JP2017179096A - Adhesive composition and adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive composition capable of forming an adhesive layer low in dielectric constant and excellent in reworkability and adhesive force and an application thereof.SOLUTION: There is provided an adhesive composition which contains a (meth)acrylic polymer containing a constitutional unit (A) derived from alkylene methacrylate having a branched alkyl group with 5 to 9 carbon atoms and a constitutional unit (B) derived from a monomer having a hydroxyl group and having glass transition temperature of -55°C to -20°C, a (meth)acrylic oligomer containing a constitutional unit derived from a monomer with weight average molecular weight of 3,500 to 100,000 and a hydroxyl group and having glass transition temperature of -50°C or more and a crosslinking agent with the (meth)acrylic oligomer of 0.1 pts.mass to 10 pts.mass based on 100 pts.mass of the (meth)acrylic polymer.SELECTED DRAWING: None

Description

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

  A touch sensor is used for an input device of an electronic device such as a mobile phone or a portable information terminal. The touch sensor is generally composed of a plurality of members such as a glass substrate, a transparent conductive film, and a design film. ing. These members are laminated via a pressure-sensitive adhesive composition formed of an adhesive composition. Moreover, in a touch panel mounting apparatus, the various displays represented by the liquid crystal display and the touch sensor are laminated | stacked via the adhesive composition formed with an adhesive composition, for example.

With the recent thinning of touch panel-equipped devices, the adhesive layer is also required to be thin. However, when trying to reduce the thickness of the adhesive layer, the capacitance inside the touch sensor increases, which may cause malfunction. Therefore, a pressure-sensitive adhesive layer having a low relative dielectric constant is required so that the capacitance does not increase even when the pressure-sensitive adhesive layer is thinned.
In response to this requirement, for example, in Patent Document 1, as a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having a low relative dielectric constant, an alkyl (meth) acrylate having a branched alkyl group at an ester terminal and a linear alkyl group are included. A pressure-sensitive adhesive composition containing a (meth) acrylic polymer obtained by polymerizing an alkyl (meth) acrylate having an ester terminal at a predetermined ratio is disclosed. Furthermore, Patent Document 1 describes that a pressure-sensitive adhesive composition to which a (meth) acrylic oligomer is added can increase the adhesive force without increasing the dielectric constant.

In addition, when manufacturing touch sensors, when various optical members represented by transparent conductive films are bonded, problems such as misalignment and quality defects occur, and the various optical members are covered by glass substrates. The work is peeled off from the adherend, and new various optical members are pasted. For this reason, the pressure-sensitive adhesive layer is required to have a characteristic that a part of the pressure-sensitive adhesive layer does not remain on the adherend during reattachment work, so-called reworkability.
In response to this requirement, for example, Patent Document 2 discloses a pressure-sensitive adhesive composition containing a high molecular weight acrylic copolymer, a low molecular weight acrylic copolymer, and a silane coupling agent.

JP 2013-194170 A JP 2013-10837 A

  By the way, in recent years, malfunctions due to noise generated from various displays have been a problem in touch panel-equipped devices. Therefore, the pressure-sensitive adhesive composition for a touch sensor for bonding various displays and a touch sensor has a dielectric constant lower than that of a conventional one, specifically a relative dielectric constant measured at 100 kHz is 4.0 or less, preferably 3.5. Formation of the following pressure-sensitive adhesive layers is required.

  Moreover, when the adhesive force of an adhesive layer is strong, there exists a tendency for a part of adhesive layer to remain on a to-be-adhered body, and for rework property to be inferior. On the other hand, when it is going to improve rework property, the adhesive force with an adherend will fall. Thus, reworkability and adhesive strength are mutually contradictory performances.

For example, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition described in Patent Document 1 is a structural unit derived from a crosslinkable monomer such as a structural unit derived from a monomer having a hydroxyl group. (Meth) An acrylic oligomer is not contained, and the cohesive force near the interface of the adherend is low, so that there is a problem that the reworkability is inferior.
Further, for example, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition described in Patent Document 2 has low adhesive strength in order to improve reworkability. For this reason, in a touch panel-mounted device having this pressure-sensitive adhesive layer, various optical members may be peeled off during use, for example, due to an impact caused by dropping.

  Furthermore, the reworkability of the pressure-sensitive adhesive layer can be adjusted by adding a polymer containing a structural unit derived from a monomer having a polyorganosiloxane skeleton, such as silicone oil, to the pressure-sensitive adhesive composition. However, the pressure-sensitive adhesive composition containing silicone oil has extremely low adhesive strength, and it is difficult to obtain desired performance. Further, the silicone oil that bleeds out from the adhesive layer may cause contamination of various members due to transfer or migration.

  As described above, it has been difficult to provide a pressure-sensitive adhesive composition that can form a pressure-sensitive adhesive layer that is excellent in both reworkability and pressure-sensitive adhesiveness while maintaining a strict performance of a relative dielectric constant of 4.0 or less.

This invention is made | formed in view of the above situations, and makes it a subject to achieve the following objectives.
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 relative dielectric constant and excellent reworkability and adhesive strength.
Another object of the present invention is to provide a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a low relative dielectric constant and excellent reworkability and adhesive strength.

Specific means for solving the problems include the following aspects.
<1> A structural unit (A) derived from an alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms and a structural unit (B) derived from a monomer having a hydroxyl group, and having a glass transition temperature. A (meth) acrylic polymer having a temperature of −55 ° C. or higher and −20 ° C. or lower;
A (meth) acrylic oligomer having a weight average molecular weight of 3,500 to 100,000, including a structural unit derived from a monomer having a hydroxyl group, and having a glass transition temperature of −50 ° C. or higher;
A crosslinking agent,
The adhesive composition whose content of the said (meth) acrylic-type oligomer is 0.1 mass part-10 mass parts with respect to 100 mass parts of said (meth) acrylic-type polymers.

<2> The content rate of the structural unit derived from the monomer having a hydroxyl group in the (meth) acrylic oligomer is 10% by mass or more and 60% by mass or less with respect to all the structural units of the (meth) acrylic oligomer. The pressure-sensitive adhesive composition according to <1>.
<3> The pressure-sensitive adhesive composition according to <1> or <2>, further including a styrene polymer.
<4> The pressure-sensitive adhesive composition according to any one of <1> to <3>, wherein the (meth) acrylic polymer further includes a structural unit derived from an alkyl acrylate.
<5> The pressure-sensitive adhesive composition according to <4>, wherein the alkyl acrylate is n-butyl acrylate.
<6> The pressure-sensitive adhesive composition according to <4>, wherein the alkyl acrylate is 2-ethylhexyl acrylate.

<7> The pressure-sensitive adhesive composition according to any one of <1> to <6>, further including an ethylenically unsaturated compound containing one or more ethylenically unsaturated groups.
<8> The pressure-sensitive adhesive composition according to any one of <1> to <7>, which is used for bonding the constituent members of the touch sensor.
<9> A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of <1> to <8>.

ADVANTAGE OF THE INVENTION According to this invention, the adhesive composition which can form the adhesive layer with a low relative dielectric constant and excellent in both rework property and adhesive force is provided.
The present invention also provides a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a low relative dielectric constant and excellent reworkability and adhesive strength.

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

In the present specification, a numerical range indicated using “to” means a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In this specification, the amount of each component in the composition is the total amount of the plurality of substances present in the composition unless there is a specific indication when there are a plurality of substances corresponding to each component in the composition. Means.

  In the present specification, “(meth) acrylate” is a term including both acrylate and methacrylate, and “(meth) acryl” is a term including both acrylic and methacrylic.

  In the present specification, the “(meth) acrylic polymer” is a homopolymer or copolymer having a weight average molecular weight (Mw) of 200,000 or more, and 50 masses of all structural units constituting the polymer. % Or more, preferably 90% by mass or more of a polymer containing a structural unit derived from a monomer having a (meth) acryloyl group.

[Adhesive composition]
The pressure-sensitive adhesive composition of the present invention comprises a structural unit (A) derived from an alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms (hereinafter also referred to as “structural unit (A)”) and a hydroxyl group. And a (meth) acrylic polymer having a glass transition temperature of −55 ° C. or higher and −20 ° C. or lower, which includes a structural unit (B) derived from the monomer it has (hereinafter also referred to as “structural unit (B)”). (Hereinafter also referred to as “specific (meth) acrylic polymer”) and a structural unit derived from a monomer having a weight average molecular weight of 3,500 to 100,000 and having a hydroxyl group, and having a glass transition temperature. Includes a (meth) acrylic oligomer (hereinafter also referred to as “specific oligomer”) having a temperature of −50 ° C. or higher and a crosslinking agent.
Moreover, as for the adhesive composition of this invention, content of a specific oligomer is 0.1 mass part-10 mass parts with respect to 100 mass parts of specific (meth) acrylic-type polymers.

The pressure-sensitive adhesive composition used for the touch sensor is required to have a performance capable of forming a pressure-sensitive adhesive layer having both a low relative dielectric constant, reworkability, and adhesive strength.
It is considered that the relative dielectric constant of the pressure-sensitive adhesive layer can be lowered to some extent by adjusting the composition of the (meth) acrylic polymer contained in the pressure-sensitive adhesive composition, for example.
However, in order to achieve both low dielectric constant, reworkability, and adhesive strength, an adhesive composition capable of forming an adhesive layer having a low relative dielectric constant is expected to improve reworkability and adhesive strength. Increasing the number of structural units derived from the monomer possessed increases the dielectric constant.
A monomer having a hydroxyl group has a large dipole moment. Therefore, the relative dielectric constant of a polymer containing a large number of structural units derived from a monomer having a hydroxyl group tends to be high.

