WO2023054581A1

WO2023054581A1 - Adhesive composition, adhesive, adhesive sheet, adhesive sheet with release film, laminate for image display device, curved image display device, adhesive composition for curved optical member

Info

Publication number: WO2023054581A1
Application number: PCT/JP2022/036429
Authority: WO
Inventors: 鉄也浅野; 一樹野原; 遼太島中
Original assignee: 三菱ケミカル株式会社
Priority date: 2021-09-30
Filing date: 2022-09-29
Publication date: 2023-04-06
Also published as: TW202323487A; KR20240065251A

Abstract

The present invention relates to the useful improvement of an adhesive composition that can be used for multistage curing and to the use thereof.　The adhesive composition contains an acrylic resin (A) and a photoinitiator (B). The acrylic resin (A) is a polymerization product of a copolymer component (a). The copolymer component (a) contains an alkyl acrylate (a1) that has a glass transition temperature of -30 to 50°C when a homopolymer is formed and an alkyl methacrylate (a2) that has a glass transition temperature of -10 to 120°C when a homopolymer is formed. The total content of alkyl acrylate (a1) and alkyl methacrylate (a2) is 5 wt% or more relative to 100 wt% of copolymer component (a). Application examples of the adhesive composition relate to an adhesive, an adhesive sheet, an adhesive sheet with a release film, a laminate for an image display device, a curved image display device, and an adhesive composition for a curved optical member.

Description

Adhesive composition, adhesive, adhesive sheet, adhesive sheet with release film, laminate for image display device, curved image display device, adhesive composition for curved optical member

The present invention mainly relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive, a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive sheet with a release film, a laminate for an image display device, a curved image display device, and a pressure-sensitive adhesive composition for a curved optical member.
This application is based on Japanese Patent Application No. 2021-160337 filed with the Japan Patent Office on September 30, 2021, Japanese Patent Application No. 2021-160485 filed with the Japan Patent Office on September 30, 2021 and September 2021. A priority is claimed based on Japanese Patent Application No. 2021-160488 filed with the Japan Patent Office on May 30, and the contents thereof are incorporated herein.

In recent years, touch panels that combine a display and a position input device are widely used in mobile devices such as televisions, personal computer monitors, notebook computers, mobile phones, smart phones, and tablet terminals. Among them, the capacitive touch panel is commonly used.
A touch panel is usually composed of an organic EL or liquid crystal display, a transparent conductive film substrate (ITO substrate), and a protective film (protective glass). A transparent adhesive sheet is used to bond these touch panel members together.

Since it is necessary to bond members of various shapes to the transparent pressure-sensitive adhesive sheet, the pressure-sensitive adhesive for the transparent pressure-sensitive adhesive sheet is bonded together in a low crosslinked state before being completely cured. Therefore, sufficient adhesive physical properties are required in the process until the low-crosslinking adhesive layer is completely cured.
For example, when the transparent adhesive sheet is attached to a member having a complicated shape, it is likely that the transparent adhesive sheet sticks to an area other than the intended location, resulting in an attachment failure. Therefore, there is a demand for a transparent pressure-sensitive adhesive sheet with low tackiness.
In addition, in order to fix members having complicated shapes to each other, it is required to suppress peeling of the transparent adhesive sheet from the member under stress. Therefore, there is a demand for a transparent pressure-sensitive adhesive sheet having high constant load holding power even in a low cross-linked state.

In addition, the adhesive layer after complete curing is required to have excellent performance not only in terms of adhesive physical properties such as normal adhesive strength, but also in terms of reliability when bonding various materials such as polarizing plates and glass. For example, in order to obtain excellent durability after complete curing, the degree of cross-linking is required to be as low as possible until it is attached to an adherend. It is also required to efficiently increase the degree of cross-linking at the time of complete curing.

Therefore, it is expected that the adhesive layer can be sufficiently adhered to the adherend by laminating the adhesive layer to the adherend in a low crosslinked state. Further, when the pressure-sensitive adhesive sheet is completely cured in a state of being laminated to an adherend in a low-crosslinking state, the pressure-sensitive adhesive sheet has a high degree of cross-linking, which is expected to improve durability.
Generally, in the primary curing, the resin is cured by thermal crosslinking or by irradiation with active energy rays, and in the complete curing, it is cured by crosslinking by irradiation with active energy rays. As a pressure-sensitive adhesive sheet using such a multi-stage curing pressure-sensitive adhesive, for example, the pressure-sensitive adhesive sheets described in Patent Documents 1 to 3 can be mentioned.

Patent Document 1 discloses that a solvent-based pressure-sensitive adhesive made of an acrylic resin further uses an organic solvent that is easily volatile under general drying conditions, and is blended with a specific proportion of an ethylenically unsaturated monomer that is difficult to evaporate. It is
In addition, in Patent Document 2, in order to form a three-dimensional network structure of a solvent-type acrylic acid ester-based pressure-sensitive adhesive without using a cross-linking agent, a hydrogen abstraction type photoinitiator is used, and light irradiation is performed after the coating and drying process. It is disclosed that the aging process is omitted by doing so.
Furthermore, Patent Literature 3 discloses that a pressure-sensitive adhesive with high level conformability and blister resistance can be obtained by using an acrylic resin with a high glass transition temperature.

JP 2012-111939 A JP 2017-210542 A WO2017/022770

However, none of Patent Literatures 1 to 3 take into account adhesive physical properties in a low-crosslinking state during primary curing. Therefore, there is room for improvement since adhesive physical properties may be insufficient in a low-crosslinking state during primary curing. In particular, in applications where the pressure-sensitive adhesive sheet after primary curing is attached to an adherend having a complex shape to which a strong stress is applied, defects such as peeling of the pressure-sensitive adhesive sheet occur after the attachment.

A first aspect of the present invention is mainly a pressure-sensitive adhesive composition that can be used for multistage curing, in which excellent adhesive physical properties are obtained in a low cross-linked state after primary curing, and excellent adhesive properties are obtained even after complete curing. It is an object of the present invention to provide a pressure-sensitive adhesive composition capable of obtaining good pressure-sensitive adhesive physical properties and reliability; a pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition; and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive.

The second aspect of the present invention is mainly a pressure-sensitive adhesive composition that can be used for multistage curing, in which excellent adhesive physical properties are obtained in a low cross-linked state after primary curing, and excellent adhesive properties are obtained even after complete curing. It is an object of the present invention to provide a pressure-sensitive adhesive composition capable of obtaining good pressure-sensitive adhesive physical properties and reliability; a pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition; and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive.

A third aspect of the present invention is a pressure-sensitive adhesive composition that can be used mainly for multistage curing, and has excellent adhesion even when it is attached to an adherend having a complicated shape that is subjected to strong stress. An object of the present invention is to provide a pressure-sensitive adhesive composition from which a pressure-sensitive adhesive sheet is obtained; a pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition; and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive.

As a result of intensive studies by the present inventors in order to solve the problems related to the above first aspect, a pressure-sensitive adhesive composition containing an acrylic resin obtained using a copolymer component of a specific composition and a specific photoinitiator It is possible to achieve excellent adhesive physical properties such as low tackiness and high constant load holding power even in a low cross-linked state after primary curing, as well as excellent adhesive physical properties and reliability after complete curing. I found

A first aspect of the present invention contains an acrylic resin (A) and a photoinitiator (B); the acrylic resin (A) is a polymerization product of the following copolymerization component (a) Yes; the glass transition temperature based on the dynamic viscoelasticity of the acrylic resin (A) is −10° C. or higher; A pressure-sensitive adhesive composition containing an internal hydrogen abstraction type photoinitiator (b2).

The copolymer component (a) according to the first aspect includes an alkyl acrylate (a1) having a glass transition temperature of −30 to 50° C. when forming a homopolymer, and an alkyl acrylate (a1) having a glass transition temperature when forming a homopolymer. containing at least an alkyl methacrylate (a2) with a temperature of −10 to 120° C. and a hydroxyl group-containing monomer (a3), wherein the weight ratio of the alkyl acrylate (a1) to the alkyl methacrylate (a2) is 5/95 to 55/45; and the total content of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is 30 to 70% by weight based on the copolymerization component (a).

In order to solve the above-described problems related to the second aspect, the present inventors conducted intensive studies and found that an adhesive composition containing an acrylic resin obtained by using a copolymer component of a specific composition and a specific photoinitiator It is possible to achieve excellent adhesive physical properties such as low tackiness and high constant load holding power even in a low cross-linked state after primary curing, as well as excellent adhesive physical properties and reliability after complete curing. I found

A second aspect of the present invention contains an acrylic resin (A) and a photoinitiator (B); the acrylic resin (A) is a polymerization product of the following copolymerization component (a) Yes; the acrylic resin (A) has a glass transition temperature based on dynamic viscoelasticity of −10° C. or higher; and the photoinitiator (B) contains an intramolecular hydrogen abstraction type photoinitiator (b1) , is an adhesive composition.

The copolymer component (a) according to the second aspect is an alkyl (meth)acrylate (a1) having an alkyl group having 12 or less carbon atoms and having a homopolymer glass transition temperature of -20 to 120°C. and; a hydroxyalkyl monomer (a2) containing an alkyl chain, a hydroxyl group and an ethylenically unsaturated group; 30% by weight or more with respect to 100% by weight; the content of the hydroxyalkyl monomer (a2) is 0.1% by weight or more with respect to 100% by weight of the copolymerization component (a); The average carbon number of the alkyl chain of the hydroxyalkyl monomer (a2) in (a) is 2.1 or more.

In order to solve the above-mentioned problems related to the third aspect, the present inventors conducted intensive studies and found that an adhesive composition containing an acrylic resin obtained using a copolymer component of a specific composition and a specific photoinitiator By using a material, it is possible to obtain a pressure-sensitive adhesive sheet that can adhere to complex-shaped adherends that are subject to stress even at the time of primary curing without peeling off, and the pressure-sensitive adhesive sheet that exhibits excellent durability after complete curing. is obtained.

A third aspect of the present invention contains an acrylic resin (A) and a photoinitiator (B); the acrylic resin (A) has a homopolymer glass transition temperature of −30° C. or higher. It is a polymerization product of a copolymer component (a) containing a branched alkyl (meth)acrylate (a1); and the acrylic resin (A) has a glass transition temperature based on dynamic viscoelasticity of −10° C. or higher. the weight average molecular weight of the acrylic resin (A) is 400,000 or less; and the photoinitiator (B) is an intramolecular hydrogen abstraction photoinitiator (b1) and an intermolecular hydrogen abstraction photoinitiator. A pressure-sensitive adhesive composition containing (b2).

According to the first aspect of the present invention, a pressure-sensitive adhesive composition that can be used for multistage curing, in which excellent adhesive physical properties are obtained in a low cross-linked state after primary curing, and excellent adhesive properties are obtained even after complete curing. Provided are a pressure-sensitive adhesive composition that provides excellent pressure-sensitive adhesive physical properties and reliability; a pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition; and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive.

According to the second aspect of the present invention, a pressure-sensitive adhesive composition that can be used for multi-stage curing, in which excellent adhesive physical properties are obtained in a low cross-linked state after primary curing, and excellent adhesive properties are obtained even after complete curing. Provided are a pressure-sensitive adhesive composition that provides excellent pressure-sensitive adhesive physical properties and reliability; a pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition; and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive.

According to the third aspect of the present invention, a pressure-sensitive adhesive composition that can be used for multi-stage curing and has excellent adhesion even when it is attached to an adherend having a complex shape that is subjected to strong stress. Provided are a pressure-sensitive adhesive composition from which a pressure-sensitive adhesive sheet is obtained; a pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition; and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive.

The meanings of the following terms used in this specification are shown below.
"(Meth)acryl" means acryl or methacryl.
"(Meth)acryloyl" means acryloyl or methacryloyl.
"(Meth)acrylate" means acrylate or methacrylate.
"Acrylic resin" is a resin obtained by polymerizing a monomer component containing at least one (meth)acrylic monomer.
"Sheet" is a term that conceptually includes sheets, films, and tapes.
"Homopolymer" means a homopolymer of a monomer.
"-" indicating a numerical range means that the numerical values before and after it are included as lower and upper limits.

[First aspect]
Embodiments of the first aspect of the present invention are described in detail below, but are disclosed as representative examples of preferred embodiments.

<Adhesive composition>
The pressure-sensitive adhesive composition according to the first aspect contains an acrylic resin (A) and a photoinitiator (B). The pressure-sensitive adhesive composition according to the first aspect comprises an acrylic resin (A), a photoinitiator (B), a cross-linking agent (C), a silane coupling agent (D), a carbodiimide compound (E), Other optional components may be further contained as necessary. Each component will be described in order below.

(Acrylic resin (A))
The acrylic resin (A) according to the first aspect is a polymerization product of a specific copolymer component (a). Copolymer component (a) is a general term for monomer components having a polymerizable double bond. The copolymerization component (a) does not contain a polymerization initiator and a polymerization solvent.

The specific copolymer component (a) according to the first aspect includes an alkyl acrylate (a1) having a glass transition temperature of -30 to 50 ° C. when forming a homopolymer, and a glass transition temperature when forming a homopolymer. It contains at least an alkyl methacrylate (a2) having a temperature of -10 to 120°C and a hydroxyl group-containing monomer (a3). The copolymer component (a) according to the first aspect comprises an alkyl acrylate (a1) having a glass transition temperature of −27 to 50° C. and an alkyl methacrylate having a glass transition temperature of 0 to 120° C. when forming a homopolymer. (a2) and an ethylenically unsaturated monomer (a4) other than the hydroxyl group-containing monomer (a3) may be further contained as necessary.

[Alkyl acrylate (a1)]
The glass transition temperature (hereinafter referred to as “Tg”) of the homopolymer of the alkyl acrylate (a1) according to the first aspect is −30 to 50° C., preferably −27 to 45° C., more preferably − 10 to 43°C, more preferably -5 to 10°C. When the Tg is within the range, the effects of the first aspect of the present invention are obtained.

A homopolymer of alkyl acrylate (a1) is a homopolymer of alkyl acrylate (a1). As the Tg of the homopolymer of alkyl acrylate (a1), a standard analytical value described in Wiley publication "POLYMER HANDBOOK" or the like can be used.

Examples of the alkyl acrylate (a1) according to the first aspect include methyl acrylate (Tg: 8°C), ethyl acrylate (Tg: -22°C), isobutyl acrylate (Tg: -26°C), tert-butyl acrylate ( Tg: 41°C), cyclohexyl acrylate (Tg: 15°C), and the like. Among them, methyl acrylate is preferable from the viewpoint of adhesive physical properties.
Alkyl acrylate (a1) may be used alone or in combination of two or more.

[Alkyl methacrylate (a2)]
The Tg of the homopolymer of alkyl methacrylate (a2) according to the first aspect is -10 to 120°C, preferably 0 to 110°C, more preferably 20 to 105°C, still more preferably 40 to 70°C. . When the Tg is within the range, the effects of the first aspect of the present invention are obtained.
The homopolymer of alkyl methacrylate (a2) according to the first aspect is a homopolymer of alkyl methacrylate (a2). As the Tg of the homopolymer of alkyl methacrylate (a2), a standard analytical value described in "POLYMER HANDBOOK" published by Wiley, etc. can be adopted.

Examples of the alkyl methacrylate (a2) according to the first aspect include methyl methacrylate (Tg: 105°C), ethyl methacrylate (Tg: 65°C), n-butyl methacrylate (Tg: 20°C), isobutyl methacrylate (Tg: 48° C.), cyclohexyl methacrylate (Tg: 66° C.), tert-butyl methacrylate (Tg: 107° C.), and the like.
One alkyl methacrylate (a2) may be used alone, or two or more thereof may be used in combination.
Among them, methyl methacrylate, ethyl methacrylate and isobutyl methacrylate are preferred.

[Hydroxyl group-containing monomer (a3)]
The hydroxyl group-containing monomer (a3) according to the first aspect contains one or more hydroxyl groups and an ethylenically unsaturated group. Examples of the hydroxyl group-containing monomer (a3) include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxy hydroxyl group-containing alkyl (meth)acrylate such as octyl (meth)acrylate;
caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; oxyalkylene-modified monomers such as polyethylene glycol mono(meth)acrylate and polybutylene glycol mono(meth)acrylate;
2-acryloyloxyethyl-2-hydroxyethyl phthalic acid, N-methylol (meth)acrylamide, hydroxyethyl acrylamide and other primary hydroxyl group-containing monomers;
Secondary hydroxyl group-containing monomers such as 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-chloro 2-hydroxypropyl (meth) acrylate;
Tertiary hydroxyl group-containing monomers such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate;
is mentioned.

Among them, primary hydroxyl group-containing alkyl (meth) acrylate is preferable in that it can be cured efficiently at the time of complete curing, and 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate can be used together It is particularly preferred to use butyl (meth)acrylate alone.

[Ethylenically unsaturated monomer (a4)]
In the first embodiment, the copolymerization component (a) may optionally further contain a copolymerizable ethylenically unsaturated monomer (a4) other than the monomers (a1) to (a3). .
Other copolymerizable ethylenically unsaturated monomers (a4) include, for example, alkyl (meth)acrylates such as n-butyl acrylate and 2-ethylhexyl (meth)acrylate (provided that alkyl acrylate (a1) and alkyl methacrylate ( except for a2));
Phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenyldiethylene glycol (meth) acrylate, phenoxy polyethylene glycol (meth) acrylate, phenoxy polyethylene glycol-polypropylene glycol-(meth) acrylate, orthophenylphenoxyethyl Aromatic ring-containing monomers such as (meth)acrylates and nonylphenol ethylene oxide adduct (meth)acrylates;
Alicyclic-containing monomers such as cyclohexyloxyalkyl (meth)acrylate, tert-butylcyclohexyloxyethyl (meth)acrylate, isobornyl methacrylate, dicyclopentanyl (meth)acrylate;
2-Methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 2-butoxyethyl (meth) acrylate, 2-butoxydiethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) Acrylates, methoxytriethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, octoxypolyethyleneglycol-polypropyleneglycol mono(meth)acrylate, lauroxy Ether chain-containing monomers such as polyethylene glycol mono (meth) acrylate and stearoxy polyethylene glycol mono (meth) acrylate;
acrylic acid dimers such as (meth)acrylic acid and β-carboxyethyl acrylate;
Carboxy group-containing monomers such as crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, N-glycolic acid, cinnamic acid;
(Meth)acrylamide, N-(n-butoxyalkyl)(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dimethylaminoalkyl(meth)acrylamide, etc. The amide group-containing monomer of;
benzophenone-containing monomers such as 4-(meth)acryloyloxybenzophenone;
Acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinylpyridine, vinylpyrrolidone, dialkyl itaconate, dialkyl fumarate Ester, allyl alcohol, acryl chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethyl allyl vinyl ketone and the like.
The ethylenically unsaturated monomers (a4) may be used alone or in combination of two or more.

Examples of ethylenically unsaturated monomers having two or more ethylenically unsaturated groups include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene Glycol di(meth)acrylate, divinylbenzene and the like can also be used in combination.

[Composition of the copolymer component (a) according to the first aspect]
In the first aspect, the content of the alkyl acrylate (a1) is 5% by weight or more, preferably 5 to 45% by weight, more preferably 10 to 40% by weight, relative to the copolymer component (a). , particularly preferably 12 to 35% by weight, particularly preferably 15 to 30% by weight.
If the content is too small, the adhesive properties in the primary cured state tend to deteriorate. If the content is too large, adhesive physical properties after complete curing tend to deteriorate.

In the first aspect, the content of the alkyl methacrylate (a2) is 5% by weight or more, preferably 10 to 60% by weight, more preferably 15 to 55% by weight, particularly It is preferably 20 to 45% by weight.
If the content is too small, the adhesive properties in the primary cured state tend to deteriorate. If the content is too large, the adhesive physical properties after complete curing tend to deteriorate.

In the copolymer component (a) according to the first aspect, the content ratio (a1/a2) of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is 5/95 to 55/45 by weight, preferably 15. /85 to 50/50, particularly preferably 20/80 to 40/60.

In the first aspect, the total content of alkyl acrylate (a1) and alkyl methacrylate (a2) is preferably 30 to 70% by weight, more preferably 35 to 65% by weight, relative to copolymerization component (a). %, particularly preferably 40 to 60% by weight.
If the total content of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is within the above numerical range, it is preferable because adhesive physical properties in a low crosslinked state in the primary cured state will be good.

In the first aspect, the content of the hydroxyl group-containing monomer (a3) is more preferably 5-30% by weight, even more preferably 10-25% by weight, and particularly preferably 15-20% by weight. If the content of the hydroxyl group-containing monomer (a3) is too small, the moist heat resistance after complete curing tends to decrease. If the content of the hydroxyl group-containing monomer (a3) is too high, the adhesive physical properties after complete curing tend to deteriorate.

In the copolymerization component (a) according to the first aspect, the total content of the alkyl acrylate (a1) and the alkyl methacrylate (a2) and the content ratio (a1+a2)/(a3) of the hydroxyl group-containing monomer (a3) is the weight ratio 95/5 to 50/50 is preferred, 85/15 to 70/30 is more preferred, and 80/20 to 75/25 is particularly preferred. When the content ratio (a1+a2)/(a3) is within the above numerical range, the adhesive physical properties in the primary cured state are excellent.

When the copolymerization component (a) according to the first aspect contains the ethylenically unsaturated monomer (a4), the content of the ethylenically unsaturated monomer (a4) is relative to 100% by weight of the copolymerization component (a) is usually 50% by weight or less, preferably 45% by weight or less, more preferably 40% by weight or less. If the content of the ethylenically unsaturated monomer (a4) is too high, the adhesion property tends to be lowered when low crosslinking is achieved.

In the first aspect, the acrylic resin (A) comprises a structural unit based on the alkyl acrylate (a1), a structural unit based on the alkyl methacrylate (a2), and a structural unit based on the hydroxyl group-containing monomer (a3). It can also be said that it is a polymer. In this case, the acrylic resin (A) includes structural units based on the alkyl acrylate (a1), structural units based on the alkyl methacrylate (a2), structural units based on the hydroxyl group-containing monomer (a3), and ethylenic It may further have a structural unit based on the unsaturated monomer (a4), if necessary. At this time, the ratio of structural units based on each monomer can be determined according to the composition of the copolymer component (a), and the preferred embodiment is also the same.

The glass transition temperature based on the dynamic viscoelasticity of the acrylic resin (A) according to the first aspect is −10° C. or higher, preferably −5 to 20° C., more preferably 0 to 15° C., particularly preferably 2 ~13°C. If the glass transition temperature based on the dynamic viscoelasticity of the acrylic resin (A) is too high, there is a tendency for the pressure-sensitive adhesive layer to be less conformable to irregularities and less adhesive, resulting in a decrease in adhesive force. If the glass transition temperature based on the dynamic viscoelasticity of the acrylic resin (A) is too low, there is a tendency for the adhesive physical properties at the time of low crosslinking to deteriorate.

The glass transition temperature based on dynamic viscoelasticity is obtained by the following measuring method.
An acrylic resin solution containing only the acrylic resin (A) according to the first embodiment and the organic solvent is prepared by adding an appropriate organic solvent. After adjusting the concentration of the acrylic resin solution, it is coated on a release sheet so that the thickness after drying becomes 50 μm. After that, the organic solvent is removed by drying by heat treatment or the like at 90 to 105 ° C. for 5 to 10 minutes, and then this is attached to a release sheet, and an acrylic resin containing 99% or more of the acrylic resin (A) A resin sheet is produced. After that, a plurality of acrylic resin sheets are laminated to produce an acrylic resin sheet having a thickness of about 800 μm.
The dynamic viscoelasticity of the produced sheet was measured under the following conditions, and the temperature at which the loss tangent (loss elastic modulus G''/storage elastic modulus G' = tan δ) was maximized was read, based on the dynamic viscoelasticity. It is defined as the glass transition temperature of the acrylic resin (A).

