KR102494129B1 - Adhesive composition and adhesive sheet - Google Patents

Abstract

Structural unit (A) derived from an alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms is 40% by mass or more with respect to all structural units, and structural unit (B) derived from a monomer having a hydroxyl group is used as all structural units. A pressure-sensitive adhesive composition containing a (meth)acrylic polymer and a styrenic polymer in an amount of 5% by mass or more and 15% by mass or less, and applications thereof.

Description

Adhesive composition and adhesive sheet {ADHESIVE COMPOSITION AND ADHESIVE SHEET}

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

BACKGROUND OF THE INVENTION Touch sensors are used for input devices of electronic devices such as mobile phones and portable information terminals. A touch sensor is generally composed of a plurality of members such as a glass substrate, a transparent conductive film, and a decorative film. These members are laminated via an adhesive layer formed of an adhesive composition. In addition, in a device equipped with a touch panel, a liquid crystal display (LCD) and a touch sensor are laminated through an adhesive layer formed of an adhesive composition.

Attempts have been made to impart various performances to the pressure-sensitive adhesive composition used in touch panels (hereinafter, also referred to as "adhesive composition for touch panels").

For example, with the recent slimming of touch panels, slimming is also required for the pressure-sensitive adhesive layer. However, when trying to slim the pressure-sensitive adhesive layer, malfunction may occur because the capacitance inside the touch panel increases. Therefore, a pressure-sensitive adhesive layer having a low dielectric constant is required so that the capacitance does not increase even when the pressure-sensitive adhesive layer is slimmed down.

In response to this demand, for example, Japanese Unexamined Patent Publication No. 2013-194170 discloses an alkyl (meth)acrylate having a branched chain alkyl group at an ester terminal and an ester having a linear alkyl group as a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having a low dielectric constant. Disclosed is a pressure-sensitive adhesive composition comprising a (meth)acrylic polymer obtained by polymerizing an alkyl (meth)acrylate having a terminal at a predetermined ratio.

Moreover, the property (it is also called "heat-and-moisture whitening resistance" hereafter) which is hard to whiten under a high-temperature, high-humidity environment (henceforth a "moist heat environment") is also calculated|required by the adhesive composition for touch panels. Whitening of the pressure-sensitive adhesive layer in a moist heat environment occurs when the pressure-sensitive adhesive layer contains moisture.

In response to this request, for example, Japanese Patent Publication No. 2012-504512 discloses a pressure-sensitive adhesive composition containing a large amount of a hydroxyl group-containing monomer capable of forming a pressure-sensitive adhesive layer having heat-and-moisture whitening resistance.

However, in recent years, malfunction due to noise generated from a liquid crystal display (LCD) or the like has become a problem in a device equipped with a touch panel. For this reason, the adhesive composition for touch panels to which a liquid crystal display (LCD) and a touch sensor are bonded has a relative permittivity lower than before, specifically a relative permittivity of less than 3.5, preferably difficult performance such as formation of an adhesive layer of 3.0 or less is required.

It is considered that the dielectric constant of the pressure-sensitive adhesive layer can be lowered to some extent by, for example, adjusting the composition of the (meth)acrylic polymer contained in the pressure-sensitive adhesive composition.

However, in the pressure-sensitive adhesive composition capable of forming an adhesive layer having a low dielectric constant in order to achieve both low dielectric constant and moisture-heat whitening resistance, Japanese Patent Publication No. 2012-504512 discloses in anticipation of the effect of suppressing moist-heat whitening As described above, when a large amount of the hydroxyl group-containing monomer is blended, the dielectric constant increases. In addition, the dielectric constant of the pressure-sensitive adhesive layer is increased even when an additive generally used for suppression of wet-heat whitening, specifically a (meth)acrylic additive is used.

In this way, it was difficult to impart excellent heat-and-moisture whitening resistance while maintaining the strict performance of relative permittivity of less than 3.5.

This invention was made|formed in view of the above circumstances, and makes it a subject to achieve the following objective.

That is, an object of the present invention is to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having a low dielectric constant and excellent heat-and-moisture whitening resistance.

Another object of the present invention is to provide a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a low dielectric constant and excellent heat-and-moisture whitening resistance.

Specific means for solving the problems include the following aspects.

<1> Structural unit (A) derived from an alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms is 40% by mass or more with respect to the total structural units and structural unit (B) derived from a monomer having a hydroxyl group A pressure-sensitive adhesive composition containing a (meth)acrylic polymer and a styrenic polymer in an amount of 5% by mass or more and 15% by mass or less based on the total constituent units.

<2> The adhesive composition according to <1>, wherein the content of the structural unit (A) in the (meth)acrylic polymer is 60% by mass or more with respect to all structural units of the (meth)acrylic polymer.

<3> The adhesive composition according to <1> or <2>, wherein the monomer having a hydroxyl group in the structural unit (B) is a hydroxyalkyl methacrylate.

<4> The pressure-sensitive adhesive composition according to any one of <1> to <3>, wherein the (meth)acrylic polymer has a glass transition temperature of -55°C or more and -15°C or less.

<5> The adhesive composition according to any one of <1> to <4>, wherein the weight average molecular weight of the styrenic polymer is 1,000 or less.

<6> The adhesive composition according to any one of <1> to <5>, wherein the content of the styrenic polymer is 0.01 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the (meth)acrylic polymer.

The adhesive composition in any one of <1>-<6> used in order to bond a <7> liquid crystal display and a touch sensor together.

<8> A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a crosslinked structure formed by a crosslinking reaction of the pressure-sensitive adhesive composition according to any one of <1> to <7>.

According to the present invention, a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having a low relative permittivity and excellent heat-and-moisture whitening resistance is provided.

Further, according to the present invention, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a low dielectric constant and excellent heat-and-moisture whitening resistance is provided.

Hereinafter, specific embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments at all, and can be implemented with appropriate changes within the scope of the object of the present invention.

In this specification, the numerical range indicated by using "~" means a range including the numerical values described before and after "~" as the minimum and maximum values, respectively.

In the present specification, the amount of each component in the composition refers to the total amount of a plurality of substances present in the composition, unless otherwise specified, when a plurality of substances corresponding to each component are present in the composition.

In this specification, "(meth)acrylate" is a term that includes both acrylate and methacrylate, and "(meth)acryl" is a term that includes both acryl and methacryl.

In the present specification, "(meth)acrylic polymer" is a homopolymer or copolymer having a weight average molecular weight (Mw) of 200,000 or more, and 50% by mass or more of all constituent units constituting the polymer, preferably 90% by mass or more ( meth) means a polymer that is a structural unit derived from an acrylic monomer.

In the present specification, "styrenic polymer" is a homopolymer or copolymer having a weight average molecular weight (Mw) of 300 or more and 5000 or less, and 50% by mass or more of the total constituent units constituting the polymer, preferably 90% by mass or more, is styrenic. It means a polymer which is a structural unit derived from a monomer.

In this specification, "monomer" and "monomer" have the same meaning.

[Adhesive composition]

The pressure-sensitive adhesive composition of the present invention contains a structural unit (A) derived from an alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms (hereinafter, also referred to as "structural unit (A)") in an amount of 40 mass based on all structural units. % or more and a (meth)acrylic polymer containing 5% by mass or more and 15% by mass or less of the structural unit (B) “hereinafter also referred to as the structural unit (B)”) derived from a monomer having a hydroxyl group (hereinafter referred to as “structural unit (B)”) , also referred to as "specific (meth)acrylic polymer") and a styrene polymer.

The performance which can form the adhesive layer which has both a low dielectric constant and excellent heat-and-moisture whitening resistance is requested|required of the adhesive composition used for a touch panel.

It is considered that the dielectric constant of the pressure-sensitive adhesive layer can be lowered to some extent by, for example, adjusting the composition of the acrylic polymer contained in the pressure-sensitive adhesive composition.

However, in the pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having a low dielectric constant in order to achieve both low dielectric constant and excellent damp-heat whitening resistance, a large amount of hydroxyl group-containing monomer is blended in anticipation of damp-heat whitening inhibitory effect, or wet-heat whitening The use of additives generally used for suppression, specifically (meth)acrylic additives, increases the dielectric constant.

In contrast, the pressure-sensitive adhesive composition of the present invention contains 40% by mass or more of the structural unit (A) derived from an alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms and a monomer having a hydroxyl group with respect to the total structural units. By containing a (meth)acrylic polymer and a styrenic polymer containing 5% by mass or more and 15% by mass or less of the structural unit (B) with respect to the total structural units, the relative dielectric constant is less than 3.5, preferably 3.0 or less, and has heat-and-moisture whitening resistance. This excellent adhesive layer can be formed.

Although it is not clear why the pressure-sensitive adhesive composition of the present invention can exhibit such an effect, the present inventors speculate as follows.

Alkyl methacrylates used in the production of specific (meth)acrylic polymers have a large molar volume and a small dipole moment because the alkyl group has a large number of carbon atoms of 5 or more and a branched structure. Therefore, a (meth)acrylic polymer having a large molar volume and a small dipole moment can be produced.

In addition, since the alkyl methacrylate used in the production of a specific (meth)acrylic polymer has 9 or less carbon atoms in its alkyl group, a (meth)acrylic polymer having a small volumetric shrinkage and a large molar volume can be produced.

