range of −80 ° C. or higher and −50 ° C. or lower, particularly preferably in the range of −75 ° C. or higher and −55 ° C. or lower, and most preferably in the range of −75 ° C. or higher and −60 ° C. or lower. ..
When the glass transition temperature of the specific (meth) acrylic copolymer is -20 ° C or lower, the increase in the adhesive strength of the pressure-sensitive adhesive layer when heat-treated at a high temperature is further suppressed, so that after the heat treatment at a high temperature Also, the adhesive layer tends to maintain good adhesiveness and peelability to the adherend more easily.

For the glass transition temperature of the specific (meth) acrylic copolymer, the absolute temperature (unit: K; hereinafter the same) calculated from the following formula 1 is changed to the Celsius temperature (unit: ° C; hereinafter the same). It is a converted value.
1 / Tg = m1 / Tg1 + m2 / Tg2 + ... + m (k-1) / Tg (k-1) + mk / Tgk (Equation 1)

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

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

The "glass transition temperature represented by the Celsius temperature when made into a homopolymer" of a typical monomer is -76 ° C for 2-ethylhexyl acrylate (2EHA) and -10 ° C for 2-ethylhexyl methacrylate (2EHMA). , N-butyl acrylate (n-BA) at −57 ° C., n-butyl methacrylate (n-BMA) at 21 ° C., t-butyl acrylate (t-BA) at 41 ° C., t-butyl methacrylate (t-BMA). Is 107 ° C, i-butyl methacrylate (i-BMA) is 48 ° C, methyl acrylate (MA) is 5 ° C, methyl methacrylate (MMA) is 103 ° C, isobonyl methacrylate (IBXMA) is 155 ° C, and isobonyl acrylate (IBXA). ) Is 96 ° C, ethyl acrylate (EA) is -27 ° C, methacrylic acid is 185 ° C, 4-hydroxybutyl acrylate (4HBA) is -39 ° C, 2-hydroxyethyl acrylate (2HEA) is -15 ° C, 2-hydroxy. Ethyl methacrylate (2HEMA) at 55 ° C, 2-hydroxypropyl acrylate (2HPA) at -7 ° C, acrylic acid (AA) at 163 ° C, i-octyl acrylate (i-OA) at -75 ° C, dimethylaminoethyl methacrylate ( DM) is 18 ° C., ω-carboxy-polycaprolactone (n≈2) monoacrylate is −30 ° C., and 2-acryloyloxyethyl-succinic acid is −40 ° C.

The glass transition temperature of the specific (meth) acrylic copolymer can be appropriately adjusted by using, for example, two or more types of monomers having different glass transition temperatures when used as a homopolymer.

<< Weight average molecular weight of specific (meth) acrylic copolymer >>
The weight average molecular weight (also referred to as "Mw") of the specific (meth) acrylic copolymer is preferably in the range of 200,000 or more and 1.2 million or less, and more preferably in the range of 200,000 or more and 1 million or less. It is more preferably in the range of 200,000 or more and 800,000 or less, and particularly preferably in the range of 200,000 or more and 700,000 or less.
When the weight average molecular weight of the specific (meth) acrylic copolymer is 200,000 or more, the formed pressure-sensitive adhesive layer has a more appropriate cohesive force, so that it can be peeled off even when heat-treated at a high temperature. At the time, the surface of the adherend tends to be less likely to be contaminated.
When the weight average molecular weight of the specific (meth) acrylic copolymer is 1.2 million or less, the pressure-sensitive adhesive composition tends to have a more appropriate viscosity and thus a tendency to further improve the coatability.

The weight average molecular weight of the specific (meth) acrylic copolymer 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 copolymer is applied to a release paper and dried at 100 ° C. for 1 minute to obtain a film-like specific (meth) acrylic copolymer.
(2) A sample solution having a solid content concentration of 0.2% by mass is obtained by using the film-shaped specific (meth) acrylic copolymer obtained in (1) above and tetrahydrofuran. The "solid content concentration" here means the mass ratio of the specific (meth) acrylic copolymer to the sample solution.
(3) Using gel permeation chromatography (GPC), the weight average molecular weight of the specific (meth) acrylic copolymer 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) [Built-in to HLC-8220, Tosoh Corporation]
Column: TSK-GEL GMHXL [Tosoh Co., Ltd.] connected in series 4 Column temperature: 40 ° C
Eluent: Tetrahydrofuran Sample solution injection volume: 100 μL
Flow rate: 0.8 mL / min

The weight average molecular weight of the specific (meth) acrylic copolymer can be adjusted to a desired value 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.

<< Content of specific (meth) acrylic copolymer >>
The content of the specific (meth) acrylic copolymer in the pressure-sensitive adhesive composition of the present invention is not particularly limited, but is, for example, 65% by mass or more and 99.99% by mass with respect to the total solid content in the pressure-sensitive adhesive composition. It is preferably in the range of% or less, more preferably in the range of 70% by mass or more and 99.99% by mass or less, further preferably in the range of 75% by mass or more and 99.95% by mass or less, and more preferably 80% by mass. It is particularly preferably in the range of% or more and 99.95% by mass or less.
In the present specification, the "total solid content in the pressure-sensitive adhesive composition" means the total mass of the pressure-sensitive adhesive composition when the pressure-sensitive adhesive composition does not contain a solvent, and the pressure-sensitive adhesive composition contains a solvent. When included, it means the mass of the residue obtained by removing the solvent from the pressure-sensitive adhesive composition.

[Method for producing specific (meth) acrylic copolymer]
The method for producing the specific (meth) acrylic copolymer is not particularly limited.
The specific (meth) acrylic copolymer is obtained by polymerizing the above-mentioned monomers by a known polymerization method typified by, for example, a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, and a massive polymerization method. Can be manufactured by
As the polymerization method, the solution polymerization method is preferable because the treatment step is relatively simple and can be performed in a short time in preparing the pressure-sensitive adhesive composition of the present invention after production.

In the solution polymerization method, 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 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.
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, tetraline, and decalin. And aromatic hydrocarbon compounds 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. Represented by group or alicyclic hydrocarbon compounds, ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate. Ester compounds, acetone, methyl ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, and ketone compounds typified by methylcyclohexanone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl Glycol ether compounds typified by ether and 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 alcohol compounds typified by butyl alcohol.

In the production of the specific (meth) acrylic copolymer, it is preferable to use an organic solvent that does not easily cause chain transfer during the polymerization reaction of the aromatic hydrocarbon compound, the ester compound, the ketone compound and the like, and in particular, the specific (meth) acrylic. From the viewpoint of solubility of the system copolymer, ease of polymerization reaction, etc., it is preferable to use at least one selected from the group consisting of ethyl acetate, toluene, and methyl ethyl ketone.

At the time of the polymerization reaction, only one kind of organic solvent may be used, or two or more kinds may be used.

