JP2023095067A - optical adhesive sheet - Google Patents

Abstract

To provide an optical adhesive sheet suitable for a use in a flexible device.SOLUTION: An adhesive sheet 10 is an optical adhesive sheet. The adhesive sheet 10 has a distortion stress S200 (N/cm2) as a distortion stress at 200% elongation in a first tensile test under a condition of 25°C and a tensile speed 50 mm/min., and a distortion stress S'200 (N/cm2) as a distortion stress at 200% elongation in a second tensile test under a condition of 25°C and a tensile speed 600 mm/min., and a ratio of the distortion stress S200 to the distortion stress S'200 is 0.8 or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical adhesive sheet.

A display panel has a laminated structure including elements such as, for example, a pixel panel, a polarizer, a touch panel and a cover film. In the manufacturing process of such a display panel, for example, an optically transparent adhesive sheet (optical adhesive sheet) is used for bonding the elements included in the laminated structure.

On the other hand, the development of display panels that can be repeatedly folded (foldable) for smartphones and tablet terminals is progressing. Specifically, the foldable display panel is repeatedly deformable between a bent shape and a flat non-bent shape. In such a foldable display panel, each element in the laminated structure is manufactured to be repeatedly foldable, and a thin optical adhesive sheet is used for bonding between such elements. An optical pressure-sensitive adhesive sheet for flexible devices such as foldable display panels is described, for example, in Patent Document 1 below.

JP 2018-111754 A

Conventionally, the optical pressure-sensitive adhesive sheet is easily peeled off from the element as the adherend at the fold portion of the foldable display panel. This is because when the display panel is folded, a relatively large tensile stress is locally generated in the folded portion of the optical adhesive sheet. At the bent portion of the optical adhesive sheet, peeling between the optical adhesive sheet and the element is more likely to occur as the tensile stress applied to the element (adherend) increases, for example, in the shear direction. In addition, in the folding process of the foldable display panel, the faster the folding speed, the greater the stress generated in the optical adhesive sheet, and the more likely peeling occurs between the optical adhesive sheet and the element. Occurrence of the peeling causes malfunction of the device and is not preferable. Optical pressure-sensitive adhesive sheets for foldable display panels are required to be highly resistant to peeling from elements (adherends).

On the other hand, as flexible devices, rollable display panels are also being developed. A rollable display panel can be repeatedly deformed, for example, between a rolled shape after being rolled up in whole or in part and a flat shape after being rolled out as a whole. In such a rollable display panel, each element in the laminated structure is manufactured to be repeatedly deformable, and a thin optical adhesive sheet is used for bonding between such elements. When the rollable display panel is rolled, the optical adhesive sheet bonded to the rolled element continues to receive tensile stress from the rolled element as a whole. Further, in the process of winding the rollable display panel, the faster the winding speed, the greater the stress generated in the optical adhesive sheet, and the more likely peeling occurs between the optical adhesive sheet and the element. Such an optical pressure-sensitive adhesive sheet is required at a very high level to be difficult to peel off from elements (adherends).

The present invention provides an optical pressure-sensitive adhesive sheet suitable for use in flexible devices.

The present invention [1] is an optical pressure-sensitive adhesive sheet, and the strain stress S ₂₀₀ (N/cm ² ) at 200% elongation in the first tensile test under the conditions of 25° C. and a tensile speed of 50 mm/min. and has a strain stress S' ₂₀₀ (N/cm ² ) as a strain stress at 200% elongation in the second tensile test under the conditions of 25 ° C. and a tensile speed of 600 mm / min, and the strain stress S' An optical pressure-sensitive adhesive sheet, wherein the ratio of strain stress _S200 to ₂₀₀ is 0.8 or less.

The present invention [2] relates to the above [1], wherein the ratio of the strain stress S ₅₀₀ (N/cm ² ) at 500% elongation in the first tensile test to the strain stress S ₂₀₀ is 1.8 or less. Includes the optical adhesive sheet described.

The present invention [3] includes the optical pressure-sensitive adhesive sheet according to [1] or [2] above, wherein the strain stress _S1000 at 1000% elongation in the first tensile test is 18 N/cm ² or less.

The present invention [4] relates to the above [1, wherein the ratio of the strain stress S' ₅₀₀ (N/cm ² ) at 500% elongation in the second tensile test to the strain stress S' ₂₀₀ is 1.7 or less. ] to [3] includes the optical pressure-sensitive adhesive sheet described in any one.

The present invention [5] is the optical pressure-sensitive adhesive according to any one of [1] to [4] above, wherein the strain stress _S′1000 at 1000% elongation in the second tensile test is 25 N/cm ² or less. Including sheet.

In the optical pressure-sensitive adhesive sheet of the present invention, as described above, the strain stress S ₂₀₀ (N/cm ² ) at 200% elongation in the first tensile test (25° C., tensile speed 50 mm/min) was measured in the second tensile test ( 25° C., tensile speed 600 mm/min), the ratio to strain stress S′ ₂₀₀ (N/cm ² ) at 200% elongation is as small as 0.8 or less. Such an optical pressure-sensitive adhesive sheet is suitable for suppressing internal stress such as tensile stress generated in the optical pressure-sensitive adhesive sheet when the adherend to which the pressure-sensitive adhesive sheet is adhered is deformed. Suitable for suppressing peeling of Such an optical pressure-sensitive adhesive sheet is suitable for use in flexible devices.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram of one Embodiment of the optical adhesive sheet of this invention. An example of how to use the optical pressure-sensitive adhesive sheet of the present invention is shown. FIG. 2A shows the step of bonding the optical adhesive sheet to the first adherend, and FIG. 2B shows the step of bonding the first adherend and the second adherend via the optical adhesive sheet. 2C represents the aging process.

A pressure-sensitive adhesive sheet 10 as an embodiment of the optical pressure-sensitive adhesive sheet of the present invention has a sheet shape with a predetermined thickness and spreads in a direction perpendicular to the thickness direction H (plane direction), as shown in FIG. The adhesive sheet 10 has an adhesive surface 11 on one surface in the thickness direction H and an adhesive surface 12 on the other surface in the thickness direction H. FIG. 1 exemplarily shows a state in which release liners L1 and L2 are adhered to adhesive surfaces 11 and 12 of an adhesive sheet 10. As shown in FIG. A release liner L1 is placed on the adhesive surface 11 . A release liner L2 is placed on the adhesive surface 12 . The release liners L1 and L2 are each peeled off at a predetermined timing when the adhesive sheet 10 is used.

