JP7074283B2 - Adhesive composition and adhesive sheet - Google Patents

Description

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

The pressure-sensitive adhesive composition used in various display devices is required to be able to form a pressure-sensitive adhesive layer that exhibits light peelability at the initial stage of bonding and high adhesive strength after heating.

In response to such a requirement, for example, Patent Document 1 describes a pressure-sensitive adhesive sheet having a base material and a pressure-sensitive adhesive layer laminated on at least one side of the base material, wherein the pressure-sensitive adhesive layer is made of stainless steel. The adhesive strength N1 after being bonded and left at 23 ° C for 10 seconds is 1.0 N / 20 mm or less, and the adhesive layer is bonded to stainless steel and aged at 80 ° C for 5 minutes. The force N2 is 3.0 N / 20 mm or more, N2 / N1 is 5.0 or more, and the pressure-sensitive adhesive layer is functional with 100 parts by mass of the polymer (A) having a glass transition temperature of less than 0 ° C. A monomer having a polyorganosiloxane skeleton having a base equivalent of 1,000 g / mol or more and less than 15,000 g / mol and a monomer having a glass transition temperature of a homopolymer having a glass transition temperature of 40 ° C. or more are contained as a monomer unit, and the weight average molecular weight is 10,000. A pressure-sensitive adhesive sheet containing 0.1 part by mass to 20 parts by mass of the polymer (B) which is more than 100,000 is disclosed.
Further, for example, Patent Document 2 describes 100 parts by mass of the polymer (A) having a glass transition temperature of less than 0 ° C. and a polyorganosiloxane skeleton having a functional group equivalent of 1,000 g / mol or more and 4,600 g / mol or less. 0.1 mass of polymer (B) containing the monomer (B1) and the homopolymer having a glass transition temperature of 40 ° C. or higher as a monomer unit and having a weight average molecular weight of 10,000 or more and less than 100,000. The polymer (B) contains 10% by mass to 20% by mass of the monomer (B1) and 30% by mass to 50% by mass of the monomer (B2). The pressure-sensitive adhesive composition is disclosed.

International Publication No. 2015/163115 Japanese Unexamined Patent Publication No. 2017-203164

In recent years, with the diversification of consumer tastes, display devices are required to have high design. Therefore, displays having a curved surface shape are being distributed in the market. A flexible optical member is generally used for a display having a curved surface shape.

By the way, when a display having a curved surface shape and an optical member are bonded to each other by using an adhesive composition, wrinkles may occur when the adhesive layer follows the bending of the optical member. Therefore, the pressure-sensitive adhesive composition used for bonding a display having a curved surface shape and an optical member forms a pressure-sensitive adhesive layer that exhibits light peelability at the initial stage of bonding and high adhesive strength after heating. In addition to being able to do so, it is desirable to be able to form an adhesive layer that is less likely to wrinkle.

Regarding the above points, Patent Document 1 and Patent Document 2 do not describe wrinkles that may occur when a display having a curved surface shape and an optical member are bonded to each other, and do not mention anything about suppressing wrinkles. do not have.

The problem to be solved by the present invention is that it exhibits light peelability at the initial stage of bonding, exhibits high adhesive strength after heating, and is used for bonding a display having a curved surface shape and an optical member. It is an object of the present invention to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer, which is less likely to cause wrinkles.
Further, an object to be solved by the present invention is to provide a pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition.

Specific means for solving the problem include the following aspects.
<1> The (meth) acrylic polymer (A) having a glass transition temperature of less than 0 ° C.
A (meth) acrylic copolymer (B) having a weight average molecular weight in the range of 100,000 or more and less than 400,000 is included.
The (meth) acrylic copolymer (B) has a structural unit derived from the monomer (B1) having an organosiloxane skeleton and a glass transition temperature of 40 ° C. or higher when used as a homopolymer (meth). ) The functional group equivalent of the monomer (B1) containing the acrylic monomer (B2) and having the organosiloxane skeleton is in the range of 400 g / mol or more and 15,000 g / mol or less. The content of the structural unit derived from the (meth) acrylic monomer (B2) is in the range of 30% by mass or more and 50% by mass or less with respect to all the structural units.
The content of the (meth) acrylic copolymer (B) is in the range of 0.1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic polymer (A). Agent composition.

<2> The monomer (B1) having the organosiloxane skeleton is at least one compound selected from the group consisting of the compound represented by the following formula (1) and the compound represented by the formula (2). The pressure-sensitive adhesive composition according to <1>.

In formulas (1) and (2), R ¹ represents a hydrogen atom or a methyl group, R ² represents a monovalent organic group, and m and n each independently represent an integer of 0 or more. ..

<3> The pressure-sensitive adhesive composition according to <1> or <2>, wherein the gel fraction after crosslinking is 40% by mass or more.
<4> The content of the structural unit derived from the monomer (B1) having the organosiloxane skeleton in the (meth) acrylic copolymer (B) is 10% by mass or more and 20 by mass or more with respect to all the structural units. The pressure-sensitive adhesive composition according to any one of <1> to <3>, which is in the range of mass% or less.
<5> A pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition according to any one of <1> to <4>.

According to the present invention, it exhibits light peelability at the initial stage of bonding, exhibits high adhesive strength after heating, and causes wrinkles even when used for bonding a display having a curved surface shape and an optical member. A pressure-sensitive adhesive composition that is difficult to form a pressure-sensitive adhesive layer is provided.
Further, according to the present invention, there is provided a pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer formed by the above-mentioned pressure-sensitive adhesive composition.

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

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

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

As used herein, the term "adhesive" means an object that comes into contact with the pressure-sensitive adhesive layer on the opposite side of the substrate during use, and for example, a display can be an adherend.
In the present specification, the term "base material" refers to, for example, various optical members, and the term "base material" is used in distinction from the term "adhesive body".

As used herein, the term "(meth) acrylic (co) polymer" means that the content of structural units derived from a monomer having a (meth) acryloyl group is the total structural unit (that is, (meth) acrylic). It means a (co) polymer which is 50% by mass or more of (the total constituent unit of the polymer).

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". , "(Meta) acryloyl" is a term that includes both "acryloyl" and "methacrylic".

In the present specification, "n-" means normal, "i-" means iso, "s-" means secondary, and "t-" means tertiary.

In the present specification, the specific (meth) acrylic polymer (A) and the specific (meth) acrylic copolymer (B) are collectively referred to as “specific (meth) acrylic polymer”.

[Adhesive composition]
The pressure-sensitive adhesive composition of the present invention has a (meth) acrylic polymer (A) having a glass transition temperature (Tg) of less than 0 ° C. and a weight average molecular weight (Mw) in the range of 100,000 or more and less than 400,000. The (meth) acrylic copolymer (B) contains a (meth) acrylic copolymer (B), and the (meth) acrylic copolymer (B) is a structural unit derived from a monomer (B1) having an organosiloxane skeleton and a homopolymer. The functional unit of the polymer (B1) having an organosiloxane skeleton, which comprises a structural unit derived from a (meth) acrylic monomer (B2) having a glass transition temperature (Tg) of 40 ° C. or higher. The base equivalent is in the range of 400 g / mol or more and 15,000 g / mol or less, and the content of the constituent units derived from the (meth) acrylic monomer (B2) is 30 with respect to all the constituent units. The content is in the range of mass% or more and 50% by mass or less, and the content of the (meth) acrylic copolymer (B) is 0.1 part by mass with respect to 100 parts by mass of the (meth) acrylic polymer (A). The range is 20 parts by mass or less.
According to the pressure-sensitive adhesive composition of the present invention, when it is used for bonding a display having a curved surface shape and an optical member, it exhibits light peelability at the initial stage of bonding, exhibits high adhesive strength after heating, and has a curved surface shape. However, it is possible to form an adhesive layer that is less likely to cause wrinkles.
Although it is not clear why the pressure-sensitive adhesive composition of the present invention may exert such an effect, the present inventors speculate as follows. However, the following speculation does not limitly interpret the pressure-sensitive adhesive composition of the present invention, but is described as an example.

The monomer (B1) having an organosiloxane skeleton tends to have the (meth) acrylic copolymer (B) unevenly distributed at the interface with the adherend due to the low polarity derived from the structure.
The pressure-sensitive adhesive composition of the present invention contains a (meth) acrylic copolymer (B) containing a structural unit derived from a monomer (B1) having an organosiloxane skeleton, and also contains a (meth) acrylic copolymer. Since the weight average molecular weight (Mw) of the polymer (B) is less than 400,000, the (meth) acrylic copolymer (B) is appropriately unevenly distributed at the interface with the adherend at the initial stage of bonding. Therefore, it is presumed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention exhibits light peelability at the initial stage of bonding.

The (meth) acrylic copolymer (B) contained in the pressure-sensitive adhesive composition of the present invention has a glass transition temperature (Tg) of 40 ° C. or higher when used as a homopolymer (meth) acrylic monomer. Since the constituent unit derived from (B2) is contained in a specific amount, the cohesive force of the formed pressure-sensitive adhesive layer becomes appropriate, and the pressure-sensitive adhesive force is increased by heating. Further, since the pressure-sensitive adhesive composition of the present invention contains the (meth) acrylic polymer (A) having a glass transition temperature (Tg) of less than 0 ° C., the pressure-sensitive adhesive layer formed is relative to the adherend. Shows moderate wettability.
From the above, it is presumed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention exhibits high adhesive strength after heating.

In the pressure-sensitive adhesive composition of the present invention, the weight average molecular weight (Mw) of the (meth) acrylic copolymer (B) is 100,000 or more, so that the pressure-sensitive adhesive layer formed exhibits an appropriate cohesive force. Therefore, it is presumed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention is unlikely to cause wrinkles even when used for bonding a display having a curved surface shape and an optical member.