On the other hand, since the pressure-sensitive adhesive composition of the present invention has the above-described configuration, it is possible to form a pressure-sensitive adhesive layer that is excellent in both low dielectric constant, reworkability, and adhesive strength.
The reason why the pressure-sensitive adhesive composition of the present invention can exhibit such an effect is not clear, but the present inventors presume as follows.

The alkyl methacrylate used for the production of the specific (meth) acrylic polymer has a large number of carbon atoms in the alkyl group of 5 or more and a branched structure, so that the molar volume is large and the dipole moment is small. Therefore, a (meth) acrylic polymer having a large molar volume and a small dipole moment can be produced.
Moreover, since the alkyl methacrylate used for the production of the specific (meth) acrylic polymer has 9 or less carbon atoms in the alkyl group, the volumetric shrinkage when the polymer is made is small, and the (meth) acrylic having a large molar volume. A polymer can be produced.
The pressure-sensitive adhesive composition of the present invention is considered to be capable of forming a pressure-sensitive adhesive layer having a low relative dielectric constant by containing a (meth) acrylic polymer having a small dipole moment and a large molar volume.

  When a pressure-sensitive adhesive layer is formed using the pressure-sensitive adhesive composition of the present invention containing a specific (meth) acrylic polymer and a specific oligomer, the weight average molecular weight of the specific oligomer is suitably in the range of 3,500 to 100,000. Since it is small, the specific oligomer is localized near the interface of the pressure-sensitive adhesive layer over time. Next, the pressure-sensitive adhesive composition is a state in which the specific (meth) acrylic polymer and the specific oligomer are localized, and the hydroxyl group of the specific (meth) acrylic polymer and the hydroxyl group of the specific oligomer are cross-linked by a cross-linking agent. Form a structure. For this reason, the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition of the present invention has a high crosslink density near the interface of the pressure-sensitive adhesive layer and exhibits excellent reworkability, and the viscoelasticity of the entire pressure-sensitive adhesive layer is appropriate. Excellent adhesive strength. Moreover, since the quantity of the structural unit derived from the monomer which has the hydroxyl group of the whole adhesive layer can be decreased, the raise of a dielectric constant can be suppressed.

  Since each component which the adhesive composition of this invention contains is excellent in compatibility, the haze of the adhesive layer formed is low, and it is hard to impair the transparency of the display part of a touchscreen mounting apparatus.

Moreover, according to the adhesive composition of this invention, the adhesive layer which has strong adhesive force can be formed.
In a portable electronic device, a member may be peeled off due to an influence such as dropping. According to the pressure-sensitive adhesive composition of the present invention, since a pressure-sensitive adhesive layer having a strong pressure-sensitive adhesive force can be formed, peeling of a member due to impact can be prevented.

Furthermore, according to the pressure-sensitive adhesive composition of the present invention, since a pressure-sensitive adhesive layer having a strong pressure-sensitive adhesive force can be formed, moisture penetration between the member and the pressure-sensitive adhesive layer can be suppressed, and the pressure-sensitive adhesive in a high-temperature and high-humidity environment Whitening of the layer is difficult to occur.
In the present specification, the property that does not easily whiten under a high-temperature and high-humidity environment (hereinafter also referred to as “wet heat environment”) is also referred to as wet heat whitening property.

By the way, in the manufacturing process of a touch panel, when laminating members constituting a touch sensor (hereinafter also referred to as “touch sensor constituent members”), each member is bonded according to the size of each member. An adhesive sheet cut with a blade (that is, a sheet having an adhesive layer) is often used. If the pressure-sensitive adhesive layer adheres to the cutting blade when the pressure-sensitive adhesive sheet is cut, the pressure-sensitive adhesive layer may be deformed and the pressure-sensitive adhesive layer may protrude from the touch sensor constituent member. Therefore, the pressure-sensitive adhesive layer is required to have a property (hereinafter also referred to as “workability”) that allows the pressure-sensitive adhesive sheet to be easily processed without adhering to the cutting blade when the pressure-sensitive adhesive sheet is cut.
According to the pressure-sensitive adhesive composition of the present invention, a pressure-sensitive adhesive layer having excellent processability can be formed, so that the problem that the pressure-sensitive adhesive layer adheres to the cutting blade when the pressure-sensitive adhesive sheet is cut and hardly protrudes from the touch sensor constituent member.

[Specific (meth) acrylic polymer]
The specific (meth) acrylic polymer includes a structural unit (A) derived from an alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms, and a structural unit (B) derived from a monomer having a hydroxyl group. including.
That is, the specific (meth) acrylic polymer is a polymer obtained by copolymerizing at least an alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms and a monomer having a hydroxyl group.

<Structural unit (A)>
The structural unit (A) is derived from an alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms.
As described above, since the structural unit (A) has 5 to 9 carbon atoms of the branched alkyl group, the dipole moment is small, the molar volume is large, and the relative dielectric constant is 4.0 or less. Preferably, it tends to be as low as 3.5 or less.
Moreover, when the carbon number of the branched alkyl group of the alkyl methacrylate is 9 or less, the pressure-sensitive adhesive composition has a good balance between viscoelasticity and cohesive force when used as a pressure-sensitive adhesive layer, and is excellent in reworkability and pressure-sensitive adhesive force. It becomes.
Furthermore, the number of carbon atoms of the branched alkyl group of the alkyl methacrylate is preferably 7 to 9 from the viewpoint of relative dielectric constant and workability.

Examples of the alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms include 2-ethylhexyl methacrylate, isopentyl methacrylate, isohexyl methacrylate, isoheptyl methacrylate, isooctyl methacrylate, and isononyl methacrylate.
Among these, as the alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms, 2-ethylhexyl methacrylate is preferable from the viewpoint of relative dielectric constant.

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

  The content of the structural unit (A) in the specific (meth) acrylic polymer is not particularly limited as long as the effects of the present invention are not impaired, but from the viewpoint of relative dielectric constant, workability, and adhesive strength, 10 mass% or more and 90 mass% or less are preferable with respect to all the structural units of a specific (meth) acrylic-type polymer, and 20 mass% or more and 70 mass% or less are more preferable.

<Structural unit (B)>
The structural unit (B) is derived from a monomer having a hydroxyl group.
In the pressure-sensitive adhesive composition of the present invention, the specific (meth) acrylic polymer contains the structural unit (B) and can undergo a crosslinking reaction with a crosslinking agent described later. Good balance, excellent reworkability and adhesive strength.

Examples of the monomer having a hydroxyl group include a monomer having a hydroxyl group and an ethylenically unsaturated bond group.
Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 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 (meta ) 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 and the like.

As the monomer having a hydroxyl group, hydroxyalkyl (meth) acrylate is preferable, and hydroxyalkyl methacrylate is more preferable.
Further, as the hydroxyalkyl methacrylate, the compatibility and copolymerization with an alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms is good, and the crosslinking reaction with a crosslinking agent is good. , Hydroxyalkyl methacrylate having a hydroxyalkyl group having 1 to 5 carbon atoms is preferable, hydroxyalkyl methacrylate having a hydroxyalkyl group having 2 to 4 carbon atoms is more preferable, and having a hydroxyethyl group having 2 carbon atoms. More preferred is hydroxyethyl methacrylate.

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

The content of the structural unit (B) in the specific (meth) acrylic polymer is not particularly limited as long as the effects of the present invention are not impaired, but from the viewpoint of relative dielectric constant, reworkability, and adhesive strength, 1 mass% or more and 20 mass% or less are preferable with respect to all the structural units of a specific (meth) acrylic-type polymer, and 5 mass% or more and 15 mass% or less are more preferable.
If the content of the structural unit (B) is 1% by mass or more, it can sufficiently undergo a crosslinking reaction with a crosslinking agent to be described later, so that the balance between viscoelasticity and cohesive force becomes better, and the reworkability is more excellent. Since it becomes a thing, it is preferable. Moreover, if the content rate of a structural unit (B) is 1 mass% or more, it will become difficult to generate | occur | produce a bubble also in a wet heat environment, and it will become an adhesive composition with the more outstanding external appearance.
Moreover, since the content rate of a structural unit (B) can make a dielectric constant lower, 20 mass% or less is more preferable with respect to all the structural units of a specific (meth) acrylic-type polymer.

The specific (meth) acrylic polymer has a ratio of the content of the structural unit (B) to the content of the structural unit (A) [content of the structural unit (B) / content of the structural unit (A)]. The mass ratio is preferably 1/2 to 1/10, and more preferably 1/5 to 1/7.
When the ratio of the content rate of the structural unit (B) to the content rate of the structural unit (A) is within a range of 1/2 to 1/10 in terms of mass ratio, the balance of relative dielectric constant, reworkability, and adhesive strength It becomes the adhesive composition which can form the more excellent adhesive layer.

<Other structural units>
-Structural unit (C)-
In addition to the structural unit (A) and the structural unit (B), the specific (meth) acrylic polymer further includes a structural unit derived from an alkyl (meth) acrylate other than the structural unit (A) (hereinafter referred to as “structural unit ( C) ").).
The specific (meth) acrylic polymer contains the structural unit (C) in addition to the structural unit (A) and the structural unit (B), so that the adhesive layer has viscoelasticity and cohesive force. The pressure-sensitive adhesive composition has a better balance and is more excellent in reworkability and adhesive strength.

The structural unit (C) is preferably an alkyl (meth) acrylate having an alkyl group having 4 to 10 carbon atoms from the viewpoint of imparting reworkability and adhesive force, and an alkyl acrylate having an alkyl group having 4 to 10 carbon atoms. More preferred.
Such alkyl (meth) acrylates include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl acrylate, 2 -Ethylhexyl acrylate, n-nonyl (meth) acrylate, isononyl acrylate, n-decyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate and the like.