Adhesive sheet 10 is an optically transparent adhesive sheet that is placed at a light-passing location in a flexible device. Flexible devices include, for example, flexible display panels. Flexible display panels include, for example, foldable display panels and rollable display panels. A flexible display panel has a laminated structure including elements such as, for example, a pixel panel, a polarizer, a touch panel and a cover film. The pressure-sensitive adhesive sheet 10 is used, for example, in the process of manufacturing a flexible display panel to bond elements included in a laminated structure.

The adhesive sheet 10 has a strain stress _S200 as a strain stress at 200% elongation in the first tensile test under the conditions of 25 ° C. and a tensile speed of 50 mm / min. It has strain stress _S'200 as strain stress at 200% elongation in the second tensile test, and the ratio of strain stress _S200 to strain stress _S'200 ( _S200 / _S'200 ) is 0.8 or less. Specifically, the method of conducting the first tensile test and the second tensile test is as described later with regard to the examples. A configuration in which the ratio (S ₂₀₀ /S′ ₂₀₀ ) is as small as 0.8 or less is suitable for suppressing internal stress such as tensile stress generated in the adhesive sheet 10 when the adherend to which the adhesive sheet 10 is bonded is deformed. Therefore, it is suitable for suppressing peeling of the pressure-sensitive adhesive sheet 10 from the adherend. Such an adhesive sheet 10 is suitable for use in flexible devices.

The ratio (S ₂₀₀ /S′ ₂₀₀ ) is preferably 0.75 or less, more preferably 0.7 or less, still more preferably 0.67 or less, and still more preferably 0.65 or less, from the viewpoint of suppressing the above-described peeling. , more preferably 0.63 or less. The ratio (S ₂₀₀ /S' ₂₀₀ ) is, for example, 0.1 or more or 0.3 or more.

The ratio (S 500 /S 200 ) of the strain stress S ₅₀₀ (N/cm ² ) at 500% elongation in the first tensile test to the strain stress S ₂₀₀ (S ₅₀₀ /S ₂₀₀ ) is generated depending on the degree of deformation of the adhesive sheet 10 during low-speed deformation. From the viewpoint of suppressing the stress difference, it is preferably 1.8 or less, more preferably 1.6 or less, even more preferably 1.5 or less, and still more preferably 1.4 or less. The ratio ( _S500 / _S200 ) is, for example, 0.1 or more, 0.5 or more, or 1 or more.

The ratio of the strain stress _S'500 (N/ ^cm2 ) at 500% elongation in the second tensile test to the strain stress _S'200 ( _S'500 / _S'200 ) is the deformation of the pressure-sensitive adhesive sheet 10 during high-speed deformation. is preferably 1.7 or less, more preferably 1.5 or less, even more preferably 1.3 or less, and still more preferably 1.2 or less, from the viewpoint of suppressing the difference in generated stress due to the degree of . The ratio ( _S'500 / _S'200 ) is, for example, 0.1 or more, 0.5 or more, or 0.8 or more.

The strain stress S ₂₀₀ is preferably 15 N/cm 2 or less, more preferably 12 N/cm ² or less, and further preferably 15 N/cm 2 or less, more preferably 12 N/cm ² or less, from the viewpoint of suppressing the above-described peeling by suppressing the stress generated during and after low-speed deformation in the adhesive sheet 10. It is preferably 9 N/cm ² or less, more preferably 6 N/cm ² or less, even more preferably 4.5 N/cm ² or less, even more preferably 4 N/cm ² or less, and particularly preferably 3.8 N/cm ² or less. be. The strain stress S ₂₀₀ is, for example, 0.5 N/cm ² or more, 1 N/cm ² or 1.5 N/cm ² or more. Methods for adjusting the strain stress _S200 include, for example, adjusting the monomer composition of the base polymer in the adhesive sheet 10, adjusting the molecular weight, adjusting the blending amount, and adjusting the degree of cross-linking. Such strain stress adjustment method is the same for strain stresses S ₅₀₀ and S ₁₀₀₀ .

The strain stress _S500 is preferably 16 N/cm 2 or less, more preferably 12 N/cm ² or less, and further preferably 16 N/cm 2 or less, more preferably 12 N/cm ² or less, from the viewpoint of suppressing the above-described peeling by suppressing the stress generated during and after low-speed deformation in the adhesive sheet 10. It is preferably 8 N/cm ² or less, more preferably 6 N/cm ² or less, still more preferably 5 N/cm ² or less, and particularly preferably 4.8 N/cm ² or less. The strain stress S ₅₀₀ is, for example, 0.5 N/cm ² or more, 1 N/cm ² or more, or 3 N/cm ² or more.

The strain stress S ₁₀₀₀ at 1000% elongation in the first tensile test (25 ° C., tensile speed 50 mm / min) is the viewpoint of suppressing the above-mentioned peeling by suppressing the stress generated during and after low-speed deformation in the adhesive sheet 10. , preferably 18 N/cm ² or less, more preferably 15 N/cm ² or less, even more preferably 12 N/cm ^{2 or} less, still more preferably 10 N/cm ² or less, even more preferably 8 N/cm ² or less, particularly preferably 7.5 N/cm ² or less. The strain stress S ₁₀₀₀ is, for example, 1 N/cm ² or more, 5 N/cm ² or more, or 7 N/cm ² or more.

The strain stress S′ ₂₀₀ is preferably 14 N/cm ² or less, more preferably 11 N/cm ² or less, from the viewpoint of suppressing the stress generated during and after high-speed deformation in the adhesive sheet 10 and suppressing the above-described peeling. It is more preferably 8 N/cm ² or less, still more preferably 7 N/cm ² or less, even more preferably 6 N/cm ² or less, and particularly preferably 5.5 N/cm ² or less. The strain stress S′ ₂₀₀ is, for example, 0.5 N/cm ² or more, 1 N/cm ² or 2 N/cm ² or more. Methods for adjusting the strain stress S′ ₂₀₀ include, for example, adjusting the monomer composition of the base polymer in the adhesive sheet 10, adjusting the molecular weight, adjusting the compounding amount, and adjusting the degree of cross-linking. Such strain stress adjustment method is the same for strain stresses _S'500 and _S'1000 .

