JP2023034108A - Adhesive sheet, adhesive sheet for flexible image display device surface protective film, and laminate for flexible image display device surface protective film - Google Patents

Abstract

To provide an adhesive sheet having good flexibility and excellent oil resistance.SOLUTION: The adhesive sheet is formed from a photocurable adhesive composition [I] containing a (meth)acrylic copolymer (A) and a photopolymerization initiator (B). The ratio (O/C) of the number of oxygen atoms to the number of carbon atoms in the adhesive sheet measured by X-ray photoelectron spectroscopy is 0.25-0.5%. The (meth)acrylic copolymer (A) is a (meth)acrylic copolymer containing a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a1).SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive sheet for a surface protection film of a flexible image display device, and a laminate for a surface protection film of a flexible image display device, and more specifically, it has sufficient adhesiveness, flexibility, and oil resistance. The present invention relates to a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive sheet for a flexible image display device surface protection film, and a laminate for a flexible image display device surface protection film.

In recent years, flexible image display devices using organic light emitting diodes (OLEDs) and quantum dots (QDs) have been developed and are being widely commercialized.
Examples of flexible image display devices include a bendable device having a curved image display surface, a foldable device that can be repeatedly bent, a rollable device that can be wound up, and a stretchable device that can be expanded and contracted.
In such a flexible image display device, not only optical properties but also flexibility, especially high durability against bending are required.

For example, Patent Literature 1 discloses a laminate film with an adhesive layer that does not cause disturbance in the image displayed at the folded portion after being repeatedly folded.
Patent Document 2 discloses a double-sided pressure-sensitive adhesive sheet having a glass transition temperature and storage elastic modulus within a predetermined range, which does not break or peel even in a bending test close to an actual use environment, and a flexible sheet for image display devices. A laminate having a member is disclosed.

By the way, the cover window member of the display screen used in the flexible image display device as described above is expensive, and in some cases, a surface protective film is further laminated on the surface of the cover window to prevent scratches.
The surface protection film for the display screen requires not only surface protection properties but also high durability against bending.

Furthermore, in recent years, when using laptops, tablets, and smartphones, there are many opportunities for human fingers to come into contact with the housing and image display screen, and the surface of the skin is exposed to sebum, cosmetics, etc. in addition to sweat. Therefore, during long-term use, for example, the oily component gradually penetrates from the edge of the joint between the protective panel and the housing, and penetrates the adhesive layer of the adhesive sheet, resulting in adhesion. Since the pressure-sensitive adhesive of the sheet protrudes from the edge of the adherend, or the adhesion strength is lowered and peeling occurs, there is an increasing demand for improvement of oil resistance.

For example, Patent Document 3 discloses a pressure-sensitive adhesive containing a hydroxyl group-containing (meth)acrylic resin and an isocyanate curing agent. It is described that improvement of sebum property etc. was aimed at.

JP 2020-196255 A WO2018/173896 JP 2020-45443 A

However, although the techniques disclosed in Patent Literatures 1 and 2 take into account durability during bending, they do not take oil resistance into account.
In addition, in Patent Document 3, although oil resistance is studied, it contains methyl acrylate (Tg: 8 ° C.), methyl methacrylate (Tg: 105 ° C.), and an isocyanate cross-linking agent that increase the cohesive force. The glass transition temperature of the agent is high, and the flexibility required in recent years, especially at low temperatures, is still insufficient, and further improvement is required in terms of both flexibility and oil resistance.

Under such circumstances, the present invention provides a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive sheet for a surface protection film of a flexible image display device, and a laminate for a surface protection film of a flexible image display device, which have good flexibility and excellent oil resistance. intended to provide

However, in view of such circumstances, the present inventors diligently studied an excellent pressure-sensitive adhesive sheet that achieves both flexibility and oil resistance, especially a pressure-sensitive adhesive sheet for a surface protection film used in a flexible image display device. In the photocurable pressure-sensitive adhesive composition [I] containing the copolymer (A) and the photopolymerization initiator (B), a (meth)acrylic containing a structural site derived from the hydroxyl group-containing (meth)acrylate (a1) In the adhesive sheet formed from the photocurable adhesive composition [I] using the system copolymer, the ratio of the number of oxygen atoms to the number of carbon atoms (O / C) is within a predetermined range, so that the flexible The present inventors have completed the present invention based on the finding that the oil resistance is good and the oil resistance is excellent.

That is, the present invention has the following aspects.
[1]
A pressure-sensitive adhesive sheet formed from a photocurable pressure-sensitive adhesive composition [I] containing a (meth)acrylic copolymer (A) and a photopolymerization initiator (B),
The pressure-sensitive adhesive sheet has a ratio of the number of oxygen atoms to the number of carbon atoms (O/C) measured by X-ray photoelectron spectroscopy of 0.25 to 0.5,
The pressure-sensitive adhesive sheet, wherein the (meth)acrylic copolymer (A) is a (meth)acrylic copolymer containing a structural site derived from the hydroxyl group-containing (meth)acrylate (a1).
[2]
The (meth)acrylic copolymer (A) is derived from an alkyl (meth)acrylate (a2) containing a structural moiety derived from the hydroxyl group-containing (meth)acrylate (a1) and an alkyl group having 1 to 10 carbon atoms. The pressure-sensitive adhesive sheet according to [1], which is a (meth)acrylic copolymer containing a structural moiety.
[3]
The adhesive sheet according to [1] or [2], wherein the hydroxyl group-containing (meth)acrylate (a1) is a (meth)acrylate containing a hydroxyalkyl group having 3 to 10 carbon atoms.
[4]
The adhesive sheet according to any one of [1] to [3], wherein the (meth)acrylic copolymer (A) has a weight average molecular weight of 600,000 to 1,500,000.
[5]
The pressure-sensitive adhesive sheet according to any one of [1] to [4], wherein the photocurable pressure-sensitive adhesive composition [I] further contains a cross-linking agent (C).
[6]
The pressure-sensitive adhesive sheet according to any one of [1] to [5], wherein the storage shear modulus (G') of the pressure-sensitive adhesive sheet at -20°C is 500 kPa or less.
[7]
The pressure-sensitive adhesive sheet according to any one of [1] to [6], wherein the pressure-sensitive adhesive sheet has a gel fraction of 30 to 95% by weight.
[8]
The pressure-sensitive adhesive sheet according to any one of [1] to [7], wherein the degree of swelling of the pressure-sensitive adhesive sheet with respect to oleic acid is 25% by weight or less.
[9]
The pressure-sensitive adhesive sheet according to any one of [1] to [8], which is used as a surface protective film for flexible image display devices.
[10]
A pressure-sensitive adhesive sheet for a surface protective film of a flexible image display device comprising the pressure-sensitive adhesive sheet according to any one of [1] to [9].
[11]
A laminate for a flexible image display device surface protective film, in which the adhesive sheet according to any one of [1] to [9] and a surface protective film are laminated,
The surface protective film has a surface hardness of 400 MPa or more at a contact depth of 200 to 400 nm measured by a nanoindenter, and is subjected to a bending test of 200,000 times at -20 ° C. under the condition of curvature radius (R) = 1.5 mm. A laminate for a surface protective film for a flexible image display device, which is a member that does not change in appearance when subjected to .
[12]
The laminate for a surface protective film of a flexible image display device according to [11], wherein the surface protective film contains any member selected from polyethylene terephthalate film, polyimide film, aramid film, and glass plate.

The pressure-sensitive adhesive sheet according to one embodiment of the present invention has a surface protection function and flexibility while being used in a flexible image display device, for example, and has excellent oil resistance. It becomes a sheet.

An example of an embodiment of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below.
In the present invention, the term "film" conceptually includes sheets, films and tapes.
In addition, the expression "panel" such as an image display panel, a protective panel, etc. includes a plate, a sheet and a film.

In the present invention, when described as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, "X or more and Y or less" and "preferably larger than X" or "preferably Y It also includes the meaning of "less than".
In addition, when described as "X or more" (X is an arbitrary number), it includes the meaning of "preferably greater than X" unless otherwise specified, and is described as "Y or less" (Y is an arbitrary number). If not otherwise specified, it also includes the meaning of "preferably smaller than Y".
Furthermore, "X and/or Y (X and Y are arbitrary configurations)" means at least one of X and Y, and means only X, only Y, and X and Y. It is something to do.