(Measurement conditions for dynamic viscoelasticity)
Measuring instrument: dynamic viscoelasticity measuring device (trade name: DVA-225, manufactured by IT Instrumentation & Control Co., Ltd.)
Deformation mode: Shear Strain: 0.1%
Measurement temperature: -100 to 60°C
Measurement frequency: 1Hz

In the first aspect, the acrylic resin (A) preferably has a weight average molecular weight of 50,000 to 500,000, more preferably 100,000 to 400,000, even more preferably 150,000 to 350,000. If the weight-average molecular weight of the acrylic resin (A) is too large, the viscosity tends to be too high, resulting in poor coatability and handling. If the weight-average molecular weight of the acrylic resin (A) is too small, the cohesive force tends to decrease and the adhesive physical properties tend to decrease.
The weight-average molecular weight of the acrylic resin (A) is the weight-average molecular weight at the completion of production. The weight average molecular weight is measured for the acrylic resin (A) that has not been heated or the like after production.

The weight average molecular weight of the acrylic resin (A) is the weight average molecular weight in terms of standard polystyrene molecular weight. The weight-average molecular weight was measured using a high-performance liquid chromatograph ("Waters 2695 (body)" and "Waters 2414 (detector)" manufactured by Nippon Waters Co., Ltd.) using a column: Shodex GPC KF-806L (exclusion limit molecular weight: 2 × 10 ⁷ , separation Range: 100 to 2×10 ⁷ , Number of theoretical plates: 10,000 plates/line, Filler material: Styrene-divinylbenzene copolymer, Filler particle diameter: 10 μm) are connected in series.
Number average molecular weight can also be measured using a similar method. Further, the dispersity is obtained from the weight average molecular weight and the number average molecular weight.

The degree of dispersion (weight average molecular weight/number average molecular weight) of the acrylic resin (A) is preferably 15 or less, more preferably 10 or less, even more preferably 7 or less, and particularly preferably 5 or less. If the degree of dispersion of the acrylic resin (A) is too high, the durability of the pressure-sensitive adhesive layer tends to decrease. Moreover, there is also a tendency that foaming or the like is likely to occur. If the degree of dispersion of the acrylic resin (A) is too low, the handleability tends to deteriorate. The lower limit of the dispersity is usually 1.1 due to manufacturing limitations.

[Method for producing acrylic resin (A)]
In the first aspect, the acrylic resin (A) can be produced by polymerizing a copolymer component (a) containing an alkyl acrylate (a1), an alkyl methacrylate (a2), and a hydroxyl group-containing monomer (a3).
The copolymerization component (a) according to the first aspect may further contain an ethylenically unsaturated monomer (a4) as an optional polymerization component.

Examples of polymerization methods for the acrylic resin (A) include conventionally known polymerization methods such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. Solution polymerization is preferred in terms of safety and stability of the reaction and the ability to produce the acrylic resin (A) with any monomer composition.
An example of a preferred method for producing the acrylic resin (A) according to the first aspect is shown below.

For example, solution polymerization can be carried out by mixing or dropping the copolymerization component (a) according to the first aspect and the polymerization initiator into an organic solvent.
Examples of organic solvents used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene;
Aliphatic hydrocarbons such as n-hexane; Esters such as methyl acetate, ethyl acetate and butyl acetate; Aliphatic alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol and isopropyl alcohol; Acetone, methyl ethyl ketone, methyl isobutyl ketones such as ketones and cyclohexanone; aliphatic ethers such as dimethyl ether and diethyl ether; aliphatic halogenated hydrocarbons such as methylene chloride and ethylene chloride; and cyclic ethers such as tetrahydrofuran.
Among these organic solvents, esters and ketones are preferred, and ethyl acetate, acetone and methyl ethyl ketone are particularly preferred.
An organic solvent may be used individually by 1 type, and may use 2 or more types together.

As the polymerization initiator used in the polymerization reaction, an azo polymerization initiator, a peroxide polymerization initiator, or the like, which is a normal radical polymerization initiator, can be used.
Examples of azo polymerization initiators include 2,2′-azobis(2-methylbutyronitrile), 2,2′-azobisisobutyronitrile, (1-phenylethyl)azodiphenylmethane, 2,2′ -azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and the like. be done.

Peroxide-based polymerization initiators include, for example, benzoyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, tert-butylperoxypivalate, tert-hexylperoxypivalate, tert-hexyl peroxyneodecanoate, diisopropyl peroxycarbonate, diisobutyryl peroxide and the like.

Among them, azo polymerization initiators are preferred, and 2,2'-azobisisobutyronitrile and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) are more preferred.
One polymerization initiator may be used alone, or two or more polymerization initiators may be used in combination.

The amount of the polymerization initiator used is usually 0.001 to 10 parts by weight, preferably 0.1 to 8 parts by weight, more preferably 0.5 to 6 parts by weight, per 100 parts by weight of the copolymer component (a). parts, particularly preferably 1 to 4 parts by weight, more preferably 1.5 to 3 parts by weight, most preferably 2 to 2.5 parts by weight. When the amount of the polymerization initiator used is too small, the rate of polymerization of the acrylic resin (A) decreases, and the amount of residual monomer tends to increase. Moreover, the weight average molecular weight of acrylic resin (A) tends to increase. If the amount used is too large, the acrylic resin (A) tends to gel.

Polymerization conditions for solution polymerization are not particularly limited, and polymerization can be carried out according to conventionally known polymerization conditions. For example, the copolymerization component (a) and the polymerization initiator can be mixed or dropped into an organic solvent for polymerization.

The polymerization temperature in the polymerization reaction is usually 40 to 120°C, preferably 50 to 90°C from the viewpoint of stable reaction. If the polymerization temperature is too high, the acrylic resin (A) tends to gel easily. If the polymerization temperature is too low, the activity of the polymerization initiator will decrease, resulting in a decrease in the rate of polymerization and a tendency for the amount of residual monomers to increase.
The polymerization time in the polymerization reaction is not particularly limited, but it is 0.5 hours or longer, preferably 1 hour or longer, more preferably 2 hours or longer, and particularly preferably 5 hours or longer after the last addition of the polymerization initiator.
The polymerization reaction is preferably carried out while refluxing the solvent in order to facilitate heat removal.

(Photoinitiator (B))
The photoinitiator (B) according to the first aspect contains an intramolecular hydrogen abstraction photoinitiator (b1) and an intermolecular hydrogen abstraction photoinitiator (b2).
The photoinitiator (B) according to the first aspect is other than the intramolecular hydrogen abstraction photoinitiator (b1) and the intermolecular hydrogen abstraction photoinitiator (b2) within a range that does not impair the effects of the invention. may further contain another photoinitiator (b3).

[Intramolecular hydrogen abstraction type photoinitiator (b1)]
The intramolecular hydrogen abstraction type photoinitiator (b1) according to the first aspect has a structure capable of generating radicals by abstraction of hydrogen from the photoinitiator itself. For example, the intramolecular hydrogen abstraction type photoinitiator (b1) may have a phenylglyoxylate structure or the like.
Examples of the intramolecular hydrogen abstraction type photoinitiator (b1) include oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester, methyl phenylglyoxylate and the like.
Among these, oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester having multiple cross-linking points in the molecule is preferable from the viewpoint of cross-linking efficiency at the time of complete curing.
As a commercial product, IGM RESINS B.I. V. "Omnirad MBF" and "Omnirad 754" manufactured by the company.

[Intermolecular hydrogen abstraction type photoinitiator (b2)]
The intermolecular hydrogen abstraction type photoinitiator (b2) according to the first aspect has a structure capable of generating radicals by abstracting hydrogen from sources other than the photoinitiator itself. The intermolecular hydrogen abstraction photoinitiator (b2) may have, for example, a benzophenone structure.
For example, benzophenone, 4-methyl-benzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3′-dimethyl-4-methoxybenzophenone, 4-(meth)acryloyloxybenzophenone, 4-[2- ((meth)acryloyloxy)ethoxy]benzophenone, 4-(meth)acryloyloxy-4′-methoxybenzophenone, carboxymethoxymethoxybenzophenone-polyethylene glycol 250 diester, methyl 2-benzoylbenzoate, 4-(1,3-acryloyl) -1,4,7,10,13-pentaoxotridecyl)benzophenone and the like.

Among these, 2,4,6-trimethylbenzophenone is preferred because it is a low-viscosity liquid and is easy to handle. In addition, 4-(meth)acryloyloxybenzophenone, 4-[2-((meth)acryloyloxy)ethoxy]benzophenone, 4-(meth)acryloyloxy-, which have multiple cross-linking points in the molecule, can be highly crosslinked. 4′-Methoxybenzophenone, carboxymethoxymethoxybenzophenone-polyethylene glycol 250 diester are preferred.
Commercially available products include "MBP" manufactured by Shinryo Corporation and IGM RESINS B.I. V. "OmniradBP", "Omnirad 4MBZ", "Esacure TZT", "Omnipol BP" manufactured by the company.

[Other photoinitiator (b3)]
Other photoinitiators (b3) according to the first aspect include, for example, diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 4-(2-hydroxy ethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexylphenylketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, 2-benzyl-2-dimethylamino -acetophenones such as 1-(4-morpholinophenyl)butanone, 2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone oligomers;
Benzoins such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether;
2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenyl acylphosphone oxides such as phosphine oxide;
are mentioned.

As auxiliary agents for the photoinitiator (B) according to the first aspect, triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler's ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethyl Benzoic acid, ethyl 4-dimethylaminobenzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2,4-diethylthioxanthone , 2,4-diisopropylthioxanthone and the like can also be used in combination.
The auxiliary agent for the photoinitiator (B) may be used alone or in combination of two or more.

(Crosslinking agent (C))
The pressure-sensitive adhesive composition according to the first aspect preferably further contains a cross-linking agent (C) in addition to the acrylic resin (A) and the photoinitiator (B).
Examples of the cross-linking agent (C) include an active energy ray cross-linking agent (c1) and a thermal cross-linking agent (c2). The active energy ray cross-linking agent (c1) and the thermal cross-linking agent (c2) may be used alone or in combination of two or more.

When only the active energy ray cross-linking agent (c1) is contained as the cross-linking agent (C) according to the first aspect, multistage curing can be achieved only by controlling the dose of active energy ray. Moreover, when the active energy ray cross-linking agent (c1) and the thermal cross-linking agent (c2) are contained as the cross-linking agent (C), multistage curing can be achieved by using both heat curing and active energy ray curing.
By controlling the cross-linking reaction in this way, the cohesive force of the entire adhesive layer can be adjusted, and stable adhesive physical properties can be obtained after primary curing and after complete curing.

[Active energy ray cross-linking agent (c1)]
Examples of the active energy ray cross-linking agent (c1) according to the first aspect include polyfunctional cross-linking agents containing two or more ethylenically unsaturated groups in one molecule.
For example, hexanediol di(meth)acrylate, butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, (poly)ethylene glycol mono(meth)acrylate ) acrylate, (poly)butylene glycol mono (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, (poly) tetramethylene glycol di (meth) acrylate, (poly ) pentamethylene glycol di(meth)acrylate, (poly)hexamethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol Hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, EO-modified glycerin tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate , isocyanuric acid ethylene oxide-modified tri(meth)acrylate, polyfunctional urethane(meth)acrylate, and the like.
Among them, (meth)acrylates containing two ethylenically unsaturated groups are preferable in terms of the balance of adhesive physical properties after curing, and in particular, (poly)ethylene glycol di(meth)acrylate and (poly)propylene glycol. Di(meth)acrylate and (poly)tetramethylene glycol di(meth)acrylate are preferred.
Polyfunctional cross-linking agents may be used alone or in combination of two or more.

[Thermal cross-linking agent (c2)]
The thermal cross-linking agent (c2) according to the first aspect can exhibit excellent adhesion by reacting mainly with functional groups derived from functional group-containing monomers that are constituent monomers of the acrylic resin (A). For example, isocyanate cross-linking agent (c2-1), epoxy cross-linking agent (c2-2), aziridine cross-linking agent (c2-3), melamine cross-linking agent (c2-4), aldehyde cross-linking agent (c2-5 ), an amine cross-linking agent (c2-6), and a metal chelate cross-linking agent (c2-7). Among these, the isocyanate-based cross-linking agent (c2-1) is preferably used in terms of improving adhesion to the substrate and reactivity with the acrylic resin (A).
The thermal cross-linking agent (c2) may be used alone or in combination of two or more.

Examples of the isocyanate-based cross-linking agent (c2-1) include tolylene diisocyanate-based compounds such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate;
xylylene diisocyanate compounds such as 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, tetramethyl xylylene diisocyanate;
Aromatic isocyanate compounds such as 1,5-naphthalene diisocyanate and triphenylmethane triisocyanate;
Hexamethylene diisocyanate compounds such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate, aliphatic isocyanate compounds such as lysine diisocyanate;
Alicyclic isocyanate compounds such as isophorone diisocyanate;
Adducts of these isocyanate compounds and polyol compounds such as trimethylolpropane;
burettes and isocyanurates of these isocyanate compounds;
etc.

Among the isocyanate-based cross-linking agents (c2-1), it is preferable to use aromatic isocyanate-based compounds from the viewpoint of excellent reactivity, and tolylene diisocyanate-based compounds are particularly preferable. Moreover, from the viewpoint of suppressing yellowing, it is preferable to use an aliphatic isocyanate-based compound, and particularly preferably a hexamethylene diisocyanate-based compound.

Examples of the epoxy-based cross-linking agent (c2-2) include bisphenol A/epichlorohydrin type epoxy resin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, and 1,6-hexane. Diol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidylerythritol, diglycerol polyglycidyl ether and the like.

Examples of aziridine-based cross-linking agents (c2-3) include tetramethylolmethane-tri-β-aziridinylpropionate, trimethylolpropane-tri-β-aziridinylpropionate, and N,N'-diphenylmethane. -4,4'-bis(1-aziridinecarboxamide), N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide) and the like.

Melamine-based cross-linking agents (c2-4) include, for example, hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexaptoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resins. etc.

Aldehyde-based cross-linking agents (c2-5) include, for example, glyoxal, malondialdehyde, succindialdehyde, maleinedialdehyde, glutaredialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

Examples of amine-based cross-linking agents (c2-6) include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetramine, isophoronediamine, amino resins, and polyamides.

Examples of metal chelate cross-linking agents (c2-7) include acetylacetone and acetoacetyl ester linkages of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium and zirconium. position compounds and the like.

(Silane coupling agent (D))
The pressure-sensitive adhesive composition according to the first aspect further contains a silane coupling agent (D) as a compound other than the acrylic resin (A), the photoinitiator (B) and the cross-linking agent (C). is preferable in terms of improving

The silane coupling agent (D) is an organosilicon compound containing in its structure one or more reactive functional groups and one or more alkoxy groups bonded to silicon atoms. The silane coupling agent (D) includes monomer type and oligomer type.

Examples of reactive functional groups in the silane coupling agent (D) include epoxy groups, (meth)acryloyl groups, mercapto groups, hydroxyl groups, carboxy groups, amino groups, amide groups, isocyanate groups, and the like. Among these, an epoxy group and a mercapto group are preferable from the viewpoint of excellent durability and reworkability.

The content of reactive functional groups in the silane coupling agent (D) is preferably 3,000 g/mol or less, more preferably 1,500 g/mol or less, and even more preferably 1,000 g/mol or less. When the reactive functional group is within the above numerical range, the balance between durability and reworkability is improved. The lower limit of the content of reactive functional groups in the silane coupling agent (D) is 200 g/mol.

As the silicon-bonded alkoxy group in the silane coupling agent (D), an alkoxy group having 1 to 8 carbon atoms is preferable from the viewpoint of durability and storage stability. Among them, a methoxy group and an ethoxy group are more preferable.
The silane coupling agent (D) may have a reactive functional group and an organic functional group other than the silicon-bonded alkoxy group, such as an alkyl group or a phenyl group.

Examples of the silane coupling agent (D) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxymethylsilane, γ-glycidoxypropyltrimethoxysilane, γ-glycid. xypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, methyltri(glycidyl)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β- (3,4-epoxycyclohexyl)ethyltrimethoxysilane and the like. Among them, γ-glycidoxypropyltrimethoxysilane is preferable from the viewpoint of heat resistance.
Silane coupling agents (D) may be used alone or in combination of two or more.

(Carbodiimide compound (E))
The pressure-sensitive adhesive composition according to the first aspect contains a carbodiimide compound (E) as a compound other than the acrylic resin (A), the photoinitiator (B), the cross-linking agent (C) and the silane coupling agent (D). It is preferable to further contain from the viewpoint of heat resistance.
Carbodiimide compounds (E) include, for example, bis(2,6-diisopropylphenyl)carbodiimide, dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, tert-butylisopropylcarbodiimide, diphenylcarbodiimide, di-tert- Examples include monocarbodiimides such as butylcarbodiimide and didodecylcarbodiimide, polycarbodiimides containing multiple carbodiimides, and cyclic carbodiimides. Among them, from the viewpoint of heat resistance, monocarbodiimide compounds are preferable, and bis(2,6-diisopropylphenyl)carbodiimide is more preferable.
The carbodiimide compound (E) may be used alone or in combination of two or more.

(optional component)
The pressure-sensitive adhesive composition according to the first aspect may optionally contain a pressure-sensitive adhesive as another optional component. The pressure-sensitive adhesive composition according to the first aspect may contain conventionally known additives such as cross-linking accelerators, antistatic agents, tackifiers and functional dyes.

(Composition of adhesive composition)
In the first aspect, the content of the acrylic resin (A) is preferably 80% by weight or more, more preferably 90 to 99.9% by weight, and 92 to 99.9% by weight with respect to the entire pressure-sensitive adhesive composition. is more preferred. When the content of the acrylic resin (A) is within the above numerical range, excellent adhesive physical properties are likely to be obtained in a low crosslinked state after primary curing.

In the first aspect, the content of the photoinitiator (B) is preferably 0.1 to 5.0 parts by weight, preferably 0.5 to 4.0 parts by weight, relative to 100 parts by weight of the acrylic resin (A). is more preferred, and 1.0 to 3.0 parts by weight is even more preferred. When the content of the photoinitiator (B) is within the above numerical range, sufficient curability can be obtained during complete curing.

In the first embodiment, the content of the intramolecular hydrogen abstraction type photoinitiator (b1) is preferably 0.1 to 5.0 parts by weight, preferably 0.5 to 5.0 parts by weight, based on 100 parts by weight of the acrylic resin (A). 3.0 parts by weight is more preferred.
If the content of the intramolecular hydrogen abstraction type photoinitiator (b1) is too high, there is a tendency for discoloration to occur after wet heat durability. If the content of the intramolecular hydrogen abstraction type photoinitiator (b1) is too low, the degree of cross-linking will not increase, and the adhesive physical properties during primary curing and the durability after complete curing will tend to deteriorate.

In the first aspect, the content of the intermolecular hydrogen abstraction type photoinitiator (b2) is preferably 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the acrylic resin (A), and 0.5 to 2.0 parts by weight is more preferred.
If the content of the intermolecular hydrogen abstraction type photoinitiator (b2) is too high, the durability tends to deteriorate due to bleeding out. If the content of the intermolecular hydrogen abstraction type photoinitiator (b2) is too small, the degree of cross-linking will not increase, and the adhesive properties during primary curing and the durability after complete curing will tend to deteriorate.

In the first embodiment, when the photoinitiator (B) contains another photoinitiator (b3), the content of the photoinitiator (b3) is 2.0 parts per 100 parts by weight of the acrylic resin (A). 0 weight part or less is preferable, and 1.0 weight part or less is more preferable.

In the first aspect, when the pressure-sensitive adhesive composition contains the cross-linking agent (C), the content of the cross-linking agent (C) is usually preferably 20 parts by weight or less with respect to 100 parts by weight of the acrylic resin (A). , more preferably 0.001 to 10 parts by weight, more preferably 0.1 to 7.5 parts by weight. If the content of the cross-linking agent (C) is too large, the adhesive strength tends to decrease. If the content of the cross-linking agent (C) is too small, the durability tends to decrease.

In the first aspect, when the adhesive composition contains the active energy ray cross-linking agent (c1), the content of the active energy ray cross-linking agent (c1) is usually based on 100 parts by weight of the acrylic resin (A) 0.01 to 20 parts by weight is preferable, 0.1 to 10 parts by weight is more preferable, and 0.5 to 7.5 parts by weight is even more preferable.
If the content of the active energy ray cross-linking agent (c1) is too small, there is a tendency that sufficient durability cannot be obtained due to insufficient cohesion. If the content of the active energy ray cross-linking agent (c1) is too large, the adhesive physical properties during primary curing tend to be lowered.

When the pressure-sensitive adhesive composition contains the thermal cross-linking agent (c2) in the first aspect, the content of the thermal cross-linking agent (c2) is usually 0.001 per 100 parts by weight of the acrylic resin (A). ~5 parts by weight is preferred, 0.02 to 1 part by weight is more preferred, and 0.05 to 0.5 parts by weight is even more preferred.
If the content of the thermal cross-linking agent (c2) is too small, the cohesive force tends to be insufficient, and the adhesive physical properties tend to deteriorate during the primary curing. If the content of the thermal cross-linking agent (c2) is too large, the adhesive strength tends to decrease at the time of complete curing.

In the first aspect, when the pressure-sensitive adhesive composition contains a silane coupling agent (D), the content of the silane coupling agent (D) is from 0.001 to 100 parts by weight of the acrylic resin (A). 3 parts by weight is preferred, 0.005 to 1 part by weight is more preferred, 0.01 to 0.5 parts by weight is even more preferred, and 0.015 to 0.3 parts by weight is particularly preferred.
If the content of the silane coupling agent (D) is too small, it tends to be difficult to obtain the effect of improving the durability. If the content of the silane coupling agent (D) is too large, the adhesive strength tends to decrease due to the influence of bleeding out and the like.

In the first aspect, when the pressure-sensitive adhesive composition contains the carbodiimide compound (E), the content of the carbodiimide compound (E) is 0.01 to 10 parts by weight with respect to 100 parts by weight of the acrylic resin (A). 0.1 to 5 parts by weight is more preferred, 0.2 to 2 parts by weight is even more preferred, and 0.3 to 1 part by weight is particularly preferred.
If the content of the carbodiimide-based compound (E) is too small, the thermal stability of the acrylic resin (A) tends to decrease. If the content of the carbodiimide-based compound (E) is too large, there is a tendency for durability to decrease due to the effects of bleeding out and the like.

In the first aspect, when the adhesive composition contains other adhesives and additives, the content of the other adhesives and additives is 10 parts by weight or less with respect to 100 parts by weight of the acrylic resin (A). is preferred, and 5 parts by weight or less is more preferred.

(Preparation of adhesive composition)
Acrylic resin (A), photoinitiator (B), if necessary, cross-linking agent (C), silane coupling agent (D), carbodiimide compound (E), by mixing other optional components A pressure-sensitive adhesive composition according to one aspect can be obtained.
The mixing method is not particularly limited, and various methods such as a method of mixing each component at once, a method of mixing an arbitrary component and then mixing the remaining components all at once or sequentially can be adopted.

(Application)
The pressure-sensitive adhesive composition according to the first aspect can be suitably used as a pressure-sensitive adhesive for a multi-stage curing pressure-sensitive adhesive sheet that cures in a plurality of stages. According to the pressure-sensitive adhesive composition according to the first aspect, excellent pressure-sensitive adhesive physical properties can be obtained even in a low crosslinked state after primary curing. Furthermore, after complete curing, not only adhesive physical properties such as ordinary adhesive strength but also excellent durability is exhibited when members of various types and shapes such as polarizing plates and glass are bonded together.

The pressure-sensitive adhesive composition according to the first aspect has low tackiness even in a low cross-linking state after primary curing, and has excellent adhesive physical properties such as high constant load holding power, thereby improving workability and reliability. Therefore, it is particularly suitable for use as an adhesive or an adhesive sheet for use in touch panels, image display devices, and the like.