Among these, n-butyl acrylate is preferable from the viewpoint of low glass transition temperature when a homopolymer is used, the elasticity necessary for reworkability can be imparted, and reworkability can be remarkably improved without increasing the relative dielectric constant. .
When the specific (meth) acrylic polymer contains a structural unit derived from n-butyl acrylate, the pressure-sensitive adhesive composition of the present invention improves reworkability particularly when peeling under high-speed conditions.

  In addition, it has excellent compatibility with alkyl methacrylates having a branched alkyl group having 5 to 9 carbon atoms, has a low glass transition temperature when it is made into a homopolymer, and has improved reworkability without significantly increasing the relative dielectric constant. From the viewpoint of improvement, 2-ethylhexyl acrylate is preferable.

  When the specific (meth) acrylic polymer includes the structural unit (C), the alkyl (meth) acrylate as the structural unit (C) may be used alone or in combination of two or more. May be.

When the specific (meth) acrylic polymer includes the structural unit (C), the content of the structural unit (C) is 5 with respect to all the structural units of the specific (meth) acrylic polymer from the viewpoint of relative dielectric constant. The mass is preferably 80% by mass or less and more preferably 20% by mass or less and 70% by mass or less.
Further, when the specific (meth) acrylic polymer contains n-butyl acrylate as the structural unit (C), the content of n-butyl acrylate is specific (meth) acrylic from the viewpoint of relative dielectric constant and reworkability. 10 mass% or more and 45 mass% or less are preferable with respect to all the structural units of a polymer.
When the specific (meth) acrylic polymer contains 2-ethylhexyl acrylate as the structural unit (C), the content of 2-ethylhexyl acrylate is such that the alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms From the viewpoint of compatibility and the balance between viscoelasticity and cohesive force necessary for the expression of reworkability and adhesive strength, it is 10 mass% or more and 70 mass% or less with respect to all the structural units of the specific (meth) acrylic polymer. Is preferred.

-Other structural units-
The specific (meth) acrylic polymer can contain other structural units other than the structural units described above, if necessary.
Examples of the other structural unit include a structural unit derived from a monomer having a cyclic group, a structural unit 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 a styrene derivative, and (meth) acrylate having a cyclic group is preferable.
In the case where the specific (meth) acrylic polymer includes a structural unit derived from a monomer having a cyclic group, the content of the structural unit is determined from the viewpoint of wet heat whitening and adhesive strength. 5 mass% or less is preferable with respect to all the structural units of a polymer, and 3 mass% or less is more preferable.

Examples of the acidic group in the monomer having an acidic group include a carboxy 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 carboxy group from the viewpoint of controlling the crosslinking reaction rate between the specific (meth) acrylic copolymer and the crosslinking agent.
Monomers having a carboxy group include (meth) acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, cinnamic acid and other unsaturated carboxylic acids, carboxyethyl acrylate (for example, β-carboxyethyl acrylate) Carboxyalkyl acrylates such as carboxypentyl acrylate, acrylic dimers, acrylic trimers, itaconic anhydride, maleic anhydride, and fumaric anhydride.
When the specific (meth) acrylic polymer includes a structural unit derived from a monomer having an acidic group, the content is 0.5 mass relative to the total structural unit of the specific (meth) acrylic polymer. % Or less is preferable.
The pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention is typified by a transparent electrode of a touch sensor, for example, when the content of the structural unit derived from the monomer having an acidic group is 0.5% by mass or less. Since the metal corrosion can be suppressed when coming into contact with various metals, it can be suitably used for touch sensor applications.
In addition, the content of the structural unit derived from the monomer having an acidic group is more preferably 0.2% by mass or less with respect to all the structural units of the specific (meth) acrylic polymer, and it is not included in the metal. This is particularly preferable from the viewpoint of corrosion inhibition.

<Physical properties of specific (meth) acrylic polymer>
The glass transition temperature (Tg) of the specific (meth) acrylic polymer is −55 ° C. or higher and −20 ° C. or lower. More preferably, the glass transition temperature of the specific (meth) acrylic polymer is −50 ° C. or higher and −30 ° C. or lower.
Since the glass transition temperature of the specific (meth) acrylic polymer is −55 ° C. or higher, the balance between viscoelasticity and cohesive force is good, and when used as an adhesive layer, the adhesive strength and workability are excellent. Since it is 20 ° C. or less, the breaking strength becomes sufficiently large when the pressure-sensitive adhesive layer is formed, and the pressure-sensitive adhesive layer does not break at the time of reworking work that peels and removes from the adherend and reattaches various optical members. Excellent reworkability.

In this specification, the glass transition temperature (Tg) of the specific (meth) acrylic polymer is a molar average glass transition temperature determined by the following calculation.
Tg1, Tg2,..., And Tgn in the following formula are the glass transition temperatures (Tg) of the homopolymers of monomer 1, monomer 2,. Yes, converted to absolute temperature (K). m1, m2,... and mn are mole fractions of the respective monomers.
In addition, although absolute temperature (K) is used for calculation of glass transition temperature (Tg), when describing glass transition temperature (Tg) in this specification, Celsius degree (degreeC) may be used.

  As used herein, “glass transition temperature (Tg) of homopolymer” refers to the monomer homopolymer using a differential scanning calorimeter (DSC) (product name: EXSTAR6000, manufactured by Seiko Instruments Inc.), nitrogen. The measurement is performed under the conditions of 10 mg of a measurement sample and a heating rate of 10 ° C./min.

  Typical monomer “glass transition temperature (Tg) of homopolymer” is 2-ethylhexyl methacrylate is −10 ° C., 2-ethylhexyl acrylate is −76 ° C., and isobutyl methacrylate is 48 ° C. N-butyl methacrylate is 21 ° C., lauryl methacrylate is −65 ° C., 2-hydroxyethyl acrylate is −15 ° C., 2-hydroxyethyl methacrylate is 55 ° C., and isodecyl methacrylate is −41 ° C. T-butyl acrylate is 41 ° C., t-butyl methacrylate is 107 ° C., and acrylic acid is 163 ° C.

  The weight average molecular weight (Mw) of the specific (meth) acrylic polymer is not particularly limited. For example, it is easy to follow the processability and the step when the pressure-sensitive adhesive layer is used (hereinafter referred to as “step-following property”). In this case, the number is preferably 200,000 to 1,000,000, more preferably 300,000 to 800,000, and still more preferably 400,000 to 600,000.

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

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

(1) A specific (meth) acrylic polymer solution 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 specific (meth) acrylic polymer obtained in the above (1) is dissolved in tetrahydrofuran so as to have 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 specific (meth) acrylic polymer are measured as standard polystyrene equivalent values under the following conditions. To do.

(conditions)
GPC: HLC-8220 GPC (manufactured by Tosoh Corporation)
Column: 4 TSK-GEL GMHXL used (manufactured by Tosoh Corporation)
Mobile phase solvent: Tetrahydrofuran Flow rate: 0.6 mL / min Column temperature: 40 ° C

<Method for producing specific (meth) acrylic polymer>
The method for producing the specific (meth) acrylic polymer is not particularly limited. The specific (meth) acrylic polymer includes the above-described monomers, that is, alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms, a monomer having a hydroxyl group, and other monomers as necessary. It can be produced by polymerizing with a monomer.
The polymerization method of the specific (meth) acrylic polymer is not particularly limited, and can be appropriately selected from commonly used polymerization methods. Examples of the polymerization method include solution polymerization, emulsion polymerization, and suspension polymerization. Among these, a solution polymerization method is preferable as the polymerization method because the production can be performed relatively easily.

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

Organic solvents used in the polymerization reaction include aromatic carbonization such as benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, aromatic naphtha, etc. Hydrogen, n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, terpine oil and other aliphatic or alicyclic hydrocarbons, ethyl acetate, acetic acid Esters such as n-butyl, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, methyl benzoate, acetone, methyl ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, methyl Ketones such as cyclohexanone, ethylene glycol monomethyl Glycol ethers such as ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl Alcohols, such as alcohol, i-butyl alcohol, s-butyl alcohol, t-butyl alcohol, are mentioned.
In the production of the specific (meth) acrylic polymer, it is preferable to use an organic solvent that hardly causes chain transfer during the polymerization reaction of esters, ketones, and the like. From the viewpoint of solubility of the specific (meth) acrylic polymer and ease of polymerization reaction, the organic solvent is preferably at least one selected from the group consisting of ethyl acetate and methyl ethyl ketone, and 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, an organic peroxide, an azo compound, or the like used in a usual solution polymerization method can be used.
Organic peroxides include t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate , T-butyl peroxypivalate, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) butane, 2,2-bis (4,4-di-t-octylperoxycyclohexyl) butane Is mentioned.
As the azo compound, 2,2′-azobis-i-butylnitrile, 2,2′-azobis-2,4-dimethylvaleronitrile, 2,2′-azobis-4-methoxy-2,4-dimethylvaleronitrile 1,1'-azobis-cyclohexane-1-carbonitrile, 2,2'-azobis (methyl isobutyrate), and the like.

  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. From this viewpoint, an azo compound is preferable.

  The amount of the polymerization initiator used is preferably 0.01 parts by mass or more and 2 parts by mass or less, and 0.1 parts by mass with respect to 100 parts by mass of the total amount of monomers constituting the specific (meth) acrylic polymer. More preferred is 1 part by mass or less.

  The polymerization temperature for producing the 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) of a specific (meth) acrylic-type polymer, and dispersion degree (Mw / Mn) are polymerization temperature, time, solvent amount, the kind and quantity of a catalyst, and It can be easily adjusted by the kind and amount of the polymerization initiator.