The strain stress S′ ₅₀₀ is preferably 20 N/cm ² or less, more preferably 15 N/cm ² or less, from the viewpoint of suppressing the stress generated during and after high-speed deformation in the adhesive sheet 10 and suppressing the above-described peeling. It is more preferably 12 N/cm ² or less, still more preferably 10 N/cm ² or less, even more preferably 8 N/cm ² or less, and particularly preferably 7.5 N/cm ² or less. The strain stress S′ ₅₀₀ is, for example, 0.5 N/cm ² or more, 1 N/cm ² or more, or 3 N/cm ^{2 or} more.

The strain stress S' ₁₀₀₀ at 1000% elongation in the second tensile test (25 ° C., tensile speed 600 mm / min) suppresses the stress generated during and after high-speed deformation in the adhesive sheet 10 to suppress the above-mentioned peeling. ^{From the viewpoint of _} is 15 N/cm ² or less. The strain stress S′ ₁₀₀₀ is, for example, 1 N/cm ² or more, 5 N/cm ² or more, or 8 N/cm ² or more.

After the pressure-sensitive adhesive sheet 10 is attached to the polyimide film, the adhesive strength exhibited by the polyimide film in a peel test under the conditions of 25° C., a peel angle of 180°, and a tensile speed of 300 mm/min is preferably 2 N/10 mm. 3 N/10 mm or more, more preferably 3.5 N/10 mm or more, still more preferably 4 N/10 mm or more, and particularly preferably 4.5 N/10 cm ² or more. The adhesive force is, for example, 20 N/10 mm or less.

The adhesive sheet 10 is a sheet-like pressure-sensitive adhesive formed from an adhesive composition. The adhesive sheet 10 (adhesive composition) contains at least a base polymer.

The base polymer is an adhesive component that makes the adhesive sheet 10 exhibit adhesiveness. Base polymers include, for example, acrylic polymers, silicone polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyvinyl ether polymers, vinyl acetate/vinyl chloride copolymers, modified polyolefin polymers, epoxy polymers, fluoropolymers, and rubber polymers. The base polymer may be used alone or in combination of two or more. From the viewpoint of ensuring good transparency and adhesiveness in the adhesive sheet 10, an acrylic polymer is preferably used as the base polymer.

The acrylic polymer is a copolymer of monomer components containing 50% by mass or more of (meth)acrylic acid ester. "(Meth)acrylic" means acrylic and/or methacrylic.

As the (meth)acrylic acid ester, an alkyl (meth)acrylic acid ester is preferably used, and an alkyl (meth)acrylic acid ester having an alkyl group having 1 to 20 carbon atoms is more preferably used. The (meth)acrylic acid alkyl ester may have a linear or branched alkyl group, or may have a cyclic alkyl group such as an alicyclic alkyl group.

Examples of (meth)acrylic acid alkyl esters having a linear or branched alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and isobutyl (meth)acrylate. , s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, (meth)acrylate heptyl acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, Isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (i.e., lauryl acrylate), isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, ( Pentadecyl meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctacyl (meth)acrylate, and nonadecyl (meth)acrylate.

Examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include, for example, (meth)acrylic acid cycloalkyl esters, (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring, and tricyclic (Meth)acrylic acid esters having the above aliphatic hydrocarbon rings can be mentioned. Cycloalkyl (meth)acrylates include, for example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. Examples of (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth)acrylate. (Meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring include, for example, dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate , 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

The (meth)acrylic acid alkyl ester in the pressure-sensitive adhesive sheet 10 preferably has an alkyl group having 3 to 12 carbon atoms from the viewpoint of balancing the flexibility and adhesive strength required for the pressure-sensitive adhesive sheet for use in flexible devices. At least one selected from (meth)acrylic acid alkyl esters is used, more preferably selected from (meth)acrylic acid alkyl esters having an alkyl group having 3 to 12 carbon atoms, the number of carbon atoms in the alkyl group is relative A first (meth)acrylic acid alkyl ester having a relatively large carbon number and a second (meth)acrylic acid alkyl ester having a relatively small number of carbon atoms in the alkyl group are used in combination, more preferably having 6 to 8 carbon atoms. A (meth)acrylic acid alkyl ester having an alkyl group and a (meth)acrylic acid alkyl ester having an alkyl group having 5 or less carbon atoms are used in combination, and a linear alkyl group having 6 to 8 carbon atoms is particularly preferable. and a (meth)acrylic acid alkyl ester having an alkyl group having 5 or less carbon atoms are used in combination.

The ratio of the (meth)acrylic acid alkyl ester in the monomer component is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more, particularly preferably 92% by mass or more. The same ratio is, for example, 99% by mass or less. When the first and second (meth)acrylic acid alkyl esters are used in combination, the proportion of the first (meth)acrylic acid alkyl ester in the monomer component is determined from the viewpoint of the balance between the flexibility and adhesive strength of the adhesive sheet 10. Therefore, it is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 55% by mass or more, particularly preferably 58% by mass or more, and preferably 80% by mass or less, more preferably 70% by mass. Below, more preferably 65% by mass or less, particularly preferably 62% by mass or less. The ratio of the second (meth)acrylic acid alkyl ester in the monomer component is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably, from the viewpoint of the balance between the flexibility and adhesive strength of the adhesive sheet 10. is 28% by mass or more, preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 32% by mass or less.

The monomer component may contain a copolymerizable monomer copolymerizable with the (meth)acrylic acid alkyl ester. Examples of copolymerizable monomers include monomers having a polar group. Polar group-containing monomers include, for example, hydroxyl group-containing monomers, carboxy group-containing monomers, and monomers having a nitrogen atom-containing ring. The polar group-containing monomer is useful for modifying the acrylic polymer, such as introducing cross-linking points into the acrylic polymer and securing the cohesive strength of the acrylic polymer.

Examples of hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, ( 4-hydroxybutyl meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate.