Since the pressure-sensitive adhesive composition of the present invention contains the (meth) acrylic copolymer (B) in a specific amount with respect to the (meth) acrylic polymer (A), it is lightly peelable at the initial stage of bonding and after heating. It is presumed that it is possible to form an adhesive layer having a good balance of high adhesive strength and resistance to wrinkles when used for bonding a display having a curved shape and an optical member.

For the pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive composition described in Patent Document 1 (International Publication No. 2015/163115) and the pressure-sensitive adhesive composition described in Patent Document 2 (Japanese Patent Laid-Open No. 2017-203164). The product contains a copolymer containing a structural unit derived from a monomer having an organosiloxane skeleton, but the weight average molecular weight (Mw) of the copolymer is less than 100,000, so that the pressure-sensitive adhesive layer is formed. Insufficient cohesive force. Therefore, when used for bonding a display having a curved surface shape and an optical member, wrinkles are likely to occur due to insufficient cohesive force of the copolymer unevenly distributed at the interface with the display (see, for example, Comparative Example 3 described later).

Further, the present inventors have a curved surface shape by extremely lowering the weight average molecular weight (Mw) of the (meth) acrylic copolymer containing a structural unit derived from a monomer having an organosiloxane skeleton. It has been confirmed that an adhesive layer that is less likely to wrinkle can be formed even when used for bonding a display and an optical member. However, on the other hand, if the weight average molecular weight (Mw) of the (meth) acrylic copolymer is too low, it tends to foam due to heating (see, for example, Comparative Example 1 described later).
According to the pressure-sensitive adhesive composition of the present invention, when used for bonding a display having a curved surface shape and an optical member, it is possible to obtain an effect that not only wrinkles but also a pressure-sensitive adhesive layer in which bubbles are less likely to occur can be formed.

[(Meta) acrylic polymer (A)]
The pressure-sensitive adhesive composition of the present invention has a glass transition temperature (Tg) of less than 0 ° C. (meth) acrylic polymer (A) [hereinafter, also referred to as “specific (meth) acrylic polymer (A)”. 〕including.
The specific (meth) acrylic polymer (A) may be a homopolymer obtained by polymerizing one kind of monomer, or a copolymer obtained by polymerizing two or more kinds of monomers. May be.
The specific (meth) acrylic polymer (A) is preferably a copolymer, for example, from the viewpoint of easily adjusting the glass transition temperature (Tg) to a desired value.
The structural unit contained in the specific (meth) acrylic polymer (A) is not particularly limited.
The specific (meth) acrylic polymer (A) preferably contains, for example, the following structural units.

<Constituent unit derived from (meth) acrylic acid alkyl ester monomer>
The specific (meth) acrylic polymer (A) preferably contains a structural unit derived from the (meth) acrylic acid alkyl ester monomer.
The structural unit derived from the (meth) acrylic acid alkyl ester monomer contributes to the adjustment of the adhesive strength of the pressure-sensitive adhesive layer.

As used herein, the "constituent unit derived from the (meth) acrylic acid alkyl ester monomer" means a structural unit formed by addition polymerization of the (meth) acrylic acid alkyl ester monomer.

The type of the (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 carbon number of the alkyl group is preferably in the range of 1 to 18 and more preferably in the range of 1 to 12 from the viewpoint of the adhesive force of the formed pressure-sensitive adhesive layer on the adherend and the adhesion to the substrate. ..

Examples of the (meth) acrylic acid alkyl ester monomer include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, s-butyl (meth) acrylate, and 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 Examples thereof include (meth) acrylate, n-dodecyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, and isobornyl (meth) acrylate.
Among these, as the (meth) acrylic acid alkyl ester monomer, for example, methyl acrylate (MA) can be easily produced from the viewpoint of easily producing a (meth) acrylic polymer having a glass transition temperature (Tg) of less than 0 ° C. , N-butyl acrylate (n-BA), and 2-ethylhexyl acrylate (2EHA) are preferably selected from the group consisting of at least one.

When the specific (meth) acrylic polymer (A) contains a structural unit derived from the (meth) acrylic acid alkyl ester monomer, the specific (meth) acrylic polymer (A) contains one structural unit derived from the (meth) acrylic acid alkyl ester monomer. It may contain only two kinds or more.

When the specific (meth) acrylic polymer (A) contains a structural unit derived from the (meth) acrylic acid alkyl ester monomer, the (meth) acrylic acid alkyl ester in the specific (meth) acrylic polymer (A) The content (ratio) of the constituent units derived from the monomer is preferably 50% by mass or more, more preferably 60% by mass or more, based on all the constituent units of the specific (meth) acrylic polymer (A). 70% by mass or more is more preferable, and 80% by mass or more is particularly preferable.
The upper limit of the content (ratio) of the structural unit derived from the (meth) acrylic acid alkyl ester monomer in the specific (meth) acrylic polymer (A) is not particularly limited, and for example, the specific (meth) acrylic With respect to all the constituent units of the polymer (A), 100% by mass or less is preferable, 99% by mass or less is more preferable, and 98% by mass or less is further preferable.

<Constituent unit derived from a monomer having a carboxy group>
The specific (meth) acrylic polymer (A) may contain a structural unit derived from a monomer having a carboxy group.
When the specific (meth) acrylic polymer (A) contains a structural unit derived from a monomer having a carboxy group, the adhesive strength of the formed pressure-sensitive adhesive layer after heating tends to be higher.

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

The type of the monomer having a carboxy group is not particularly limited.
Specific examples of the monomer having a carboxy group include acrylic acid (AA), methacrylic acid (MAA), succinic acid, maleic anhydride, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, and ω-carboxy-polycaprolactone. Examples thereof include mono (meth) acrylate (for example, ω-carboxy-polycaprolactone (n≈2) monoacrylate), succinic acid ester (for example, 2-acryloyloxyethyl-succinic acid) and the like.
Among these, as the monomer having a carboxy group, for example, when a cross-linking agent (particularly, an isocyanate-based cross-linking agent) is contained, the reactivity with the cross-linking agent is good, and the pressure-sensitive adhesive to be formed. Acrylic acid (AA) is preferred from the viewpoint of showing a tendency for the adhesive strength of the layer to be higher after heating.

When the specific (meth) acrylic polymer (A) contains a structural unit derived from a monomer having a carboxy group, it may contain only one structural unit derived from the monomer having a carboxy group. Two or more kinds may be included.

When the specific (meth) acrylic polymer (A) contains a structural unit derived from a monomer having a carboxy group, it is derived from the monomer having a carboxy group in the specific (meth) acrylic polymer (A). The content rate (ratio) of the structural unit is preferably in the range of 0.5% by mass or more and 20% by mass or less with respect to all the structural units of the specific (meth) acrylic polymer (A), and is 1% by mass or more and 15% by mass. The range of% or less is more preferable, and the range of 2% by mass or more and 10% by mass or less is further preferable.
The content of the structural unit derived from the monomer having a carboxy group in the specific (meth) acrylic polymer (A) is 0.5 with respect to all the structural units of the specific (meth) acrylic polymer (A). When it is mass% or more, the adhesive strength of the formed pressure-sensitive adhesive layer after heating tends to be higher.
The content of the structural unit derived from the monomer having a carboxy group in the specific (meth) acrylic polymer (A) is 20% by mass with respect to all the structural units of the specific (meth) acrylic polymer (A). The following indicates that the light peelability of the pressure-sensitive adhesive layer at the initial stage of bonding is less likely to be impaired.

<Constituent unit derived from a monomer having a hydroxyl group>
The specific (meth) acrylic polymer (A) may contain a structural unit derived from a monomer having a hydroxyl group.
When the specific (meth) acrylic polymer (A) contains a structural unit derived from a monomer having a hydroxyl group, the adhesive strength of the formed pressure-sensitive adhesive layer after heating tends to be higher.

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

The type of the monomer having a hydroxyl group is not particularly limited.
Specific examples of the monomer having a hydroxyl group include 2-hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-. Hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, 3-methyl-3-hydroxybutyl (meth) acrylate, 1,1 -Dimethyl-3-hydroxybutyl (meth) acrylate, 1,3-dimethyl-3-hydroxybutyl (meth) acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth) acrylate, 2-ethyl-3- Examples thereof include hydroxyhexyl (meth) acrylate and N-hydroxyethyl (meth) acrylamide.
Among these, as the monomer having a hydroxyl group, hydroxyalkyl (meth) acrylate is preferable from the viewpoint of copolymerizability with the above-mentioned (meth) acrylic acid alkyl ester monomer.
The hydroxyalkyl (meth) acrylate has, for example, good compatibility and copolymerizability with the above-mentioned (meth) acrylic acid alkyl ester monomer, and a cross-linking agent (particularly, an isocyanate-based cross-linking agent). A hydroxyalkyl (meth) acrylate having a hydroxyalkyl group having 1 to 5 carbon atoms is preferable, and a hydroxyalkyl group having 2 to 4 carbon atoms is preferable from the viewpoint that the reactivity with the cross-linking agent is good when the above-mentioned substances are contained. Hydroxyalkyl (meth) acrylates are more preferred.

When the specific (meth) acrylic polymer (A) contains a structural unit derived from a monomer having a hydroxyl group, it may contain only one structural unit derived from the monomer having a hydroxyl group. 2 It may contain more than seeds.

When the specific (meth) acrylic polymer (A) contains a structural unit derived from a monomer having a hydroxyl group, the structural unit derived from the monomer having a hydroxyl group in the specific (meth) acrylic polymer (A) The content (ratio) of is preferably in the range of 0.5% by mass or more and 30% by mass or less with respect to all the constituent units of the specific (meth) acrylic polymer (A), and is 1% by mass or more and 25% by mass or less. Is more preferable, and a range of 5% by mass or more and 20% by mass or less is further preferable.
The content of the structural unit derived from the monomer having a hydroxyl group in the specific (meth) acrylic polymer (A) is 0.5% by mass with respect to all the structural units of the specific (meth) acrylic polymer (A). When it is% or more, the adhesive strength of the formed adhesive layer after heating tends to be higher.
The content of the structural unit derived from the monomer having a hydroxyl group in the specific (meth) acrylic polymer (A) is 30% by mass or less with respect to all the structural units of the specific (meth) acrylic polymer (A). If this is the case, the light peelability of the pressure-sensitive adhesive layer at the initial stage of bonding tends to be less likely to be impaired.

