Adhesive sheet, laminated sheet and flexible image display device

Abstract

To provide an adhesive sheet that has excellent adhesion but yet has excellent flexibility at low temperature and also has excellent restorability.SOLUTION: An adhesive sheet is formed from an adhesive composition [I] containing an acrylic polymer (A) and a radical-polymerizable compound (B). The acrylic polymer (A) includes a structural site derived from an alkyl methacrylate (a1) with a C5-20 alkyl group and a structural site derived from a hydroxy group-containing methacrylate (a2). The radical-polymerizable compound (B) includes a dimethacrylate (B1) with a C5-20 alkylene group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet that can be suitably used for bonding components of curved image displays and bendable flexible image displays, and to a laminate sheet and flexible image display device that use the pressure-sensitive adhesive sheet. [Background technology]

[0002] In recent years, curved and flexible image display devices using organic light-emitting diodes (OLEDs) and quantum dots (QDs) have been developed and are becoming widely commercialized. In such an image display device, a plurality of component sheets such as a cover lens, a circular polarizer, a touch film sensor, and a light-emitting element are laminated together with a transparent adhesive sheet to form a laminated structure, and each laminated structure can be regarded as a laminated sheet formed by laminating component sheets and adhesive sheets.

[0003] Foldable flexible image display devices have various problems caused by interlayer stress when folded. For example, layers may peel off when folded (delamination: the phenomenon in which layers peel off is called "delamination"). Therefore, there is a demand for laminated sheets that do not peel off when folded.

[0004] There is also a need for a laminated sheet that, when the screen is opened from a folded state, quickly returns to a flat state without being affected by being placed in a bent state. Furthermore, repeated folding operations can cause stress to be applied to the component sheet that is the adherend of the adhesive sheet, which can cause cracks and eventually break. Therefore, there is a demand for a laminated sheet that is durable enough to withstand repeated folding operations, especially at low temperatures, which are even more severe conditions.

[0005] Regarding foldable flexible image display devices, for example, Patent Document 1 discloses an adhesive composition for foldable displays, which comprises a thermosetting resin and a crosslinking agent, the thermosetting resin containing units derived from a compound containing at least one N or O and at least one unshared electron pair in the molecule, and the thermosetting resin having a glass transition temperature of −70° C. or lower, an adhesive film using the same, and a foldable display including the same. Specifically, the publication discloses an adhesive composition for foldable displays, which comprises a thermosetting resin copolymerized with carbitol acrylate, ethylhexyl acrylate, and acrylic acid, blended with a composition blended with an epoxy-based crosslinking agent or an isocyanate-based crosslinking agent, an adhesive film using the same, and a foldable display including the same. Furthermore, Patent Documents 2 and 3 disclose pressure-sensitive adhesives that aim to improve durability and conformability to uneven surfaces by focusing on distortion and distortion recovery when a shear force is applied. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2021-500445 [Patent Document 2] Japanese Patent Publication No. 2020-196903 [Patent Document 3] Japanese Patent Publication No. 2020-143284 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the adhesive film containing a large amount of carbitol acrylate disclosed in Patent Document 1 has a small storage modulus at low temperatures, so it can reduce stress caused by folding, but on the other hand, it has a problem of low adhesive strength and is prone to delamination with the component sheet when folded, particularly at low temperatures.In addition, because carbitol acrylate easily relieves internal stress by internal rotation around the ether bond, it also has a problem of fold marks not disappearing quickly when folding is performed.

[0008] Furthermore, although the above Patent Documents 2 and 3 aim to improve durability and step-following ability, they are not related to adhesive sheets used for bonding components of flexible image display devices, and do not take into consideration any specific issues that arise when folding operations are performed, such as delamination and recovery, and therefore Patent Documents 2 and 3 do not solve these issues.

[0009] Therefore, the present invention relates to an adhesive sheet formed from an adhesive composition containing an acrylic polymer, and a laminate sheet formed by laminating the adhesive sheet with a component sheet, and provides an adhesive sheet and laminate sheet used for bonding components of a flexible image display device, which have excellent durability (also referred to as "low-temperature flexural durability") that prevents delamination when folded at low temperatures, and excellent restorability (also referred to as "strain recovery") that quickly returns to a flat state when folded, and further provides a flexible image display device using these. [Means for solving the problem]

[0010] However, in view of these circumstances, the present inventors have conducted extensive research and have found that a pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition containing an acrylic polymer and a radically polymerizable compound, in which an acrylic polymer containing a relatively long-chain alkyl group and a hydroxyl group is used as the acrylic polymer, and a di(meth)acrylate having a relatively long-chain alkylene group is further used in combination, can have good adhesive strength, excellent flexibility at low temperatures, and also excellent recovery, and have completed the present invention.

[0011] That is, the present invention has the following aspects. [1] A pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition [I] containing an acrylic polymer (A) and a radically polymerizable compound (B), the acrylic polymer (A) contains a structural moiety derived from an alkyl (meth)acrylate (a1) having an alkyl group with 5 to 20 carbon atoms and a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a2), The pressure-sensitive adhesive sheet, wherein the radically polymerizable compound (B) comprises a di(meth)acrylate (B1) having an alkylene group having 5 to 20 carbon atoms. [2] The pressure-sensitive adhesive sheet according to [1], wherein the alkyl(meth)acrylate (a1) is a linear aliphatic alkyl(meth)acrylate. [3] The pressure-sensitive adhesive sheet according to [1] or [2], wherein the acrylic polymer (A) has a weight-average molecular weight of 600,000 to 1,500,000. [4] The pressure-sensitive adhesive sheet according to any one of [1] to [3], wherein the alkylene group in the di(meth)acrylate (B1) is a linear alkylene group. [5] The pressure-sensitive adhesive sheet according to any one of [1] to [4], wherein the content of the radically polymerizable compound (B) is 0.1 to 10 parts by weight per 100 parts by weight of the acrylic polymer (A). [6] The pressure-sensitive adhesive sheet according to any one of [1] to [5], wherein the pressure-sensitive adhesive sheet has a storage shear modulus (G') at -20°C of 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], which is used for bonding components of a flexible image display device. [9] A laminated sheet comprising a component sheet having a tensile strength of 10 to 900 MPa at 25°C measured in accordance with ASTM D882 on at least one side of the pressure-sensitive adhesive sheet according to any one of [1] to [8].

[10] A laminate sheet comprising the pressure-sensitive adhesive sheet according to any one of [1] to [8] on at least one side of a component sheet having a tensile strength of 10 to 900 MPa at 25°C measured in accordance with ASTM D882.

[11] The laminate sheet according to [9] or

[10] , wherein the component sheet is a resin sheet containing, as a main component, at least one resin selected from the group consisting of polyester resin, cycloolefin resin, triacetyl cellulose resin, polymethyl methacrylate resin, epoxy resin, polyimide resin, aramid resin, and polyurethane resin, or glass.

[12] A flexible image display device comprising the laminate sheet according to any one of [9] to

[11] . [Effects of the Invention]

[0012] The adhesive sheet according to one embodiment of the present invention is an adhesive sheet formed from an adhesive composition containing a specific hydroxyl group-containing acrylic polymer and a specific di(meth)acrylate, and therefore has good adhesive strength, excellent flexibility at low temperatures, and also excellent recovery properties, making it particularly suitable for use as an adhesive sheet for flexible image display devices. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below. In the present invention, the term "film" includes the term "sheet", and the term "sheet" includes the term "film". Furthermore, when the term "panel" is used, such as an image display panel or a protective panel, it encompasses a plate, a sheet, and a film.

[0014] In the present invention, when it is stated that "X to Y" (X and Y are any numbers), unless otherwise specified, it means "X or more and Y or less", and also means "preferably larger than X" or "preferably smaller than Y". Furthermore, when it is stated that the amount is "X or more" (X is any number), it also means that the amount is "preferably greater than X" unless otherwise specified, and when it is stated that the amount is "Y or less" (Y is any number), it also means that the amount is "preferably smaller than Y" unless otherwise specified. Furthermore, "X and / or Y (X and Y are any configuration)" means at least one of X and Y, and can mean three possibilities: X only, Y only, or X and Y.

[0015] In the present invention, the term "major component" refers to a component that has a significant effect on the properties of the target object, and the content of the component is usually 30% by weight or more, preferably 35% by weight or more, and more preferably 50% by weight or more in the target object. Furthermore, the component is often the component that accounts for the largest weight ratio in the target object, and when it accounts for 50% by weight or more, it is expected to account for 55% by weight or more, of which 60% by weight or more, of which 70% by weight or more, of which 80% by weight or more, and of which 90% by weight or more (including 100% by weight). In the present invention, "(meth)acrylic" encompasses "acrylic" and "methacrylic", "(meth)acrylate" encompasses "acrylate" and "methacrylate", and "(meth)acryloyl" encompasses "acryloyl" and "methacryloyl". Furthermore, the term "acrylic polymer" refers to a polymer containing a monomer unit derived from (meth)acrylate, and includes (meth)acrylic copolymers.

[0016] <<This adhesive sheet>> An adhesive sheet according to one embodiment of the present invention (also referred to as "the adhesive sheet") is an adhesive sheet formed from an adhesive composition [I] containing an acrylic polymer (A) and a radically polymerizable compound (B), and is particularly useful as an adhesive sheet used for bonding components of flexible image display devices.