The ratio of the hydroxy group-containing monomer in the monomer component is preferably 1% by mass or more, more preferably 3% by mass or more, from the viewpoint of introducing a crosslinked structure into the acrylic polymer and ensuring cohesive force in the pressure-sensitive adhesive sheet 10. It is preferably 5% by mass or more, particularly preferably 7% by mass or more. The same ratio is preferably 30% by mass or less, more preferably 20% by mass or less, from the viewpoint of adjusting the polarity of the acrylic polymer (related to compatibility between various additive components in the adhesive sheet 10 and the acrylic polymer).

Carboxy group-containing monomers include, for example, acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

The ratio of the carboxyl group-containing monomer in the monomer component is preferably 0 from the viewpoint of introducing a crosslinked structure into the acrylic polymer, ensuring the cohesive force of the adhesive sheet 10, and ensuring the adhesion of the adhesive sheet 10 to the adherend. 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 0.8% by mass or more. The same proportion is preferably 10% by mass or less, more preferably 5% by mass or less, from the viewpoints of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of acid corrosion of the adherend.

Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl -3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N -vinylthiazole, and N-vinylisothiazole.

The ratio of the monomer having a nitrogen atom-containing ring in the monomer component is preferably 0.5% by mass or more from the viewpoint of ensuring the cohesive force of the adhesive sheet 10 and ensuring the adhesion of the adhesive sheet 10 to the adherend. , more preferably 1% by mass or more, and still more preferably 1.5% by mass or more. The same ratio is preferably 20% by mass or less from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (related to compatibility between various additive components and the acrylic polymer in the adhesive sheet 10). , more preferably 10% by mass or less.

The monomer component may contain other copolymerizable monomers. Other copolymerizable monomers include, for example, acid anhydride monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, alkoxy group-containing monomers, and aromatic vinyl compounds. be done. These other copolymerizable monomers may be used alone, or two or more of them may be used in combination.

The monomer component is preferably the first (meth)acrylic acid alkyl ester (the number of carbon atoms in the alkyl group is relatively large), a second (meth)acrylic acid alkyl ester (wherein the number of carbon atoms in the alkyl group is relatively small), a hydroxy group-containing monomer, and a monomer having a nitrogen atom-containing ring. The first (meth)acrylic acid alkyl ester is more preferably a (meth)acrylic acid alkyl ester having an alkyl group having 6 to 8 carbon atoms, and more preferably a linear (meth)acrylic acid ester having 6 to 8 carbon atoms. A (meth)acrylic acid alkyl ester having an alkyl group, particularly preferably at least one selected from the group consisting of n-octyl acrylate (NOAA) and n-hexyl acrylate (HxA). The second (meth)acrylic acid alkyl ester is more preferably a (meth)acrylic acid alkyl ester having an alkyl group having 5 or less carbon atoms, and more preferably butyl acrylate (BA). The hydroxy group-containing monomer is more preferably at least one selected from the group consisting of 4-hydroxybutyl acrylate (4HBA) and 2-hydroxyethyl acrylate (2HEA). The monomer having a nitrogen atom-containing ring is more preferably N-vinyl-2-pyrrolidone (NVP) from the viewpoint of designing the adhesive sheet 10 to have a relatively high elastic modulus from room temperature to high temperature.

The base polymer preferably has a crosslinked structure. As a method for introducing a crosslinked structure into the base polymer, the base polymer having a functional group capable of reacting with the crosslinker and the crosslinker are blended in the adhesive composition, and the base polymer and the crosslinker are reacted in the adhesive sheet. method (first method), and a base in which a polyfunctional monomer as a cross-linking agent is included in the monomer component forming the base polymer, and a branched structure (cross-linked structure) is introduced into the polymer chain by polymerization of the monomer component. A method of forming a polymer (second method) is included. These methods may be used in combination.

Examples of the cross-linking agent used in the first method include compounds that react with functional groups (hydroxy groups, carboxy groups, etc.) contained in the base polymer. Such crosslinkers include, for example, isocyanate crosslinkers, peroxide crosslinkers, epoxy crosslinkers, oxazoline crosslinkers, aziridine crosslinkers, carbodiimide crosslinkers, and metal chelate crosslinkers. The cross-linking agents may be used alone, or two or more of them may be used in combination. As the cross-linking agent, an isocyanate cross-linking agent, a peroxide cross-linking agent, and an epoxy cross-linking agent are preferably used because they are highly reactive with the hydroxy groups and carboxy groups in the base polymer and facilitate the introduction of a cross-linked structure. be done.

Examples of isocyanate cross-linking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, isocyanates, and polymethylene polyphenyl isocyanates. The isocyanate cross-linking agent also includes derivatives of these isocyanates. Examples of the isocyanate derivative include isocyanurate-modified products and polyol-modified products. Commercially available isocyanate cross-linking agents include, for example, Coronate L (trimethylolpropane adduct of tolylene diisocyanate, manufactured by Tosoh), Coronate HL (trimethylolpropane adduct of hexamethylene diisocyanate, manufactured by Tosoh), Coronate HX (hexa isocyanurate of methylene diisocyanate, manufactured by Tosoh), Takenate D110N (trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals), and Takenate 600 (1,3-bis(isocyanatomethyl)cyclohexane, manufactured by Mitsui Chemicals) are mentioned.

Peroxide crosslinking agents include dibenzoyl peroxide, di(2-ethylhexyl)peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t- butyl peroxyneodecanoate, t-hexyl peroxypivalate, and t-butyl peroxypivalate.

Examples of epoxy cross-linking agents include bisphenol A, epichlorohydrin type epoxy resin, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether. , diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

An isocyanate cross-linking agent (especially a bifunctional isocyanate cross-linking agent) and a peroxide cross-linking agent are preferable from the viewpoint of ensuring the flexibility of the pressure-sensitive adhesive sheet 10 . An isocyanate cross-linking agent (especially a trifunctional isocyanate cross-linking agent) is preferable from the viewpoint of ensuring the durability of the pressure-sensitive adhesive sheet 10 . In the base polymer, difunctional isocyanate and peroxide crosslinkers form softer two-dimensional crosslinks, while trifunctional isocyanate crosslinkers form stronger three-dimensional crosslinks. From the viewpoint of achieving both durability and flexibility of the adhesive sheet 10, it is preferable to use a trifunctional isocyanate cross-linking agent together with a peroxide cross-linking agent and/or a bifunctional isocyanate cross-linking agent.