<Adhesive>
The pressure-sensitive adhesive according to the first aspect is obtained by cross-linking the pressure-sensitive adhesive composition according to the first aspect described above. By cross-linking (curing) the pressure-sensitive adhesive composition of the present invention, the acrylic resin (A) contained in the pressure-sensitive adhesive composition forms a cross-linked structure at least either intramolecularly or intermolecularly. As a result, the pressure-sensitive adhesive composition of the present invention is crosslinked to become the pressure-sensitive adhesive according to the first aspect.
When the acrylic resin (A) has an active energy ray crosslinkable structural site, a crosslinked structure can be formed by irradiation with an active energy ray.

The pressure-sensitive adhesive according to the first aspect exhibits multistage curability that allows curing in multiple stages. The pressure-sensitive adhesive according to the first aspect becomes in a low crosslinked state by primary curing before complete curing. Complete curing and primary curing are not always clearly distinguishable, but can be distinguished, for example, by differences in gel fraction and dynamic viscoelasticity.

Curing means is not particularly limited in either the primary curing step or the complete curing step, and heating or irradiation with active energy rays may be used. Further, the primary curing step may be divided into a plurality of times, or multistage curing may be performed to achieve a completely cured state.
Since the pressure-sensitive adhesive according to the first aspect has excellent adhesive physical properties after primary curing, it is suitably used for bonding optical members constituting touch panels, image display devices, and the like.

It can also be said that the adhesive according to the first aspect contains at least the crosslinked product of the acrylic resin (A) according to the first aspect. The crosslinked product may be a partially crosslinked product in which at least part of the acrylic resin (A) is partially crosslinked, or a completely crosslinked product in which the acrylic resin (A) is entirely crosslinked. good. Moreover, the adhesive according to the first aspect may contain both a partially crosslinked product and a completely crosslinked product of the acrylic resin (A).

<Adhesive sheet>
The pressure-sensitive adhesive sheet according to the first aspect has a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to the first aspect. The pressure-sensitive adhesive sheet according to the first aspect can exhibit multistage curability in which the pressure-sensitive adhesive layer is cured in a plurality of stages.

A pressure-sensitive adhesive sheet can be obtained by providing a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to the first aspect on a base sheet. Also, a double-sided pressure-sensitive adhesive sheet can be obtained by providing a pressure-sensitive adhesive layer on a release sheet.
Further, a substrate-less double-faced PSA sheet can be produced by forming a PSA layer on a release sheet in place of the base sheet, and laminating the release sheet on the opposite side of the PSA layer. A thick pressure-sensitive adhesive layer may be further formed by further forming a pressure-sensitive adhesive layer on the formed pressure-sensitive adhesive layer.
The pressure-sensitive adhesive sheet and double-sided pressure-sensitive adhesive sheet thus obtained are used by peeling off the release sheet from the pressure-sensitive adhesive layer.

Examples of the method for producing the pressure-sensitive adhesive sheet according to the first aspect include the following methods (i) and (ii).
(i) A method of forming a pressure-sensitive adhesive sheet after applying a coating liquid in which the pressure-sensitive adhesive composition according to the first aspect is dissolved in a solvent.
(ii) A method of forming an adhesive sheet after melting the adhesive composition according to the first aspect by heating.

The method (i) will be explained.
When a pressure-sensitive adhesive sheet is formed after applying a coating liquid in which the pressure-sensitive adhesive composition according to the first aspect is dissolved in a solvent, the coating containing the pressure-sensitive adhesive composition according to the first aspect is coated with an appropriate organic solvent. Adjust the concentration of the working liquid and apply it directly onto the substrate sheet. After that, it is dried by heat treatment or the like at 80 to 105° C. for 0.5 to 10 minutes, and then attached to a base sheet or a release sheet. After that, the adhesive composition is crosslinked (cured) by irradiation with active energy rays or aged, and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer can be produced.

As the organic solvent used for adjusting the concentration, those listed as the organic solvent used for the polymerization reaction of the acrylic resin (A) can be used. The concentration of the pressure-sensitive adhesive composition is usually 20-60% by weight, preferably 30-50% by weight, as a solid content.

The method (ii) will be described.
When the pressure-sensitive adhesive composition according to the first aspect is melted by heating to form a pressure-sensitive adhesive sheet, the melted state is coated on one or both sides of the base sheet, and then the base sheet is cooled, or by a T-die or the like. A pressure-sensitive adhesive layer is formed on one side or both sides of the substrate sheet to a desired thickness by extrusion lamination or the like on the material sheet. Then, a pressure-sensitive adhesive sheet can be produced by laminating a release sheet on the surface of the pressure-sensitive adhesive layer, if necessary.

In addition, after forming the adhesive layer on the base sheet, if necessary, the active energy ray irradiation treatment is performed, and the adhesive composition having the adhesive layer is cured (crosslinked) by aging. A sheet can be made.
Further, a substrate-less double-sided PSA sheet can be produced by forming a PSA layer on a release sheet and laminating the release sheet on the opposite side of the PSA layer.
The pressure-sensitive adhesive sheet and double-sided pressure-sensitive adhesive sheet thus obtained are used by peeling off the release sheet from the pressure-sensitive adhesive layer.

Examples of the base sheet include polyester resins such as polyethylene naphtate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate/isophthalate copolymer; polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; polyvinyl fluoride; Polyethylene fluoride resins such as polyvinylidene fluoride and polyethylene fluoride; polyamides such as nylon 6 and nylon 6,6; polyvinyl chloride, polyvinyl chloride/vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl Vinyl polymers such as alcohol copolymers, polyvinyl alcohol and vinylon; Cellulose resins such as cellulose triacetate and cellophane; Acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate and polybutyl acrylate. Polystyrene; Polycarbonate; Polyarylate; Synthetic resin sheet such as polyimide,
Metal foil such as aluminum, copper, iron, etc.
High-quality paper, glassine paper, etc.
Textiles and non-woven fabrics made of glass fiber, natural fiber, synthetic fiber and the like can be mentioned. These base sheets can be used as a single-layer body or as a multi-layer body in which two or more types are laminated. Among these, a synthetic resin sheet is preferable from the viewpoint of weight reduction.

As the release sheet, for example, various synthetic resin sheets exemplified in the base sheet, paper, woven fabric, non-woven fabric, etc. that have been subjected to release treatment can be used. As the release sheet, it is preferable to use, for example, a silicon-based release sheet.

The method of applying the adhesive composition is not particularly limited. For example, methods such as roll coating, die coating, gravure coating, comma coating, slot coating and screen printing can be used.

As active energy rays, rays such as far-ultraviolet rays, ultraviolet rays, near-ultraviolet rays, and infrared rays; electromagnetic waves such as X-rays and γ-rays; electron beams; proton beams; Curing with UV light is preferred in terms of curing speed, availability of irradiation equipment, price, and the like.

Regarding the gel fraction of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet before complete curing, it is possible to easily bond the adherend regardless of the shape of the adherend, and the pressure-sensitive adhesive layer can hold the adherend after bonding. From the point of view, it is preferably 0.1 to 60% by weight, more preferably 1 to 50% by weight, particularly preferably 5 to 45% by weight.

The gel fraction after complete curing of the adhesive layer of the adhesive sheet is preferably 50 to 95% by weight, more preferably 55 to 90% by weight, and particularly preferably 60% by weight, from the viewpoint of durability and adhesive strength. ~85% by weight. If the gel fraction is too low, cohesive strength tends to decrease, resulting in a decrease in durability. If the gel fraction is too high, there is a tendency for cohesive strength to increase and adhesive strength to decrease.

The gel fraction can be appropriately adjusted, for example, by the following method.
・Adjust the amount of active energy ray irradiation.
- Adjust the content of the active energy ray-crosslinkable structural site in the acrylic resin (A).
- Adjust the types and amounts of the photoinitiator (B) and the cross-linking agent (C).

The gel fraction is a measure of the degree of cross-linking (degree of curing), and is calculated, for example, by the following method. That is, an adhesive sheet (without a release sheet) in which an adhesive layer is formed on a polymer sheet (for example, polyethylene terephthalate (PET) film, etc.) serving as a base material is wrapped with a 200-mesh SUS wire mesh. , and the weight percentage of the undissolved pressure-sensitive adhesive component remaining in the wire mesh after being immersed in toluene maintained at 23°C for 24 hours is defined as the gel fraction. However, it is calculated by subtracting the weight of the substrate from the weight before and after the toluene dissolution.

The thickness of the adhesive layer of the adhesive sheet is usually preferably 50-3000 μm, more preferably 75-1000 μm, and particularly preferably 100-350 μm. If the thickness of the pressure-sensitive adhesive layer is too thin, there is a tendency for the impact absorption to decrease. If the thickness of the pressure-sensitive adhesive layer is too thick, for example, when the adhesive layer is attached to an optical member, the overall thickness tends to increase, resulting in a decrease in practicality.

The thickness of the adhesive layer is obtained by subtracting the measured thickness of the constituent members other than the adhesive layer from the measured thickness of the entire laminate containing the adhesive layer using Mitutoyo's "ID-C112B". value.

The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to the first aspect preferably has a haze value of 2% or less, more preferably 0 to 1.5%, particularly preferably 0 when the thickness of the pressure-sensitive adhesive layer is 100 μm. ~1%. If the haze value is too high, the pressure-sensitive adhesive layer tends to whiten and the transparency tends to decrease.
The haze value is obtained by measuring diffuse transmittance and total light transmittance using HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.), and obtained diffuse transmittance (DT) and total light transmittance (TT) values. was substituted into the following [Equation 1] for calculation. This machine complies with JIS K7361-1.
Haze value (%) = (DT/TT) x 100 [Formula 1]

In the first aspect, an optical member with a pressure-sensitive adhesive layer can be obtained by laminating the pressure-sensitive adhesive layer on the optical member. For example, the pressure-sensitive adhesive layer surface of the pressure-sensitive adhesive sheet according to the first embodiment in which the pressure-sensitive adhesive layer is formed on the release sheet is attached to the optical member, and then the release sheet is peeled off to obtain the optical member with the pressure-sensitive adhesive layer. can be obtained. Optical members can also be bonded together using the above double-sided pressure-sensitive adhesive sheet.

Examples of optical members include members that make up touch panels and image display devices. Examples include displays (organic EL, liquid crystal), transparent conductive film substrates (ITO substrates), protective films (glass), transparent antennas (films), transparent wiring, and the like.

Preferred embodiments of the first aspect described above include, but are not limited to, the following [A1] to [A7].
[A1] contains an acrylic resin (A) and a photoinitiator (B), the acrylic resin (A) is a polymerization product of the following copolymerization component (a), and the acrylic resin (A) has a glass transition temperature based on dynamic viscoelasticity of −10° C. or higher, and the copolymer component (a) is an alkyl acrylate having a glass transition temperature of −30 to 50° C. when a homopolymer is formed. (a1), an alkyl methacrylate (a2) having a glass transition temperature of −10 to 120° C. when forming a homopolymer, and a hydroxyl group-containing monomer (a3), wherein the alkyl acrylate (a1) and the alkyl The weight ratio of the methacrylate (a2) is 5/95 to 55/45, and the total content of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is 30 to 70 weight relative to the copolymer component (a). %, and the photoinitiator (B) comprises an intramolecular hydrogen abstraction type photoinitiator (b1) and an intermolecular hydrogen abstraction type photoinitiator (b2).
[A2] The pressure-sensitive adhesive composition according to [A1], further containing a cross-linking agent (C).
[A3] The adhesive composition according to [A1] or [A2], wherein the acrylic resin (A) has a weight average molecular weight of 50,000 to 500,000.
[A4] A pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition according to any one of [A1] to [A3].
[A5] The pressure-sensitive adhesive according to [A4], wherein the cross-linking is performed by irradiation with an active energy ray.
[A6] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to [A4] or [A5].
[A7] The pressure-sensitive adhesive sheet according to [A6], wherein the pressure-sensitive adhesive layer is multi-stage curing in which it is cured in a plurality of stages.

[Second aspect]
Embodiments of the second aspect of the present invention are described in detail below and are disclosed as representative examples of preferred embodiments.

<Adhesive composition>
The pressure-sensitive adhesive composition according to the second aspect contains an acrylic resin (A) and a photoinitiator (B). The pressure-sensitive adhesive composition according to the second aspect comprises an acrylic resin (A), a photoinitiator (B), a cross-linking agent (C), a silane coupling agent (D), a carbodiimide compound (E), Other optional components may be further contained as necessary. Hereinafter, each component will be described in order.

(Acrylic resin (A))
The acrylic resin (A) according to the second aspect is a polymerization product of a specific copolymer component (a). Copolymer component (a) is a general term for monomer components having a polymerizable double bond. The copolymerization component (a) does not contain a polymerization initiator and a polymerization solvent.

The specific copolymer component (a) according to the second aspect is an alkyl (meth)acrylate ( It contains at least a1) and a hydroxyalkyl monomer (a2) containing an alkyl chain, a hydroxyl group and an ethylenically unsaturated group. The copolymer component (a) according to the second aspect may further contain an ethylenically unsaturated monomer (a3) excluding the alkyl (meth)acrylate (a1) and the hydroxyalkyl monomer (a2), if necessary. .

[Alkyl (meth)acrylate (a1)]
The alkyl (meth)acrylate (a1) according to the second aspect has an alkyl group having 12 or less carbon atoms. The number of carbon atoms in the alkyl group of the alkyl (meth)acrylate (a1) is preferably 8 or less, more preferably 4 or less. When the number of carbon atoms in the alkyl group of the alkyl (meth)acrylate (a1) is equal to or less than the above upper limit, excellent adhesion physical properties are likely to be obtained in a low crosslinked state after primary curing.

The alkyl (meth)acrylate (a1) according to the second aspect is a monomer whose homopolymer has a glass transition temperature (hereinafter referred to as "Tg") of -20 to 120°C.
The Tg of the homopolymer of alkyl (meth)acrylate (a1) according to the second aspect is preferably 0 to 105°C, more preferably 5 to 70°C. Since the Tg of the homopolymer of the alkyl (meth)acrylate (a1) is within the above numerical range, it is possible to obtain a pressure-sensitive adhesive sheet with excellent adhesion even when it is attached to an adherend having a complicated shape which is strongly stressed.

A homopolymer of alkyl (meth)acrylate (a1) is a homopolymer of alkyl (meth)acrylate (a1). As the Tg of the homopolymer of the alkyl (meth)acrylate (a1), a standard analytical value described in "Polymer Handbook" published by Wiley, etc. can be used.

Examples of the alkyl (meth)acrylate (a1) according to the second aspect include methyl acrylate (Tg: 8°C), tert-butyl acrylate (Tg: 41°C), cyclohexyl acrylate (Tg: 15°C), isobol Nil acrylate (Tg: 97°C), methyl methacrylate (Tg: 105°C), ethyl methacrylate (Tg: 65°C), n-butyl methacrylate (Tg: 20°C), isobutyl methacrylate (Tg: 48°C), tert-butyl Methacrylate (Tg: 107°C), 2-ethylhexyl methacrylate (Tg: -10°C), chlorhexyl methacrylate (Tg: 66°C), and the like. Among them, methyl acrylate, methyl methacrylate, ethyl methacrylate, and isobutyl methacrylate are preferred from the viewpoint of adhesive physical properties.
Alkyl (meth)acrylates (a1) may be used alone or in combination of two or more.

[Hydroxyalkyl monomer (a2)]
The hydroxyalkyl monomer (a2) according to the second aspect contains an alkyl chain, a hydroxyl group and an ethylenically unsaturated group.
The hydroxyalkyl monomer (a2) according to the second aspect can be represented, for example, by the following general formula.
_CH2 =CHR-XY-OH
In the formula, R is a hydrogen atom or a methyl group, X is an oxygen atom, COO or CONH, and Y is a linear or branched alkyl chain.

The average carbon number of the alkyl chain of the hydroxyalkyl monomer (a2) in the copolymer component (a) according to the second aspect is 2.1 or more, preferably 2.1 to 8.0, more preferably 2.4 to 6.0, particularly preferably 2.6 to 4.0. If the average number of carbon atoms in the alkyl chain of the hydroxyalkyl monomer (a2) is too small, there is a tendency for the reliability of complete curing to decrease. If the average number of carbon atoms in the alkyl chain of the hydroxyalkyl monomer (a2) is too large, the adhesive properties after primary curing tend to deteriorate.

Here, when the copolymerization component (a) according to the second aspect contains one type of hydroxyalkyl monomer (a2), the average carbon number of the alkyl chain of the hydroxyalkyl monomer (a2) is The number of carbon atoms in the alkyl chain of the alkyl monomer (a2) is the same.
On the other hand, when the copolymer component (a) according to the second aspect contains two or more hydroxyalkyl monomers (a2), the average carbon number of the alkyl chains of the hydroxyalkyl monomers (a2) is The weight average value of the number of carbon atoms in the alkyl chain of the hydroxyalkyl monomer (a2) in the copolymerization component (a) according to the embodiment.

For example, the copolymerization component (a) according to the second aspect is a hydroxyalkyl monomer (a2), w _s parts by weight of monomer s and _wt parts by weight of monomer with respect to 100 parts by weight of copolymerization component (a) t, the average carbon number n of the alkyl chain of the hydroxyalkyl monomer (a2) in the copolymer component (a) according to the second embodiment is determined as follows.

n=n _s ×w _s /(w _s +w _t )+n _t ×w _t /(w _s +w _t )
Here, _ns is the number of carbon atoms in the alkyl chain of monomer s, and _nt is the number of carbon atoms in the alkyl chain of monomer t.
When the copolymerization component (a) according to the second aspect contains three or more hydroxyalkyl monomers (a2), the alkyl The average number of carbon atoms in the chain is determined.

Examples of the hydroxyalkyl monomer (a2) according to the second aspect include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, ) acrylate, 6-hydroxyhexyl (meth) acrylate, 7-hydroxyheptyl (meth) acrylate, primary hydroxyl group-containing (meth) acrylate such as 8-hydroxyoctyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2 -Hydroxyalkyl (meth)acrylate monomers such as secondary or tertiary hydroxyl group-containing (meth)acrylates such as hydroxybutyl (meth)acrylate, 2,2-dimethyl 2-hydroxyethyl (meth)acrylate; N-(2-hydroxy hydroxyalkyl (meth)acrylamides such as ethyl)(meth)acrylamide, N-(4-hydroxybutyl)(meth)acrylamide, N-(6-hydroxyhexyl)(meth)acrylamide;
Hydroxyalkyl vinyl ethers such as 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether and 6-hydroxyhexyl vinyl ether can be mentioned.
The hydroxyalkyl monomers (a2) may be used singly or in combination of two or more.
Among these, primary hydroxyl group-containing (meth)acrylates are preferred, and 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate can be used together or 4-hydroxybutyl (meth)acrylate can be used alone. Especially preferred.

[Ethylenically unsaturated monomer (a3)]
The copolymerization component (a) according to the second aspect includes, if necessary, other copolymerizable ethylenically unsaturated monomers (a3) other than the alkyl (meth)acrylate (a1) and the hydroxyalkyl monomer (a2). Further, it may be contained.
Other copolymerizable ethylenically unsaturated monomers (a3) include, for example, alkyl (meth)acrylates such as n-butyl acrylate and 2-ethylhexyl (meth)acrylate (whereas alkyl (meth)acrylate (a1) except.);
Phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenyldiethylene glycol (meth) acrylate, phenoxy polyethylene glycol (meth) acrylate, phenoxy polyethylene glycol-polypropylene glycol-(meth) acrylate, orthophenylphenoxyethyl Aromatic ring-containing monomers such as (meth)acrylates and nonylphenol ethylene oxide adduct (meth)acrylates;
Alicyclic-containing monomers such as cyclohexyloxyalkyl (meth)acrylate, tert-butylcyclohexyloxyethyl (meth)acrylate, isobornyl methacrylate, dicyclopentanyl (meth)acrylate;
2-Methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 2-butoxyethyl (meth) acrylate, 2-butoxydiethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) Acrylates, methoxytriethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, octoxypolyethyleneglycol-polypropyleneglycol mono(meth)acrylate, lauroxy Ether chain-containing monomers such as polyethylene glycol mono (meth) acrylate and stearoxy polyethylene glycol mono (meth) acrylate;
(Meth)acrylic acid, acrylic acid dimers such as β-carboxyethyl acrylate, carboxylates such as crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, N-glycolic acid and cinnamic acid group-containing monomer;
Polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, caprolactone-modified 2-hydroxyethyl (meth) acrylate, 2-acryloyloxyethyl-2-hydroxyethyl phthalic acid and other hydroxyalkyl monomers other than (a2) a hydroxyl group-containing monomer;
(Meth)acrylamide, N-(n-butoxyalkyl)(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dimethylaminoalkyl(meth)acrylamide, etc. The amide group-containing monomer of;
benzophenone-containing monomers such as 4-(meth)acryloyloxybenzophenone;
Acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinylpyridine, vinylpyrrolidone, dialkyl itaconate, dialkyl fumarate Ester, allyl alcohol, acryl chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethyl allyl vinyl ketone and the like.
The ethylenically unsaturated monomers (a3) may be used alone or in combination of two or more.

[Composition of the copolymer component (a) according to the second aspect]
In the second aspect, the content of the alkyl (meth)acrylate (a1) is 30% by weight or more relative to 100% by weight of the copolymer component (a). The content of the alkyl (meth)acrylate (a1) is preferably 35 to 75% by weight, more preferably 40 to 65% by weight, even more preferably 45 to 60% by weight. If the content of the alkyl (meth)acrylate (a1) is too small, the adhesive properties in the primary cured state tend to be lowered. If the content of the alkyl (meth)acrylate (a1) is too high, the adhesive physical properties after complete curing tend to deteriorate.

In the second aspect, the content of the hydroxyalkyl monomer (a2) is 0.1% by weight or more, preferably 0.1 to 30% by weight, based on 100% by weight of the copolymer component (a), and 5 to 30% by weight is more preferred, and 10 to 25% by weight is even more preferred. If the content of the hydroxyalkyl monomer (a2) is too small, the adhesive properties in the primary cured state tend to be lowered. If the content of the hydroxyalkyl monomer (a2) is too high, the adhesive properties after complete curing tend to deteriorate.

In the copolymer component (a) according to the second aspect, the content ratio (a1/a2) of the alkyl (meth)acrylate (a1) and the hydroxyalkyl monomer (a2) is preferably 95/5 to 50/50 by weight. , more preferably 85/15 to 70/30, particularly preferably 80/20 to 75/25. When the content ratio (a1/a2) is within the above numerical range, the adhesive physical properties in the primary cured state are excellent.

When the copolymerization component (a) according to the second aspect contains the ethylenically unsaturated monomer (a3), the content of the ethylenically unsaturated monomer (a3) is relative to 100% by weight of the copolymerization component (a) is usually 50% by weight or less, preferably 40% by weight or less, more preferably 35% by weight or less. If the content of the ethylenically unsaturated monomer (a3) is too high, the adhesion property tends to be lowered when low crosslinking is achieved.

It can also be said that the acrylic resin (A) according to the second aspect is a copolymer having structural units based on the alkyl (meth)acrylate (a1) and structural units based on the hydroxyalkyl monomer (a2). In this case, the acrylic resin (A) is based on the ethylenically unsaturated monomer (a3) in addition to the structural unit based on the alkyl (meth)acrylate (a1) and the structural unit based on the hydroxyalkyl monomer (a2). It may further have structural units as necessary. At this time, the ratio of structural units based on each monomer can be determined according to the composition of the copolymer component (a), and the preferred embodiment is also the same.

The glass transition temperature based on the dynamic viscoelasticity of the acrylic resin (A) according to the second aspect is −10° C. or higher, preferably −5 to 20° C., more preferably 0 to 15° C., particularly preferably 2 ~13°C. If the glass transition temperature based on the dynamic viscoelasticity of the acrylic resin (A) is too high, there is a tendency for the pressure-sensitive adhesive layer to be less conformable to irregularities and less adhesive, resulting in a decrease in adhesive strength. If the glass transition temperature based on the dynamic viscoelasticity of the acrylic resin (A) is too low, there is a tendency for the adhesive physical properties at the time of low crosslinking to deteriorate.

