KR20230098039A - Optical adhesive sheet - Google Patents

Abstract

Provided is an optical adhesive sheet suitable for flexible device use. According to the present invention, an adhesive sheet (10) is an optical adhesive sheet. The adhesive sheet (10) has a strain stress S_200 (N/cm^2) as a strain stress at 200 % elongation in a first tensile test under the conditions of 25℃ 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 a second tensile test under the conditions of 25℃ and a tensile speed of 600 mm/min, wherein a ratio of the strain stress S_200 to the strain stress S'_200 is 0.8 or less.

Description

Optical adhesive sheet {OPTICAL ADHESIVE SHEET}

The present invention relates to an optical adhesive sheet.

The display panel has a laminated structure including elements such as, for example, a pixel panel, a polarizing plate, 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 elements included in the laminated structure.

Meanwhile, for smartphones and tablet terminals, development of display panels capable of being repeatedly bent (foldable) is in progress. Specifically, the foldable display panel can be repeatedly deformed between a curved shape and a flat non-curved shape. In such a foldable display panel, each element in the laminated structure is manufactured to be repeatedly bendable, and a thin optical adhesive sheet is used for bonding between such elements. About an optical adhesive sheet for flexible devices, such as a foldable display panel, it describes, for example in patent document 1 below.

Japanese Unexamined Patent Publication No. 2018-111754

Conventionally, the optical adhesive sheet is easily peeled off from the element as the adherend at the bending portion of the foldable display panel. This is because when the display panel is bent, a relatively large tensile stress is locally generated in the bent portion of the optical adhesive sheet. In the bent portion of the optical adhesive sheet, peeling is likely to occur between the optical adhesive sheet and the element as the tensile stress in the shear direction, for example, to the element (adherent) is greater. In addition, in the bending process of the foldable display panel, the faster the bending speed, the greater the stress generated in the optical adhesive sheet, and peeling between the optical adhesive sheet and the element is likely to occur. Occurrence of the said peeling becomes a cause of malfunction of a device, and is not preferable. Optical adhesive sheets for foldable display panels are required to be difficult to peel off from elements (substrates) at a high level.

On the other hand, as a flexible device, development of a rollable (rollable) display panel is also progressing. The rollable display panel can be repeatedly deformed between, for example, a rolled shape after being wholly or partially rolled up, and a flat shape after wholly drawn out. 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 element as a whole. In addition, 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 peeling is likely to occur between the optical adhesive sheet and the element. Such an optical adhesive sheet is required to be difficult to peel off from elements (adherents) at a very high level.

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

The present invention [1] is an optical adhesive sheet, which has a strain stress S ₂₀₀ (N/cm ² ) at 200% elongation in a first tensile test at 25° C. and a tensile speed of 50 mm/min. As 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, the strain stress S ' ₂₀₀ (N / cm ² ), and the strain stress S' and an optical adhesive sheet having a ratio of _{the deformation stress S 200 to} 200 of 0.8 or less.

This invention [2] is described in [1] above, 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. An optical adhesive sheet is included.

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

In the present invention [4], 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, [1] -The optical adhesive sheet as described in any one of [3] is included.

The present invention [5] includes the optical adhesive sheet according to any one of [1] to [4] above, wherein the deformation stress S' ₁₀₀₀ at 1000% elongation in the second tensile test is 25 N/cm ² or less. do.

As described above, in the optical adhesive sheet of the present invention, the strain stress S ₂₀₀ (N/cm ² ) at 200% elongation in the first tensile test (25°C, tensile speed 50 mm/min), the second tensile The ratio to strain stress S' ₂₀₀ (N/cm ² ) at 200% elongation in the test (25°C, tensile speed 600 mm/min) is as small as 0.8 or less. Such an optical adhesive sheet is suitable for suppressing internal stress such as tensile stress generated in the optical adhesive sheet when the adherend to which the adhesive sheet is bonded is deformed, and therefore, It is suitable for suppressing peeling of an optical adhesive sheet. Such an optical adhesive sheet is suitable for flexible device applications.