<Other building blocks>
The specific (meth) acrylic polymer (A) is the above-mentioned structural unit, that is, the structural unit derived from the (meth) acrylic acid alkyl ester monomer, carboxy, within the range in which the effect of the present invention is exhibited. It may contain a structural unit derived from a monomer having a group and a structural unit other than the structural unit derived from the monomer having a hydroxyl group (so-called other structural units).

Examples of the monomers constituting other structural units include (meth) acrylate having an aromatic ring represented by benzyl (meth) acrylate and phenoxyethyl (meth) acrylate, methoxyethyl (meth) acrylate, and ethoxy. Alkoxyalkyl (meth) acrylate represented by ethyl (meth) acrylate, styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and aromatic monovinyl represented by vinyltoluene, acrylonitrile and Examples thereof include vinyl cyanide typified by methacrylonitrile, and vinyl esters typified by vinyl acrylate, vinyl acetate, vinyl propionate, and vinyl versatic acid. In addition, various derivatives of these monomers can be mentioned.

<< Glass transition temperature of specific (meth) acrylic polymer (A) >>
The glass transition temperature (Tg) of the specific (meth) acrylic polymer (A) is less than 0 ° C., preferably −20 ° C. or lower, more preferably −30 ° C. or lower, still more preferably −40 ° C. or lower.
When the glass transition temperature (Tg) of the specific (meth) acrylic polymer (A) is less than 0 ° C., the formed adhesive layer has an appropriate wettability to the adherend and has a high adhesive force after heating. Can be shown.
The lower limit of the glass transition temperature (Tg) of the specific (meth) acrylic polymer (A) is not particularly limited, and is preferably −70 ° C. or higher from the viewpoint of adhesive strength to the adherend, for example.

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

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

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

The "glass transition temperature (Tg) represented by the Celsius temperature (° C) when made into a homopolymer" of a typical monomer is -76 ° C for 2-ethylhexyl acrylate (2EHA) and 2-ethylhexyl methacrylate (2-ethylhexyl methacrylate). 2EHMA) is -10 ° C, n-butyl acrylate (n-BA) is -57 ° C, n-butyl methacrylate (n-BMA) is 21 ° C, t-butyl acrylate (t-BA) is 41 ° C, t-butyl. Methacrylate (t-BMA) at 107 ° C, i-butyl methacrylate (i-BMA) at 48 ° C, methyl acrylate (MA) at 5 ° C, methyl methacrylate (MMA) at 103 ° C, and isobonyl methacrylate (IBXMA) at 155 ° C. , Isobonyl acrylate (IBXA) 96 ° C, ethyl acrylate (EA) -27 ° C, 2-ethylhexyl acrylate (2EHA) -76 ° C, methacrylic acid 185 ° C, 4-hydroxybutyl acrylate (4HBA) -39 ° C., 2-hydroxyethyl acrylate (2HEA) at -15 ° C, 2-hydroxyethyl methacrylate (2HEMA) at 55 ° C, acrylic acid (AA) at 163 ° C, isooctyl acrylate (i-OA) at -75 ° C, dimethyl. Aminoethyl 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 (Tg) of the specific (meth) acrylic polymer (A) is appropriately adjusted by using, for example, two or more types of monomers having different glass transition temperatures (Tg) when used as a homopolymer. can.

<< Weight average molecular weight of specific (meth) acrylic polymer (A) >>
The weight average molecular weight (Mw) of the specific (meth) acrylic polymer (A) is preferably in the range of 400,000 or more and 2 million or less, more preferably in the range of 500,000 or more and 2 million or less, and 500,000 or more and 1.5 million or less. The range is more preferred.
When the weight average molecular weight (Mw) of the specific (meth) acrylic polymer (A) is 400,000 or more, the light peelability of the pressure-sensitive adhesive layer at the initial stage of bonding tends to be less likely to be impaired.
When the weight average molecular weight (Mw) of the specific (meth) acrylic copolymer (A) is 2 million or less, the adhesive strength of the formed pressure-sensitive adhesive layer after heating tends to be higher.

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

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

The weight average molecular weight (Mw) of the specific (meth) acrylic polymer (A) can be determined by adjusting the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, and the like. , Can be set to the desired value.

<< Content of specific (meth) acrylic polymer (A) >>
The content of the specific (meth) acrylic polymer (A) in the pressure-sensitive adhesive composition of the present invention is not particularly limited, and is, for example, 40% by mass or more and 99% by mass with respect to the total solid content in the pressure-sensitive adhesive composition. The range of% or less is preferable, the range of 50% by mass or more and 99% by mass or less is more preferable, and the range of 60% by mass or more and 99% by mass or less is further preferable.
When the content of the specific (meth) acrylic polymer (A) in the pressure-sensitive adhesive composition of the present invention is 40% by mass or more with respect to the total solid content in the pressure-sensitive adhesive composition, the pressure-sensitive adhesive layer is formed. The adhesive strength after heating tends to be higher.
When the content of the specific (meth) acrylic polymer (A) in the pressure-sensitive adhesive composition of the present invention is 99% by mass or less with respect to the total solid content in the pressure-sensitive adhesive composition, the pressure-sensitive adhesive at the initial stage of bonding. The light peelability of the layer tends to be less likely to be impaired.
In the present specification, the "total solid content in the pressure-sensitive adhesive composition" means the total mass of the pressure-sensitive adhesive composition when the pressure-sensitive adhesive composition does not contain a volatile component such as a solvent, and the pressure-sensitive adhesive. When the composition contains a volatile component such as a solvent, it means the mass of the residue obtained by removing the volatile component such as a solvent from the pressure-sensitive adhesive composition.

[(Meta) acrylic copolymer (B)]
The pressure-sensitive adhesive composition of the present invention is a (meth) acrylic copolymer having a weight average molecular weight (Mw) in the range of 100,000 or more and less than 400,000, and is a monomer (B1) having an organosiloxane skeleton. The derived structural unit and the (meth) acrylic monomer (B2) having a glass transition temperature of 40 ° C. or higher when made into a homopolymer [hereinafter, "specific (meth) acrylic monomer (B2)"". Also called. ], And the functional group equivalent of the monomer (B1) having an organosiloxane skeleton containing the constituent unit is in the range of 400 g / mol or more and 15,000 g / mol or less, and is a (meth) acrylic single amount. The content of the constituent units derived from the body (B2) is in the range of 30% by mass or more and 50% by mass or less with respect to all the constituent units (meth) acrylic copolymer (B) [hereinafter, "specified (specific (B2)". Also referred to as "meth) acrylic copolymer (B)". 〕including.
The content of the specific (meth) acrylic copolymer (B) in the pressure-sensitive adhesive composition of the present invention is 0.1 part by mass with respect to 100 parts by mass of the specific (meth) acrylic polymer (A). The range is 20 parts by mass or less.

<Constituent unit derived from the monomer (B1) having an organosiloxane skeleton>
The specific (meth) acrylic copolymer (B) contains a structural unit derived from the monomer (B1) having an organosiloxane skeleton.
The monomer (B1) having an organosiloxane skeleton has a relatively low polarity. Therefore, when the specific (meth) acrylic copolymer (B) contains a structural unit derived from the monomer (B1) having an organosiloxane skeleton, the specific (meth) acrylic copolymer is contained at the initial stage of bonding. When (B) is appropriately unevenly distributed at the interface with the adherend, the pressure-sensitive adhesive layer can exhibit light peelability.

In the present specification, the "constituent unit derived from the monomer (B1) having an organosiloxane skeleton" means a structural unit formed by addition polymerization of the monomer (B1) having an organosiloxane skeleton. ..

The functional group equivalent of the monomer (B1) having an organosiloxane skeleton is, for example, in the range of 400 g / mol or more and 15,000 g / mol or less from the viewpoint of availability, and 400 g / mol or more and 12,000 g / mol. The following range is preferred.
The functional group equivalent of the monomer (B1) having an organosiloxane skeleton is preferably 500 g / mol or more, more preferably 1,000 g / mol or more, for example, from the viewpoint of light peelability at the initial stage of bonding. More preferably, it is 000 g / mol or more.
The functional group equivalent of the monomer (B1) having an organosiloxane skeleton is preferably 10,000 g / mol or less, more preferably 8,500 g / mol or less, for example, from the viewpoint of improving the adhesive strength after heating. It is preferable, and more preferably 7,000 g / mol or less.

As used herein, the term "functional group equivalent" means the mass of the main skeleton (for example, polydimethylsiloxane) bonded to each functional group, and is expressed as a converted value per 1 mol of functional group.
The functional group equivalent of a monomer having an organosiloxane skeleton is calculated from the spectral intensity of ¹ H-NMR (so-called proton NMR) obtained by measurement using a nuclear magnetic resonance (NMR) device.
Specifically, in ¹ H-NMR, the spectral intensity of H (for example, H of Si- (CH ₃ ) ₂ ) bonded to silicon of the siloxane structure via C and the H of C-CH ₃ of the functional group. , SH H, or C = CH ₂ H with spectral intensity.

Since the chemical formula of the siloxane structure and the chemical formula of the functional group are known in advance, they are included in the measurement sample from the ratio of the number of Si- (CH ₃ ) ₂ of the siloxane structure to the number of C = CH ₂ of the functional group. , The ratio (A / B) of the number A of the siloxane structure having a Si- (CH ₃ ) ₂ bond to the number B of the functional groups can be found.
Since the molecular weight of each siloxane structure having Si- (CH ₃ ) ₂ bonds (here, dimethylsiloxane) is known, the number A of the siloxane structure and the number of functional groups are added to the molecular weight of each siloxane structure. The value obtained by multiplying the ratio with B (that is, A / B) is the mass of the siloxane structure having a Si- (CH ₃ ) ₂ bond per functional group, that is, the mass of the main skeleton, and the mass thereof. The value multiplied by the number of avocadro is the functional group equivalent (unit: g / mol).