[Specific oligomer]
The pressure-sensitive adhesive composition of the present invention contains a specific oligomer.
The specific oligomer includes a structural unit derived from a monomer having a hydroxyl group.
Since the specific oligomer contains a structural unit derived from a monomer having a hydroxyl group and undergoes a crosslinking reaction with a crosslinking agent described later, the pressure-sensitive adhesive composition of the present invention has viscoelasticity and cohesive strength when used as a pressure-sensitive adhesive layer. The balance is good, and both reworkability and adhesive strength are excellent.

Examples of the monomer having a hydroxyl group include a monomer having a hydroxyl group and an ethylenically unsaturated bond group.
The structural unit derived from the monomer having a hydroxyl group contained in the specific oligomer may be the same as the monomer exemplified in the description of the structural unit (B) of the specific (meth) acrylic polymer.
The structural unit derived from the monomer having a hydroxyl group contained in the specific oligomer and the structural unit derived from the monomer having a hydroxyl group contained in the specific (meth) acrylic polymer (B) may be the same, May be different.
The structural unit derived from the monomer having a hydroxyl group contained in the specific oligomer is preferably a structural unit derived from 2-hydroxyethyl (meth) acrylate because the crosslinking reaction with the crosslinking agent is good.

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

The content of the structural unit derived from the monomer having a hydroxyl group in the specific oligomer is not particularly limited, but from the viewpoint of relative dielectric constant, reworkability, and adhesive strength, it is based on the total structural unit of the specific oligomer. 10 mass% or more and 60 mass% or less are preferable, and 20 mass% or more and 50 mass% or less are more preferable.
In addition, if the content rate of the structural unit derived from the monomer having a hydroxyl group is 10% by mass or more, a crosslinking reaction with the crosslinking agent can be sufficiently performed. Since it becomes a more excellent adhesive composition, it is preferable. Moreover, if the content rate of the structural unit derived from the monomer which has a hydroxyl group is 60 mass% or less, it will be hard to gelatinize at the time of preparation of a specific oligomer, and both the rework property and adhesive force of an adhesive layer are more excellent. preferable.

The specific oligomer preferably includes a structural unit derived from a monomer other than the monomer having a hydroxyl group. By further including such a structural unit, a pressure-sensitive adhesive composition having excellent compatibility with a specific (meth) acrylic polymer and a low haze when used as a pressure-sensitive adhesive layer.
The structural unit derived from the monomer other than the monomer having a hydroxyl group is the same structural unit as the structural unit (A) and the structural unit (C) that can be contained in the specific (meth) acrylic polymer described above. Examples thereof include a structural unit derived from an alkyl (meth) acrylate, a structural unit derived from a monomer having a cyclic group, and a structural unit derived from a monomer having an acidic group.
The structural unit derived from a monomer other than the monomer having a hydroxyl group contained in the specific oligomer may be the same as the structural unit (A) and the structural unit (C) contained in the specific (meth) acrylic polymer. Well, it can be different.

  When a specific oligomer contains a structural unit derived from an alkyl (meth) acrylate, it is excellent in compatibility with the specific (meth) acrylic polymer, and the specific oligomer is localized near the interface of the pressure-sensitive adhesive layer while keeping the haze low. Therefore, a structural unit derived from t-butyl acrylate, t-butyl methacrylate and 2-ethylhexyl acrylate is preferable.

  In addition, a specific oligomer may also contain the structural unit derived from the monomer which has an acidic group as a structural unit derived from monomers other than the monomer which has a hydroxyl group. The content of the structural unit derived from the monomer having an acidic group is preferably 0.2% by mass or less with respect to all the structural units of the specific oligomer, and it is particularly preferable from the viewpoint of inhibiting corrosion of the metal.

The glass transition temperature of the specific oligomer is −50 ° C. or higher. More preferably, the glass transition temperature of the specific oligomer is −50 ° C. or more and 50 ° C. or less.
Since the glass transition temperature of the specific oligomer is −50 ° C. or higher, when the pressure-sensitive adhesive composition of the present invention is used as a pressure-sensitive adhesive layer, the balance between viscoelasticity and cohesive force is improved, and both the pressure-sensitive adhesive force and reworkability are both Excellent.
In addition, the glass transition temperature of a specific oligomer is the value calculated | required by the method similar to a specific (meth) acrylic-type polymer.

The weight average molecular weight of the specific oligomer is 3,500 to 100,000. More preferably, it is 3,800-50,000.
As described above, because the weight average molecular weight of the specific oligomer is 100,000 or less, the specific oligomer is localized near the interface of the pressure sensitive adhesive layer over time, and the specific (meth) acrylic polymer is The hydroxyl group possessed and the hydroxyl group possessed by the specific oligomer can form a crosslinked structure near the interface by the crosslinking agent, and the reworkability is excellent. Further, since the weight average molecular weight of the specific oligomer is 100,000 or less, the compatibility with the specific (meth) acrylic polymer is excellent, the haze of the pressure-sensitive adhesive layer is lowered, and the cross-linking reaction proceeds appropriately.
Moreover, since the weight average molecular weight of the specific oligomer is at least 3,500 or more, the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition of the present invention can form a cross-linked structure with sufficient reworkability in the vicinity of the interface.

The weight average molecular weight of the specific oligomer is a value measured by the same method as that for the specific (meth) acrylic polymer.
In addition, the dispersion degree (Mw / Mn) of a specific oligomer is not specifically limited, For example, it can be set as 1.1-10.

The pressure-sensitive adhesive composition of the present invention contains 0.1 to 10 parts by mass of the specific oligomer with respect to 100 parts by mass of the specific (meth) acrylic polymer. More preferably, it is 0.2 mass part-5 mass parts, More preferably, it is 0.3 mass part-1.0 mass part.
Since the pressure-sensitive adhesive composition of the present invention contains 0.1 part by mass or more of the specific oligomer with respect to 100 parts by mass of the specific (meth) acrylic polymer, the pressure-sensitive adhesive layer has a specific (meth) acrylic weight as described above. The hydroxyl group possessed by the coalescence and the hydroxyl group possessed by the specific oligomer can form a crosslinked structure near the interface by the crosslinking agent, and the reworkability is excellent. Further, since 10 parts by mass or less of the specific oligomer is contained with respect to 100 parts by mass of the specific (meth) acrylic polymer, the pressure-sensitive adhesive layer has a low relative dielectric constant of 4.0 or less and excellent adhesive strength.

The method for producing the specific oligomer is not particularly limited. The specific oligomer can be produced by polymerizing a monomer having a hydroxyl group and, if necessary, another monomer.
The manufacturing method of a specific oligomer is based on the manufacturing method of the specific (meth) acrylic-type polymer as stated above.

[Crosslinking agent]
The pressure-sensitive adhesive composition of the present invention contains a crosslinking agent.
Since the pressure-sensitive adhesive composition of the present invention contains a crosslinking agent as described above, the hydroxyl group of the specific (meth) acrylic polymer and the hydroxyl group of the specific oligomer undergo a crosslinking reaction with the crosslinking agent, Good balance with cohesive strength, excellent reworkability and adhesive strength.
The crosslinking agent is not particularly limited as long as it can form a crosslinked structure with the specific (meth) acrylic polymer and the specific oligomer.
The pressure-sensitive adhesive composition of the present invention may contain one kind of crosslinking agent or two or more kinds.

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

As polyisocyanate compounds, aliphatic polyisocyanate compounds such as xylylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, tolylene diisocyanate, aliphatics such as hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated products of aromatic polyisocyanate compounds, etc. Or an alicyclic polyisocyanate compound etc. are mentioned.
In addition, a dimer or trimer of the polyisocyanate compound, an adduct of the polyisocyanate compound and a polyol compound such as trimethylolpropane, a biuret of the isocyanate compound, and the like can be used as the polyisocyanate compound.

Among these, as the crosslinking agent, an aromatic polyisocyanate compound is particularly preferable from the viewpoint of the reactivity of the crosslinking reaction and the pot life of the pressure-sensitive adhesive composition.
The aromatic polyisocyanate compound is preferably at least one selected from the group consisting of a dimer, trimer, and adduct of xylylene diisocyanate, and an adduct of xylylene diisocyanate is particularly preferable.
These aromatic polyisocyanate compounds may be used individually by 1 type, and may use 2 or more types together.

  Examples of the polyisocyanate compound include “Coronate (registered trademark) HX”, “Coronate (registered trademark) HL-S”, “Coronate (registered trademark) 2234”, “Aquanate (registered trademark) 200”, and “Aquanate (registered trademark). ) 210 ”(manufactured by Tosoh Corporation),“ Desmodule (registered trademark) N3300 ”,“ Desmodule (registered trademark) N3400 ”(manufactured by Sumika Covestrourethane Co., Ltd.),“ Duranate (registered) Trademark) E-405-80T "," Duranate (registered trademark) 24A-100 "," Duranate (registered trademark) TSE-100 "(manufactured by Asahi Kasei Chemicals Corporation)," Takenate (registered trademark) D-110N " ”,“ Takenate (registered trademark) D-120N ”,“ Takenate (registered trademark) M-631N ”,“ MT-Olestar (registered) Trademark) NP1200 "[or, Mitsui Chemicals Co., Ltd.] can be preferably used those sold by the trade name.