Examples of the polymerization initiator include organic peroxides and azo compounds used in ordinary solution polymerization methods.
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'-azobisisobutyronitrile [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 copolymer, it is preferable to use a polymerization initiator that does not cause a graft reaction during the polymerization reaction, and in particular, the use of an azo compound is preferable.

At the time of the polymerization reaction, only one kind of polymerization initiator may be used, or two or more kinds of polymerization initiators may be used.

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

A chain transfer agent may be used in the production of the specific (meth) acrylic copolymer, if necessary.
Examples of the chain transfer agent include cyanoacetic acid, an alkyl ester compound having 1 to 8 carbon atoms of cyanoacetic acid, bromoacetic acid, an alkyl ester compound having 1 to 8 carbon atoms of bromoacetic acid, α-methylstyrene, anthracene, phenanthrene, and fluorene. , And aromatic compounds such as 9-phenylfluorene, p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and aromatic nitro compounds such as p-nitrotoluene, benzoquinone and A benzoquinone derivative typified by 2,3,5,6-tetramethyl-p-benzoquinone, a borane derivative typified by tributylborane, carbon tetrabromide, carbon tetrachloride, 1,1,2,2-tetrabromoethane. , Tribromoethylene, trichloroethylene, bromotrichloromethane, tribromomethane, halogenated hydrocarbon compounds typified by 3-chloro-1-propene, aldehyde compounds typified by chloral and furaldehyde, alkyl having 1 to 18 carbon atoms. For mercaptan compounds, aromatic mercaptan compounds typified by thiophenol and toluene mercaptan, mercaptoacetic acid, alkyl ester compounds having 1 to 10 carbon atoms of mercaptoacetic acid, hydroxyalkyl mercaptan compounds having 1 to 12 carbon atoms, and pinen and turpinolene. A typical terpen compound can be mentioned.

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

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

[Crosslinking agent]
The pressure-sensitive adhesive composition of the present invention contains a cross-linking agent.
The type of cross-linking agent is not particularly limited.
Examples of the cross-linking agent include an isocyanate-based cross-linking agent, an epoxy-based cross-linking agent, and a metal chelate-based cross-linking agent.
Among these, an isocyanate-based cross-linking agent is preferable as the cross-linking agent.

As used herein, the term "isocyanate-based cross-linking agent" refers to a compound having two or more isocyanate groups in the molecule (so-called polyisocyanate compound). Further, the "epoxy-based cross-linking agent" refers to a compound having two or more epoxy groups in the molecule (so-called bifunctional or higher epoxy compound). Further, the "metal chelate-based cross-linking agent" refers to a metal chelate compound (hereinafter, also simply referred to as "metal chelate compound") that functions as a cross-linking agent.

Examples of the polyisocyanate compound include aromatic polyisocyanate compounds such as xylylene diisocyanate (XDI), diphenylmethane diisocyanate, triphenylmethane triisocyanate, and tolylene diisocyanate (TDI), hexamethylene diisocyanate (HMDI), and pentamethylene diisocyanate (PDI). , Isophorone diisocyanate, aliphatic or alicyclic polyisocyanate compounds such as hydrogenated additives of aromatic polyisocyanate compounds, and the like.
The polyisocyanate compound includes a dimer, trimeric or pentameric of the polyisocyanate compound, an adduct of the polyisocyanate compound and a polyol compound such as trimethylolpropane, and a biuret of the polyisocyanate compound. And so on.

As the isocyanate-based cross-linking agent, a commercially available product can be used.
Examples of commercially available isocyanate-based cross-linking agents include "Coronate (registered trademark) HX", "Coronate (registered trademark) HL-S", "Coronate (registered trademark) L", and "Coronate (registered trademark) L-45E". , "Coronate® 2031", "Coronate® 2030", "Coronate® 2234", "Coronate® 2785", "Aquanate® 200", and " Aquanate (registered trademark) 210 "[above, Toso Co., Ltd.]," Sumijuru (registered trademark) N3300 "," Death Module (registered trademark) N3400 ", and" Sumijuru (registered trademark) N-75 "[ Sumika Cobestro Urethane Co., Ltd.], "Duranate (registered trademark) E-405-80T", "Duranate (registered trademark) AE700-100", "Duranate (registered trademark) 24A-100", and "Duranate" (Registered Trademark) TSE-100 "[above, Asahi Kasei Co., Ltd.], and" Takenate (Registered Trademark) D-110N "," Takenate (Registered Trademark) D-120N "," Takenate (Registered Trademark) M-631N , "MT-Orester® NP1200", and "Stavio® XD-340N" [above, Mitsui Kagaku Co., Ltd.].

Examples of the bifunctional or higher functional 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, and 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 -Dibromoneopentyl glycol diglycidyl ether, trimethylpropan triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, diglycidyl adipate, diglycidyl phthalate, tris (glycidyl) isocyanurate, tris (glycidyl) Examples thereof include xicethyl) isocyanurate, 1,3-bis (N, N-glycidyl aminomethyl) cyclohexane, N, N, N', N'-tetraglycidyl-1,3-benzenedi (methaneamine) and the like.

As the epoxy-based cross-linking agent, a commercially available product can be used.
Examples of commercially available epoxy-based cross-linking agents include "TETRAD (registered trademark) -X" and "TETRAD (registered trademark) -C" [above, Mitsubishi Gas Chemical Company, Inc.].

Examples of the metal chelate compound include aluminum monoacetylacetonate bis (ethylacetoacetate), aluminumtris (ethylacetacetate), and aluminum chelate compounds typified by aluminumtris (acetylacetonate), titanium chelate compounds, and zirconium chelate compounds. Examples thereof include cobalt chelate compounds.

As the metal chelate-based cross-linking agent, a commercially available product can be used.
Examples of commercially available metal chelate-based cross-linking agents include "aluminum chelate A", "aluminum chelate D", and "ALCH-TR" [above, Kawaken Fine Chemicals Co., Ltd.].

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.

The content of the cross-linking agent in the pressure-sensitive adhesive composition of the present invention is not particularly limited, and is appropriately set according to, for example, the type of the cross-linking agent.
For example, when the pressure-sensitive adhesive composition of the present invention contains an isocyanate-based cross-linking agent as a cross-linking agent, the content of the isocyanate-based cross-linking agent in the pressure-sensitive adhesive composition is based on 100 parts by mass of the specific (meth) acrylic copolymer. , 0.1 part by mass or more and preferably 15 parts by mass or less, more preferably 0.3 parts by mass or more and 13 parts by mass or less, and 0.5 parts by mass or more and 12 parts by mass or less. Is more preferable.
When the content of the isocyanate-based cross-linking agent in the pressure-sensitive adhesive composition of the present invention is 0.1 part by mass or more with respect to 100 parts by mass of the specific (meth) acrylic copolymer, the pressure-sensitive adhesive layer formed is: Even when heat-treated at a high temperature, the surface of the adherend tends to be less likely to be contaminated during peeling.
When the content of the isocyanate-based cross-linking agent in the pressure-sensitive adhesive composition of the present invention is 15 parts by mass or less with respect to 100 parts by mass of the specific (meth) acrylic copolymer, the pressure-sensitive adhesive layer formed is at a high temperature. Even when heat-treated, it tends to maintain good adhesiveness and peelability to the adherend more easily. Further, when the adherend is copper, it tends to better suppress discoloration due to oxidation of copper.