When the specific (meth) acrylic copolymer (B) contains a monomer (B1) having two or more kinds of organosiloxane skeletons having different functional group equivalents, the functional group equivalents are arithmetically averaged values. Means.
In the present specification, when the (meth) acrylic copolymer contains a monomer having two or more kinds of organosiloxane skeletons having different functional group equivalents, "functional group equivalent of the monomer having an organosiloxane skeleton". Is calculated by the following formula.
Functional group equivalent of a monomer having an organosiloxane skeleton (g / mol) = [Functional equivalent of monomer 1 x compounding amount of monomer 1 + functional group equivalent of monomer 2 x monomer 2 Blending amount + ... + Functional group equivalent of monomer n x blending amount of monomer n] / [blending amount of monomer 1 + blending amount of monomer 2 + ... + monomer n Blending amount]

The type of the monomer (B1) having an organosiloxane skeleton is any monomer having an organosiloxane skeleton and having a functional group equivalent in the range of 400 g / mol or more and 15,000 g / mol or less. Is not particularly limited.
As a specific example of the monomer (B1) having an organosiloxane skeleton, for example, at least one selected from the group consisting of the compound represented by the following formula (1) and the compound represented by the formula (2). Examples include compounds.

In the formula (1) and the formula (2), R ¹ represents a hydrogen atom or a methyl group, and a methyl group is preferable.
In the formula (1) and the formula (2), R ² represents a monovalent organic group.
The monovalent organic group represented by ^R2 may be linear, may have a branch, or may be cyclic. Examples of the monovalent organic group include an alkyl group, an alkenyl group, an alkynyl group, an aryl group and the like, and an alkyl group is preferable.
When R ² represents an alkyl group, the alkyl group having 1 to 12 carbon atoms is preferable, the alkyl group having 1 to 6 carbon atoms is more preferable, and the alkyl group having 1 to 4 carbon atoms is further preferable.
Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, an s-butyl group, a t-butyl group and the like. , Methyl group is preferred.
Examples of the alkenyl group in which R ² represents an alkenyl group include a vinyl group, an allyl group, a 2-propenyl group and the like, and a vinyl group is preferable.
Examples of the alkynyl group when R ² represents an alkynyl group include an ethynyl group, a propargyl group, a propa-2-in-1-yl group and the like, and an ethynyl group is preferable.
Examples of the aryl group when R ² represents an aryl group include a phenyl group, a tolyl group, a pyridyl group and the like, and a phenyl group is preferable.
m and n each independently represent an integer of 0 or more. For m, an integer of 1 to 10 is preferable, and an integer of 1 to 6 is more preferable. n is preferably an integer of 1 to 250, more preferably an integer of 5 to 200.

As the monomer (B1) having an organosiloxane skeleton, a commercially available product can be used.
Examples of commercially available products of the monomer (B1) having an organosiloxane skeleton are X-22-2404 [trade name, functional group equivalent: 420 g / mol, Shin-Etsu Chemical Industry Co., Ltd.], X-22-174ASX [ Product name, functional group equivalent: 900 g / mol, Shin-Etsu Chemical Industry Co., Ltd.], X-22-174DX [Product name, functional group equivalent: 4600 g / mol, Shin-Etsu Chemical Industry Co., Ltd.], KF-2012 [Product name , Functional group equivalent: 4600 g / mol, Shin-Etsu Chemical Industry Co., Ltd.], X-22-2426 [trade name, functional group equivalent: 12,000 g / mol, Shin-Etsu Chemical Industry Co., Ltd.] and the like.
All of the above commercially available products correspond to the compounds represented by the formula (2).

The specific (meth) acrylic copolymer (B) may contain only one type of structural unit derived from the monomer (B1) having an organosiloxane skeleton, or may contain two or more types.

The content of the structural unit derived from the monomer (B1) having an organosiloxane skeleton in the specific (meth) acrylic copolymer (B) is the total structural unit of the specific (meth) acrylic copolymer (B). On the other hand, the range of 10% by mass or more and 30% by mass or less is preferable, the range of 10% by mass or more and 25% by mass or less is more preferable, and the range of 10% by mass or more and 20% by mass or less is further preferable.
The content of the structural unit derived from the monomer (B1) having an organosiloxane skeleton in the specific (meth) acrylic copolymer (B) is the total structural unit of the specific (meth) acrylic copolymer (B). On the other hand, when it is 10% by mass or more, the light peelability of the pressure-sensitive adhesive layer at the initial stage of bonding tends to be less likely to be impaired.
The content of the structural unit derived from the monomer (B1) having an organosiloxane skeleton in the specific (meth) acrylic copolymer (B) is the total structural unit of the specific (meth) acrylic copolymer (B). On the other hand, when it is 30% by mass or less, the adhesive strength of the pressure-sensitive adhesive layer tends to be higher when the pressure-sensitive adhesive layer is heated at a low temperature for a short time.

<Constituent unit derived from specific (meth) acrylic monomer (B2)>
The specific (meth) acrylic copolymer (B) has a glass transition temperature (Tg) of 40 ° C. or higher when used as a homopolymer (meth) acrylic monomer (B2) [that is, the specific (meth) acrylic copolymer (meth). ) Acrylic monomer (B2)], and the content of the structural unit derived from the specific (meth) acrylic monomer (B2) is the specific (meth) acrylic copolymer (). The range is 30% by mass or more and 50% by mass or less with respect to all the constituent units of B).

In the present specification, the "constituent unit derived from the specific (meth) acrylic monomer (B2)" refers to a structural unit formed by addition polymerization of the specific (meth) acrylic monomer (B2). means.
Further, in the present specification, the “(meth) acrylic monomer” means a monomer having a (meth) acryloyl group.

The specific (meth) acrylic monomer (B2) has a glass transition temperature (Tg) of 40 ° C. or higher, preferably 50 ° C. or higher, more preferably 60 ° C. or higher, and more preferably 80 ° C. when used as a homopolymer. The above is more preferable.
When the glass transition temperature (Tg) when the specific (meth) acrylic monomer (B2) is used as a homopolymer is 40 ° C. or higher, a pressure-sensitive adhesive layer showing high adhesive strength can be formed after heating.
The upper limit of the glass transition temperature (Tg) when the specific (meth) acrylic monomer (B2) is used as a homopolymer is not particularly limited, and is preferably 120 ° C. or lower, for example.

As the specific (meth) acrylic monomer (B2), for example, an unsubstituted (meth) acrylic acid alkyl ester monomer is preferable from the viewpoint of adhesive strength to an adherend.
The alkyl group of the (meth) acrylic acid alkyl ester monomer may be linear, branched or cyclic.
The number of carbon atoms of the alkyl group is preferably in the range of 1 to 18, and more preferably in the range of 1 to 12, for example, from the viewpoint of adhesiveness to the adherend and adhesion to the substrate.

Specific examples of the (meth) acrylic alkyl ester monomer having a glass transition temperature (Tg) of 40 ° C. or higher when used as a homopolymer include methyl methacrylate (MMA, Tg when used as a homopolymer): 103. ° C.), i-butyl methacrylate (i-BMA, Tg when made into a homopolymer: 48 ° C.), t-butyl acrylate (t-BA, Tg when made into a homopolymer: 41 ° C.), t-butyl Examples thereof include methacrylate (t-BMA, Tg when made into a homopolymer: 107 ° C.).

The specific (meth) acrylic copolymer (B) may contain only one type of structural unit derived from the specific (meth) acrylic monomer (B2), or may contain two or more types.

The content (ratio) of the structural unit derived from the specific (meth) acrylic monomer (B2) in the specific (meth) acrylic copolymer (B) is the specific (meth) acrylic copolymer (B). The range is 30% by mass or more and 50% by mass or less, preferably 35% by mass or more and 50% by mass or less, more preferably 35% by mass or more and 45% by mass or less, and 40% by mass with respect to all the constituent units of. The range of% or more and 45% by mass or less is more preferable.
The content of the structural unit derived from the specific (meth) acrylic monomer (B2) in the specific (meth) acrylic copolymer (B) is the total composition of the specific (meth) acrylic copolymer (B). When it is 30% by mass or more with respect to the unit, the cohesive force becomes appropriate due to the specific (meth) acrylic copolymer (B), so that a pressure-sensitive adhesive layer showing high adhesive force is formed after heating. obtain.
The content of the structural unit derived from the specific (meth) acrylic monomer (B2) in the specific (meth) acrylic copolymer (B) is the total composition of the specific (meth) acrylic copolymer (B). When it is 50% by mass or less with respect to the unit, the wettability to the adherend is not easily impaired, so that a pressure-sensitive adhesive layer showing high adhesive strength can be formed after heating.

<Other building blocks>
The specific (meth) acrylic copolymer (B) is a structural unit derived from the above-mentioned structural unit, that is, a monomer (B1) having an organosiloxane skeleton, within the range in which the effect of the present invention is exhibited. , And a structural unit other than the structural unit derived from the specific (meth) acrylic monomer (B2) (so-called other structural unit) may be contained.

Examples of the monomer constituting the other structural unit include (meth) acrylic alkyl ester monomers having a glass transition temperature (Tg) of less than 40 ° C. when made into a homopolymer.
Examples of the monomer constituting the other structural unit include (meth) acrylate having an aromatic ring represented by benzyl (meth) acrylate and phenoxyethyl (meth) acrylate, methoxyethyl (meth) acrylate, and the like. And alkoxyalkyl (meth) acrylate represented by ethoxyethyl (meth) acrylate, styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and aromatic monovinyl represented by vinyltoluene, Examples thereof include vinyl cyanide represented by acrylonitrile and methacrylonitrile, and vinyl esters represented by vinyl acrylate, vinyl acetate, vinyl propionate, and vinyl versatic acid. In addition, various derivatives of these monomers can be mentioned.