1 is a schematic cross-sectional view of an embodiment of an optical adhesive sheet of the present invention.
2 shows an example of a method of using the optical adhesive sheet of the present invention. Fig. 2A shows a step of bonding the optical adhesive sheet to a first adherend, Fig. 2B shows a step of bonding the first adherend and the second adherend via the optical adhesive sheet, and Fig. 2C shows aging represents the process.

As shown in Fig. 1, the adhesive sheet 10 as an embodiment of the optical adhesive sheet of the present invention has a sheet shape with a predetermined thickness and spreads in a direction (surface direction) orthogonal to the thickness direction H. . The adhesive sheet 10 has an adhesive face 11 on one side in the thickness direction H and an adhesive face 12 on the other side in the thickness direction H. 1 shows the state in which peeling liners L1 and L2 are bonded to the adhesive faces 11 and 12 of the adhesive sheet 10 by way of example. The peeling liner L1 is disposed on the adhesive face 11 . The peeling liner L2 is disposed on the adhesive surface 12 . The release liners L1 and L2 are each separated at a predetermined timing when the pressure-sensitive adhesive sheet 10 is used.

The adhesive sheet 10 is an optically transparent adhesive sheet disposed at a light passage location in a flexible device. As a flexible device, a flexible display panel is mentioned, for example. As a flexible display panel, a foldable display panel and a rollable display panel are mentioned, for example. A flexible display panel has a laminated structure including elements such as a pixel panel, a film-like polarizing plate (polarizing film), a touch panel, and a cover film, for example. The adhesive sheet 10 is used for bonding elements included in a laminated structure to each other in a manufacturing process of a flexible display panel, for example.

The pressure-sensitive adhesive sheet 10 has a strain stress S ₂₀₀ as a strain stress at 200% elongation in the first tensile test under conditions of 25°C and a tensile speed of 50 mm/min, and It has a strain stress S' ₂₀₀ as the strain stress at 200% elongation in the second tensile test under the condition, and the ratio of the strain stress S ₂₀₀ to the strain stress S' ₂₀₀ (S ₂₀₀ /S' ₂₀₀ ) is 0.8 or less. am. Methods for conducting the first tensile test and the second tensile test are as described below in relation to Examples specifically. A configuration in which the ratio (S ₂₀₀ /S' ₂₀₀ ) is as small as 0.8 or less is used to suppress internal stress such as tensile stress generated in the PSA sheet 10 when the adherend to which the PSA sheet 10 is bonded is deformed. and therefore suitable for suppressing peeling of the PSA sheet 10 from the adherend. Such an adhesive sheet 10 is suitable for flexible device applications.

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, even more preferably 0.65 or less, still more preferably, from the viewpoint of suppressing the aforementioned peeling. It is preferably less than 0.63. The ratio (S ₂₀₀ /S' ₂₀₀ ) is, for example, 0.1 or more or 0.3 or more.

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

The ratio of the deformation stress S' ₅₀₀ (N/cm ² ) at 500% elongation in the second tensile test to the deformation stress S' ₂₀₀ (S' ₅₀₀ /S' ₂₀₀ ) is the pressure-sensitive adhesive sheet during high-speed deformation. (10) From the viewpoint of suppressing the difference in generated stress depending on the degree of deformation, it is preferably 1.7 or less, more preferably 1.5 or less, still more preferably 1.3 or less, still more preferably 1.2 or less. The ratio (S' ₅₀₀ /S' ₂₀₀ ) is, for example, 0.1 or more, 0.5 or more, or 0.8 or more.

