JP7280840B2 - PSA COMPOSITION FOR HEAT-RESISTANT ADHESIVE SHEET AND HEAT-RESISTANT ADHESIVE SHEET - Google Patents

Description

TECHNICAL FIELD The present invention relates to a PSA composition for a heat-resistant PSA sheet and a heat-resistant PSA sheet.

A heat-resistant pressure-sensitive adhesive sheet is used for the purpose of protecting the electronic member in the heat treatment process during the manufacture of the electronic member, which is represented by the hot press step and the solder reflow step. The pressure-sensitive adhesive layer of the heat-resistant pressure-sensitive adhesive sheet is required to have properties that make it difficult for the adhesive strength to excessively increase or decrease due to heat treatment.
Conventionally, as a method for improving the heat resistance of an adhesive sheet, a method using a copolymer containing a structural unit derived from a nitrogen-containing monomer as a raw material for an adhesive composition is known.

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

JP 2013-177568 A JP 2012-196953 A

In recent years, heat-resistant adhesive sheets are being required to be used at temperatures much higher than conventional ones, such as 260°C. Usually, when a pressure-sensitive adhesive sheet is used in a high-temperature environment, the adhesive strength of the pressure-sensitive adhesive layer increases, and the problem of difficulty in peeling from the adherend tends to occur. In addition, 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 adhesive sheet is peeled off from the adherend, adhesive residue is left on the surface of the adherend, making it easy to contaminate the adherend. . Furthermore, when the cohesive strength of the adhesive layer decreases, if the adherend is a copper foil, air may enter between the adhesive sheet and the copper foil, causing unintended detachment or oxidation of the copper foil. It may cause discoloration.
Therefore, the pressure-sensitive adhesive composition used for the heat-resistant pressure-sensitive adhesive sheet, for example, even when used in a high temperature environment of 260 ° C., can maintain good adhesiveness and releasability to the adherend, It is required to be able to form a pressure-sensitive adhesive layer that is less likely to contaminate the surface of an adherend and that can suppress oxidation of the adherend.

Regarding the above point, the pressure-sensitive adhesive compositions described in Patent Documents 1 and 2 are not intended to be used at a temperature of 260°C, which is much higher than conventional ones. Further, according to the study of the present inventors, the adhesive layer formed from the adhesive composition 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 is known that adhesive residue tends to be left on the surface of the adherend during peeling.

The problem to be solved by the present invention is that even when heat treated at a high temperature (for example, 260 ° C.), it is possible to maintain good adhesiveness and releasability to the adherend, and the adherend when peeled. An object of the present invention is to provide an adhesive composition for a heat-resistant adhesive sheet and a heat-resistant adhesive sheet, which can form an adhesive layer that hardly contaminates the surface and can suppress oxidation of an adherend.

Specific means for solving the problems include the following aspects.
<1> 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, wherein the N-methoxymethyl A heat-resistant pressure-sensitive adhesive sheet containing a (meth)acrylic copolymer in which the content of structural units derived from acrylamide is in the range of 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 to 1.0 The pressure-sensitive adhesive composition for a heat-resistant pressure-sensitive adhesive sheet according to <1>.
<3> 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 structural units. A pressure-sensitive adhesive composition for a heat-resistant pressure-sensitive 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-sensitive adhesive composition for a heat-resistant pressure-sensitive adhesive sheet 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 number of carbon atoms in the alkyl group in the (meth)acrylic acid alkyl ester monomer is in the range of 4 to 12. Adhesive composition.
<6> The (meth)acrylic acid alkyl ester monomer includes a (meth)acrylic acid alkyl ester monomer having a glass transition temperature of −20° C. or lower when converted into a homopolymer <1> to <5> The adhesive composition for a heat-resistant adhesive sheet according to any one of 5>.
<7> A heat-resistant adhesive sheet comprising an adhesive layer formed from the adhesive composition for a heat-resistant adhesive sheet 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 releasability to the adherend can be maintained, and the surface of the adherend is not contaminated during peeling. Provided are a pressure-sensitive adhesive composition for a heat-resistant pressure-sensitive adhesive sheet and a heat-resistant pressure-sensitive adhesive sheet that can form a pressure-sensitive adhesive layer that is difficult to oxidize and that can suppress oxidation of an adherend.

Specific embodiments of the present invention will be described in detail below. However, the present invention is by no means limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the purpose of the present invention.

In this specification, the numerical range indicated using "to" means a range including the numerical values before and after "to" as the minimum and maximum values, respectively.
In the numerical ranges described stepwise in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the upper limit or lower limit of the numerical range described in other steps. . Moreover, in the numerical ranges described in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the values shown in the examples.
In the present specification, a combination of two or more preferred aspects is a more preferred aspect.
In the present specification, the amount of each component means the total amount of the multiple types of substances unless otherwise specified when there are multiple types of substances corresponding to each component.

As used herein, the term "(meth)acrylic copolymer" means that the content of structural units derived from a monomer having a (meth)acryloyl group is the total structural units [i.e., (meth)acrylic copolymer total structural units of the polymer] is 50% by mass or more.

As used herein, the term "adhesive composition" means a liquid or paste substance before completion of the cross-linking reaction.
As used herein, the term “adhesive layer” means a film made of a substance (a so-called crosslinked product of the adhesive composition) after completion of the crosslinking reaction in the adhesive composition.

As used herein, "(meth)acrylic" is a term that includes both "acrylic" and "methacrylic", and "(meth)acrylate" is a term that includes both "acrylate" and "methacrylate". , "(meth)acryloyl" is a term encompassing both "acryloyl" and "methacryloyl".

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

[Adhesive composition for heat-resistant adhesive sheet]
The pressure-sensitive adhesive composition for a heat-resistant pressure-sensitive adhesive sheet of the present invention (hereinafter also simply referred to as "pressure-sensitive adhesive composition") includes structural units derived from N-methoxymethylacrylamide and structural units derived from a monomer having a hydroxyl group. , and a structural unit derived from a (meth)acrylic acid alkyl ester monomer, and the content of the structural unit derived from the N-methoxymethylacrylamide is 6% by mass or more and 30% by mass or less with respect to all structural units. A (meth)acrylic copolymer in the range of [hereinafter also referred to as a “specific (meth)acrylic copolymer”. ] and a cross-linking agent.
According to the pressure-sensitive adhesive composition of the present invention, even when heat-treated at a high temperature (for example, 260 ° C.), it can maintain good adhesiveness and releasability to the adherend, and when peeled, the adherend It is possible to form a pressure-sensitive adhesive layer that is less likely to contaminate the surface of the adherend and that can suppress oxidation of the adherend.
Although the reason why the pressure-sensitive adhesive composition of the present invention can exhibit such effects is not clear, the present inventors speculate as follows. However, the following assumptions are not intended to limit the interpretation of the pressure-sensitive adhesive composition of the present invention, but are explained as an example.

The pressure-sensitive adhesive composition of the present invention comprises, 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, relatively highly polar N-methoxymethylacrylamide Since it contains a (meth)acrylic copolymer containing a structural unit derived from in an amount within a specific range, and a cross-linking agent, the pressure-sensitive adhesive layer formed is moderately adhered to the adherend, and the initial ( It is believed to exhibit good adhesiveness and releasability to adherends prior to so-called heat treatment.