<< Weight average molecular weight of specific (meth) acrylic copolymer (B) >>
The weight average molecular weight (Mw) of the specific (meth) acrylic copolymer (B) is in the range of 100,000 or more and less than 400,000, preferably in the range of 100,000 or more and 350,000 or less, and preferably 100,000 or more and 300,000 or less. The range is more preferable, and the range of 200,000 or more and 300,000 or less is further preferable.
When the weight average molecular weight (Mw) of the specific (meth) acrylic copolymer (B) is 100,000 or more, adhesion that does not easily cause wrinkles even when used for bonding a display having a curved surface shape and an optical member. It can form a layer of agent.
When the weight average molecular weight (Mw) of the specific (meth) acrylic copolymer (B) is less than 400,000, the compatibility with the specific (meth) acrylic copolymer (A) becomes good. Further, since the specific (meth) acrylic copolymer (B) is appropriately unevenly distributed at the interface with the adherend at the initial stage of bonding, the pressure-sensitive adhesive layer may exhibit light peelability.

The weight average molecular weight (Mw) of the specific (meth) acrylic copolymer (B) is measured by the same method as the weight average molecular weight (Mw) of the specific (meth) acrylic polymer (A) described above. The value.

For the weight average molecular weight (Mw) of the specific (meth) acrylic copolymer (B), the polymerization temperature, the polymerization time, the amount of the organic solvent used, the type of the polymerization initiator, the amount of the polymerization initiator used, etc. shall be adjusted. Therefore, the desired value can be obtained.

<< Content of specific (meth) acrylic copolymer (B) >>
The content of the specific (meth) acrylic copolymer (B) in the pressure-sensitive adhesive composition of the present invention is 0.1 part by mass or more and 20 parts by mass with respect to 100 parts by mass of the specific (meth) acrylic polymer (A). The range is 0.1 parts by mass or more, preferably 15 parts by mass or less, more preferably 0.1 parts by mass or more and 10 parts by mass or less, and 0.5 parts by mass or more and 10 parts by mass or less. The range is more preferred.
The content of the specific (meth) acrylic copolymer (B) in the pressure-sensitive adhesive composition of the present invention is 0.1 part by mass or more with respect to 100 parts by mass of the specific (meth) acrylic polymer (A). This means that the pressure-sensitive adhesive composition of the present invention positively contains the specific (meth) acrylic copolymer (B).
When the content of the specific (meth) acrylic copolymer (B) in the pressure-sensitive adhesive composition of the present invention is 20 parts by mass or less with respect to 100 parts by mass of the specific (meth) acrylic polymer (A). A pressure-sensitive adhesive layer is formed that has a good balance of light peelability at the initial stage of bonding, high adhesive strength after heating, and resistance to wrinkles when used for bonding a display having a curved shape and an optical member. obtain.

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

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

Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, alcohol compounds and the like.
More specifically, examples of the organic solvent used in the polymerization reaction include benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetraline and decalin. And aromatic hydrocarbons represented by aromatic naphtha, n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and fat represented by terepine oil. Esters typified by based or alicyclic hydrocarbons, ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate. Classes, acetone, methyl ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, and ketones typified by methylcyclohexanone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether. , And glycol ethers typified by diethylene glycol monobutyl ether, as well as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t-. Examples thereof include alcohols typified by butyl alcohol.
At the time of the polymerization reaction, only one of these organic solvents may be used, or two or more of these organic solvents may be mixed and used.

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

Examples of the polymerization initiator include organic peroxides and azo compounds used in ordinary solution polymerization.
Examples of the organic peroxide include t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propylperoxydicarbonate, and di-2-ethylhexylperoxydi. Carbonate, t-butylperoxypivalate, 2,2-bis (4,4-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 can be mentioned.
Examples of the azo compound include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis (2,4-dimethylvaleronitrile) (ABVN), and 2,2'-azobis (4-). Methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis (cyclohexane-1-carbonitrile), and 2,2'-azobis (isobutyric acid) dimethyl.

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

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

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

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

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

[Crosslinking agent]
The pressure-sensitive adhesive composition of the present invention preferably contains a cross-linking agent.
The type of cross-linking agent is not particularly limited.
Examples of the cross-linking agent include isocyanate-based cross-linking agents and epoxy-based cross-linking agents. Further, as the cross-linking agent, a metal chelate compound can also be used.

As used herein, the term "isocyanate-based cross-linking agent" means a compound having two or more isocyanate groups in the molecule (so-called polyisocyanate compound). Further, the "epoxy-based cross-linking agent" means a compound having at least one epoxy group in the molecule (so-called epoxy compound).

Examples of the polyisocyanate compound include aromatic polyisocyanate compounds such as xylylene diisocyanate (XDI), diphenylmethane diisocyanate, triphenylmethane triisocyanate, and tolylene diisocyanate (TDI), hexamethylene diisocyanate (HMDI), and pentamethylene diisocyanate (PDI). , Isophoron diisocyanate, aliphatic or alicyclic polyisocyanate compounds such as hydrogenated additives of aromatic polyisocyanate compounds and the like.
Examples of the polyisocyanate compound include a dimer, a trimer, or a pentamer of the polyisocyanate compound, an adduct of the polyisocyanate compound and a polyol compound such as trimethylolpropane, and a biuret of the isocyanate compound. Can also be mentioned.

As the polyisocyanate compound, a commercially available product can be used.
Examples of commercially available polyisocyanate compounds are "Coronate (registered trademark) HX", "Coronate (registered trademark) HL-S", "Coronate (registered trademark) L", and "Coronate (registered trademark) L-45E". , "Coronate® 2031", "Coronate® 2030", "Coronate® 2234", "Coronate® 2785", "Aquanate® 200", and "Aqua". Nate (registered trademark) 210 ”[above, Tosoh Co., Ltd.],“ Sumijuru (registered trademark) N3300 ”,“ Death Module (registered trademark) N3400 ”, and“ Sumijuru (registered trademark) N-75 ”[more than , Sumika Cobestro Urethane Co., Ltd.], "Duranate (registered trademark) E-405-80T", "Duranate (registered trademark) AE700-100", "Duranate (registered trademark) 24A-100", and "Duranate (registered trademark) "TSE-100" [above, Asahi Kasei Co., Ltd.], "Takenate (registered trademark) D-110N", "Takenate (registered trademark) D-120N", "Takenate (registered trademark) M-631N" , "MT-Orester (registered trademark) NP1200", and "Stavio (registered trademark) XD-340N" [above, Mitsui Kagaku Co., Ltd.].

Examples of the epoxy compound include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1, 6-Hexanediol diglycidyl ether, polytetramethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, resorcin diglycidyl ether, 2,2-dibromoneopentyl Glycodiglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, adipate diglycidyl ester, phthalic acid diglycidyl ester, tris (glycidyl) isocyanurate, tris (glycidoxyethyl) isocia Examples thereof include nurate, 1,3-bis (N, N-glycidylaminomethyl) cyclohexane, N, N, N', N'-tetraglycidyl-1,3-benzenedi (methaneamine) and the like.

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

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

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

When the pressure-sensitive adhesive composition of the present invention contains a cross-linking agent, it may contain only one kind of cross-linking agent, or may contain two or more kinds of cross-linking agents.

When the pressure-sensitive adhesive composition of the present invention contains a cross-linking agent, the content of the cross-linking agent in the pressure-sensitive adhesive composition is not particularly limited and is appropriately set according to the type of the cross-linking agent.
For example, when the pressure-sensitive adhesive composition of the present invention contains an isocyanate-based cross-linking agent as a cross-linking agent, the content of the isocyanate-based cross-linking agent in the pressure-sensitive adhesive composition is the total content of all the polymers contained in the pressure-sensitive adhesive composition. The range of 0.05 parts by mass or more and 10 parts by mass or less is preferable, the range of 0.1 parts by mass or more and 10 parts by mass or less is more preferable, and the range of 0.1 parts by mass or more and 5 parts by mass or less is preferable with respect to 100 parts by mass. Is more preferable.
For example, when the pressure-sensitive adhesive composition of the present invention contains an epoxy-based cross-linking agent as a cross-linking agent, the content of the epoxy-based cross-linking agent in the pressure-sensitive adhesive composition is the total content of all the polymers contained in the pressure-sensitive adhesive composition. The range of 0.01 parts by mass or more and 3 parts by mass or less is preferable, the range of 0.01 parts by mass or more and 1 part by mass or less is more preferable, and the range of 0.01 parts by mass or more and 0.5 parts by mass or less is preferable with respect to 100 parts by mass. The range of is more preferable.

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

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

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

[Other ingredients]
The pressure-sensitive adhesive composition of the present invention may contain components other than the above-mentioned components (so-called other components), if necessary, as long as the effects of the present invention are not impaired.
Other components include polymers other than the above-mentioned polymers, cross-linking catalysts, tackifiers, antioxidants, colorants (eg, dyes and pigments), light stabilizers (eg, UV absorbers), and charging. Examples include various additives such as inhibitors.

When the pressure-sensitive adhesive composition of the present invention contains these 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.

<Gel fraction after cross-linking>
When the pressure-sensitive adhesive composition of the present invention contains a specific (meth) acrylic polymer having a crosslinkable functional group and a cross-linking agent, the gel content after cross-linking is preferably 40% by mass or more. It is more preferably in the range of 40% by mass or more and 90% by mass or less, and further preferably in the range of 40% by mass or more and 85% by mass or less.
When the gel fraction after cross-linking is 40% by mass or more, it tends to show higher adhesive strength after heating.