From the viewpoint of ensuring the cohesive force of the adhesive sheet 10, the amount of the cross-linking agent is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 100 parts by mass of the base polymer. It is 0.07 parts by mass or more. From the viewpoint of ensuring good tackiness in the pressure-sensitive adhesive sheet 10, the amount of the cross-linking agent blended with respect to 100 parts by mass of the base polymer is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 3 parts by mass or less. be.

In the second method, the monomer components (including the polyfunctional monomer for introducing the crosslinked structure and other monomers) may be polymerized at once or in multiple stages. In the multi-stage polymerization method, first, a monofunctional monomer for forming the base polymer is polymerized (prepolymerization), thereby containing a partially polymerized product (a mixture of a polymerized product with a low degree of polymerization and an unreacted monomer). A prepolymer composition is prepared. Next, after adding a polyfunctional monomer as a cross-linking agent to the prepolymer composition, the partially polymerized product and the polyfunctional monomer are polymerized (main polymerization).

Examples of polyfunctional monomers include polyfunctional (meth)acrylates containing two or more ethylenically unsaturated double bonds per molecule. As the polyfunctional monomer, a polyfunctional acrylate is preferable from the viewpoint that a crosslinked structure can be introduced by active energy ray polymerization (photopolymerization).

Polyfunctional (meth)acrylates include bifunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional or higher polyfunctional (meth)acrylates.

Examples of bifunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and 1,6-hexanediol. Di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, stearic acid-modified pentaerythritol di(meth)acrylate, dicyclopentenyl di(meth)acrylate meth)acrylate, di(meth)acryloyl isocyanurate, and alkylene oxide-modified bisphenol di(meth)acrylate.

Trifunctional (meth)acrylates include, for example, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate.

Tetrafunctional or higher polyfunctional (meth)acrylates include, for example, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol penta( meth)acrylates, and dipentaerythritol hexa(meth)acrylates.

As the polyfunctional (meth)acrylate, a polyfunctional (meth)acrylate having a tetrafunctionality or more is preferably used, and dipentaerythritol hexaacrylate is more preferably used.

In the monomer component, the amount of the polyfunctional monomer as a cross-linking agent is, from the viewpoint of ensuring the cohesive force of the pressure-sensitive adhesive sheet 10, relative to 100 parts by mass of the monofunctional monomer, for example, 0.01 parts by mass or more, preferably It is 0.03 parts by mass or more, more preferably 0.05 parts by mass or more, and still more preferably 0.07 parts by mass or more. From the viewpoint of ensuring good tackiness in the adhesive sheet 10, the amount of the polyfunctional monomer is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, more preferably 100 parts by mass of the monofunctional monomer. The amount is 3 parts by mass or less, more preferably 1 part by mass or less, still more preferably 0.5 parts by mass or less, even more preferably 0.2 parts by mass or less, and particularly preferably 0.1 parts by mass or less.

Acrylic polymers can be formed by polymerizing the monomer components described above. Polymerization methods include, for example, solution polymerization, solventless photopolymerization (eg, UV polymerization), bulk polymerization, and emulsion polymerization. Ethyl acetate and toluene, for example, are used as solvents for solution polymerization. Moreover, as a polymerization initiator, for example, a thermal polymerization initiator and a photopolymerization initiator are used. The amount of the polymerization initiator used is, for example, 0.05 parts by mass or more, preferably 0.08 parts by mass or more, and for example, 1 part by mass or less, preferably 0.5 parts by mass, relative to 100 parts by mass of the monomer component. It is below the department.

Thermal polymerization initiators include, for example, azo polymerization initiators and peroxide polymerization initiators. Examples of azo polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionate)dimethyl, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2- imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis(2-methylpropionamidine) disulfate, and 2,2'-azobis(N,N'-dimethyleneisobutyramidine) dihydrochloride mentioned. Peroxide polymerization initiators include, for example, dibenzoyl peroxide, t-butyl permaleate, and lauroyl peroxide.

Examples of photopolymerization initiators include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, and photoactive oxime-based photopolymerization initiators. benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators. .

The weight-average molecular weight of the base polymer is preferably 100,000 or more, more preferably 300,000 or more, and still more preferably 500,000 or more, from the viewpoint of ensuring the cohesive force of the adhesive sheet 10 . The weight average molecular weight of the base polymer is measured by gel permeation chromatography (GPC) and calculated by polystyrene conversion.

The glass transition temperature (Tg) of the base polymer is preferably 0°C or lower, more preferably -10°C or lower, and even more preferably -20°C or lower. The glass transition temperature is, for example, −80° C. or higher.

As the glass transition temperature (Tg) of the base polymer, the glass transition temperature (theoretical value) obtained based on the following Fox formula can be used. The Fox equation is a relational expression between the glass transition temperature Tg of a polymer and the glass transition temperature Tgi of a homopolymer of monomers constituting the polymer. In the Fox formula below, Tg represents the glass transition temperature (° C.) of the polymer, Wi represents the weight fraction of the monomer i constituting the polymer, and Tgi represents the glass transition of the homopolymer formed from the monomer i. Indicates temperature (°C). Literature values can be used for the glass transition temperature of homopolymers. For example, in "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) and "New Polymer Bunko 7: Introduction to Synthetic Resins for Paints" (Kyozo Kitaoka, Kobunshi Publications, 1995), , which lists the glass transition temperatures of various homopolymers. On the other hand, the glass transition temperature of a homopolymer of a monomer can also be determined by the method specifically described in JP-A-2007-51271.

Fox's formula 1/(273+Tg)=Σ[Wi/(273+Tgi)]

The adhesive composition may contain a silane coupling agent. The content of the silane coupling agent in the pressure-sensitive adhesive composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, relative to 100 parts by mass of the base polymer. The content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less.