In general, a heat-treated pressure-sensitive adhesive layer tends to have increased adhesive strength and is difficult to separate from an adherend. In general, the reason why the adhesive strength of the adhesive layer increases due to heat treatment is that the adhesive layer becomes flexible in a high-temperature environment, and spreads over the adherend, increasing the adhesive strength with the adherend interface. It is considered to be for The pressure-sensitive adhesive composition of the present invention includes, in addition to structural units derived from a monomer having a hydroxyl group and structural units derived from a (meth)acrylic acid alkyl ester monomer, N- Since it contains a (meth)acrylic copolymer containing structural units derived from methoxymethylacrylamide in an amount within a specific range, the resulting pressure-sensitive adhesive layer exhibits a self-crosslinking reaction of N-methoxymethylacrylamide during heat treatment. Curing shrinkage occurs, and it is thought that an excessive increase in adhesive strength due to wetting and spreading on the adherend is suppressed. Therefore, it is believed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention can maintain good adhesiveness and releasability to adherends even when subjected to heat treatment at a high temperature of 260°C. Conceivable.

Generally, a heat-treated pressure-sensitive adhesive layer has a reduced cohesive force, and is likely to leave an adhesive residue on the surface of the adherend when it is peeled off from the adherend. The pressure-sensitive adhesive composition of the present invention includes, in addition to structural units derived from a monomer having a hydroxyl group and structural units derived from a (meth)acrylic acid alkyl ester monomer, N- Since it contains a (meth)acrylic copolymer containing structural units derived from methoxymethylacrylamide in an amount within a specific range, the formed pressure-sensitive adhesive layer undergoes a self-crosslinking reaction of N-methoxymethylacrylamide when heat-treated. progresses, and the decrease in cohesive force is thought to be suppressed. For this reason, it is believed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention is unlikely to contaminate the surface of the adherend during peeling, even when heat-treated at a high temperature of, for example, 260°C. be done.

Further, the pressure-sensitive adhesive composition of the present invention contains a (meth)acrylic copolymer containing a structural unit derived from highly polar N-methoxymethylacrylamide in an amount within a specific range. In the case of copper, the adhesion becomes better, the pressure-sensitive adhesive layer is suppressed from lifting from the adherend, and oxidation of copper caused by oxygen mixed in the interface between the pressure-sensitive adhesive layer and the adherend is suppressed. It is possible.
By the way, when the pressure-sensitive adhesive sheet is attached to the adherend, oxygen may enter between the pressure-sensitive adhesive layer and the adherend. When this mixed oxygen acts on the adherend, the adherend may be oxidized, resulting in spotty traces. In particular, in the heat press process, which is one of the manufacturing processes for electronic components, the adhesive sheet attached to the adherend is sandwiched between the upper and lower metal plates, so the interface between the adherend and the adhesive layer becomes closed. , when oxygen is mixed, it is difficult to release the oxygen to the outside. Therefore, speck-like traces (also referred to as "bubble traces") are likely to occur due to oxygen remaining at the interface between the adherend and the pressure-sensitive adhesive layer. In particular, when the adherend is a copper foil, there is a tendency for bubble traces to occur more easily. The pressure-sensitive adhesive composition of the present invention is a (meth)acrylic type containing a structural unit derived from N-methoxymethylacrylamide that generates methanol, which has a reducing action on copper oxide, in a specific range when thermally crosslinked. Since it contains a copolymer, it is thought that the appearance of bubble traces can be suppressed.

[Specific (meth)acrylic copolymer]
The pressure-sensitive adhesive composition of the present invention comprises 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. , a (meth)acrylic copolymer in which the content of structural units derived from N-methoxymethylacrylamide is in the range of 6% by mass or more and 30% by mass or less with respect to all structural units [that is, a specific (meth) acrylic copolymer].

<Structural Unit Derived from N-Methoxymethylacrylamide>
The specific (meth)acrylic copolymer (A) contains structural units derived from N-methoxymethylacrylamide.

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

The content of structural units derived from N-methoxymethylacrylamide in the specific (meth)acrylic copolymer is 6% by mass or more and 30% by mass or less with respect to all structural units of the specific (meth)acrylic copolymer. 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.
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 the total structural units of the specific (meth)acrylic copolymer, formation The pressure-sensitive adhesive layer that is coated shows a tendency to hardly contaminate the surface of the adherend during peeling, even if it is heat-treated at a high temperature.
When the content of structural units derived from N-methoxymethylacrylamide in the specific (meth)acrylic copolymer is 30% by mass or less with respect to the total structural units of the specific (meth)acrylic copolymer, formation The pressure-sensitive adhesive layer that is coated tends to be able to suppress oxidation of the adherend even when heat-treated at a high temperature.

<Structural Unit Derived from Monomer Having Hydroxyl Group>
A specific (meth)acrylic copolymer contains a structural unit derived from a monomer having a hydroxyl group. A hydroxyl group of a structural unit derived from a monomer having a hydroxyl group can form a crosslinked structure through a crosslinking reaction with a crosslinking agent described below.

As used herein, the term “structural 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 hydroxyl group-containing monomer is not particularly limited.
Specific examples of monomers having a hydroxyl group include 2-hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 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- Hydroxyhexyl (meth)acrylate, N-hydroxyethyl (meth)acrylamide and the like.
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, hydroxyalkyl having a hydroxyalkyl group having 1 to 5 carbon atoms (Meth)acrylates are preferred, hydroxyalkyl (meth)acrylates having a hydroxyalkyl group having 2 to 4 carbon atoms are more preferred, and the group consisting of 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, and 2-hydroxyethyl acrylate At least one more selected 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 thereof.

The content of structural units derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer is 1% by mass or more and 25% by mass based on the total 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, even more preferably in the range of 5% by mass or more and 15% by mass or less, and 5% by mass or more and 10% by mass. It is particularly preferable that the content is in the range of mass % or less.
When the content of structural units derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer is 1% by mass or more with respect to all structural units of the specific (meth)acrylic copolymer, Since the pressure-sensitive adhesive layer to be formed has a more moderate cohesive force, even when heat-treated at a high temperature, it is easier to maintain good adhesion and peelability to the adherend, and when peeling shows a tendency to make the surface of the adherend less likely to be contaminated.
When the content of structural units derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer is 25% by mass or less with respect to the total structural units of the specific (meth)acrylic copolymer, The formed pressure-sensitive adhesive layer tends to be able to better suppress oxidation of the adherend even when heat-treated at a high temperature.

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

In the present specification, "a structural unit derived from a (meth)acrylic acid alkyl ester monomer" means a structural unit formed by addition polymerization of a (meth)acrylic acid alkyl ester monomer.
In addition, 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.
The number of carbon atoms in the alkyl group, for example, 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 more preferably in the range of 4 or more and 12 or less, from the viewpoint of adhesive strength. More preferred.
In particular, when the number of carbon atoms in the alkyl group is in the range of 4 to 12, the pressure-sensitive adhesive layer formed has a more moderate cohesive force, so even when heat-treated at a high temperature, Good adhesiveness and releasability are more likely to be maintained, and the surface of the adherend is less likely to be contaminated during release.