As used herein, the "gel fraction after cross-linking of the pressure-sensitive adhesive composition" is the percentage of solvent-insoluble content measured using ethyl acetate as the extraction solvent. Specifically, the gel fraction after crosslinking of the pressure-sensitive adhesive composition is measured according to the following (1) to (4).
(1) Approximately 0.15 g of the crosslinked pressure-sensitive adhesive composition (that is, the pressure-sensitive adhesive layer) was attached to a 250-mesh wire mesh (100 mm × 100 mm) whose mass was accurately measured with a precision balance, and the gel component leaked. Fold the wire mesh 5 times with the attached adhesive layer inside so that it does not exist, and use it as a sample. After that, the mass is accurately measured with a precision balance.
(2) The obtained sample is immersed in 80 mL of ethyl acetate for 3 days.
(3) The sample is taken out, washed with a small amount of ethyl acetate, and dried at 120 ° C. for 24 hours. After that, the mass is accurately measured with a precision balance.
(4) Calculate the gel fraction by the following formula.
Gel fraction (unit: mass%) = (ZX) / (YX) x 100
However, X is the mass of the wire mesh (unit: g), Y is the mass of the wire mesh to which the adhesive layer is attached before immersion (unit: g), and Z is the mass of the wire mesh to which the adhesive layer is attached and dried after immersion. (Unit: g).

<Use>
The pressure-sensitive adhesive composition of the present invention is preferably used, for example, for attachment to a display.
The pressure-sensitive adhesive composition of the present invention exhibits light peelability at the initial stage of bonding, exhibits high adhesive strength after heating, and wrinkles even when used for bonding a display having a curved surface shape and an optical member. Since it is possible to form an adhesive layer that is unlikely to cause an adhesive layer, it is particularly suitable for applications in which a display having a curved surface shape and an optical member are bonded to each other.
Examples of the display having a curved surface shape include a curved surface shape having a radius of curvature of 7,000 mm or less.

[Adhesive sheet]
The pressure-sensitive adhesive sheet of the present invention comprises a pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention.
The pressure-sensitive adhesive sheet of the present invention may be a non-base material type pressure-sensitive adhesive sheet having no base material, or may be a base material type pressure-sensitive adhesive sheet having an adhesive layer on at least one side of the base material.

In the pressure-sensitive adhesive sheet of the present invention, the exposed pressure-sensitive adhesive layer may be protected by a release film. The release film is not particularly limited as long as it can be easily peeled off from the pressure-sensitive adhesive layer, and examples thereof include a resin film having at least one surface subjected to an easy peeling treatment with a release treatment agent. Examples of the resin film include a polyester film typified by a polyethylene terephthalate film. Examples of the stripping agent include fluororesins, paraffin waxes, silicones, long-chain alkyl group compounds and the like.
The release film protects the surface of the pressure-sensitive adhesive layer until the pressure-sensitive adhesive sheet is put into practical use, and is peeled off during use.

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

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

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

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

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

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

The method for drying the pressure-sensitive adhesive composition applied on the surface of the base material or the release film is not particularly limited, and examples thereof include natural drying, heat drying, hot air drying, and vacuum drying.
The drying temperature and drying time of the pressure-sensitive adhesive composition applied on the surface of the base material or the release film are not particularly limited, and depend on the thickness of the applied pressure-sensitive adhesive composition, the amount of the organic solvent in the pressure-sensitive adhesive composition, and the like. It is set appropriately.

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

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 typified by aluminum, copper, and SUS (stainless steel), (meth) acrylic resin, ABS resin, polyethylene terephthalate, and various resins typified by polyimide. Examples include various inorganic materials typified by glass.
The pressure-sensitive adhesive sheet of the present invention can be particularly suitably used for attachment to an adherend made of SUS, polyimide, or glass.

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

[Manufacturing of (meth) acrylic polymer A]
[Manufacturing Example A-1]
237 parts by mass of ethyl acetate and 0.05 parts by mass of 2,2'-azobisisobutyronitrile (AIBN; polymerization initiator) in a reactor equipped with a stirrer, a reflux condenser, a sequential dropping device, and a thermometer. I prepared the department.
Then, in another container, 454 parts by mass of a monomer mixed solution consisting of 408.6 parts by mass of n-butyl acrylate (n-BA) and 45.4 parts by mass of acrylic acid (AA) was prepared.
Of the prepared monomer mixture, 80 parts by mass was first charged into the above reactor, heated, and refluxed at the reflux temperature for 10 minutes.
Then, under the reflux temperature condition, the remaining amount of 374 parts by mass of the monomer mixed solution and the mixed solution of 196 parts by mass of ethyl acetate and 0.17 parts by mass of AIBN were sequentially added dropwise over 120 minutes to complete the addition. It was later reacted for 70 minutes. Then, a mixed solution of 50 parts by mass of ethyl acetate and 0.790 parts by mass of AIBN was sequentially added dropwise over 60 minutes, and the reaction was carried out for 90 minutes after the completion of the addition.
After completion of the reaction, the reaction mixture was diluted with ethyl acetate to obtain a solution of the (meth) acrylic polymer A-1 having a solid content of 34% by mass.
The term "solid content" as used herein means a residue obtained by removing volatile components such as a solvent from the solution of the (meth) acrylic polymer A-1. The same applies to the following (meth) acrylic polymers A-2 to A-9 solutions.

[Manufacturing Examples A-2 to A-9]
In Production Example A-1, the monomer composition of the (meth) acrylic polymer was changed to the monomer composition shown in Table 1, and at least the amount of the organic solvent and the amount of the polymerization initiator used were at least. By adjusting one of them, the same operation as in Production Example A-1 was performed except that the weight average molecular weight (Mw) of the (meth) acrylic polymer was changed to the weight average molecular weight (Mw) shown in Table 1. Then, each solution of (meth) acrylic polymer A-2 to A-9 was obtained.

Of the (meth) acrylic polymers A-1 to A-9 obtained above, the (meth) acrylic polymers A-1 to A-6 and A-9 are specified (meth) in the present invention. Corresponds to the acrylic polymer (A).

Table 1 shows the monomer composition (unit: mass%), glass transition temperature (Tg, unit: ° C.), and weight average molecular weight (Mw) of the (meth) acrylic polymers A-1 to A-9.
The glass transition temperature (Tg) of the (meth) acrylic polymer A was calculated by the same method as the glass transition temperature (Tg) of the specific (meth) acrylic polymer (A) described above. The weight average molecular weight (Mw) of the (meth) acrylic polymer A was measured by the same method as the weight average molecular weight (Mw) of the specific (meth) acrylic polymer (A) described above.

Details of each monomer shown in Table 1 are as shown below.
"N-BA": n-butyl acrylate "MA": methyl acrylate "t-BA": t-butyl acrylate "2EHA": 2-ethylhexyl acrylate "MMA": methyl methacrylate "AA": acrylic acid "2HEA": 2-Hydroxyethyl acrylate

In Table 1, "-" means that the monomer in the corresponding column is not used.
In Table 1, "glass transition temperature (Tg)" is simply referred to as "Tg", and "weight average molecular weight (Mw)" is simply referred to as "Mw".

[Manufacturing of (meth) acrylic copolymer B]
[Manufacturing Example B-1]
36 parts by mass of ethyl acetate and 24 parts by mass of butyl acetate were placed in a reactor equipped with a stirrer, a reflux condenser, a sequential dropping device, and a thermometer.
Next, in another container, methyl methacrylate (MMA) [glass transition temperature (Tg) when made into a homopolymer: 103 ° C., specific (meth) acrylic monomer (B2)] 40.0 parts by mass, n. -Butyl methacrylate (n-BMA) [glass transition temperature (Tg) when made into a homopolymer] 20.0 parts by mass, 2-ethylhexyl methacrylate (2-EHMA) [when made into a homopolymer Glass transition temperature (Tg): -10 ° C] 20.0 parts by mass, polymer having an organosiloxane skeleton [trade name: KF-2012, functional group equivalent: 4600 g / mol, Shin-Etsu Chemical Industry Co., Ltd.] 20 A mixed solution containing 0.0 parts by mass, 1.7 parts by mass of 2,2'-azobis (isobutyric acid) dimethyl (polymerization initiator), 24 parts by mass of ethyl acetate, and 16 parts by mass of butyl acetate was prepared.
Then, this solution was sequentially added dropwise to the above reactor under reflux temperature conditions over 180 minutes, and the reaction was carried out for 180 minutes after the completion of the addition.
After completion of the reaction, the reaction mixture was diluted with ethyl acetate to obtain a solution of the (meth) acrylic copolymer B-1 having a solid content of 50% by mass.
The term "solid content" as used herein means a residue obtained by removing volatile components such as a solvent from the solution of the (meth) acrylic copolymer B-1. The same applies to the following (meth) acrylic copolymers B-2 to B-15 solutions.

[Production Examples B-2, B-3, and B-8 to B-11]
In Production Example B-1, by adjusting at least one of the amount of the organic solvent used and the amount of the polymerization initiator used, the weight average molecular weight (Mw) of the (meth) acrylic copolymer is shown in Table 2. The same operation as in Production Example B-1 was performed except that the average molecular weight (Mw) was changed, and each of the (meth) acrylic copolymers B-2, B-3, and B-8 to B-11. A solution was obtained.

[Production Examples B-4 to B-7 and B-12 to B-15]
In Production Example B-1, the monomer composition of the (meth) acrylic copolymer was changed to the monomer composition shown in Table 2, and the amount of the organic solvent used and the amount of the polymerization initiator used were different. Same as Production Example B-1 except that the weight average molecular weight (Mw) of the (meth) acrylic copolymer was changed to the weight average molecular weight (Mw) shown in Table 2 by adjusting at least one of them. The operation was carried out to obtain solutions of (meth) acrylic copolymers B-4 to B-7 and B-12 to B-15.