The pressure-sensitive adhesive composition of the present invention is considered to be able to form a pressure-sensitive adhesive layer having a low dielectric constant of less than 3.5, preferably 3.0 or less, by containing a (meth)acrylic polymer having a large molar volume and a small dipole moment.

However, whitening of the pressure-sensitive adhesive layer occurs due to inflow of moisture into the pressure-sensitive adhesive layer under a moist heat environment. Moisture causing whitening flows in from the end of the pressure-sensitive adhesive layer or between the pressure-sensitive adhesive layer and the adherend.

Styrenic polymers exhibit hydrophobicity. The inventors of the present invention believe that when a pressure-sensitive adhesive layer is formed using a pressure-sensitive adhesive composition containing a styrenic polymer, ingress of moisture into the pressure-sensitive adhesive layer can be suppressed because the styrenic polymer exists locally near the interface of the pressure-sensitive adhesive layer in a moist heat environment. That is, it is thought that the adhesive composition of this invention is excellent in moist heat whitening resistance when it is set as an adhesive layer by containing the styrenic polymer which shows hydrophobicity.

In general, it is difficult for acrylic polymers and styrenic polymers to be compatible. Therefore, the adhesive layer formed using the adhesive composition containing these polymers tends to whiten. In addition, even if the acrylic polymer and the styrenic polymer are compatible, the pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition containing these polymers tends to whiten, and it is considered that the pressure-sensitive adhesive layer tends to whiten particularly under a moist heat environment where moisture easily flows into the pressure-sensitive adhesive layer. . In the present invention, the compatibility problem is solved by combining a styrenic polymer with a specific (meth)acrylic polymer, and formation of a pressure-sensitive adhesive layer that is difficult to whiten not only at room temperature but also under a more severe moist heat environment is realized.

Moreover, since the adhesive composition of this invention contains a hydrophobic styrenic polymer, formation of the adhesive layer with a low dielectric constant is also attained. Since hydrophobic styrenic polymers have low polarity and a small dipole moment, it is thought that they also contribute to a decrease in dielectric constant.

Further, in the present invention, since the (meth)acrylic polymer contains a structural unit derived from a monomer having a hydroxyl group, the pressure-sensitive adhesive layer and moisture are compatible even when moisture flows from between the pressure-sensitive adhesive layer and the adherend under a moist heat environment. It is thought that whitening of an adhesive layer can be suppressed by doing it.

Since each component contained in the pressure-sensitive adhesive composition of the present invention has excellent compatibility, the HAZE of the pressure-sensitive adhesive layer formed is low and it is difficult to damage the transparency of the display unit of the device equipped with a touch panel.

Further, according to the pressure-sensitive adhesive composition of the present invention, a pressure-sensitive adhesive layer having strong adhesive strength can be formed.

In a portable electronic device, there is a possibility that a member may be peeled off by receiving an impact such as falling. According to the pressure-sensitive adhesive composition of the present invention, since a pressure-sensitive adhesive layer having strong adhesive strength can be formed, peeling of members due to impact can be prevented.

By the way, in the manufacturing process of a touch panel, when laminating the members constituting the touch sensor (hereinafter, also referred to as "touch sensor constituent members"), bonding of each member involves an adhesive sheet cut with a cutting blade according to the size of each member (i.e., , a sheet having an adhesive layer) is often used. When the pressure-sensitive adhesive sheet is cut, if the pressure-sensitive adhesive layer adheres to the cutting blade, the pressure-sensitive adhesive layer is deformed and the pressure-sensitive adhesive layer is pushed out of the touch sensor constituent member in some cases. For this reason, the PSA layer is required to have a property (hereinafter also referred to as "workability") that the PSA sheet can be easily processed without adhering to the cutting blade when the PSA sheet is cut.

Since the pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer having excellent processability, it is difficult to cause a problem that the pressure-sensitive adhesive layer adheres to the cutting blade and is pushed out of the touch sensor component when cutting the pressure-sensitive adhesive sheet.

Furthermore, according to the pressure-sensitive adhesive composition of the present invention, it is possible to form a pressure-sensitive adhesive layer that is resistant to bubbles and has excellent durability even with the passage of time under a moist heat environment.

[Specific (meth)acrylic polymer]

The specific (meth)acrylic polymer contains 40% by mass or more of structural unit (A) derived from an alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms and a structural unit derived from a monomer having a hydroxyl group relative to the total structural units. (B) is 5 mass % or more and 15 mass % or less with respect to all structural units.

That is, the specific (meth)acrylic polymer is a polymer obtained by copolymerizing an alkyl methacrylate having at least a branched chain alkyl group having 5 to 9 carbon atoms with a monomer having a hydroxyl group.

Hereinafter, each structural unit in a specific (meth)acrylic polymer is described.

<Component unit (A)>

The structural unit (A) is derived from an alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms.

When the number of carbon atoms in the branched chain alkyl group of the alkyl methacrylate is 5 or more, the molar volume of the alkyl methacrylate is large and the dipole moment is small, resulting in a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having a low dielectric constant.

When the number of carbon atoms in the branched chain alkyl group of the alkyl methacrylate is 9 or less, the volumetric shrinkage ratio when the alkyl methacrylate is used as a polymer is small and the molar volume of the (meth)acrylic polymer is large, so that the dielectric constant is less than 3.5, preferably 3.0 or less. tends to decrease to In addition, since polymerizability of alkyl methacrylate deteriorates as the number of carbon atoms in the branched chain alkyl group increases, it becomes difficult to obtain a polymer having a high molecular weight. That is, when the number of carbon atoms in the branched chain alkyl group of the constituent unit (A) is 9 or less, a polymer having a high molecular weight can be obtained. Furthermore, when the number of carbon atoms in the branched chain alkyl group of the alkyl methacrylate is 9 or less, the pressure-sensitive adhesive composition has high cohesive force and excellent processability and durability when used as an adhesive layer.

Further, from the viewpoint of dielectric constant and workability, the number of carbon atoms of the branched chain alkyl group of the alkyl methacrylate is preferably 7 to 9.

As the alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms, 2-ethylhexyl methacrylate, isopentyl methacrylate, isohexyl methacrylate, isoheptyl methacrylate, isooctyl methacrylate, isononyl A methacrylate etc. are mentioned.

Among these, as an alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms, 2-ethylhexyl methacrylate is preferable from the viewpoint of dielectric constant.

Alkyl methacrylates having a branched chain alkyl group having 5 to 9 carbon atoms may be used alone or in combination of two or more.

The content rate of the structural unit (A) in the specific (meth)acrylic polymer is 40% by mass or more with respect to all structural units of the specific (meth)acrylic polymer.

When the content rate of the structural unit (A) is 40% by mass or more with respect to all the structural units of the specific (meth)acrylic polymer, the pressure-sensitive adhesive composition can form a pressure-sensitive adhesive layer having a low dielectric constant.

In addition, the content rate of the structural unit (A) in the specific (meth)acrylic polymer is preferably 50% by mass or more, and preferably 60% by mass, based on the total structural units of the specific (meth)acrylic polymer from the viewpoint of dielectric constant, processability and adhesiveness. % or more is more preferable.

Furthermore, the content rate of the structural unit (A) in the specific (meth)acrylic polymer is preferably 90% by mass or less, and more preferably 85% by mass or less, with respect to all the structural units of the specific (meth)acrylic polymer from the viewpoint of heat-and-moisture whitening resistance. do.

<Component unit (B)>

The constituent unit (B) is derived from a monomer having a hydroxyl group.

Since the specific (meth)acrylic polymer contains the structural unit (B) and can react with a crosslinking agent described later, the pressure-sensitive adhesive composition of the present invention has high cohesion and excellent processability and durability when used as a pressure-sensitive adhesive layer.

As a monomer which has a hydroxyl group, the monomer which has a hydroxyl group and an ethylenically unsaturated bond group is mentioned, for example.

As a monomer having a hydroxyl group, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 3 -Methyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, glycerin mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, poly(ethylene glycol-propylene glycol) Mono(meth)acrylate, N-methylol(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, allyl alcohol, methallyl alcohol, etc. are mentioned.

As a monomer which has a hydroxyl group, hydroxyalkyl (meth)acrylate is preferable, and hydroxyalkyl methacrylate is more preferable.

In addition, as the hydroxyalkyl methacrylate, the compatibility and copolymerizability with the alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms and the crosslinking reaction with the crosslinking agent are good, so that a carbon number of 1 to 5 Hydroxyalkyl methacrylates having a hydroxyalkyl group are preferred, hydroxyalkyl methacrylates having a hydroxyalkyl group having 2 to 4 carbon atoms are more preferred, and 2-hydroxy having a hydroxyethyl group having 2 carbon atoms. Ethyl methacrylate is more preferred.

In addition, a (meth)acrylic polymer having good compatibility and copolymerizability exhibits good transparency with a total light transmittance of 85% or more.

The monomer which has a hydroxyl group may be used individually by 1 type, and may use 2 or more types together.

The content rate of the structural unit (B) in the specific (meth)acrylic polymer is 5% by mass or more and 15% by mass or less with respect to all structural units of the specific (meth)acrylic polymer.