Specific examples of (meth) acrylic acid alkyl ester monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, s-butyl (meth) acrylates, t-butyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate and the like.

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 converted into a homopolymer. It is more preferable to contain a (meth)acrylic acid alkyl ester monomer having a glass transition temperature in the range of -80 ° C. or higher and -20 ° C. or lower when the glass transition temperature is -80 when used as a homopolymer. It is more preferable to contain a (meth)acrylic acid alkyl ester monomer in the range of -50°C or lower, and the glass transition temperature of the homopolymer is in the range of -80°C or higher and -55°C or lower. It is particularly preferred to contain (meth)acrylic acid alkyl ester monomers.
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 less when converted to a homopolymer, when heat-treated at a high temperature Since the increase in the adhesive strength of the adhesive layer is further suppressed, even after heat treatment at a high temperature, the adhesive layer tends to maintain good adhesiveness and releasability to the adherend more easily.

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

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

Although the content of structural units derived from (meth)acrylic acid alkyl ester monomers in the specific (meth)acrylic copolymer is not particularly limited, for example, all structural units of the specific (meth)acrylic copolymer is preferably 50% by mass or more, more preferably in the range of 50% by mass to 93% by mass, more preferably in the range of 69% by mass to 92.5% by mass, A range of 74% by mass or more and 90% by mass or less is particularly preferable.
Here, the content of structural units derived from the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic copolymer is 50% relative to the total structural units of the specific (meth)acrylic copolymer. % by mass or more means that the structural unit derived from the (meth)acrylic acid alkyl ester monomer is contained as a main component of the structural unit constituting the specific (meth)acrylic copolymer. do.

<Structural Unit Derived from Monomer Having Carboxy Group>
The specific (meth)acrylic copolymer may contain structural units derived from a monomer having a carboxy group. A carboxy group of a structural unit derived from a monomer having a carboxy group can form a crosslinked structure through a cross-linking reaction with a cross-linking agent described below.

As used herein, the term "structural 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 monomers having a carboxy group include acrylic acid, methacrylic acid, crotonic acid, maleic anhydride, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, ω-carboxy-polycaprolactone mono(meth)acrylate [ For example, ω-carboxy-polycaprolactone (n≈2) monoacrylate], succinic acid ester (eg, 2-acryloyloxyethyl-succinic acid), and the like.

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

The content of structural units derived from a monomer having a carboxy group in the specific (meth)acrylic copolymer is not particularly limited.
The specific (meth)acrylic copolymer does not contain structural units derived from a monomer having a carboxy group, or the content of structural units derived from a monomer having a carboxy group is specified (meta ) With respect to all 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 does not contain a structural unit derived from a monomer having a carboxy group, or , The content of structural units derived from a 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 structural units of the specific (meth)acrylic copolymer. is more preferable, and it is even more preferable not to contain a structural unit derived from a monomer having a carboxy group.

<Other structural units>
The specific (meth)acrylic copolymer may contain structural units other than the structural units described above (so-called other structural units) as long as the effects of the present invention are exhibited.

Examples of monomers constituting other structural units include (meth)acrylates having an aromatic ring represented by benzyl (meth)acrylate and phenoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate and ethoxyethyl Alkoxyalkyl (meth)acrylates typified by (meth)acrylates, styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and aromatic monovinyls typified by vinyltoluene, acrylonitrile and methacrylates. vinyl cyanides typified by lonitrile; and vinyl esters typified by vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate. Various derivatives of these monomers are also included.

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 thereof.

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 less, more preferably in the range of −80° C. or more and −20° C. or less, 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. .
If 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 high temperature is further suppressed, so after heat treatment at high temperature also shows a tendency that good adhesiveness and releasability of the adhesive layer to the adherend are more likely to be maintained.

The glass transition temperature of the specific (meth)acrylic copolymer is obtained by converting the absolute temperature (unit: K; hereinafter the same) calculated from the following formula 1 to the Celsius temperature (unit: ℃; hereinafter the same.) This is the converted value.
1/Tg=m1/Tg1+m2/Tg2+...+m(k-1)/Tg(k-1)+mk/Tgk (Formula 1)

In formula 1, Tg1, Tg2, . Each represents the glass transition temperature indicated. m1, m2, . −1)+mk=1.
The absolute temperature can be converted to a Celsius temperature by subtracting 273 from the absolute temperature, and the Celsius temperature can be converted to an absolute temperature by adding 273 to the Celsius temperature.

As used herein, the term "glass transition temperature expressed as an absolute temperature when a homopolymer is used" refers to a glass transition temperature expressed as an absolute temperature of a homopolymer produced by polymerizing the monomer alone. means temperature.
The glass transition temperature of the homopolymer was measured using a differential scanning calorimeter (DSC) [model number: EXSTAR6000, Seiko Instruments Inc.] under the conditions of a measurement sample of 10 mg and a heating rate of 10°C/min in a nitrogen stream. The inflection 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 converted to a homopolymer" of representative monomers is -76 ° C. for 2-ethylhexyl acrylate (2EHA) and -10 ° C. for 2-ethylhexyl methacrylate (2EHMA). , n-butyl acrylate (n-BA) is −57° C., n-butyl methacrylate (n-BMA) is 21° C., t-butyl acrylate (t-BA) is 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, isobornyl methacrylate (IBXMA) is 155°C, isobornyl 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) is 55 ° C., 2-hydroxypropyl acrylate (2HPA) is -7 ° C., acrylic acid (AA) is 163 ° C., i-octyl acrylate (i-OA) is -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, for example, by using two or more monomers having different glass transition temperatures when converted into homopolymers.

<<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 to 1,200,000, more preferably in the range of 200,000 to 1,000,000. It is 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 pressure-sensitive adhesive layer formed has a more moderate cohesive force. It tends to make the surface of the adherend less likely to be contaminated.
When the weight-average molecular weight of the specific (meth)acrylic copolymer is 1,200,000 or less, the pressure-sensitive adhesive composition has a more moderate viscosity, so that the applicability tends to be further improved.

The weight average molecular weight of the specific (meth)acrylic copolymer is a value measured by the following method. Specifically, it is measured according to the following (1) to (3).
(1) A solution of the specific (meth)acrylic copolymer is applied to release paper and dried at 100° C. for 1 minute to obtain a film-like specific (meth)acrylic copolymer.
(2) Using the film-like specific (meth)acrylic copolymer obtained in (1) above and tetrahydrofuran, a sample solution having a solid content concentration of 0.2% by mass is obtained. The term "solid content concentration" as used herein means the mass ratio of the specific (meth)acrylic copolymer in the sample solution.
(3) Using gel permeation chromatography (GPC), measure the weight average molecular weight of the specific (meth)acrylic copolymer 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 into HLC-8220, Tosoh Corporation]
Column: Four TSK-GEL GMHXL [Tosoh Corporation] connected in series Column temperature: 40°C
Eluent: Tetrahydrofuran Injection volume of sample solution: 100 μL
Flow rate: 0.8 mL/min

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

<<Specific (meth)acrylic copolymer content>>
The content of the specific (meth)acrylic copolymer in the pressure-sensitive adhesive composition of the present invention is not particularly limited. % or less, more preferably 70% by mass or more and 99.99% by mass or less, even more preferably 75% by mass or more and 99.95% by mass or less, and 80% by mass % or more and 99.95 mass % or less is particularly preferable.
As used herein, "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. When included, it means the mass of the residue after 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-described monomers by a known polymerization method represented by, for example, a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, and a bulk polymerization method. can be manufactured by
As the polymerization method, the solution polymerization method is preferable because the processing steps are relatively simple and can be performed in a short period of time when preparing the pressure-sensitive adhesive composition of the present invention after production.