[0017] <<Adhesive composition [I]>> The pressure-sensitive adhesive composition [I] contains an acrylic polymer (A) and a radically polymerizable compound (B), and preferably contains the acrylic polymer (A) as a main component.

[0018] <Acrylic polymer (A)> The acrylic polymer (A) used in the present invention is an acrylic polymer containing a structural moiety derived from an alkyl(meth)acrylate (a1) having an alkyl group with 5 to 20 carbon atoms and a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a2). Preferably, the acrylic polymer (A) is obtained by copolymerizing the alkyl(meth)acrylate (a1) having an alkyl group with 5 to 20 carbon atoms and the hydroxyl group-containing (meth)acrylate (a2) as copolymerization components. Alternatively, the acrylic polymer (A) may be obtained by copolymerizing the alkyl(meth)acrylate (a1) having an alkyl group with 5 to 20 carbon atoms and the hydroxyl group-containing (meth)acrylate (a2) with another monomer component (a3) ​​as copolymerization components.

[0019] <Alkyl (meth)acrylate (a1) having an alkyl group with 5 to 20 carbon atoms> Examples of the alkyl (meth)acrylate (a1) having 5 to 20 carbon atoms in the alkyl group include linear alkyl (meth)acrylates such as n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, and n-decyl (meth)acrylate; branched alkyl (meth)acrylates such as isopentyl (meth)acrylate, neopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and isodecyl (meth)acrylate; and alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate and t-butylcyclohexyl (meth)acrylate. These may be used alone or in combination of two or more.

[0020] Among these, linear alkyl (meth)acrylates are preferred from the viewpoint of adhesion and recovery, and in particular, linear alkyl (meth)acrylates having an alkyl group of 6 to 18 carbon atoms, further 6 to 16, and especially 8 to 12 carbon atoms are preferred from the viewpoint of suppressing an increase in storage shear modulus (G') at low temperatures and improving flexibility, such as n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, and decyl (meth)acrylate. Of these, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, and n-decyl (meth)acrylate are preferred, with n-octyl (meth)acrylate being particularly preferred.

[0021] Acrylate is particularly preferred from the viewpoint of suppressing an increase in storage shear modulus (G') at low temperatures and improving flexibility.

[0022] In the present invention, the alkyl (meth)acrylate (a1) having 5 to 20 carbon atoms in the alkyl group preferably accounts for 50 to 95% by weight, more preferably 60 to 90% by weight, and particularly preferably 70 to 85% by weight, of the total copolymerization components constituting the acrylic polymer (A) in order to suppress an increase in the storage shear modulus (G') at low temperatures. When the proportion of the alkyl (meth)acrylate (a1) is equal to or greater than the lower limit, an increase in the storage shear modulus (G') at low temperatures can be suppressed, and when it is equal to or less than the upper limit, it is preferable in terms of achieving compatibility with other physical properties such as adhesiveness.

[0023] <Hydroxyl group-containing (meth)acrylate (a2)> Examples of the hydroxyl group-containing (meth)acrylate (a2) include hydroxy(meth)acrylates such as 2-hydroxyethyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate, 5-hydroxypentyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate, and 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; Examples of such hydroxyl group-containing (meth)acrylates include oxyalkylene-modified (meth)acrylates such as ethylene glycol (meth)acrylate, primary hydroxyl group-containing (meth)acrylates such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate, secondary hydroxyl group-containing (meth)acrylates such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate, and tertiary hydroxyl group-containing (meth)acrylates such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate, etc. These may be used alone or in combination of two or more.

[0024] Among the hydroxyl group-containing (meth)acrylates (a2), in terms of reducing the storage shear modulus (G') at low temperatures, primary hydroxyl group-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate are preferred, and hydroxyl group-containing (meth)acrylates having a hydroxyalkyl group having 1 to 10 carbon atoms, more preferably 1 to 6, and even more preferably 2 to 4 carbon atoms, such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are particularly preferred, with 2-hydroxyethyl (meth)acrylate being particularly preferred.

[0025] From the viewpoint of adhesive strength, the content of the hydroxyl group-containing (meth)acrylate (a2) is preferably 5 to 50% by weight, more preferably 10 to 40% by weight, and particularly preferably 15 to 30% by weight, based on the total copolymerization components of the acrylic polymer (A). When the content of the hydroxyl group-containing (meth)acrylate (a2) is equal to or greater than the lower limit, high adhesiveness is obtained, and when it is equal to or less than the upper limit, an increase in the storage shear modulus (G') at low temperatures can be suppressed, which is preferable.

[0026] In the present invention, a monomer component (a3) ​​(excluding the above-mentioned (a1) and (a2) components) copolymerizable with the alkyl (meth)acrylate (a1) and / or hydroxyl group-containing (meth)acrylate (a2) in which the alkyl group has 5 to 20 carbon atoms can also be used in combination. Examples of such a monomer component (a3) ​​include ethylenically unsaturated group monomers having a functional group other than a hydroxyl group, alkyl (meth)acrylates containing an alkyl group having 1 to 4 carbon atoms or more than 20 carbon atoms, and other copolymerizable monomers. These can be used alone or in combination of two or more types.

[0027] Examples of the ethylenically unsaturated group monomer having a functional group other than a hydroxyl group (hereinafter, sometimes referred to as a "functional group-containing ethylenically unsaturated monomer") include a functional group-containing monomer having a nitrogen atom, a carboxy group-containing monomer, an acetoacetyl group-containing monomer, and a glycidyl group-containing monomer. Among these, functional group-containing monomers having a nitrogen atom are preferred in terms of imparting cohesive strength and crosslinking-promoting action, more preferably amino group-containing monomers, amide group-containing monomers, and isocyanate group-containing monomers, and even more preferably amino group-containing monomers.

[0028] 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; secondary amino group-containing (meth)acrylates such as t-butylaminoethyl (meth)acrylate and t-butylaminopropyl (meth)acrylate; and tertiary amino group-containing (meth)acrylates such as ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, and dimethylaminopropylacrylamide.

[0029] Examples of the amide group-containing monomer include (meth)acrylamide; N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, Nn-butyl(meth)acrylamide, diacetone(meth)acrylamide, and N,N'-methylenebis(meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-ethylmethylacrylamide, and N,N-diallyl(meth)acrylamide; hydroxyalkyl(meth)acrylamides such as N-hydroxymethyl(meth)acrylamide and N-hydroxyethyl(meth)acrylamide; and alkoxyalkyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide and N-(n-butoxymethyl)(meth)acrylamide.

[0030] Examples of the isocyanate group-containing monomer include 2-(meth)acryloyloxyethyl isocyanate and alkylene oxide adducts thereof, etc. The isocyanate group may be protected with a blocking agent such as methyl ethyl ketone oxime, 3,5-dimethylpyrazole, 1,2,4-triazole, or diethyl malonate.

[0031] Examples of the carboxy group-containing monomer include (meth)acrylic acid, carboxyethyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxypropyl phthalic acid, 2-(meth)acryloyloxyethyl maleic acid, 2-(meth)acryloyloxypropyl maleic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxypropyl succinic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid, monomethyl maleate, and monomethyl itaconate.

[0032] Examples of the acetoacetyl group-containing monomer include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate.

[0033] Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

[0034] 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 preferably 30% by weight or less, more preferably 20% by weight or less, even more preferably 10% by weight or less, and particularly preferably 5% by weight or less, based on the total copolymerization components of the acrylic polymer (A), from the viewpoint of reducing the decrease in adhesiveness due to bleed-out. The lower limit is usually 0% by weight.

[0035] Examples of the alkyl (meth)acrylate containing an alkyl group having 1 to 4 carbon atoms or more than 20 carbon atoms include linear alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and icosyl (meth)acrylate; and branched alkyl (meth)acrylates such as isopropyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, and isoicosyl (meth)acrylate. These may be used alone or in combination of two or more.

[0036] When the alkyl (meth)acrylate containing the alkyl group having 1 to 4 carbon atoms or more than 20 carbon atoms is contained, the upper limit of the content is preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 5% by weight or less, based on the total copolymerization components of the acrylic polymer (A), from the viewpoint of maintaining recovery properties. The lower limit is usually 0% by weight.

[0037] Examples of the other copolymerizable monomers include aromatic (meth)acrylates such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyl diethylene glycol (meth)acrylate, phenoxy polyethylene glycol (meth)acrylate, phenoxy polyethylene glycol-polypropylene glycol-(meth)acrylate, and 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, and 4-methacryloyloxyethoxybenzophenone. Examples of suitable vinyl monomers include (meth)acrylates having a benzophenone structure, such as benzophenone, 4-methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone, and mixtures thereof, acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl stearate, vinyl propionate, vinyl acetate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, vinylpyridine, vinylpyrrolidone, dialkyl itaconate esters, dialkyl fumarate esters, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone. These may be used alone or in combination of two or more.

[0038] The acrylic polymer (A) may have a photoactive moiety, such as a polymerizable carbon-carbon double bond group, introduced into its side chain, which can enhance the crosslinking efficiency of the pressure-sensitive adhesive composition [I] and crosslink the pressure-sensitive adhesive composition [I] in a shorter time, thereby increasing productivity.