When the content of the structural unit (B) is 5% by mass or more with respect to all the structural units of the specific (meth)acrylic polymer, compatibility between the adhesive layer and water increases, so that the adhesive layer is less likely to whiten. Therefore, it becomes the adhesive composition which can form the adhesive layer excellent in heat-and-moisture whitening resistance. In addition, when the content of the structural unit (B) is 5% by mass or more with respect to all the structural units of the specific (meth)acrylic polymer, it can sufficiently react with the crosslinking agent described later, so that the adhesive composition has high cohesive force and excellent processability when used as an adhesive layer. becomes Furthermore, when the content of the structural unit (B) is 5% by mass or more with respect to all the structural units of the specific (meth)acrylic polymer, the pressure-sensitive adhesive composition is less likely to generate bubbles even in a moist heat environment and has excellent durability.

If the content rate of the structural unit (B) is 15% by mass or less with respect to all the structural units of the specific (meth)acrylic polymer, it becomes an adhesive composition capable of forming an adhesive layer with a low dielectric constant.

The content rate of the structural unit (B) in the specific (meth)acrylic polymer is preferably 10% by mass or less with respect to all structural units of the specific (meth)acrylic polymer from the viewpoint of the dielectric constant.

In the specific (meth)acrylic polymer, the content of the structural unit (A) is 40% by mass or more with respect to all the structural units, and the ratio of the content of the structural unit (B) to the content of the structural unit (A) (the structural unit (B) It is preferable that the content rate/content rate of structural unit (A) of) is 1/2.5 to 1/8.5 in terms of mass ratio.

When the ratio of the content of the structural unit (B) to the content of the structural unit (A) is within the above range in terms of mass ratio, a pressure-sensitive adhesive layer having a better balance of dielectric constant, moisture-heat whitening resistance, adhesive strength, processability and durability can be formed. It becomes an adhesive composition.

<Other constituent units>

-Component unit (C)-

In addition to the structural units (A) and (B), the specific (meth)acrylic polymer may further contain a structural unit derived from an alkyl acrylate (hereinafter, also referred to as "structural unit (C)").

The specific (meth)acrylic polymer further includes a structural unit (C) in addition to the structural units (A) and (B), thereby resulting in a pressure-sensitive adhesive composition having higher cohesive force and superior processability and durability when used as a pressure-sensitive adhesive layer.

As the alkyl acrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, n-nonyl acrylate, isononyl acrylate rate, n-decyl acrylate, lauryl acrylate, stearyl acrylate and the like.

Among these, 2-ethylhexyl acrylate is preferable from the viewpoint of dielectric constant and heat-and-moisture whitening resistance.

When a specific (meth)acrylic-type polymer contains structural unit (C), alkyl acrylate may be used individually by 1 type, and may use 2 or more types together.

As the structural unit (C), a structural unit derived from an alkyl acrylate having a branched chain alkyl group having 5 to 9 carbon atoms is preferable from the viewpoint of dielectric constant and heat-and-moisture whitening resistance.

A pressure-sensitive adhesive capable of forming a pressure-sensitive adhesive layer having a lower dielectric constant and better heat-and-moisture whitening resistance by further including a structural unit derived from an alkyl acrylate having a branched chain alkyl group having a specific (meth)acrylic polymer having 5 to 9 carbon atoms. Although the reason for the composition is not clear, it is estimated as follows.

Since alkyl acrylates having an alkyl group having 5 to 9 carbon atoms have a lower glass transition temperature when used as a homopolymer than alkyl methacrylates having an alkyl group having 5 to 9 carbon atoms, it is used when producing (meth)acrylic polymers. By replacing a part of the alkyl methacrylate with an alkyl acrylate, the glass transition temperature of the (meth)acrylic polymer can be lowered and the wettability of the pressure-sensitive adhesive composition can be improved. Therefore, when a pressure-sensitive adhesive layer is formed with such an adhesive composition and, for example, the touch sensor constituent members are bonded together, the adhesion between the touch sensor constituent member and the pressure-sensitive adhesive layer is improved, and moisture penetration is prevented from the interface between the touch sensor constituent member and the pressure-sensitive adhesive layer. thought to be suppressed. Furthermore, since the alkyl group of the alkyl acrylate has 5 or more carbon atoms and is highly hydrophobic, it is thought that penetration of moisture into the pressure-sensitive adhesive layer from other than the interface between the touch sensor constituent member and the pressure-sensitive adhesive layer is suppressed. Since whitening of the adhesive layer by water|moisture content is suppressed by combining these, it is thought that heat-and-moisture whitening resistance improves more.

In addition, when the alkyl group of the alkyl acrylate is a branched chain alkyl group, the molar volume becomes larger than that of an alkyl acrylate having a straight chain alkyl group having the same number of carbon atoms. Therefore, it is thought that the dielectric constant of the adhesive layer becomes lower.

When the specific (meth)acrylic polymer contains the structural unit (C), the content of the structural unit (C) is 5% by mass or more with respect to all the structural units of the specific (meth)acrylic polymer from the viewpoint of dielectric constant and heat-and-moisture whitening resistance. This is preferable, and 10 mass % or more is more preferable.

The content of the structural unit (C) is preferably 50% by mass or less, and more preferably 25% by mass or less, with respect to all the structural units of the specific (meth)acrylic polymer, from the viewpoint of balance between the relative permittivity and heat-and-moisture whitening resistance.

It is preferable that the content of the specific (meth)acrylic polymer is 10% by mass or more of the structural unit (C) with respect to all the structural units, and the content of the structural unit (B) is 10% by mass or more with respect to all the structural units.

When the specific (meth)acrylic polymer contains 10% by mass or more of the structural unit (B) and the structural unit (C), respectively, when the pressure-sensitive adhesive layer is formed, moisture permeation into the pressure-sensitive adhesive layer is suppressed and compatibility with moisture of the pressure-sensitive adhesive layer Since this becomes high, heat-and-moisture whitening resistance can be further improved.

-Other constituent units-

A specific (meth)acrylic polymer may contain other structural units than the aforementioned structural units as needed.

Examples of other structural units include structural units derived from a monomer having a cyclic group, structural units derived from a monomer having an acidic group, and the like.

Examples of the cyclic group in the monomer having a cyclic group include an aromatic hydrocarbon group, an aromatic heterocyclic group, and a cyclic aliphatic hydrocarbon group.

Examples of the monomer having a cyclic group include (meth)acrylate having a cyclic group, (meth)acrylamide having a cyclic group, and styrene derivatives, and (meth)acrylate having a cyclic group is preferable.

When the specific (meth)acrylic polymer contains a structural unit derived from a monomer having a cyclic group, the content of this structural unit is 5% by mass with respect to all structural units of the specific (meth)acrylic polymer from the viewpoint of heat-and-moisture whitening resistance and adhesive strength. The following is preferable, and 3 mass % or less is more preferable.

In the monomer having an acidic group, examples of the acidic group include a carboxyl group, a sulfonic acid group, and a phosphoric acid group. Among these, the acidic group in the monomer having an acidic group is preferably a carboxyl group from the viewpoint of controlling the reaction rate between the (meth)acrylic copolymer and the crosslinking agent.

Examples of the monomer having a carboxy group include unsaturated carboxylic acids such as (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and cinnamic acid; carboxyethyl acrylate (eg β-carboxyethyl acrylate); and unsaturated dicarboxylic acid anhydrides such as alkyl acrylate, acrylic acid dimer, acrylic acid trimer, itaconic acid anhydride, maleic acid anhydride, and fumaric anhydride.

When the specific (meth)acrylic polymer contains a structural unit derived from a monomer having an acidic group, the content of this structural unit is preferably 0.5% by mass or less with respect to all structural units of the specific (meth)acrylic polymer.

Since corrosion of a metal can be suppressed when an adhesive layer contacts metal, such as a transparent electrode of a touchscreen, when the content rate of the structural unit derived from the monomer which has an acidic group is 0.5 mass % or less, for example, adhesive for touch panel use It can be used more suitably as a composition.

The content of structural units derived from monomers having an acidic group is more preferably 0.2% by mass or less based on all structural units of the specific (meth)acrylic polymer, and it is particularly preferred from the viewpoint of suppressing metal corrosion that they are not included.

<Physical properties of specific (meth)acrylic polymer>

The glass transition temperature (Tg) of a specific (meth)acrylic polymer is not particularly limited, preferably -55°C or more -15°C or less, more preferably -40°C or more -15°C or less, -35°C or more -18°C C or less is more preferable.

When the glass transition temperature (Tg) of the specific (meth)acrylic polymer is within the above range, the cohesive force is higher when used as a pressure-sensitive adhesive layer, the workability and durability of the pressure-sensitive adhesive layer are excellent, and the adhesive strength when used as a pressure-sensitive adhesive layer is higher.

In the present specification, the glass transition temperature (Tg) of a specific (meth)acrylic polymer is a molar average glass transition temperature determined by the following calculation.

Tg ₁ , Tg ₂ , . . . in the following formula. … and Tg _n is monomer 1, monomer 2, . . . … and monomer n as the glass transition temperature (Tg) of each homopolymer, which is calculated in terms of absolute temperature (K). m ₁ , m ₂ , . . . … and m _n is the mole fraction of each monomer.