In the pressure-sensitive adhesive composition of the present invention, the content of the crosslinking agent is not particularly limited, and is preferably 0.05 part by mass to 3.0 parts by mass with respect to 100 parts by mass of the specific (meth) acrylic polymer, for example. When the pressure-sensitive adhesive composition of the present invention contains 0.05 parts by mass or more of a cross-linking agent with respect to 100 parts by mass of the specific (meth) acrylic polymer, it appropriately cross-links to exhibit higher adhesive strength, and 3. When the content is 0 part by mass or less, an extreme increase in cohesive force due to an excessive crosslinking reaction does not occur, and a decrease in adhesive force can be further suppressed.
In the pressure-sensitive adhesive composition of the present invention, the content of the crosslinking agent is 0.05 with respect to 100 parts by mass of the specific (meth) acrylic polymer from the viewpoint of the adhesive strength of the pressure-sensitive adhesive layer and the step following ability. More preferably, they are 0.1 mass part or more and 1.0 mass part or less, More preferably, 0.1 mass part or more and 0.5 mass part or less are more preferable, 0.15 mass part or more and 0.3 mass part or less are especially preferable.

[Styrene polymer]
The pressure-sensitive adhesive composition of the present invention preferably contains a styrene polymer in addition to the specific (meth) acrylic polymer.
The styrene polymer is a polymer containing a styrene monomer as a constituent unit.
The pressure-sensitive adhesive composition of the present invention may contain one kind of styrenic polymer, or may contain two or more kinds having different monomer compositions, weight average molecular weights, and the like.

As described above, the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition of the present invention may be used in a wet heat environment. A normal pressure-sensitive adhesive composition is likely to have a problem of whitening when it contains moisture in a humid heat environment. Moisture that causes whitening flows from the end of the pressure-sensitive adhesive layer or between the pressure-sensitive adhesive layer and the adherend.
Styrenic polymers are hydrophobic. When the pressure-sensitive adhesive composition of the present invention contains a styrenic polymer, the pressure-sensitive adhesive layer can suppress the inflow of moisture because the styrenic polymer is localized near the interface of the pressure-sensitive adhesive layer in a moist heat environment, and moist heat whitening. The property is particularly excellent.

  When the pressure-sensitive adhesive composition of the present invention contains a styrene polymer, the wet heat whitening property can be improved without increasing the relative dielectric constant because it contains a hydrophobic styrene polymer.

Styrene monomers that can constitute the styrene polymer include styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, diethyl styrene, triethyl styrene, propyl styrene, butyl styrene, hexyl styrene, octyl styrene), chloro Examples thereof include monomers having a styrene skeleton such as styrene and bromostyrene.
Among these, as the styrene monomer, styrene is preferable from the viewpoint of availability because it does not have a functional group capable of undergoing a crosslinking reaction with a crosslinking agent.

The styrenic polymer may be a polymer of one or two or more styrenic monomers, or may be a copolymer of a styrenic monomer and another monomer.
The copolymer of the styrene monomer and the other monomer is not particularly limited, and examples thereof include a copolymer of the styrene monomer and n-butyl acrylate, methyl methacrylate, butadiene, acrylonitrile and the like. It is done.
Among these, as the styrene-based polymer, a polymer of a styrene-based monomer is preferable from the viewpoint of obtaining a pressure-sensitive adhesive composition having a lower relative dielectric constant and capable of forming a pressure-sensitive adhesive layer that is superior in wet heat whitening. Further, a polymer of only a styrene monomer is more preferable, and a homopolymer of a styrene monomer is still more preferable. A styrene polymer is particularly preferred, and a styrene homopolymer is most preferred.

The styrene polymer may be a hydride (hereinafter also referred to as “hydrogenated styrene polymer”).
When the styrene polymer is a hydrogenated styrene polymer, the hydrogenation rate (unit:%) of the hydrogenated styrene polymer is not particularly limited, and can be, for example, 10% to 99%. .

The weight average molecular weight of the styrene polymer is preferably 1,000 or less, and more preferably 700 or less.
When the weight average molecular weight of the styrenic polymer is 1,000 or less, the compatibility with the specific (meth) acrylic polymer becomes better, and a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer that is superior in wet heat whitening property; Become. Moreover, when the weight average molecular weight of the styrene-based polymer is 1000 or less, a pressure-sensitive adhesive composition in which bubbles are hardly generated even in a wet heat environment.
The weight average molecular weight of the styrene polymer is preferably 400 or more.
The weight average molecular weight of the styrene polymer is measured in the same manner as the method for measuring the weight average molecular weight of the specific (meth) acrylic polymer described above.

  A commercially available product can be used as the styrene polymer. Examples of commercially available products include Piclastic A5 (trade name, styrene homopolymer, weight average molecular weight: 500) manufactured by EASTMAN CHEMICAL, Regalrez 1018 (trade name, hydride of styrene homopolymer, weight average molecular weight: 500). , Piccolastic A75 (trade name, styrene homopolymer, weight average molecular weight: 1,200), YS Resin SX100 (trade name, styrene homopolymer, weight average molecular weight: 2,500) manufactured by Yashara Chemical Co., Ltd. It is done.

  When the pressure-sensitive adhesive composition of the present invention contains a styrenic polymer, the content thereof is from the viewpoint of obtaining a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having a lower relative dielectric constant and excellent wet heat whitening property. , With respect to 100 parts by mass of the specific (meth) acrylic polymer, preferably 0.01 parts by mass or more and 20 parts by mass or less, relative permittivity, wet heat whitening property, compatibility with the specific (meth) acrylic polymer, From the viewpoint of obtaining a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having a better balance of pressure-sensitive adhesive force, reworkability and workability, 0.1 part by mass or more and 15 parts by mass with respect to 100 parts by mass of the specific (meth) acrylic polymer More preferred is 1 part by mass or more and still more preferred is 10 parts by mass or less.

-Styrene polymer production method-
The method for producing the styrene polymer is not particularly limited. The styrene polymer can be produced by polymerizing a styrene monomer and, if necessary, another monomer.
The polymerization method of the styrene polymer is not particularly limited, and can be appropriately selected from commonly used polymerization methods. Examples of the polymerization method include solution polymerization, emulsion polymerization, and suspension polymerization. Among these, a solution polymerization method is preferable as the polymerization method because the production can be performed relatively easily.

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

  The weight average molecular weight of the styrene polymer can be easily adjusted by the polymerization temperature, time, amount of solvent, type and amount of catalyst, and type and amount of polymerization initiator.

[Ethylenically unsaturated compound containing one or more ethylenically unsaturated groups]
The pressure-sensitive adhesive composition of the present invention may contain an ethylenically unsaturated compound containing one or more ethylenically unsaturated groups as necessary. The ethylenically unsaturated compound preferably contains two or more ethylenically unsaturated groups.
When the pressure-sensitive adhesive composition of the present invention contains an ethylenically unsaturated compound, the pressure-sensitive adhesive layer has a crosslinked structure in the vicinity of the interface between the hydroxyl group of the specific (meth) acrylic polymer and the hydroxyl group of the specific oligomer. After the formation, the ethylenically unsaturated compound undergoes a curing reaction, for example, by irradiation with active energy rays, so that a stronger adhesive force can be obtained and the peeling of the adhesive layer due to the gas generated from the adherend and the appearance defect are suppressed. it can. Moreover, when there is a step in the adherend, it is possible to suppress a problem represented by peeling from the adherend by irradiating and curing the active energy ray after the pressure-sensitive adhesive layer sufficiently follows the step.
In addition, when the pressure-sensitive adhesive composition of the present invention contains an ethylenically unsaturated compound, if it is before the curing reaction by irradiation of active energy rays to the pressure-sensitive adhesive layer, as in the case of not containing the ethylenically unsaturated compound, The pressure-sensitive adhesive layer can be easily peeled off from the adherend.

The ethylenically unsaturated compound containing one or more ethylenically unsaturated groups is not particularly limited. For example, ethylene oxide modified bifunctional (meth) acrylate, ethylene oxide modified trifunctional (meth) acrylate, propylene oxide modified bifunctional (meth) Examples include acrylate and propylene oxide-modified trifunctional (meth) acrylate.
As ethylene oxide-modified bifunctional (meth) acrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) Examples include acrylate, hexanediol EO-modified diacrylate, bisphenol A EO-modified di (tri) acrylate, and isocyanuric acid EO-modified diacrylate.
Examples of the ethylene oxide-modified trifunctional (meth) acrylate include trimethylolpropane EO-added tri (meth) acrylate and isocyanuric acid EO-modified tri (meth) acrylate.
Examples of the propylene oxide-modified bifunctional (meth) acrylate include dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, and neopentyl glycol PO-modified diacrylate.
Examples of the propylene oxide-modified trifunctional (meth) acrylate include trimethylolpropane PO-added tri (meth) acrylate.
Examples of the tetrafunctional or higher functional polyfunctional (meth) acrylate include pentaerythritol EO modified tetra (meth) acrylate and pentaerythritol PO modified tetra (meth) acrylate.

  A commercially available product can be used as the ethylenically unsaturated compound containing one or more ethylenically unsaturated groups. Examples of commercially available products include, for example, Biscoat # 335HP (trade name, tetraethylene glycol diacrylate) manufactured by Osaka Organic Chemical Industry Co., Ltd.

  In addition, when the adhesive composition of this invention contains an ethylenically unsaturated compound, you may contain a photoinitiator. By irradiating the adhesive composition of the present invention with an active energy ray typified by ultraviolet rays, the ethylenically unsaturated compound starts a polymerization reaction by the action of the photopolymerization initiator.

Examples of the photopolymerization initiator include acetophenone initiators, benzoin ether initiators, benzophenone initiators, hydroxyalkylphenone initiators, thioxanthone initiators, and amine initiators. Examples of the acetophenone initiator include diethoxyacetophenone and benzyldimethyl ketal. Examples of the benzoin ether initiator include benzoin and benzoin methyl ether. Examples of the benzophenone initiator include benzophenone and methyl o-benzoylbenzoate. Examples of the hydroxyalkylphenone initiator include 1-hydroxy-cyclohexyl-phenyl-ketone. Examples of the thioxanthone initiator include 2-isopropylthioxanthone and 2,4-dimethylthioxanthone. Examples of the amine initiator include triethanolamine and ethyl 4-dimethylbenzoate.
A photoinitiator may be used individually by 1 type and may use 2 or more types together.