In the solution polymerization method, generally, a predetermined organic solvent, monomers, a polymerization initiator, and optionally a chain transfer agent are charged in a polymerization tank, and stirred at the reflux temperature of the organic solvent in a nitrogen stream. Heat and react for several hours while stirring. In this case, at least part of the organic solvent, monomer, polymerization initiator and/or chain transfer agent may be added sequentially.

Organic solvents 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 specific examples of the organic solvent used during the polymerization reaction include benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic hydrocarbon compounds typified by aromatic naphtha, fats typified by n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and turpentine. 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 represented by methyl cyclohexanone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl Ethers and glycol ether compounds typified by diethylene glycol monobutyl ether, and methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t- Alcohol compounds represented by butyl alcohol are mentioned.

In the production of the specific (meth)acrylic copolymer, it is preferable to use an organic solvent that is unlikely to cause chain transfer during the polymerization reaction of aromatic hydrocarbon compounds, ester compounds, ketone compounds, etc. In particular, the specific (meth)acrylic It is preferable to use at least one selected from the group consisting of ethyl acetate, toluene, and methyl ethyl ketone from the viewpoint of the solubility of the system copolymer, the ease of the polymerization reaction, and the like.

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

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

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

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

If necessary, a chain transfer agent may be used in the production of the specific (meth)acrylic copolymer.
Examples of chain transfer agents include cyanoacetic acid, cyanoacetic acid alkyl ester compounds having 1 to 8 carbon atoms, bromoacetic acid, bromoacetic acid alkyl ester compounds having 1 to 8 carbon atoms, α-methylstyrene, anthracene, phenanthrene, and fluorene. , and aromatic compounds represented by 9-phenylfluorene, aromatic nitro compounds represented by p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and p-nitrotoluene, benzoquinone and Benzoquinone derivatives typified by 2,3,5,6-tetramethyl-p-benzoquinone, borane derivatives typified by tributylborane, carbon tetrabromide, carbon tetrachloride, 1,1,2,2-tetrabromoethane Halogenated hydrocarbon compounds typified by , tribromoethylene, trichlorethylene, bromotrichloromethane, tribromomethane, and 3-chloro-1-propene; aldehyde compounds typified by chloral and furaldehyde; alkyls having 1 to 18 carbon atoms; Mercaptan compounds, aromatic mercaptan compounds represented by thiophenol and toluene mercaptan, mercaptoacetic acid, alkyl ester compounds of mercaptoacetic acid having 1 to 10 carbon atoms, hydroxyalkyl mercaptan compounds having 1 to 12 carbon atoms, and pinene and terpinolene Representative terpene compounds are 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. It can be set as appropriate.

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

[Crosslinking agent]
The adhesive composition of the present invention contains a cross-linking agent.
The type of cross-linking agent is not particularly limited.
Examples of cross-linking agents include isocyanate-based cross-linking agents, epoxy-based cross-linking agents, and metal chelate-based cross-linking agents.
Among these, the 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). The term "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). A "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.

Polyisocyanate compounds 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, and aliphatic or alicyclic polyisocyanate compounds such as hydrogenated products of aromatic polyisocyanate compounds.
Further, the polyisocyanate compound may be a dimer, trimer, or pentamer of the polyisocyanate compound, an adduct of the polyisocyanate compound and a polyol compound such as trimethylolpropane, or a biuret of the polyisocyanate compound. And so on.

A commercial item can be used as an isocyanate type crosslinking agent.
Examples of commercially available isocyanate cross-linking agents include "Coronate (registered trademark) HX", "Coronate (registered trademark) HL-S", "Coronate (registered trademark) L", "Coronate (registered trademark) L-45E ", "Coronate (R) 2031", "Coronate (R) 2030", "Coronate (R) 2234", "Coronate (R) 2785", "Aquanate (R) 200", and " Aquanate (registered trademark) 210” [above, Tosoh Corporation], “Sumidule (registered trademark) N3300”, “Desmodur (registered trademark) N3400”, and “Sumidule (registered trademark) N-75” [ Sumika Covestro 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” [Asahi Kasei Corporation], and “Takenate (registered trademark) D-110N”, “Takenate (registered trademark) D-120N”, “Takenate (registered trademark) M-631N ”, “MT-Olestar (registered trademark) NP1200”, and “STABIO (registered trademark) XD-340N” [all manufactured by Mitsui Chemicals, Inc.].

Di- or higher-functional epoxy compounds 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, trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, adipate diglycidyl ester, phthalate diglycidyl ester, tris(glycidyl) isocyanurate, tris(glycidide) xyethyl)isocyanurate, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-1,3-benzenedi(methanamine) and the like.

A commercially available product can be used as the epoxy-based cross-linking agent.
Examples of commercially available epoxy-based cross-linking agents include "TETRAD (registered trademark)-X" and "TETRAD (registered trademark)-C" (manufactured by Mitsubishi Gas Chemical Company, Inc.).

Examples of metal chelate compounds include aluminum chelate compounds typified by aluminum monoacetylacetonate bis(ethylacetoacetate), aluminum tris(ethylacetoacetate), and aluminum tris(acetylacetonate), titanium chelate compounds, zirconium chelate compounds, cobalt chelate compounds and the like.

A commercial item can be used as a metal chelate type crosslinking agent.
Examples of commercially available metal chelate-based cross-linking agents include "Aluminum chelate A", "Aluminum chelate D", and "ALCH-TR" (manufactured by Kawaken Fine Chemicals Co., Ltd.).

The pressure-sensitive adhesive composition of the present invention may contain only one cross-linking agent, or may contain two or more 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, for example, according to the type of 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 relative to 100 parts by mass of the specific (meth)acrylic copolymer. , preferably in the range of 0.1 to 15 parts by mass, more preferably in the range of 0.3 to 13 parts by mass, and in the range of 0.5 to 12 parts by mass 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 parts 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 adherend surface 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 formed pressure-sensitive adhesive layer can be Even when heat-treated, it tends to maintain good adhesiveness and releasability to adherends. Moreover, when the adherend is copper, it tends to be able 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>>
(Meth) 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 acrylic copolymer [that is, the number of moles of crosslinkable functional groups in the crosslinker / (meta) The total number of moles of hydroxyl groups and carboxy groups in the acrylic copolymer] is not particularly limited, but for example, it is preferably in the range of 0.05 or more and 1.2 or less, and is preferably in the range of 0.1 or more and 1.0 or less. It is more preferably in the range, more 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 cross-linking agent to the total number of moles of hydroxyl groups and carboxyl groups in the (meth)acrylic copolymer is 0.05 or more, the formed pressure-sensitive adhesive layer can be formed at a high temperature. Good adhesiveness and releasability to the adherend are more likely to be maintained, and the surface of the adherend tends to be less contaminated during delamination.
When the 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 is 1.2 or less, the pressure-sensitive adhesive layer formed is maintained at a high temperature. Even when the heat treatment is performed at , it shows a tendency to be able to suppress the oxidation of the adherend more satisfactorily.