The glass transition temperature based on dynamic viscoelasticity is obtained by the following measuring method.
An acrylic resin solution containing only the acrylic resin (A) and the organic solvent is prepared by using a suitable organic solvent. After adjusting the concentration of the acrylic resin solution, it is coated on a release sheet so that the thickness after drying becomes 50 μm. After that, the organic solvent is removed by drying by heat treatment at 90 to 105° C. for 5 to 10 minutes, and then this is attached to a release sheet to prepare an acrylic resin sheet containing 99% or more acrylic resin. do. After that, a plurality of acrylic resin sheets are laminated to produce an acrylic resin sheet having a thickness of about 800 μm. The dynamic viscoelasticity of the produced sheet was measured under the following conditions, and the temperature at which the loss tangent (loss elastic modulus G''/storage elastic modulus G' = tan δ) was maximized was read, based on the dynamic viscoelasticity. It is defined as the glass transition temperature of the acrylic resin (A).

In the second aspect, the acrylic resin (A) preferably has a weight average molecular weight of 50,000 to 500,000, more preferably 100,000 to 400,000, even more preferably 150,000 to 350,000. If the weight-average molecular weight of the acrylic resin (A) is too large, the viscosity tends to be too high, resulting in poor coatability and handling. If the weight-average molecular weight of the acrylic resin (A) is too small, the cohesive force tends to decrease and the adhesive physical properties tend to decrease.
The weight-average molecular weight of the acrylic resin (A) is the weight-average molecular weight at the completion of production. The weight average molecular weight is measured for the acrylic resin (A) that has not been heated or the like after production.

[Method for producing acrylic resin (A)]
In the second aspect, the acrylic resin (A) can be produced by polymerizing a copolymer component (a) containing an alkyl (meth)acrylate (a1) and a hydroxyalkyl monomer (a2).
The copolymerization component (a) according to the second aspect may further contain an ethylenically unsaturated monomer (a3) as an optional polymerization component.

Examples of polymerization methods for the acrylic resin (A) include conventionally known polymerization methods such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. Solution polymerization is preferred in terms of safety and stability of the reaction and the ability to produce the acrylic resin (A) with any monomer composition.
An example of a preferred method for producing the acrylic resin (A) according to the second aspect is shown below.

For example, solution polymerization can be carried out by mixing or dropping the copolymerization component (a) according to the second aspect and the polymerization initiator into an organic solvent.
Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as n-hexane; esters such as methyl acetate, ethyl acetate and butyl acetate; Aliphatic alcohols such as ethyl alcohol, n-propyl alcohol and isopropyl alcohol; Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; Aliphatic ethers such as dimethyl ether and diethyl ether; Fats such as methylene chloride and ethylene chloride halogenated hydrocarbons; cyclic ethers such as tetrahydrofuran;
Among these organic solvents, esters and ketones are preferred, and ethyl acetate, acetone and methyl ethyl ketone are particularly preferred.
An organic solvent may be used individually by 1 type, and may use 2 or more types together.

As the polymerization initiator used for the polymerization reaction, an azo polymerization initiator, a peroxide polymerization initiator, or the like, which is a normal radical polymerization initiator, can be used.
Examples of azo polymerization initiators include 2,2′-azobis(2-methylbutyronitrile), 2,2′-azobisisobutyronitrile, (1-phenylethyl)azodiphenylmethane, 2,2′ -azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and the like. be done.

The polymerization temperature in the polymerization reaction is usually 40 to 120°C, preferably 50 to 90°C from the viewpoint of stable reaction. If the polymerization temperature is too high, the acrylic resin (A) tends to gel easily. If the polymerization temperature is too low, the activity of the polymerization initiator will decrease, resulting in a decrease in the rate of polymerization, which tends to increase the amount of residual monomers.
The polymerization time in the polymerization reaction is not particularly limited, but it is 0.5 hours or longer, preferably 1 hour or longer, more preferably 2 hours or longer, and particularly preferably 5 hours or longer after the last addition of the polymerization initiator.
The polymerization reaction is preferably carried out while refluxing the solvent in order to facilitate heat removal.

(Photoinitiator (B))
The photoinitiator (B) according to the second aspect contains an intramolecular hydrogen abstraction type photoinitiator (b1). The photoinitiator (B) according to the second aspect preferably further contains an intermolecular hydrogen abstraction type photoinitiator (b2).
The photoinitiator (B) according to the second aspect is other than the intramolecular hydrogen abstraction photoinitiator (b1) and the intermolecular hydrogen abstraction photoinitiator (b2), as long as it does not impair the effects of the invention. may further contain another photoinitiator (b3).

[Intramolecular hydrogen abstraction type photoinitiator (b1)]
The intramolecular hydrogen abstraction type photoinitiator (b1) according to the second aspect has a structure capable of generating radicals by abstracting hydrogen from the photoinitiator itself. For example, the intramolecular hydrogen abstraction type photoinitiator (b1) may have a phenylglyoxylate structure or the like.
Examples of the intramolecular hydrogen-abstracting photoinitiator (b1) according to the second aspect include oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester and methyl phenylglyoxylate. etc.
Among these, oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester having multiple cross-linking points in the molecule is preferable from the viewpoint of cross-linking efficiency at the time of complete curing.
As a commercial product, IGM RESINS B.I. V. "Omnirad MBF" and "Omnirad 754" manufactured by the company.

[Intermolecular hydrogen abstraction type photoinitiator (b2)]
The intermolecular hydrogen abstraction type photoinitiator (b2) according to the second aspect has a structure capable of generating radicals by abstracting hydrogen from sources other than the photoinitiator itself. The intermolecular hydrogen abstraction photoinitiator (b2) may have, for example, a benzophenone structure.
As the intermolecular hydrogen abstraction type photoinitiator (b2) according to the second aspect, for example, benzophenone, 4-methyl-benzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3′-dimethyl- 4-Methoxybenzophenone, 4-(meth)acryloyloxybenzophenone, 4-[2-((meth)acryloyloxy)ethoxy]benzophenone, 4-(meth)acryloyloxy-4′-methoxybenzophenone, carboxymethoxymethoxybenzophenone-polyethylene Glycol 250 diester, methyl 2-benzoylbenzoate, 4-(1,3-acryloyl-1,4,7,10,13-pentoxotridecyl)benzophenone, and the like.

Among these, 4-(meth)acryloyloxybenzophenone, 4-[2-((meth)acryloyloxy)ethoxy]benzophenone, and 4-(meth)acryloyloxybenzophenone, which have multiple crosslink points in the molecule, can be highly crosslinked. Acryloyloxy-4'-methoxybenzophenone, carboxymethoxymethoxybenzophenone-polyethylene glycol 250 diester are preferred.
Commercially available products include "MBP" manufactured by Shinryo Corporation and IGM RESINS B.I. V. "Omnirad BP", "Omnirad 4MBZ", "Esacure TZT", "Omnipol BP" manufactured by the company.

[Other photoinitiator (b3)]
Other photoinitiators (b3) according to the second aspect include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 4-(2-hydroxyethoxy) Phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexylphenylketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, 2-benzyl-2-dimethylamino-1 -Acetophenones such as (4-morpholinophenyl)butanone, 2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone oligomers;
Benzoins such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether;
2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenyl Acylphosphone oxides such as phosphine oxide are included.

As auxiliary agents for the photoinitiator (B) according to the second aspect, triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler's ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethyl Benzoic acid, ethyl 4-dimethylaminobenzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2,4-diethylthioxanthone , 2,4-diisopropylthioxanthone and the like can also be used in combination.
The auxiliary agent for the photoinitiator (B) may be used alone or in combination of two or more.

(Crosslinking agent (C))
The pressure-sensitive adhesive composition according to the second aspect preferably further contains a cross-linking agent (C) in addition to the acrylic resin (A) and the photoinitiator (B).
Examples of the cross-linking agent (C) include an active energy ray cross-linking agent (c1) and a thermal cross-linking agent (c2).
The active energy ray cross-linking agent (c1) and the thermal cross-linking agent (c2) may be used alone or in combination of two or more.

When only the active energy ray cross-linking agent (c1) is contained as the cross-linking agent (C), multistage curing is possible only by controlling the dose of active energy ray. Moreover, when the active energy ray cross-linking agent (c1) and the thermal cross-linking agent (c2) are contained as the cross-linking agent (C), multistage curing can be achieved by using both heat curing and active energy ray curing.
By controlling the cross-linking reaction in this way, the cohesive force of the entire adhesive layer can be adjusted, and stable adhesive physical properties can be obtained after primary curing and after complete curing.

[Active energy ray cross-linking agent (c1)]
Examples of the active energy ray cross-linking agent (c1) include polyfunctional cross-linking agents containing two or more ethylenically unsaturated groups in one molecule.
For example, hexanediol di(meth)acrylate, butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, (poly)ethylene glycol mono(meth)acrylate ) acrylate, (poly)butylene glycol mono (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, (poly) tetramethylene glycol di (meth) acrylate, (poly ) pentamethylene glycol di(meth)acrylate, (poly)hexamethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol Hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, EO-modified glycerin tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate , isocyanuric acid ethylene oxide-modified tri(meth)acrylate, polyfunctional urethane(meth)acrylate, and the like.
Among them, (meth)acrylates containing two ethylenically unsaturated groups are preferable in terms of the balance of adhesive physical properties after curing, and in particular, (poly)ethylene glycol di(meth)acrylate and (poly)propylene glycol. Di(meth)acrylate and (poly)tetramethylene glycol di(meth)acrylate are preferred.
Polyfunctional cross-linking agents may be used alone or in combination of two or more.

[Thermal cross-linking agent (c2)]
The thermal cross-linking agent (c2) can exhibit excellent adhesion by reacting with functional groups derived from functional group-containing monomers that are mainly constituent monomers of the acrylic resin (A). For example, isocyanate cross-linking agent (c2-1), epoxy cross-linking agent (c2-2), aziridine cross-linking agent (c2-3), melamine cross-linking agent (c2-4), aldehyde cross-linking agent (c2-5 ), amine-based cross-linking agents (c2-6), and metal chelate-based cross-linking agents (c2-7). Among these, the isocyanate-based cross-linking agent (c2-1) is preferably used in terms of improving adhesion to the substrate and reactivity with the acrylic resin (A).
The thermal cross-linking agent (c2) may be used alone or in combination of two or more.

(Silane coupling agent (D))
The pressure-sensitive adhesive composition according to the second aspect further contains a silane coupling agent (D) as a compound other than the acrylic resin (A), the photoinitiator (B) and the cross-linking agent (C). is preferable in terms of improving

Silane coupling agents (D) include, for example, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxymethylsilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxy propyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, methyltri(glycidyl)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-( 3,4-epoxycyclohexyl)ethyltrimethoxysilane and the like. Among them, γ-glycidoxypropyltrimethoxysilane is preferable from the viewpoint of heat resistance.
Silane coupling agents (D) may be used alone or in combination of two or more.

(Carbodiimide compound (E))
The pressure-sensitive adhesive composition according to the second aspect contains a carbodiimide compound (E) as a compound other than the acrylic resin (A), the photoinitiator (B), the cross-linking agent (C) and the silane coupling agent (D). It is preferable to further contain from the viewpoint of heat resistance.
Carbodiimide compounds (E) include, for example, bis(2,6-diisopropylphenyl)carbodiimide, dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, tert-butylisopropylcarbodiimide, diphenylcarbodiimide, di-tert- Examples include monocarbodiimides such as butylcarbodiimide and didodecylcarbodiimide, polycarbodiimides containing multiple carbodiimides, and cyclic carbodiimides. Among them, from the viewpoint of heat resistance, monocarbodiimide compounds are preferable, and bis(2,6-diisopropylphenyl)carbodiimide is more preferable.
The carbodiimide compound (E) may be used alone or in combination of two or more.

(Optional component)
The pressure-sensitive adhesive composition according to the second aspect may contain a pressure-sensitive adhesive as another optional component, if necessary. The pressure-sensitive adhesive composition according to the second aspect may contain conventionally known additives such as cross-linking accelerators, antistatic agents, tackifiers and functional dyes.

(Composition of adhesive composition)
In the second aspect, the content of the acrylic resin (A) is preferably 80% by weight or more, more preferably 90 to 99.9% by weight, and 92 to 99.9% by weight with respect to the entire pressure-sensitive adhesive composition. is more preferred. When the content of the acrylic resin (A) is within the above numerical range, excellent adhesive physical properties are likely to be obtained in a low crosslinked state after primary curing.

In the second aspect, the content of the photoinitiator (B) is preferably 0.1 to 5.0 parts by weight, preferably 0.5 to 4.0 parts by weight, relative to 100 parts by weight of the acrylic resin (A). is more preferred, and 1.0 to 3.0 parts by weight is even more preferred. When the content of the photoinitiator (B) is within the above numerical range, sufficient curability can be obtained upon complete curing.

In the second embodiment, the content of the intramolecular hydrogen abstraction type photoinitiator (b1) is preferably 0.1 to 5.0 parts by weight, preferably 0.5 to 3 parts by weight, relative to 100 parts by weight of the acrylic resin (A). 0 parts by weight is more preferred.
If the content of the intramolecular hydrogen abstraction type photoinitiator (b1) is too high, there is a tendency for discoloration to occur after wet heat durability. If the content of the intramolecular hydrogen abstraction type photoinitiator (b1) is too low, the degree of cross-linking will not increase, and the adhesive physical properties during primary curing and the durability after complete curing will tend to deteriorate.

In the second aspect, when the photoinitiator (B) contains the intermolecular hydrogen abstraction photoinitiator (b2), the content of the intermolecular hydrogen abstraction photoinitiator (b2) is the acrylic resin (A) It is preferably 0.1 to 3.0 parts by weight, more preferably 0.5 to 2.0 parts by weight, per 100 parts by weight.
If the content of the intermolecular hydrogen abstraction type photoinitiator (b2) is too high, bleed out tends to deteriorate the durability. If the content of the intermolecular hydrogen abstraction type photoinitiator (b2) is too small, the degree of cross-linking does not increase, and the adhesive properties during primary curing and the durability after complete curing tend to deteriorate.

In the second embodiment, when the photoinitiator (B) contains another photoinitiator (b3), the content of the photoinitiator (b3) is 2.0 parts per 100 parts by weight of the acrylic resin (A). 0 weight part or less is preferable, and 1.0 weight part or less is more preferable.

In the second aspect, when the pressure-sensitive adhesive composition contains the cross-linking agent (C), the content of the cross-linking agent (C) is usually preferably 20 parts by weight or less with respect to 100 parts by weight of the acrylic resin (A). , more preferably 0.001 to 10 parts by weight, more preferably 0.1 to 7.5 parts by weight. If the content of the cross-linking agent (C) is too large, the adhesive strength tends to decrease. If the content of the cross-linking agent (C) is too small, the durability tends to decrease.

In the second aspect, when the pressure-sensitive adhesive composition contains the active energy ray cross-linking agent (c1), the content of the active energy ray cross-linking agent (c1) is usually based on 100 parts by weight of the acrylic resin (A) 0.01 to 20 parts by weight is preferable, 0.1 to 10 parts by weight is more preferable, and 0.5 to 7.5 parts by weight is even more preferable.
If the content of the active energy ray cross-linking agent (c1) is too small, there is a tendency that sufficient durability cannot be obtained due to insufficient cohesion. If the content of the active energy ray cross-linking agent (c1) is too large, the adhesive physical properties during the primary curing tend to deteriorate.

When the pressure-sensitive adhesive composition contains the thermal cross-linking agent (c2) in the second aspect, the content of the thermal cross-linking agent (c2) is usually 0.001 per 100 parts by weight of the acrylic resin (A). ~5 parts by weight is preferred, 0.02 to 1 part by weight is more preferred, and 0.05 to 0.5 parts by weight is even more preferred.
If the content of the thermal cross-linking agent (c2) is too small, the cohesive force tends to be insufficient and the adhesive physical properties tend to deteriorate during the primary curing. If the content of the thermal cross-linking agent (c2) is too large, the adhesive strength tends to decrease at the time of complete curing.

In the second aspect, the active energy ray cross-linking agent (c1) and the thermal cross-linking agent (c2) may be used together as the cross-linking agent (C). When used in combination, the content ratio (c1/c2) of the active energy ray cross-linking agent (c1) and the thermal cross-linking agent (c2) is preferably 100/1 to 100/50 in weight ratio.

In the second aspect, when the pressure-sensitive adhesive composition contains a silane coupling agent (D), the content of the silane coupling agent (D) is from 0.001 to 100 parts by weight of the acrylic resin (A). 3 parts by weight is preferred, 0.005 to 1 part by weight is more preferred, 0.01 to 0.5 parts by weight is even more preferred, and 0.015 to 0.3 parts by weight is particularly preferred.
If the content of the silane coupling agent (D) is too small, it tends to be difficult to obtain the effect of improving the durability. If the content of the silane coupling agent (D) is too large, the adhesive strength tends to decrease due to the influence of bleeding out and the like.

In the second aspect, when the pressure-sensitive adhesive composition contains the carbodiimide compound (E), the content of the carbodiimide compound (E) is 0.01 to 10 parts by weight with respect to 100 parts by weight of the acrylic resin (A). part is preferred, 0.1 to 5 parts by weight is more preferred, 0.2 to 2 parts by weight is even more preferred, and 0.3 to 1 part by weight is particularly preferred.
If the content of the carbodiimide compound (E) is too small, the thermal stability of the acrylic resin (A) tends to decrease. If the content of the carbodiimide-based compound (E) is too high, there is a tendency for durability to decrease due to the effects of bleeding out and the like.

In the second aspect, when the adhesive composition contains other adhesives and additives, the content of the other adhesives and additives is 10 parts by weight or less with respect to 100 parts by weight of the acrylic resin (A). is preferred, and 5 parts by weight or less is more preferred.

(Preparation of adhesive composition)
Acrylic resin (A), photoinitiator (B), if necessary, cross-linking agent (C), silane coupling agent (D), carbodiimide compound (E), by mixing other optional components A pressure-sensitive adhesive composition according to the second aspect can be obtained.
The mixing method is not particularly limited, and various methods such as a method of mixing each component at once, a method of mixing an arbitrary component and then mixing the remaining components all at once or sequentially can be adopted.

(Application)
The pressure-sensitive adhesive composition according to the second aspect can be suitably used as a pressure-sensitive adhesive for a multi-stage curing pressure-sensitive adhesive sheet that cures in a plurality of stages. According to the pressure-sensitive adhesive composition of the second aspect, excellent pressure-sensitive adhesive physical properties can be obtained even in a low crosslinked state after primary curing. Furthermore, after complete curing, not only adhesive physical properties such as ordinary adhesive strength but also excellent durability is exhibited when members of various types and shapes such as polarizing plates and glass are bonded together.

The pressure-sensitive adhesive composition according to the second aspect has low tackiness even in a low cross-linking state after primary curing, and has excellent adhesive physical properties such as high constant load holding power, thereby improving workability and reliability. Therefore, it is particularly suitable for use as an adhesive or an adhesive sheet for use in touch panels, image display devices, and the like.

<Adhesive>
The pressure-sensitive adhesive according to the second aspect is obtained by cross-linking the pressure-sensitive adhesive composition according to the second aspect described above. By cross-linking (curing) the pressure-sensitive adhesive composition according to the second aspect, the acrylic resin (A) contained in the pressure-sensitive adhesive composition forms a cross-linked structure at least either intramolecularly or intermolecularly. As a result, the pressure-sensitive adhesive composition according to the second aspect is crosslinked to become the pressure-sensitive adhesive according to the second aspect.
When the acrylic resin (A) has an active energy ray crosslinkable structural site, a crosslinked structure can be formed by irradiation with an active energy ray.

The pressure-sensitive adhesive according to the second aspect exhibits multistage curability that allows curing in multiple stages. The pressure-sensitive adhesive according to the second aspect becomes in a low crosslinked state by primary curing before complete curing. Complete curing and primary curing are not always clearly distinguishable, but can be distinguished, for example, by differences in gel fraction and dynamic viscoelasticity.

Curing means is not particularly limited in either the primary curing step or the complete curing step, and heating or irradiation with active energy rays may be used. Further, the primary curing step may be divided into a plurality of times, or multistage curing may be performed to achieve a completely cured state.
Since the pressure-sensitive adhesive according to the second aspect is excellent in adhesive properties after primary curing, it is suitably used for bonding optical members constituting touch panels, image display devices, and the like.

It can also be said that the adhesive according to the second aspect contains at least the crosslinked product of the acrylic resin (A) according to the second aspect. The crosslinked product may be a partially crosslinked product in which at least part of the acrylic resin (A) is partially crosslinked, or a completely crosslinked product in which the acrylic resin (A) is entirely crosslinked. good. Moreover, the adhesive according to the second aspect may contain both a partially crosslinked product and a completely crosslinked product of the acrylic resin (A).

<Adhesive sheet>
The pressure-sensitive adhesive sheet according to the second aspect has a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to the second aspect. The pressure-sensitive adhesive sheet according to the second aspect can exhibit multistage curability in which the pressure-sensitive adhesive layer is cured in a plurality of stages.

A pressure-sensitive adhesive sheet can be obtained by providing a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to the second aspect on a base sheet. Also, a double-sided pressure-sensitive adhesive sheet can be obtained by providing a pressure-sensitive adhesive layer on a release sheet.
Furthermore, a substrate-less double-faced PSA sheet can be produced by forming a PSA layer on a release sheet in place of the base sheet, and laminating the release sheet on the opposite side of the PSA layer. A thick pressure-sensitive adhesive layer may be further formed by further forming a pressure-sensitive adhesive layer on the formed pressure-sensitive adhesive layer.
The pressure-sensitive adhesive sheet and double-sided pressure-sensitive adhesive sheet thus obtained are used by peeling off the release sheet from the pressure-sensitive adhesive layer.

Examples of the method for producing the pressure-sensitive adhesive sheet according to the second aspect include the following methods (i) and (ii).
(i) A method of forming a pressure-sensitive adhesive sheet after applying a coating liquid in which the pressure-sensitive adhesive composition according to the second aspect is dissolved in a solvent.
(ii) A method of forming an adhesive sheet after melting the adhesive composition according to the second aspect by heating.

The method (i) will be explained.
When a pressure-sensitive adhesive sheet is formed after applying a coating liquid in which the pressure-sensitive adhesive composition according to the second aspect is dissolved in a solvent, the coating containing the pressure-sensitive adhesive composition according to the second aspect is coated with an appropriate organic solvent. Adjust the concentration of the working liquid and apply it directly onto the substrate sheet. After that, it is dried by heat treatment or the like at 80 to 105° C. for 0.5 to 10 minutes, and then attached to a base sheet or a release sheet. After that, the adhesive composition is crosslinked (cured) by irradiation with active energy rays or aged, and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer can be produced.

The method (ii) will be described.
When the pressure-sensitive adhesive composition according to the second aspect is melted by heating to form a pressure-sensitive adhesive sheet, the melted state is coated on one or both sides of the base sheet, and then the base sheet is cooled, or by a T-die or the like. A pressure-sensitive adhesive layer is formed on one side or both sides of the substrate sheet to a desired thickness by a method such as extrusion lamination on the material sheet. Then, a pressure-sensitive adhesive sheet can be produced by bonding a release sheet to the surface of the pressure-sensitive adhesive layer, if necessary.

In addition, after forming the adhesive layer on the base sheet, if necessary, the active energy ray irradiation treatment is performed, and the adhesive composition having the adhesive layer is cured (crosslinked) by aging. Sheets can be made.
Further, a substrate-less double-sided PSA sheet can be produced by forming a PSA layer on a release sheet and laminating the release sheet on the opposite side of the PSA layer.
The pressure-sensitive adhesive sheet and double-sided pressure-sensitive adhesive sheet thus obtained are used by peeling off the release sheet from the pressure-sensitive adhesive layer.