<< Ratio of the number of moles of crosslinkable functional groups in the crosslinker to the total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer >>
Ratio of the number of moles of crosslinkable functional groups in the crosslinker to the total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer [that is, the number of moles of crosslinkable functional groups in the crosslinker / (meth) The total number of moles of hydroxyl groups and carboxy groups in the acrylic copolymer] is not particularly limited, but is preferably in the range of 0.05 or more and 1.2 or less, and 0.1 or more and 1.0 or less. It is more preferably in the range, further preferably in the range of 0.1 or more and 0.5 or less, and particularly preferably in the range of 0.3 or more and 0.5 or less.
When the ratio of the number of moles of crosslinkable functional groups in the crosslinker to the total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer is 0.05 or more, the pressure-sensitive adhesive layer formed becomes high temperature. Even when the heat treatment is carried out in (1), good adhesiveness and peelability to the adherend are more likely to be maintained, and the surface of the adherend is less likely to be contaminated during peeling.
When the ratio of the number of moles of crosslinkable functional groups in the crosslinker to the total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer is 1.2 or less, the pressure-sensitive adhesive layer formed becomes high temperature. Even when the heat treatment is performed in the above, the oxidation of the adherend tends to be suppressed more satisfactorily.

In the present specification, the "crosslinkable functional group in the crosslinking agent" means a functional group possessed by the crosslinking agent and capable of crosslinking with a hydroxyl group and a carboxy group in the (meth) acrylic copolymer. However, for example, when the cross-linking agent is an isocyanate-based cross-linking agent, it means an isocyanate group, and when the cross-linking agent is an epoxy cross-linking agent, it means an epoxy group.

As used herein, the number of moles of crosslinkable functional groups means the total number of moles of all the crosslinkable functional groups when there are a plurality of crosslinkable functional groups.

Ratio of the number of moles of crosslinkable functional groups in the crosslinker to the total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer [that is, the number of moles of crosslinkable functional groups in the crosslinker / (meth) The total number of moles of hydroxyl groups and carboxy groups in the acrylic copolymer] is calculated by the following formulas (1) to (3).

Number of moles of crosslinkable functional groups in the crosslinker [Unit: mmol / solid content of the crosslinker 100 g]
= [Content of crosslinkable functional group in crosslinker (unit: mass%) / Solid content of crosslinker (unit: mass%) x amount of crosslinker (unit: g)] / Chemical formula of crosslinkable functional group Amount (unit: g / mol) x 1000 ... (1)

Total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer [Unit: mmol / Solid content of (meth) acrylic copolymer 100 g]
= [Content rate (unit: mass%) of the structural unit derived from the monomer having a hydroxyl group in the specific (meth) acrylic copolymer / the molecular weight (unit: mass%) of the structural unit derived from the monomer having a hydroxyl group. g / mol) × Derived from a monomer having a hydroxyl group Number of hydroxyl groups (valence) × 1000] + [Derived from a monomer having a carboxy group in a (meth) acrylic copolymer Content of the structural unit (unit: mass%) / Molecular weight of the structural unit derived from the monomer having a carboxy group (unit: g / mol) × carboxy group in the structural unit derived from the monomer having a carboxy group Number (valence) x 1000] ... (2)

Ratio of the number of moles of crosslinkable functional groups in the cross-linking agent to the total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer = the value obtained by the calculation formula (1) / the value obtained by the calculation formula (2) Value ... (3)

When the cross-linking agent is a metal chelate-based cross-linking agent, for example, the hydroxyl group contained in the specific (meth) acrylic copolymer is coordinated with the central metal in the metal chelate compound which is the metal chelate-based cross-linking agent. Therefore, by replacing the valence of the central metal with the number of functional groups, the number of moles of the metal chelate compound used in the calculation of the molar equivalent ratio (so-called molar equivalent) can be obtained.
In the present invention, for example, since the valence of the central metal in the aluminum chelate compound which is a metal chelate-based cross-linking agent is 3, the aluminum chelate compound is replaced with one having 3 mol functional groups per mol. Can be calculated.

The number of moles of the metal chelate compound is a value calculated from the following formula.
Number of moles of metal chelate compound = (A × B / C) / (D 1 × E 1 / F 1 + D 2 × E 2 / F 2 + ···· + D n × E n × F n)
A = Metal valence of metal chelate compound B = Mass number of parts of metal chelate compound (amount as solid content)
C = molecular weight of metal chelate compound
D ₁ , D ₂ , ... D _n = Content (mass%) of each monomer having at least one of a hydroxyl group and a carboxy group in all the monomers used in the specific (meth) acrylic copolymer. )
E _{1, E} 2, the total number of hydroxyl and carboxyl groups contained in one molecule of the monomer having at least one of the · · · _{E n} = hydroxyl and carboxy groups _{F 1, F 2, ··· F} n = Molecular weight of each monomer having at least one of a hydroxyl group and a carboxy group used in a specific (meth) acrylic copolymer. In addition, n represents the number of types of monomers used, for example, use. When there is only one type of monomer, _{only D 1} is used in the calculation, and D ₂ ... D _n is not used in the calculation.

[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 specific (meth) acrylic copolymer described above.

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

When the pressure-sensitive adhesive composition of the present invention contains an organic solvent, the content of the organic solvent is not particularly limited and can be appropriately set according to the intended purpose.

[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.
Examples of other components include polymers other than specific (meth) acrylic copolymers, cross-linking catalysts, antioxidants, colorants (for example, dyes and pigments), light stabilizers (for example, ultraviolet absorbers), and the like. Be done.

When the pressure-sensitive adhesive composition of the present invention contains other components, the content of the other components can be appropriately set as long as the effects of the present invention are exhibited.

<Use>
The pressure-sensitive adhesive composition of the present invention is suitable for a heat-resistant pressure-sensitive adhesive sheet.
The pressure-sensitive adhesive composition of the present invention can maintain good adhesiveness and peelability to the adherend even when heat-treated at a high temperature (for example, 260 ° C.), and the surface of the adherend at the time of peeling can be maintained. Since it is possible to form an adhesive layer that is less likely to contaminate the material and can suppress the oxidation of the adherend, for example, the parts are temporarily fixed in the heat treatment process during the manufacture of electronic members represented by the heat pressing process and the solder reflow process. It is preferable to use it for forming a pressure-sensitive adhesive layer in a pressure-sensitive adhesive sheet for protecting an electronic member, because the effect of the pressure-sensitive adhesive composition of the present invention is more exhibited.
The pressure-sensitive adhesive composition of the present invention can be applied regardless of the material of the adherend such as resin (for example, polyimide) and metal (for example, copper).