[0039] Examples of a method for introducing a polymerizable carbon-carbon double bond group into the side chain of the acrylic polymer (A) include a method in which a copolymer containing the above-mentioned hydroxyl group-containing (meth)acrylate (a2) or a functional group-containing ethylenically unsaturated monomer is prepared, and then a compound having a polymerizable carbon-carbon double bond group and a functional group reactive with the functional group is subjected to a condensation or addition reaction while maintaining the activity of the polymerizable carbon-carbon double bond group.

[0040] Examples of combinations of these functional groups include an epoxy group (glycidyl group) and a carboxy group, an amino group and a carboxy group, an amino group and an isocyanate group, an epoxy group (glycidyl group) and an amino group, a hydroxyl group and an epoxy group, and a hydroxyl group and an isocyanate group. Among these combinations of functional groups, a combination of a hydroxyl group and an isocyanate group is preferred because of the ease of reaction control. Of these, a combination in which the copolymer has a hydroxyl group and the compound has an isocyanate group is preferred.

[0041] Examples of the isocyanate compound having a polymerizable carbon-carbon double bond group include the above-mentioned 2-(meth)acryloyloxyethyl isocyanate and alkylene oxide adducts thereof.

[0042] The content of the compound having a functional group reactive with the functional group and a polymerizable carbon-carbon double bond group is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, even more preferably 1 part by weight or less, and particularly preferably 0.1 parts by weight or less, per 100 parts by weight of the acrylic polymer (A), from the viewpoint of improving adhesiveness and stress relaxation properties. The lower limit is usually 0 part by weight.

[0043] The glass transition temperature (Tg) of the acrylic polymer (A) is preferably −20° C. or lower in order to suppress an increase in the storage shear modulus (G′) at low temperatures, more preferably −23° C. or lower, even more preferably −25° C. or lower, and particularly preferably −30° C. or lower. Due to concerns about adhesive overflow and the like, the lower limit of the glass transition temperature (Tg) is usually −50° C.

[0044] In the present invention, the glass transition temperature (Tg) of the acrylic polymer (A) can be determined by reading the temperature at which the loss tangent (loss modulus G" / storage modulus G'=tanδ) becomes maximum when the dynamic viscoelasticity is measured in a shear mode at a frequency of 1 Hz using a dynamic viscoelasticity measuring device. For example, the acrylic polymer (A) is molded into a cylindrical body with a diameter of 8 mm (height of 1.0 mm), and the loss tangent (tanδ) of this can be measured using a viscoelasticity measuring device (manufactured by TA Instruments, product name "DHR 2") under the following measurement conditions.

[0045] (Measurement conditions) Measurement jig: Φ8mm parallel plate Distortion: 0.1% Frequency: 1Hz ·Measurement temperature: -60~100℃ Heating rate: 5℃ / min

[0046] The weight average molecular weight (Mw) of the acrylic polymer (A) is preferably 600,000 or more, more preferably 700,000 or more, and even more preferably 800,000 or more, from the viewpoint of obtaining a pressure-sensitive adhesive composition [I] with high cohesive strength. The upper limit of the weight average molecular weight (Mw) of the acrylic polymer (A) is preferably 1.5 million or less, more preferably 1.2 million or less, and even more preferably 1.1 million or less, from the viewpoints of ease of handling and uniform stirring.

[0047] In the present invention, the weight average molecular weight (Mw) can be determined, for example, as follows. (Method for measuring weight-average molecular weight) The weight average molecular weight (Mw) can be determined by dissolving 4 mg of acrylic polymer (A) in 12 mL of tetrahydrofuran (THF) to prepare a measurement sample, and measuring the molecular weight distribution curve using a gel permeation chromatography (GPC) analyzer (Tosoh Corporation, HLC-8320GPC) under the following conditions: Guard column: TSKguardcolumnHXL Separation column: TSKgel GMHXL (4 columns) ·Temperature: 40℃ ·Injection volume: 100μL Polystyrene equivalent Solvent: THF ·Flow rate: 1.0mL / min

[0048] <Radical polymerizable compound (B)> The pressure-sensitive adhesive composition [I] contains a radically polymerizable compound (B) in addition to the acrylic polymer (A). This allows the pressure-sensitive adhesive composition [I] to form a crosslinked structure, which can impart cohesive strength and high recovery upon bending to the pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet). The pressure-sensitive adhesive layer has an appropriate cohesive strength, which can prevent glue from leaking out when wound into a roll and maintain good adhesiveness. Furthermore, the high recovery upon bending can improve fold marks and prevent delamination at bent portions.

[0049] It is important that the radical polymerizable compound (B) contains a di(meth)acrylate (B1) having an alkylene group having 5 to 20 carbon atoms (hereinafter, sometimes abbreviated as "di(meth)acrylate (B1)"), which provides the effect of having good adhesive strength, excellent flexibility at low temperatures, and excellent recovery, particularly rapid recovery.

[0050] In the di(meth)acrylate (B1), when the number of carbon atoms in the alkylene group is equal to or greater than the lower limit, good restoring properties can be imparted, and when the number is equal to or less than the upper limit, adhesive strength is not impaired, which is preferable. The alkylene group preferably has 5 to 15 carbon atoms, more preferably 7 to 13 carbon atoms, and particularly preferably 9 to 11 carbon atoms, from the viewpoint of recovery.

[0051] Specific examples of the di(meth)acrylate (B1) include pentanediol di(meth)acrylate, hexadiol di(meth)acrylate, heptanediol di(meth)acrylate, octanediol di(meth)acrylate, nonanediol di(meth)acrylate, decanediol di(meth)acrylate, undecanediol di(meth)acrylate, and dodecanediol di(meth)acrylate. Among these, decanediol di(meth)acrylate is preferred from the viewpoints of versatility, recovery, and low storage shear modulus (G') at low temperatures. Furthermore, acrylates are particularly preferred from the viewpoint of suppressing an increase in storage shear modulus (G') at low temperatures and improving flexibility. These may be used alone or in combination of two or more.

[0052] In addition, the alkylene group in the di(meth)acrylate (B1) is preferably a linear alkylene group from the viewpoint of recovery.

[0053] As the radical polymerizable compound (B), a radical polymerizable compound (B2) other than the di(meth)acrylate (B1) can also be used in combination. Examples of the radical polymerizable compound (B2) include (meth)acrylic monomers and (meth)acrylic oligomers having two or more functional groups other than the di(meth)acrylate (B1), which can be used alone or in combination of two or more.

[0054] 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, tricyclodecane dimethacrylate, tricyclodecane dimethanol di(meth)acrylate, bisphenol A polyethoxy di(meth)acrylate, bisphenol A polypropoxy di(meth)acrylate, and bisphenol F polyethoxy di(meth)acrylate. Dioxydi(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 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, polytetramethylene glycol di(meth)acrylate, tris(acryloxyethyl) isocyanurate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate tri(meth)acrylate, tripentaerythritol hexa(meth)acrylate, tripentaerythritol penta(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, di(meth)acrylate of hydroxypivalic acid neopentyl glycol adduct ε-caprolactone, trimethylolpropane tri(meth)acrylate, trimethylolpropane polyethoxytri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and the like.

[0055] Examples of the (meth)acrylic oligomer having two or more functional groups include polyfunctional (meth)acrylic oligomers such as polyester (meth)acrylate oligomers, epoxy (meth)acrylate oligomers, urethane (meth)acrylate oligomers, and polyether (meth)acrylate oligomers. Among these, urethane (meth)acrylate oligomers are preferred from the viewpoint of imparting appropriate toughness to the cured product.

[0056] The content of the radical polymerizable compound (B) is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, and even more preferably 1 part by weight or more, relative to 100 parts by weight of the acrylic polymer (A), from the viewpoint of imparting shape stability to the pressure-sensitive adhesive sheet and durability when formed into a laminate sheet. The upper limit is preferably 10 parts by weight or less, more preferably 7 parts by weight or less, particularly preferably 5 parts by weight or less, and even more preferably 3 parts by weight or less, from the viewpoint of reducing the storage shear modulus (G') at low temperatures.

[0057] It is also important to use the di(meth)acrylate (B1) as the radical polymerizable compound (B), and the content of the di(meth)acrylate (B1) is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, even more preferably 0.7 parts by weight or more, and particularly preferably 1 part by weight or more, relative to 100 parts by weight of the acrylic polymer (A). The upper limit is preferably 10 parts by weight or less, more preferably 7 parts by weight or less, particularly preferably 5 parts by weight or less, and even more preferably 3 parts by weight or less, in order to maintain high adhesiveness. It is preferable to use a di(meth)acrylate (B1) as the main component of the radical polymerizable compound (B), and it is particularly preferable to use only the di(meth)acrylate (B1) as the radical polymerizable compound (B).

[0058] In addition to the radically polymerizable compound (B), a thermal crosslinking agent can be used in combination in order to further increase the crosslink density and improve long-term reliability. Examples of such thermal crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, aldehyde-based crosslinking agents, amine-based crosslinking agents, and metal chelate-based crosslinking agents. Among these, it is preferable to use an isocyanate-based crosslinking agent because of its excellent reactivity with the acrylic polymer (A).