The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to the second aspect preferably has a haze value of 2% or less, more preferably 0 to 1.5%, particularly preferably 0 when the thickness of the pressure-sensitive adhesive layer is 100 μm. ~1%. If the haze value is too high, the pressure-sensitive adhesive layer tends to whiten and the transparency tends to decrease.
The haze value is obtained by measuring diffuse transmittance and total light transmittance using HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.), and obtained diffuse transmittance (DT) and total light transmittance (TT) values. was substituted into the following [Equation 1] for calculation. This machine complies with JIS K7361-1.
Haze value (%) = (DT/TT) x 100 [Formula 1]

In the second aspect, an optical member with a pressure-sensitive adhesive layer can be obtained by laminating the pressure-sensitive adhesive layer on the optical member. For example, after the adhesive layer surface of the adhesive sheet according to the second embodiment in which the adhesive layer is formed on the release sheet is attached to the optical member, the release sheet is peeled off to obtain the optical member with the adhesive layer. can be obtained. Optical members can also be bonded together using the above double-sided pressure-sensitive adhesive sheet.

Preferred embodiments of the second aspect described above include, but are not limited to, the following [B1] to [B8].
[B1] contains an acrylic resin (A) and a photoinitiator (B), the acrylic resin (A) is a polymerization product of the following copolymerization component (a), and the acrylic resin A pressure-sensitive adhesive composition, wherein (A) has a glass transition temperature based on dynamic viscoelasticity of −10° C. or higher, and the photoinitiator (B) contains an intramolecular hydrogen abstraction type photoinitiator (b1).
The copolymer component (a) includes an alkyl (meth)acrylate (a1) having an alkyl group having 12 or less carbon atoms and having a homopolymer glass transition temperature of −20 to 120° C., and an alkyl chain. At least a hydroxyalkyl monomer (a2) containing a hydroxyl group and an ethylenically unsaturated group is contained, and the content of the alkyl (meth)acrylate (a1) is based on 100% by weight of the copolymerization component (a) is 30% by weight or more, the content of the hydroxyalkyl monomer (a2) is 0.1% by weight or more with respect to 100% by weight of the copolymerization component (a), and the content of the copolymerization component (a) is The average carbon number of the alkyl chain of the hydroxyalkyl monomer (a2) is 2.1 or more.
[B2] The pressure-sensitive adhesive composition according to [B1], wherein the photoinitiator (B) further contains an intermolecular hydrogen abstraction type photoinitiator (b2).
[B3] The pressure-sensitive adhesive composition according to [B1] or [B2], further containing a cross-linking agent (C).
[B4] The adhesive composition according to any one of [B1] to [B3], wherein the acrylic resin (A) has a weight average molecular weight of 50,000 to 500,000.
[B5] A pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition according to any one of [B1] to [B4].
[B6] The pressure-sensitive adhesive according to [B5], wherein the cross-linking is performed by irradiation with an active energy ray.
[B7] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to [B5] or [B6].
[B8] The pressure-sensitive adhesive sheet according to [B7], wherein the pressure-sensitive adhesive layer is multi-stage curing in which it is cured in a plurality of stages.

[Third aspect]
Embodiments of the third aspect of the present invention are described in detail below, but are disclosed as representative examples of preferred embodiments.

<Adhesive composition>
The pressure-sensitive adhesive composition according to the third aspect contains an acrylic resin (A) and a photoinitiator (B). The pressure-sensitive adhesive composition according to the third aspect comprises an acrylic resin (A), a photoinitiator (B), a cross-linking agent (C), a silane coupling agent (D), a carbodiimide compound (E), It may further contain other optional components. Hereinafter, each component will be described in order.

(Acrylic resin (A))
The acrylic resin (A) according to the third aspect is a polymerization product of a copolymer component (a) containing a branched alkyl (meth)acrylate (a1) whose homopolymer has a glass transition temperature of −30° C. or higher. be. Copolymer component (a) is a general term for monomer components having a polymerizable double bond. The copolymerization component (a) does not contain a polymerization initiator and a polymerization solvent.

The copolymerization component (a) according to the third aspect includes, in addition to the branched alkyl (meth)acrylate (a1), a hydroxyl group-containing (meth)acrylate (a2) and an active energy ray-crosslinkable structural site (meth) At least one selected from the group consisting of acrylic acid ester monomers (a3) and ethylenically unsaturated monomers (a4) may be further contained as necessary.

[Branched alkyl (meth)acrylate (a1)]
The branched alkyl (meth)acrylate (a1) according to the third aspect is a (meth)acrylate having a branched alkyl group.
The number of carbon atoms in the branched alkyl group of the branched alkyl (meth)acrylate (a1) is not particularly limited. For example, 30 or less is preferable, 20 or less is more preferable, and 3 to 10 is even more preferable. The lower limit on the number of carbon atoms required to form a normal branch is 3.

The branched alkyl (meth)acrylate (a1) according to the third aspect is a monomer whose homopolymer has a glass transition temperature (hereinafter referred to as “Tg”) of −30° C. or higher.
The Tg of the homopolymer of the branched alkyl (meth)acrylate (a1) according to the third aspect is preferably -30 to 150°C, more preferably -20 to 140°C, still more preferably -15 to 130°C. and particularly preferably -10 to 100°C. Since the Tg of the homopolymer of the branched alkyl (meth)acrylate (a1) is within the above numerical range, it is possible to obtain a pressure-sensitive adhesive sheet with excellent adhesion even when it is attached to an adherend having a complex shape that is subjected to strong stress. .

The homopolymer of the branched alkyl (meth)acrylate (a1) according to the third aspect is a homopolymer of the branched alkyl (meth)acrylate (a1). As the Tg of the homopolymer of the branched alkyl (meth)acrylate (a1), a standard analytical value described in "Polymer Handbook" published by Wiley can be used.

Examples of the branched alkyl (meth)acrylate (a1) according to the third aspect include 2-ethylhexyl methacrylate (Tg: -10°C), isobutyl methacrylate (Tg: 48°C), tert-butyl methacrylate (Tg: 107°C ) and the like. Among them, 2-ethylhexyl methacrylate and isobutyl methacrylate are preferable from the viewpoint of adhesive properties.
Branched alkyl (meth)acrylates (a1) may be used alone or in combination of two or more.

[Hydroxyl group-containing (meth)acrylate (a2)]
The hydroxyl group-containing (meth)acrylate (a2) according to the third aspect is a (meth)acrylate having a hydroxyl group (excluding branched alkyl (meth)acrylates (a1)).
By including the hydroxyl group-containing (meth)acrylate (a2) in the polymerizable component constituting the acrylic resin (A), a structural site derived from the polar group-containing monomer is introduced into the acrylic resin (A).

Examples of the hydroxyl group-containing (meth)acrylate (a2) according to the third aspect include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxy hydroxyalkyl acrylates such as hexyl (meth)acrylate and 8-hydroxyoctyl (meth)acrylate;
caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth)acrylate;
Oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate;
Primary hydroxyl group-containing (meth)acrylates such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate, N-methylol (meth)acrylamide, and hydroxyethylacrylamide;
Secondary hydroxyl group-containing (meth)acrylates such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-chloro 2-hydroxypropyl (meth)acrylate;
Examples include hydroxyl group-containing (meth)acrylates such as 2,2-dimethyl-2-hydroxyethyl (meth)acrylate. Among them, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred.
The hydroxyl group-containing (meth)acrylates (a2) may be used alone or in combination of two or more.

The hydroxyl group-containing (meth)acrylate (a2) according to the third aspect preferably contains a small amount of di(meth)acrylate that may be contained as an impurity in the hydroxyl group-containing (meth)acrylate (a2). Specifically, the content of di(meth)acrylate that can be contained in the hydroxyl group-containing (meth)acrylate (a2) is preferably 0.5% by weight or less, more preferably 0.2% by weight or less, and particularly preferably 0.2% by weight or less. is 0.1% by weight or less, more preferably 0% by weight.

The hydroxyl group-containing (meth)acrylate (a2) according to the third aspect often contains acrylic acid as an impurity, and its content is usually 0.001 in the hydroxyl group-containing (meth)acrylate (a2). It is about 0.5% by weight, and it is preferable to use a smaller amount.

[(Meth)acrylate Monomer (a3) Containing Active Energy Ray Crosslinkable Structural Site]
The acrylic resin (A) according to the third aspect can also have an active energy ray crosslinkable structural site. The active energy ray crosslinkable structural site is a structure capable of forming a crosslinked structure by reacting with a part of the acrylic resin (A) or other curing components that may be contained in the pressure-sensitive adhesive composition by irradiation with an active energy ray. It is a part.
In the third aspect, the active energy ray-crosslinkable structural site is preferably a benzophenone-based crosslinkable structural site because of its high reactivity and excellent improvement in cohesive strength.
Therefore, the copolymer component (a) according to the third aspect is a (meth)acrylic acid ester monomer (a3) containing an active energy ray-crosslinkable structural site (provided, however, that a branched alkyl (meth)acrylate (a1) and a hydroxyl group (excluding the containing (meth)acrylate (a2)) is preferably further contained.

As the (meth)acrylic acid ester monomer (a3) containing an active energy ray crosslinkable structural site according to the third aspect, a (meth)acrylic acid ester monomer having a benzophenone-based crosslinkable structural site is exposed to ultraviolet rays and electron beams. It is preferable in that an efficient crosslinked structure can be formed by an active energy ray such as. Examples thereof include 4-(meth)acryloyloxybenzophenone and the like.
The (meth)acrylic acid ester monomer (a3) containing an active energy ray-crosslinkable structural site may be used alone or in combination of two or more.

Further, when introducing the active energy ray-crosslinkable structural site into the acrylic resin (A), in addition to copolymerizing the active energy ray-crosslinkable structural site-containing (meth)acrylic acid ester monomer (a3), acrylic It is also possible to introduce an ethylenically unsaturated group as an active energy ray crosslinkable structural site by allowing hydroxyl groups to be contained in the resin (A) and reacting the hydroxyl groups with an ethylenically unsaturated group-containing isocyanate compound.

[Ethylenically unsaturated monomer (a4)]
The copolymer component (a) according to the third aspect is a branched alkyl (meth)acrylate (a1), a hydroxyl group-containing (meth)acrylate (a2) and a (meth)acrylic acid ester monomer (a3), other copolymers A polymerizable ethylenically unsaturated monomer (a4) may be further contained as necessary.

Other copolymerizable ethylenically unsaturated monomers (a4) according to the third aspect include alkyl (meth)acrylates such as methyl (meth)acrylate, n-butyl (meth)acrylate and 2-ethylhexyl acrylate. (Excluding branched alkyl (meth)acrylate (a1), hydroxyl group-containing (meth)acrylate (a2) and (meth)acrylate monomer (a3));
Phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenyldiethylene glycol (meth) acrylate, phenoxy polyethylene glycol (meth) acrylate, phenoxy polyethylene glycol-polypropylene glycol-(meth) acrylate, orthophenylphenoxyethyl Aromatic ring-containing monomers such as (meth)acrylates and nonylphenol ethylene oxide adduct (meth)acrylates;
Alicyclic-containing monomers such as cyclohexyloxyalkyl (meth)acrylate, tert-butylcyclohexyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate;
2-Methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 2-butoxyethyl (meth) acrylate, 2-butoxydiethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) Acrylates, methoxytriethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, octoxypolyethyleneglycol-polypropyleneglycol mono(meth)acrylate, lauroxy Ether chain-containing monomers such as polyethylene glycol mono (meth) acrylate and stearoxy polyethylene glycol mono (meth) acrylate;
(Meth)acrylic acid, acrylic acid dimers such as β-carboxyethyl acrylate, carboxylates such as crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, N-glycolic acid and cinnamic acid group-containing monomer;
(Meth)acrylamide, N-(n-butoxyalkyl)(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dimethylaminoalkyl(meth)acrylamide, etc. The amide group-containing monomer of;
Acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinylpyridine, vinylpyrrolidone, dialkyl itaconate, dialkyl fumarate Ester, allyl alcohol, acryl chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethyl allyl vinyl ketone and the like.
Other ethylenically unsaturated monomers (a4) may be used alone or in combination of two or more.

For the purpose of increasing the molecular weight of the acrylic resin (A), ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol Compounds having two or more ethylenically unsaturated groups such as di(meth)acrylate and divinylbenzene can also be used in combination.

[Composition of the copolymer component (a) according to the third aspect]
In the third aspect, the content of the branched alkyl (meth)acrylate (a1) is preferably 10% by weight or more, more preferably 10 to 60% by weight, more preferably 15 to 15% by weight, based on 100% by weight of the copolymer component (a). 50% by weight is more preferred, and 20 to 45% by weight is particularly preferred.
If the content of the branched alkyl (meth)acrylate (a1) is too small, the adhesive properties tend to deteriorate during primary curing. If the content of the branched alkyl (meth)acrylate (a1) is too high, the adhesive properties after complete curing tend to deteriorate.

In the third aspect, the content of the hydroxyl group-containing (meth)acrylate (a2) is preferably 5% by weight or more, more preferably 10 to 40% by weight, more preferably 12 to 12% by weight, based on 100% by weight of the copolymer component (a). 30% by weight is more preferred. If the content of the hydroxyl group-containing (meth)acrylate (a2) is too small, the moisture and heat resistance tends to decrease. If the content of the hydroxyl group-containing (meth)acrylate (a2) is too high, the acrylic resin tends to undergo a self-crosslinking reaction, which tends to lower the heat resistance.

In the third aspect, the content of the (meth)acrylate monomer (a3) is preferably 0.01 to 5% by weight, preferably 0.1 to 2% by weight, relative to 100% by weight of the copolymer component (a). is more preferred, and 0.2 to 1% by weight is even more preferred.
If the content of the (meth)acrylic acid ester monomer (a3) is too small, there is a tendency for the holding power of the active energy ray to form a crosslinked structure to decrease. Moreover, when forming a crosslinked structure for producing a processable adhesive sheet, a large amount of active energy radiation is required. As a result, a large amount of energy is required to produce the pressure-sensitive adhesive sheet, which tends to make efficient production difficult.
If the content of the (meth)acrylic acid ester monomer (a3) is too high, the cohesive force of the entire system tends to be too high and the adhesive force tends to decrease.

In the third aspect, the content of the other ethylenically unsaturated monomer (a4) is usually preferably 80% by weight or less, more preferably 70% by weight or less, more preferably 70% by weight or less, based on 100% by weight of the copolymerization component (a). Weight % or less is more preferable.
If the content of the other ethylenically unsaturated monomer (a4) is too high, the adhesive physical properties at the time of low cross-linking may deteriorate.

It can also be said that the acrylic resin (A) according to the third aspect is a polymer having structural units based on the alkyl (meth)acrylate (a1). Further, in this case, the acrylic resin (A) includes, in addition to the structural unit based on the branched alkyl (meth)acrylate (a1), the structural unit based on the hydroxyl group-containing (meth)acrylate (a2), and the (meth)acrylic acid ester monomer. It may further have at least one selected from the group consisting of structural units based on (a3) and structural units based on the ethylenically unsaturated monomer (a4), if necessary. At this time, the ratio of structural units based on each monomer can be determined according to the composition of the copolymer component (a), and the preferred embodiment is also the same.

The glass transition temperature based on the dynamic viscoelasticity of the acrylic resin (A) according to the third aspect is -10°C or higher, preferably -5 to 20°C, more preferably 0 to 15°C, and 2 to 13°C. is more preferred. If the glass transition temperature based on dynamic viscoelasticity is too high, the pressure-sensitive adhesive layer tends to be less conformable to irregularities and less adhesive, resulting in a decrease in adhesive force. If the glass transition temperature based on dynamic viscoelasticity is too low, adhesive physical properties at the time of low cross-linking tend to decrease.

In the third aspect, the acrylic resin (A) has a weight average molecular weight of 400,000 or less, preferably 10,000 to 350,000, more preferably 50,000 to 300,000, and 100,000 to 290. ,000 is more preferred, and 150,000 to 280,000 is particularly preferred. If the weight-average molecular weight of the acrylic resin (A) is too large, the viscosity tends to be too high, resulting in poor coatability and handling. If the weight-average molecular weight of the acrylic resin (A) is too small, the cohesive force tends to decrease and the adhesive physical properties tend to decrease.
The weight-average molecular weight of the acrylic resin (A) is the weight-average molecular weight at the time of completion of production, and is the weight-average molecular weight of the acrylic resin (A) that has not been heated or the like after production.

The weight average molecular weight of the acrylic resin (A) is the weight average molecular weight in terms of standard polystyrene molecular weight. A column: Shodex GPC KF-806L (exclusion limit molecular weight: 2 × 10 ⁷ , separation range: 100 up to 2×10 ⁷ , theoretical plate number: 10000 plates/line, filler material: styrene-divinylbenzene copolymer, filler particle diameter: 10 μm) are connected in series.
Number average molecular weight can also be measured using a similar method. Further, the dispersity is obtained from the weight average molecular weight and the number average molecular weight.

[Method for producing acrylic resin (A)]
In the third aspect, the acrylic resin (A) can be produced by polymerizing a copolymer component (a) containing a branched alkyl (meth)acrylate (a1).
The copolymerization component (a) according to the third aspect includes optional polymerization components such as hydroxyalkyl (meth)acrylate (a2), (meth)acrylic acid ester monomer (a3), and ethylenically unsaturated monomer (a4). It may be further contained as necessary.

Examples of polymerization methods for the acrylic resin (A) include conventionally known polymerization methods such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. Solution polymerization is preferred in terms of safety and stability of the reaction and the ability to produce the acrylic resin (A) with any monomer composition.
An example of a preferred method for producing the acrylic resin (A) according to the third aspect is shown below.

For example, solution polymerization can be carried out by mixing or dropping the copolymerization component (a) according to the third aspect and the polymerization initiator into an organic solvent.
Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as n-hexane; esters such as methyl acetate, ethyl acetate and butyl acetate; Aliphatic alcohols such as ethyl alcohol, n-propyl alcohol and isopropyl alcohol; Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; Aliphatic ethers such as dimethyl ether and diethyl ether; Fats such as methylene chloride and ethylene chloride halogenated hydrocarbons; cyclic ethers such as tetrahydrofuran; Among them, esters and ketones are preferred, and ethyl acetate, acetone and methyl ethyl ketone are particularly preferred.
An organic solvent may be used individually by 1 type, and may use 2 or more types together.

The amount of the polymerization initiator used is usually 0.001 to 10 parts by weight, preferably 0.1 to 8 parts by weight, more preferably 0.5 to 6 parts by weight, per 100 parts by weight of the copolymer component (a). parts, particularly preferably 1 to 4 parts by weight, more preferably 1.5 to 3 parts by weight, most preferably 2 to 2.5 parts by weight. When the amount of the polymerization initiator used is too small, the rate of polymerization of the acrylic resin (A) decreases, and the amount of residual monomer tends to increase. Moreover, the weight average molecular weight of acrylic resin (A) tends to increase. If the amount of the polymerization initiator used is too large, the acrylic resin (A) tends to gel.

The polymerization temperature in the polymerization reaction is usually 40 to 120°C, preferably 50 to 90°C from the viewpoint of stable reaction. If the polymerization temperature is too high, the acrylic resin (A) tends to gel easily. If the polymerization temperature is too low, the activity of the polymerization initiator will decrease, resulting in a decrease in the rate of polymerization and an increase in residual monomers.

The polymerization time in the polymerization reaction is not particularly limited, but it is 0.5 hours or longer, preferably 1 hour or longer, more preferably 2 hours or longer, and particularly preferably 5 hours or longer after the last addition of the polymerization initiator.
The polymerization reaction is preferably carried out while refluxing the solvent in order to facilitate heat removal.

(Photoinitiator (B))
The photoinitiator (B) according to the third aspect contains an intramolecular hydrogen abstraction photoinitiator (b1) and an intermolecular hydrogen abstraction photoinitiator (b2). The photoinitiator (B) according to the third aspect is other than the intramolecular hydrogen abstraction photoinitiator (b1) and the intermolecular hydrogen abstraction photoinitiator (b2) within a range that does not impair the effects of the invention. may further contain another photoinitiator (b3).

[Intramolecular hydrogen abstraction type photoinitiator (b1)]
Examples of the intramolecular hydrogen-abstracting photoinitiator (b1) according to the third aspect include oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester and oxy-phenyl- Mixtures of acetic acid 2-[2-hydroxy-ethoxy]-ethyl esters, methyl benzoylformate, and the like.
Among these, oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester and oxy-phenyl-acetic acid 2-[2-hydroxy- A mixture of ethoxy]-ethyl esters is preferred.
As a commercial product, IGM RESINS B.I. V. "Omnirad 754" and "Omnirad MBF" manufactured by the company.

[Intermolecular hydrogen abstraction type photoinitiator (b2)]
Examples of the intermolecular hydrogen abstraction type photoinitiator (b2) according to the third aspect include benzophenone, 4-methyl-benzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3′-dimethyl -4-methoxybenzophenone, 4-(meth)acryloyloxybenzophenone, 4-[2-((meth)acryloyloxy)ethoxy]benzophenone, 4-(meth)acryloyloxy-4'-methoxybenzophenone, carboxymethoxymethoxybenzophenone- Examples include polyethylene glycol 250 diester. Among them, 2,4,6-trimethylbenzophenone is preferable because it is liquid and easy to handle. In addition, 4-(meth)acryloyloxybenzophenone, 4-[2-((meth)acryloyloxy)ethoxy]benzophenone, and 4-(meth)acryloyloxy, which have multiple crosslink points in the molecule, can be highly crosslinked. -4'-Methoxybenzophenone, carboxymethoxymethoxybenzophenone-polyethylene glycol 250 diester are preferred.
Commercially available products include "MBP" manufactured by Shinryo Corporation and IGM RESINS B.I. V. "Omnirad BP", "Omnirad 4MBZ", "Esacure TZT", "Omnipol BP" manufactured by the company.

[Other photoinitiator (b3)]
Another photoinitiator (b3) according to the third aspect is oxyphenyl-acetic acid 2-[2-oxo-2-phenylacetoxyethoxy]ethyl ester of an intramolecularly cleaved acetophenone photoinitiator;
Diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl Phenyl ketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, 2-hydroxy-2-methyl- Acetophenones such as 1-[4-(1-methylvinyl)phenyl]propanone oligomers;
Benzoins such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether;
2-isopropylthioxanthone, 4-isopropylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, 1-chloro-4-propoxythioxanthone, 2-(3-dimethylamino-2-hydroxy)-3,4- Thioxanthones such as dimethyl-9H-thioxanthone-9-one mesochloride;
2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenyl Acylphosphone oxides such as phosphine oxide can be mentioned.

As auxiliary agents for the photoinitiator (B) according to the third aspect, triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler's ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethyl Benzoic acid, ethyl 4-dimethylaminobenzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2,4-diethylthioxanthone , 2,4-diisopropylthioxanthone and the like can also be used in combination.
The auxiliary agent for the photoinitiator (B) may be used alone or in combination of two or more.

(Crosslinking agent (C))
The pressure-sensitive adhesive composition according to the third aspect preferably further contains a cross-linking agent (C) in addition to the acrylic resin (A) and the photoinitiator (B).
Examples of the cross-linking agent (C) include an active energy ray cross-linking agent (c1) and a thermal cross-linking agent (c2).
The active energy ray cross-linking agent (c1) and the thermal cross-linking agent (c2) may be used alone or in combination of two or more.

When only the active energy ray cross-linking agent (c1) is contained as the cross-linking agent (C), multistage curing is possible only by controlling the active energy ray dose. Moreover, when the active energy ray cross-linking agent (c1) and the thermal cross-linking agent (c2) are contained as the cross-linking agent (C), multistage curing can be achieved by using both heat curing and active energy ray curing. By controlling the cross-linking reaction in this way, the cohesive force of the entire adhesive layer can be adjusted, and stable adhesive physical properties can be obtained after primary curing and after complete curing.

[Active energy ray cross-linking agent (c1)]
The active energy ray cross-linking agent (c1) includes a monofunctional cross-linking agent containing one ethylenically unsaturated group in one molecule, and a polyfunctional cross-linking agent containing two or more ethylenically unsaturated groups in one molecule. A cross-linking agent may be mentioned. Among them, polyfunctional cross-linking agents are preferred.