[Other ingredients]
The pressure-sensitive adhesive composition of the present invention may contain other components than the components described above, if necessary. Other components include crosslinking catalysts, chelating agents, silane coupling agents, tackifiers, plasticizers, softeners, release aids, dyes, pigments, inorganic fillers, surfactants, UV absorbers, antioxidants and Examples thereof include metal corrosion inhibitors.
Examples of the peeling aid include a polymer (silicone oil) containing a structural unit derived from a monomer having a polyorganosiloxane skeleton.
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.
In addition, the adhesive composition of this invention shows the outstanding rework property even if it does not contain the polymer containing the structural unit derived from the monomer which has polyorganosiloxane frame | skeleton especially.

[Usage]
Since the pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer having a low relative dielectric constant and excellent reworkability and adhesive strength, for example, a touch panel equipped with various displays typified by liquid crystal displays and organic EL displays It can be suitably used for bonding each constituent member of the touch sensor with a device.
Specifically, it is preferably used when constituting a touch sensor by bonding constituent members such as a glass substrate, a transparent conductive film, a design film, and a polarizing plate.
Since the pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer with a low relative dielectric constant, even when the pressure-sensitive adhesive layer is thin, the capacitance inside the touch sensor is maintained at an appropriate value during operation of the touch sensor. Therefore, malfunction caused by capacitance can be suppressed.

[Adhesive sheet]
The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer including a crosslinked structure formed by a crosslinking 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 crosslinked structure in which the specific (meth) acrylic polymer and the specific oligomer contained in the above-described pressure-sensitive adhesive composition of the present invention are formed by a crosslinking agent. The pressure-sensitive adhesive layer has a low relative dielectric constant and excellent reworkability and adhesive strength.

  The pressure-sensitive adhesive sheet of the present invention may be a pressure-sensitive adhesive sheet having no base material (non-base material type), or a pressure-sensitive adhesive sheet having a base material (with a base material type). For example, from the viewpoint of visibility when applied to bonding of touch sensor constituent members, 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, the material of the base material includes a resin film, for example, a polyester film such as polyethylene terephthalate (PET).
Moreover, it is preferable that a base material is transparent.
The thickness of a base material is not specifically limited, For example, 5 micrometers-100 micrometers are preferable.

The exposed surface of the pressure-sensitive adhesive layer may be protected by a release film.
A release film will not be specifically limited if it can peel from an adhesive layer easily. Examples of the release film include a resin film (for example, a polyester film such as PET) that has been subjected to an easy release treatment using a release treatment agent on at least one surface.
Examples of the release treatment agent include fluorine-based resins, paraffin wax, silicone, and long-chain alkyl group compounds.
The release film protects the surface of the pressure-sensitive adhesive layer until the pressure-sensitive adhesive sheet is practically used, and is peeled off during use.

  The thickness of the pressure-sensitive adhesive layer is not particularly limited, and can be appropriately set according to the use, required performance, and the like. The thickness of the pressure-sensitive adhesive layer is preferably set in the range of 15 μm to 300 μm, for example, from the viewpoint of step following ability and the 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, from the viewpoints of workability, reworkability, and adhesive strength, and more preferably 45% by mass. % To 65% by mass is more preferable.
In the present specification, the gel fraction of the pressure-sensitive adhesive layer is a ratio of a solvent-insoluble content measured using ethyl acetate as an extraction solvent. Specifically, the measurement is performed according to the following (1) to (4).

-Measuring method of gel fraction-
(1) About 0.25 g of the adhesive layer is affixed to a 250-mesh wire mesh (100 mm × 100 mm) whose mass has been accurately measured with a precision balance. Then, the wire mesh is folded five times to obtain a sample. Thereafter, 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) A sample is taken out, washed with a small amount of ethyl acetate, and dried at 120 ° C. for 24 hours. Thereafter, the mass is accurately measured with a precision balance.
(4) The gel fraction is calculated by the following formula.
Gel fraction (mass%) = (Z−X) / (Y−X) × 100
Where X is the mass (g) of the wire mesh, Y is the mass (g) before immersion of the wire mesh with the adhesive layer attached, and Z is the mass (g) of the wire mesh with the adhesive layer attached after drying. is there.

The pressure-sensitive adhesive layer preferably has a low haze from the viewpoint of visibility when the pressure-sensitive adhesive sheet of the present invention is applied to bonding of a touch sensor constituent member. Specifically, the total light transmittance in the visible light wavelength region (JIS K 7361 (1997)) is preferably 85% or more, more preferably 90% or more.
The haze of the pressure-sensitive adhesive layer (JIS K 7136 (2000)) is preferably less than 2.0% from the viewpoint of visibility when the pressure-sensitive adhesive sheet of the present invention is applied to the bonding of the touch sensor constituent member. Less than 0% is more preferable, and less than 0.5% is still more preferable.

[Method for producing adhesive sheet]
The production method of 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.
Non-base type pressure-sensitive adhesive sheet is prepared by, for example, applying a pressure-sensitive adhesive composition to the release-treated surface of a release film, drying it, causing a crosslinking reaction to form a pressure-sensitive adhesive layer, and then separating another layer on this pressure-sensitive adhesive layer. It can be produced by stacking the films so that the release treatment surface is in contact.
The base material type pressure-sensitive adhesive sheet is obtained by, for example, applying a pressure-sensitive adhesive composition on both sides of a base material, causing a crosslinking reaction to form a pressure-sensitive adhesive layer, and then on the pressure-sensitive adhesive layer formed on both sides of the base material. Each can be produced by stacking the release films so that the release-treated surfaces are in contact with each other.
The substrate-type pressure-sensitive adhesive sheet is, for example, coated with a pressure-sensitive adhesive composition on the release-treated surface of a release film, dried, caused a crosslinking reaction to form a pressure-sensitive adhesive layer, and then provided with a release film. It can also be produced by a method in which the pressure-sensitive adhesive layer is stacked on both surfaces of the substrate.

  As a method for applying the pressure-sensitive adhesive composition to a release film, a substrate, etc., a known application method using a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, etc. Is mentioned.

[Touch sensor]
The touch sensor 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 sensor, a transparent conductive film, a design film, or the like is laminated by an adhesive layer and stacked (for example, transparent conductive film / adhesive layer / transparent conductive film / adhesive layer). / Design film).

  As described above, the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition of the present invention has a low relative dielectric constant and excellent reworkability and adhesive strength. In the touch sensor having such an adhesive layer, since the capacitance inside the touch sensor is maintained at an appropriate value during operation, malfunction due to the capacitance is suppressed. Moreover, since the crosslink density in the interface vicinity of an adhesive layer is high, it shows the outstanding rework property, and since the viscoelasticity and cohesion force in the whole adhesive layer are appropriate, it shows the outstanding adhesive force.

  The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention is also excellent in reworkability, pressure-sensitive adhesive strength, and processability. Touch panel-equipped devices equipped with a touch sensor having such a pressure-sensitive adhesive layer are difficult to peel off even when subjected to impacts such as dropping, and manufacturing problems such as the pressure-sensitive adhesive composition sticking out between bonded components Is unlikely to occur.

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

[Production of (meth) acrylic polymer]
[Production Example A-1]
In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser and a sequential dropping device, 147 parts by mass of ethyl acetate and 0.05 part by mass of 2,2′-azobis (2,4-dimethylvaleronitrile) were charged.
On the other hand, in another container, 300 parts by mass of 2-ethylhexyl methacrylate (2EHMA, alkyl methacrylate having a branched alkyl group having 8 carbon atoms) (50% by mass with respect to all structural units), n-butyl acrylate (n- BA) A single amount composed of 240 parts by mass (40% by mass with respect to all structural units) and 60 parts by mass (10% by mass with respect to all structural units) of 2-hydroxyethyl acrylate (2HEA, a monomer having a hydroxyl group) 600 parts by mass of body mixture was prepared. Of this monomer mixture, 150 parts by mass were charged into a reaction vessel, heated, and refluxed at reflux temperature for 20 minutes.
Subsequently, the remaining 450 parts by mass of the monomer mixture, 33 parts by mass of ethyl acetate, and 0.03 mass of 2,2′-azobis (2,4-dimethylvaleronitrile) were added to the reaction vessel under reflux temperature conditions. Were successively added dropwise over 90 minutes, and after completion of the dropwise addition, a polymerization reaction was further carried out over 90 minutes. After this polymerization reaction, a mixed solution of 15 parts by mass of ethyl acetate and 0.13 parts by mass of t-butyl peroxypivalate is successively added dropwise to the reaction vessel over 30 minutes. Upon completion, a (meth) acrylic polymer A-1 was produced.
The obtained (meth) acrylic polymer A-1 has a weight average molecular weight (Mw) of 450,000, a dispersity (Mw / Mn) of 6.1, and a glass transition temperature (Tg). -35 ° C. The weight average molecular weight (Mw), number average molecular weight (Mn), and glass transition temperature (Tg) were measured or calculated by the method described above.

[Production Examples A-2 to A-4, Comparative Production Examples a-1 to a-4]
(Meth) acrylic polymers A-2 to A-4 and a-1 to a-4 were prepared in the same manner as in Production Example A-1, except that the monomer composition was changed to the composition shown in Table 1. Manufactured.
Table 1 shows the weight average molecular weight (Mw) and glass transition temperature (Tg) of the obtained (meth) acrylic polymers A-2 to A-4 and a-1 to a-4.