[0059] <Photopolymerization initiator (C)> In the present invention, it is preferable to further contain a photopolymerization initiator (C) in addition to the acrylic polymer (A) and the radically polymerizable compound (B). The photopolymerization initiator (C) may be any compound that generates radicals when exposed to active energy rays.

[0060] Photopolymerization initiators (C) are broadly classified into two types based on the radical generation mechanism: cleavage-type photopolymerization initiators that can generate radicals by cleaving and decomposing the single bond of the initiator itself, and hydrogen abstraction-type photopolymerization initiators that form an exciplex between the excited initiator and a hydrogen donor in the system and can transfer hydrogen from the hydrogen donor.

[0061] The photopolymerization initiator (C) may be either a cleavage-type photopolymerization initiator or a hydrogen-abstraction-type photopolymerization initiator, and may be used either alone or in combination with one or more of these.

[0062] In the present invention, it is preferable to use a hydrogen abstraction photopolymerization initiator, since the acrylic polymer (A) itself does not require a functional group such as a polymerizable carbon-carbon double bond group and crosslinking can be efficiently carried out.

[0063] Examples of the cleavage-type photopolymerization initiator include 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-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), methyl phenylglyoxylate, 2-benzyl-2-dimethylamino- Examples of such compounds include 1-(4-morpholinophenyl)butan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-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 oxide, and derivatives thereof.

[0064] Examples of the hydrogen abstraction photopolymerization initiator include benzophenone, 4-methylbenzophenone, 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. Among these, 4-methylbenzophenone and 2,4,6-trimethylbenzophenone are preferred.

[0065] The content of the photopolymerization initiator (C) is usually 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, and more preferably 1 to 3 parts by weight, per 100 parts by weight of the acrylic polymer (A). When the content is equal to or greater than the lower limit, poor curing tends to be prevented, while when the content is equal to or less than the upper limit, deterioration in solution stability such as precipitation from the pressure-sensitive adhesive composition [I] tends to be suppressed, and problems such as embrittlement and coloration tend to be suppressed.

[0066] <Other ingredients> The pressure-sensitive adhesive composition [I] may contain, as "other components", as needed, various additives such as plasticizers, silane coupling agents, ultraviolet absorbers, rust inhibitors, tackifying resins, antioxidants, light stabilizers, metal deactivators, antioxidants, moisture absorbers, rust inhibitors, and inorganic particles, to the extent that the effects of the present invention are not impaired. If necessary, a reaction catalyst such as a tertiary amine compound, a quaternary ammonium compound, or a tin laurate compound may be appropriately contained. These may be used alone or in combination of two or more.

[0067] (plasticizer) A plasticizer is a material that improves processability and flexibility by softening a resin with 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 them, urethane (meth)acrylate oligomers are preferred from the viewpoint of imparting appropriate toughness to the cured product.

[0068] (Silane coupling agent) Silane coupling agents are organosilicon compounds containing, in their 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 groups, (meth)acryloyl groups, mercapto groups, hydroxyl groups, carboxy groups, amino groups, amide groups, and isocyanate groups. Among these, epoxy groups and mercapto groups are preferred in terms of balance of durability.

[0069] The alkoxy group bonded to the silicon atom preferably contains an alkoxy group having 1 to 8 carbon atoms from the viewpoint of durability and storage stability, and is particularly preferably a methoxy group or an ethoxy group. The silane coupling agent may have an organic substituent other than the reactive functional group and the alkoxy group bonded to the silicon atom, such as an alkyl group or a phenyl group.

[0070] Examples of the silane coupling agent used in the present invention include monomeric epoxy group-containing silane coupling agents, which are silane compounds such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; and silane coupling agents in which a part of the silane compounds is hydrolyzed and condensed, or in which the silane compounds are combined with methyltriethoxysilane, ethyltriethoxysilane, and the like. oligomeric epoxy group-containing silane coupling agents, which are silane compounds obtained by co-condensation of alkyl group-containing silane compounds such as silane, methyltrimethoxysilane, and ethyltrimethoxysilane; monomeric mercapto group-containing silane coupling agents, which are silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, γ-mercaptopropyldimethoxymethylsilane, and 3-mercaptopropylmethyldimethoxysilane; and silane coupling agents, which are silane compounds obtained by hydrolysis and condensation polymerization of a part of the silane compounds .... and an alkyl group-containing silane compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, or ethyltrimethoxysilane, which are co-condensed oligomeric mercapto group-containing silane coupling agents; and (meth)acryloyl group-containing silane compounds such as 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, or 3-acryloxypropyltrimethoxysilane. Coupling agents: amino group-containing silane coupling agents such as N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, and N-phenyl-3-aminopropyltrimethoxysilane; isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane;Examples include vinyl group-containing silane coupling agents such as vinyltrimethoxysilane and vinyltriethoxysilane; These may be used alone or in combination of two or more.

[0071] Among these, epoxy group-containing silane coupling agents and mercapto group-containing silane coupling agents are preferably used because of their excellent durability, and epoxy group-containing silane coupling agents are particularly preferred.

[0072] 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, and further preferably 0.05 to 1 part by weight, relative to 100 parts by weight of the acrylic polymer (A). When the content is equal to or greater than the lower limit, durability tends to be improved, and when the content is equal to or less than the upper limit, durability tends to be improved.

[0073] (ultraviolet absorber) Examples of the ultraviolet absorber include benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, benzoxazine-based ultraviolet absorbers, etc. These ultraviolet absorbers can be used alone or in combination of two or more.

[0074] The content of the ultraviolet absorber is preferably 0.01 to 20 parts by weight, particularly preferably 0.1 to 15 parts by weight, and further preferably 0.5 to 10 parts by weight, relative to 100 parts by weight of the acrylic polymer (A). When the content is equal to or greater than the lower limit, lightfastness reliability tends to improve, and when the content is equal to or less than the upper limit, yellowing resistance tends to improve.

[0075] (rust inhibitor) As the rust inhibitor, for example, triazoles, benzotriazoles, etc. are preferable, and they can prevent corrosion of optical members. The content of the rust inhibitor is preferably 0.01 to 5 parts by weight, and more preferably 0.1 to 3 parts by weight, per 100 parts by weight of the acrylic polymer (A).

[0076] The content of the other components is preferably 5 parts by weight or less, particularly preferably 1 part by weight or less, and even more preferably 0.5 parts by weight or less, based on 100 parts by weight of the acrylic polymer (A). If the content is too high, the compatibility with the acrylic polymer (A) decreases, and durability tends to decrease.

[0077] The pressure-sensitive adhesive composition [I] is prepared by mixing predetermined amounts of the acrylic polymer (A) and the radically polymerizable compound (B), preferably further a photopolymerization initiator (C), and, if necessary, other components such as a silane coupling agent, an ultraviolet absorber, and a rust inhibitor. The pressure-sensitive adhesive composition [I] thus obtained is used for pressure-sensitive adhesive sheets, particularly pressure-sensitive adhesive sheets used for bonding components of flexible image display devices.

[0078] <Configuration> The present adhesive sheet may be a single-layer sheet consisting of only an adhesive layer (also referred to as "the present adhesive layer") formed from the adhesive composition [I], or a multi-layer sheet in which multiple present adhesive layers are laminated.

[0079] <Physical properties of this adhesive sheet> The pressure-sensitive adhesive sheet can have the following physical properties.

[0080] (storage shear modulus) The pressure-sensitive adhesive sheet preferably has a storage shear modulus at -20°C (G'(-20°C)) of 500 kPa or less, more preferably 400 kPa or less, even more preferably 300 kPa or less, and especially preferably 200 kPa or less, as determined by dynamic viscoelasticity measurement in shear mode at a frequency of 1 Hz. The lower limit of the storage shear modulus (G'(-20°C)) of the pressure-sensitive adhesive sheet is preferably 50 kPa or more, from the viewpoint of preventing adhesive extrusion and maintaining the shape of the pressure-sensitive adhesive sheet.

[0081] When the storage shear modulus (G'(-20°C)) of the adhesive sheet is within the above range, for example, when the adhesive sheet is adhered to a component sheet to form a laminated sheet or a flexible image display component, the interlayer stress when the laminated sheet or flexible image display component is bent can be reduced, particularly at low to high temperatures, and delamination and cracking of the component sheet or flexible component can be suppressed.

[0082] From the viewpoint of obtaining high adhesiveness, the storage shear modulus at 60°C (G'(60°C)) of this adhesive sheet is preferably 100 kPa or less, more preferably 50 kPa or less, even more preferably 30 kPa or less, and especially preferably 20 kPa or less, as determined by dynamic viscoelasticity measurement in shear mode at a frequency of 1 Hz. The lower limit of the storage shear modulus (G'(60°C)) of the pressure-sensitive adhesive sheet is preferably 1 kPa or more, from the viewpoint of preventing adhesive extrusion and maintaining the shape of the pressure-sensitive adhesive sheet.

[0083] (loss shear modulus) The loss shear modulus (G"(23°C)) of this PSA sheet at 23°C, obtained by dynamic viscoelasticity measurement in shear mode at a frequency of 1 Hz, is preferably 8 kPa or more, more preferably 10 kPa or more, and particularly preferably 12 kPa or more. On the other hand, the upper limit of the loss shear modulus (G"(23°C)) is preferably 400 kPa or less, from the viewpoint of reducing stress during bending.