The deformation stress S ₂₀₀ is preferably 15 N/cm 2 or less, more preferably 12 N/cm ² or less, from the viewpoint of suppressing the stress generated during and after the low-speed deformation of the pressure-sensitive adhesive sheet 10 and suppressing the aforementioned peeling. ² or less, more preferably 9 N/cm ² or less, still more preferably 6 N/cm ² or less, even more preferably 4.5 N/cm ² or less, still more preferably 4 N/cm ² or less, particularly preferably 3.8 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 more, or 1.5 N/cm ² or more. Examples of methods for adjusting the strain stress S ₂₀₀ include adjusting the monomer composition of the base polymer in the pressure-sensitive adhesive sheet 10, adjusting the molecular weight, adjusting the compounding amount, and adjusting the degree of crosslinking. This strain stress adjusting method is the same for strain stresses S ₅₀₀ and S ₁₀₀₀ .

The deformation stress S ₅₀₀ is preferably 16 N/cm 2 or less, more preferably 12 N/cm ² or less, from the viewpoint of suppressing the stress generated during and after the low-speed deformation of the pressure-sensitive adhesive sheet 10 to suppress the aforementioned peeling. ² or less, more preferably 8 N/cm ² or less, still 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 deformation stress S ₁₀₀₀ at 1000% elongation in the first tensile test (25°C, tensile speed 50 mm/min) suppresses the stress generated during and after the low-speed deformation of the pressure-sensitive adhesive sheet 10, thereby achieving the above-described peeling From the viewpoint of suppressing, it is preferably 18 N/cm ² or less, more preferably 15 N/cm ² or less, still more preferably 12 N/cm ² or less, still more preferably 10 N/cm ² or less, still 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 the high-speed deformation of the adhesive sheet 10 and suppressing the aforementioned peeling. cm ² or less, more preferably 8 N/cm ² or less, still more preferably 7 N/cm ² or less, still 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} more, or 2 N/cm ^{2 or} more. Examples of methods for adjusting the strain stress S′ ₂₀₀ include adjusting the monomer composition of the base polymer in the pressure-sensitive adhesive sheet 10, adjusting the molecular weight, adjusting the compounding amount, and adjusting the degree of crosslinking. This strain stress adjusting 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 the high-speed deformation of the pressure-sensitive adhesive sheet 10 to suppress the aforementioned peeling. cm ² or less, more preferably 12 N/cm ² or less, still more preferably 10 N/cm ² or less, still 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 deformation stress S′ ₁₀₀₀ at 1000% elongation in the second tensile test (25° C., tensile speed 600 mm/min) suppresses stress generated during and after high-speed deformation in the adhesive sheet 10, From the viewpoint of suppressing peeling, it is preferably 25 N/cm ² or less, more preferably 22 N/cm ² or less, still more preferably 20 N/cm ² or less, still more preferably 18 N/cm ² or less, still more preferably is 17 N/cm ² or less, particularly preferably 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 adhesive sheet 10 is bonded to the polyimide film, the adhesive force exhibited to the polyimide film in a peel test under the peel conditions of 25° C., a peel angle of 180°, and a tensile speed of 300 mm/min is preferably is 2 N/10 mm or more, more preferably 3 N/10 mm or more, still 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 said adhesive force is 20 N/10 mm or less, for example.

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

The base polymer is an adhesive component that develops adhesiveness in the adhesive sheet 10 . Examples of the base polymer include acrylic polymers, silicone polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyvinyl ether polymers, vinyl acetate/vinyl chloride copolymers, modified polyolefin polymers, epoxy polymers, and fluoropolymers. , and rubber polymers. A base polymer may be used independently, and two or more types may be used together. From the viewpoint of ensuring good transparency and adhesiveness of the adhesive sheet 10, an acrylic polymer is preferably used as the base polymer.

An acrylic polymer is a copolymer of monomer components containing a (meth)acrylic acid ester in a proportion of 50% by mass or more. A "(meth)acryl" means an acryl and/or methacryl.