[Heat-resistant adhesive sheet]
The heat-resistant pressure-resistant adhesive sheet of the present invention (hereinafter, also simply referred to as “adhesive sheet”) includes a pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention.
Since the heat-resistant pressure-sensitive adhesive sheet of the present invention includes a pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention, it is good for an adherend even when heat-treated at a high temperature (for example, 260 ° C.). Adhesiveness and peelability can be maintained, the surface of the adherend is less likely to be contaminated during peeling, and oxidation of the adherend can be suppressed.

The pressure-sensitive adhesive sheet of the present invention may be a base-free type pressure-sensitive adhesive sheet having no base material, or may be a base-based type pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on at least one side of the base material.

When the pressure-sensitive adhesive sheet of the present invention is a base material type pressure-sensitive adhesive sheet, the base material is not particularly limited as long as the pressure-sensitive adhesive layer can be formed on the base material.
Examples of the base material include polyester resin, acetate resin, polyether sulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin, acrylic resin, vinyl chloride resin, and ABS (Acrylonitrile). Butadiene Styrene) Examples thereof include films containing resins such as resins and fluororesins.

The substrate may contain various additives such as plasticizers, colorants (eg dyes and pigments), heat stabilizers, light stabilizers, antistatic agents, flame retardants and the like.
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 not particularly limited, but is preferably 30 μm or more, for example.

In the pressure-sensitive adhesive sheet of the present invention, 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 from the pressure-sensitive adhesive layer. For example, a resin film having one or both sides surface-treated with a release treatment agent (so-called easy peeling treatment). Can be mentioned.
Examples of the resin film include a polyester film typified by a polyethylene terephthalate (PET) 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 pressure-sensitive adhesive sheet is put into practical use, and is peeled off during use.

The thickness of the pressure-sensitive adhesive layer is not particularly limited, and can be appropriately set depending on, for example, the type of the base material. In general, the thickness of the pressure-sensitive adhesive layer is generally in the range of 1 μm or more and 100 μm or less, preferably in the range of 5 μm or more and 50 μm or less, and more preferably in the range of 10 μm or more and 30 μm or less.

The adherend of the pressure-sensitive adhesive sheet of the present invention is not particularly limited.
The material of the adherend is represented by, for example, various metals typified by copper, aluminum, and SUS (stainless steel), polyimide-based resin, acrylic-based resin, ABS resin, and polyester-based resin (for example, PET). Examples thereof include various resins and various inorganic materials typified by glass.
The pressure-sensitive adhesive sheet of the present invention can be particularly suitably used for attachment to an adherend made of copper. The pressure-sensitive adhesive composition of the present invention contains a specific unit (meth) derived from N-methoxymethylacrylamide that self-crosslinks in a high temperature environment and generates methanol that has a reducing action on copper oxide in a specific range. ) Since it contains an acrylic copolymer, the pressure-sensitive adhesive sheet of the present invention tends to be less likely to generate bubble marks even when oxygen mixed in the interface between the pressure-sensitive adhesive layer and the adherend remains. Further, since the pressure-sensitive adhesive layer provided in the pressure-sensitive adhesive sheet of the present invention has excellent adhesion to the adherend, oxygen is unlikely to be mixed into the interface between the pressure-sensitive adhesive layer and the adherend, and discoloration of copper due to oxidation is unlikely to occur. Show a tendency.

The method for producing the pressure-sensitive adhesive sheet of the present invention is not particularly limited.
The pressure-sensitive adhesive sheet of the present invention can be produced, for example, by the following method.
In the case of a base-free type pressure-sensitive adhesive sheet, first, the pressure-sensitive adhesive composition of the present invention is applied onto the surface of the release film to form a coating film. Then, the formed coating film is dried. It has a laminated structure of release film / adhesive layer / release film by stacking the dried coating film on the exposed surface that does not come into contact with the release film so that the surface of another release film is in contact with the coating film and then curing it. , A base-free type adhesive sheet can be manufactured.

In the case of a base material type pressure-sensitive adhesive sheet, the pressure-sensitive adhesive composition of the present invention is applied onto the surface of the base material, dried, and then cured to form a pressure-sensitive adhesive layer. This makes it possible to manufacture a base material type pressure-sensitive adhesive sheet having a laminated structure of a base material / pressure-sensitive adhesive layer.

As another method, for example, the following method can be mentioned.
The pressure-sensitive adhesive composition of the present invention is applied onto the surface of the release film, dried, and then cured to form a pressure-sensitive adhesive layer. The formed pressure-sensitive adhesive layer is then transferred to the substrate.
That is, the surface of the release film on which the pressure-sensitive adhesive layer is formed is bonded to the base material and pressed to produce a laminate having a laminated structure of the base material / pressure-sensitive adhesive layer / release film, and then the release film is formed. By peeling off, a base material type pressure-sensitive adhesive sheet having a laminated structure of a base material / pressure-sensitive adhesive layer can be produced.

Further, as another method, for example, the following method can be mentioned.
The pressure-sensitive adhesive composition of the present invention is applied onto the surface of the release film and then dried to prepare a film with a pressure-sensitive adhesive. Next, by adhering the base material to the adhesive surface of the film with the pressure-sensitive adhesive and curing it, a base material-type pressure-sensitive adhesive sheet having a laminated structure of a base material / pressure-sensitive adhesive layer / release film can be produced.

The method of applying the pressure-sensitive adhesive composition on the surface of the base material or the release film is not particularly limited, and for example, a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a knife coater, a spray coater, etc. A known method using a bar coater, an applicator, or the like can be mentioned.
The amount of the pressure-sensitive adhesive composition applied onto the surface of 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 pressure-sensitive adhesive composition applied on the surface of 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 pressure-sensitive adhesive composition applied on the surface of the base material or the release film are not particularly limited, and depend on the thickness of the applied pressure-sensitive adhesive composition, the amount of the organic solvent in the pressure-sensitive adhesive composition, and the like. Is set as appropriate.
An example of the drying condition is a condition of drying at 70 ° C. to 120 ° C. for 1 minute to 3 minutes using a hot air dryer.

Curing is performed, for example, in an environment of 20 ° C. to 35 ° C. for 4 to 7 days.
Curing completes the cross-linking reaction of the pressure-sensitive adhesive composition to form a pressure-sensitive adhesive layer.

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.