[0084] When the loss shear modulus (G"(23°C)) of the pressure-sensitive adhesive sheet is within the above range, the adhesive strength of the pressure-sensitive adhesive sheet can be further increased.

[0085] (Maximum point of loss tangent (tanδ) and glass transition temperature (Tg)) The pressure-sensitive adhesive sheet preferably has a maximum loss tangent (tan δ) obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz at or below -30°C. The lower limit is usually -50°C. The maximum point of the loss tangent (tanδ) can be interpreted as the glass transition temperature (Tg), and when the glass transition temperature (Tg) is within the above range, it becomes easier to adjust the storage shear modulus (G'(-20°C)) of the pressure-sensitive adhesive sheet to 500 kPa or less.

[0086] When only one inflection point is observed in the loss tangent (tanδ) obtained by dynamic viscoelasticity measurement in shear mode at a frequency of 1 Hz, in other words, when the tanδ curve exhibits a single peak, it can be considered that the glass transition temperature (Tg) is single.

[0087] The "maximum point" of the loss tangent (tan δ) means the point having the largest value in a specified range or the entire range among the peak values ​​in the tan δ curve, that is, the inflection points where the tan δ curve changes from positive (+) to negative (-) when differentiated.

[0088] The elastic modulus (storage shear modulus) G', viscous modulus (loss shear modulus) G" and tan δ=G" / G' at various temperatures can be measured using a strain rheometer.

[0089] The storage shear modulus (G'), loss shear modulus (G"), and loss tangent (tan δ) can be adjusted to within the above-mentioned ranges by adjusting the types and weight average molecular weights of the components of the pressure-sensitive adhesive composition [I] constituting the pressure-sensitive adhesive sheet (for example, the acrylic polymer (A) and the radically polymerizable compound (B)), and by further adjusting the gel fraction of the pressure-sensitive adhesive sheet. However, this method is not limited to these.

[0090] (Resilience) This pressure-sensitive adhesive sheet can be subjected to a shear strain equivalent to 7 times its thickness at 25°C, maintained for 10 minutes, and then its recovery can be measured by reading the strain value (residual strain value) 1 minute or 10 minutes after the stress is removed. Recovery can be calculated using the following formula. Restorability (%) = [(700 - residual strain value) / 700] x 100

[0091] If the adhesive sheet has such resilience, it can be made into an adhesive sheet with excellent resilience that does not leave fold marks due to being placed in a bent state, even when the adhesive sheet is attached to a component sheet and subjected to a folding operation at low or high temperatures. From this viewpoint, it is preferable that the recovery calculated from the residual strain values ​​1 minute and 10 minutes after the stress is removed by applying a shear strain equivalent to 7 times the thickness at 25°C and maintaining the applied strain for 10 minutes is 40% or more, particularly 50% or more, further 70% or more, and especially 80% or more. Since a higher recovery is preferable, the upper limit is 100%.

[0092] In order to improve the restoring properties of the pressure-sensitive adhesive sheet, it is preferable to use, as the radically polymerizable compound (B), a bifunctional (meth)acrylate monomer having an alkylene group of a certain length or more, specifically, a di(meth)acrylate (B1) containing an alkylene group having 5 to 20 carbon atoms, and it is further preferable to make the acrylic polymer (A) contain a structural moiety derived from an alkyl (meth)acrylate (a1) having an alkyl group having 5 to 20 carbon atoms.

[0093] In this case, the bifunctional (meth)acrylate having an alkylene group of a certain length or more bonds the side chains of the acrylic polymer (A) together, thereby strengthening the entanglement of the polymer chains. This increases the entropy difference before and after elongation, and the entropy elasticity improves the recovery property. However, the method for adjusting the restorability is not limited to these methods.

[0094] (gel fraction) The gel fraction of the pressure-sensitive adhesive sheet is preferably 30 to 95% by weight, more preferably 50 to 90% by weight, even more preferably 55 to 85% by weight, and particularly preferably 60 to 85% by weight. When the gel fraction of the pressure-sensitive adhesive sheet is at least the lower limit, the shape can be sufficiently maintained, and when it is at most the upper limit, the adhesive strength can be increased. The gel fraction is a measure of the degree of crosslinking (degree of hardening) and can be measured under the measurement conditions described in the examples below.

[0095] (total light transmittance, haze) The total light transmittance of the pressure-sensitive adhesive sheet is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more.

[0096] Furthermore, the present pressure-sensitive adhesive sheet preferably has a haze of 1.0% or less, more preferably 0.8% or less, and particularly preferably 0.5% or less. Since the haze of the present pressure-sensitive adhesive sheet is 1.0% or less, it can be used for applications in image display devices. In order to set the haze of the present pressure-sensitive adhesive sheet within the above range, it is preferable that the present pressure-sensitive adhesive sheet does not contain particles such as organic particles.

[0097] <Thickness> The thickness of the present pressure-sensitive adhesive sheet is not particularly limited, and if the thickness is 10 μm or more, the sheet has good handleability, and if the thickness is 1000 μm or less, the sheet can be made thinner. Therefore, the thickness of the present pressure-sensitive adhesive sheet is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 20 μm or more, and even more preferably 25 μm or more. On the other hand, the upper limit is preferably 1000 μm or less, more preferably 500 μm or less, particularly preferably 250 μm or less, even more preferably 100 μm or less, and even more preferably 50 μm or less.

[0098] <Preferred uses of this adhesive sheet> This adhesive sheet is used for bonding components that constitute display components (also referred to as "display components"), in particular flexible components for displays used in producing displays, and is used as an adhesive component for flexible displays used in producing flexible displays. The flexible member may be the same as that described later.

[0099] <Method of manufacturing the present pressure-sensitive adhesive sheet> Next, a method for producing the pressure-sensitive adhesive sheet will be described. However, the following description is merely an example of a method for producing the present pressure-sensitive adhesive sheet, and the present pressure-sensitive adhesive sheet is not limited to sheets produced by this production method.

[0100] In producing the present adhesive sheet, a pressure-sensitive adhesive composition [I] for forming the present adhesive sheet is prepared, which contains an acrylic polymer (A), a radically polymerizable compound (B), a photopolymerization initiator (C), and other components as needed, and the pressure-sensitive adhesive composition [I] is formed into a sheet, crosslinked, i.e., polymerized, to harden the sheet, and then processed as needed to produce the present adhesive sheet.

[0101] In addition, in producing the present adhesive sheet, the adhesive composition [I] for forming the present adhesive sheet is prepared in the same manner as described above, and then coated onto a component sheet or a flexible component, and the adhesive composition [I] is cured to form the present adhesive sheet. However, the method is not limited to this.

[0102] When preparing the pressure-sensitive adhesive composition [I] for forming the pressure-sensitive adhesive sheet, the raw materials may be kneaded using a temperature-controllable kneader (e.g., a single-screw extruder, a twin-screw extruder, a planetary mixer, a twin-screw mixer, a pressure kneader, etc.). When mixing various raw materials, various additives such as silane coupling agents and antioxidants may be blended together with the resin in advance and then supplied to the kneader, or all materials may be melt-mixed in advance and then supplied, or a master batch in which only the additives are concentrated in the resin may be prepared and then supplied.

[0103] The pressure-sensitive adhesive composition [I] can be formed into a sheet by any known method, such as wet lamination, dry lamination, extrusion casting using a T-die, extrusion lamination, calendaring, inflation, injection molding, and liquid injection curing. Among these, when producing a sheet, wet lamination, extrusion casting, and extrusion lamination are preferred.

[0104] The pressure-sensitive adhesive composition [I] can be cured by irradiating it with active energy rays to produce a cured product. In addition to irradiating it with active energy rays, it can also be further cured by heating. In particular, the pressure-sensitive adhesive sheet can be produced by irradiating a molded product, for example, a sheet, of the pressure-sensitive adhesive composition [I] with active energy rays. In addition to the irradiation with active energy rays, the composition can also be further cured by heating.

[0105] Furthermore, the irradiation energy, irradiation time, irradiation method, etc. of the active energy rays are not particularly limited as long as they can activate the photopolymerization initiator (C) and polymerize the monomer components. When a hydrogen abstraction type photopolymerization initiator is used as the photopolymerization initiator (C), a hydrogen abstraction reaction also occurs from the acrylic polymer (A), and the acrylic polymer (A) is incorporated into the crosslinked structure, thereby forming a crosslinked structure with many crosslinking points. Therefore, the present pressure-sensitive adhesive sheet is preferably one that is cured using a hydrogen abstraction type photopolymerization initiator.

[0106] In 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 then coated using various coating techniques. When a coating method is used, the present pressure-sensitive adhesive sheet can be obtained by heat curing in addition to the above-mentioned curing by irradiation with active energy rays. In the case of coating, the thickness of the present pressure-sensitive adhesive sheet can be adjusted by the coating thickness and the solids concentration of the coating liquid.