As the (meth)acrylic acid ester, an alkyl (meth)acrylic acid ester is preferably used, and more preferably, a (meth)acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group is 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 the alkyl (meth)acrylate having a linear or branched alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and (meth)acrylate. s-butyl acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, (meth)acrylate 2 -Ethylhexyl, (meth)acrylate n-octyl, (meth)acrylate isooctyl, (meth)acrylate nonyl, (meth)acrylate isononyl, (meth)acrylate decyl, (meth)acrylate isodecyl, (meth) Undecyl acrylate, dodecyl (meth)acrylate (ie lauryl (meth)acrylate), isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate , cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, and nonadecyl (meth)acrylate.

Examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include (meth)acrylic acid cycloalkyl esters, (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylic acid esters having a tricyclic or more aliphatic hydrocarbon ring. ) acrylic acid ester. Examples of the (meth)acrylic acid cycloalkyl ester include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. As (meth)acrylic acid ester which has a bicyclic aliphatic hydrocarbon ring, isobornyl (meth)acrylate is mentioned, for example. Examples of (meth)acrylic acid esters having tricyclic or more aliphatic hydrocarbon rings include dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, and tricyclopentanyl (meth)acrylate. , 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

As the (meth)acrylic acid alkyl ester, in the adhesive sheet 10, from the viewpoint of balancing the softness and adhesive force required for the adhesive sheet for flexible devices, preferably a (meth) having an alkyl group having 3 to 12 carbon atoms A first alkyl (meth)acrylate having a relatively large number of carbon atoms in the alkyl group, wherein at least one selected from alkyl acrylates is used, and more preferably selected from alkyl (meth)acrylates having an alkyl group having 3 to 12 carbon atoms. An ester 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, a (meth)acrylic acid alkyl ester having an alkyl group having 6 to 8 carbon atoms and an alkyl group having 5 or less carbon atoms A (meth)acrylic acid alkyl ester having a linear alkyl group having 6 to 8 carbon atoms is particularly preferably used in combination with a (meth)acrylic acid alkyl ester having a C 6 to 8 linear alkyl group and a (meth)acrylic acid alkyl ester having a C 5 or less alkyl group. do.

The proportion of (meth)acrylic acid alkyl ester in the monomer component is preferably 50% by mass or more, more preferably 70% by mass or more, from the viewpoint of appropriately expressing basic properties such as adhesiveness in the adhesive sheet 10 , More preferably 90% by mass or more, particularly preferably 92% by mass or more. The ratio is, for example, 99% by mass or less. When the first and second alkyl (meth)acrylates are used in combination, the ratio of the first alkyl (meth)acrylates in the monomer component is, from the viewpoint of the balance between the softness of the pressure-sensitive adhesive sheet 10 and the adhesive force, It is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, particularly preferably 58% by mass or more, and more preferably 80% by mass or less, more preferably 70% by mass or less, 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, from the viewpoint of the balance between the softness of the adhesive sheet 10 and the adhesive force, It is more preferably 28% by mass or more, and is also 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 also contain a copolymerizable monomer copolymerizable with (meth)acrylic acid alkyl ester. As a copolymerizable monomer, the monomer which has a polar group is mentioned, for example. Examples of the polar group-containing monomer include a hydroxy group-containing monomer, a carboxy group-containing monomer, and a monomer having a nitrogen atom-containing ring. The polar group-containing monomer is useful for modifying the acrylic polymer, such as introducing a crosslinking point into the acrylic polymer and securing cohesive force of the acrylic polymer.

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

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

Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

The ratio of the carboxy group-containing monomer in the monomer component is determined by introducing a crosslinked structure into the acrylic polymer, securing cohesive force in the adhesive sheet 10, and adhesion to the adherend in the adhesive sheet 10. From the viewpoint of ensuring, it is preferably 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 ratio is preferably 10% by mass or less, more preferably 5% by mass or less, from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend by acid.