The details of the monomer composition shown in Table 1 are as follows.
2EHMA: 2-ethylhexyl methacrylate (alkyl methacrylate having a branched alkyl group having 8 carbon atoms)
2EHA: 2-ethylhexyl acrylate (alkyl acrylate having a branched alkyl group having 8 carbon atoms)
IDMA: Isodecyl methacrylate (alkyl methacrylate having a branched alkyl group having 10 carbon atoms)
NBA: n-butyl acrylate (alkyl acrylate having a linear alkyl group with 4 carbon atoms)
NBMA: n-butyl methacrylate (alkyl methacrylate having a linear alkyl group with 4 carbon atoms)
2HEA: 2-hydroxyethyl acrylate (monomer having a hydroxyl group)
In addition, "-" described in Table 1 means that the corresponding component is not used.

[Production of (meth) acrylic oligomer]
[Production Example B-1]
In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser and a sequential dropping device, 28 parts by mass of ethyl acetate and 21 parts by mass of butyl acetate were added and heated, and maintained at the reflux temperature for 10 minutes. Subsequently, under reflux temperature conditions, 60 parts by mass of t-butyl acrylate (tBA) (60% by mass with respect to all structural units) and 40 parts by mass of 2-hydroxyethyl acrylate (2HEA, monomer having a hydroxyl group) (total 40 mass% with respect to the structural unit), 10 parts by mass of ethyl acetate and 10 parts by mass of dimethyl 2,2-azobis (2-methylpropionate) (trade name: V-601, manufactured by Wako Pure Chemical Industries, Ltd.) The monomer mixed solution consisting of was sequentially added dropwise over 180 minutes, and after completion of the addition, the reaction was further completed over 230 minutes to produce (meth) acrylic oligomer B-1.
The obtained (meth) acrylic oligomer B-1 has a solid content of 61% by mass, a weight average molecular weight (Mw) of 9,000, and a dispersity (Mw / Mn) of 2.0. And glass transition temperature (Tg) was 10 degreeC. The weight average molecular weight (Mw), number average molecular weight (Mn), and glass transition temperature (Tg) were measured or calculated by the method described above.

[Production Examples B-2 to B-9, Comparative Production Examples b-1 to b-3]
(Meth) acrylic oligomers B-2 to B-9 and b-1 to b-3 are produced in the same manner as in Production Example B-1, except that the monomer composition is changed to the composition shown in Table 2. did.
Table 2 shows the weight average molecular weights (Mw) and glass transition temperatures (Tg) of the obtained (meth) acrylic oligomers B-2 to B-9 and b-1 to b-3.

The details of the monomer composition shown in Table 2 are as follows.
TBA: t-butyl acrylate 2EHA: 2-ethylhexyl acrylate tBMA: t-butyl methacrylate 2HEA: 2-hydroxyethyl acrylate (monomer having a hydroxyl group)
AA: acrylic acid (monomer having an acidic group)
In addition, "-" of Table 2 means that the corresponding component is not used.

[Example 1]
-Preparation of adhesive composition-
A styrene polymer (trade name: Piccolastic A5, styrene homopolymer, weight average molecular weight: 500) manufactured by EASTMAN CHEMICAL was dissolved in ethyl acetate, and an ethyl acetate solution of the styrene polymer (solid content: 50% by mass) was obtained. Prepared.
1 part by mass of (meth) acrylic oligomer B-1 as a solid content and 100 parts by mass of (meth) acrylic polymer A-1 as a solid content, and an ethyl acetate solution of a styrene polymer (styrene type) 2 parts by mass of a polymer as a solid content) and 0.2 parts by mass of a cross-linking agent [trade name: Takenate (registered trademark) D-110N, manufactured by Mitsui Chemicals, Inc.] which is an aromatic polyisocyanate compound as a solid content The mixture was further diluted with ethyl acetate and mixed, and the pressure-sensitive adhesive of Example 1 containing (meth) acrylic polymer A-1, (meth) acrylic oligomer B-1, styrene polymer and crosslinking agent was added. An agent composition was prepared.

-Preparation of test samples-
The thickness of the pressure-sensitive adhesive layer after drying on the release-treated surface of a release film (trade name: Film Vina 100E, manufactured by Fujimori Kogyo Co., Ltd.) that has been easily peel-treated with a silicone-based release treatment. Was applied to form a coating layer. Thereafter, the obtained release film having the coating layer was dried at 100 ° C. for 2 minutes to form a layer on the release film. The surface from which this layer was exposed was bonded to a separately prepared release film (trade name: Film Vina 100E, manufactured by Fujimori Kogyo Co., Ltd.) to produce a non-base type pressure-sensitive adhesive sheet. Thereafter, curing was carried out for 4 days in an environment of a temperature of 23 ° C. and 50% RH to advance the crosslinking reaction, thereby obtaining a test sample having a pressure-sensitive adhesive layer containing a crosslinked structure.
The gel fraction of the produced test sample was 59.0% by mass. The gel fraction was measured by the method described above.

[Examples 2 to 17, Comparative Examples 1 to 10]
Except having changed into the composition shown in Table 3, it carried out similarly to Example 1, and prepared the adhesive composition, and produced the sample for a test.

The details of the crosslinking agent described in Table 3 are as follows.
XDI: m-xylylene diisocyanate (trade name: Takenate (registered trademark) D-110N, manufactured by Mitsui Chemicals, Inc., aromatic polyisocyanate compound)
TDI: Trimeryl adduct of trimethylolpropane and tolylene diisocyanate (trade name: Coronate (registered trademark) L, manufactured by Tosoh Corporation, aromatic polyisocyanate compound)

Moreover, the detail of the silicone oil of Table 3 is as follows.
Silicone oil: Side chain amino-modified silicone oil (trade name: KF-859, manufactured by Shin-Etsu Chemical Co., Ltd.)

[Example 18]
Viscoat # 335HP (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), which is an ethylenically unsaturated compound containing 100 parts by mass of the pressure-sensitive adhesive composition prepared in Example 2 as a solid content and four ethylenically unsaturated groups. Example 18 18 parts by weight of tetraethylene glycol diacrylate) and IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone) manufactured by BASF as a photopolymerization initiator were added and mixed as a solid content. Then, a test sample was prepared in the same manner as in Example 2.

[Evaluation]
About the obtained test samples of Examples 1 to 17 and Comparative Examples 1 to 10, the dielectric constant, reworkability, adhesive strength, compatibility and wet heat whitening were evaluated according to the following methods.
In addition, the adhesive strength of the test sample of Example 18 was evaluated.
The results are shown in Table 3.

1. Relative permittivity One release film of the produced test sample was peeled off and bonded to an electrolytic copper foil (thickness: 10 μm, NC-WC treated product, manufactured by Furukawa Electric Co., Ltd.). Thereafter, the other release film of the test sample was peeled off, and the other side of the test sample from which the other release film was peeled was bonded to the side of the adhesive layer exposed. The procedure for bonding the test samples was repeated until the pressure-sensitive adhesive layer had a thickness of 200 μm. When the pressure-sensitive adhesive layer had a thickness of 200 μm, the release film of the test sample bonded last was peeled off, and an electrolytic copper foil was bonded to the surface where the pressure-sensitive adhesive layer was exposed. The sample obtained by laminating the adhesive layer having a thickness of 200 μm between the two electrolytic copper foils thus obtained was cut into a size of 50 mm × 50 mm to obtain a sample for measuring the relative permittivity, and the relative permittivity Was measured.
The relative dielectric constant was measured under the following conditions using a material analyzer 4291B manufactured by Agilent Technologies.

-Condition-
Measuring jig: Dielectric Test Fixture 16453A (manufactured by Agilent Technologies)
Measurement frequency: 100 kHz

  The relative dielectric constant was evaluated according to the following criteria. In the following evaluation criteria, A and B are levels having no practical problem, and C is a level having a practical problem.

-Evaluation criteria-
A: The relative dielectric constant is 3.5 or less.
B: The relative dielectric constant exceeds 3.5 and is 4.0 or less.
C: The relative dielectric constant exceeds 4.0.

2. Reworkability One release film of the produced test sample was peeled, and the surface on which the pressure-sensitive adhesive layer was exposed was bonded to optical glass (manufactured by Matsunami Glass Industrial Co., Ltd., optical soda glass). This was left for 1 hour under conditions of 80 ° C. and 0% RH, then peeled off at room temperature (23 ° C.) at a rate of about 1 m / min, and the residue of the adhesive layer on the optical glass was visually observed. Reworkability was evaluated based on the above criteria. Note that the smaller the adhesive layer remains on the adherend, the better. The evaluation criteria A and B in the following evaluation criteria are levels that have no practical problems, and C is a level that has practical problems.

-Evaluation criteria-
A: No residual adhesive layer is observed.
B: The adhesive layer remains in 0.1% or more and less than 5% of the peeled area.
C: The adhesive layer remains in 5% or more of the peeled area.