[0107] For example, the pressure-sensitive adhesive composition [I] can be dissolved in a solvent, coated on a release film, dried, and cured by active energy ray irradiation to form the present pressure-sensitive adhesive sheet. Furthermore, a release film may be laminated, if necessary. In this case, the pressure-sensitive adhesive composition [I] may be coated on a release film, dried, cured by active energy ray irradiation, and a release film may be laminated thereon. Alternatively, the pressure-sensitive adhesive sheet may be formed by coating on a release film, drying, laminating a release film, and then curing by active energy ray irradiation.

[0108] The solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition [I], and examples thereof include ester solvents such as methyl acetate, ethyl acetate, methyl acetoacetate, and ethyl acetoacetate; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aromatic solvents such as toluene and xylene; and alcohol solvents such as methanol, ethanol, and propyl alcohol. These can be used alone or in combination of two or more. Among them, ethyl acetate, acetone, methyl ethyl ketone, and toluene are preferred in terms of solubility, drying properties, cost, etc., and ethyl acetate is particularly preferred.

[0109] In terms of drying property, the content of the solvent is preferably 600 parts by weight or less, more preferably 500 parts by weight or less, even more preferably 400 parts by weight or less, and particularly preferably 300 parts by weight or less, relative to 100 parts by weight of the acrylic polymer (A), while 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. The coating method may be any conventional method such as roll coating, die coating, gravure coating, comma coating, screen printing, or bar coating.

[0110] The solvent content in the pressure-sensitive adhesive composition [I] after drying is preferably 1% by weight or less, more preferably 0.5% by weight or less, particularly preferably 0.1% by weight or less, and most preferably 0% by weight.

[0111] The drying temperature is usually 40 to 150° C., more preferably 45 to 140° C., even more preferably 50 to 130° C., and particularly preferably 55 to 120° C. Within this temperature range, the solvent can be removed efficiently and relatively safely while suppressing thermal deformation of the release film.

[0112] The drying time is usually 1 to 30 minutes, more preferably 3 to 25 minutes, and even more preferably 5 to 20 minutes. When the drying time is within this range, the solvent can be removed efficiently and sufficiently.

[0113] Drying methods include, for example, drying with a dryer, drying with a heated roll, drying by blowing hot air onto the film, etc. Among these, using a dryer is preferred because it allows for uniform and easy drying. These methods can be used alone or in combination of two or more.

[0114] Examples of the active energy rays used in the active energy ray irradiation include light rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, infrared rays, and visible light rays, as well as ionizing radiation such as X-rays, α-rays, β-rays, γ-rays, electron beams, proton beams, and neutron beams. Among these, ultraviolet rays are preferred from the viewpoints of suppressing damage to optical device components and controlling reactions. Furthermore, curing by ultraviolet irradiation is advantageous in terms of curing speed, ease of availability of irradiation equipment, cost, and the like.

[0115] Examples of light sources for ultraviolet irradiation include high-pressure mercury lamps, ultra-high-pressure mercury lamps, carbon arc lamps, metal halide lamps, xenon lamps, chemical lamps, electrodeless discharge lamps, and LEDs, all of which emit light in the wavelength range of 150 to 450 nm. Of these, it is preferable to use a high-pressure mercury lamp.

[0116] The amount of active energy ray irradiation (cumulative light amount) is 30 to 3000 mJ / cm from the viewpoint of curing. 2 is preferred, and more preferably 100 to 2000 mJ / cm 2 , and more preferably 300 to 1500 mJ / cm 2 This is carried out under the following conditions. After irradiation with active energy rays, the degree of cure can be increased by heating, if necessary.

[0117] A release film may be provided on at least one surface of the pressure-sensitive adhesive sheet obtained above to prevent blocking and adhesion of foreign matter.

[0118] As such a release film, any known release film can be used appropriately. As the material for the release film, for example, a film such as a polyester film, a polyolefin film, a polycarbonate film, a polystyrene film, an acrylic film, a triacetyl cellulose film, or a fluororesin film that has been coated with a silicone resin to provide a release treatment, or release paper, etc. can be appropriately selected and used.

[0119] The thickness of the release film is not particularly limited, but from the viewpoint of processability and handling, it is preferably 10 to 250 μm, more preferably 25 to 200 μm, and even more preferably 35 to 190 μm.

[0120] If necessary, the sheet may be embossed or have various irregularities (such as a cone, pyramid, or hemisphere).In addition, the sheet may be subjected to various surface treatments such as corona treatment, plasma treatment, and primer treatment in order to improve adhesion to various component sheets.

[0121] The present pressure-sensitive adhesive sheet can also be provided as a pressure-sensitive adhesive sheet with a release film by laminating a release film on one or both sides of the pressure-sensitive adhesive layer (the present pressure-sensitive adhesive sheet) made of the pressure-sensitive adhesive composition [I].

[0122] <<This laminated sheet>> A laminate sheet according to an embodiment of the present invention (hereinafter sometimes referred to as "the present laminate sheet") is a sheet comprising the present pressure-sensitive adhesive sheet and other layers. Of the layers constituting the present laminate sheet, the thickness of the present pressure-sensitive adhesive sheet preferably accounts for 10 to 90% of the total thickness of the present laminate sheet, more preferably 20% to 80%, and even more preferably 30% to 70%. The present laminate sheet is preferably one in which a component sheet is provided on at least one side of the present pressure-sensitive adhesive sheet, or one in which the present pressure-sensitive adhesive sheet is provided on at least one side of a component sheet.

[0123] It is preferable that the present laminate sheet is a laminate sheet having a configuration in which, for example, a component sheet (hereinafter sometimes referred to as a "first component sheet"), the present adhesive sheet, and another component sheet (hereinafter sometimes referred to as a "second component sheet") are laminated in this order. The present pressure-sensitive adhesive sheet can be attached to a first member sheet and / or a second member sheet to produce the present laminate sheet, although the production method is not limited to this. The first member sheet and the second member sheet may be the same or different.

[0124] <Component sheet> The component sheets that make up this laminate sheet, i.e., the component sheets that are attached to this pressure-sensitive adhesive sheet (including the "first component sheet" and / or the "second component sheet"), can be, for example, a resin sheet containing as its main component at least one resin selected from the group consisting of polyester resin, cycloolefin resin, triacetyl cellulose resin, polymethyl methacrylate resin, epoxy resin, polyimide resin, aramid resin, and polyurethane resin, or glass such as thin film glass. Here, thin film glass refers to glass having the thickness of the component sheets listed above. In particular, the 25°C tensile strength (ASTM D882) of resin sheets whose main component is cycloolefin resin is low, at 40 to 60 MPa at a thickness of 100 μm. In the case of laminated sheets using component sheets with such low tensile strength, cracks tend to occur when bent, and it has been difficult to eliminate these cracks using conventional technology.

[0125] As the member sheet, any conventionally known material can be used, and although there are no particular limitations, the following are preferred examples. PET film "Mitsubishi Chemical Corporation, S100, thickness 50 μm" (tensile strength: 73 MPa) PEN film (Teijin, FS205S, thickness 50 μm) (tensile strength: 193 MPa) PI film "KOLON, C_50, thickness 53um" (tensile strength: 204MPa)

[0126] The "main component" refers to the component that accounts for the largest weight ratio among the resin components that make up the component sheet, and specifically, it is a component that accounts for 50% by weight or more of the component sheet or the resin composition that forms the component sheet, and it is even more preferable that it accounts for 55% by weight or more, and even more preferably 60% by weight or more.

[0127] Depending on the configuration of the flexible image display device and the position of the adhesive sheet, examples of the first component sheet and the second component sheet include a cover lens, a polarizing plate, a retardation film, a barrier film, a touch sensor film, a light-emitting element, etc. In particular, in consideration of the configuration of the image display, it is preferable that the first member sheet has a touch input function. When the present laminate sheet has the above-mentioned second member sheet, the second member sheet may also have a touch input function.

[0128] (Tensile strength at 25°C) Furthermore, with regard to the first component sheet, the tensile strength at 25°C measured in accordance with ASTM D882 (also referred to as "25°C tensile strength (ASTM D882)") is preferably 10 to 900 MPa, more preferably 15 MPa or more and 800 MPa or less, and even more preferably 20 MPa or more and 700 MPa or less. If the 25°C tensile strength (ASTM D882) of the first member sheet is within the above range, it is preferable because it is less likely to crack when bent.

[0129] When the present laminate sheet has the second component sheet described above, the tensile strength of the second component sheet at 25°C measured in accordance with ASTM D882 is preferably 10 to 900 MPa, more preferably 15 MPa or more and 800 MPa or less, and even more preferably 20 MPa or more and 700 MPa or less. If the 25°C tensile strength (ASTM D882) of the second member sheet is within the above range, it is preferable because it is less likely to crack when bent.

[0130] In particular, it is preferable that both the first member sheet and the second member sheet have a tensile strength at 25° C. measured in accordance with ASTM D882 of 10 to 900 MPa. The first member sheet and the second member sheet may be made of the same material or different materials.

[0131] Examples of the member sheets having high tensile strength (including the first member sheet and the second member sheet) include polyimide films and polyethylene naphthalate (PEN) films, and the tensile strength of these films is generally 900 MPa or less. The lower limit is usually 50 MPa. On the other hand, examples of the member sheets having a slightly low tensile strength include polyethylene terephthalate (PET) film, triacetyl cellulose (TAC) film, and cycloolefin polymer (COP) film, which usually have a tensile strength of 10 MPa or more, with the upper limit usually being 200 MPa. Even if the present laminate sheet is provided with component sheets made of such a material with a relatively low tensile strength, the action of the present pressure-sensitive adhesive sheet can prevent defects such as cracking.