In the present invention, the "main component" means a component that greatly affects the properties of the object, and the content of the component is usually 30% by weight or more in the object, preferably 35% by weight. above, more preferably at least 50% by weight.
Further, in the present invention, "(meth)acryl" means to include acryl and methacryl, "(meth)acrylate" means to include acrylate and methacrylate, and "(meth)acryloyl" is meant to include acryloyl and methacryloyl.
In the present invention, "X and/or Y (X and Y are arbitrary configurations)" means at least one of X and Y, and there are three types of X only, Y only, and X and Y means

A pressure-sensitive adhesive sheet according to one embodiment of the present invention is formed from a photocurable pressure-sensitive adhesive composition [I] containing a (meth)acrylic copolymer (A) and a photopolymerization initiator (B).

<Photocurable adhesive composition [I]>
The photocurable pressure-sensitive adhesive composition [I] used in the present invention will be described.
The photocurable pressure-sensitive adhesive composition (hereinafter sometimes abbreviated as "pressure-sensitive adhesive composition") [I] contains a (meth)acrylic copolymer (A) and a photopolymerization initiator (B) It is.

The pressure-sensitive adhesive composition [I] is preferably cured with an active energy ray because it facilitates adjustment of the crosslink density and the degree of curing, and causes less damage to the substrate and the like.
The pressure-sensitive adhesive composition [I] may be one that can be cured in multiple stages as described later.

[(Meth)acrylic copolymer (A)]
The (meth)acrylic copolymer (A) is a (meth)acrylic copolymer containing a structural site derived from a hydroxyl group-containing (meth)acrylate (a1), and in particular, as a copolymer component, a hydroxyl group-containing It preferably contains (meth)acrylate (a1).
Furthermore, the (meth)acrylic copolymer (A) is derived from an alkyl (meth)acrylate (a2) containing a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a1) and an alkyl group having 1 to 10 carbon atoms. In particular, it contains a hydroxyl group-containing (meth)acrylate (a1) and an alkyl (meth)acrylate (a2) containing an alkyl group having 1 to 10 carbon atoms as a copolymer component. is preferred.

In addition to the hydroxyl group-containing (meth)acrylate (a1) and the alkyl (meth)acrylate (a2) containing an alkyl group having 1 to 10 carbon atoms, an ethylenically unsaturated monomer (a3) copolymerizable therewith may be contained as a copolymerization component.

Examples of the hydroxyl group-containing (meth)acrylate (a1) include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, Hydroxy (meth) acrylates such as 8-hydroxyoctyl (meth) acrylate, caprolactone-modified hydroxy (meth) acrylates such as caprolactone-modified 2-hydroxyethyl (meth) acrylate, diethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, etc. Oxyalkylene-modified (meth)acrylates, primary hydroxyl group-containing (meth)acrylates such as 2-acryloyloxyethyl-2-hydroxyethyl phthalic acid; 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, secondary hydroxyl group-containing (meth)acrylates such as 3-chloro-2-hydroxypropyl (meth)acrylate; tertiary hydroxyl group-containing (meth)acrylates such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate; can be done. These can be used singly or in combination of two or more.

Among the hydroxyl group-containing (meth)acrylates (a1), primary hydroxyl group-containing (meth)acrylates such as 2-hydroxy (meth)acrylate, 4- Hydroxy (meth) acrylate, 2-hydroxypropyl (meth) acrylate and the like are preferred, and particularly hydroxy (meth) acrylates having 3 to 10 carbon atoms, such as 4-hydroxybutyl (meth) acrylate and 2-hydroxypropyl (meth) Acrylates are preferred, especially 4-hydroxybutyl (meth)acrylate.

The lower limit of the content of the hydroxyl group-containing (meth)acrylate (a1) is usually 3% by weight or more with respect to the entire copolymerization component of the (meth)acrylic copolymer (A) from the viewpoint of adhesive strength. Yes, preferably 5% by weight or more, more preferably 8% by weight or more, still more preferably 10% by weight or more, and particularly preferably 12% by weight or more.
On the other hand, the upper limit of the content of the hydroxyl group-containing (meth)acrylate (a1) is usually 60% by weight or less, preferably 45% by weight or less, from the viewpoint of suppressing an increase in the storage shear modulus (G') at low temperatures. , more preferably 35% by weight or less, still more preferably 30% by weight or less, and particularly preferably 25% by weight or less.

Examples of the alkyl (meth)acrylate (a2) containing an alkyl group having 1 to 10 carbon atoms (excluding the component (a1)) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, ) acrylate, n-butyl (meth) acrylate, n-pentyl (meth) acrylate, n-hexyl (meth) acrylate, n-heptyl (meth) acrylate, n-octyl (meth) acrylate, n-nonyl (meth) acrylate , n-decyl (meth)acrylate and other linear alkyl (meth)acrylates; isopropyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate Branched alkyl (meth)acrylates such as acrylates, neopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate; cyclohexyl (meth)acrylate, t- Alicyclic (meth)acrylates such as butylcyclohexyl (meth)acrylate and the like can be mentioned. These may be used singly or in combination of two or more.

Among these, straight-chain alkyl (meth)acrylates are preferred from the viewpoint of adhesiveness and resilience, and in particular straight-chain alkyl (meth)acrylates having 4 to 8 carbon atoms, further 4 to 6 carbon atoms, from the viewpoint of oil resistance. n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, especially n-butyl (meth)acrylate are preferred.

Also, from the viewpoint of improving cohesion as an adhesive, it is preferable to use alkyl (meth)acrylates having 1 to 3 carbon atoms, such as methyl (meth)acrylate and ethyl (meth)acrylate.

Moreover, from the viewpoint of suppressing an increase in the storage shear modulus (G') at low temperatures, acrylates are particularly preferred.

In the present invention, as the ethylenically unsaturated monomer (a3) copolymerizable with the hydroxyl group-containing (meth)acrylate (a1) and/or the alkyl (meth)acrylate (a2) containing an alkyl group having 1 to 10 carbon atoms, (excluding the above components (a1) and (a2)), for example, ethylenically unsaturated group monomers having functional groups other than hydroxyl groups, (meth)acrylates containing alkyl groups having 11 to 20 carbon atoms, and other copolymerization and the like can be exemplified. These can be used singly or in combination of two or more.

Examples of the ethylenically unsaturated group monomer having a functional group other than a hydroxyl group (hereinafter sometimes referred to as "functional group-containing ethylenically unsaturated monomer") include, for example, a functional group-containing monomer having a nitrogen atom, a carboxy group-containing monomer, Examples include acetoacetyl group-containing monomers, glycidyl group-containing monomers, and the like.
Among these, functional group-containing monomers having a nitrogen atom are preferable, more preferably amino group-containing monomers, amide group-containing monomers, and isocyanate group-containing monomers, and even more preferably, in terms of imparting cohesive force and cross-linking promoting action. It is an amino group-containing monomer.

Examples of the amino group-containing monomer as the functional group-containing monomer having a nitrogen atom include primary amino group-containing (meth)acrylates such as aminomethyl (meth)acrylate and aminoethyl (meth)acrylate; t-butylamino Secondary amino group-containing (meth)acrylates such as ethyl (meth)acrylate and t-butylaminopropyl (meth)acrylate; ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate , dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, and tertiary amino group-containing (meth)acrylates such as dimethylaminopropyl acrylamide.

Examples of the amide group-containing monomer include (meth)acrylamide; N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-propyl (meth)acrylamide, Nn-butyl (meth)acrylamide, diacetone (Meth)acrylamide, N-alkyl(meth)acrylamide such as N,N'-methylenebis(meth)acrylamide; N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl (Meth)acrylamide, N,N-dialkyl(meth)acrylamide such as N,N-ethylmethylacrylamide, N,N-diallyl(meth)acrylamide; N-hydroxymethyl(meth)acrylamide, N-hydroxyethyl(meth) hydroxyalkyl (meth)acrylamides such as acrylamide; alkoxyalkyl (meth)acrylamides such as N-methoxymethyl (meth)acrylamide and N-(n-butoxymethyl) (meth)acrylamide.

Examples of the isocyanate group-containing monomer include 2-(meth)acryloyloxyethyl isocyanate and alkylene oxide adducts thereof. The isocyanate group may be protected with a blocking agent such as methyl ethyl ketone oxime, 3,5-dimethylpyrazole, 1,2,4-triazole and diethyl malonate.