In addition, although absolute temperature (K) is used for calculation of glass transition temperature (Tg), when describing glass transition temperature (Tg) in this specification, there are cases in which Celsius temperature (° C.) is used.

The "glass transition temperature (Tg) of a homopolymer" as used herein is measured by measuring the homopolymer of the monomer using a differential scanning calorimetry (DSC) (product name: EXSTAR6000, manufactured by Seiko Instruments Co., Ltd.) in a nitrogen stream at a temperature rise rate of 10 mmg. The inflection point of the DSC curve obtained by measuring under conditions of 10° C./min was taken as the glass transition temperature (Tg) of the homopolymer.

The "glass transition temperature (Tg) of a homopolymer" of representative monomers is 2-ethylhexyl methacrylate: -10°C, 2-ethylhexyl acrylate: -76°C, isobutyl methacrylate: 48°C, normal butyl methacrylate. Acrylate: 21°C, lauryl methacrylate: -65°C, 2-hydroxyethyl acrylate: -15°C, 2-hydroxyethyl methacrylate: 55°C, isodecyl methacrylate: -41°C, Cyclohexyl methacrylate: 56°C, etc.

The weight average molecular weight (Mw) of the specific (meth)acrylic polymer is not particularly limited, and is, for example, 20 10,000 or more and 1 million or less are preferable, 300,000 or more and 800,000 or less are more preferable, and 400,000 or more and 600,000 or less are still more preferable.

The degree of dispersion (Mw/Mn), which is the ratio between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of a specific (meth)acrylic polymer, is preferably 20 or less, and more preferably 3 or more and 15 or less, from the viewpoint of step followability, 4.5 or more and 8 or less are more preferable.

The weight average molecular weight (Mw) and number average molecular weight (Mn) of a specific (meth)acrylic polymer are values measured according to the following (1) to (3) using gel permeation chromatography (GPC).

(1) A solution of a specific (meth)acrylic polymer is applied to release paper and dried at 100°C for 2 minutes to obtain a film-like (meth)acrylic polymer.

(2) The film-like (meth)acrylic polymer obtained in (1) above was dissolved in tetrahydrofuran to a solid content of 0.2% by mass.

(3) Using gel permeation chromatography (GPC), the weight average molecular weight (Mw) and number average molecular weight (Mn) of the (meth)acrylic polymer are measured as standard polystyrene equivalent values under the following conditions.

(condition)

GPC: HLC-8220 GPC (product of Tosoh Co., Ltd.)

Column: TSK-GEL GMHXL 4 pieces used (Toso Co., Ltd. product)

Mobile phase solvent: tetrahydrofuran

Flow rate: 0.6mL/min

Column temperature: 40°C

<Method for producing specific (meth)acrylic polymer>

The manufacturing method of a specific (meth)acrylic polymer is not specifically limited. A specific (meth)acrylic polymer can be produced by polymerizing the above-mentioned monomers, that is, an alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms, a monomer having a hydroxyl group, and other monomers as necessary.

The polymerization method of a specific (meth)acrylic polymer is not particularly limited, and can be appropriately selected from commonly used polymerization methods. Examples of polymerization methods include solution polymerization, emulsion polymerization, and suspension polymerization. Among these, as the polymerization method, the solution polymerization method is preferable from the viewpoint of relatively simple production.

In the solution polymerization method, a predetermined organic solvent, a monomer, a polymerization initiator and, if necessary, a chain transfer agent are generally put into a polymerization tank, and heated and reacted for several hours while stirring at the reflux temperature of the organic solvent in a nitrogen stream. In this case, at least a part of the organic solvent, the monomer, the polymerization initiator and/or the chain transfer agent may be sequentially added.

Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbons such as benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha. Fatty or alicyclic hydrocarbons such as n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and turpentine oil, ethyl acetate, n-butyl acetate, Esters such as n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, methyl benzoate, acetone, methyl ethyl ketone, methyl-i-butyl ketone, isophorone, cyclo Ketones such as hexanone and methylcyclohexanone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, etc. alcohols such as glycol ethers, methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t-butyl alcohol.

When preparing a specific (meth)acrylic polymer, it is preferable to use an organic solvent that does not easily cause chain transfer during polymerization such as esters and ketones. From the standpoint of the solubility of the specific (meth)acrylic polymer and the ease of polymerization, the organic solvent is preferably at least one selected from the group consisting of ethyl acetate and methyl ethyl ketone, more preferably ethyl acetate.

An organic solvent may be used individually by 1 type, and may use 2 or more types together.

As the polymerization initiator, organic peroxides and azo compounds used in conventional solution polymerization methods can be used.

As the organic peroxide, t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propylperoxy dicarbonate, di-2-ethylhexyl peroxy Dicarbonate, t-butylperoxypivalate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)butane, 2,2-bis(4,4-di-t-octylperoxy cyclohexyl)butane.

Examples of the azo compound include 2,2'-azobis-i-butyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, and 2,2'-azobis-4-methoxy-2,4 -Dimethylvaleronitrile, 1,1'-azobis-cyclohexane-1-carbonitrile, 2,2'-azobis (methyl isobutyrate), etc. are mentioned.

When producing a specific (meth)acrylic polymer, it is preferable to use a polymerization initiator that does not cause a graft reaction during polymerization, and from this point of view, an azo compound is preferable.

The usage amount of the polymerization initiator is preferably 0.01 part by mass or more and 2 parts by mass or less, more preferably 0.1 part by mass or more and 1 part by mass or less, based on 100 parts by mass of the total amount of the monomers constituting the specific (meth)acrylic polymer.

The polymerization temperature in the case of producing a specific (meth)acrylic polymer is preferably 60°C to 100°C, more preferably 70°C to 95°C, and still more preferably 80°C to 95°C.

In addition, the weight average molecular weight (Mw) and number average molecular weight (Mn) and dispersion degree (Mw/Mn) of the specific (meth)acrylic polymer are the polymerization temperature, time, amount of solvent, type and amount of catalyst, and type and amount of polymerization initiator. can be easily adjusted accordingly.

[Styrenic polymer]

The pressure-sensitive adhesive composition of the present invention contains a styrenic polymer.

The pressure-sensitive adhesive composition of the present invention may contain a styrenic polymer alone, or may contain two or more kinds having different monomeric compositions, weight average molecular weights, and the like.

Styrenic polymers exhibit hydrophobicity. As described above, when the present inventors form a pressure-sensitive adhesive layer using a pressure-sensitive adhesive composition containing a styrenic polymer, the inflow of moisture into the pressure-sensitive adhesive layer can be suppressed because the styrenic polymer locally exists near the interface of the pressure-sensitive adhesive layer in a moist heat environment. I think there is. That is, it is thought that the adhesive composition of this invention is excellent in moist heat whitening resistance when it is set as an adhesive layer by containing the styrenic polymer which shows hydrophobicity.

Styrene-based monomers capable of constituting the styrenic polymer include styrene and alkyl styrene (methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, diethyl styrene, triethyl styrene, propyl styrene, butyl styrene, hexyl styrene, octyl styrene, etc.) and monomers having a styrene skeleton such as halogenated styrene (chlorostyrene, bromostyrene, etc.).

Among these, as the styrene-based monomer, styrene is preferable from the viewpoint of not having a functional group capable of reacting with a crosslinking agent and being readily available.

In addition, when the styrenic monomer does not react with the crosslinking agent and does not form a crosslinked structure, localized presence in the vicinity of the interface of the pressure-sensitive adhesive layer of the above-described styrenic polymer is more likely to occur, and heat-and-moisture whitening resistance is further improved.

The styrenic polymer may be a polymer of one or more styrenic monomers, or a copolymer of a styrenic monomer and other monomers.

The copolymer of a styrenic monomer and another monomer is not particularly limited, and examples thereof include copolymers of a styrenic monomer and n-butyl acrylate, methyl methacrylate, butadiene, and acrylonitrile.

Among these, as the styrenic polymer, from the viewpoint of obtaining an adhesive composition capable of forming an adhesive layer having a lower relative dielectric constant and a more excellent moist heat whitening resistance, a polymer of one or two or more styrenic monomers is preferable, and one type of styrene Polymers of based monomers are more preferred. Further, a polymer of styrene and a styrene-based monomer other than styrene is more preferred, and a homopolymer of styrene is particularly preferred.

The styrenic polymer may be a hydride (hereinafter also referred to as "hydrogenated styrene polymer").

When the styrenic polymer is a hydrogenated styrenic polymer, the hydrogenation rate (unit: %) of the hydrogenated styrenic polymer is not particularly limited, and can be, for example, 10% or more and 99% or less.

The hydrogenation rate of the hydrogenated styrenic polymer was calculated using ¹ H-NMR as the integrated value of the peaks of the main chain styrenic polymer and the hydrogenated aryl group at 0.5 ppm to 3.0 ppm and the unhydrogenated aryl group at 6.5 ppm to 7.2 ppm. It is obtained from the ratio of integrated values of peaks.

1000 or less are preferable and, as for the weight average molecular weight (Mw) of a styrenic polymer, 700 or less are more preferable.