As used herein, the term "crosslinkable functional group in the crosslinker" means a functional group possessed by the crosslinker and capable of crosslinkage reaction with the hydroxyl group and carboxy group in the (meth)acrylic copolymer. 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.

In the present specification, the number of moles of crosslinkable functional groups means the total number of moles of all crosslinkable functional groups when there are a plurality of crosslinkable functional groups.

(Meth) 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 acrylic copolymer [that is, the number of moles of crosslinkable functional groups in the crosslinker / (meta) The total number of moles of hydroxyl groups and carboxyl groups in the acrylic copolymer] is obtained by the following calculation formulas (1) to (3).

Number of moles of crosslinkable functional groups in crosslinker [unit: mmol/solid content of crosslinker 100 g]
= [content of crosslinkable functional group in crosslinker (unit: mass %) / solid content of crosslinker (unit: mass%) × 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 of structural units derived from monomers having hydroxyl groups in the specific (meth)acrylic copolymer (unit: mass%) / molecular weight of structural units derived from monomers having hydroxyl groups (units: g / mol) × number of hydroxyl groups in the structural unit derived from the monomer having a hydroxyl group (valence) × 1000] + [(meth) derived from the monomer having a carboxy group in the acrylic copolymer Constituent unit content (unit: mass %) / molecular weight of structural unit derived from monomer having carboxy group (unit: g/mol) × carboxy group in structural unit derived from monomer having carboxy group number (valence) × 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 = Value obtained by calculation formula (1) / Calculated by 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 (so-called molar equivalents) of the metal chelate compound used for calculating the molar equivalent ratio 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 of functional groups per 1 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 x B/C)/( _D1 x _E1 / _F1 + _D2 x _E2 / _F2 + ... + _Dn x _En x _Fn )
A = metal valence of metal chelate compound B = number of parts by mass of metal chelate compound (amount as solid content)
C = molecular weight of the metal chelate compound
D ₁ , D ₂ , . . . D _n = content of each monomer having at least one of hydroxyl group and carboxy group in all monomers used in specific (meth)acrylic copolymer (mass % )
E ₁ , E ₂ , . . . _En = total number of hydroxyl groups and carboxy groups contained in one molecule of each monomer having at least one of hydroxyl group and carboxy group F ₁ , F ₂ , _. = Molecular weight of each monomer having at least one of a hydroxyl group and a carboxy group used in a specific (meth)acrylic copolymer Note that n represents the number of types of monomers used, for example, If only one monomer is used, only D ₁ is used in the calculation and D ₂ . . . D _n are 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 those similar to 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.

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 purpose.

[Other ingredients]
The pressure-sensitive adhesive composition of the present invention may, if necessary, contain components other than the components described above (so-called other components) within a range that does not impair the effects of the present invention.
Other components include polymers other than specific (meth)acrylic copolymers, crosslinking catalysts, antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., 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 within the range in which the effects of the present invention are exhibited.

<Application>
The pressure-sensitive adhesive composition of the present invention is suitable for heat-resistant pressure-sensitive adhesive sheets.
The pressure-sensitive adhesive composition of the present invention can maintain good adhesiveness and releasability to the adherend even when heat-treated at a high temperature (for example, 260 ° C.), and when peeled, the surface of the adherend can be , and can form a pressure-sensitive adhesive layer that can suppress oxidation of the adherend. Since the effect of the adhesive composition of the present invention is more exhibited, it is preferable to use it for forming a pressure-sensitive adhesive layer in a pressure-sensitive adhesive sheet for protecting electronic members.
The pressure-sensitive adhesive composition of the present invention can be applied regardless of the material of the adherend, such as resin (eg, polyimide) and metal (eg, copper).

[Heat-resistant adhesive sheet]
The heat-resistant adhesive sheet of the present invention (hereinafter also simply referred to as "adhesive sheet") comprises an adhesive layer formed from the 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 from the pressure-sensitive adhesive composition of the present invention, even when heat-treated at a high temperature (for example, 260 ° C.), it has good adhesion to the adherend. 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 substrate-free pressure-sensitive adhesive sheet having no substrate, or a substrate-containing pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on at least one side of a substrate.

When the pressure-sensitive adhesive sheet of the present invention is a substrate-containing pressure-sensitive adhesive sheet, the substrate is not particularly limited as long as a pressure-sensitive adhesive layer can be formed on the substrate.
Examples of base materials include polyester-based resins, acetate-based resins, polyethersulfone-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, polyolefin-based resins, acrylic-based resins, vinyl chloride-based resins, ABS (Acrylonitrile Butadiene Styrene) resins, films containing resins such as 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 substrate may be partially or wholly patterned.

The thickness of the substrate is generally 500 μm or less, preferably 300 μm or less, more preferably 200 μm or less.
Although the lower limit of the thickness of the substrate is not particularly limited, it 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 with a release film.
The release film is not particularly limited as long as it can be easily separated from the pressure-sensitive adhesive layer. is mentioned.
Examples of resin films include polyester films typified by polyethylene terephthalate (PET) films.
Examples of release agents include fluorine-based resins, 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 to 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, for example, according to the type of substrate. In general, the thickness of the pressure-sensitive adhesive layer is generally in the range of 1 μm to 100 μm, preferably in the range of 5 μm to 50 μm, and more preferably in the range of 10 μm to 30 μm.

The adherend of the pressure-sensitive adhesive sheet of the present invention is not particularly limited.
Examples of the material of the adherend include various metals such as copper, aluminum, and SUS (stainless steel), polyimide resins, acrylic resins, ABS resins, and polyester resins (e.g., PET). and various inorganic materials such as glass.
The pressure-sensitive adhesive sheet of the present invention can be suitably used for adhering to an adherend made of copper, in particular. The pressure-sensitive adhesive composition of the present invention self-crosslinks in a high-temperature environment and contains a specific (meta- ) Since the adhesive sheet of the present invention contains an acrylic copolymer, even when oxygen mixed in remains at the interface between the adhesive layer and the adherend, the adhesive sheet of the present invention tends not to cause traces of air bubbles. In addition, 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 less likely to enter the interface between the pressure-sensitive adhesive layer and the adherend, and discoloration of copper due to oxidation is less likely to occur. show trends.