Examples of the carboxy group-containing monomer include (meth)acrylic acid, carboxyethyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2- (Meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxypropyl phthalate, 2-(meth)acryloyloxyethyl maleate, 2-(meth)acryloyloxypropyl maleate, 2-(meth)acryloyloxyethyl Succinic acid, 2-(meth)acryloyloxypropylsuccinic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid, monomethyl maleate, monomethyl itaconate and the like can be mentioned.

Examples of the acetoacetyl group-containing monomer include 2-(acetoacetoxy)ethyl (meth)acrylate and allylacetoacetate.

Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and allylglycidyl (meth)acrylate.

These functional group-containing ethylenically unsaturated monomers may be used alone or in combination of two or more.
The upper limit of the content of the functional group-containing ethylenically unsaturated monomer is the copolymerization component of the (meth)acrylic copolymer (A) from the viewpoint of reducing the possibility of deterioration of adhesiveness and oil resistance due to bleeding out. It is preferably 30% by weight or less, more preferably 20% by weight or less, still more preferably 10% by weight or less, and particularly preferably 5% by weight or less based on the whole. The lower limit is usually 0% by weight.

Examples of (meth)acrylates containing an alkyl group having 11 to 20 carbon atoms include undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, cetyl (meth)acrylate, Linear alkyl (meth)acrylates such as stearyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, 2 - branched alkyl (meth)acrylates such as ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, 3,5,5-trimethyl Alicyclic (meth)acrylates such as cyclohexane (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, and the like. be able to. These may be used singly or in combination of two or more.

In addition, the upper limit of the content when containing the (meth)acrylate containing an alkyl group having 11 to 20 carbon atoms is, from the viewpoint of maintaining oil resistance, the (meth)acrylic copolymer (A) It is preferably 40% by weight or less, more preferably 30% by weight or less, and still more preferably 20% by weight or less, based on the total copolymer component. The lower limit is usually 0% by weight.

Examples of other copolymerizable monomers include phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenyldiethylene glycol (meth) acrylate, phenoxy polyethylene glycol (meth) acrylate, and phenoxy polyethylene glycol-polypropylene. Aromatic (meth)acrylates such as glycol-(meth)acrylate, nonylphenol ethylene oxide adduct (meth)acrylate, 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone , 4-acryloyloxyethoxy-4′-methoxybenzophenone, 4-acryloyloxy-4′-bromobenzophenone, 4-acryloyloxyethoxy-4′-bromobenzophenone, 4-methacryloyloxybenzophenone, 4-methacryloyloxyethoxybenzophenone, 4 -methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone and mixtures thereof (Meth)acrylates having a benzophenone structure, acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl stearate, vinyl propionate, vinyl acetate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone , itaconic acid dialkyl ester, fumaric acid dialkyl ester, allyl alcohol, acryl chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethyl allyl vinyl ketone, and the like. These can be used singly or in combination of two or more.

The (meth)acrylic copolymer (A) may have a photoactive site, such as a polymerizable carbon double bond group, introduced into the side chain. Thereby, the cross-linking efficiency of the pressure-sensitive adhesive composition [I] can be increased, and the pressure-sensitive adhesive composition [I] can be cross-linked by irradiation with active energy rays for a shorter time, and the productivity can be increased.

Methods for introducing a polymerizable carbon double bond group into the side chain of the (meth)acrylic copolymer (A) include, for example, the hydroxyl group-containing (meth)acrylate (a1) described above and the functional group-containing ethylenically unsaturated monomer. After that, a compound having a functional group capable of reacting with these functional groups and a polymerizable carbon double bond group is condensed while maintaining the activity of the polymerizable carbon double bond group, or A method of addition reaction can be mentioned.

Combinations of these functional groups include epoxy group (glycidyl group) and carboxy group, amino group and carboxy group, amino group and isocyanate group, epoxy group (glycidyl group) and amino group, hydroxyl group and epoxy group, hydroxyl group and isocyanate group. etc. can be mentioned. Among these combinations of functional groups, a combination of a hydroxyl group and an isocyanate group is preferable because of ease of reaction control. Among them, a combination in which the copolymer has a hydroxyl group and the compound has an isocyanate group is preferable.
Examples of the isocyanate compound having a polymerizable carbon double bond group include the above-described 2-(meth)acryloyloxyethyl isocyanate and alkylene oxide adducts thereof.

The content of the compound having a functional group capable of reacting with the functional group and a polymerizable carbon double bond group is, from the viewpoint of improving adhesiveness and stress relaxation properties, the (meth)acrylic copolymer (A) 100 It is preferably 10 parts by weight or less, more preferably 8 parts by weight or less, still more preferably 5 parts by weight or less, and particularly preferably 3 parts by weight or less. In addition, it is preferable that it is 1 weight part or more from the point of reaction efficiency.

The glass transition temperature (Tg) of the (meth)acrylic copolymer (A) is preferably −20° C. or less, more preferably − It is 23° C. or lower, more preferably -25° C. or lower, particularly preferably -30° C. or lower. The lower limit of the glass transition temperature (Tg) is usually -50°C.

In the present invention, the glass transition temperature (Tg) of the (meth)acrylic copolymer (A) is measured using a dynamic viscoelasticity measuring device in a shear mode at a frequency of 1 Hz. It is obtained by reading the temperature at which the loss tangent (loss elastic modulus G″/storage elastic modulus G′=tan δ) is maximized.
For example, the (meth)acrylic copolymer (A) is molded into a cylindrical body (height 1.0 mm) having a diameter of 8 mm, and a viscoelasticity measuring device (manufactured by TA Instruments, product name "DHR 2”) can be used to measure the loss tangent (tan δ) under the following measurement conditions.

(Measurement condition)
・Measurement jig: Φ8mm parallel plate ・Distortion: 0.1%
・Frequency: 1Hz
・Measurement temperature: -60 to 100°C
・Temperature increase rate: 5°C/min

The weight-average molecular weight (Mw) of the (meth)acrylic copolymer (A) is preferably 600,000 or more, more preferably 70, from the viewpoint of obtaining a pressure-sensitive adhesive composition [I] with high cohesion. 10,000 or more, more preferably 800,000 or more.
In addition, the upper limit of the weight average molecular weight (Mw) of the (meth)acrylic copolymer (A) is preferably 1,500,000 or less, more preferably 1,200,000 or less, from the viewpoint of handleability and uniform stirring. , more preferably 1,100,000 or less.

In the present invention, the weight average molecular weight (Mw) can be obtained, for example, as follows.
(Method for measuring weight average molecular weight)
4 mg of (meth)acrylic copolymer (A) was dissolved using 12 mL of tetrahydrofuran (THF) as a measurement sample, and a gel permeation chromatography (Gel Permeation Chromatography: GPC) analyzer (Tosoh Corporation The weight average molecular weight (Mw) can be obtained by measuring the molecular weight distribution curve under the following conditions using HLC-8320GPC (manufactured by the company).
・Guard column: TSKguard column HXL
・ Separation column: TSKgelGMHXL (4 columns)
・Temperature: 40℃
・Injection volume: 100 μL
・Polystyrene conversion ・Solvent: THF
・Flow rate: 1.0 mL/min

[Photoinitiator (B)]
The photopolymerization initiator (B) may be any compound that generates radicals upon exposure to active energy rays.
The photopolymerization initiator (B) is broadly classified into two groups according to the mechanism of radical generation: a cleavage type photopolymerization initiator capable of cleaving and decomposing a single bond of the initiator itself to generate radicals, and an excited initiator. and a hydrogen abstraction type photopolymerization initiator capable of forming an exciplex with a hydrogen donor in the system and transferring hydrogen of the hydrogen donor.

The photopolymerization initiator (B) may be either a cleavage type photopolymerization initiator or a hydrogen abstraction type photopolymerization initiator, and may be used either singly or in combination. Further, each may be used singly or in combination of two or more.

In the present invention, the (meth)acrylic copolymer (A) itself does not require a functional group such as a carbon-carbon double bond, and a hydrogen abstraction type photopolymerization initiator is used because it can be efficiently crosslinked. is preferred.

Examples of the cleavage-type photopolymerization initiator include 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxycyclohexylphenylketone, 2-hydroxy-2-methyl-1-phenyl-propane-1 -one, 1-(4-(2-hydroxyethoxy)phenyl)-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-[4-{4-(2-hydroxy- 2-methyl-propionyl)benzyl}phenyl]-2-methyl-propan-1-one, oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone), phenylglyoxy Methyl ricate, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1 -one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, bis(2,4,6-trimethylbenzoyl) -phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine Oxides, derivatives thereof, and the like can be mentioned.