Examples of polyfunctional cross-linking agents include hexanediol di(meth)acrylate, butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, (Poly)ethylene glycol mono(meth)acrylate, (poly)butylene glycol mono(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, (poly)tetramethylene glycol Di(meth)acrylate, (poly)pentamethylene glycol di(meth)acrylate, (poly)hexamethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri (meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, EO-modified glycerin tri(meth)acrylate, Examples include tetramethylolmethane tri(meth)acrylate, isocyanuric acid ethylene oxide-modified tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, urethane (meth)acrylate and the like.
Among them, (meth)acrylates containing two ethylenically unsaturated groups are preferable in terms of the balance of adhesive physical properties after curing, and in particular, (poly)ethylene glycol di(meth)acrylate and (poly)propylene glycol. Di(meth)acrylate and (poly)tetramethylene glycol di(meth)acrylate are preferred.
Polyfunctional cross-linking agents may be used alone or in combination of two or more.

[Thermal cross-linking agent (c2)]
The thermal cross-linking agent (c2) can exhibit excellent adhesion by reacting with functional groups derived from functional group-containing monomers that are mainly constituent monomers of the acrylic resin (A). For example, isocyanate cross-linking agent (c2-1), epoxy cross-linking agent (c2-2), aziridine cross-linking agent (c2-3), melamine cross-linking agent (c2-4), aldehyde cross-linking agent (c2-5 ), amine-based cross-linking agents (c2-6), and metal chelate-based cross-linking agents (c2-7).
Among them, the isocyanate-based cross-linking agent (c2-1) is preferably used in terms of improving adhesion to the substrate and reactivity with the acrylic resin (A).
The thermal cross-linking agent (c2) may be used alone or in combination of two or more.

Examples of the isocyanate-based cross-linking agent (c2-1) include tolylene diisocyanate-based compounds such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate;
xylylene diisocyanate compounds such as 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, tetramethyl xylylene diisocyanate;
Aromatic isocyanate compounds such as 1,5-naphthalene diisocyanate and triphenylmethane triisocyanate;
Hexamethylene diisocyanate compounds such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate, and aliphatic isocyanate compounds such as lysine diisocyanate;
Alicyclic isocyanate compounds such as isophorone diisocyanate;
Adducts of these isocyanate compounds and polyol compounds such as trimethylolpropane;
burettes and isocyanurates of these isocyanate compounds;
etc.

(Silane coupling agent (D))
The pressure-sensitive adhesive composition according to the third aspect further contains a silane coupling agent (D) as a compound other than the acrylic resin (A), the photoinitiator (B) and the cross-linking agent (C). is preferable in terms of improving

Silane coupling agents (D) include, for example, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxymethylsilane, γ-glycidoxypropyltrimethoxysilane, γ-glycid xypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, methyltri(glycidyl)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β- (3,4-epoxycyclohexyl)ethyltrimethoxysilane and the like.
Among them, γ-glycidoxypropyltrimethoxysilane is preferable from the viewpoint of heat resistance.
Silane coupling agents (D) may be used alone or in combination of two or more.

(Carbodiimide compound (E))
The pressure-sensitive adhesive composition according to the third aspect contains a carbodiimide compound (E) as a compound other than the acrylic resin (A), the photoinitiator (B), the cross-linking agent (C) and the silane coupling agent (D). Further containing is preferable from the viewpoint of heat resistance.
Carbodiimide compounds (E) include, for example, bis(2,6-diisopropylphenyl)carbodiimide, dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, tert-butylisopropylcarbodiimide, diphenylcarbodiimide, di-tert- Examples include monocarbodiimides such as butylcarbodiimide and didodecylcarbodiimide, polycarbodiimides containing multiple carbodiimides, and cyclic carbodiimides.
Among them, from the viewpoint of heat resistance, monocarbodiimide compounds and bis(2,6-diisopropylphenyl)carbodiimide are preferred.
The carbodiimide compound (E) may be used alone or in combination of two or more.

(Optional component)
The pressure-sensitive adhesive composition according to the third aspect may optionally contain a pressure-sensitive adhesive as another optional component. The pressure-sensitive adhesive composition according to the third aspect may contain conventionally known additives such as cross-linking accelerators, antistatic agents, tackifiers and functional dyes.

(Composition of adhesive composition)
In the third aspect, the content of the acrylic resin (A) is preferably 80% by weight or more, more preferably 90 to 99.9% by weight, and 92 to 99.9% by weight with respect to the entire pressure-sensitive adhesive composition. is more preferred. When the content of the acrylic resin (A) is within the above numerical range, it is easy to obtain a pressure-sensitive adhesive sheet exhibiting excellent pressure-sensitive adhesive physical properties in a low crosslinked state after primary curing.

In the third aspect, the content of the photoinitiator (B) is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5.0 parts by weight, relative to 100 parts by weight of the acrylic resin (A). Preferably, 0.5 to 3.0 parts by weight is more preferable. When the content of the photoinitiator (B) is within the above numerical range, sufficient curability can be obtained upon complete curing.

In the third aspect, the content of the intramolecular hydrogen abstraction type photoinitiator (b1) is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5.0 parts by weight, relative to 100 parts by weight of the acrylic resin (A). Parts by weight are more preferred. If the content of the intramolecular hydrogen abstraction type photoinitiator (b1) is too high, the adhesive strength after complete curing tends to decrease. If the content of the intramolecular hydrogen abstraction type photoinitiator (b1) is too small, the adhesion property tends to deteriorate at a low degree of cross-linking.

In the third aspect, the content of the intermolecular hydrogen abstraction type photoinitiator (b2) is preferably 0.01 to 10 parts by weight, preferably 0.1 to 5.0 parts by weight, relative to 100 parts by weight of the acrylic resin (A). Parts by weight are more preferred. If the content of the intermolecular hydrogen abstraction type photoinitiator (b2) is too high, the adhesive strength after complete curing tends to decrease. If the content of the intermolecular hydrogen abstraction type photoinitiator (b2) is too small, the adhesion properties at a low degree of crosslinking tend to deteriorate.

In the third aspect, when the pressure-sensitive adhesive composition contains the cross-linking agent (C), the content of the cross-linking agent (C) is usually preferably 20 parts by weight or less with respect to 100 parts by weight of the acrylic resin (A). 0.001 to 15 parts by weight is more preferred, and 0.1 to 10 parts by weight is even more preferred. If the content of the cross-linking agent (C) is too large, the adhesive strength tends to decrease. If the content of the cross-linking agent (C) is too small, the adhesive physical properties under high temperature conditions tend to deteriorate.

In the third aspect, when the adhesive composition contains the active energy ray cross-linking agent (c1), the content of the active energy ray cross-linking agent (c1) is usually based on 100 parts by weight of the acrylic resin (A) 0.01 to 20 parts by weight is preferable, 0.1 to 10 parts by weight is more preferable, and 0.5 to 7.5 parts by weight is even more preferable.
If the content of the active energy ray cross-linking agent (c1) is too small, there is a tendency that sufficient durability cannot be obtained due to insufficient cohesion. If the content of the active energy ray cross-linking agent (c1) is too large, the adhesive physical properties during primary curing tend to be lowered.

In the third aspect, when the pressure-sensitive adhesive composition contains the thermal cross-linking agent (c2), the content of the thermal cross-linking agent (c2) is usually 0.00 per 100 parts by weight of the acrylic resin (A). 001 to 5 parts by weight is preferred, 0.02 to 1 part by weight is more preferred, and 0.05 to 0.5 parts by weight is even more preferred.
If the content of the thermal cross-linking agent (c2) is too small, the cohesive force tends to be insufficient and the adhesive physical properties tend to deteriorate during the primary curing. If the content of the thermal cross-linking agent (c2) is too large, the adhesive strength tends to decrease at the time of complete curing.

In the third aspect, it is preferable to use an active energy ray cross-linking agent (c1) and a thermal cross-linking agent (c2) together as the cross-linking agent (C). When used in combination, the content ratio (c1/c2) of the active energy ray cross-linking agent (c1) and the thermal cross-linking agent (c2) is preferably 100/1 to 100/50 in weight ratio.

In the third aspect, when the pressure-sensitive adhesive composition contains a silane coupling agent (D), the content of the silane coupling agent (D) is from 0.001 to 100 parts by weight of the acrylic resin (A). 3 parts by weight is preferred, 0.005 to 1 part by weight is more preferred, 0.01 to 0.5 parts by weight is even more preferred, and 0.015 to 0.3 parts by weight is particularly preferred.
If the content of the silane coupling agent (D) is too small, it tends to be difficult to obtain the effect of improving the durability. If the content of the silane coupling agent (D) is too large, the adhesive strength tends to decrease due to the influence of bleeding out and the like.

In the third aspect, when the adhesive composition contains the carbodiimide compound (E), the content of the carbodiimide compound (E) is 0.01 to 10 parts by weight with respect to 100 parts by weight of the acrylic resin (A). 0.1 to 5 parts by weight is more preferred, 0.2 to 2 parts by weight is even more preferred, and 0.3 to 1 part by weight is particularly preferred.
If the content of the carbodiimide-based compound (E) is too small, the thermal stability of the acrylic resin (A) tends to decrease. If the content of the carbodiimide-based compound (E) is too large, there is a tendency for durability to decrease due to the effects of bleeding out and the like.

In the third aspect, when the adhesive composition contains other adhesives and additives, the content of the other adhesives and additives is 10 parts by weight or less with respect to 100 parts by weight of the acrylic resin (A). is preferred, and 5 parts by weight or less is more preferred.

(Preparation of adhesive composition)
Acrylic resin (A), photoinitiator (B), if necessary, cross-linking agent (C), silane coupling agent (D), carbodiimide compound (E), by mixing other optional components A pressure-sensitive adhesive composition according to the third aspect can be obtained.
The mixing method is not particularly limited, and various methods such as a method of mixing each component at once, a method of mixing arbitrary components and then mixing the remaining components all at once or sequentially can be adopted.

(Application)
The pressure-sensitive adhesive composition according to the third aspect can be suitably used as a pressure-sensitive adhesive for a multi-stage curing pressure-sensitive adhesive sheet that cures in a plurality of stages. According to the pressure-sensitive adhesive composition of the third aspect, excellent pressure-sensitive adhesive physical properties can be obtained in terms of low tackiness and high constant load holding power even in a low crosslinked state after primary curing. After complete curing, it not only has adhesive physical properties such as ordinary adhesive strength, but also has excellent durability when bonding members of various types and shapes such as polarizing plates and glass.

The pressure-sensitive adhesive composition according to the third aspect can continue to adhere to complex shapes that are subject to stress even in a low-crosslinking state after primary curing, and can be completely cured thereafter. Therefore, it is particularly suitable for use as an adhesive or an adhesive sheet for use in touch panels, image display devices, and the like.

<Adhesive>
The pressure-sensitive adhesive according to the third aspect is obtained by cross-linking the pressure-sensitive adhesive composition according to the third aspect described above. By cross-linking (curing) the pressure-sensitive adhesive composition according to the third aspect, the acrylic resin (A) contained in the pressure-sensitive adhesive composition forms a cross-linked structure at least either intramolecularly or intermolecularly. As a result, the pressure-sensitive adhesive composition according to the third aspect is crosslinked to become the pressure-sensitive adhesive according to the third aspect.
When the acrylic resin (A) has an active energy ray crosslinkable structural site, a crosslinked structure can be formed by irradiation with an active energy ray.

The pressure-sensitive adhesive according to the third aspect exhibits multistage curability that allows curing in multiple stages. The pressure-sensitive adhesive according to the third aspect becomes in a low crosslinked state by primary curing before complete curing. Complete curing and primary curing are not always clearly distinguishable, but can be distinguished, for example, by differences in gel fraction and dynamic viscoelasticity.

Curing means is not particularly limited in either the primary curing step or the complete curing step, and heating or irradiation with active energy rays may be used. Further, the primary curing process may be divided into a plurality of times, and multistage curing may be performed to achieve a completely cured state.
Since the pressure-sensitive adhesive according to the third aspect is excellent in adhesive properties after primary curing, it is suitably used for bonding optical members constituting touch panels, image display devices, and the like.

It can also be said that the adhesive according to the third aspect contains at least the crosslinked product of the acrylic resin (A) according to the third aspect. The crosslinked product may be a partially crosslinked product in which at least part of the acrylic resin (A) is partially crosslinked, or a completely crosslinked product in which the acrylic resin (A) is entirely crosslinked. good. Moreover, the pressure-sensitive adhesive according to the third aspect may contain both a partially crosslinked product and a completely crosslinked product of the acrylic resin (A).

<Adhesive sheet>
A pressure-sensitive adhesive sheet according to the third aspect has a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to the third aspect. The pressure-sensitive adhesive sheet according to the third aspect can exhibit multistage curability in which the pressure-sensitive adhesive layer is cured in multiple stages.

A pressure-sensitive adhesive sheet can be obtained by providing a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to the third aspect on a base sheet. Also, a double-sided pressure-sensitive adhesive sheet can be obtained by providing a pressure-sensitive adhesive layer on a release sheet.
Further, a substrate-less double-faced PSA sheet can be produced by forming a PSA layer on a release sheet in place of the base sheet, and laminating the release sheet on the opposite side of the PSA layer. A thick pressure-sensitive adhesive layer may be further formed by further forming a pressure-sensitive adhesive layer on the formed pressure-sensitive adhesive layer.
The pressure-sensitive adhesive sheet and double-sided pressure-sensitive adhesive sheet thus obtained are used by peeling off the release sheet from the pressure-sensitive adhesive layer.

Examples of the method for producing the pressure-sensitive adhesive sheet according to the third aspect include the following methods (i) and (ii).
(i) A method of forming a pressure-sensitive adhesive sheet after applying a coating liquid in which the pressure-sensitive adhesive composition according to the third aspect is dissolved in a solvent.
(ii) A method of forming an adhesive sheet after melting the adhesive composition according to the third aspect by heating.

The method (i) will be explained.
When a pressure-sensitive adhesive sheet is formed after applying a coating liquid in which the pressure-sensitive adhesive composition according to the third aspect is dissolved in a solvent, the coating containing the pressure-sensitive adhesive composition according to the third aspect is coated with an appropriate organic solvent. Adjust the concentration of the working liquid and apply it directly onto the substrate sheet. After that, it is dried by heat treatment or the like at 80 to 105° C. for 0.5 to 10 minutes, and then attached to a base sheet or a release sheet. After that, the adhesive composition is crosslinked (cured) by irradiation with active energy rays or aged, and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer can be produced.

The method (ii) will be described.
When the pressure-sensitive adhesive composition according to the third aspect is melted by heating to form a pressure-sensitive adhesive sheet, the melted state is coated on one or both sides of the base sheet, and then the base sheet is cooled, or a T-die or the like is used. A pressure-sensitive adhesive layer is formed on one side or both sides of the substrate sheet to a desired thickness by a method such as extrusion lamination on the material sheet. Then, a pressure-sensitive adhesive sheet can be produced by bonding a release sheet to the surface of the pressure-sensitive adhesive layer, if necessary.

The gel fraction after complete curing of the adhesive layer of the adhesive sheet is preferably 50 to 95% by weight, more preferably 55 to 90% by weight, and particularly preferably 60 to 85% by weight, from the viewpoint of durability and adhesive strength. %. If the gel fraction is too low, cohesive strength tends to decrease, resulting in a decrease in durability. If the gel fraction is too high, there is a tendency for cohesive strength to increase and adhesive strength to decrease.

The thickness of the adhesive layer of the adhesive sheet is usually preferably 50-3000 μm, more preferably 75-1000 μm, and particularly preferably 100-350 μm. If the thickness of the pressure-sensitive adhesive layer is too thin, there is a tendency for the impact absorption to decrease. If the thickness of the pressure-sensitive adhesive layer is too thick, for example, when it is attached to an optical member, the overall thickness tends to increase, resulting in a decrease in practicality.

The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to the third aspect preferably has a haze value of 2% or less, more preferably 0 to 1.5%, particularly preferably 0 when the thickness of the pressure-sensitive adhesive layer is 100 μm. ~1%. If the haze value is too high, the pressure-sensitive adhesive layer tends to whiten and the transparency tends to decrease.
The haze value is obtained by measuring diffuse transmittance and total light transmittance using HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.), and obtained diffuse transmittance (DT) and total light transmittance (TT) values. was substituted into the following [Equation 1] for calculation. This machine complies with JIS K7361-1.
Haze value (%) = (DT/TT) x 100 [Formula 1]

In the third aspect, an optical member with a pressure-sensitive adhesive layer can be obtained by laminating the pressure-sensitive adhesive layer on the optical member. For example, the pressure-sensitive adhesive layer surface of the pressure-sensitive adhesive sheet according to the third embodiment in which the pressure-sensitive adhesive layer is formed on the release sheet is attached to the optical member, and then the release sheet is peeled off to obtain the optical member with the pressure-sensitive adhesive layer. can be obtained. Optical members can also be bonded together using the above double-sided pressure-sensitive adhesive sheet.

Preferred embodiments of the third aspect described above include, but are not limited to, the following [C1] to [C6].
[C1] Contains an acrylic resin (A) and a photoinitiator (B), and the acrylic resin (A) is a branched alkyl (meth)acrylate having a homopolymer glass transition temperature of −30° C. or higher It is a polymerization product of a copolymer component (a) containing (a1), the acrylic resin (A) has a glass transition temperature based on dynamic viscoelasticity of −10° C. or higher, and the acrylic resin ( A) has a weight average molecular weight of 400,000 or less, and the photoinitiator (B) contains an intramolecular hydrogen abstraction photoinitiator (b1) and an intermolecular hydrogen abstraction photoinitiator (b2). A pressure-sensitive adhesive composition.
[C2] The pressure-sensitive adhesive composition according to [C1], further containing a cross-linking agent (C).
[C3] A pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition according to [C1] or [C2].
[C4] The pressure-sensitive adhesive according to [C3], wherein the cross-linking is performed by irradiation with an active energy ray.
[C5] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to [C3] or [C4].
[C6] The pressure-sensitive adhesive sheet according to [C5], wherein the pressure-sensitive adhesive layer is multi-stage curing in which it is cured in a plurality of stages.

Preferred embodiments of the present invention include, but are not limited to, [1] to [26] below.
[1] Contains an acrylic resin (A) and a photoinitiator (B), the acrylic resin (A) is a polymerization product of the following copolymerization component (a), and the copolymerization Component (a) consists of an alkyl acrylate (a1) having a glass transition temperature of −30 to 50° C. when forming a homopolymer, and an alkyl acrylate having a glass transition temperature of −10 to 120° C. when forming a homopolymer. and a methacrylate (a2), wherein the total content of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is 5% by weight or more relative to 100% by weight of the copolymer component (a). agent composition.
[2] The adhesive composition according to [1], wherein the copolymer component (a) further contains a hydroxyl group-containing monomer (a3).
[3] The pressure-sensitive adhesive composition according to [2], wherein the content of the hydroxyl group-containing monomer (a3) is 0.1% by weight or more relative to 100% by weight of the copolymer component (a).
[4] The adhesive composition according to any one of [1] to [3], wherein the acrylic resin (A) has a glass transition temperature based on dynamic viscoelasticity of −10° C. or higher.
[5] The adhesive composition according to any one of [1] to [4], wherein the acrylic resin (A) has a weight average molecular weight of 50,000 to 500,000.
[6] The adhesive composition according to any one of [1] to [5], wherein the acrylic resin (A) has a weight average molecular weight of 50,000 to 400,000.
[7] The pressure-sensitive adhesive composition according to any one of [1] to [6], wherein the weight ratio of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is 5/95 to 55/45.
[8] Any one of [1] to [7], wherein the total content of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is 30 to 70% by weight relative to the copolymer component (a) The pressure-sensitive adhesive composition according to .
[9] The copolymerization component (a) according to any one of [1] to [8], further comprising a hydroxyl group-containing monomer (a4) containing an alkyl chain, a hydroxyl group and an ethylenically unsaturated group. Adhesive composition.
[10] The pressure-sensitive adhesive according to any one of [1] to [9], wherein the hydroxyl-containing monomer (a3) in the copolymer component (a) has an average alkyl chain carbon number of 2.1 or more. Composition.
[11] The pressure-sensitive adhesive composition according to any one of [1] to [10], wherein one of the alkyl acrylate (a1) and the alkyl methacrylate (a2) has a branched alkyl group.
[12] Any one of [1] to [11], wherein the photoinitiator (B) contains an intramolecular hydrogen abstraction photoinitiator (b1) or an intermolecular hydrogen abstraction photoinitiator (b2) The adhesive composition described.
[13] Any one of [1] to [12], wherein the photoinitiator (B) contains an intramolecular hydrogen abstraction photoinitiator (b1) and an intermolecular hydrogen abstraction photoinitiator (b2). The adhesive composition described.
[14] The pressure-sensitive adhesive composition according to any one of [1] to [13], further containing a cross-linking agent (C).
[15] A pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition according to any one of [1] to [14].
[16] The pressure-sensitive adhesive according to [15], wherein the cross-linking is performed by irradiation with an active energy ray.
[17] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to [15] or [16].
[18] The pressure-sensitive adhesive sheet according to [17], wherein the pressure-sensitive adhesive layer is multi-stage curing that cures in a plurality of stages.
[19] A pressure-sensitive adhesive sheet with a release film, comprising a laminated structure in which a release film is laminated on at least one side of the pressure-sensitive adhesive sheet of [17] or [18].
[20] A laminate for an image display device, comprising a laminated structure in which two image display device constituent members are laminated via the pressure-sensitive adhesive sheet of [17] or [18], and the two image display devices One of the device constituent members is a cover glass having a curved surface shape, and the other of the two image display device constituent members is a touch sensor, an image display panel, a surface protective film, an antireflection film, a color filter, and a polarized light. A laminate for an image display device, which is at least one selected from the group consisting of films and retardation films.
[21] A curved image display device comprising the laminate for an image display device according to [20].
[22] It contains an acrylic resin (A), the acrylic resin (A) is a polymerization product of the following copolymerization component (a), and the copolymerization component (a) is an alkyl acrylate (a1 ) and an alkyl methacrylate (a2).
[23] The pressure-sensitive adhesive composition for curved optical members according to [22], wherein the copolymer component (a) further contains a hydroxyl group-containing monomer (a3).
[24] The adhesive composition for curved optical members according to [22] or [23], wherein the weight ratio of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is 5/95 to 55/45.
[25] Any one of [22] to [24], wherein the total content of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is 10% by weight or more with respect to the copolymer component (a) The pressure-sensitive adhesive composition for curved optical members described above.
[26] The adhesive composition for curved optical members according to any one of [22] to [25], further comprising a photopolymerization initiator.

As described above, each aspect of the present invention has been described by exemplifying specific embodiments, but each embodiment is presented as an example and does not limit the scope of the present invention. Each aspect and each embodiment thereof described in this specification can be variously modified within the scope of achieving the effect of the invention, and within the practicable range, in the description of other aspects Any combination of the disclosed features is possible.

[Examples and comparative examples of the first aspect]
EXAMPLES Examples and comparative examples of the first aspect of the present invention will be specifically described below, but the present invention is not limited to the following descriptions. In the examples, "parts" and "%" mean weight basis. In addition, regarding the weight average molecular weight of the acrylic resin (A), the measurement of the glass transition temperature based on dynamic viscoelasticity, the thickness of the adhesive layer, and the haze value (%), the above-described embodiment according to the first aspect Measured according to the described method.

<Abbreviations, raw materials>
(Alkyl acrylate (a1))
・MA: methyl acrylate (Tg of homopolymer: 8°C)
・ tBA: tert-butyl acrylate (Tg of homopolymer: 41 ° C.)

(Alkyl methacrylate (a2))
・MMA: methyl methacrylate (Tg of homopolymer: 105°C)
・EMA: Ethyl methacrylate (Tg of homopolymer: 65°C)
IBMA: isobutyl methacrylate (Tg of homopolymer: 48°C)

(Hydroxyl group-containing monomer (a3))
・4HBA: 4-hydroxybutyl acrylate ・HEA: 2-hydroxyethyl acrylate

(Ethylenically unsaturated monomer (a4))
2EHA: 2-ethylhexyl acrylate (Tg of homopolymer: -70°C)

・ ADVN: 2,2'-azobis (2,4-dimethylvaleronitrile) (10-hour half-life temperature 52 ° C.)