The method for producing the pressure-sensitive adhesive sheet of the present invention is not particularly limited.
The pressure-sensitive adhesive sheet of the invention can be produced, for example, by the following method.
In the case of a substrate-free pressure-sensitive adhesive sheet, first, the pressure-sensitive adhesive composition of the present invention is applied onto the surface of a release film to form a coating film. Next, the formed coating film is dried. After drying, the exposed surface of the coating film that does not contact the release film is overlapped so that the surface of another release film is in contact, and then cured to form a laminate structure of release film / adhesive layer / release film. , it is possible to manufacture a substrate-free pressure-sensitive adhesive sheet.

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

Another method includes, for example, the following method.
A pressure-sensitive adhesive layer is formed by applying the pressure-sensitive adhesive composition of the present invention on the surface of the release film, drying it, and curing it. Then, the formed adhesive layer is transferred to the substrate.
That is, the surface of the release film on which the pressure-sensitive adhesive layer is formed is adhered to the substrate and pressed to produce a laminate having a laminated structure of substrate/adhesive layer/release film, and then the release film is removed. By peeling, it is possible to produce a substrate-based pressure-sensitive adhesive sheet having a laminated structure of substrate/adhesive layer.

Moreover, another method includes, for example, the following method.
After applying the pressure-sensitive adhesive composition of the present invention on the surface of the release film, it is dried to produce a film with pressure-sensitive adhesive. Next, a base material is attached to the adhesive surface of the adhesive-attached film and cured to produce a base-material type pressure-sensitive adhesive sheet having a laminated structure of base material/adhesive layer/release film.

The method of applying the pressure-sensitive adhesive composition onto the surface of the base material or release film is not particularly limited. A known method using a bar coater, an applicator, or the like can be mentioned.
The amount of the pressure-sensitive adhesive composition to be applied onto the surface of the substrate or 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 substrate or release film is not particularly limited, and includes air drying, heat drying, hot air drying, vacuum drying and the like.
The drying temperature and drying time of the pressure-sensitive adhesive composition applied to the surface of the substrate or release film are not particularly limited, and may vary depending on the thickness of the pressure-sensitive adhesive composition applied, the amount of organic solvent in the pressure-sensitive adhesive composition, and the like. is set appropriately.
An example of the drying conditions includes conditions 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 adhesive composition to form an adhesive layer.

EXAMPLES Hereinafter, the present invention will be described more specifically 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.

[Production of (meth)acrylic copolymer]
[Production Example 1]
190.0 parts by mass of ethyl acetate [organic solvent] and 2,2'-azobisisobutyronitrile [AIBN; polymerization Initiator] 0.05 part by mass was charged. Then, 2-ethylhexyl acrylate [2EHA; acrylic acid alkyl ester monomer, Tg as a homopolymer: -76°C] 260.0 parts by mass, N-methoxymethylacrylamide (NMMA) 120.0 parts by mass, and 2-hydroxyethyl methacrylate [2HEMA; a monomer having a hydroxyl group] 385.0 parts by mass were prepared, and 100.9 parts by mass of this (monomer mixture equivalent to 25.2% by mass of) was charged into the reactor, heated, and refluxed at 85° C. (reflux temperature) for 20 minutes. Next, while maintaining the temperature in the reactor 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 50.0 parts of ethyl acetate Part by mass and 0.5 part by mass of 2,2'-azobisisobutyronitrile (AIBN) were successively added dropwise over 90 minutes, and after completion of the dropwise addition, a polymerization reaction was carried out for 75 minutes.
Then, a mixture of 27.0 parts by mass of ethyl acetate and 1.99 parts by mass of dimethyl 2,2'-azobis(isobutyrate) [polymerization initiator] was added dropwise over 50 minutes. A 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 was 45% by mass to obtain a solution of the (meth)acrylic copolymer of Production Example 1.

The term "solid content concentration" as used herein means the mass ratio of the (meth)acrylic copolymer in 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 organic solvent used and the polymerization initiator 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. Operations were performed to obtain solutions of the (meth)acrylic copolymers 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 organic solvent used and the polymerization initiator used. By adjusting at least one of the amounts, the weight average molecular weight (Mw) of the (meth)acrylic copolymer was adjusted to the weight average molecular weight (Mw) shown in Table 2. Same as in Production Example 1 Operations were performed 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 copolymers of Production Examples 1 to 27 [unit: 10,000 (indicated as “×10 ⁴ ” in the table) )] are shown in Tables 1 and 2.

The weight-average molecular weight (Mw) of the (meth)acrylic copolymers 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. 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 described in Tables 1 and 2 are as shown below.
"2EHA": 2-ethylhexyl acrylate [Tg as a homopolymer: -76°C, acrylic acid alkyl ester monomer]
"n-BA": n-butyl acrylate [Tg as a homopolymer: -57°C, acrylic acid alkyl ester monomer]
"MA": methyl acrylate [Tg as a homopolymer: 5 ° C., acrylic acid alkyl ester monomer]
"MMA": methyl methacrylate [Tg as a homopolymer: 103°C, methacrylic acid alkyl ester monomer]
"NMMA": N-methoxymethylacrylamide "NEMA": N-ethoxymethylacrylamide "NBMA": N-butoxymethylacrylamide "2HEMA": 2-hydroxyethyl methacrylate [a monomer having a hydroxyl group]
"4HBA": 4-hydroxybutyl acrylate [a monomer having a hydroxyl group]
"2HEA": 2-hydroxyethyl acrylate [a monomer having a hydroxyl group]
"DMAEA": dimethylaminoethyl acrylate "AA": acrylic acid [monomer having a carboxy group]

In Tables 1 and 2, "-" written in the column of monomer composition means that the corresponding monomer in that column is not included.
In Tables 1 and 2, "weight average molecular weight" is indicated as "Mw".

[Preparation of adhesive composition]
[Example 1]
100 parts by mass of the (meth)acrylic copolymer solution of Production Example 1 (solid content conversion value), and as a cross-linking agent, Coronate (registered trademark) L-45E [trade name, isocyanate-based cross-linking agent, tolylene diisocyanate ( TDI) and trimethylolpropane (TMP) adduct, solid content: 45% by mass, isocyanate group content: 7.9% by mass, Tosoh Corporation] 3.0 parts by mass (solid content conversion value) and , were sufficiently mixed to obtain a pressure-sensitive adhesive composition of Example 1.
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 [i.e., crosslinkability in the crosslinker] The number of moles of functional groups/total number of moles of hydroxyl groups and carboxyl groups 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 carboxyl groups in the (meth)acrylic copolymer is calculated using the formulas (1) to (3) described above. It is what I did. Specifically, it was calculated as follows. Coronate (registered trademark) L-45E, which is an isocyanate cross-linking agent, has a solid content of 45% by mass and an isocyanate group content of 7.9% by mass. Also, the chemical formula weight of the isocyanate group is 42. Further, the molecular weight of the structural unit derived from 2-hydroxyethyl methacrylate, which is a monomer having a hydroxyl group, is 130.