Examples of the monomer having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, and N- Vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylphy Peridine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazine- 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, from the viewpoint of securing the cohesive force in the adhesive sheet 10 and securing the adhesive force of the adherend in the adhesive sheet 10. It is 0.5 mass % or more, More preferably, it is 1 mass % or more, More preferably, it is 1.5 mass % or more. The ratio is preferably 20 mass 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 in the adhesive sheet 10 and the acrylic polymer). % or less, more preferably 10% by mass or less.

The monomer component may contain other copolymerizable monomers. Examples of other copolymerizable monomers include 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. These other copolymerizable monomers may be used independently, or two or more types may be used together.

The monomer component is preferably a first (meth)acrylic acid alkyl ester (an alkyl group having a relatively large number of carbon atoms), from the viewpoint of both securing the adhesive strength of the adhesive sheet 10 and suppressing stress generated during deformation. ), a second (meth)acrylic acid alkyl ester (the alkyl group has a relatively small number of carbon atoms), 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 of 6 to 8 carbon atoms, and still more preferably a (meth)acrylic acid alkyl ester having a linear alkyl group of 6 to 8 carbon atoms. ) It is an acrylic acid alkyl ester, Especially preferably, it is at least one selected from the group which consists 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 of 5 or less carbon atoms, and still more preferably n-butyl (BA) acrylate. The hydroxyl 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 modulus of elasticity from room temperature to high temperature.

The base polymer preferably has a crosslinked structure. As a method for introducing a cross-linked structure into the base polymer, a base polymer having a functional group capable of reacting with the cross-linking agent and a cross-linking agent are mixed in an adhesive composition, and the base polymer and the cross-linking agent are reacted in the pressure-sensitive adhesive sheet (Method 1), and the base polymer A method (second method) of forming a base polymer having a branched structure (crosslinked structure) introduced into the polymer chain by including a polyfunctional monomer as a crosslinking agent in a monomer component that forms there is. These methods may be used together.

Examples of the crosslinking agent used in the first method include compounds that react with functional groups (such as hydroxyl and carboxyl groups) contained in the base polymer. Examples of such crosslinking agents include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents. A crosslinking agent may be used independently and two or more types may be used together. As the crosslinking agent, an isocyanate crosslinking agent, a peroxide crosslinking agent, and an epoxy crosslinking agent are preferably used from the viewpoint that the reactivity with the hydroxy group and the carboxy group in the base polymer is high and introduction of a crosslinked structure is easy.

Examples of the isocyanate crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, and hydrogenated xylylene diisocyanate. nate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthaline diisocyanate, triphenylmethane triisocyanate , and polymethylene polyphenyl isocyanate. Moreover, derivatives of these isocyanates are also mentioned as an isocyanate crosslinking agent. As the said isocyanate derivative, an isocyanurate modified body and a polyol modified body are mentioned, for example. As a commercially available isocyanate crosslinking agent, for example, Coronate L (trimethylolpropane adduct of tolylene diisocyanate, manufactured by Tosoh), Coronate HL (of hexamethylene diisocyanate) Trimethylolpropane adduct, manufactured by Tosoh), Coronate HX (isocyanurate of hexamethylene diisocyanate, manufactured by Tosoh), Takenate D110N (trimethylol of xylylene diisocyanate) propane adduct, manufactured by Mitsui Chemicals), and Takenate 600 (1,3-bis(isocyanatomethyl)cyclohexane, manufactured by Mitsui Chemicals).

As the peroxide crosslinking agent, dibenzoyl peroxide, di(2-ethylhexyl) peroxydicarbonate, di(4-t-butylcyclohexyl) peroxydicarbonate, di-sec-butyl peroxydicarbonate, t-butyl per oxyneodecanoate, t-hexyl peroxypivalate, and t-butyl peroxypivalate.