[Manufacturing of (meth) acrylic copolymer]
[Manufacturing Example 1]
Ethyl acetate [organic solvent] 190.0 parts by mass and 2,2'-azobisisobutyronitrile [AIBN; polymerization] in a reactor equipped with a thermometer, a stirrer, a reflux condenser, and a sequential dropping device. Initiator] 0.05 parts by mass was charged. Next, 260.0 parts by mass of 2-ethylhexyl acrylate [2EHA; acrylic acid alkyl ester monomer, Tg when made into a homopolymer: -76 ° C.], 120.0 parts by mass of N-methoxymethylacrylamide (NMMA), And 2-Hydroxyethyl methacrylate [2HEMA; monomer having a hydroxyl group] 385.0 parts by mass of a monomer mixed solution containing 20.0 parts by mass was prepared, of which 100.9 parts by mass (monomer mixed solution) was prepared. (Equivalent to 25.2% by mass of) was charged into the reactor, heated, and refluxed at 85 ° C. (reflux temperature) for 20 minutes. Next, with the temperature inside the reactor maintained at the reflux temperature, the remaining 299.1 parts by mass of the monomer mixture (corresponding to 74.8% by mass of the monomer mixture) and ethyl acetate 50.0. A parts by mass and 0.5 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) were sequentially added dropwise over 90 minutes, and after completion of the addition, a polymerization reaction was carried out for 75 minutes.
Next, a mixed solution of 27.0 parts by mass of ethyl acetate and 1.99 parts by mass of 2,2'-azobis (isobutyric acid) dimethyl [polymerization initiator] was sequentially added dropwise over 50 minutes, and 120 parts after completion of the addition. The polymerization reaction was carried out for a minute.
After completion of the reaction, the obtained polymerization reaction product was diluted with ethyl acetate so that the solid content concentration became 45% by mass to obtain a solution of the (meth) acrylic copolymer of Production Example 1.

The "solid content concentration" here means the mass ratio of the (meth) acrylic copolymer to the solution of the (meth) acrylic copolymer.
The same applies to each solution of the (meth) acrylic copolymer of Production Examples 2 to 27 below.

[Production Examples 2 to 14]
In Production Examples 2 to 14, the monomer composition of the (meth) acrylic copolymer was changed to the monomer composition shown in Table 1, and the amount of the organic solvent used and the polymerization initiator were used. The same as in Production Example 1 except that the weight average molecular weight (Mw) of the (meth) acrylic copolymer was adjusted to the weight average molecular weight (Mw) shown in Table 1 by adjusting at least one of the amounts. The operation was carried out to obtain each solution of the (meth) acrylic copolymer of Production Examples 2 to 14 having a solid content concentration of 45% by mass.

[Production Examples 15 to 27]
In Production Examples 15 to 27, the monomer composition of the (meth) acrylic copolymer was changed to the monomer composition shown in Table 2, and the amount of the organic solvent used and the polymerization initiator were used. The same as in Production Example 1 except that the weight average molecular weight (Mw) of the (meth) acrylic copolymer was adjusted to the weight average molecular weight (Mw) shown in Table 2 by adjusting at least one of the amounts. The operation was carried out to obtain solutions of the (meth) acrylic copolymers of Production Examples 15 to 27 having a solid content concentration of 45% by mass.

Monomer composition (unit: mass%) and weight average molecular weight (Mw) of the (meth) acrylic copolymer of Production Examples 1 to 27 [Unit: 10,000 (in the table, expressed as "× 10 ⁴ ") )] Are shown in Tables 1 and 2.

The weight average molecular weight (Mw) of the (meth) acrylic copolymer of Production Examples 1 to 27 is the same as the method for measuring the weight average molecular weight (Mw) of the specific (meth) acrylic copolymer described above. Measured by method.

Among the (meth) acrylic copolymers obtained above, the (meth) acrylic copolymers of Production Examples 1 to 17 correspond to the specific (meth) acrylic copolymers in the present invention. ..

Details of each monomer shown in Tables 1 and 2 are as shown below.
"2EHA": 2-ethylhexyl acrylate [Tg when made into a homopolymer: -76 ° C, acrylic acid alkyl ester monomer]
"N-BA": n-butyl acrylate [Tg when made into a homopolymer: -57 ° C., acrylic acid alkyl ester monomer]
"MA": Methyl acrylate [Tg when made into a homopolymer: 5 ° C., acrylic acid alkyl ester monomer]
"MMA": Methyl methacrylate [Tg when made into a homopolymer: 103 ° C., methacrylic acid alkyl ester monomer]
"NMMA": N-methoxymethylacrylamide "NEMA": N-ethoxymethylacrylamide "NBMA": N-butoxymethylacrylamide "2HEMA": 2-hydroxyethyl methacrylate [monomer having a hydroxyl group]
"4HBA": 4-Hydroxybutyl acrylate [monomer having a hydroxyl group]
"2HEA": 2-hydroxyethyl acrylate [monomer having a hydroxyl group]
"DMAEA": Dimethylaminoethyl acrylate "AA": Acrylic acid [monomer having a carboxy group]

In Tables 1 and 2, "-" described in the column of monomer composition means that the monomer corresponding to the column is not contained.
In Tables 1 and 2, the "weight average molecular weight" is expressed as "Mw".

[Preparation of adhesive composition]
[Example 1]
100 parts by mass (solid content conversion value) of the (meth) acrylic copolymer solution of Production Example 1 and coronate (registered trademark) L-45E as a cross-linking agent [trade name, isocyanate-based cross-linking agent, toluene diisocyanate ( Adhesive of TDI) and trimethylolpropane (TMP), solid content: 45% by mass, isocyanate group content: 7.9% by mass, Toso Co., Ltd.] 3.0 parts by mass (solid content conversion value) , Was thoroughly mixed to obtain the pressure-sensitive adhesive composition of Example 1.
The ratio of the number of moles of crosslinkable functional groups in the crosslinker to the total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer in the obtained pressure-sensitive adhesive composition [that is, the crosslinkability in the crosslinker. The number of moles of the functional group / the total number of moles of the hydroxyl group and the carboxy group in the (meth) acrylic copolymer] was 0.3.

The ratio of the number of moles of crosslinkable functional groups in the crosslinker to the total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer is calculated using the above-mentioned formulas (1) to (3). It was done. Specifically, it was calculated as follows. The isocyanate-based cross-linking agent Coronate (registered trademark) L-45E has a solid content of 45% by mass and an isocyanate group content of 7.9% by mass. The chemical formula of the isocyanate group is 42. The molecular weight of the structural unit derived from 2-hydroxyethyl methacrylate, which is a monomer having a hydroxyl group, is 130.