Examples of the hydrogen abstraction type photopolymerization initiator include benzophenone, 4-methyl-benzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3'-dimethyl-4-methoxybenzophenone, 4-(meth ) acryloyloxybenzophenone, methyl 2-benzoylbenzoate, methyl benzoylformate, bis(2-phenyl-2-oxoacetic acid)oxybisethylene, 4-(1,3-acryloyl-1,4,7,10,13- Pentaoxotridecyl)benzophenone, thioxanthone, 2-chlorothioxanthone, 3-methylthioxanthone, 2,4-dimethylthioxanthone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-t-butylanthraquinone, 2-aminoanthraquinone and derivatives thereof etc. can be mentioned. Among them, 4-methylbenzophenone and 2,4,6-trimethylbenzophenone are preferred.

The content of the photopolymerization initiator (B) is usually 0.1 to 10 parts by weight, especially 0.5 to 5 parts by weight, based on 100 parts by weight of the (meth)acrylic copolymer (A). It is preferably 1 to 3 parts by weight. When the content is at least the lower limit, there is a tendency to prevent poor curing, and when the content is at most the upper limit, it is easy to suppress deterioration in solution stability such as precipitation from the adhesive composition [I], and embrittlement and It tends to help control coloring problems.

[Crosslinking agent (C)]
The pressure-sensitive adhesive composition [I] preferably contains a cross-linking agent (C) in addition to the (meth)acrylic copolymer (A) and the photopolymerization initiator (B).

By including the cross-linking agent (C) in the pressure-sensitive adhesive composition [I], the pressure-sensitive adhesive composition [I] forms a crosslinked structure and imparts cohesion and appropriate toughness to the pressure-sensitive adhesive layer (adhesive sheet). can be done. When the adhesive layer has appropriate toughness, it is possible to prevent the surface of the image display device constituent member from undulating and to prevent the adhesive layer from being deformed and cracked at the time of cutting.

The cross-linking agent (C) is a compound and/or composition that forms a cross-linked structure in the pressure-sensitive adhesive composition [I], such as a (meth)acrylic monomer or (meth)acrylic oligomer having two or more functional groups. etc. can be mentioned. These can be used singly or in combination of two or more.

Examples of (meth)acrylic monomers having two or more functional groups include 1,4-butanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin glycidyl ether di( meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tricyclodecanedimethacrylate, tricyclodecanedimethanol di(meth)acrylate, bisphenol A polyethoxydi(meth)acrylate ) acrylate, bisphenol A polypropoxy di (meth) acrylate, bisphenol F polyethoxy di (meth) acrylate, ethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane trioxyethyl (meth) acrylate, ε - caprolactone-modified tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate, pentaerythritol tri (meth) acrylate, propoxylated pentaerythritol tri (meth) acrylate, ethoxylated pentaerythritol tri (meth) acrylate, pentaerythritol tetra ( meth)acrylate, propoxylated pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, poly Tetramethylene glycol di(meth)acrylate, tris(acryloxyethyl)isocyanurate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, tripentaerythritol hexa(meth)acrylate, tripentaerythritol penta( meth)acrylate, neopentylglycol hydroxybivalate di(meth)acrylate, di(meth)acrylate of ε-caprolactone adduct of neopentyl hydroxybivalate, trimethylolpropane tri(meth)acrylate, trimethylolpropane poly Ethoxy tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate and the like can be mentioned.
Among them, from the viewpoint of imparting appropriate toughness to the cured product, (meth)acrylic monomers are preferable, and among them, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, polytetramethylene glycol di (meth) A polyfunctional (meth)acrylic monomer having an alkylene glycol skeleton such as acrylate, particularly a bifunctional (meth)acrylic monomer is more preferable.

The weight average molecular weight of the (meth)acrylic monomer having two or more functional groups is preferably 100 or more, more preferably 200 or more, and even more preferably 250 or more, from the viewpoint of imparting appropriate flexibility to the cured product. Note that the upper limit is usually 1,000.

Moreover, when the pressure-sensitive adhesive composition [I] is cured with visible light, a cured product with high toughness can be obtained. In other words, the cross-linking agent (C) is preferably a (meth)acrylic oligomer having two or more functional groups, and has a weight average molecular weight of 3000 or more, from the viewpoint of obtaining a cured product having appropriate flexibility. It is preferably 5,000 or more, still more preferably 8,000 or more, and particularly preferably 10,000 or more. The upper limit of the weight average molecular weight is usually 100,000.
For the measurement of the weight average molecular weight, the method for measuring the weight average molecular weight of the (meth)acrylic copolymer (A) is applied mutatis mutandis.

Examples of (meth)acrylic oligomers having two or more functional groups include polyfunctional (meth)acrylic oligomers such as polyester (meth)acrylate, epoxy (meth)acrylate, urethane (meth)acrylate, and polyether (meth)acrylate. Oligomers may be mentioned.
Among these, urethane (meth)acrylate oligomers are preferred from the viewpoint of imparting appropriate toughness to the cured product.

The content of the cross-linking agent (C) is 100 parts by weight of the (meth)acrylic copolymer (A) from the viewpoint of being able to impart the shape stability of the pressure-sensitive adhesive sheet and the durability of the laminate. On the other hand, it is preferably 1 part by weight or more, more preferably 2 parts by weight or more, still more preferably 4 parts by weight or more, and particularly preferably 10 parts by weight or more.
Regarding the upper limit of the content of the cross-linking agent (C), from the viewpoint of ensuring adhesiveness, it is preferably 100 parts by weight or less, and 60 parts by weight with respect to 100 parts by weight of the (meth)acrylic copolymer (A). The following is more preferable, 40 parts by weight or less is more preferable, and 30 parts by weight or less is particularly preferable.

Moreover, in addition to the cross-linking agent (C), a thermal cross-linking agent (C') can be used in combination from the viewpoint of further improving cross-linking density and improving long-term reliability.
Examples of the thermal cross-linking agent (C′) include isocyanate-based cross-linking agents, epoxy-based cross-linking agents, aziridine-based cross-linking agents, melamine-based cross-linking agents, aldehyde-based cross-linking agents, amine-based cross-linking agents, and metal chelate-based cross-linking agents. be done. Among these, it is preferable to use an isocyanate-based cross-linking agent from the viewpoint of excellent reactivity with the (meth)acrylic copolymer (A).

<Other ingredients>
The pressure-sensitive adhesive composition [I] contains, as "other components", as long as the effects of the present invention are not impaired, for example, a plasticizer, a silane coupling agent, an ultraviolet absorber, an antirust agent, and a tackifying resin. In addition, various additives such as antioxidants, light stabilizers, metal deactivators, anti-aging agents, moisture absorbers, rust preventives, inorganic particles, etc., can be incorporated as appropriate.
Moreover, if necessary, a reaction catalyst such as a tertiary amine compound, a quaternary ammonium compound, a tin laurate compound, or the like may be appropriately contained.
These can be used singly or in combination of two or more.

(Plasticizer)
A plasticizer is a material for improving workability and flexibility by softening a resin having a high elastic modulus. Examples of the plasticizer include monofunctional (meth)acrylic oligomers such as polyester (meth)acrylate, urethane (meth)acrylate, and polyether (meth)acrylate. Among these, urethane (meth)acrylate oligomers are preferred from the viewpoint of imparting appropriate toughness to the cured product.

(Silane coupling agent)
A silane coupling agent is an organosilicon compound containing in its structure at least one reactive functional group and at least one alkoxy group bonded to a silicon atom. Examples of the reactive functional group include epoxy group, (meth)acryloyl group, mercapto group, hydroxyl group, carboxy group, amino group, amide group, and isocyanate group. groups, mercapto groups are preferred.

From the standpoint of durability and storage stability, the silicon-bonded alkoxy group preferably contains an alkoxy group having 1 to 8 carbon atoms, and particularly preferably a methoxy group or an ethoxy group.
The silane coupling agent may have a reactive functional group and an organic substituent other than the silicon-bonded alkoxy group, such as an alkyl group or a phenyl group.