When the weight average molecular weight (Mw) of the styrenic polymer is 1000 or less, it becomes an adhesive composition capable of forming an adhesive layer having better compatibility with a specific (meth)acrylic polymer and having better heat-and-moisture whitening resistance. Moreover, if the weight average molecular weight (Mw) of a styrenic polymer is 1000 or less, it becomes an adhesive composition which can form the adhesive layer which is hard to generate|occur|produce bubbles and is more excellent in durability also in a moist heat environment.

Moreover, as for the weight average molecular weight (Mw) of a styrenic polymer, 400 or more are preferable.

The weight average molecular weight (Mw) of the styrenic polymer is measured in the same manner as the method for measuring the weight average molecular weight (Mw) of the specific (meth)acrylic polymer described above.

A commercial item can be used as a styrenic polymer. Examples of commercial products include Piccolastic A5 (trade name, styrene homopolymer, weight average molecular weight: 500) from EASTMAN CHEMICAL, Regalrez 1018 (trade name, styrene homopolymer hydride, weight average molecular weight: 500), Piccolastic A75 (trade name, styrene alone). polymer, weight average molecular weight: 1200), Yasuhara Chemical Co., Ltd. product YS Resin SX100 (trade name, styrene homopolymer, weight average molecular weight: 2500), and the like.

In the pressure-sensitive adhesive composition of the present invention, the content of the styrenic polymer is 0.01 mass with respect to 100 parts by mass of the specific (meth)acrylic polymer from the viewpoint of obtaining an adhesive composition capable of forming an adhesive layer having a lower relative permittivity and better heat-and-moisture whitening resistance. Part or more and preferably 20 parts by mass or less, and obtaining an adhesive composition capable of forming a pressure-sensitive adhesive layer having a better balance of relative permittivity, moist heat whitening resistance, compatibility with a specific (meth)acrylic polymer, adhesive force, processability and durability From a viewpoint, 0.1 part by mass or more and 15 parts by mass or less are more preferable, and 1 part by mass or more and 10 parts by mass or less are still more preferable with respect to 100 parts by mass of the specific (meth)acrylic polymer.

-Method for producing styrenic polymer-

The manufacturing method of a styrenic polymer is not specifically limited. A styrenic polymer can be produced by polymerizing a styrenic monomer and other monomers as needed.

The polymerization method of the styrenic polymer is not particularly limited, and can be appropriately selected from commonly used polymerization methods. Examples of polymerization methods include solution polymerization, emulsion polymerization, and suspension polymerization. Among these, as the polymerization method, the solution polymerization method is preferable from the viewpoint of relatively simple production.

In the solution polymerization method, a predetermined organic solvent, a monomer, a polymerization initiator and, if necessary, a chain transfer agent are generally put into a polymerization tank, and heated and reacted for several hours while stirring at the reflux temperature of the organic solvent in a nitrogen stream. In this case, at least a part of the organic solvent, the monomer, the polymerization initiator and/or the chain transfer agent may be sequentially added.

In addition, the weight average molecular weight (Mw) of the styrenic polymer can be easily adjusted according to the polymerization temperature, time, amount of solvent, type and amount of catalyst, and type and amount of polymerization initiator.

[Crosslinking agent]

It is preferable that the adhesive composition of this invention contains a crosslinking agent.

When the pressure-sensitive adhesive composition of the present invention contains a crosslinking agent, one type of crosslinking agent may be included, or two or more types may be included.

When the pressure-sensitive adhesive composition of the present invention includes a crosslinking agent, the crosslinking agent is not particularly limited as long as it can form a crosslinked structure by reacting with a specific (meth)acrylic polymer.

Examples of the crosslinking agent include polyisocyanate compounds, polyepoxy compounds, polyaziridine compounds, melamine formaldehyde condensates, and metal chelate compounds. Among these, as the crosslinking agent, a polyisocyanate compound is preferable from the viewpoint of the reactivity of the crosslinking reaction and the stability to environmental changes after crosslinking.

Examples of the polyisocyanate compound include aromatic polyisocyanate compounds such as xylylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, and tolylene diisocyanate, hydrogenated products of hexamethylene diisocyanate, isophorone diisocyanate, and aromatic polyisocyanate compounds. Aliphatic or alicyclic polyisocyanate compounds, such as these, etc. are mentioned.

Dimers or trimers of the polyisocyanate compounds, adducts of the polyisocyanate compounds and polyol compounds such as trimethylolpropane, and biuret compounds of the isocyanate compounds can also be used as the polyisocyanate compounds.

Among these, the polyisocyanate compound is preferably at least one selected from the group consisting of a dimer, a trimer, and an adduct of xylylene diisocyanate, and an adduct of xylylene diisocyanate is particularly preferable.

These polyisocyanate compounds may be used individually by 1 type, and may use two or more types together.

As the polyisocyanate compound, "Colonate (registered trademark) HX", "Colonate (registered trademark) HL-S", "Colonate (registered trademark) 2234", "Aquanate (registered trademark) 200", "Aquanate ( “Registered trademark) 210” [above, product of Tosoh Co., Ltd.], “Death module (registered trademark) N3300”, “Death module (registered trademark) N3400” [above, product of Sumitomo Bayer Urethane Co., Ltd.], “Duranate (a product of Sumitomo Bayer Urethane Co., Ltd.) “Registered trademark) E-405-80T”, “Duranate (registered trademark) 24A-100”, “Duranate (registered trademark) TSE-100” [above, manufactured by Asahi Kasei Chemicals Co., Ltd.], “Takenate ( "Takenate (registered trademark) D-120N", "Takenate (registered trademark) M-631N", "MT-Olester (registered trademark) NP1200" [above, Mitsui Chemical Co., Ltd. ) product] can be suitably used according to the commercial name.

When the pressure-sensitive adhesive composition of the present invention contains a crosslinking agent, the content of the crosslinking agent is preferably 0.05 parts by mass or more and 1.0 parts by mass or less, and 0.1 parts by mass or less, based on 100 parts by mass of the specific (meth)acrylic polymer, from the viewpoint of the adhesive strength of the pressure-sensitive adhesive layer and conformability to steps. Part or more and 0.5 parts by mass or less are more preferable, and 0.15 parts by mass or more and 0.3 parts by mass or less are still more preferable.

[Other Ingredients]

The adhesive composition of this invention may contain other components other than the component demonstrated above as needed. Other components that may be included in the pressure-sensitive adhesive composition of the present invention include a crosslinking catalyst, a chelating agent, a silane coupling agent, a tackifier, a plasticizer, a softener, a release aid, a dye, a pigment, an inorganic filler, a surfactant, an ultraviolet absorber, an antioxidant, and a metal. A corrosion inhibitor, various monomers, etc. are mentioned.

As various monomers, an ultraviolet curable monomer is mentioned, for example. The ultraviolet curable monomer may have, for example, two or more ethylenically unsaturated bond groups. When the pressure-sensitive adhesive composition of the present invention contains the above various monomers, the pressure-sensitive adhesive layer may be formed by polymerizing these various monomers.

You may form the adhesive layer of the structure which added and polymerized the said monomer to the adhesive composition of this invention.

When the pressure-sensitive adhesive composition of the present invention contains these other components, the content of these other components can be appropriately set within the range in which the effects of the present invention are exhibited.

[Usage]

Since the pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer having a low relative permittivity and excellent heat-and-moisture whitening resistance, it is suitably used, for example, for bonding touch sensor structural members. Specifically, it is preferably used when configuring a touch sensor by bonding together touch sensor constituent members such as a glass substrate, a transparent conductive film, and a design film.

However, in recent years, malfunction due to noise generated from a liquid crystal display (LCD) or the like in a device equipped with a touch panel has become a problem, and an adhesive composition capable of forming an adhesive layer having a lower dielectric constant than before has been required.

The pressure-sensitive adhesive composition of the present invention satisfies the difficult performance of being able to form a pressure-sensitive adhesive layer having a dielectric constant of less than 3.5, preferably 3.0 or less, and has excellent heat-and-moisture whitening resistance, so it is used to bond a liquid crystal display (LCD) and a touch sensor. It is particularly suitable as an adhesive composition to be.

Since the pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer having a low dielectric constant, even when the thickness of the pressure-sensitive adhesive layer is thin, the capacitance inside the touch panel is maintained at an appropriate value during operation of the touch panel and malfunctions due to the capacitance are prevented. can be suppressed

In addition, the pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition of the present invention is difficult to whiten due to the influence of the use environment such as high temperature (for example, 85 ° C.) and high humidity (for example, 90% RH), and has excellent moisture-heat whitening resistance. Initial visibility can be maintained.

Moreover, when the member provided with the adhesive composition of this invention is left to stand in a car in summer, a temperature rise may occur to about 85 degreeC.

[Adhesive Sheet]

The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer including a cross-linked structure formed by a cross-linking reaction of the pressure-sensitive adhesive composition of the present invention. That is, the pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer including a cross-linked structure formed by the reaction of a specific (meth)acrylic polymer included in the above-described pressure-sensitive adhesive composition of the present invention and a crosslinking agent. This pressure-sensitive adhesive layer has a low dielectric constant and is excellent in heat-and-moisture whitening resistance.

The PSA sheet of the present invention may be a PSA sheet having no base material (base material type) or a PSA sheet having a base material (base material type). For example, from the viewpoint of transparency, the pressure-sensitive adhesive sheet of the present invention is preferably a non-base material type pressure-sensitive adhesive sheet.