Of the (meth) acrylic copolymers B-1 to B-15 obtained above, the (meth) acrylic copolymers B-1 to B-7 are the specific (meth) acrylic copolymers in the present invention. Corresponds to the copolymer (B).

Monomer composition (unit: mass%) of (meth) acrylic copolymers B-1 to B-15, functional group equivalent (unit: g / mol) of monomer having an organosiloxane skeleton, and weight average. The molecular weight (Mw) is shown in Table 2.
The functional group equivalent of the monomer having an organosiloxane skeleton was calculated by the same method as that of the monomer (B1) having an organosiloxane skeleton described above. The weight average molecular weight (Mw) of the (meth) acrylic copolymer B was measured by the same method as the weight average molecular weight (Mw) of the specific (meth) acrylic polymer (A) described above.

Details of each monomer shown in Table 2 are as shown below.
"MMA": Methyl methacrylate [Glass transition temperature (Tg) when made into a homopolymer, 103 ° C., specific (meth) acrylic monomer (B2)]
"N-BMA": n-butyl methacrylate [glass transition temperature (Tg) when made into a homopolymer: 21 ° C.]
"I-BMA": i-butyl methacrylate [glass transition temperature (Tg) when made into a homopolymer, 48 ° C., specific (meth) acrylic monomer (B2)]
"2EHMA": 2-ethylhexyl methacrylate [Glass transition temperature (Tg) when made into a homopolymer: -10 ° C]

"KF-2012" [trade name, functional group equivalent: 4,600 g / mol, Shin-Etsu Chemical Industry Co., Ltd.]: Compound having an organosiloxane skeleton (B1), compound represented by the formula (2) "X" -22-174ASX "[trade name, functional group equivalent: 900 g / mol, Shin-Etsu Chemical Industry Co., Ltd.]: Compound having an organosiloxane skeleton (B1), compound represented by the formula (2)" X-22 " -2404 "[trade name, functional group equivalent: 420 g / mol, Shin-Etsu Chemical Industry Co., Ltd.]: Compound having an organosiloxane skeleton (B1), compound represented by the formula (2)" X-22-2426 " [Commercial name, functional group equivalent: 12,000 g / mol, Shin-Etsu Chemical Industry Co., Ltd.]: Compound having an organosiloxane skeleton (B1), compound represented by the formula (2) "X-22-174DX" [Commercial name, functional group equivalent: 4,600 g / mol, Shin-Etsu Chemical Industry Co., Ltd.]: Compound having an organosiloxane skeleton (B1), compound represented by the formula (2).

In Table 2, "-" means that the monomer in the corresponding column is not used.
In Table 2, "glass transition temperature (Tg)" is simply referred to as "Tg", and "weight average molecular weight (Mw)" is simply referred to as "Mw".

[Preparation of adhesive composition]
[Example 1]
100 parts by mass (solid content conversion value) of the solution of the (meth) acrylic polymer A-1, 3.0 parts by mass (solid content conversion value) of the solution of the (meth) acrylic copolymer B-1, and isocyanate. System cross-linking agent [trade name: Coronate (registered trademark) L-45E, adduct of tolylene diisocyanate (TDI) and trimethylolpropane (TMP), solid content: 45% by mass, Toso Co., Ltd.] 3.0% by mass Parts (solid content conversion value) were sufficiently mixed to obtain the pressure-sensitive adhesive composition of Example 1.

[Examples 2 to 14]
In Examples 2 to 14, the same operations as in Example 1 were carried out except that the composition of the pressure-sensitive adhesive composition was changed to the composition shown in Table 3, to obtain a pressure-sensitive adhesive composition.

[Comparative Examples 1 to 12]
In Comparative Examples 1 to 12, the same operations as in Example 1 were carried out except that the composition of the pressure-sensitive adhesive composition was changed to the composition shown in Table 4, to obtain a pressure-sensitive adhesive composition.

[Measurement and evaluation]
1. 1. Measurement of gel fraction of a release film [trade name: Film Vina (registered trademark) 100E-0010N023, Fujimori Kogyo Co., Ltd.] in which the pressure-sensitive adhesive composition prepared above is easily peeled off with a silicone-based release treatment agent. It was applied to the peeled surface so that the thickness after drying was 20 μm, and a coating film was formed. Next, the formed coating film was dried at 100 ° C. for 1 minute using a hot air circulation type dryer to form an adhesive film on the release film.
Next, the exposed surface of the adhesive film was laminated on the peeled surface of a separately prepared release film [trade name: Film Vina (registered trademark) 100E-0010N023, Fujimori Kogyo Co., Ltd.], and then the atmosphere temperature was 35. The cross-linking reaction was allowed to proceed by curing in an environment of ° C. and 45% RH for 4 days to obtain a base-free type pressure-sensitive adhesive sheet having a laminated structure of a release film / adhesive layer / release film.
For the pressure-sensitive adhesive composition of Example 10 containing no cross-linking agent, a pressure-sensitive adhesive sheet was prepared by the same procedure. However, in the pressure-sensitive adhesive composition of Example 10, the crosslinking reaction did not proceed.
Using the pressure-sensitive adhesive layer of the obtained pressure-sensitive adhesive sheet, the gel fraction after cross-linking of the pressure-sensitive adhesive composition was measured by the method described above.
The results are shown in Tables 3 and 4.

2. 2. Adhesive strength (preparation of adhesive sheet for evaluation)
Polyethylene terephthalate (PET) film [trade name: Teijin (registered trademark) Tetron (registered trademark) film, model number: G2P2, thickness: 50 μm, Teijin Film Solution (Teijin Film Solution) Co., Ltd.] was applied to the easy-adhesion-treated surface so that the thickness after drying was 20 μm to form a coating film. Next, the formed coating film was dried at 100 ° C. for 1 minute using a hot air circulation type dryer to form an adhesive film on the PET film.
Next, the peeled surface of the peeling film [trade name: Film Vina (registered trademark) 100E-0010N023, Fujimori Kogyo Co., Ltd.] in which the exposed surface of the adhesive film was easily peeled with a separately prepared silicone-based peeling agent. After being laminated on top of each other, the film was cured in an environment with an atmospheric temperature of 35 ° C. and 45% RH for 4 days to allow the cross-linking reaction to proceed to obtain an evaluation adhesive sheet.
For the pressure-sensitive adhesive composition of Example 10 containing no cross-linking agent, a pressure-sensitive adhesive sheet was prepared by the same procedure. However, in the pressure-sensitive adhesive composition of Example 10, the crosslinking reaction did not proceed.
The prepared pressure-sensitive adhesive sheet for evaluation has a laminated structure of PET film / pressure-sensitive adhesive layer, and the surface of the pressure-sensitive adhesive layer is protected by a release film.

2-1. Adhesive strength against stainless steel The evaluation adhesive sheet produced above was cut into a size of 25 mm × 150 mm, and two evaluation adhesive sheet pieces were prepared.
The release film is peeled off from the two prepared adhesive sheet pieces for evaluation, and the surface of the pressure-sensitive adhesive layer exposed by the peeling is separated into different stainless steel plates [trade name: SUS304 (BA), Paltek Corporation] (hereinafter, Specimens A-1 and A-2 were prepared by laminating and adhering them on the surface of "SUS" as appropriate, and then reciprocating and crimping a 2 kg roller twice.

(1) Initial Adhesive Strength The test piece A-1 was left in an environment with an atmospheric temperature of 23 ° C. and 50% RH for 30 minutes.
With respect to the test piece A-1 after being left to stand, the adhesive force (unit: N / 25 mm) when the evaluation adhesive sheet piece is peeled 180 ° in the long side (150 mm) direction from the SUS is measured by A & D Co., Ltd. The measurement was carried out using a single column type material tester (model number: STA-1225) of And Day under the conditions of an ambient temperature of 23 ° C. and a peeling speed of 300 mm / min in an environment of 50% RH. Then, the initial adhesive strength to SUS was evaluated according to the following evaluation criteria.
The results are shown in Tables 3 and 4.
If the evaluation result is "A" or "B", it is judged that there is no practical problem.

-Evaluation criteria-
A: The adhesive strength is less than 1N / 25 mm.
B: The adhesive strength is 1N / 25 mm or more and less than 3N / 25 mm.
C: Adhesive strength is 3N / 25mm or more.

(2) Adhesive strength after heating The test piece A-2 was left in a dryer set at a temperature of 70 ° C. for 20 minutes, then taken out from the dryer, and placed in an environment with an atmospheric temperature of 23 ° C. and 50% RH for 30 minutes. Left for a minute.
With respect to the test piece A-2 after being left to stand, the adhesive force (unit: N / 25 mm) when the evaluation adhesive sheet piece is peeled 180 ° in the long side (150 mm) direction from the SUS is measured by A & D Co., Ltd. The measurement was carried out using a single column type material tester (model number: STA-1225) of And Day under the conditions of an ambient temperature of 23 ° C. and a peeling speed of 300 mm / min in an environment of 50% RH. Then, the adhesive strength after heating to SUS was evaluated according to the following evaluation criteria.
When zipping (a phenomenon in which minute vibration occurs without smooth peeling) occurs, the average value of the maximum and minimum values of the measured adhesive force was adopted.
The results are shown in Tables 3 and 4.
If the evaluation result is "A" or "B", it is judged that there is no practical problem.

-Evaluation criteria-
A: The adhesive strength is 10 N / 25 mm or more.
B: The adhesive strength is 7 N / 25 mm or more and less than 10 N / 25 mm.
C: Adhesive strength is less than 7N / 25mm.

2-2. Adhesive strength against glass The evaluation adhesive sheet produced above was cut into a size of 25 mm × 150 mm, and two evaluation adhesive sheet pieces were prepared.
The release film is peeled off from the two prepared adhesive sheet pieces for evaluation, and the surface of the adhesive film exposed by the peeling is separated into different glass plates (trade names: FLOAT GLASS, TAIWAN GLASS IND.CORP.) (Hereinafter, as appropriate). After being laminated and bonded on the surface of "glass"), a 2 kg roller was reciprocated twice and crimped to prepare test pieces B-1 and B-2.