Silane coupling agents used in the present invention include, for example, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyl. A monomeric epoxy group-containing silane coupling agent, which is a silane compound such as methyldimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, or a part of the silane compound undergoes hydrolytic condensation polymerization, an oligomeric epoxy group-containing silane coupling agent, which is a silane compound obtained by cocondensation of the silane compound and an alkyl group-containing silane compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane;
Monomeric mercapto group-containing silane coupling agents that are silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, γ-mercaptopropyldimethoxymethylsilane, 3-mercaptopropylmethyldimethoxysilane, and the above-mentioned A silane compound obtained by hydrolytic condensation polymerization of a part of the silane compound or co-condensation of the silane compound and an alkyl group-containing silane compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, etc. an oligomeric mercapto group-containing silane coupling agent;
(Meth), such as 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, etc. acryloyl group-containing silane coupling agent;
N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, amino group-containing silane coupling agents such as N-phenyl-3-aminopropyltrimethoxysilane;
an isocyanate group-containing silane coupling agent such as 3-isocyanatopropyltriethoxysilane;
Examples thereof include vinyl group-containing silane coupling agents such as vinyltrimethoxysilane and vinyltriethoxysilane.
These may be used independently and may use 2 or more types together.

Among these, epoxy group-containing silane coupling agents and mercapto group-containing silane coupling agents are preferably used from the viewpoint of excellent durability, and epoxy group-containing silane coupling agents are particularly preferred.

The content of the silane coupling agent is preferably 0.005 to 10 parts by weight, particularly preferably 0.01 to 5 parts by weight, relative to 100 parts by weight of the (meth)acrylic copolymer (A). part, more preferably 0.05 to 1 part by weight. When the content is at least the lower limit, the durability tends to be improved, and when the content is at most the upper limit, the durability tends to be improved.

(Ultraviolet absorber)
Examples of UV absorbers include benzophenone UV absorbers, benzotriazole UV absorbers, triazine UV absorbers, salicylic acid UV absorbers, cyanoacrylate UV absorbers, and benzoxazine UV absorbers. These ultraviolet absorbers can be used singly or in combination of two or more.

The content of the ultraviolet absorber is preferably 0.01 to 20 parts by weight, particularly preferably 0.1 to 15 parts by weight, with respect to 100 parts by weight of the (meth)acrylic copolymer (A). , more preferably 0.5 to 10 parts by weight. When the content is at least the lower limit, the light resistance reliability tends to be improved, and when the content is at most the upper limit, the yellowing resistance tends to be improved.

(anti-rust)
As the antirust agent, for example, triazoles, benzotriazoles, and the like are preferable, and can prevent corrosion of optical members.
The content of the antirust agent is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the (meth)acrylic copolymer (A), especially 0.1 to 3 parts by weight. Preferably.

The content of the other components is preferably 5 parts by weight or less, particularly preferably 1 part by weight or less, more preferably 0.5 parts by weight, based on 100 parts by weight of the (meth)acrylic copolymer (A). It is not more than parts by weight, and the lower limit is usually 0 parts by weight. If the content is too high, the compatibility with the (meth)acrylic copolymer (A) tends to decrease, resulting in a decrease in durability.

The pressure-sensitive adhesive composition [I] includes a (meth)acrylic copolymer (A) and a photopolymerization initiator (B), and optionally a cross-linking agent (C), a silane coupling agent, an ultraviolet absorber, It is prepared by mixing predetermined amounts of a rust inhibitor and other components.
The pressure-sensitive adhesive composition [I] thus obtained can be used for pressure-sensitive adhesive sheets, particularly pressure-sensitive adhesive sheets for surface protective films of flexible image display devices.

<This adhesive sheet>
The pressure-sensitive adhesive sheet according to one embodiment of the present invention and the pressure-sensitive adhesive sheet for a surface protection film of a flexible image display device (hereinafter sometimes collectively referred to as "the present pressure-sensitive adhesive sheet") can be produced, for example, as follows. can.

[ I] is prepared, the adhesive composition [I] is molded into a sheet, cross-linked or polymerized to be cured, and processed appropriately as necessary to produce the present adhesive sheet.

Alternatively, the adhesive composition [I] is prepared, coated on a member sheet or flexible member, and cured to form a laminate containing the adhesive sheet. Just do it.
However, it is not limited to this method.

When preparing the pressure-sensitive adhesive composition [I] for forming the present pressure-sensitive adhesive sheet, the raw materials are mixed with a temperature-controllable kneader (e.g., single-screw extruder, twin-screw extruder, planetary mixer, twin-screw mixer, pressure kneader etc.).
When mixing various raw materials, various additives such as silane coupling agents and antioxidants may be blended in advance with the resin and then supplied to the kneader, or all the materials may be melted and mixed in advance. Alternatively, a masterbatch in which only the additive is concentrated in the resin in advance may be prepared and supplied.

Methods for forming the pressure-sensitive adhesive composition [I] into a sheet include known methods such as a wet lamination method, a dry lamination method, an extrusion casting method using a T-die, an extrusion lamination method, a calendar method, an inflation method, and injection molding. , injection curing method, etc. can be employed. Among them, the wet lamination method, the extrusion casting method, and the extrusion lamination method are suitable for producing a sheet.

In addition, the pressure-sensitive adhesive composition [I] can be cured by irradiating it with an active energy ray to produce a cured product. In addition to irradiation with active energy rays, it is also possible to further cure by heating.
In particular, the present pressure-sensitive adhesive sheet can be produced by irradiating an active energy ray to a molded product, for example, a sheet obtained by molding the pressure-sensitive adhesive composition [I]. In addition to irradiation with active energy rays, it is also possible to further cure by heating.

Moreover, the irradiation energy, irradiation time, irradiation method, and the like of the active energy ray are not particularly limited as long as the monomer component can be polymerized by activating the photopolymerization initiator (B).
When a hydrogen abstraction type photopolymerization initiator is used as the photopolymerization initiator (B), a hydrogen abstraction reaction also occurs from the (meth)acrylic copolymer (A), and the (meth)acrylic copolymer (A ) can be incorporated into the crosslinked structure to form a crosslinked structure with many crosslink points.
Therefore, it is preferable that the pressure-sensitive adhesive sheet is cured using a hydrogen-abstracting photopolymerization initiator.

Moreover, as another embodiment of the method for producing the pressure-sensitive adhesive sheet, the pressure-sensitive adhesive composition [I] can be dissolved in an appropriate solvent and various coating techniques can be used.
When a coating method is used, the pressure-sensitive adhesive sheet can also be obtained by thermal curing in addition to curing by irradiation with active energy rays. In the case of coating, the thickness of the pressure-sensitive adhesive sheet can be adjusted by the thickness of the coating and the solid content concentration of the coating liquid.

For example, the pressure-sensitive adhesive sheet can be formed by dissolving the pressure-sensitive adhesive composition [I] in a solvent, coating it on a release film, drying it, and curing it by irradiation with active energy rays. Furthermore, you may laminate|stack a release film as needed. In this case, the release film may be coated and dried, cured by active energy ray irradiation, and the release film may be laminated thereon, or the release film may be coated and dried, and the release film may be laminated and then cured by irradiation with active energy rays to form the present pressure-sensitive adhesive sheet.

Such a solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition [I]. Examples include ketone solvents such as methyl isobutyl ketone, aromatic solvents such as toluene and xylene, and alcohol solvents such as methanol, ethanol and propyl alcohol. These can be used singly or in combination of two or more. Among them, ethyl acetate, acetone, methyl ethyl ketone, and toluene are more preferable from the viewpoint of solubility, drying property, price, and the like, and ethyl acetate is particularly preferably used.

The content of the solvent is preferably 600 parts by weight or less, more preferably 500 parts by weight or less, and further preferably 400 parts by weight or less with respect to 100 parts by weight of the (meth)acrylic copolymer (A) in terms of drying properties. Preferably, 350 parts by weight or less is particularly preferred. On the other hand, it is preferably 1 part by weight or more, more preferably 50 parts by weight or more, even more preferably 100 parts by weight or more, and particularly preferably 150 parts by weight or more.
As a coating method, a conventional method such as roll coating, die coating, gravure coating, comma coating, screen printing and bar coating can be used.

In addition, the thickness of the adhesive composition [I] after drying is preferably 1 to 200 μm, more preferably 5 to 100 μm, and still more preferably 1 to 200 μm so that the effects of the present invention can be effectively exhibited. is coated so as to be 10 to 50 μm.

In the drying, the solvent content in the adhesive composition [I] is preferably 1% by weight or less, more preferably 0.5% by weight or less, and particularly preferably 0.1% by weight or less. , most preferably 0% by weight.

The drying temperature is usually 40 to 150°C, preferably 45 to 140°C, still more preferably 50 to 130°C, and particularly preferably 55 to 120°C. Within the above temperature range, the solvent can be removed efficiently and relatively safely while suppressing thermal deformation of the release film.