Calculation formula (1)
Number of moles of crosslinkable functional groups in the crosslinker [Unit: mmol / solid content of the crosslinker 100 g]
= Content of crosslinkable functional group in crosslinker (unit: mass%) / solid content of crosslinker (unit: mass%) x amount of crosslinker (unit: g) / chemical formula amount of crosslinkable functional group (unit: g) Unit: g / mol) x 1000
= 7.9 (mass%) / 45 (mass%) x 3 (g) / 42 (g / mol) x 1000 = 12.53 ... ≒ 12.5

Calculation formula (2)
Total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer [Unit: mmol / Solid content of (meth) acrylic copolymer 100 g]
= [Content rate (unit: mass%) of the structural unit derived from the monomer having a hydroxyl group in the (meth) acrylic copolymer / the molecular weight (unit: g) of the structural unit derived from the monomer having a hydroxyl group / Mol) × Number of hydroxyl groups in the constituent unit derived from the monomer having hydroxyl group (valence) × 1000] + [Structure derived from the monomer having carboxy group in the (meth) acrylic copolymer Unit content (unit: mass%) / molecular weight of the structural unit derived from the monomer having a carboxy group (unit: g / mol) × of the carboxy group in the structural unit derived from the monomer having a carboxy group Number (valence) x 1000]
= [5.0 (parts by mass) / 100 (parts by mass) x 100 (%) / 130 (g / mol) x 1 x 1000] = 38.46 ... ≒ 38.5

Calculation formula (3)
Ratio of the number of moles of crosslinkable functional groups in the crosslinker to the total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer [that is, the number of moles of crosslinkable functional groups in the crosslinker / (meth) Total number of moles of hydroxyl groups and carboxy groups in the acrylic copolymer]
= Value calculated by calculation formula (1) / Value calculated by calculation formula (2) = 12.5 / 38.5 = 0.32 ... ≒ 0.3

[Examples 2-26]
In Example 1, the same operations as in Example 1 were carried out except that the composition of the pressure-sensitive adhesive composition was changed to the composition shown in Table 3, and each pressure-sensitive adhesive composition of Examples 2 to 26 was obtained.

[Comparative Examples 1 to 10]
In Example 1, the same operations as in Example 1 were carried out except that the composition of the pressure-sensitive adhesive composition was changed to the composition shown in Table 4, and each pressure-sensitive adhesive composition of Comparative Examples 1 to 10 was obtained.

The composition of the pressure-sensitive adhesive compositions of Examples 1 to 26 and Comparative Examples 1 to 10 and the crosslinkability in the cross-linking agent with respect to the total number of moles of hydroxyl groups and carboxy groups in the (meth) acrylic copolymer. The ratio of the number of moles of the functional group [that is, the number of moles of the crosslinkable functional group in the cross-linking agent / the total number of moles of the hydroxyl group and the carboxy group in the (meth) acrylic copolymer] is shown in Tables 3 and 4.

Details of each of the cross-linking agents shown in Tables 3 and 4 are as shown below.
"Coronate L-45E": Isocyanate-based cross-linking agent, adduct of toluene diisocyanate (TDI) and trimethylolpropane (TMP), solid content: 45% by mass, isocyanate group content: 7.9% by mass, Toso (stock)
"Takenate D-110N": Isocyanate-based cross-linking agent, xylylene diisocyanate (XDI), solid content: 75% by mass, isocyanate group content: 11.5% by mass, Takeda Pharmaceutical Company Limited
"TETRAD-X": Epoxy cross-linking agent, solid content: 100% by mass, epoxy group content: 90% by mass, Mitsubishi Gas Chemical Company, Inc.
"Coronate HX": Isocyanate-based cross-linking agent, isocyanurate of hexamethylene diisocyanate (HMDI), solid content: 100% by mass, isocyanate group content: 21.3% by mass, Toso Co., Ltd.
The above "coronate", "takenate", and "TETRAD" are all registered trademarks.

<Preparation of adhesive sheet for evaluation test>
Using the pressure-sensitive adhesive composition obtained above, a pressure-sensitive adhesive sheet for evaluation test was prepared as follows. A pressure-sensitive adhesive composition was applied to the surface of a polyimide film [product name: Kapton (registered trademark), Toray DuPont Co., Ltd.] so that the coating amount after drying was 10 g / m ^{2 to form a coating film.} .. Next, the formed coating film was dried using a hot air circulation type dryer under drying conditions of a drying temperature of 100 ° C. and a drying time of 60 seconds to form an adhesive film on the polyimide film. Next, the exposed surface of the adhesive film is overlaid on the surface-treated surface of a release film [trade name: Film Vina (registered trademark) 100E-0010N023, Fujimori Kogyo Co., Ltd.] surface-treated with a silicone-based release treatment agent. , Pressed and bonded using a pressure nip roll. Next, the obtained laminate was allowed to stand in an environment of an atmospheric temperature of 23 ° C. and 50% RH for 1 week and cured to allow the cross-linking reaction to proceed to form a polyimide film / adhesive layer / release film. An evaluation test adhesive sheet having the above was obtained.

[evaluation]
1. 1. The adhesive sheet for the adhesive strength evaluation test was cut into a size of 25 mm × 150 mm, and seven pieces of the adhesive sheet for the evaluation test were prepared. Hereinafter, the six evaluation test adhesive sheet pieces are a first evaluation test adhesive sheet piece, a second evaluation test adhesive sheet piece, a third evaluation test adhesive sheet piece, and a fourth evaluation test adhesive sheet. A piece, a fifth evaluation test pressure-sensitive adhesive sheet piece, a sixth evaluation test pressure-sensitive adhesive sheet piece, and a seventh evaluation test pressure-sensitive adhesive sheet piece.
Of the seven evaluation test adhesive sheet pieces, for the first to third evaluation test adhesive sheet pieces, the release film of the evaluation test adhesive sheet piece (composition: polyimide film / adhesive layer / release film) is peeled off. Then, the surface of the pressure-sensitive adhesive layer exposed by peeling is placed on the surface of a polyimide (PI) film [trade name: Kapton (registered trademark) 100H, Toray DuPont Co., Ltd.] and then crimped using a pressure nip roll. And pasted together.
Regarding the fourth to sixth evaluation test adhesive sheet pieces, the release film of the evaluation test adhesive sheet piece (composition: polyimide film / adhesive layer / release film) was peeled off, and the surface of the pressure-sensitive adhesive layer exposed by the peeling. Was laminated on the surface of a copper foil [trade name: NC-WC, thickness: 10 μm, Furukawa Denki Kogyo Co., Ltd.], and then pressure-bonded and bonded using a pressure nip roll.
Regarding the seventh evaluation test adhesive sheet piece, the release film of the evaluation test adhesive sheet piece (composition: polyimide film / adhesive layer / release film) was peeled off, and the surface of the pressure-sensitive adhesive layer exposed by the peeling was made of copper. It was laminated on the surface of a foil [trade name: NC-WC, thickness: 10 μm, Furukawa Denki Kogyo Co., Ltd.], and bonded as it was without pressurization.

(1) Initial stage (adhesion: polyimide film)
The first evaluation test adhesive sheet piece was attached to a polyimide film and then allowed to stand for 24 hours in an environment with an atmospheric temperature of 23 ° C. and 50% RH. Then, for the first evaluation test adhesive sheet piece after standing, an A & D single column type material tester (model number: STA-1225) was used as a measuring device, and the ambient temperature was 23 ° C. In an environment of 50% RH, under the condition of a peeling speed of 0.3 m / min, the first evaluation test adhesive sheet piece (structure: polyimide film / adhesive layer) is 180 in the long side (150 mm) direction from the polyimide film. ° The adhesive strength (unit: N / 25 mm) when peeled off was measured and used as the initial adhesive strength (adhesion: polyimide film).