The pressure-sensitive adhesive composition may contain other components as necessary. Other ingredients include, for example, solvents, tackifiers, plasticizers, softeners, antioxidants, fillers, colorants, UV absorbers, antioxidants, surfactants, and antistatic agents. The solvent includes, for example, a polymerization solvent that is optionally used during polymerization of the acrylic polymer, and a solvent that is added to the polymerization reaction solution after polymerization. Examples of the solvent include ethyl acetate and toluene.

The pressure-sensitive adhesive sheet 10 can be produced, for example, by coating the above-described pressure-sensitive adhesive composition on the release liner L1 (first release liner) to form a coating film, and then drying the coating film.

Examples of the release liner L1 include a flexible plastic film. Examples of the plastic film include polyethylene terephthalate film, polyethylene film, polypropylene film, and polyester film. The thickness of the release liner L1 is, for example, 3 μm or more and, for example, 200 μm or less. The surface of the release liner L1 is preferably release-treated.

Examples of methods for applying the adhesive composition include roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, and lip coating. , and die coats. The drying temperature of the coating film is, for example, 50°C to 200°C. The drying time is, for example, 5 seconds to 20 minutes.

A release liner L2 (second release liner) may be further laminated on the adhesive sheet 10 on the release liner L1. The release liner L2 is preferably a flexible plastic film with a release-treated surface. As the release liner L2, the plastic film described above for the release liner L1 can be used.

As described above, the adhesive sheet 10 in which the adhesive surfaces 11 and 12 are covered and protected by the release liners L1 and L2 can be manufactured.

The thickness of the pressure-sensitive adhesive sheet 10 is preferably 10 μm or more, more preferably 15 μm or more, from the viewpoints of ensuring sufficient adhesion to adherends and handleability. The thickness of the adhesive sheet 10 is preferably 300 μm or less, more preferably 200 μm or less, still more preferably 100 μm or less, and particularly preferably 50 μm or less, from the viewpoint of thinning the flexible device.

The haze of the adhesive sheet 10 is preferably 3% or less, more preferably 2% or less, and more preferably 1% or less. The haze of the adhesive sheet 10 can be measured using a haze meter according to JIS K7136 (2000). Examples of the haze meter include "NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. and "HM-150 type" manufactured by Murakami Color Research Laboratory.

The total light transmittance of the adhesive sheet 10 is preferably 60% or higher, more preferably 80% or higher, and even more preferably 85% or higher. The total light transmittance of the adhesive sheet 10 is, for example, 100% or less. The total light transmittance of the adhesive sheet 10 can be measured according to JIS K 7375 (2008).

2A to 2C show an example of how to use the adhesive sheet 10. FIG.

In this method, first, as shown in FIG. 2A, the adhesive sheet 10 is adhered to one surface in the thickness direction H of the first member 21 (adherend). The first member 21 is, for example, one element in the laminated structure of the flexible display panel. Examples of such elements include a pixel panel, a polarizing plate, a touch panel, and a cover film (the same applies to the second member 22 described later). By this step, the adhesive sheet 10 for bonding with another member is provided on the first member 21 .

Next, as shown in FIG. 2B , one side of the first member 21 in the thickness direction H and the other side of the second member 22 in the thickness direction H through the adhesive sheet 10 on the first member 21 . join the sides. The second member 22 is, for example, another element in the laminated structure of the flexible display panel.

Next, as shown in FIG. 2C, the adhesive sheet 10 between the first member 21 and the second member 22 is aged. Aging increases the bonding strength between the adhesive sheet 10 and the members 21 and 22 . The aging temperature is, for example, 20°C to 160°C. The aging time is, for example, 1 minute to 21 days. When autoclave treatment (heat and pressure treatment) is performed as aging, the temperature is, for example, 30° C. to 80° C., the pressure is, for example, 0.1 to 0.8 MPa, and the treatment time is, for example, 15 minutes or longer.

In the adhesive sheet 10 used in the manufacturing process of the flexible display panel as described above, the ratio (S ₂₀₀ /S' ₂₀₀ ) is as small as 0.8 or less as described above. Such a configuration is suitable for suppressing internal stress such as tensile stress generated in the adhesive sheet 10 when the adherend to which the adhesive sheet 10 is bonded is deformed. suitable for suppressing Such an adhesive sheet 10 is suitable for use in flexible devices.

EXAMPLES The present invention will be specifically described below with reference to Examples. However, the invention is not limited to the examples. In addition, the specific numerical values such as the compounding amount (content), physical property values, parameters, etc. described below are the corresponding compounding amounts ( content), physical property values, parameters, etc., upper limits (values defined as “less than” or “less than”) or lower limits (values defined as “greater than” or “greater than”).

[Example 1]
<Preparation of prepolymer composition>
In a flask, 60 parts by mass of n-octyl acrylate (NOAA), 30 parts by mass of butyl acrylate (BA), 8 parts by mass of 4-hydroxybutyl acrylate (4HBA), and N-vinyl-2-pyrrolidone ( NVP) and 2 parts by mass of 2,2-dimethoxy-1,2-diphenyl-1-one (product name "Omnirad 651", manufactured by IGM Resins) as a first photopolymerization initiator. 05 parts by mass and 0.05 parts by mass of 1-hydroxycyclohexylphenyl ketone (product name “Omnirad 184”, manufactured by IGM Resins) as a second photopolymerization initiator, and then the mixture is subjected to a nitrogen atmosphere. Part of the monomer components in the mixture was polymerized by irradiating with ultraviolet rays at , to obtain a first prepolymer composition (containing monomer components that had not undergone polymerization reaction) with a polymerization rate of about 10%.

<Preparation of adhesive composition>
100 parts by mass of the first prepolymer composition, 0.08 parts by mass of dipentaerythritol hexaacrylate (DPHA) as a cross-linking agent, and 2,2-dimethoxy-1,2-diphenyl-1- as a photopolymerization initiator On (product name "Omnirad 651", manufactured by IGM Resins) 0.05 parts by weight and 0.3 parts by weight of a silane coupling agent (product name "KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd.) are mixed to form the first adhesive. A composition was obtained.