The drying time is usually 1 to 30 minutes, more preferably 3 to 25 minutes, still more preferably 5 to 20 minutes. Within the above time range, the solvent can be removed efficiently and sufficiently.

Examples of the drying method include drying using a dryer, hot rolls, and drying by blowing hot air onto the film. Among them, it is preferable to use a dryer from the viewpoint of uniform and easy drying. These can be used singly or in combination of two or more.

Examples of the active energy ray in the active energy ray irradiation include far ultraviolet rays, ultraviolet rays, near ultraviolet rays, infrared rays, visible rays, X rays, α rays, β rays, γ rays, electron beams, proton rays, neutron rays, and the like. of ionizing radiation. Among them, ultraviolet light is preferable from the viewpoint of suppressing damage to optical device constituent members and controlling reaction.
Curing by ultraviolet irradiation is also advantageous in terms of curing speed, availability of irradiation equipment, price, and the like.

As a light source for ultraviolet irradiation, high-pressure mercury lamps, ultra-high-pressure mercury lamps, carbon arc lamps, metal halide lamps, xenon lamps, chemical lamps, electrodeless discharge lamps, LEDs, etc., which emit light in the wavelength range of 150 to 450 nm can be used. Among them, it is preferable to use a high-pressure mercury lamp.

The active energy ray irradiation amount (accumulated light amount) is preferably 30 to 3000 mJ/cm ² , more preferably 100 to 2000 mJ/cm ² , and still more preferably 300 to 1500 mJ/cm ² from the viewpoint of curing. .
After the active energy ray irradiation, heating may be performed as necessary to increase the degree of curing.

By irradiation with active energy rays, the adhesive composition [I] is cured to form the present adhesive sheet. The thickness of the pressure-sensitive adhesive sheet formed is preferably 1 to 200 μm, particularly preferably 5 to 100 μm, further preferably 10 to 50 μm. When it is at least the above lower limit, the adhesive physical properties tend to be stable, and when it is at most the above upper limit, it is easy to dry efficiently, and concerns such as paste extrusion when formed into a roll can be reduced.

A release film may be provided on at least one surface of the pressure-sensitive adhesive sheet obtained above from the viewpoint of blocking prevention and foreign matter adhesion prevention.

As such a release film, a known release film can be appropriately used.
Materials for the release film include, for example, polyester film, polyolefin film, polycarbonate film, polystyrene film, acrylic film, triacetylcellulose film, fluororesin film, etc., coated with silicone resin for release treatment, A release paper or the like can be appropriately selected and used.

The thickness of the release film is not particularly limited. Among them, for example, from the viewpoint of workability and handleability, the thickness is preferably 10 to 250 μm, more preferably 25 to 200 μm, and more preferably 35 to 190 μm.

Also, if necessary, embossing or various irregularities (conical, pyramidal, hemispherical, etc.) processing may be performed.
In addition, various surface treatments such as corona treatment, plasma treatment, and primer treatment may be performed on the surface for the purpose of improving adhesion to various member sheets.

In addition, the gel fraction of the adhesive sheet is preferably 30 to 95% by weight, more preferably 35 to 90% by weight, still more preferably 40 to 85% by weight. When it is at least the above lower limit, the risk of the paste oozing out over time tends to be reduced, which is preferable.
The gel fraction serves as an index of the degree of crosslinking (degree of curing), and can be measured under the measurement conditions described in Examples below.

The ratio (O/C) of the number of oxygen atoms to the number of carbon atoms of the pressure-sensitive adhesive sheet can be measured by X-ray photoelectron spectroscopy (XPS). It is important because it is well-balanced in A preferable range of such ratio (O/C) is 0.25 to 0.4, more preferably 0.26 to 0.35, particularly preferably 0.27 to 0.34, particularly preferably 0.28. ~0.32. If it is too small, the oil resistance will be lowered, and if it is too large, the storage shear modulus (G') at low temperature will be too high, and the flexibility (especially dynamic bending property) will be lowered.

In order to adjust the ratio (O / C) to the above range, for example, (1) the amount of copolymerization of hydroxyl group-containing (meth)acrylate is increased, or (2) the main monomer component in the copolymerization component has a carbon chain. Using a relatively short monomer component, (3) introducing an oxyalkylene chain into the (meth)acrylic copolymer (A), or (4) combining methods (1) to (3) as appropriate. However, from the viewpoint of oil resistance, it is preferable to include the method (2).

The ratio (O/C) can be measured under the measurement conditions described in Examples below.

The adhesive strength of the adhesive sheet to the transparent polyimide film (peeling angle: 180 °, peeling speed 300 mm / min) is preferably 4 to 30 N / cm, more preferably 4.5 to 20 N / cm, more preferably 5 to 15 N/cm. Within this range, there is sufficient adhesiveness, and there is a tendency to be suitably used as an adhesive sheet for a surface protective film for a flexible image display device.
The adhesive strength can be measured under the measurement conditions described in Examples below.

The lower the swelling rate of the pressure-sensitive adhesive sheet against oleic acid, the better the oil resistance. Most preferably 0% by weight.
The swelling rate can be measured under the measurement conditions described in Examples below.

The glass transition temperature (Tg) of the pressure-sensitive adhesive sheet is preferably −20° C. or lower, more preferably −23° C. or lower, further preferably −20° C. or lower from the viewpoint of suppressing an increase in storage shear modulus (G′) at low temperatures. 25° C. or less, particularly preferably −30° C. or less. The lower limit of the glass transition temperature (Tg) is usually -50°C.
The glass transition temperature (Tg) can be measured under the measurement conditions described in Examples below.

The storage shear modulus (G') of the pressure-sensitive adhesive sheet at −20° C. is preferably 500 kPa or less, more preferably 400 kPa or less, from the viewpoint of preventing delamination during bending, particularly at high speeds or at low temperatures. is. It should be noted that the lower limit is preferably 50 kPa from the viewpoint of preventing the paste from oozing out and maintaining the shape of the adhesive sheet.
The storage shear modulus (G′) at −20° C. can be measured under the measurement conditions described in Examples below.

The storage shear modulus (G') of the pressure-sensitive adhesive sheet at 60°C is preferably 200 kPa or less, more preferably 100 kPa or less, and still more preferably 50 kPa or less from the viewpoint of maintaining high adhesion. The lower limit is preferably 1 kPa from the viewpoint of preventing the paste from oozing out and maintaining the shape of the adhesive sheet.
The storage shear modulus (G′) at 60° C. can be measured under the measurement conditions described in Examples below.

The restorability of the pressure-sensitive adhesive sheet is preferably 30% or more, more preferably 35% or more, and still more preferably 40% or more. The upper limit is 100% because the higher the restorability, the better.
The resilience can be measured under the measurement conditions described in Examples below.

The pressure-sensitive adhesive sheet thus obtained can be laminated, for example, with a surface protection film made of various members to form a laminate for a surface protection film of a flexible image display device.

The surface protective film preferably has a surface hardness of 400 MPa or more, more preferably 450 MPa or more, and particularly preferably 500 MPa or more at a contact depth of 200 to 400 nm measured by a nanoindenter. The upper limit is usually 9 GPa. Within this range, sufficient scratch resistance and impact resistance can be obtained when a laminate for a surface protection film for a flexible image display device is formed.
In addition, the surface protective film is preferably a member that does not change in appearance when subjected to a bending test of 200,000 times at -20 ° C. under the condition of curvature radius (R) = 1.5 mm. is preferable because when a laminate for a surface protective film for a flexible image display device is formed, crease marks and delamination are less likely to occur at the bent portion.

In the present invention, the surface hardness of the surface protective film was evaluated by nanoindentation.
Generally, in the nanoindentation method, the indenter of the nanoindenter is pushed into the sample to a predetermined depth (contact depth) with a constant load (loading), and then the indenter is pulled up until the indenter is separated from the sample (unloading). , from the relationship between displacement and load (load-displacement curve) at that time, the mechanical properties of the surface of the sample are analyzed.
The surface hardness in the present invention was calculated from the following formula under the following measurement conditions.
H _IT =F _MAX /A _p
(H _IT : surface hardness, F _MAX : maximum test load, A _p : projected contact area)

(Measurement condition)
・ Measuring device: TI980 manufactured by Bruker
・Maximum load: 1000uN
・Indenter material: diamond ・Indenter shape: Berkovich ・Applied load: 1mN
・Contact depth: 300 nm

Examples of the surface protective film include members such as polyethylene terephthalate film, polyimide film, aramid film, and glass plate. Among them, polyethylene terephthalate film is preferable from the viewpoint of versatility, polyimide film is preferable from the viewpoint of reducing the bending angle, and glass plate is preferable from the viewpoint of obtaining high surface strength. Polyimide film and glass plate are particularly effective because of their high surface hardness. is.