When the pressure-sensitive adhesive sheet of the present invention has a base material, a resin film (for example, a polyester film such as polyethylene terephthalate (PET)) can be used as a material for the base material.

Also, the base material is preferably transparent.

The thickness of the base material is not particularly limited, and is preferably 5 μm to 100 μm, for example, from the viewpoint of durability.

The exposed surface of the pressure-sensitive adhesive layer may be protected with a release film.

The peeling film is not particularly limited as long as it can easily peel from the pressure-sensitive adhesive layer. As a peeling film, the resin film (for example, polyester film, such as PET) in which the easy peeling process using the peeling agent was given to at least one surface, for example.

Fluororesin, paraffin wax, silicone, a long-chain alkyl group compound etc. are mentioned as a peeling agent.

The peeling 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 application, required performance, and the like. The thickness of the pressure-sensitive adhesive layer is preferably set in the range of, for example, 20 μm to 300 μm from the viewpoint of conformability to steps and productivity of the pressure-sensitive adhesive sheet.

The gel fraction of the pressure-sensitive adhesive layer is preferably 35% by mass or more and 90% by mass or less, more preferably 40% by mass or more and 80% by mass or less, and 45% by mass or more and 65% by mass or less from the viewpoints of workability, adhesive strength, and step followability. more preferable

In the present specification, the gel fraction of the pressure-sensitive adhesive layer is the ratio of the solvent insoluble content measured using ethyl acetate as an extraction solvent. Specifically, it is measured according to the following (1) to (4).

-Measurement method of gel fraction-

(1) Attach about 0.25 g of the adhesive layer to a 250 mesh wire mesh (100 mm × 100 mm) whose mass was accurately measured with a precision balance, and fold the wire mesh 5 times with the attached adhesive layer facing inside so that the gel powder does not leak. do. 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) Take out the sample, wash it with a small amount of ethyl acetate, and dry it at 120°C for 24 hours. After that, the mass is accurately measured with a precision balance.

(4) Calculate the gel fraction by the formula below.

Gel fraction (mass %) = (Z-X) / (Y-X) × 100

However, X is the mass (g) of the wire mesh, Y is the mass (g) of the wire mesh to which the adhesive layer is attached, and Z is the mass (g) of the wire mesh to which the adhesive layer after immersion and drying is attached.

The pressure-sensitive adhesive layer preferably has high transparency from the viewpoint of visibility when the pressure-sensitive adhesive sheet of the present invention is applied to bonding of touch sensor constituent members and bonding of liquid crystal displays (LCDs) and touch sensors. Specifically, the total light transmittance (JIS K 7361 (1997)) in the visible light wavelength region is preferably 85% or more, more preferably 90% or more.

The haze (JIS K 7136 (2000)) of the pressure-sensitive adhesive layer is preferably less than 2.0% from the viewpoint of visibility when the pressure-sensitive adhesive sheet of the present invention is applied to bonding of touch sensor constituent members and bonding of liquid crystal displays (LCDs) and touch sensors. And, less than 1.0% is more preferable, and 0.5% or less is still more preferable.

[Method of producing adhesive sheet]

The manufacturing method of the adhesive sheet of this invention is not specifically limited. The pressure-sensitive adhesive sheet of the present invention can be produced, for example, by the following method.

In the non-based adhesive sheet, for example, a pressure-sensitive adhesive composition is applied to the release-treated surface of a release film, dried to cause a crosslinking reaction to form an adhesive layer, and then a separate release film is applied on the release-treated surface. It can be made by overlapping them so that they come into contact.

For example, in the base material type pressure-sensitive adhesive sheet, a pressure-sensitive adhesive composition is applied to both sides of a base material, a cross-linking reaction is formed to form a pressure-sensitive adhesive layer, and then a peeling film is overlapped so that the peeling treatment surface is in contact with each other on the pressure-sensitive adhesive layer formed on both sides of the base material. can be produced by

In addition, the adhesive sheet of the oil base material type, for example, applies an adhesive composition to the release treated surface of the release film, dries it to cause a crosslinking reaction to form an adhesive layer, and then applies the resulting adhesive layer with the release film to both sides of the base material. It can also be produced by the overlapping method.

As a method for applying the pressure-sensitive adhesive composition to a release film, base material, etc., a known coating method using a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, or the like can be mentioned.

[Touch panel]

A touch panel using the pressure-sensitive adhesive composition or pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer formed of the above-described pressure-sensitive adhesive composition of the present invention. For example, in a capacitive touch panel, a transparent conductive film, a design film, etc. are bonded together with an adhesive layer to form a layered structure (eg, transparent conductive film / adhesive layer / transparent conductive film / adhesive layer / design film) A touch sensor and a liquid crystal display (LCD) are bonded together by an adhesive layer.

As described above, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention has a low dielectric constant and excellent heat-and-moisture whitening resistance. Since the touch panel having such an adhesive layer maintains the capacitance inside the touch panel at an appropriate value during operation, malfunction due to the capacitance is suppressed. In addition, since the pressure-sensitive adhesive layer is less likely to whiten under the influence of use environments such as high temperature and high humidity, initial visibility can be maintained.

The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention has excellent adhesive strength, processability and durability. Even if a touch panel having such an adhesive layer receives an impact such as a drop, the constituent members are unlikely to be peeled off, and manufacturing defects such as the adhesive composition protruding from between bonded constituent members are difficult to occur. In addition, since bubbles are not easily generated even in a use environment such as high temperature and high humidity, visibility is difficult to be impaired.

Example

Hereinafter, the present invention will be described in more detail by examples. The present invention is not limited to the following examples as long as the main points are not exceeded.

[Preparation of (meth)acrylic polymer]

[Production Example 1]

147 parts by mass of ethyl acetate and 0.05 part by mass of 2,2'-azobis(2,4-dimethylvaleronitrile) were placed in a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser and a sequential dropping device.

On the other hand, in another container, 420 parts by mass of 2-ethylhexyl methacrylate (2EHMA, an alkyl methacrylate having a branched chain alkyl group having 8 carbon atoms) (70% by mass relative to all structural units), 2-ethylhexyl acrylate ( 2EHA, an alkyl acrylate having a branched chain alkyl group having 8 carbon atoms) 120 parts by mass (20% by mass relative to the total constituent units) and 60 parts by mass of 2-hydroxyethyl methacrylate (2HEMA, a monomer having a hydroxyl group) (total 600 parts by mass of a monomer mixture solution consisting of 10% by mass relative to the constituent unit) was prepared. 150 mass parts of this monomer liquid mixture were put into reaction container, and it heated and refluxed for 20 minutes at the reflux temperature.

Next, the remaining 450 parts by mass of the monomer liquid mixture, 33 parts by mass of ethyl acetate, and 0.03 parts by mass of 2,2'-azobis (2,4-dimethylvaleronitrile) were sequentially added dropwise into the reaction vessel under reflux temperature conditions over 90 minutes. , After completion of the dropwise addition, the polymerization reaction was carried out over an additional 90 minutes. After this polymerization reaction, a mixed solution of 15 parts by mass of ethyl acetate and 0.13 part by mass of t-butylperoxypivalate was sequentially dropped into the reaction vessel over 30 minutes, and after the completion of the dropping, the reaction was further completed over 150 minutes (meta) An acrylic polymer A-1 was prepared.

The obtained (meth)acrylic polymer A-1 had a weight average molecular weight (Mw) of 500,000, a degree of dispersion (Mw/Mn) of 6.1, and a glass transition temperature (Tg) of -20°C. In addition, the weight average molecular weight (Mw), number average molecular weight (Mn), and glass transition temperature (Tg) were measured or calculated by the methods described above.

[Production Examples 2 to 5]

Except for changing the monomer composition in Production Example 1 to the composition shown in Table 1, (meth)acrylic polymers A-2 to A-5 were prepared in the same manner as in Production Example 1.

Table 1 shows the weight average molecular weight (Mw), degree of dispersion (Mw/Mn), and glass transition temperature (Tg) of the obtained (meth)acrylic polymers A-2 to A-5.

[Comparative Manufacturing Examples 1 to 9]

Solutions of (meth)acrylic polymers a-1 to a-9 were prepared in the same manner as in Production Example 1 except that the monomer composition was changed to the composition shown in Table 2 in Production Example 1.

Table 2 shows the weight average molecular weight (Mw), degree of dispersion (Mw/Mn), and glass transition temperature (Tg) of the obtained (meth)acrylic polymers a-1 to a-9.

The detail of the monomer composition of Table 1 and Table 2 is as follows.

2EHMA: 2-ethylhexyl methacrylate (an alkyl methacrylate having a branched chain alkyl group having 8 carbon atoms)

2EHA: 2-ethylhexyl acrylate (an alkyl acrylate having a branched chain alkyl group having 8 carbon atoms)

iBMA: isobutyl methacrylate (alkyl methacrylate having a branched chain alkyl group having 4 carbon atoms)

nBMA: normal butyl methacrylate (alkyl methacrylate having a straight-chain alkyl group having 4 carbon atoms)

LMA: lauryl methacrylate (alkyl methacrylate having a straight-chain alkyl group having 12 carbon atoms)

2HEA: 2-hydroxyethyl acrylate (monomer having a hydroxyl group)

2HEMA: 2-hydroxyethyl methacrylate (monomer having a hydroxyl group)

In addition, "-" of Table 1 and Table 2 means that the said component is not used.