<Formation of adhesive layer>
The first pressure-sensitive adhesive composition was applied onto the release-treated surface of the first release liner (product name “Diafoil MRF #38”, thickness 38 μm, manufactured by Mitsubishi Chemical Corporation) having a release-treated surface on one side to form a coating film. formed. Next, the release-treated surface of a second release liner (Product name: "DIAFOIL MRN#38", thickness: 38 µm, manufactured by Mitsubishi Chemical Corporation) having a release-treated surface on one side was placed on the coating film on the first release liner. pasted together. Next, the coating film between the release liners was irradiated with ultraviolet rays, and the coating film was photocured to form a pressure-sensitive adhesive layer (thickness: 50 μm). In the ultraviolet irradiation, a black light was used as the irradiation light source, and the irradiation intensity was set at 5 mW/cm ² .

As described above, a pressure-sensitive adhesive sheet (50 μm thick) of Example 1 with a double-sided release liner was produced. The composition of the pressure-sensitive adhesive sheet of Example 1 is shown in Table 1 in units of parts by mass (the same applies to Examples and Comparative Examples described later).

[Example 2]
In the preparation of the pressure-sensitive adhesive composition, the amount of the cross-linking agent was changed to 0.04 parts by weight instead of 0.08 parts by weight, and the photopolymerization initiator was not added. A pressure-sensitive adhesive sheet of Example 2 was produced in the same manner as the pressure-sensitive adhesive sheet.

[Example 3]
A pressure-sensitive adhesive sheet of Example 3 was produced in the same manner as the pressure-sensitive adhesive sheet of Example 1, except for the following. In the preparation of the prepolymer composition, the amount of the first photopolymerization initiator (product name "Omnirad 651") is changed to 0.035 parts by weight instead of 0.05 parts by weight, and the second photopolymerization initiator ( Product name "Omnirad 184") was changed to 0.035 parts by mass instead of 0.05 parts by mass. In the preparation of the pressure-sensitive adhesive composition, the amount of the cross-linking agent was changed from 0.08 parts by weight to 0.02 parts by weight, and no photopolymerization initiator was added.

[Example 4]
A pressure-sensitive adhesive sheet of Example 4 was produced in the same manner as the pressure-sensitive adhesive sheet of Example 1, except for the following. In the preparation of the prepolymer composition, the amount of the first photopolymerization initiator (product name "Omnirad 651") is changed to 0.07 parts by weight instead of 0.05 parts by weight, and the second photopolymerization initiator ( Product name "Omnirad 184") was changed from 0.05 parts by weight to 0.07 parts by weight. In the preparation of the pressure-sensitive adhesive composition, the amount of the cross-linking agent was changed from 0.08 parts by weight to 0.04 parts by weight, and no photopolymerization initiator was added.

[Example 5]
A pressure-sensitive adhesive sheet of Example 5 was produced in the same manner as the pressure-sensitive adhesive sheet of Example 1, except for the following. In the preparation of the prepolymer composition, the amount of NOAA was changed from 60 parts by mass to 70 parts by mass, and the amount of BA was changed from 30 parts by mass to 20 parts by mass. In the preparation of the pressure-sensitive adhesive composition, the amount of the cross-linking agent was changed from 0.08 parts by weight to 0.05 parts by weight, and no photopolymerization initiator was added.

[Example 6]
A pressure-sensitive adhesive sheet of Example 6 was produced in the same manner as the pressure-sensitive adhesive sheet of Example 1, except for the following. In the preparation of the pressure-sensitive adhesive composition, the blending amount of the cross-linking agent was changed from 0.08 parts by weight to 0.05 parts by weight.

[Comparative Example 1]
<Preparation of prepolymer composition>
In a flask, a monomer mixture containing 57 parts by weight of butyl acrylate (BA), 12 parts by weight of cyclohexyl acrylate (CHA), and 31 parts by weight of 4-hydroxybutyl acrylate (2HBA) was irradiated with a first light. After adding 0.09 parts by mass of a polymerization initiator (product name "Omnirad 651", manufactured by IGM Resins) and 0.09 parts by mass of a second photopolymerization initiator (product name "Omnirad 184", manufactured by IGM Resins), A part of the monomer components in the mixture was polymerized by irradiating the mixture with ultraviolet rays in a nitrogen atmosphere to obtain a second prepolymer composition with a polymerization rate of about 10%.

<Preparation of adhesive composition>
100 parts by mass of the second prepolymer composition, 0.12 parts by mass of DPHA as a cross-linking agent, and 0.3 parts by mass of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) are mixed, A second adhesive composition was obtained.

<Formation of adhesive layer>
The first and second release liners were formed in the same manner as the formation of the pressure-sensitive adhesive layer (including ultraviolet irradiation) in Example 1, except that the second pressure-sensitive adhesive composition was used instead of the first pressure-sensitive adhesive composition. Sandwiched adhesive layers (thickness 50 μm) were formed.

As described above, a pressure-sensitive adhesive sheet (thickness: 50 μm) of Comparative Example 1 with a double-sided release liner was produced.

<Tensile test>
The pressure-sensitive adhesive sheets of Examples 1 to 6 and Comparative Example 1 were examined for strain stress generated in the following first tensile test and second tensile test.

Specifically, first, a required number of measurement samples were prepared for each pressure-sensitive adhesive sheet. In preparing the sample for measurement, first, a piece of adhesive sheet with double-sided release liner (30 mm width×100 mm length) was cut out from the adhesive sheet with double-sided release liner. Next, after peeling off one release liner from the same sheet piece, the adhesive sheet piece was wound on the other release liner in the length direction so as not to introduce air bubbles into a cylindrical shape (column height 30 mm). . Thus, a cylindrical pressure-sensitive adhesive sheet piece was obtained as a sample for measurement. Next, the measurement sample is subjected to a tensile test using a Tensilon type tensile tester (product name "Autograph AG-50NX plus", manufactured by Shimadzu Corporation) in an environment of 25 ° C. and 50% relative humidity. , the tensile stress generated during the tensile process was measured (first tensile test). This gave a stress-strain curve (load-elongation curve). In this tensile test, the initial chuck-to-chuck distance was 10 mm, the measurement sample (cylindrical pressure-sensitive adhesive sheet piece) was pulled in the height direction of the cylinder, and the pulling rate was 50 mm/min. As the measurement results in such a first tensile test, the strain stress S ₂₀₀ (N/cm ² ) at 200% elongation, the strain stress S ₅₀₀ (N/cm ² ) at 500% elongation, and 1000% elongation and strain stress S ₁₀₀₀ (N/cm ² ) are shown in Table 1 (the pressure-sensitive adhesive sheet of Comparative Example 1 broke before 1000% elongation in the first tensile test). Also shown in Table 1 is the ratio of strain stress _S500 to strain stress _S200 .