(2) After heat treatment (adhesion: polyimide film)
The second evaluation test adhesive sheet piece was attached to a polyimide film and then allowed to stand for 24 hours in an environment with an atmospheric temperature of 23 ° C. and 50% RH. Next, the second evaluation test adhesive sheet piece after standing was allowed to stand in a hot air circulation type dryer [model: PHH-200, ESPEC CO., LTD.] Set at 260 ° C. for 30 minutes, and then the atmospheric temperature. It was allowed to stand in an environment of 23 ° C. and 50% RH for 3 hours. Next, the adhesive strength of the second evaluation test adhesive sheet piece after standing was measured by the same method as the adhesive strength measurement in the above "(1) Initial (adhesion: polyimide film)", and after heat treatment. Adhesive strength (adhesive body: polyimide film).

(3) After hot pressing (adhesion: polyimide film)
The third evaluation test adhesive sheet piece was attached to a polyimide film and then allowed to stand for 24 hours in an environment with an atmospheric temperature of 23 ° C. and 50% RH. Next, the third evaluation test adhesive sheet piece after standing was heat-pressed ^{for 30 minutes under the condition of a pressure of 20 kg / cm 2} using a heat press machine set at 260 ° C., and then the atmosphere temperature was 23 ° C., 50. It was allowed to stand in an environment of% RH for 3 hours. Next, the adhesive strength of the third evaluation test adhesive sheet piece after standing was measured by the same method as the adhesive strength measurement in the above "(1) Initial (adhesion: polyimide film)", and hot-pressed. It was used as the later adhesive strength (adhesion: polyimide film).

(4) Initial (adhesive body: copper foil)
The fourth evaluation test adhesive sheet piece was attached to a copper foil and then allowed to stand for 24 hours in an environment with an atmospheric temperature of 23 ° C. and 50% RH. Then, with respect to the fourth evaluation test adhesive sheet piece after standing, the adhesive strength was measured by the same method as the measurement of the adhesive strength in the above "(1) Initial (adhesion: polyimide film)", and the initial (1) initial (adhesive body: polyimide film) Adhesive strength of the adherend: copper foil).

(5) After heat treatment (adhesive body: copper foil)
The fifth evaluation test adhesive sheet piece was attached to a copper foil and then allowed to stand for 24 hours in an environment with an atmospheric temperature of 23 ° C. and 50% RH. Next, the fifth evaluation test adhesive sheet piece after standing was allowed to stand in a hot air circulation type dryer [model: PHH-200, ESPEC CO., LTD.] Set at 260 ° C. for 30 minutes, and then the atmospheric temperature. It was allowed to stand in an environment of 23 ° C. and 50% RH for 3 hours. Next, with respect to the fifth evaluation test adhesive sheet piece after standing, the adhesive strength was measured by the same method as the measurement of the adhesive strength in the above "(1) Initial (adhesion: polyimide film)", and after the heat treatment. Adhesive strength (adhesive body: copper foil).

(6) After hot pressing (adhesive body: copper foil)
The sixth evaluation test adhesive sheet piece was attached to a copper foil and then allowed to stand for 24 hours in an environment with an atmospheric temperature of 23 ° C. and 50% RH. Next, the sixth evaluation test adhesive sheet piece after standing was heat-pressed ^{for 30 minutes under the condition of a pressure of 20 kg / cm 2} using a heat press machine set at 260 ° C., and then the atmosphere temperature was 23 ° C., 50. It was allowed to stand in an environment of% RH for 3 hours. Next, the adhesive strength of the sixth evaluation test adhesive sheet piece after standing was measured by the same method as the adhesive strength measurement in the above "(1) Initial (adhesion: polyimide film)", and hot-pressed. It was used as the later adhesive strength (adhesive body: copper foil).

The adhesive strength at the initial stage, after heat treatment, and after hot pressing was evaluated according to the following evaluation criteria.
The results are shown in Tables 5 and 6.
If the evaluation result is "A", "B", or "C", it is judged that there is no practical problem.
The fact that the evaluation result is "A", "B", or "C" means that unintentional peeling from the adherend does not occur, and the adherend can be easily peeled off from the adherend. It means that the pressure-sensitive adhesive layer exhibits good adhesiveness and peelability.

-Evaluation criteria-
A: The initial adhesive strength is 1.0 N / 25 mm or more and less than 2.0 N / 25 mm.
B: The initial adhesive strength is 0.7 N / 25 mm or more and less than 1.0 N / 25 mm, or 2.0 N / 25 mm or more and less than 5.0 N / 25 mm.
C: The initial adhesive strength is 0.4 N / 25 mm or more and less than 0.7 N / 25 mm, or 5.0 N / 25 mm or more and less than 10.0 N / 25 mm.
D: The initial adhesive strength is less than 0.4 N / 25 mm, or 10.0 N / 25 mm or more.

2. Stain resistance (1) Polyimide film The surface of the polyimide film after measuring the initial adhesive strength, the polyimide film after measuring the adhesive strength after heat treatment, and the polyimide film after measuring the adhesive strength after hot pressing. Was visually observed, and the stain resistance (adhesion: polyimide film) was evaluated according to the following evaluation criteria.
The results are shown in Tables 5 and 6.
If the evaluation result is "A", "B", or "C", it is judged that there is no practical problem.

-Evaluation criteria-
A: No adhesive residue is confirmed at the initial stage, after heat treatment, and after hot pressing.
B: At least one of the initial stage, after heat treatment, and after hot pressing, a slight amount of adhesive residue is confirmed on the peripheral edge of the bonding.
C: At least one of the initial stage, after heat treatment, and after hot pressing, adhesive residue is confirmed on the bonding peripheral edge, but no adhesive residue is confirmed on the bonding surface.
D: At least one of the initial stage, after heat treatment, and after hot pressing, adhesive residue is confirmed on the bonded surface.

(2) Copper foil Visually inspect the surface of the copper foil after measuring the initial adhesive strength, the copper foil after measuring the adhesive strength after heat treatment, and the copper foil after measuring the adhesive strength after hot pressing. The stain resistance (adhesion: copper foil) was evaluated according to the same evaluation criteria as the stain resistance of the above "(1) Polygonic film".
The results are shown in Tables 5 and 6.
If the evaluation result is "A", "B", or "C", it is judged that there is no practical problem.

3. 3. Oxidation resistance (1) Presence or absence of discoloration The surfaces of the copper foil after measuring the adhesive strength after heat treatment and the copper foil after measuring the adhesive strength after hot pressing are visually observed and evaluated as follows. The oxidation resistance was evaluated based on the presence or absence of discoloration according to the criteria.
The results are shown in Tables 5 and 6.
If the evaluation result is "A", "B", or "C", it is judged that there is no practical problem.