[Example 1]

-Preparation of adhesive composition-

The styrenic polymer B-1 shown in Table 3 was dissolved in ethyl acetate to prepare an ethyl acetate solution (solid content: 50% by mass) of the styrenic polymer B-1. 2 parts by mass of the ethyl acetate solution of the styrenic polymer B-1 was added as a solid content to 100 parts by mass of the (meth)acrylic polymer A-1, and ethyl acetate was further added to dilute the solid content to 45% by mass, and the (meth)acrylic polymer A polymer solution containing A-1 and styrenic polymer B-1 was obtained.

The resulting polymer solution and a crosslinking agent (trade name: Takenate (registered trademark) D-110N, polyisocyanate compound, manufactured by Mitsui Chemicals Co., Ltd.) were mixed to obtain (meth)acrylic polymer A-1 as solid content, 100 parts by mass of styrene polymer An adhesive composition containing 0.2 parts by mass of 1 part by mass and a crosslinking agent as a solid content of B-1 as a solid content was prepared.

-Production of test samples-

The prepared pressure-sensitive adhesive composition is applied to the peel-treated surface of a release film (trade name: Film Biner 100E, manufactured by Fujimori Kogyo Co., Ltd.) easily peeled with a silicone-based release treatment agent so that the thickness of the adhesive layer after drying is 50 μm to form a coating layer. did Then, the release film having the obtained coating layer was dried under drying conditions at 100°C for 2 minutes to form an adhesive layer on the release film. The surface on which the pressure-sensitive adhesive layer was exposed was adhered to a separately prepared release film (trade name: Film Biner 100E, manufactured by Fujimori Kogyo Co., Ltd.) to prepare a non-base material type pressure-sensitive adhesive sheet. Thereafter, by curing for 4 days in an environment of 23° C. and 50% RH, a crosslinking reaction proceeded to obtain a test sample having a pressure-sensitive adhesive layer containing a crosslinked structure.

The gel fraction of the prepared test sample was 59.0% by mass. In addition, the gel fraction was measured by the method mentioned above.

The detail of the styrenic polymer of Table 3 is as follows.

B-1 (trade name: Piccolastic A5, styrene homopolymer, weight average molecular weight: 500, manufactured by EASTMAN CHEMICAL)

B-2 (trade name: Piccolastic A75, styrene homopolymer, weight average molecular weight: 1200, manufactured by EASTMAN CHEMICAL)

B-3 (trade name: YS Resin SX100, styrene homopolymer, weight average molecular weight: 2500, manufactured by Yasuhara Chemical Co., Ltd.)

B-4 (trade name: Regalrez 1018, hydride of styrene homopolymer, hydrogenation rate measured by the method described above: 97.4%, weight average molecular weight: 500, manufactured by EASTMAN CHEMICAL)

[Example 2 to Example 8]

Except having changed the composition of the adhesive composition to the composition shown in Table 4 using the styrenic polymer shown in Table 3, it carried out similarly to Example 1, prepared the adhesive composition, and produced the test sample.

[Example 9 to Example 12]

A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, except that the (meth)acrylic polymer shown in Table 1 was used and the composition of the pressure-sensitive adhesive composition was changed to the composition shown in Table 5, and samples for testing were prepared.

[Comparative Example 1 and Comparative Example 2]

A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, except that the (meth)acrylic polymer shown in Table 1 was used and the composition of the pressure-sensitive adhesive composition was changed to the composition shown in Table 4, and samples for testing were prepared.

[Comparative Example 3 to Comparative Example 11]

A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, except that the (meth)acrylic polymer shown in Table 2 was used and the composition of the pressure-sensitive adhesive composition was changed to the composition shown in Table 6, and samples for testing were prepared.

[Preparation of (meth)acrylic additives]

<Preparation Example C-1>

28 parts by mass of ethyl acetate and 21 parts by mass of butyl acetate were added to a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser, and a sequential dropping device, and the mixture was heated and the reflux temperature was maintained for 10 minutes.

Next, 40 parts by mass of n-butyl acrylate (BA) (40% by mass with respect to all structural units) and 20 parts by mass of methyl acrylate (MA) (20% by mass with respect to all structural units) in a reaction vessel under reflux temperature conditions , 40 parts by mass of 2-hydroxyethyl acrylate (2HEA) (40% by mass relative to the total constituent units), 10 parts by mass of ethyl acetate, 10 parts by mass of butyl acetate and dimethyl 2,2-azobis (2-methylpropio A mixture of 10 parts by mass of Nate) (trade name: V-601, manufactured by Wako Junyaku Kogyo Co., Ltd.) was sequentially added dropwise over 180 minutes, and after the completion of the dropwise addition, the reaction was further completed over 230 minutes.

After completion of the reaction, ethyl acetate was put into the reaction vessel and diluted so that the solid content was 58% by mass, thereby preparing (meth)acrylic additive C-1.

The obtained (meth)acrylic additive C-1 had a weight average molecular weight (Mw) of 7000. In addition, the weight average molecular weight (Mw) was measured by the method mentioned above.

<Preparation Example C-2>

In Production Example C-1, 40 parts by mass of n-butyl acrylate (BA) (40% by mass with respect to all structural units), 20 parts by mass of methyl acrylate (MA) (20% by mass with respect to all structural units) and 2- Instead of 40 parts by mass of hydroxyethyl acrylate (2HEA) (40% by mass based on total units) 90 parts by mass of t-butyl methacrylate (tBMA) (90% by mass based on total units) and 2-hydroxy A (meth)acrylic additive C-2 was prepared in the same manner as in Preparation Example C-1, except that 10 parts by mass of ethyl methacrylate (2HEMA) (10% by mass relative to the total structural units) was used.

The obtained (meth)acrylic additive C-2 had a weight average molecular weight (Mw) of 7000.

[Comparative Example 12]

A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, except that the (meth)acrylic additive C-1 obtained above was used and the composition of the pressure-sensitive adhesive composition was changed to the composition shown in Table 7, and samples for testing were prepared.

[Comparative Example 13]

A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the composition of the pressure-sensitive adhesive composition was changed to the composition shown in Table 7 using the (meth)acrylic additive C-2 obtained above, and a test sample was prepared.

[evaluation]

Relative dielectric constant, heat-and-moisture whitening resistance, compatibility, adhesive force, workability, and durability were evaluated for the obtained test samples according to the following methods. A result is shown in Table 4 - Table 7.

1. Relative dielectric constant

The peeling film on one side of the prepared test sample was peeled off and attached to an electrolytic copper foil (thickness: 10 μm, NC-WC treated product, manufactured by Furukawa Electric Industry Co., Ltd.). Then, the peeling film of the other side of the test sample was peeled off, and the side of the test sample from which the peeling film on the other side was peeled off was glued to the side where the pressure-sensitive adhesive layer was exposed. The procedure of piecing together the test samples was repeated until the pressure-sensitive adhesive layer became 200 μm thick. When the pressure-sensitive adhesive layer reached a thickness of 200 μm, the peeling film of the test sample that was finally put together was peeled off, and an electrolytic copper foil was pasted on the surface where the pressure-sensitive adhesive layer was exposed. The sample in which the pressure-sensitive adhesive layer of 200 μm thickness was laminated between the two electrolytic copper foils obtained in this way was cut into 50 mm × 50 mm size, and the relative dielectric constant was measured as a sample for measuring the relative dielectric constant.

In addition, the dielectric constant was measured under the following conditions using Material Analyzer 4291B manufactured by Agilent Technologies.

-condition-

Measurement jig: Dielectric Test Fixture 16453A (product of Agilent Technologies)

Measurement frequency: 100kHz

2. Moisture heat whitening resistance

The prepared test sample was cut into a size of 80 mm × 60 mm. Peel off the release film on one side of the test sample, overlap the surface where the adhesive layer is exposed on a glass plate (optical soda glass, size: 250 mm × 200 mm, manufactured by Matsunami Glass Industry Co., Ltd.) with a thickness of 1.8 mm, and press it using a desktop laminating machine. It was set as the sample for the damp heat whitening resistance test.

The haze (unit: %) (hereinafter referred to as "haze before test injection") of the sample for the damp heat whitening resistance test was measured using NDH 5000SP manufactured by Nippon Denshoku Industries Co., Ltd.

Next, the sample for the moist heat whitening resistance test was left for 500 hours in an environment of 85 ° C. and 90% RH, and then cooled for 10 minutes in an environment of 23 ° C. and 50% RH. referred to as "haze after injection") was measured.

A value (ΔH) obtained by subtracting the value of "haze before test injection" from the value of "haze after test injection" was obtained, and heat-and-moisture whitening resistance was evaluated according to the following evaluation criteria. Moreover, it shows that it is excellent in damp-heat whitening resistance, so that (DELTA)H is small.

-Evaluation standard-

A: ΔH is less than 1.0.

B: ΔH is 1.0 or more and less than 2.0.

C: (DELTA)H is 2.0 or more and less than 4.0.

D: ΔH is 4.0 or more.