(1) Initial Adhesive Strength The test piece B-1 was left in an environment with an atmospheric temperature of 23 ° C. and 50% RH for 30 minutes.
With respect to the test piece B-1 after being left to stand, the adhesive force (unit: N / 25 mm) when the evaluation adhesive sheet piece is peeled 180 ° in the long side (150 mm) direction from the glass is measured by A. Co., Ltd. The measurement was carried out using a single column type material tester (model number: STA-1225) of And Day under the conditions of an ambient temperature of 23 ° C. and a peeling speed of 300 mm / min in an environment of 50% RH. Then, the initial adhesive strength to the glass was evaluated according to the following evaluation criteria.
The results are shown in Tables 3 and 4.
If the evaluation result is "A" or "B", it is judged that there is no practical problem.

-Evaluation criteria-
A: The adhesive strength is less than 1N / 25 mm.
B: The adhesive strength is 1N / 25 mm or more and less than 3N / 25 mm.
C: Adhesive strength is 3N / 25mm or more.

(2) Adhesive strength after heating The test piece B-2 was left in a dryer set at a temperature of 70 ° C. for 20 minutes, then taken out from the dryer, and placed in an environment with an atmospheric temperature of 23 ° C. and 50% RH for 30 minutes. Left for a minute.
With respect to the test piece B-2 after being left to stand, the adhesive force (unit: N / 25 mm) when the evaluation adhesive sheet piece is peeled 180 ° in the long side (150 mm) direction from the glass is measured by A. Co., Ltd. The measurement was carried out using a single column type material tester (model number: STA-1225) of And Day under the conditions of an ambient temperature of 23 ° C. and a peeling speed of 300 mm / min in an environment of 50% RH. Then, the adhesive strength after heating to the glass was evaluated according to the following evaluation criteria.
When zipping (a phenomenon in which minute vibration occurs without smooth peeling) occurs, the average value of the maximum and minimum values of the measured adhesive force was adopted.
The results are shown in Tables 3 and 4.
If the evaluation result is "A" or "B", it is judged that there is no practical problem.

-Evaluation criteria-
A: The adhesive strength is 10 N / 25 mm or more.
B: The adhesive strength is 7 N / 25 mm or more and less than 10 N / 25 mm.
C: Adhesive strength is less than 7N / 25mm.

3. 3. Wrinkles The same operation as in "Preparation of evaluation adhesive sheet" in "2. Adhesive strength" was performed to prepare an evaluation adhesive sheet. Next, the prepared pressure-sensitive adhesive sheet for evaluation was cut into a size of 25 mm × 150 mm, and a piece of the pressure-sensitive adhesive sheet for evaluation was prepared.
The release film was peeled off from the prepared adhesive sheet piece for evaluation, and the surface of the adhesive layer exposed by the peeling was overlapped with the surface of SUS and bonded, and then a 2 kg roller was reciprocated twice to crimp the test piece C. Was produced.
The test piece C was left in a dryer set at a temperature of 70 ° C. for 20 minutes, then taken out from the dryer and left in an environment with an atmospheric temperature of 23 ° C. and 50% RH for 30 minutes. Then, the test piece C after being left was bent by 90 °.
The test piece C after bending was visually observed to confirm the presence and degree of wrinkles. Then, the difficulty of wrinkling was evaluated according to the following evaluation criteria.
The results are shown in Tables 3 and 4.
If the evaluation result is "A" or "B", it is judged that there is no practical problem.

-Evaluation criteria-
A: No wrinkles are confirmed.
B: Wrinkles are slightly confirmed.
C: Wrinkles have been confirmed and are not practically acceptable.

4. Foaming The same operation as in "Preparation of evaluation adhesive sheet" in "2. Adhesive strength" was performed to prepare an evaluation adhesive sheet. Next, the prepared pressure-sensitive adhesive sheet for evaluation was cut into a size of 25 mm × 150 mm, and a piece of the pressure-sensitive adhesive sheet for evaluation was prepared.
The release film was peeled off from the prepared adhesive sheet piece for evaluation, and the surface of the adhesive layer exposed by the peeling was overlapped with the surface of SUS and bonded, and then the 2 kg roller was reciprocated twice to crimp the test piece D. Was produced.
The test piece D was left in a dryer set at a temperature of 70 ° C. for 20 minutes, then taken out from the dryer and left in an environment with an atmospheric temperature of 23 ° C. and 50% RH for 30 minutes.
The test piece D after being left to stand was visually observed to confirm the presence and degree of foaming. Then, the difficulty of generating bubbles was evaluated according to the following evaluation criteria.
The results are shown in Tables 3 and 4.
If the evaluation result is "A" or "B", it is judged that there is no practical problem.

-Evaluation criteria-
A: No foaming is confirmed.
B: Foaming is slightly confirmed.
C: Foaming has been confirmed and is not practically acceptable.

"TETRAD-X" described in the column of the cross-linking agent in Table 3 indicates TETRAD®-X (trade name, solid content: 100% by mass) of Mitsubishi Gas Chemical Company, Inc.
In Tables 3 and 4, "-" means that there is no corresponding item.
In Tables 3 and 4, "wrinkles" are referred to as "wrinkles".

As shown in Table 3, the pressure-sensitive adhesive layers formed by the pressure-sensitive adhesive compositions of Examples 1 to 14 have low adhesive strength and light peelability at the initial stage of bonding, and have high adhesion after heating. It was confirmed to show power.
Further, it was confirmed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive compositions of Examples 1 to 14 is unlikely to cause wrinkles due to bending. From this, it is presumed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive compositions of Examples 1 to 14 is unlikely to cause wrinkles even when used for bonding a display having a curved surface shape and an optical member. ..
Further, it was confirmed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive compositions of Examples 1 to 14 was less likely to generate bubbles.

On the other hand, as shown in Table 4, the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 1 in which the weight average molecular weight of the (meth) acrylic copolymer B is 4,000 has high adhesion after heating. It was confirmed that it did not show any force. Further, it was confirmed that the pressure-sensitive adhesive composition of Comparative Example 1 was likely to generate bubbles.
The pressure-sensitive adhesive composition of Comparative Example 2 in which the weight average molecular weight of the (meth) acrylic copolymer B is 28,400, the pressure-sensitive adhesive composition of Comparative Example 3 in which it is 88,000, and the comparative example in which it is 22,000. It was confirmed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of 12 is likely to cause wrinkles due to bending.
From the results of Comparative Examples 1 to 3, it was found that if the weight average molecular weight of the (meth) acrylic copolymer B is too low, wrinkles due to bending are less likely to occur, but bubbles are likely to occur.

It was confirmed that the pressure-sensitive adhesive composition of Comparative Example 4 in which the weight average molecular weight of the (meth) acrylic copolymer B was 552,000 had high adhesive strength at the initial stage of bonding and did not show light peelability.

It was confirmed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive compositions of Comparative Examples 5 and 6 in which the glass transition temperature of the (meth) acrylic polymer A was 0 ° C. or higher did not show high adhesive strength after heating. rice field.

The content of the constituent units derived from the (meth) acrylic monomer having a glass transition temperature of 40 ° C. or higher when used as a homopolymer is higher than that of all the constituent units of the (meth) acrylic copolymer B. It was confirmed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 7 in an amount of more than 50% by mass did not show high adhesive strength after heating.
The pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 8 containing no structural unit derived from a (meth) acrylic monomer having a glass transition temperature of 40 ° C. or higher when used as a homopolymer is added. It was confirmed that it did not show high adhesive strength after warming.
The content of the constituent units derived from the (meth) acrylic monomer having a glass transition temperature of 40 ° C. or higher when used as a homopolymer is higher than that of all the constituent units of the (meth) acrylic copolymer B. It was confirmed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 9 in an amount of less than 30% by mass did not show high adhesive strength after heating.

The pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 10 in which the content of the (meth) acrylic copolymer B exceeds 100 parts by mass with respect to 100 parts by mass of the (meth) acrylic-based polymer A is added. It was confirmed that it did not show high adhesive strength after warming.

It was confirmed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 11 containing no (meth) acrylic copolymer B had high adhesive strength at the initial stage of bonding and did not show light peelability.

Claims (5)

The (meth) acrylic polymer (A) having a glass transition temperature of less than 0 ° C.
A (meth) acrylic copolymer (B) having a weight average molecular weight in the range of 100,000 or more and less than 400,000 is included.
The (meth) acrylic copolymer (B) has a structural unit derived from the monomer (B1) having an organosiloxane skeleton and a glass transition temperature of 40 ° C. or higher when used as a homopolymer (meth). ) The functional group equivalent of the monomer (B1) containing the acrylic monomer (B2) and having the organosiloxane skeleton is in the range of 400 g / mol or more and 15,000 g / mol or less. The content of the structural unit derived from the (meth) acrylic monomer (B2) is in the range of 30% by mass or more and 50% by mass or less with respect to all the structural units.
The content of the (meth) acrylic copolymer (B) is in the range of 0.1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic polymer (A). Agent composition. Claimed that the monomer (B1) having an organosiloxane skeleton is at least one compound selected from the group consisting of a compound represented by the following formula (1) and a compound represented by the formula (2) below. The pressure-sensitive adhesive composition according to 1.

In formulas (1) and (2), R ¹ represents a hydrogen atom or a methyl group, R ² represents a monovalent organic group, and m and n each independently represent an integer of 0 or more. ..
The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the gel fraction after crosslinking is 40% by mass or more. The content of the structural unit derived from the monomer (B1) having the organosiloxane skeleton in the (meth) acrylic copolymer (B) is 10% by mass or more and 20% by mass or less with respect to all the structural units. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, which is in the range of 1. A pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition according to any one of claims 1 to 4.