Formula (1)
Number of moles of crosslinkable functional groups in crosslinker [unit: mmol/solid content of 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 weight of crosslinkable functional group ( Unit: g/mol) x 1000
= 7.9 (% by mass) / 45 (% by mass) x 3 (g) / 42 (g/mol) x 1000 = 12.53 ... ≈ 12.5

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 of structural units derived from a monomer having a hydroxyl group in the (meth)acrylic copolymer (unit: mass%) / molecular weight of a structural unit derived from a monomer having a hydroxyl group (unit: g / mol) × number of hydroxyl groups in a structural unit derived from a monomer having a hydroxyl group (valence) × 1000] + [(meth) composition derived from a monomer having a carboxy group in the acrylic copolymer Unit content (unit: mass %)/molecular weight of structural unit derived from monomer having carboxy group (unit: g/mol) × number of carboxy groups in structural unit derived from monomer having carboxy group number (valence) x 1000]
= [5.0 (parts by mass) / 100 (parts by mass) × 100 (%) / 130 (g / mol) × 1 × 1000] = 38.46 ≈ 38.5

Formula (3)
(Meth) 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 acrylic copolymer [that is, the number of moles of crosslinkable functional groups in the crosslinker / (meta) Total number of moles of hydroxyl groups and carboxy groups in the acrylic copolymer]
= Value calculated by formula (1)/Value calculated by formula (2) = 12.5/38.5 = 0.32 ≈ 0.3

[Examples 2 to 26]
In Example 1, except that the composition of the adhesive composition was changed to the composition shown in Table 3, the same operation as in Example 1 was performed to obtain each adhesive composition of Examples 2 to 26.

[Comparative Examples 1 to 10]
In Example 1, except that the composition of the adhesive composition was changed to the composition shown in Table 4, the same operation as in Example 1 was performed to obtain each adhesive composition of Comparative Examples 1 to 10.

Composition of the pressure-sensitive adhesive compositions of Examples 1 to 26 and Comparative Examples 1 to 10, and crosslinkability in the crosslinker with respect to the total number of moles of hydroxyl groups and carboxy groups in the (meth)acrylic copolymer Tables 3 and 4 show the molar ratio of functional groups [that is, the molar number of crosslinkable functional groups in the crosslinking agent/total molar number of hydroxyl groups and carboxyl groups in the (meth)acrylic copolymer].

Details of each cross-linking agent described in Tables 3 and 4 are as shown below.
"Coronate L-45E": isocyanate cross-linking agent, adduct of tolylene diisocyanate (TDI) and trimethylolpropane (TMP), solid content: 45% by mass, content of isocyanate group: 7.9% by mass, Tosoh (KK)
"Takenate D-110N": isocyanate cross-linking agent, xylylene diisocyanate (XDI), solid content: 75% by mass, isocyanate group content: 11.5% by mass, Mitsui Takeda Chemicals Co., Ltd.
"TETRAD-X": epoxy-based cross-linking agent, solid content: 100% by mass, content of epoxy group: 90% by mass, Mitsubishi Gas Chemical Company, Inc.
"Coronate HX": isocyanate cross-linking agent, isocyanurate form of hexamethylene diisocyanate (HMDI), solid content: 100% by mass, content of isocyanate group: 21.3% by mass, Tosoh Corporation
"Coronate", "Takenate" and "TETRAD" are all registered trademarks.

<Production of adhesive sheet for evaluation test>
Using the pressure-sensitive adhesive composition obtained above, a pressure-sensitive adhesive sheet for evaluation test was produced as follows. A pressure-sensitive adhesive composition was applied to the surface of a polyimide film [product name: Kapton (registered trademark), DuPont Toray Co., Ltd.] so that the coating amount after drying was 10 g/m ² to form a coating film. . Then, the formed coating film was dried using a hot air circulating 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 superimposed on the surface-treated surface of a release film [trade name: Film Bina (registered trademark) 100E-0010N023, Fujimori Industry Co., Ltd.] surface-treated with a silicone-based release agent. , and pressure nip rolls were used to bond and bond. Next, the resulting laminate is allowed to stand for 1 week in an environment of an atmospheric temperature of 23 ° C. and 50% RH, and cured to promote the cross-linking reaction, thereby forming a polyimide film / adhesive layer / release film. A pressure-sensitive adhesive sheet for evaluation test was obtained.

[evaluation]
1. Adhesive strength An adhesive sheet for evaluation test was cut into a size of 25 mm x 150 mm to prepare seven pieces of adhesive sheet for evaluation test. Hereinafter, the six adhesive sheet pieces for evaluation test are the first adhesive sheet piece for evaluation test, the second adhesive sheet piece for evaluation test, the third adhesive sheet piece for evaluation test, and the fourth adhesive sheet for evaluation test. They are referred to as a piece, a fifth evaluation test adhesive sheet piece, a sixth evaluation test adhesive sheet piece, and a seventh evaluation test adhesive sheet piece.
Of the seven adhesive sheet pieces for evaluation test, for the first to third adhesive sheet pieces for evaluation test, the release film of the adhesive sheet piece for evaluation test (composition: polyimide film / adhesive layer / release film) is peeled off. Then, the surface of the adhesive layer exposed by peeling is superimposed on the surface of a polyimide (PI) film [trade name: Kapton (registered trademark) 100H, Dupont Toray Co., Ltd.], and then crimped using a pressure nip roll. and pasted together.
For the 4th to 6th adhesive sheet pieces for evaluation test, the release film of the adhesive sheet piece for evaluation test (composition: polyimide film / adhesive layer / release film) is peeled off, and the surface of the adhesive layer exposed by peeling was superimposed on the surface of a copper foil [trade name: NC-WC, thickness: 10 μm, Furukawa Electric Co., Ltd.], and then bonded by pressure using pressure nip rolls.
For the seventh evaluation test adhesive sheet piece, the release film of the evaluation test adhesive sheet piece (structure: polyimide film / adhesive layer / release film) is peeled off, and the surface of the adhesive layer exposed by peeling is coated with copper. A foil [trade name: NC-WC, thickness: 10 μm, manufactured by Furukawa Electric Co., Ltd.] was superimposed on the surface of the foil, and then bonded as it was without applying pressure.

(1) Initial (adherend: polyimide film)
The first evaluation test pressure-sensitive adhesive sheet piece was attached to the polyimide film, and then allowed to stand for 24 hours in an environment with an ambient temperature of 23° C. and 50% RH. Then, for the first evaluation test adhesive sheet piece after standing, using a single column type material testing machine (model number: STA-1225) manufactured by A&D Co., Ltd. as a measuring device, the atmosphere temperature was 23 ° C. In an environment of 50% RH, under the conditions of a peeling speed of 0.3 m / min, the first evaluation test pressure-sensitive adhesive sheet piece (configuration: polyimide film / pressure-sensitive adhesive layer) was removed from the polyimide film 180 in the long side (150 mm) direction. The adhesive strength (unit: N/25 mm) when peeled was measured and taken as the initial adhesive strength (adherend: polyimide film).

(2) After heat treatment (adherend: polyimide film)
The second evaluation test pressure-sensitive adhesive sheet piece was attached to the polyimide film, and then allowed to stand for 24 hours in an atmosphere of 23° C. and 50% RH. Then, the second evaluation test pressure-sensitive adhesive sheet piece after standing was left standing for 30 minutes in a hot air circulating dryer [model: PHH-200, ESPEC Co., Ltd.] set at 260 ° C., and then the ambient temperature It was allowed to stand in an environment of 23° C. and 50% RH for 3 hours. Next, for the second evaluation test adhesive sheet piece after standing, the adhesive force is measured by the same method as the adhesive force measurement in the above "(1) Initial stage (adherend: polyimide film)", and after heat treatment. (adherend: polyimide film).