3. Compatibility

The prepared test sample was cut into a size of 80 mm × 60 mm. Peel off the release film on one side of the test sample, overlap the side with the exposed adhesive layer on a glass plate (optical soda glass, size: 250 mm × 200 mm, manufactured by Matsunami Glass Industry Co., Ltd.) with a thickness of 1.8 mm, and press it using a desktop laminating machine. Sample A for the compatibility test was used.

On the other hand, in each Example and each Comparative Example, the same as in each Example and each Comparative Example, except that components other than the (meth)acrylic polymer and the crosslinking agent (styrene polymer, styrene, and (meth)acrylic additive) were not included. The composition was prepared and samples for comparison tests were prepared. Using the prepared sample for comparison test, sample B for compatibility test was prepared in the same way as the above sample for test. In addition, since Comparative Example 1 does not contain components other than a (meth)acrylic polymer and a crosslinking agent, the sample for test and the sample for comparative test have the same composition.

Haze (unit: %) was measured for each of sample A for compatibility test and sample B for compatibility test using Nippon Denshoku Kogyo Co., Ltd. NDH 5000SP.

A value (ΔH) obtained by subtracting the value of “haze of sample A for compatibility test” from the value of “haze of sample B for compatibility test” was obtained, and compatibility was evaluated according to the following evaluation criteria. Moreover, it shows that compatibility is excellent, so that (DELTA)H is small.

-Evaluation standard-

A: ΔH is less than 0.5.

B: ΔH is 0.5 or more and less than 2.0.

C: ΔH is 2.0 or more.

4. Adhesion

The release film on one side of the prepared test sample is peeled off, and the surface where the adhesive layer is exposed is easily bonded polyethylene terephthalate (hereinafter also referred to as “PET”) film (trade name: A-4100, thickness: 100 μm, Toyobo Co., Ltd.) ) product) was attached to the easily adhesive side of the product). After cutting the test sample to which the PET film was attached to a size of 25 mm × 150 mm, peel off the other release film, overlap the exposed side of the adhesive layer on the glass plate, and use a rubber roller weighing 2 kg to smooth the surface of the adhesive layer and the glass plate. It was compressed to be in contact with each other and used as a sample for evaluating adhesive force.

After leaving this adhesive evaluation sample for 24 hours in an environment of 23 ° C. and 50% RH, the adhesive force (unit: N / 25 mm) at 180 ° peeling was measured at a peeling speed of 300 mm / min, and evaluated according to the following evaluation criteria did Moreover, the stronger the adhesive force, the better.

-Evaluation standard-

A: The adhesive force is 20 N/25 mm or more.

B: The adhesive force is 15 N/25 mm or more and less than 20 N/25 mm.

C: The adhesive strength is less than 15 N/25 mm.

5. Machinability

The workability of the pressure-sensitive adhesive layer was evaluated by the retention test of JIS Z 0237 (2009) (so-called creep evaluation). Specifically, it was evaluated by the test described below.

Peel off the release film on one side of the prepared test sample, and align the exposed side of the adhesive layer with the easily bonded side of the PET film (trade name: A-4100, thickness: 100 μm, manufactured by Toyobo Co., Ltd.) attached After cutting the test sample (hereinafter referred to as “adhesive sheet”) to which this PET film was glued together to a size of 25 mm × 50 mm, the other release film was peeled off, and stainless steel (hereinafter referred to as “SUS”) was cut from the end of the test sample to 10 mm. It was overlapped so as to be in contact with the plate and press-fitted to make a sample for evaluation of workability (bonded area: 25 mm × 10 mm).

This workability evaluation sample was held in an environment of 23° C. and 50% RH with the SUS plate in the normal direction to the ground and the unbonded portion of the adhesive sheet facing down, and a weight was attached so that a load of 1.0 kg was applied to the adhesive sheet. The moving distance of the PSA sheet 1 hour after application of the load was measured, and workability was evaluated according to the following evaluation criteria. In addition, the shorter the moving distance of the pressure-sensitive adhesive sheet, the higher the cohesive force of the pressure-sensitive adhesive and the higher the processability (so-called cutting processability).

-Evaluation standard-

A: The moving distance of the adhesive sheet is less than 0.4 mm.

B: The moving distance of the adhesive sheet is 0.4 mm or more and less than 1.0 mm.

C: The moving distance of the adhesive sheet is 1.0 mm or more.

6. Durability

The prepared test sample was cut into a size of 80 mm × 60 mm. The release film on one side of the cut test sample was peeled off, and the surface where the adhesive layer was exposed was overlaid on a glass plate (optical soda glass, size: 250 mm × 200 mm, manufactured by Matsunami Glass Industry Co., Ltd.) with a thickness of 1.8 mm, and a tabletop lamination machine was used. and pressed to make a sample for durability test.

This durability test sample was left to stand for 500 hours in an environment of 85°C and 90% RH. After standing, the appearance of the durability test sample was observed with the naked eye, and durability was evaluated according to the following evaluation criteria based on the presence or absence of bubbles and the number of bubbles generated (unit: number). Moreover, it shows that durability is excellent, so that the number of generated air bubbles is small.

-Evaluation standard-

A: Generation of air bubbles was not observed at all.

B: The number of bubbles generated is 1 or more and less than 5.

C: The number of bubbles generated is 5 or more.

Example 1 described in Tables 4, 5, and 7 is described repeatedly for convenience of comparison, and all are the same.

In Tables 4 to 7, only symbols and numbers in the product name are indicated in the "Type" column of the crosslinking agent.

"-" in Table 4 and Table 7 means that the component is not used.

40% by mass or more of structural units derived from an alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms, and 5% by mass or more of structural units derived from monomers having a hydroxyl group, based on all structural units According to the pressure-sensitive adhesive compositions of Examples 1 to 12 containing a (meth)acrylic polymer [specific (meth)acrylic polymer] and a styrenic polymer at 15% by mass or less, a pressure-sensitive adhesive layer having a low relative permittivity and excellent heat-and-moisture whitening resistance is formed Could.

In addition, the adhesive compositions of Examples 1 to 12 were excellent in compatibility of components included in these adhesive compositions.

Furthermore, according to the pressure-sensitive adhesive compositions of Examples 1 to 12, it was possible to form a pressure-sensitive adhesive layer having excellent adhesive strength, workability, and durability.

According to the comparison between Comparative Example 1 and Example 12, it can be seen that the pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition containing a specific (meth)acrylic polymer but not containing a styrene-based polymer has remarkably poor heat-and-moisture whitening resistance.

According to the comparison between Comparative Example 2 and Example 1, it can be seen that the pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition containing styrene instead of the specific (meth)acrylic polymer and the styrene-based polymer has significantly poor heat-and-moisture whitening resistance.

According to the comparison between Comparative Examples 3 to 11 and Example 1, the pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition containing a (meth)acrylic polymer and a styrenic polymer other than a specific (meth)acrylic polymer had a relative dielectric constant and heat resistance to moisture. It can be seen that at least one of the Mars results in poor evaluation.

According to the comparison between Comparative Example 1 and Comparative Example 12, when the hydrophilic (meth)acrylic additive C-1 is added to a specific (meth)acrylic polymer, the wet-heat whitening property of the pressure-sensitive adhesive layer is remarkably improved, but it can be seen that the dielectric constant increases. . On the other hand, as in Example 1, when a styrenic polymer is added to a specific (meth)acrylic polymer, it is found that the wet-heat whitening property can be significantly improved without increasing the dielectric constant of the pressure-sensitive adhesive layer.

According to the comparison between Comparative Example 1 and Comparative Example 13, when the hydrophobic (meth)acrylic additive C-2 is added to a specific (meth)acrylic polymer, improvement in the wet heat whitening property of the pressure-sensitive adhesive layer is recognized, but it is not sufficient and the dielectric constant also increases. can know that

Claims (8)

Structural unit (A) derived from an alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms is 40% by mass or more with respect to all structural units, and structural unit (B) derived from a monomer having a hydroxyl group is used as all structural units. A pressure-sensitive adhesive composition containing a (meth)acrylic polymer and a styrene-based polymer in an amount of 5% by mass or more and 15% by mass or less with respect to. The method of claim 1,
The pressure-sensitive adhesive composition wherein the content of the structural unit (A) in the (meth)acrylic polymer is 60% by mass or more with respect to all structural units of the (meth)acrylic polymer. According to claim 1 or claim 2,
The pressure-sensitive adhesive composition wherein the monomer having a hydroxyl group in the structural unit (B) is a hydroxyalkyl methacrylate. According to claim 1 or claim 2,
The pressure-sensitive adhesive composition wherein the (meth)acrylic polymer has a glass transition temperature of -55°C or higher and -15°C or lower. According to claim 1 or claim 2,
The pressure-sensitive adhesive composition wherein the weight average molecular weight of the styrenic polymer is 1,000 or less. According to claim 1 or claim 2,
An adhesive composition in which the content of the styrenic polymer is 0.01 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the (meth)acrylic polymer. According to claim 1 or claim 2,
The adhesive composition used in order to bond a liquid crystal display and a touch sensor together. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a cross-linked structure formed by a cross-linking reaction of the pressure-sensitive adhesive composition according to claim 1 or 2.