3. Adhesive strength Polyethylene terephthalate film (trade name: A-) in which one release film of the test samples prepared in Examples 1 to 17 and Comparative Examples 1 to 10 was peeled off and the surface on which the pressure-sensitive adhesive layer was exposed was subjected to easy adhesion treatment 4100, thickness: 100 μm, manufactured by Toyobo Co., Ltd.). After cutting the test sample on which this polyethylene terephthalate film was bonded to a size of 25 mm × 150 mm, the other release film was peeled off, and the surface on which the adhesive layer was exposed was optical glass (Matsunami Glass Industry Co., Ltd., An optical soda glass) was stacked on the plate, and a pressure-sensitive adhesive layer and a surface of the optical glass were pressed using a rubber roller having a weight of 2 kg to make a sample for evaluating adhesive strength.
Further, the test sample prepared in Example 18 was pressure-bonded so that the pressure-sensitive adhesive layer and the surface of the optical glass were in contact with each other using a rubber roller having a weight of 2 kg according to the above procedure, and then further 500 mJ / cm ² . The sample was irradiated with ultraviolet rays under the conditions to make an adhesive strength evaluation sample.
After these samples for evaluating adhesive strength were allowed to stand in an environment of 23 ° C. and 50% RH for 24 hours, the adhesive strength at 180 ° peeling (unit: N / 25 mm) was measured at a peeling speed of 300 mm / min. The adhesive strength was evaluated. In addition, it is so preferable that adhesive force is large. In the following evaluation criteria, A and B are levels having no practical problem, and C is a level having a practical problem.

-Evaluation criteria-
A: Adhesive strength is 20 N / 25 mm or more.
B: Adhesive strength is 15 N / 25 mm or more and less than 20 N / 25 mm.
C: Adhesive strength is less than 15 N / 25 mm.

4). Compatibility The produced test sample was cut into a size of 80 mm × 60 mm. Remove one release film of the test sample, and stack the exposed surface of the adhesive layer on a 1.8 mm thick glass plate (optical soda glass, size: 250 mm × 200 mm, manufactured by Matsunami Glass Industry Co., Ltd.) The sample was subjected to pressure bonding using a laminating machine to obtain a compatibility test sample A.
On the other hand, in each example and each comparative example, a compatibility test sample B was prepared in the same manner as in each example and each comparative example, except that no component other than the (meth) acrylic oligomer was included. The compatibility test sample A in Comparative Example 10 had a composition containing silicone oil, and the compatibility test sample B had a composition not containing silicone oil.
About each of the compatibility test sample A and the compatibility test sample B, haze (unit:%) was measured using NDH 5000SP of Nippon Denshoku Industries Co., Ltd.
A value (ΔH) obtained by subtracting the value of “the haze of the compatibility test sample A” from the value of the “haze of the compatibility test sample B” was determined, and the compatibility was evaluated according to the following criteria. In addition, it shows that compatibility is excellent, so that the value of (DELTA) H is small.

-Evaluation criteria-
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.

5). Wet heat whitening The produced test sample was cut into a size of 80 mm × 60 mm. Remove one release film of the test sample, and stack the exposed surface of the adhesive layer on a 1.8 mm thick glass plate (optical soda glass, size: 250 mm × 200 mm, manufactured by Matsunami Glass Industry Co., Ltd.) The sample was pressure-bonded using a laminating machine to obtain a wet heat whitening test sample.
The haze (unit:%) of this wet heat whitening test sample (hereinafter referred to as “haze before test introduction”) was measured using NDH 5000SP manufactured by Nippon Denshoku Industries Co., Ltd.
Next, the wet heat whitening test sample was allowed to stand for 168 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. (Hereinafter referred to as “haze after test input”) was measured.
A value (ΔH) obtained by subtracting the value of “haze before test input” from the value of “haze after test input” was determined, and the wet heat whitening property was evaluated according to the following evaluation criteria. In addition, it shows that wet heat whitening property is excellent, so that (DELTA) H is small.

-Evaluation criteria for wet heat whitening-
A: ΔH is less than 1.0.
B: ΔH is 1.0 or more and less than 2.0.
C: ΔH is 2.0 or more and less than 4.0.
D: ΔH is 4.0 or more.

A structural unit derived from an alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms and a structural unit derived from a monomer having a hydroxyl group, and having a glass transition temperature of −55 ° C. or higher and −20 ° C. or lower. (Meth) acrylic polymer having a (meth) acrylic polymer and a weight average molecular weight of 3,500 to 100,000, including a structural unit derived from a monomer having a hydroxyl group and having a glass transition temperature of −50 ° C. or higher. The pressure-sensitive adhesive composition of Examples 1 to 17, comprising an oligomer and a crosslinking agent, wherein the (meth) acrylic oligomer is 0.1 to 10 parts by mass with respect to 100 parts by mass of the (meth) acrylic polymer. According to this, it was possible to form an adhesive layer having a low relative dielectric constant and excellent reworkability and adhesive strength.
Moreover, the adhesive strength after the ultraviolet irradiation of the test sample produced in Example 18 is 22.0 N / 25 mm, which is higher than 20.0 N / 25 mm which is the adhesive strength of the test sample produced in Example 2. Indicated. In addition, when the test sample produced in Example 18 and the test sample produced in Example 2 were visually confirmed, the haze was substantially the same.
Moreover, according to the adhesive composition of Examples 1-16, the adhesive layer which is excellent in compatibility and wet heat whitening property was able to be formed.
According to the comparison between Example 2 and Example 17, it was possible to improve the wet heat whitening property of the pressure-sensitive adhesive layer without increasing the relative dielectric constant by adding the styrene-based polymer.

In the test samples of Example 1 and Example 2, the reworkability evaluation is A. When the test samples of Example 1 and Example 2 were used and the degree of residue of the pressure-sensitive adhesive layer was compared at a higher speed, more specifically at a high speed of about 20 m / min, the test sample of Example 1 was compared. In the sample, no adhesive layer remained even after peeling under high speed conditions. On the other hand, in the test sample of Example 2, the adhesive layer remained at 0.1% or more and less than 5% of the area peeled at a high speed.
Therefore, it turns out that the adhesive layer formed using the adhesive composition of Example 1 is remarkably excellent in rework property.

According to the comparison between Comparative Examples 1 and 2 and Example 2, the pressure-sensitive adhesive containing a (meth) acrylic polymer not containing a structural unit derived from an alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms It can be seen that the pressure-sensitive adhesive layer formed using the composition has a high relative dielectric constant.
According to the comparison between Comparative Example 3 and Example 2, the pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition containing the (meth) acrylic polymer having a glass transition temperature of less than −55 ° C. has a relative dielectric constant. Is high.
According to the comparison between Comparative Example 4 and Example 2, the pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition containing the (meth) acrylic polymer having a glass transition temperature exceeding −20 ° C. has reworkability. I understand that it is inferior.
According to the comparison between Comparative Example 5 and Example 2, the pressure-sensitive adhesive layer formed using a pressure-sensitive adhesive composition containing a (meth) acrylic oligomer not containing a structural unit derived from a monomer having a hydroxyl group is It can be seen that the reworkability is inferior.
According to the comparison between Comparative Example 6 and Example 2, the pressure-sensitive adhesive layer formed using a pressure-sensitive adhesive composition containing a (meth) acrylic oligomer having a weight average molecular weight exceeding 100,000 has poor reworkability. And since it is inferior in compatibility, it is unsuitable for bonding of a display and a touch sensor, for example.
According to the comparison between Comparative Example 7 and Example 2, the pressure-sensitive adhesive layer formed using a pressure-sensitive adhesive composition containing a (meth) acrylic oligomer having a glass transition temperature of less than −50 ° C. is inferior in reworkability. I understand that.
According to the comparison between Comparative Example 8 and Example 2, it was formed using a pressure-sensitive adhesive composition containing less than 0.1 part by weight of (meth) acrylic oligomer with respect to 100 parts by weight of (meth) acrylic polymer. It turns out that an adhesive layer is inferior in rework property.
According to the comparison between Comparative Example 9 and Example 2, a pressure-sensitive adhesive formed using a pressure-sensitive adhesive composition containing more than 10 parts by weight of (meth) acrylic oligomer with respect to 100 parts by weight of (meth) acrylic polymer. It can be seen that the agent layer has a high relative dielectric constant and is inferior in adhesive strength and compatibility.
According to the comparison between Comparative Example 10 and Example 2, a pressure-sensitive adhesive containing a polymer (silicone oil) containing no structural component derived from a monomer having a polyorganosiloxane skeleton without containing a (meth) acrylic oligomer. It turns out that the adhesive layer formed using the composition is inferior in adhesive force.

Claims (9)

A structural unit (A) derived from an alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms and a structural unit (B) derived from a monomer having a hydroxyl group, and having a glass transition temperature of −55 ° C. (Meth) acrylic polymer having a temperature of −20 ° C. or lower,
A (meth) acrylic oligomer having a weight average molecular weight of 3,500 to 100,000, including a structural unit derived from a monomer having a hydroxyl group, and having a glass transition temperature of −50 ° C. or higher;
A crosslinking agent,
The adhesive composition whose content of the said (meth) acrylic-type oligomer is 0.1 mass part-10 mass parts with respect to 100 mass parts of said (meth) acrylic-type polymers.   The content rate of the structural unit derived from the monomer having a hydroxyl group in the (meth) acrylic oligomer is 10% by mass or more and 60% by mass or less with respect to all the structural units of the (meth) acrylic oligomer. 2. The pressure-sensitive adhesive composition according to 1.   Furthermore, the adhesive composition of Claim 1 or Claim 2 containing a styrene-type polymer.   The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the (meth) acrylic polymer further includes a structural unit derived from an alkyl acrylate.   The pressure-sensitive adhesive composition according to claim 4, wherein the alkyl acrylate is n-butyl acrylate.   The pressure-sensitive adhesive composition according to claim 4, wherein the alkyl acrylate is 2-ethylhexyl acrylate.   The pressure-sensitive adhesive composition according to any one of claims 1 to 6, further comprising an ethylenically unsaturated compound containing one or more ethylenically unsaturated groups.   The pressure-sensitive adhesive composition according to any one of claims 1 to 7, which is used for bonding a constituent member of a touch sensor.   The adhesive sheet which has an adhesive layer formed from the adhesive composition of any one of Claims 1-8.