A coating layer may be provided on the surface of the member.
The coating layer is not particularly limited, and examples thereof include an easy-adhesion coating layer, a release layer, a hard coating layer, an antistatic coating layer, an anti-fingerprint layer, and the like.

In the present invention, the layer structure includes, for example, the following structure. However, it is not limited to these.
・ (Viewing side) hard coat / polyimide film / adhesive sheet (organic EL side) (surface hardness: 906 MPa)
・ (Viewing side) hard coat / PET film / adhesive sheet (organic EL side) (surface hardness: 418 MPa)
・ (Viewing side) Hard coat / PET film / adhesive sheet / glass (organic EL side) (surface hardness: 376 MPa)
・ (Viewing side) hard coat / PET film / adhesive sheet (organic EL side) (surface hardness: 484 MPa)

In the present invention, as a reliability test of dynamic bending of the surface protective film for a flexible image display device, a cycle evaluation of U-shaped bending was performed at a setting of curvature radius R = 1.5 mm, 60 rpm (1 Hz), and -20 ° C. It is preferable that the number of times of bending is 100,000 times or more, and more preferably 200,000 times or more, so as not to cause defects (delamination, breakage, buckling, flow) at the bent portion.

In addition, as a reliability test of dynamic bending of the surface protective film for a flexible image display device, a cycle evaluation of U-shaped bending was performed with a radius of curvature R = 1.5 mm, 60 rpm (1 Hz), 85 ° C., and 85% RH. It is preferable that the number of times of bending is 100,000 times or more, and more preferably 200,000 times or more, without causing defects (delamination, breakage, buckling, or flow) at the bent portion.

In addition, as a reliability test of static bending of the flexible image display device surface protective film, the bent state was maintained at a radius of curvature R = 1.5 mm, 85 ° C., and 85% RH, and defects in the bent portion (delamination, breakage, The storage time is preferably 24 hours or more, more preferably 120 hours or more, without buckling or flow.

<Flexible image display device>
A laminate for a surface protection film obtained from the present pressure-sensitive adhesive sheet according to one embodiment of the present invention is used by attaching it to the surface of a flexible image display device.
As an example of the flexible image display device, there is an image display device having a structure in which the surface protective film laminate and the image display device constituent members are combined and laminated.

The flexible image display device preferably has a structure in which the constituent members of the image display device and the laminate for the surface protective film are directly laminated.
At this time, the "image display device component" includes, for example, a reflective sheet, a light guide plate and a light source, a diffusion film, a prism sheet, a liquid crystal panel, a retardation plate, a glass substrate, a polarizing plate, an organic EL panel, an electrode, and an antireflection film. , a color filter, a touch sensor, a cover glass, a cover plastic, or a material in which two or more of these members are combined and integrated.
In addition to the above members, other layers such as an antistatic layer, a hard coat layer, an anchor layer, a release layer, an easy-adhesion layer, a protective layer, an anti-bleeding layer, and a flattening layer are interposed as necessary. may

Examples of such a flexible image display device include a bendable device having a curved image display surface, a foldable device that can be repeatedly bent, a rollable device that can be wound up, and a stretchable device that can be expanded and contracted. Examples of such displays include liquid crystal displays, organic EL displays, inorganic EL displays, electronic paper, plasma displays, and microelectromechanical system (MEMS) displays.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.
In the examples, "parts" and "%" mean weight standards.

<(Meth)acrylic copolymer>
Acrylic copolymers (A-1) to (A-4) and (A'-1) to (A'-2) were prepared with the copolymer component composition as shown in Table 1, and these acrylic copolymers Table 1 also shows the glass transition temperature (Tg) and weight average molecular weight (Mw) of the polymer.

[Examples 1-4, Comparative Examples 1-2]
3 parts of a mixture of 4-methylbenzophenone and 2,4,6-trimethylbenzophenone (manufactured by IGM, Esacure TZT, hydrogen abstraction type) as a photopolymerization initiator (B) with respect to 100 parts of the acrylic copolymer, 200 parts of ethyl acetate as a solvent was uniformly mixed to obtain an adhesive composition solution (solid concentration: 33%).

The pressure-sensitive adhesive composition solution was coated on a release film (manufactured by Mitsubishi Chemical Corporation, silicone release-treated polyester film, thickness 100 μm) so that the thickness after drying was 50 μm. After coating, it was placed in a dryer heated to a temperature of 90° C. and held for 7 minutes to volatilize and dry the solvent contained in the pressure-sensitive adhesive composition.
Furthermore, a laminate is formed by laminating a release film (manufactured by Mitsubishi Chemical Corporation, silicone release-treated polyester film, thickness 75 μm) on the surface of the adhesive composition after drying the solvent, and using a high-pressure mercury lamp, Through the release film, the pressure-sensitive adhesive composition is irradiated with ultraviolet rays so that the integrated light amount shown in Table 1 is obtained, and the pressure-sensitive adhesive sheet laminate (pressure-sensitive adhesive sheet with release film) (1) to (6) is obtained. Obtained.
The obtained adhesive sheet laminates (1) to (6) were evaluated as follows.

<Gel fraction>
The release film was removed from each adhesive sheet laminate prepared in Examples and Comparative Examples, and a plurality of adhesive sheets were laminated to a thickness of 1 mm. It was wrapped with a wire mesh and immersed in ethyl acetate adjusted to 23° C. for 72 hours. After drying at 75° C. for 4.5 hours, the weight of the adhesive before and after immersion in ethyl acetate was measured, and the difference between the two weights was taken as the weight of the undissolved adhesive remaining in the wire mesh. The weight percentage of the undissolved adhesive remaining in the wire mesh relative to the weight of the adhesive before immersion in ethyl acetate was calculated as the gel fraction.

<Ratio of number of oxygen atoms to number of carbon atoms (O/C)>
A pressure-sensitive adhesive sheet obtained by removing the release film from each pressure-sensitive adhesive sheet laminate prepared in Examples and Comparative Examples was used as a sample, and the ratio of the number of oxygen atoms to the number of carbon atoms (O/C) was measured as follows. .
・ Measuring device: XPS K-Alpha (manufactured by Thermo Fisher Scientific)
・X-ray: Monochromated Al Kα
・ Analysis area: 400 μmΦ
・The angle between the sample surface and the detector: 90°
・Etching: None

<Adhesive strength>
From each adhesive sheet laminate prepared in Examples and Comparative Examples, a polyethylene terephthalate film (manufactured by Mitsubishi Chemical Corporation, Diafoil "S100", thickness of 50 μm) was roll-bonded with a hand roller. Cut this into strips with a width of 10 mm and a length of 150 mm, peel off the remaining release film, and attach the exposed adhesive surface to a stainless steel plate in advance. Transparent polyimide film (main component: transparent polyimide, KOLON " C_50”, hereinafter referred to as “CPI film”) is rolled using a hand roller to produce a laminate consisting of CPI film / adhesive sheet / backing film, and this laminate is placed in a room temperature (23 ° C) environment. It was put down and allowed to stand overnight for curing to prepare a sample for adhesive force measurement.
The surface hardness of the transparent polyimide film measured by a nanoindenter at a contact depth of 200 to 400 nm was 542 MPa. Further, when a 200,000 times bending test was performed at −20° C. under the condition of curvature radius (R)=1.5 mm, there was no change in appearance.

The backing film is peeled off while being pulled at an angle forming 180° with the CPI film at a peeling speed of 300 mm / min, the tensile strength is measured with a load cell, and the 180° peel strength (N / 10 mm) of the adhesive sheet to the CPI film is measured. The adhesive strength (23°C) was measured.

<Oil resistance>
As an evaluation of oil resistance, the swelling ratio in oleic acid was measured according to the following measuring method.

[Swelling rate]
The release film was removed from each pressure-sensitive adhesive sheet laminate prepared in Examples and Comparative Examples, and a plurality of pressure-sensitive adhesive sheets were laminated to a thickness of 1 mm.
It was immersed for 1 hour in oleic acid that had been allowed to stand in an environment of 85° C./85% RH in advance.
The pressure-sensitive adhesive sheet after immersion was washed with ethanol, dried with a drier, and weighed (weight B [g]).
The swelling rate was calculated from the following formula.
Swelling rate [%] = (weight B [g] - weight A [g]) / weight A [g] x 100
The smaller the swelling ratio, the better the oil resistance.