-Evaluation criteria-
A: No discoloration is confirmed after heat treatment or hot pressing.
B: Slight discoloration is confirmed at the bonding peripheral edge portion at least after heat treatment and after hot pressing.
C: Discoloration is confirmed on the bonded peripheral edge portion at least after heat treatment and after heat pressing, but no discoloration is confirmed on the bonded surface.
D: Discoloration is confirmed on the bonded surface at least after heat treatment and after hot pressing.
-: At least after heat treatment or hot pressing, there is a remarkable adhesive residue on the bonded surface, and it is difficult to discriminate discoloration.
(2) Presence or absence of air bubble marks The seventh evaluation test adhesive sheet piece was attached to a copper foil and then allowed to stand for 24 hours in an environment with an atmospheric temperature of 23 ° C. and 50% RH. Next, the 7th evaluation test adhesive sheet piece after standing was allowed to stand in a hot air circulation type dryer [model: PHH-200, ESPEC CORPORATION] set at 260 ° C. for 30 minutes, and then the atmospheric temperature. It was allowed to stand in an environment of 23 ° C. and 50% RH for 3 hours. Next, with respect to the seventh evaluation test adhesive sheet piece after standing, an A & D single column type material tester (model number: STA-1225) was used as a measuring device, and the ambient temperature was 23 ° C. Under the condition of a peeling speed of 0.3 m / min in an environment of 50% RH, a seventh evaluation test adhesive sheet piece (composition: polyimide film / adhesive layer) is 180 in the long side (150 mm) direction from the copper foil. ° Peeled. The surface of the copper foil after peeling was visually observed, and the oxidation resistance was evaluated based on the presence or absence of spot-like discoloration (so-called bubble traces) according to the following evaluation criteria.
The results are shown in Tables 5 and 6.
If the evaluation result is "A", "B", or "C", it is judged that there is no practical problem.

-Evaluation criteria-
A: No bubble traces are confirmed.
B: The area ratio occupied by the bubble traces exceeds 0% of the bonded area and is less than 20%.
C: The area ratio occupied by the bubble trace is 20% or more and less than 50% of the bonded area.
D: The area ratio occupied by the bubble trace is 50% or more of the bonded area.
-: There is a remarkable adhesive residue on the bonded surface, and it is difficult to distinguish the bubble traces.

From the results shown in Table 5, according to the pressure-sensitive adhesive compositions of Examples 1 to 26, good adhesiveness and peelability to the adherend are maintained even when heat-treated at a high temperature of 260 ° C. It has been clarified that it is possible to form an adhesive layer that does not easily contaminate the surface of the adherend at the time of peeling and can suppress the oxidation of the adherend.

On the other hand, as shown in Table 6, the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 1 in which the (meth) acrylic copolymer does not contain a structural unit derived from a monomer having a hydroxyl group is 260. It was confirmed that when the heat treatment was performed at a high temperature of ℃, the surface of the adherend was significantly contaminated during peeling.
The pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 2 in which the content of the constituent units derived from N-methoxymethylacrylamide in the (meth) acrylic copolymer exceeds 30% by mass with respect to all the constituent units. It was confirmed that when the heat treatment was performed at a high temperature of 260 ° C., the adhesive force to the adherend was significantly reduced. Further, when the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 2 is heat-treated at a high temperature of 260 ° C., the copper foil as an adherend is remarkably discolored, and bubble marks are remarkably recorded on the copper foil. It was confirmed that it occurred and the oxidation of the adherend could not be suppressed.
Adhesives of Comparative Example 3, Comparative Example 4, and Comparative Example 9 in which the content of the structural unit derived from N-methoxymethylacrylamide in the (meth) acrylic copolymer is less than 6% by mass with respect to all the structural units. It was confirmed that the pressure-sensitive adhesive layer formed by the agent composition significantly contaminates the surface of the adherend at the time of peeling when heat-treated at a high temperature of 260 ° C.
A pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 5 in which the (meth) acrylic copolymer contains a structural unit derived from N-ethoxymethylacrylamide instead of a structural unit derived from N-methoxymethylacrylamide. Was confirmed to significantly contaminate the surface of the adherend during peeling when heat-treated at a high temperature of 260 ° C.
The (meth) acrylic copolymer is formed by the pressure-sensitive adhesive compositions of Comparative Example 6 and Comparative Example 10 containing a structural unit derived from N-butoxymethylacrylamide instead of the structural unit derived from N-methoxymethylacrylamide. It was confirmed that when all of the adhesive layers were heat-treated at a high temperature of 260 ° C., the surface of the adherend was remarkably contaminated at the time of peeling.
The pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 7 in which the (meth) acrylic copolymer does not contain a structural unit derived from N-methoxymethylacrylamide is peeled off when heat-treated at a high temperature of 260 ° C. It was confirmed that the surface of the adherend was significantly contaminated.
Adhesive formed by the pressure-sensitive adhesive composition of Comparative Example 8 in which the (meth) acrylic copolymer contains neither a structural unit derived from a monomer having a hydroxyl group nor a structural unit derived from N-methoxymethylacrylamide. It was confirmed that the agent layer could not suppress the discoloration of the copper foil.

Claims (7)

Containing a structural unit derived from N-methoxymethylacrylamide, a structural unit derived from a monomer having a hydroxyl group, and a structural unit derived from a (meth) acrylic acid alkyl ester monomer, and derived from the N-methoxymethylacrylamide. The composition of the pressure-resistant adhesive sheet for a heat-resistant adhesive sheet, which comprises a (meth) acrylic copolymer having a content of 6% by mass or more and 30% by mass or less with respect to all the structural units, and a cross-linking agent. thing. The claim that the ratio of the number of moles of the crosslinkable functional group in the crosslinking agent to the total number of moles of the hydroxyl group and the carboxy group in the (meth) acrylic copolymer is in the range of 0.1 or more and 1.0 or less. The pressure-resistant pressure-sensitive adhesive sheet pressure-sensitive adhesive composition according to 1. The heat-resistant adhesive according to claim 1 or 2, wherein the content of the structural unit derived from the monomer having a hydroxyl group is in the range of 1.5% by mass or more and 20% by mass or less with respect to all the structural units. Adhesive composition for sheets. The claim that the ratio of the number of moles of the crosslinkable functional group in the crosslinking agent to the total number of moles of the hydroxyl group and the carboxy group in the (meth) acrylic copolymer is in the range of 0.3 or more and 0.5 or less. The pressure-resistant pressure-sensitive adhesive sheet pressure-sensitive adhesive composition according to any one of claims 1 to 3. The pressure-resistant pressure-resistant pressure-sensitive adhesive sheet pressure-sensitive adhesive composition according to any one of claims 1 to 4, wherein the number of carbon atoms of the alkyl group in the (meth) acrylic acid alkyl ester monomer is in the range of 4 or more and 12 or less. thing. The (meth) acrylic acid alkyl ester monomer contains the (meth) acrylic acid alkyl ester monomer having a glass transition temperature of −20 ° C. or lower when used as a homopolymer, according to claims 1 to 5. The pressure-sensitive adhesive composition for a heat-resistant pressure-sensitive adhesive sheet according to any one of the items. A heat-resistant pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed by the pressure-resistant pressure-sensitive adhesive sheet pressure-sensitive adhesive composition according to any one of claims 1 to 6.