On the other hand, the measurement sample was subjected to a tensile test in the same manner as the first tensile test except that the tensile speed was set to 600 mm/min, and the tensile stress generated during the tensile process was measured (second tensile test). This gave a stress-strain curve (load-elongation curve). As the measurement results in such a second tensile test, the strain stress _S'200 (N/ ^cm2 ) at 200% elongation, the strain stress _S'500 (N/ ^cm2 ) at 500% elongation, and 1000% The strain stress S′ ₁₀₀₀ (N/cm ² ) during elongation is shown in Table 1 (the pressure-sensitive adhesive sheet of Comparative Example 1 broke before 1000% elongation in the second tensile test). The ratio of strain stress S ₂₀₀ to strain stress S' ₂₀₀ (S ₂₀₀ /S' ₂₀₀ ) and the ratio of S' ₅₀₀ to strain stress S' ₂₀₀ (ratio S' ₅₀₀ /S' ₂₀₀ ) are also shown in Table 1. show.

<Bending retention test>
The pressure-sensitive adhesive sheets of Examples 1 to 6 and Comparative Example 1 were subjected to a bending retention test as follows.

First, the second release liner was removed from the pressure-sensitive adhesive sheet with a double-sided release liner, and the exposed surface thereby exposed was plasma-treated. On the other hand, both sides (first side and second side) of the polarizing film having a thickness of 51 μm were also plasma-treated. The surface of a transparent polyimide film with a thickness of 80 μm and the surface of a polyethylene terephthalate (PET) film with a thickness of 125 μm were also plasma treated. In each plasma treatment, a plasma irradiation apparatus (product name “AP-TO5”, manufactured by Sekisui Kogyo Co., Ltd.) was used, the voltage was 160 V, the frequency was 10 kHz, and the treatment speed was 5000 mm/min. Then, the exposed surface of the pressure-sensitive adhesive sheet and the first surface of the polarizing film were bonded together. In this bonding, the pressure-sensitive adhesive sheet with the first release liner and the polarizing film were pressure-bonded by reciprocating a 2-kg roller once in an environment of 23°C. Next, after peeling off the first release liner from the pressure-sensitive adhesive sheet with the polarizing film, the transparent polyimide film was attached to the exposed surface of the pressure-sensitive adhesive sheet. Next, the PET film was attached to the second surface of the polarizing film via a thin adhesive sheet having a thickness of 15 μm. In this bonding, the polarizing film and the PET film were pressure-bonded by reciprocating a 2-kg roller once in an environment of 23°C. As a result, the PET film (thickness 125 μm), the thin adhesive sheet (thickness 15 μm), the polarizing film (thickness 51 μm), the adhesive sheet (thickness 50 μm), and the transparent polyimide film (thickness 80 μm) A laminated film having a laminated structure was obtained.

Next, a sample for evaluation was cut out from the laminated film thus prepared. Specifically, a rectangular sample of 35 mm×100 mm was cut out from the laminate film so that the absorption axis direction of the polarizing film was parallel to the long side direction in the sample cut out. The sample was then autoclaved for 15 minutes at 35° C. and 0.50 MPa.

Next, the sample was subjected to a flexing test using a planar object no-load U-shaped stretching tester (manufactured by Yuasa System Co., Ltd.). In this test, a bending jig was attached to a range of 20 mm from the edge of the sample to each of both ends of the sample in the long side direction, and the sample was fixed to the tester (region of 60 mm in the center of the long side direction of the sample is in an unfixed state). In addition, in this test, in a constant temperature and humidity chamber under the conditions of a temperature of 60 ° C. and a relative humidity of 95%, the sample was placed between a bent state and a non-flexed state with the PET film side surface inside, and at a bending speed of 60 rpm. was repeatedly deformed (bent) 200,000 times. Specifically, the bent form in this test is a form in which the axial direction of the bending moment acting on the sample is orthogonal to the absorption axis direction of the polarizing film. In the bending mode, the bending radius of the sample was 1.3 mm, and the bending angle was 180°. Regarding the adhesiveness of the adhesive sheet to the adherend in such a bending test, "good" indicates that no peeling occurs between the adhesive sheet and its adherend (transparent polyimide film, polarizing film). , and the case where peeling occurred was evaluated as "poor". Table 1 shows the evaluation results.

10 adhesive sheet (optical adhesive sheet)
11, 12 Adhesive surface H Thickness direction L1, L2 Release liner 21 First member 22 Second member

Claims (5)

An optical adhesive sheet,
It has a strain stress S ₂₀₀ (N/cm ² ) as a strain stress at 200% elongation in the first tensile test under the conditions of 25 ° C. and a tensile speed of 50 mm / min,
The strain stress at 200% elongation in the second tensile test under the conditions of 25 ° C. and a tensile speed of 600 mm / min has a strain stress S' ₂₀₀ (N/cm ² ),
An optical pressure-sensitive adhesive sheet, wherein the ratio of the strain stress S ₂₀₀ to the strain stress S' ₂₀₀ is 0.8 or less. The optical pressure-sensitive adhesive sheet according to claim 1, wherein the ratio of the strain stress _S500 (N/ ^cm2 ) at 500% elongation in the first tensile test to the strain stress _S200 is 1.8 or less. The optical pressure-sensitive adhesive sheet according to claim 1 or ² , wherein the strain stress _S1000 at 1000% elongation in the first tensile test is 18 N/cm2 or less. Any one of claims 1 to 3, wherein the ratio of the strain stress _S'500 (N/ ^cm2 ) at 500% elongation in the second tensile test to the strain stress _S'200 is 1.7 or less. The optical adhesive sheet described in . The optical pressure-sensitive adhesive sheet according to any one of claims 1 to ⁴ , wherein the strain stress _S'1000 at 1000% elongation in the second tensile test is 25 N/cm2 or less.

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