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

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

(5) After heat treatment (adherend: copper foil)
The fifth evaluation test pressure-sensitive adhesive sheet piece was attached to the copper foil, and then allowed to stand in an atmosphere of 23° C. and 50% RH for 24 hours. Next, the fifth evaluation test pressure-sensitive adhesive sheet piece after standing was left standing for 30 minutes in a hot air circulating dryer [model: PHH-200, Espec Co., Ltd.] set at 260 ° C., and then the ambient temperature It was allowed to stand in an environment of 23° C. and 50% RH for 3 hours. Next, for the fifth evaluation test adhesive sheet piece after standing, the adhesive force was measured by the same method as the adhesive force measurement in the above "(1) Initial stage (adherend: polyimide film)", and after heat treatment. of adhesive strength (adherend: copper foil).

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

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

-Evaluation criteria-
A: 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 For 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 heat pressing, the surface was visually observed, and the stain resistance (adherend: polyimide film) was evaluated according to the following evaluation criteria.
Tables 5 and 6 show the results.
If the evaluation result was "A", "B", or "C", it was judged that there was no practical problem.

-Evaluation criteria-
A: No adhesive residue is observed at the initial stage, after heat treatment, or 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 observed 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 observed on the peripheral edges of the bonding, but no adhesive residue is observed on the bonding surface.
D: At least one of the initial stage, after heat treatment, and after hot pressing, adhesive residue is observed on the bonded surfaces.

(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 heat pressing. The contamination resistance (adherend: copper foil) was evaluated according to the same evaluation criteria as the contamination resistance of the above "(1) polyimide film".
Tables 5 and 6 show the results.
If the evaluation result was "A", "B", or "C", it was judged that there was no practical problem.

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

-Evaluation criteria-
A: No discoloration is observed either after heat treatment or after hot pressing.
B: After heat treatment and/or after hot pressing, slight discoloration is observed in the peripheral edge of the bonding.
C: At least either after heat treatment or after hot pressing, discoloration is observed on the peripheral edge of the bonding, but no discoloration is observed on the bonding surface.
D: Discoloration is observed on the bonding surface after heat treatment and/or after hot pressing.
-: At least either after heat treatment or after hot pressing, significant adhesive residue is observed on the bonded surfaces, and discoloration is difficult to discern.
(2) Presence or Absence of Traces of Air Bubbles After the adhesive sheet piece for the seventh evaluation test was attached to the copper foil, it was allowed to stand for 24 hours in an environment with an ambient temperature of 23° C. and 50% RH. Then, the seventh evaluation test pressure-sensitive adhesive sheet piece after standing was left standing for 30 minutes in a hot air circulating dryer [model: PHH-200, Espec Co., Ltd.] set at 260 ° C., and then the ambient temperature It was allowed to stand in an environment of 23° C. and 50% RH for 3 hours. Next, for the seventh evaluation test adhesive sheet piece after standing, using a single column type material testing machine (model number: STA-1225) manufactured by A&D Co., Ltd. as a measuring device, the atmosphere temperature was 23 ° C. In an environment of 50% RH, under the conditions of a peeling speed of 0.3 m / min, the adhesive sheet piece for the seventh evaluation test (configuration: polyimide film / adhesive layer) was peeled 180 in the long side (150 mm) direction from the copper foil. ° Peeled off. The surface of the peeled copper foil was visually observed, and the oxidation resistance was evaluated based on the presence or absence of spot-like discoloration (so-called bubble marks) according to the following evaluation criteria.
Tables 5 and 6 show the results.
If the evaluation result was "A", "B", or "C", it was judged that there was no practical problem.

-Evaluation criteria-
A: No trace of air bubbles is observed.
B: The area ratio occupied by traces of air bubbles is more than 0% and less than 20% of the bonding area.
C: The area ratio occupied by traces of air bubbles is 20% or more and less than 50% of the bonding area.
D: The area ratio occupied by traces of air bubbles is 50% or more of the bonding area.
-: Remarkable adhesive residue is observed on the bonded surface, and it is difficult to distinguish traces of air bubbles.

From the results shown in Table 5, according to the adhesive compositions of Examples 1 to 26, even when heat-treated at a high temperature of 260 ° C., good adhesiveness and peelability to the adherend are maintained. It has been clarified that a pressure-sensitive adhesive layer can be formed in which the surface of the adherend is hardly contaminated during peeling and the oxidation of the adherend can be suppressed.

On the other hand, as shown in Table 6, the pressure-sensitive adhesive layer formed from 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, It was confirmed that if the heat treatment is performed at a high temperature of °C, the surface of the adherend is significantly contaminated at the time of peeling.
A pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 2 in which the content of structural units derived from N-methoxymethylacrylamide in the (meth)acrylic copolymer exceeds 30% by mass based on the total structural units. It was confirmed that heat treatment at a high temperature of 260° C. markedly reduced the adhesive force to the adherend. In addition, when the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 2 was heat-treated at a high temperature of 260 ° C., the copper foil as the adherend was remarkably discolored, and the copper foil had marked air bubble traces. It was confirmed that the oxidation of the adherend could not be suppressed.
Adhesion of Comparative Examples 3, 4, and 9 in which the content of structural units derived from N-methoxymethylacrylamide in the (meth)acrylic copolymer is less than 6% by mass with respect to the total structural units It was confirmed that any pressure-sensitive adhesive layer formed from the adhesive composition, when heat-treated at a high temperature of 260° C., markedly contaminates the surface of the adherend during peeling.
A pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 5, wherein the (meth)acrylic copolymer contains structural units derived from N-ethoxymethylacrylamide instead of structural units derived from N-methoxymethylacrylamide. It was confirmed that when heat treated at a high temperature of 260° C., the surface of the adherend is markedly contaminated at the time of peeling.
The (meth)acrylic copolymer is formed from the pressure-sensitive adhesive compositions of Comparative Examples 6 and 10 containing structural units derived from N-butoxymethylacrylamide instead of structural units derived from N-methoxymethylacrylamide. It was confirmed that any of the pressure-sensitive adhesive layers, when heat-treated at a high temperature of 260° C., markedly contaminates the surface of the adherend during peeling.
The adhesive layer formed from the adhesive composition of Comparative Example 7, in which the (meth)acrylic copolymer does not contain a structural unit derived from N-methoxymethylacrylamide, was heat-treated at a high temperature of 260 ° C., and when it was peeled off, It was confirmed that the surface of the adherend was significantly contaminated.
(Meth) acrylic copolymer, the adhesive formed by the adhesive composition of Comparative Example 8 containing neither structural units derived from a monomer having a hydroxyl group nor structural units derived from N-methoxymethylacrylamide It was confirmed that the agent layer could not suppress discoloration of the copper foil.

Claims (7)

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