[0132] <Physical properties of this laminated sheet> The present laminate sheet can have the following physical properties.

[0133] (Adhesive strength) The adhesive strength of the pressure-sensitive adhesive sheet of the present laminate sheet to the component sheet (peel angle 180°: peel speed 300 mm / min) is preferably 0.5 to 30 N / cm, more preferably 1 to 20 N / cm, and even more preferably 3 to 10 N / cm. Within this range, sufficient adhesiveness is obtained, and the sheet tends to be suitable for use as an adhesive sheet for flexible image display devices. The adhesive strength can be measured under the measurement conditions described in the Examples below.

[0134] (Dynamic bending durability) In a dynamic bending reliability test (dynamic bending durability) of this laminated sheet, a U-shaped bending cycle evaluation was conducted with a curvature radius R of 1.5 mm, 60 rpm (1 Hz), and -20°C. The number of bending cycles without any defects (delamination, breakage, buckling, or flow) occurring in the bent portion was preferably 100,000 or more, and more preferably 200,000 or more. The dynamic bending durability test can be performed under the measurement conditions described in the Examples below.

[0135] <Thickness of this laminated sheet> The thickness of the present laminate sheet is not particularly limited. For example, when the present laminate sheet is used in an image display device, if the present laminate sheet is in a sheet form and the thickness is 0.01 mm or more, the handling property is good, and if the thickness is 1 mm or less, the present laminate sheet can be made thinner. Therefore, the thickness of the present laminate sheet is preferably 0.01 mm or more, more preferably 0.03 mm or more, and particularly preferably 0.05 mm or more. On the other hand, the upper limit is preferably 1 mm or less, more preferably 0.7 mm or less, and particularly preferably 0.5 mm or less.

[0136] <Method of manufacturing the present laminate sheet> Next, a method for producing the laminate sheet will be described. However, the following description is an example of a method for producing the present laminate sheet, and the present laminate sheet is not limited to sheets produced by this production method.

[0137] The present laminate sheet can be produced by preparing an adhesive composition [I] in the same manner as in the manufacturing method of the present adhesive sheet, and then applying the adhesive composition [I] to, for example, a first component sheet and / or a second component sheet, and curing the composition to form an adhesive sheet. In this case, the method for preparing the adhesive composition [I], the coating method, the method for curing the adhesive composition [I], etc. are the same as in the method for producing the present adhesive sheet.

[0138] Alternatively, the present laminate sheet may be produced by laminating a pre-produced present pressure-sensitive adhesive sheet to the first member sheet and / or the second member sheet.

[0139] For the purpose of improving adhesiveness, the surfaces of the pressure-sensitive adhesive sheet, the first member sheet and the second member sheet may be subjected to various surface treatments such as corona treatment, plasma treatment and primer treatment.

[0140] When the present laminated sheet is configured such that a component sheet is laminated on only one side of the present adhesive sheet, a protective film having a release layer laminated thereon can also be provided on the side of the present adhesive sheet on which the component sheet is not laminated.

[0141] <<The flexible image display device member>> A flexible image display device member according to one embodiment of the present invention (hereinafter sometimes referred to as "the flexible image display device member") is a flexible image display device member having a configuration in which two flexible members are bonded together via the adhesive sheet.

[0142] Of the components of the flexible image display device member, the adhesive sheet has been described above, and the components other than the adhesive sheet will be described below.

[0143] (flexible material) Examples of flexible members constituting the flexible image display device member include flexible members for displays such as flexible displays such as organic electroluminescence (EL) displays, cover lenses (cover films), polarizing plates, polarizers, retardation films, barrier films, viewing angle compensation films, brightness enhancement films, contrast enhancement films, diffusion films, semi-transparent reflective films, electrode films, transparent conductive films, metal mesh films, and touch sensor films. Any one of these may be used alone or in combination. Examples include a combination of a flexible display with another flexible member, or a combination of a cover lens with another flexible member.

[0144] The term "flexible member" refers to a member that can be bent, particularly a member that can be repeatedly bent. In particular, it is preferable that the member be a member that can be fixed into a curved shape with a radius of curvature of 25 mm or more, and particularly a member that can withstand repeated bending at a radius of curvature of less than 25 mm, more preferably less than 3 mm.

[0145] In the above-described configuration, the main component of the flexible member may be a resin sheet or glass. Examples of materials for such resin sheets include polyester resins, cycloolefin resins, triacetyl cellulose resins, polymethyl methacrylate resins, polyurethanes, epoxy resins, polyimide resins, and aramid resins, which may be one type of resin or two or more types of resins. Among these, resin sheets containing at least one type of resin selected from the group consisting of polyester resins, cycloolefin resins, triacetyl cellulose resins, polymethyl methacrylate resins, epoxy resins, polyimide resins, aramid resins, and polyurethane resins as a main component are preferred. Here, "main component" refers to the component that occupies the largest weight ratio among the components that make up the flexible member, and specifically, it is a component that occupies 50% by weight or more of the resin composition (resin sheet) that forms the flexible member, and preferably 55% by weight or more, and particularly preferably 60% by weight or more. The flexible member may also be made of thin glass.

[0146] In the above-described configuration, it is particularly preferable that one of the two flexible members, i.e., the first flexible member, has a tensile strength at 25°C measured in accordance with ASTM D882 of 10 to 900 MPa, more preferably 15 MPa or more and 800 MPa or less, and even more preferably 20 MPa or more and 700 MPa or less. If the tensile strength (ASTM D882) at 25°C of one of the flexible members is within the above range, it is preferable since it is less likely to crack when bent.

[0147] Furthermore, the other flexible member, i.e., the second flexible member, preferably has a tensile strength at 25°C measured in accordance with ASTM D882 of 10 to 900 MPa, more preferably 15 MPa or more and 800 MPa or less, and even more preferably 20 MPa or more and 700 MPa or less. If the tensile strength (ASTM D882) at 25°C of the other flexible member is within the above range, it is preferable because it is less likely to crack when bent.

[0148] Examples of the flexible member having a high tensile strength include polyimide film, polyester film, and aramid film, and the tensile strength of these is generally 900 MPa or less. On the other hand, examples of flexible material sheets having a slightly low tensile strength include triacetyl cellulose (TAC) film and cycloolefin polymer (COP) film, and the tensile strength of these films is usually 10 MPa or more. Even if the flexible image display device member of the present invention is provided with a flexible member made of such a material with a slightly low tensile strength, the adhesive sheet can prevent defects such as cracking.

[0149] <Method of manufacturing the flexible image display device member> The method for manufacturing the flexible image display device member is not particularly limited, and as described above, the adhesive composition [I] may be applied to a flexible member to form an adhesive sheet, or an adhesive sheet may be formed in advance using the adhesive composition [I] and then laminated to the flexible member.

[0150] <<This flexible image display device>> A flexible image display device according to an embodiment of the present invention (hereinafter, sometimes referred to as "the flexible image display device") is an image display device incorporating the laminate sheet or the flexible image display device member of the present invention. For example, the flexible image display device including the laminate sheet can be formed by laminating the laminate sheet on other image display device components.

[0151] The term "flexible image display device" refers to an image display device that can be repeatedly bent without leaving any trace of bending, can quickly restore to its original state when released from bending, and can display images without distortion even when bent. More specifically, examples include image display devices made of components that can be curved and fixed to a curvature radius of 25 mm or more, and in particular, components that can withstand repeated bending at a curvature radius of less than 25 mm, and more preferably at a curvature radius of less than 3 mm.

[0152] One of the features of this laminated sheet is that it can prevent delamination and cracking of the laminated sheet even when folded in a high-temperature environment, and has good recovery properties, making it possible to manufacture flexible image display devices with excellent flexibility. [Example]

[0153] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "parts" and "%" are by weight.

[0154] <Raw materials> First, the acrylic polymers and pressure-sensitive adhesive compositions prepared in the examples and comparative examples will be described in detail.

[0155] <Acrylic polymer> Acrylic polymers (1) to (3) having copolymer component compositions as shown in Table 1 were prepared.

[0156] [Table 1]

[0157] <Radical polymerizable compound> The following radical polymerizable compounds were prepared. (B1-1): 1,10-decanediol diacrylate (DDDA) (B'-1): 1,4-butanediol diacrylate (BDDA) (B'-2): PEG600# diacrylate (PEG600#DA) (Kyoeisha Chemical Co., Ltd., "Light Acrylate 14EG-A")

[0158] <Photopolymerization initiator> Esacure TZT (IGM, a mixture of 4-methylbenzophenone and 2,4,6-trimethylbenzophenone (hydrogen abstraction type))

[0159] [Examples 1 to 5, Comparative Examples 1 to 4] According to the formulation shown in Table 2, an acrylic polymer, a radical polymerizable compound, a photopolymerization initiator, and ethyl acetate as a solvent were uniformly mixed to obtain a pressure-sensitive adhesive composition solution (solid concentration: 33%).