(Photoinitiator (B))
[Intramolecular hydrogen abstraction type photoinitiator (b1)]
- Omnirad 754: IGM Resins B.I. V. Company product [Intermolecular hydrogen abstraction type photoinitiator (b2)]
- Esacure TZT: IGM Resins B.I. V. Products manufactured by Shinryo Corporation ・MBP: Products manufactured by Shinryo Corporation

(Crosslinking agent (C))
・ Polypropylene glycol #400 diacrylate (NK Ester APG400, a product manufactured by Shin-Nakamura Chemical Co., Ltd.)

(Silane coupling agent (D))
・KBM403 (manufactured by Shin-Etsu Chemical Co., Ltd.)

<Production Example A1: Production of acrylic resin (A-A1)>
35 parts of EMA, 10 parts of MA, 5 parts of 4HBA, 10 parts of HEA and 40 parts of 2EHA were mixed to prepare a monomer solution. Ethyl acetate: 18 parts (boiling point: 77°C), methyl ethyl ketone: 18 parts (boiling point: 80°C), ADVN: 0.01 part as a polymerization initiator, and 100 parts of a premixed monomer solution are placed in a 2 L flask equipped with a condenser. After 10% of the solution was added and heated to reflux in the flask, 10 parts of ethyl acetate, 0.18 parts of ADVN, and the remaining 90% of the above monomer solution were added dropwise over 3 hours. Further, 30 minutes after dropping, a mixture of 10 parts of ethyl acetate and 0.13 parts of ADVN was added dropwise over 1 hour for reaction to obtain a solution of acrylic resin (A-A1). Table 1 shows the measurement results of the glass transition temperature based on the weight average molecular weight (Mw), dispersity, and dynamic viscoelasticity of the acrylic resin (A-A1).

<Production Examples A2 to A6, Comparative Production Examples A1 and A2>
Acrylic resin (A-A2) to acrylic resin (A-A6), acrylic resin (A'- A1) and acrylic resin (A'-A2) were produced. Table 1 shows the measurement results of the glass transition temperature based on the weight average molecular weight (Mw), dispersity, and dynamic viscoelasticity of each acrylic resin.

<Example A1>
Omnirad 754: 2.0 parts (solid content conversion), Esacure TZT: 1.0 part (solid content conversion), polypropylene glycol # for 100 parts of acrylic resin (A-A1) solution (solid content conversion) 400 diacrylate: 5.0 parts (solid content conversion) and KBM403: 0.1 part (solid content conversion) were mixed to obtain an adhesive composition. The obtained pressure-sensitive adhesive composition was adjusted to a solid content concentration of 45% with ethyl acetate, applied to a polyester release sheet so that the thickness after drying was about 50 μm, dried at 100 ° C. for 5 minutes, An adhesive composition layer was formed.

Two polyester-based release sheets on which the pressure-sensitive adhesive composition layer was formed in this manner were prepared and laminated with the pressure-sensitive adhesive composition layers opposed to each other. With both sides of the laminated pressure-sensitive adhesive composition layer sandwiched between polyester-based release sheets, a high-pressure mercury UV irradiation apparatus was used to irradiate the adhesive composition layer with a peak illuminance of 150 mW/cm ² and an integrated exposure amount of 1000 mJ/cm ² (500 mJ/cm ^{2 )} . × 2 passes) to form a pressure-sensitive adhesive layer (primary curing) to obtain a substrate-less double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer thickness of 100 μm.
Next, the release sheet on one side was peeled off from the adhesive layer of the obtained substrate-less double-sided adhesive sheet, and the exposed adhesive layer side was pressed against an easy-adhesion-treated polyethylene terephthalate (PET) sheet (thickness: 125 μm), A PET sheet with an adhesive layer having an adhesive layer thickness of 100 μm was obtained.

<Examples A2 to A6, Comparative Examples A1 and A2>
As shown in Table 2, a pressure-sensitive adhesive composition of each example was prepared in the same manner as in Example A1, except that the acrylic resin (A) and the photoinitiator (B) were changed. Then, in the same manner as in Example A1, a substrate-less double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with a thickness of 100 μm and a PET sheet with a pressure-sensitive adhesive layer were sequentially produced. Table 2 shows the composition of the pressure-sensitive adhesive composition of each example.

<Measurement method, evaluation method>
Measurement methods and evaluation methods for the adhesive compositions of Examples A1 to A6 and Comparative Examples A1 and A2 are shown below. The results are shown in Tables 3-5.

(Gel fraction: before complete curing (after primary curing))
After cutting the substrate-less double-sided pressure-sensitive adhesive sheet of each example into 40 mm × 40 mm, let it stand under the conditions of 23 ° C. × 50% RH for 30 minutes, peel off one release sheet, and expose the exposed pressure-sensitive adhesive layer side. It was pasted on a 50 mm×100 mm SUS mesh sheet (200 mesh). The rest of the release sheet was peeled off, and the pressure-sensitive adhesive layer was wrapped with the SUS mesh sheet by folding back from the central portion in the longitudinal direction of the SUS mesh sheet. The gel fraction (%) was calculated from the weight change when this was immersed in a sealed container containing 250 g of toluene kept at 23° C. for 24 hours.

(Constant load holding power (50°C): before complete curing (after primary curing))
The PET sheet with an adhesive layer of each example was cut into a size of 25 mm width x 75 mm length (adhesive layer width 25 mm x length 50 mm + non-adhesive layer width 25 mm x length 25 mm) and released. The sheet was peeled off. The exposed pressure-sensitive adhesive layer side was attached to a stainless steel plate (SUS304) by reciprocating a 2-kg roller under pressure (attachment area: 25 mm x 50 mm), and allowed to stand in an atmosphere of 50°C for 20 minutes. After that, a weight of 50 g was hung from the end in the length direction of the non-attached part (area 25 mm × 25 mm), a load of 50 g was applied in a direction of 90° to the plane of the stainless steel plate, and it was left to stand for 60 minutes in that state. , the distance at which the PET sheet was peeled off was measured. Evaluation criteria are as follows.
A: The peel distance is less than 10 mm.
B: The peel distance is 10 mm or more and less than 50 mm.
C: The PET sheet was completely peeled off and dropped.

(Probe tack: before complete curing (after primary curing))
The PET sheet with an adhesive layer of each example was cut into a size of 12 mm width x 12 mm length, the release sheet was peeled off, and a probe tack tester (manufactured by Tester Sangyo Co., Ltd., probe tack tester TE-6001) was used. , pressure time of 1 second, affixing pressure of 500 gf, pushing speed of 120 mm/min, lifting speed of 600 mm/min, probe diameter of 5.1 mm (diameter), and probe tack (unit: N) was measured. Evaluation criteria are as follows.
A: The probe tack (unit: N) is less than 5.
B... Probe tack (unit: N) is 5 or more and less than 7.5.
C: The probe tack (unit: N) is 7.5 or more and less than 10.
D... Probe tack (unit: N) is 10 or more.

(Gel fraction: after complete curing)
The substrate-less double-sided pressure-sensitive adhesive sheet of each example was irradiated with ultraviolet rays using a high-pressure mercury UV irradiation device at a peak illuminance of 150 mW/cm ² and an integrated exposure amount of 4000 mJ/cm ² (1000 mJ/cm ² × 4 passes). , 40 mm x 40 mm, and allowed to stand under conditions of 23°C x 50% RH for 30 minutes. Then, one of the release sheets was peeled off, and the exposed pressure-sensitive adhesive layer side was attached to a 50 mm×100 mm SUS mesh sheet (200 mesh). The rest of the release sheet was peeled off, and the pressure-sensitive adhesive layer was wrapped with the SUS mesh sheet by folding back from the central portion in the longitudinal direction of the SUS mesh sheet. The gel fraction (%) was calculated from the weight change when this was immersed in a sealed container containing 250 g of toluene kept at 23° C. for 24 hours.

(180 degree peel strength (23°C): after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 25 mm in width x 100 mm in length, and was irradiated with a high-pressure mercury UV irradiation device with a peak illuminance of 150 mW/cm ² and an integrated exposure of 4000 mJ/cm ² (1000 mJ). /cm ² ×4 passes), and then the release sheet was peeled off. The exposed pressure-sensitive adhesive layer side was attached to non-alkali glass ("Eagle XG" manufactured by Corning, thickness 1.1 mm) under an atmosphere of 23°C and 50% RH with two reciprocations of a 2-kg rubber roller under the same atmosphere. It was left under for 30 minutes. After that, the 180 degree peel strength (N/25 mm) was measured at normal temperature (23° C.) at a peel rate of 300 mm/min.

(Constant load holding power (80°C): after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 25 mm width x 75 mm length (adhesive layer width 25 mm x length 50 mm + non-adhesive layer width 25 mm x length 25 mm). After UV irradiation was performed using a UV irradiation apparatus under the conditions of peak illuminance: 150 mW/cm ² and cumulative exposure amount: 4000 mJ/cm ² (1000 mJ/cm ² ×4 passes), the release sheet was peeled off. The exposed pressure-sensitive adhesive layer side was attached to a stainless steel plate (SUS304) by reciprocating a 2-kg roller under pressure (attachment area: 25 mm x 50 mm), and allowed to stand in an atmosphere of 80°C for 20 minutes. After that, a weight of 50 g was hung from the end of the length direction of the non-attached part (area 25 mm × 25 mm), a load of 50 g was applied in the direction of 90 ° to the plane of the stainless steel plate, and it was left to stand for 60 minutes in that state. , the distance that the PET sheet was peeled off was measured. Evaluation criteria are as follows.
A: The peel distance is less than 5 mm.
B: The peel distance is 5 mm or more and less than 10 mm.
C: The peel distance was 10 mm or more, or the PET sheet was completely peeled and dropped.

(Holding power (80°C): after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 25 mm × 50 mm, and irradiated with a high-pressure mercury UV irradiation device at a peak illuminance of 150 mW/cm ² and an integrated exposure amount of 4000 mJ/cm ² (1000 mJ/cm ^{2 )} . 4 passes), and then the release sheet was peeled off. A stainless steel plate (SUS304) is placed on the exposed adhesive layer side, and a 2 kg roller is reciprocated to apply pressure (pasting area 25 mm × 25 mm), and a creep tester (manufactured by Tester Sangyo Co., Ltd., held with a constant humidity tank) Using a force tester BE-501), a load of 1 kg was applied in an atmosphere of 80° C. for 24 hours to measure the holding force. Evaluation criteria are as follows.
A: No deviation.
B: The deviation is less than 1.0 mm.
C: The shift was 1.0 mm or more, or the PET sheet fell.

(Heat and humidity resistance test: after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 30 mm × 50 mm and irradiated with a high-pressure mercury UV irradiation device at a peak illuminance of 150 mW/cm ² and an integrated exposure amount of 4000 mJ/cm ² (1000 mJ/cm ^{2 )} . 4 passes), and then the release sheet was peeled off. The exposed pressure-sensitive adhesive layer side was attached to non-alkali glass (“Eagle XG” manufactured by Corning, thickness 1.1 mm). After that, autoclave treatment is performed under the conditions of 50 ° C., 0.5 MPa, 20 minutes, and left to stand in an atmosphere of 23 ° C. and 50% RH for 30 minutes to form a layer structure of "non-alkali glass / adhesive layer / PET". A test piece having
Using the obtained test piece, a heat and humidity resistance test was performed for 7 days (168 hours) in an atmosphere of 60° C. and 90% RH, and the haze values before and after the heat and humidity resistance test were measured.

The haze value is obtained by measuring the diffuse transmittance and total light transmittance using a HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.), and the obtained diffuse transmittance (DT) and total light transmittance (TT) values. was substituted into the following [Equation 1] for calculation. Furthermore, the haze value increase rate (%) was calculated from the following [Formula 2]. This machine complies with JIS K7361-1.
Haze value (%) = (DT/TT) x 100 [Formula 1]
Haze value difference (%) = Haze value after moist heat resistance test - Haze value before start of moist heat resistance test [Formula 2]

The evaluation criteria for the moist heat resistance test are as follows.
A: The difference in haze value is less than 0.5%.
B...Haze value difference is 0.5% or more and less than 3.0%.
C...Haze value difference is 3.0% or more.

(Probe tack: after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 12 mm in width x 12 mm in length, and irradiated with a high-pressure mercury UV irradiation device with a peak illuminance of 150 mW/cm ² and an integrated exposure amount of 4000 mJ/cm ² (1000 mJ). / cm ² × 4 passes), the release sheet is peeled off, and a probe tack tester (manufactured by Tester Sangyo Co., Ltd., probe tack tester TE-6001) is used for a pressurization time of 5 seconds. The probe tack (unit: N) was measured under the conditions of a pressure of 1000 gf, a pushing speed of 120 mm/min, a lifting speed of 600 mm/min, and a probe diameter of 5.1 mm (diameter). Evaluation criteria are as follows.
A: The probe tack (unit: N) is less than 5.
B... Probe tack (unit: N) is 5 or more and less than 7.5.
C: The probe tack (unit: N) is 7.5 or more and less than 10.
D... Probe tack (unit: N) is 10 or more.

(curved surface durability: after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 40 mm×120 mm, and the release sheet was peeled off. The exposed pressure-sensitive adhesive layer side is pressure-bonded to one of the polarizing plates having the TAC-based film laminated on both sides of the polarizer, and the polarizing plate having the surface of the TAC-based film is laminated to form a "PET sheet/adhesive layer/polarizing plate" layer. A structured laminate was obtained.
Thereafter, the laminate was adhered and fixed to an aluminum plate (width 70 mm, length 150 mm, thickness 0.3 mm) with a tape so that the PET surface faced the surface, to prepare an aluminum plate-fixed sample. The prepared sample was bent to 5 mmφ with a mandrel tester, fixed in that state, and then autoclaved (0.5 MPa × 50 ° C. × 20 minutes). : 150 mW/cm ² , Accumulated exposure: 4000 mJ/cm ² (1000 mJ/cm ² × 4 passes), the bent sample was irradiated with ultraviolet rays to prepare a sample for evaluation of curved surface durability. The curved surface durability evaluation sample has a layer structure of PET/adhesive layer/polarizing plate/aluminum plate in order from the outside. There is an aluminum plate on the innermost side.
Using the obtained curved surface durability evaluation sample, after exposure under the conditions of 80 ° C., Dry, 7 days and 60 ° C., 90% RH, 7 days, respectively, the bending part and polarized light excluding the bending part The edge of the plate was observed and evaluated according to the following criteria.

(Evaluation criteria: bent portion)
A . . . None of floating, foaming, and paste extrusion is observed.
B . . . Floating, foaming, or paste extrusion is observed.

(Evaluation criteria: edge of polarizing plate)
A .
B . . . Air bubbles are very slightly observed at the edge.
C: Air bubbles are seen in part of the edge.
D . . . Floating and air bubbles were generated on the entire edge.

(Evaluation criteria: Comprehensive evaluation)
A . . . The bending portion was evaluated as A, and the polarizing plate end portion was evaluated as A.
B . . . The bending portion was evaluated as A, and the polarizing plate end portion was evaluated as B or C.
C . . . The bending portion was evaluated as A, and the polarizing plate end portion was evaluated as D.
D . . . The bending portion was evaluated as B, and the polarizing plate end portion was evaluated as one of A to D.

(Polarizing plate durability: after complete curing)
The substrate-less double-sided pressure-sensitive adhesive sheet of each example was cut into a size of 60 mm×100 mm, and one release sheet was peeled off. The exposed pressure-sensitive adhesive layer side was pressure-bonded to one of the polarizing plates having the TAC film laminated on both sides of the polarizer and the polarizing plate having the TAC film surface. Next, the other release sheet was peeled off, and the exposed adhesive layer side was laminated to non-alkali glass (“Eagle XG” manufactured by Corning, thickness 1.1 mm), autoclaved (50 ° C., 0.5 MPa, 20 minutes) was performed. After that, with a high-pressure mercury UV irradiation device, ultraviolet irradiation was performed from the non-alkali glass side at a peak illuminance of 150 mW/cm ² and an integrated exposure amount of 4000 mJ/cm ² (1000 mJ/cm ² × 4 passes) to improve the durability of the polarizing plate. A sample for evaluation was produced.
A sample for polarizing plate durability evaluation was allowed to stand in an atmosphere of 23°C and 50% RH for 1 day, and then subjected to a durability test for 7 days (168 hours) in an atmosphere of 80°C and an atmosphere of 60°C and 90% RH. and evaluated according to the following criteria.
A: The floating of the polarizing plate edge is less than 1 mm.
B . . . The float at the edge of the polarizing plate is less than 1 to 2 mm.
C: The float at the edge of the polarizing plate is 2 mm or more.

The pressure-sensitive adhesive sheets using the pressure-sensitive adhesive compositions of Examples A1 to A6 exhibited excellent adhesive physical properties such as low tackiness and high constant load holding power even in a low crosslinked state before complete curing (after primary curing). rice field. In addition, even after complete curing, excellent adhesion properties and durability were exhibited.
On the other hand, in Comparative Examples A1 and A2, the glass transition temperature of the acrylic resin (A) is less than -10°C. Comparative Example A1 does not contain alkyl methacrylate (a2), and the total content of alkyl acrylate (a1) and alkyl methacrylate (a2) is less than 30% by weight. In Comparative Example A2, the weight ratio of alkyl acrylate (a1) and alkyl methacrylate (a2) was 85.7/14.3.
Compared with Examples A1 to A6, these Comparative Examples A1 and A2 were inferior in adhesive physical properties in a low crosslinked state after primary curing, adhesive physical properties after complete curing, and reliability.

[Examples and comparative examples of the second aspect]
EXAMPLES Examples and comparative examples of the second aspect of the present invention will be specifically described below, but the present invention is not limited to the following description. In the examples, "parts" and "%" are based on weight. In addition, regarding the weight average molecular weight of the acrylic resin (A), the measurement of the glass transition temperature based on dynamic viscoelasticity, the thickness of the adhesive layer, and the haze value (%), the above-described embodiment according to the second aspect Measured according to the described method.

<Abbreviations, raw materials>
(Alkyl (meth)acrylate (a1))
・EMA: Ethyl methacrylate (Tg of homopolymer: 65°C)
・MA: methyl acrylate (Tg of homopolymer: 8°C)
・MMA: methyl methacrylate (Tg of homopolymer: 105°C)

(Hydroxyalkyl monomer (a2))
・4HBA: 4-hydroxybutyl acrylate ・HEA: 2-hydroxyethyl acrylate

(Ethylenically unsaturated monomer (a3))
2EHA: 2-ethylhexyl acrylate (Tg of homopolymer: -70°C)

(Photoinitiator (B))
[Intramolecular hydrogen abstraction type photoinitiator (b1)]
- Omnirad 754: IGM Resins B.I. V. Company product [Intermolecular hydrogen abstraction type photoinitiator (b2)]
- Omnipol BP: IGM Resins B.I. V. company product ・Esacure TZT: IGM Resins B.I. V. Products manufactured by Shinryo Corporation ・MBP: Products manufactured by Shinryo Corporation

<Production Example B1: Production of acrylic resin (A-B1)>
35 parts of EMA, 10 parts of MA, 5 parts of 4HBA, 10 parts of HEA and 40 parts of 2EHA were mixed to prepare a monomer solution. Ethyl acetate: 18 parts (boiling point: 77°C), methyl ethyl ketone: 18 parts (boiling point: 80°C), ADVN: 0.01 part as a polymerization initiator, and 100 parts of a premixed monomer solution are placed in a 2 L flask equipped with a condenser. 10% of the monomer solution was added and heated to reflux in a flask, and then 10 parts of ethyl acetate, 0.18 parts of ADVN, and the remaining 90% of the above monomer solution were added dropwise over 3 hours. Further, 30 minutes after dropping, a mixture of 10 parts of ethyl acetate and 0.13 parts of ADVN was added dropwise over 1 hour to react to obtain a solution of acrylic resin (A-B1). Table 6 shows the measurement results of the glass transition temperature based on the weight average molecular weight (Mw), dispersity, and dynamic viscoelasticity of the acrylic resin (A-B1).

<Production Examples B2 to B4, Comparative Production Examples B1 to B4>
Acrylic resin (A-B2) to acrylic resin (A-B4), acrylic resin (A'- B1) to acrylic resins (A'-B4) were produced. Table 6 shows the measurement results of the glass transition temperature based on the weight average molecular weight (Mw), dispersity, and dynamic viscoelasticity of each acrylic resin.

<Example B1>
Omnirad 754: 2.0 parts (solid content conversion), MBP: 1.0 part (solid content conversion), polypropylene glycol #400 for 100 parts of acrylic resin (A-B1) solution (solid content conversion) Diacrylate: 5.0 parts (converted to solid content) and KBM403: 0.1 part (converted to solid content) were mixed to obtain an adhesive composition. The obtained pressure-sensitive adhesive composition was adjusted to a solid content concentration of 45% with ethyl acetate, applied to a polyester-based release sheet so that the thickness after drying was about 50 μm, dried at 100 ° C. for 5 minutes, An adhesive composition layer was formed.

<Examples B2 to B5, Comparative Examples B1 to B4>
As shown in Table 7, a pressure-sensitive adhesive composition of each example was prepared in the same manner as in Example B1, except that the acrylic resin (A) and the photoinitiator (B) were changed. Then, in the same manner as in Example B1, a substrate-less double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with a thickness of 100 μm and a PET sheet with a pressure-sensitive adhesive layer were sequentially produced. Table 7 shows the composition of the pressure-sensitive adhesive composition of each example.

<Measurement method, evaluation method>
Measurement methods and evaluation methods for the adhesive compositions of Examples B1 to B5 and Comparative Examples B1 to B4 are shown below. The results are shown in Tables 8-10.

(Gel fraction: before complete curing (after primary curing))
After cutting the substrate-less double-sided pressure-sensitive adhesive sheet of each example into 40 mm × 40 mm, let it stand under the conditions of 23 ° C. × 50% RH for 30 minutes, peel off one release sheet, and peel off the exposed pressure-sensitive adhesive layer side. It was pasted on a 50 mm×100 mm SUS mesh sheet (200 mesh). The rest of the release sheet was peeled off, and the pressure-sensitive adhesive layer was wrapped with the SUS mesh sheet by folding back from the central portion in the longitudinal direction of the SUS mesh sheet. The gel fraction (%) was calculated from the weight change when this was immersed in a sealed container containing 250 g of toluene kept at 23° C. for 24 hours.

(Constant load holding power (50°C): before complete curing (after primary curing))
The PET sheet with an adhesive layer of each example was cut into a size of 25 mm width x 75 mm length (adhesive layer width 25 mm x length 50 mm + non-adhesive layer width 25 mm x length 25 mm) and released. The sheet was peeled off. The exposed pressure-sensitive adhesive layer side was attached to a stainless steel plate (SUS304) by reciprocating a 2-kg roller under pressure (attachment area: 25 mm x 50 mm), and allowed to stand in an atmosphere of 50°C for 20 minutes. After that, a weight of 50 g was hung from the end of the length direction of the non-attached part (area 25 mm × 25 mm), a load of 50 g was applied in the direction of 90 ° to the plane of the stainless steel plate, and it was left to stand for 60 minutes in that state. , the distance that the PET sheet was peeled off was measured. Evaluation criteria are as follows.
A: The peel distance is less than 10 mm.
B: The peel distance is 10 mm or more and less than 50 mm.
C: The PET sheet was completely peeled off and dropped.

(Probe tack: before complete curing (after primary curing))
The PET sheet with an adhesive layer of each example was cut into a size of 12 mm in width × 12 mm in length, the release sheet was peeled off, and a probe tack tester (manufactured by Tester Sangyo Co., Ltd., probe tack tester TE-6001) was used. , pressure time of 1 second, affixing pressure of 500 gf, pushing speed of 120 mm/min, lifting speed of 600 mm/min, probe diameter of 5.1 mm (diameter), and probe tack (unit: N) was measured. Evaluation criteria are as follows.
A: The probe tack (unit: N) is less than 5.
B... Probe tack (unit: N) is 5 or more and less than 7.5.
C: The probe tack (unit: N) is 7.5 or more and less than 10.
D... Probe tack (unit: N) is 10 or more.