<Flexibility>
As an evaluation of flexibility, the dynamic viscoelasticity of the adhesive sheet was measured, and from the results, the maximum temperature of the loss tangent (tan δ) (dynamic glass transition temperature: Tg) and the storage shear modulus at -20 ° C. or 60 ° C. ( G') was read.
Restorability was also evaluated as follows.

[Loss tangent (tan δ), storage shear modulus (G′)]
The release film was removed from each pressure-sensitive adhesive sheet laminate prepared in Examples and Comparative Examples, and a plurality of pressure-sensitive adhesive sheets were laminated to obtain a laminate having a thickness of 1.0 mm.
A cylindrical body (height: 1.0 mm) with a diameter of 8 mm was punched out from the laminate of the pressure-sensitive adhesive sheets thus obtained, and this was used as a sample.
The temperature dispersion of dynamic viscoelasticity of the sample was measured using a viscoelasticity measuring device (manufactured by TA Instruments, product name "DHR 2") under the following measurement conditions.
From the obtained temperature dispersion data of dynamic viscoelasticity, the peak temperature of loss tangent (tan δ) (glass transition temperature (Tg)) and the storage shear modulus G' at -20°C or 60°C were read.

(Measurement condition)
・Measurement jig: Φ8mm parallel plate ・Distortion: 0.1%
・Frequency: 1Hz
・Measurement temperature: -60 to 100°C
・Temperature increase rate: 5°C/min

[Restoration]
The release film was removed from each pressure-sensitive adhesive sheet laminate prepared in Examples and Comparative Examples, and a plurality of pressure-sensitive adhesive sheets were laminated to obtain a laminate having a thickness of 1.0 mm.
A cylindrical body (height: 1.0 mm) with a diameter of 8 mm was punched out from the laminate of the pressure-sensitive adhesive sheets thus obtained, and this was used as a sample.
The resilience of the sample was measured using a viscoelasticity measuring device (manufactured by TA Instruments, product name "DHR 2") under the following measurement conditions.
That is, after applying a shear strain corresponding to 7 times the thickness at 25° C. and maintaining it for 10 minutes, the restorability was measured by reading the residual strain value 10 minutes after the stress was removed.
Calculation of resilience is obtained from the following formula.
Restorability (%) = [(700-residual strain value) / 700] x 100

<Bending durability>
The release film of each pressure-sensitive adhesive sheet laminate prepared in Examples and Comparative Examples was removed, and CPI films (main component: transparent polyimide, "C_50" manufactured by KOLON Co., Ltd.) were laminated on both sides of the pressure-sensitive adhesive sheet with a hand roll, and bending durability was measured. A laminate sheet (sample) for sex was obtained.
The laminate sheets (samples) produced as described above were used and evaluated as follows.

[Dynamic bending durability]
The laminated sheet (sample) was subjected to a curvature radius R of 1.5 mm and a setting of 60 rpm (1 Hz) using a durability system in a constant temperature and humidity chamber and a planar body no-load U-shaped expansion tester (manufactured by Yuasa System Co., Ltd.). , under the condition of temperature -20°C, or under the condition of 85°C, 85% RH, cycle evaluation of U-shaped bending was performed. The number of cycles was evaluated at 200,000 times each. In addition, the following evaluation criteria evaluated.
◯: None of delamination, breakage, buckling, and flow occurred at the bent portion.
x: Either delamination, breakage, buckling, or flow occurred at the bent portion.

[Static bending durability]
The laminated sheet (sample) was bent at a curvature radius of R = 1.5 mm with the CPI film side inside, and stored at 85 ° C. and 85% RH for 24 hours. The static bending durability was evaluated by the restored inner angle after 1 hour. The restored inner angle was confirmed and evaluated according to the following evaluation criteria. Similarly, when the restored inner angle of only the member sheet (CPI film) was confirmed, the inner angle of the film was 60°.
◯: The inner angle of the bent portion was restored to 60° or more.
x: The inner angle of the bent portion was restored to less than 60°.

Table 2 shows the results obtained by the above measurements and evaluations.

From the above evaluation results, the pressure-sensitive adhesive sheet for a surface protective film of a flexible image display device obtained in Examples is a hydroxyl group-containing acrylic copolymer, and the O/C is within a predetermined range. While having good flexibility, it was also excellent in oil resistance. Furthermore, the static bending durability and dynamic bending durability were also excellent.
On the other hand, in the pressure-sensitive adhesive sheet for surface protection obtained in the comparative example, although it was a hydroxyl group-containing acrylic copolymer, the O/C was outside the predetermined range. It was not something to do.
In Example 1, in which 2-hydroxyethyl acrylate was used as the hydroxyl group-containing (meth)acrylate (a1), higher adhesiveness and oil resistance were obtained. On the other hand, in Examples 2 and 3, in which 4-hydroxybutyl acrylate was used as the hydroxyl group-containing (meth)acrylate (a1), the storage shear modulus (G') at -20°C could be reduced, resulting in good flexibility. All of them are very useful as pressure-sensitive adhesive sheets for surface protective films of flexible image display devices.
Therefore, it can be seen that the flexible image display device using this pressure-sensitive adhesive sheet is excellent in flexibility and oil resistance reliability.

The pressure-sensitive adhesive sheet of the present invention, particularly the pressure-sensitive adhesive sheet for a flexible image display device surface protection film, has a surface protection function and flexibility such as reliability against bending (bending durability) while it is used by being attached to an image display device. It is possible to obtain a laminate for a surface protective film which has and is also excellent in oil resistance. Therefore, the obtained laminate for surface protection film is useful as a laminate for surface protection film of various flexible image display devices such as bendable, foldable, rollable and stretchable. It is suitable for laminates for surface protective films of blue image display devices.

Claims (12)

A pressure-sensitive adhesive sheet formed from a photocurable pressure-sensitive adhesive composition [I] containing a (meth)acrylic copolymer (A) and a photopolymerization initiator (B),
The pressure-sensitive adhesive sheet has a ratio of the number of oxygen atoms to the number of carbon atoms (O/C) measured by X-ray photoelectron spectroscopy of 0.25 to 0.5,
The pressure-sensitive adhesive sheet, wherein the (meth)acrylic copolymer (A) is a (meth)acrylic copolymer containing a structural site derived from the hydroxyl group-containing (meth)acrylate (a1). The (meth)acrylic copolymer (A) is derived from an alkyl (meth)acrylate (a2) containing a structural moiety derived from the hydroxyl group-containing (meth)acrylate (a1) and an alkyl group having 1 to 10 carbon atoms. 2. The pressure-sensitive adhesive sheet according to claim 1, which is a (meth)acrylic copolymer containing structural sites. 3. The pressure-sensitive adhesive sheet according to claim 1, wherein the hydroxyl group-containing (meth)acrylate (a1) is a (meth)acrylate containing a hydroxyalkyl group having 3 to 10 carbon atoms. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the (meth)acrylic copolymer (A) has a weight average molecular weight of 600,000 to 1,500,000. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the photocurable pressure-sensitive adhesive composition [I] further contains a cross-linking agent (C). The pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein the pressure-sensitive adhesive sheet has a storage shear modulus (G') at -20°C of 500 kPa or less. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, wherein the pressure-sensitive adhesive sheet has a gel fraction of 30 to 95% by weight. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, wherein the pressure-sensitive adhesive sheet has a degree of swelling with respect to oleic acid of 25% by weight or less. The pressure-sensitive adhesive sheet according to any one of claims 1 to 8, which is used as a surface protection film for a flexible image display device. A pressure-sensitive adhesive sheet for a surface protective film of a flexible image display device comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 9. A laminate for a flexible image display device surface protective film, in which the pressure-sensitive adhesive sheet according to any one of claims 1 to 9 and a surface protective film are laminated,
The surface protective film has a surface hardness of 400 MPa or more at a contact depth of 200 to 400 nm measured by a nanoindenter, and is subjected to a bending test of 200,000 times at -20 ° C. under the condition of curvature radius (R) = 1.5 mm. A laminate for a surface protective film for a flexible image display device, which is a member that does not change in appearance when subjected to . 12. The laminate for a surface protective film of a flexible image display device according to claim 11, wherein said surface protective film comprises any member selected from polyethylene terephthalate film, polyimide film, aramid film and glass plate.