[0160] [Table 2]

[0161] The pressure-sensitive adhesive composition solution was coated onto a release film (a silicone release-treated polyester film manufactured by Mitsubishi Chemical Corporation, thickness 100 μm) so that the thickness after drying would be as shown in Table 2. After coating, the film 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 release film (a silicone release-treated polyester film manufactured by Mitsubishi Chemical Corporation, thickness 75 μm) was laminated on the surface of the adhesive composition from which the solvent had been dried to form a laminate, and the adhesive composition was irradiated with ultraviolet light through the release film using a high-pressure mercury lamp (see Table 2 for each irradiation dose) to obtain an adhesive sheet laminate (adhesive sheet with release film). The resulting pressure-sensitive adhesive sheet laminate was evaluated as follows.

[0162] <Gel fraction> The release film was removed from each pressure-sensitive adhesive sheet laminate produced in the Examples and Comparative Examples, and multiple layers of pressure-sensitive adhesive sheets were laminated to form a 1.0 mm thick laminate. An 8 mm diameter cylinder was then punched out, and this was used as a sample. This was wrapped in a 200-mesh SUS wire mesh and immersed in ethyl acetate adjusted to 23°C for 72 hours. It was then dried at 75°C for 4.5 hours, and the weights of the pressure-sensitive adhesive before and after immersion in ethyl acetate were measured, and the difference between the two weights was taken as the weight of the undissolved pressure-sensitive adhesive remaining in the wire mesh. The weight percentage of the undissolved pressure-sensitive adhesive remaining in the wire mesh relative to the weight of the pressure-sensitive adhesive before immersion in ethyl acetate was calculated as the gel fraction (%).

[0163] <Adhesive strength> One release film was removed from each of the pressure-sensitive adhesive sheet laminates produced in the Examples and Comparative Examples, and a polyethylene terephthalate film (Diafoil "S100" manufactured by Mitsubishi Chemical Corporation, 50 μm thick) was roll-laminated as a backing film to the adhesive surface of the pressure-sensitive adhesive sheet laminate using a hand roller. This was then cut into 10 mm wide x 150 mm long strips, and the remaining release film was peeled off to expose the adhesive surface, which was then roll-laminated using a hand roller to a transparent polyimide film (main component: transparent polyimide, "C_50" manufactured by KOLON Corporation, hereinafter referred to as "CPI film") that had been previously laminated to a stainless steel plate, to produce a laminate sheet consisting of CPI film / pressure-sensitive adhesive sheet / backing film. This laminate sheet was then left to stand overnight at room temperature (23°C) to cure, and a sample for adhesive strength measurement was prepared.

[0164] The backing film was peeled off at an angle of 180° to the CPI film at a peeling speed of 300 mm / min, and the tensile strength was measured using a load cell to determine the 180° peel strength (N / 10 mm) of the adhesive sheet against the CPI film, which was taken as the adhesive strength (23°C).

[0165] <Flexibility> To evaluate flexibility, the dynamic viscoelasticity of the adhesive sheet was measured, and the maximum temperature of the loss tangent (tan δ) (glass transition temperature: Tg) and the storage shear modulus (G') at -20°C and 60°C were read from the results.

[0166] [Loss tangent (tanδ), storage shear modulus (G')] The release film was removed from each of the pressure-sensitive adhesive sheet laminates produced in the Examples and Comparative Examples, and a plurality of pressure-sensitive adhesive sheets were laminated to form a laminate having a thickness of 1.0 mm. A cylindrical body with a diameter of 8 mm (height of 1.0 mm) was punched out from the obtained laminate of adhesive sheets (adhesive layers), 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 the loss tangent (tanδ) (glass transition temperature (Tg)), the storage shear modulus G' at -20°C (-20°C), and the storage shear modulus G' at 60°C (60°C) were read.

[0167] (Measurement conditions) Measurement jig: Φ8mm parallel plate Distortion: 0.1% Frequency: 1Hz ·Measurement temperature: -60~100℃ Heating rate: 5℃ / min

[0168] <Resilience> The release film was removed from each of the pressure-sensitive adhesive sheet laminates produced in the Examples and Comparative Examples, and a plurality of pressure-sensitive adhesive sheets were laminated to form a laminate having a thickness of 1.0 mm. A cylindrical body with a diameter of 8 mm (height of 1.0 mm) was punched out from the obtained laminate of adhesive sheets (adhesive layers), and this was used as a sample. The recovery properties of the samples were 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 equivalent to 7 times the thickness at 25°C and maintaining the strain for 10 minutes, the residual strain was measured 1 minute and 10 minutes after the stress was removed to measure the recovery. The resilience is calculated using the following formula: Restorability (%) = [(700 - residual strain value) / 700] x 100

[0169] <Bending durability> The release film was removed from each adhesive sheet laminate produced in the Examples and Comparative Examples, and a CPI film (main component: transparent polyimide, "C_50" manufactured by KOLON) was attached to both sides of the adhesive sheet using a hand roll to obtain a laminate sheet (sample) for bending durability. The laminated sheets (samples) prepared as described above were evaluated as follows.

[0170] (Dynamic bending durability) The laminated sheet (sample) was subjected to a U-bending cycle evaluation using a thermo-hygrostat durability system and a sheet-shaped no-load U-bending tester (manufactured by Yuasa System Co., Ltd.) with a curvature radius of R = 1.5 mm and a speed of 60 rpm (1 Hz). The temperature and number of cycles were evaluated at -20°C and 200,000 times. The evaluation criteria were as follows:

[0171] ◯: No delamination, breakage, buckling or flow occurred at the bent portion or end portion. △: Delamination, breakage, buckling or flow occurred at the edge. ×: Delamination, breakage, buckling or flow occurred at the bent portion.

[0172] The results obtained by the above measurements and evaluations are shown in Table 3.

[0173] [Table 3]

[0174] The evaluation results above show that the recovery property, particularly the rapid recovery property, of the pressure-sensitive adhesive sheet is improved by incorporating a bifunctional (meth)acrylate monomer having an alkylene group of a certain length or more into the acrylic polymer (A) as the pressure-sensitive adhesive composition. This is presumably because the bifunctional (meth)acrylate monomer crosslinks the side chains of the acrylic polymer (A), strengthening the entanglement of the polymer chains, which increases the entropy difference before and after elongation, resulting in high recovery property due to entropy elasticity. Therefore, it is clear that a flexible image display device using the present pressure-sensitive adhesive sheet has excellent reliability in terms of restorability and flexibility. [Industrial Applicability]

[0175] The pressure-sensitive adhesive sheet of the present invention has excellent durability (also referred to as "low-temperature bending durability") such that delamination does not occur when folded at low temperatures, and can provide a flexible image display device that has excellent restoring properties, quickly restoring to a flat state when folded. Therefore, the pressure-sensitive adhesive sheet is useful as a pressure-sensitive adhesive sheet for obtaining various flexible image display devices such as bendable, foldable, rollable, and stretchable, and is particularly suitable as a pressure-sensitive adhesive sheet for foldable image display devices that are subject to repeated bending.

Claims

1. A pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition [I] containing an acrylic polymer (A) and a radically polymerizable compound (B), the acrylic polymer (A) contains a structural moiety derived from a linear aliphatic alkyl (meth)acrylate (a1) having an alkyl group with 5 to 20 carbon atoms and a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a2), the radical polymerizable compound (B) contains a di(meth)acrylate (B1) having an alkylene group having 5 to 20 carbon atoms, The pressure-sensitive adhesive sheet used for bonding components of a flexible image display device, wherein the di(meth)acrylate (B1) having an alkylene group having 5 to 20 carbon atoms is a di(meth)acrylate having a linear alkylene group having 7 to 20 carbon atoms.

2. 2. The pressure-sensitive adhesive sheet used for bonding components of a flexible image display device according to claim 1, wherein the weight-average molecular weight of the acrylic polymer (A) is 600,000 to 1,500,000.

3. 3. The adhesive sheet according to claim 1, wherein the content of the radical polymerizable compound (B) is 0.1 to 10 parts by weight per 100 parts by weight of the acrylic polymer (A).

4. The pressure-sensitive adhesive sheet used for bonding components of a flexible image display device according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive sheet has a storage shear modulus (G') at -20°C of 500 kPa or less.

5. The pressure-sensitive adhesive sheet used for bonding components of a flexible image display device according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive sheet has a gel fraction of 30 to 95% by weight.

6. A laminated sheet comprising a component sheet having a tensile strength of 10 to 900 MPa at 25 ° C. measured in accordance with ASTM D882 on at least one side of the adhesive sheet used for bonding the flexible image display device component according to any one of claims 1 to 5.

7. A laminated sheet comprising a pressure-sensitive adhesive sheet used for bonding the flexible image display device component according to any one of claims 1 to 5 on at least one surface of a component sheet having a tensile strength of 10 to 900 MPa at 25 ° C. measured in accordance with ASTM D882.

8. The laminate sheet according to claim 6 or 7, wherein the component sheet is a resin sheet containing at least one resin selected from the group consisting of polyester resin, cycloolefin resin, triacetyl cellulose resin, polymethyl methacrylate resin, epoxy resin, polyimide resin, aramid resin, and polyurethane resin as a main component, or glass.

9. A flexible image display device comprising the laminate sheet according to any one of claims 6 to 8.

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