(Gel fraction: after complete curing)
The substrate-less double-sided pressure-sensitive adhesive sheet of each example was irradiated with ultraviolet rays using a high-pressure mercury UV irradiation apparatus at a peak illuminance of 150 mW/cm ² and an integrated exposure amount of 4000 mJ/cm ² (1000 mJ/cm ² × 4 passes). , 40 mm x 40 mm, and allowed to stand under the conditions of 23°C x 50% RH for 30 minutes. Then, one of the release sheets was peeled off, and the exposed pressure-sensitive adhesive layer side was attached to a 50 mm×100 mm SUS mesh sheet (200 mesh). The rest of the release sheet was peeled off, and the pressure-sensitive adhesive layer was wrapped with the SUS mesh sheet by folding back from the central portion in the longitudinal direction of the SUS mesh sheet. The gel fraction (%) was calculated from the weight change when this was immersed in a sealed container containing 250 g of toluene kept at 23° C. for 24 hours.

(180 degree peel strength (23°C): after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 25 mm in width x 100 mm in length, and was irradiated with a high-pressure mercury UV irradiation device with a peak illuminance of 150 mW/cm ² and an integrated exposure of 4000 mJ/cm ² (1000 mJ). / cm ² × 4 passes), and then the release sheet was peeled off. The exposed pressure-sensitive adhesive layer side was attached to non-alkali glass ("Eagle XG" manufactured by Corning, thickness 1.1 mm) under an atmosphere of 23°C and 50% RH with two reciprocations of a 2-kg rubber roller under the same atmosphere. It was left under for 30 minutes. After that, the 180 degree peel strength (N/25 mm) was measured at normal temperature (23° C.) at a peel speed of 300 mm/min.

(Constant load holding power (80°C): after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 25 mm width x 75 mm length (adhesive layer width 25 mm x length 50 mm + non-adhesive layer width 25 mm x length 25 mm), and high-pressure mercury After UV irradiation was performed using a UV irradiation device under the conditions of peak illuminance: 150 mW/cm ² and cumulative exposure amount: 4000 mJ/cm ² (1000 mJ/cm ² ×4 passes), the release sheet was peeled off. The exposed pressure-sensitive adhesive layer side was attached to a stainless steel plate (SUS304) by reciprocating a 2-kg roller under pressure (attachment area: 25 mm x 50 mm), and allowed to stand in an atmosphere of 80°C for 20 minutes. After that, a weight of 50 g was hung from the end in the length direction of the non-attached part (area 25 mm × 25 mm), a load of 50 g was applied in a direction of 90° to the plane of the stainless steel plate, and it was left to stand for 60 minutes in that state. , the distance that the PET sheet was peeled off was measured. Evaluation criteria are as follows.
A: The peel distance is less than 5 mm.
B: The peel distance is 5 mm or more and less than 10 mm.
C: The peel distance was 10 mm or more, or the PET sheet was completely peeled and dropped.

(Probe tack: after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 12 mm wide x 12 mm long, and irradiated with a high-pressure mercury UV irradiation device with a peak illuminance of 150 mW/cm ² and an integrated exposure amount of 4000 mJ/cm ² (1000 mJ). / cm ² × 4 passes), the release sheet is peeled off, and a probe tack tester (manufactured by Tester Sangyo Co., Ltd., probe tack tester TE-6001) is used for a pressurization time of 5 seconds. The probe tack (unit: N) was measured under the conditions of a pressure of 1000 gf/cm ² , a pushing speed of 120 mm/min, a pulling speed of 600 mm/min, and a probe diameter of 5.1 mm (diameter). Evaluation criteria are as follows.
A: The probe tack (unit: N) is less than 5.
B... Probe tack (unit: N) is 5 or more and less than 7.5.
C: The probe tack (unit: N) is 7.5 or more and less than 10.
D... Probe tack (unit: N) is 10 or more.

(Evaluation criteria: bent portion)
A . . . None of floating, foaming, and paste extrusion is observed.
B . . . Floating, foaming, or sticking out of glue is observed.

The pressure-sensitive adhesive sheets using the pressure-sensitive adhesive compositions of Examples B1 to B5 exhibited excellent adhesive physical properties such as low tackiness and high constant load holding power even in a low crosslinked state before complete curing (after primary curing). rice field. In addition, even after complete curing, excellent adhesion properties and durability were exhibited.
On the other hand, in Comparative Examples B1 and B4, the glass transition temperature of the acrylic resin (A) is less than -10°C. In Comparative Examples B1, B2 and B4, the average carbon number of the alkyl chain of the hydroxyalkyl monomer (a2) in the copolymerization component (a) is less than 2.1. Comparative Example B3 does not use an intramolecular hydrogen abstraction type photoinitiator. Compared to Examples B1 to B5, these Comparative Examples B1 to B4 were inferior in adhesive physical properties in a low crosslinked state after primary curing, and were also inferior in durability after complete curing.

[Examples and comparative examples of the third aspect]
EXAMPLES Examples and comparative examples of the third aspect of the present invention will be specifically described below, but the present invention is not limited to the following descriptions. In the examples, "parts" and "%" are based on weight. In addition, regarding the weight average molecular weight of the acrylic resin (A), the measurement of the glass transition temperature based on dynamic viscoelasticity, the thickness of the adhesive layer, and the haze value (%), the above-mentioned embodiment according to the third aspect Measured according to the described method.

<Abbreviations, raw materials>
(Acrylic resin (A))
[Branched alkyl (meth)acrylate (a1)]
iBMA: isobutyl methacrylate (Tg of homopolymer: 48°C)
2EHMA: 2-ethylhexyl methacrylate (Tg of homopolymer: -10°C)

[Hydroxyl group-containing (meth)acrylate (a2)]
- HEA: 2-hydroxyethyl acrylate (Tg of homopolymer: -15°C)

[Ethylenically unsaturated monomer (a4)]
2EHA: 2-ethylhexyl acrylate (Tg of homopolymer: -70°C)
・MA: methyl acrylate (Tg of homopolymer: 8°C)
・MMA: methyl methacrylate (Tg of homopolymer: 105°C)

(Photoinitiator (B))
[Intramolecular hydrogen abstraction type photoinitiator (b1)]
- Omnirad 754: IGM Resins B.I. V. Company product [Intermolecular hydrogen abstraction type photoinitiator (b2)]
- Esacure TZT: IGM Resins B.I. V. Products manufactured by Omnipol BP: IGM Resins B.I. V. Products manufactured by Shinryo Corporation ・MBP: Products manufactured by Shinryo Corporation

(Crosslinking agent (C))
・Polypropylene glycol #400 diacrylate (NK Ester APG400, a product manufactured by Shin-Nakamura Chemical Co., Ltd.)

<Production Example C1: Production of acrylic resin (A-C1)>
iBMA: 25 parts, 2EHA: 35 parts, MA: 25 parts, and HEA: 15 parts were mixed to prepare a monomer solution. 40 parts of methyl ethyl ketone (boiling point 80° C.) as a polymerization solvent, 0.008 parts of ADVN as a polymerization initiator, and 10% of 100 parts of the previously prepared monomer solution are placed in a 2 L flask equipped with a condenser, and After heating to reflux, a mixed solution of 0.11 parts of ADVN, 10 parts of ethyl acetate, and 90% of the remaining monomer solution was added dropwise over 3 hours. Further, 30 minutes after dropping, a mixture of 10 parts of ethyl acetate and 0.13 parts of ADVN was added dropwise over 1 hour to allow reaction to obtain a solution of acrylic resin (A-C1). Table 11 shows the measurement results of the glass transition temperature based on the weight average molecular weight (Mw), dispersity, and dynamic viscoelasticity of the acrylic resin (A-C1).

<Production Examples C2 to C4, Comparative Production Examples C1 and C2>
Acrylic resin (A-C2) to acrylic resin (A-C4), acrylic resin (A'- C1), an acrylic resin (A'-2) was produced. Table 11 shows the measurement results of the glass transition temperature based on the weight average molecular weight (Mw), dispersity, and dynamic viscoelasticity of each acrylic resin.

<Example C1>
Polypropylene glycol #400 diacrylate: 5.0 parts (solid content conversion), KBM403: 0.1 part (solid content conversion) with respect to 100 parts of acrylic resin (A-C1) solution (solid content conversion), Esacure TZT: 1.0 parts (solid content conversion) and Omnirad 754: 2.0 parts (solid content conversion) were mixed to obtain an adhesive composition. The obtained pressure-sensitive adhesive composition solution was adjusted to a solid content concentration of 50% with ethyl acetate, applied to a polyester-based release sheet so that the thickness after drying was about 50 μm, and dried at 100° C. for 5 minutes. , to form an adhesive composition layer.

Two polyester-based release sheets on which the pressure-sensitive adhesive composition layer was formed in this manner were prepared, and the two pressure-sensitive adhesive composition layers were laminated so as to face each other. With both sides of the laminated pressure-sensitive adhesive composition layer sandwiched between polyester-based release sheets, a high-pressure mercury UV irradiation apparatus was used to irradiate the adhesive composition layer with a peak illuminance of 150 mW/cm ² and an integrated exposure amount of 1000 mJ/cm ² (500 mJ/cm ^{2 )} . × 2 passes) to form a pressure-sensitive adhesive layer (primary curing) by irradiating with ultraviolet rays, to prepare a substrate-less double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer thickness of 100 µm.
Next, the release sheet on one side was peeled off from the adhesive layer of the obtained substrate-less double-sided adhesive sheet, and the exposed adhesive layer side was pressed against an easy-adhesion-treated polyethylene terephthalate (PET) sheet (thickness: 125 μm), A PET sheet with an adhesive layer having a thickness of 100 μm was produced.
In addition, the release sheet on one side was peeled off from the adhesive layer of the base-less double-sided adhesive sheet that had been primarily cured, and the exposed adhesive layer side was placed on one side of a polarizing plate having TAC films laminated on both sides of a polarizer. was pressed against the surface of the TAC film of No. to prepare a polarizing plate with an adhesive layer having a thickness of 100 μm.

<Examples C2 to C6, Comparative Examples C1 to C4>
As shown in Table 12, a pressure-sensitive adhesive composition of each example was prepared in the same manner as in Example C1, except that the type of acrylic resin (A) was changed. Then, in the same manner as in Example C1, a substrate-less double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with a thickness of 100 μm, a pressure-sensitive adhesive layer-attached PET sheet, and a pressure-sensitive adhesive layer-attached polarizing plate were sequentially produced.

<Measurement method, evaluation method>
Measurement methods and evaluation methods for the compositions of Examples C1 to C6 and Comparative Examples C1 to C4 are shown below. The results are shown in Tables 13-15.

(Probe tack: before complete curing (after primary curing))
The PET sheet with an adhesive layer of each example was cut into a size of 10 mm wide x 10 mm long, the release sheet was peeled off, and a probe tack tester (manufactured by Tester Sangyo Co., Ltd., probe tack tester TE-6001) was used. , pressure time of 1 second, affixing pressure of 1000 gf, pushing speed of 120 mm/min, lifting speed of 600 mm/min, probe diameter of 5.1 mm (diameter), and probe tack (unit: N) was measured. Evaluation criteria are as follows.
A: The probe tack (unit: N) is less than 5.
B... Probe tack (unit: N) is 5 or more and less than 7.5.
C: The probe tack (unit: N) is 7.5 or more and less than 10.
D... Probe tack (unit: N) is 10 or more.

(180 degree peel strength (23°C): after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 25 mm in width x 100 mm in length, and irradiated with a high-pressure mercury UV irradiation device with a peak illuminance of 150 mW/cm ² and an integrated exposure of 4000 mJ/cm ² (1000 mJ). / cm ² × 4 passes), and then the release sheet was peeled off. The exposed adhesive layer side was attached to non-alkali glass ("Eagle XG" manufactured by Corning, thickness 1.1 mm) in an atmosphere of 23 ° C. and 50% RH with two reciprocations of a 2 kg rubber roller. Let stand for 30 minutes below. After that, the 180 degree peel strength (N/25 mm) was measured at normal temperature (23° C.) at a peel rate of 300 mm/min.

(Constant load holding power (80°C): after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 25 mm width x 75 mm length (adhesive layer width 25 mm x length 50 mm + non-adhesive layer width 25 mm x length 25 mm). After UV irradiation was performed using a UV irradiation apparatus under the conditions of peak illuminance: 150 mW/cm ² and cumulative exposure amount: 4000 mJ/cm ² (1000 mJ/cm ² ×4 passes), the release sheet was peeled off. The exposed pressure-sensitive adhesive layer side was attached to a stainless steel plate (SUS304) by reciprocating a 2-kg roller under pressure (attachment area: 25 mm x 50 mm), and allowed to stand in an atmosphere of 80°C for 20 minutes. After that, a weight of 50 g was hung from the end of the length direction of the non-attached part (area 25 mm × 25 mm), a load of 50 g was applied in the direction of 90 ° to the plane of the stainless steel plate, and it was left to stand for 60 minutes in that state. , the distance that the PET sheet was peeled off was measured. Evaluation criteria are as follows.
A: The peel distance is less than 5 mm.
B: The peel distance is 5 mm or more and less than 10 mm.
C: The peel distance was 10 mm or more, or the PET sheet fell.

(Heat and humidity resistance: after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 30 mm × 50 mm and irradiated with a high-pressure mercury UV irradiation device at a peak illuminance of 150 mW/cm ² and an integrated exposure amount of 4000 mJ/cm ² (1000 mJ/cm ^{2 )} . 4 passes), and then the release sheet was peeled off. The exposed pressure-sensitive adhesive layer side was attached to non-alkali glass (“Eagle XG” manufactured by Corning, thickness 1.1 mm). After that, autoclave treatment is performed under the conditions of 50 ° C., 0.5 MPa, 20 minutes, and left to stand in an atmosphere of 23 ° C. and 50% RH for 30 minutes to form a layer structure of "non-alkali glass / adhesive layer / PET". A test piece having
Using the obtained test piece, a heat and humidity resistance test was performed for 7 days (168 hours) in an atmosphere of 60° C. and 90% RH, and the haze values before and after the heat and humidity resistance test were measured.

The haze value is obtained by measuring the diffuse transmittance and total light transmittance using a HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.), and the obtained diffuse transmittance (DT) and total light transmittance (TT) values. was substituted into the following formula 1 and calculated. Furthermore, the haze value increase rate (%) was calculated from the following formula 2. This machine complies with JIS K7361-1.
Haze value (%) = (DT/TT) x 100 [Formula 1]
Haze value difference (%) = Haze value after moist heat resistance test - Haze value before start of moist heat resistance test [Formula 2]
Evaluation criteria are as follows.
A: The difference in haze value is less than 0.5%.
B...Haze value difference is 0.5% or more and less than 3.0%.
C...Haze value difference is 3.0% or more.

(Probe tack: after complete curing)
The PET sheet with an adhesive layer of each example was cut into a size of 12 mm wide x 12 mm long, and irradiated with a high-pressure mercury UV irradiation device with a peak illuminance of 150 mW/cm ² and an integrated exposure amount of 4000 mJ/cm ² (1000 mJ). / cm ² × 4 passes), the release sheet is peeled off, and a probe tack tester (manufactured by Tester Sangyo Co., Ltd., probe tack tester TE-6001) is used for a pressurization time of 1 second. The probe tack (unit: N) was measured under the conditions of a pressure of 1000 gf, a pushing speed of 120 mm/min, a lifting speed of 600 mm/min, and a probe diameter of 5.1 mm (diameter). Evaluation criteria are as follows.
A: The probe tack (unit: N) is less than 5.
B... Probe tack (unit: N) is 5 or more and less than 7.5.
C: The probe tack (unit: N) is 7.5 or more and less than 10.
D... Probe tack (unit: N) is 10 or more.

(Polarizing plate durability: after complete curing)
The adhesive layer-attached polarizing plate of each example was cut into a size of 60 mm wide×100 mm long, and the release sheet was peeled off. The exposed adhesive layer side was attached to non-alkali glass (Corning "Eagle XG", thickness 1.1 mm) in an atmosphere of 23 ° C. and 50% RH by applying pressure with a 2 kg rubber roller 2 reciprocations, and then autoclaved. After treatment (0.5 MPa x 50°C x 20 minutes), peak illuminance: 150 mW/cm ² , integrated exposure: 4000 mJ/cm ² (1000 mJ/cm ² x 4 passes) with a high-pressure mercury UV irradiation device. UV irradiation was performed from the non-alkali glass side to prepare a sample for polarizing plate durability evaluation.
The obtained samples for polarizing plate durability evaluation were exposed for 7 days under dry conditions at 80° C. and conditions at 60° C. and 90% RH for 7 days, respectively.
A: The floating of the polarizing plate edge is less than 1 mm.
B . . . The float at the edge of the polarizing plate is less than 1 to 2 mm.
C: The float at the edge of the polarizing plate is 2 mm or more.

(curved surface durability: after complete curing)
The adhesive layer-attached polarizing plate of each example was cut into a size of 40 mm wide×120 mm long, and the release sheet was peeled off. The exposed pressure-sensitive adhesive layer side was attached to an easy-adhesion-treated polyethylene terephthalate (PET) sheet (thickness: 125 μm) under pressure with a rubber roller in an atmosphere of 23° C. and 50% RH. After that, it was attached to an aluminum plate (width 70 mm, length 150 mm, thickness 0.3 mm) with a tape so that the PET surface faced the surface, and fixed to prepare an aluminum plate-fixed sample. The prepared sample was bent to 5 mmφ by a mandrel tester, fixed in that state, and then autoclaved (0.5 MPa × 50 ° C. × 20 minutes). : 150 mW/cm ² , integrated exposure amount: 4000 mJ/cm ² (1000 mJ/cm ² × 4 passes), the sample in a bent state was irradiated with ultraviolet rays to prepare a sample for evaluation of curved surface durability. The curved surface durability evaluation sample has a layer structure of PET/adhesive layer/polarizing plate/aluminum plate in order from the outside. There is an aluminum plate on the innermost side.
Using the obtained sample for curved surface durability evaluation, UV irradiation was performed after exposure under the conditions of 80 ° C., Dry, 7 days and 60 ° C., 90% RH, 7 days. The edge of the polarizing plate excluding the part was observed and evaluated according to the following criteria.

The pressure-sensitive adhesive sheets using the pressure-sensitive adhesive compositions of Examples C1 to C6 exhibited excellent adhesive physical properties such as low tackiness and high constant load holding power even in a low crosslinked state before complete curing (after primary curing). . In addition, even after complete curing, excellent adhesive physical properties were exhibited.
On the other hand, in Comparative Examples C1 and C2, only one of the intramolecular hydrogen abstraction type photoinitiator and the intermolecular hydrogen abstraction type photoinitiator was used. In Comparative Examples C3 and C4, no branched alkyl (meth)acrylate having a homopolymer Tg of −30° C. or higher was used. The pressure-sensitive adhesive sheets using the pressure-sensitive adhesive compositions of Comparative Examples C1 to C4 were inferior to those of Examples C1 to C6 in adhesive physical properties in a low crosslinked state after primary curing.

A pressure-sensitive adhesive using the pressure-sensitive adhesive composition of the present invention has excellent adhesive physical properties in a low crosslinked state after primary curing. A pressure-sensitive adhesive obtained using the pressure-sensitive adhesive composition of the present invention is particularly useful as a pressure-sensitive adhesive for bonding optical members constituting touch panels, image display devices, etc., for sealing organic EL displays, and the like.

Claims

containing an acrylic resin (A) and a photoinitiator (B),
The acrylic resin (A) is a polymerization product of the following copolymer component (a),
The copolymer component (a) comprises an alkyl acrylate (a1) having a glass transition temperature of −30 to 50° C. when forming a homopolymer, and an alkyl acrylate (a1) having a glass transition temperature of −10 to 120° C. when forming a homopolymer. and an alkyl methacrylate (a2) that becomes
The pressure-sensitive adhesive composition, wherein the total content of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is 5% by weight or more relative to 100% by weight of the copolymer component (a).
The pressure-sensitive adhesive composition according to claim 1, wherein the copolymer component (a) further contains a hydroxyl group-containing monomer (a3).
The pressure-sensitive adhesive composition according to claim 2, wherein the content of the hydroxyl group-containing monomer (a3) is 0.1% by weight or more with respect to 100% by weight of the copolymer component (a).
The adhesive composition according to claim 1, wherein the acrylic resin (A) has a glass transition temperature based on dynamic viscoelasticity of -10°C or higher.
The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic resin (A) has a weight average molecular weight of 50,000 to 500,000.
The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic resin (A) has a weight average molecular weight of 50,000 to 400,000.
The pressure-sensitive adhesive composition according to claim 1, wherein the weight ratio of said alkyl acrylate (a1) and said alkyl methacrylate (a2) is from 5/95 to 55/45.
The pressure-sensitive adhesive composition according to claim 1, wherein the total content of said alkyl acrylate (a1) and said alkyl methacrylate (a2) is 30 to 70% by weight based on said copolymer component (a).
The adhesive composition according to claim 1, wherein the copolymer component (a) further contains a hydroxyl group-containing monomer (a4) containing an alkyl chain, a hydroxyl group and an ethylenically unsaturated group.
The pressure-sensitive adhesive composition according to claim 2, wherein the average number of carbon atoms in the alkyl chain of the hydroxyl group-containing monomer (a3) in the copolymer component (a) is 2.1 or more.
The pressure-sensitive adhesive composition according to claim 1, wherein one of the alkyl acrylate (a1) and the alkyl methacrylate (a2) has a branched alkyl group.
The pressure-sensitive adhesive composition according to claim 1, wherein the photoinitiator (B) contains an intramolecular hydrogen abstraction photoinitiator (b1) or an intermolecular hydrogen abstraction photoinitiator (b2).
The pressure-sensitive adhesive composition according to claim 1, wherein the photoinitiator (B) contains an intramolecular hydrogen abstraction photoinitiator (b1) and an intermolecular hydrogen abstraction photoinitiator (b2).
The pressure-sensitive adhesive composition according to claim 1, further comprising a cross-linking agent (C).
A pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition according to any one of claims 1 to 14.
The pressure-sensitive adhesive according to claim 15, wherein the cross-linking is performed by irradiation with active energy rays.
A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to claim 15 or 16.
The pressure-sensitive adhesive sheet according to claim 17, wherein the pressure-sensitive adhesive layer is multi-stage curing in which it is cured in a plurality of stages.
A pressure-sensitive adhesive sheet with a release film, comprising a laminated structure in which a release film is laminated on at least one side of the pressure-sensitive adhesive sheet according to claim 17 or 18.
A laminate for an image display device,
Two image display device constituent members have a laminated structure laminated via the pressure-sensitive adhesive sheet according to claim 17 or 18,
one of the two image display device constituent members is a cover glass having a curved shape;
The other of the two image display device constituent members is at least one or more selected from the group consisting of a touch sensor, an image display panel, a surface protective film, an antireflection film, a color filter, a polarizing film and a retardation film. , a laminate for an image display device.
A curved image display device comprising the laminate for an image display device according to claim 20.
containing an acrylic resin (A),
The acrylic resin (A) is a polymerization product of the following copolymer component (a),
A pressure-sensitive adhesive composition for a curved optical member, wherein the copolymer component (a) contains an alkyl acrylate (a1) and an alkyl methacrylate (a2).
The pressure-sensitive adhesive composition for curved optical members according to claim 22, wherein the copolymer component (a) further contains a hydroxyl group-containing monomer (a3).
The pressure-sensitive adhesive composition for curved optical members according to claim 22 or 23, wherein the weight ratio of said alkyl acrylate (a1) and said alkyl methacrylate (a2) is 5/95 to 55/45.
24. The pressure-sensitive adhesive for curved optical members according to claim 22 or 23, wherein the total content of said alkyl acrylate (a1) and said alkyl methacrylate (a2) is 10% by weight or more relative to said copolymer component (a). Composition.
The pressure-sensitive adhesive composition for curved optical members according to claim 22 or 23, further comprising a photopolymerization initiator.