Examples of the epoxy crosslinking agent include bisphenol A, epichlorohydrin type epoxy resin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidyl amine, N,N,N',N'-tetraglycy dil-m-xylylene diamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

An isocyanate crosslinking agent (particularly, a bifunctional isocyanate crosslinking agent) and a peroxide crosslinking agent are preferable from the viewpoint of securing the flexibility of the pressure-sensitive adhesive sheet 10 . An isocyanate crosslinking agent (particularly, a trifunctional isocyanate crosslinking agent) is preferable from the viewpoint of securing durability of the pressure-sensitive adhesive sheet 10 . In the base polymer, difunctional isocyanate crosslinking agents and peroxide crosslinking agents form more flexible two-dimensional crosslinking, whereas trifunctional isocyanate crosslinking agents form stronger three-dimensional crosslinking. From the viewpoint of achieving both durability and flexibility of the pressure-sensitive adhesive sheet 10, a combination of a trifunctional isocyanate crosslinking agent, a peroxide crosslinking agent, and/or a difunctional isocyanate crosslinking agent is preferred.

The compounding amount of the crosslinking agent is, for example, 0.01 part by mass or more, preferably 0.05 part by mass or more, more preferably 0.07 part by mass, based on 100 parts by mass of the base polymer, from the viewpoint of securing the cohesive force of the PSA sheet 10. More than that. From the viewpoint of ensuring good tackiness in the adhesive sheet 10, the compounding amount of the crosslinking agent relative 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. is less than

In the second method described above, the monomer component (including the polyfunctional monomer for introducing a crosslinked structure and other monomers) may be polymerized at one time or in multiple stages. In the multi-stage polymerization method, first, a monofunctional monomer for forming a base polymer is polymerized (prepolymerization), thereby preparing a prepolymer composition containing a partially polymerized product (a mixture of a polymer having a low degree of polymerization and an unreacted monomer). . Next, after adding a polyfunctional monomer as a crosslinking agent to the prepolymer composition, the partially polymerized product and the polyfunctional monomer are polymerized (main polymerization).

Examples of the polyfunctional monomer include polyfunctional (meth)acrylates containing two or more ethylenically unsaturated double bonds in one molecule. As a polyfunctional monomer, a polyfunctional acrylate is preferable from the viewpoint of being able to introduce a crosslinked structure by active energy ray polymerization (photopolymerization).

Examples of polyfunctional (meth)acrylates include bifunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional or higher functional (meth)acrylates.

Examples of the bifunctional (meth)acrylate include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene. Glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, neophene Tylglycol di(meth)acrylate, stearic acid modified pentaerythritol di(meth)acrylate, dicyclopentenyl di(meth)acrylate, di(meth)acryloylisocyanurate, and alkylene oxides Modified bisphenol di(meth)acrylate is mentioned.

Examples of the trifunctional (meth)acrylate include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate. can

Examples of the tetrafunctional or higher polyfunctional (meth)acrylate include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol monohydroxy penta(meth)acrylate. acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

As the polyfunctional (meth)acrylate, preferably, a tetrafunctional or higher functional (meth)acrylate is used, and more preferably, dipentaerythritol hexaacrylate is used.

The compounding amount of the polyfunctional monomer as a crosslinking agent in the monomer component is, for example, 0.01 parts by mass or more, preferably 0.03 parts by mass, based on 100 parts by mass of the monofunctional monomers, from the viewpoint of securing the cohesive force of the adhesive sheet 10. Part by mass or more, more preferably 0.05 part by mass or more, still more preferably 0.07 part by mass or more. From the viewpoint of ensuring good tackiness in the adhesive sheet 10, the blending amount of the polyfunctional monomer is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, more preferably 5 parts by mass or less, based on 100 parts by mass of the monofunctional monomer. Preferably it is 3 parts by mass or less, more preferably 1 part by mass or less, even more preferably 0.5 parts by mass or less, still more preferably 0.2 parts by mass or less, and particularly preferably 0.1 parts by mass or less.

An acrylic polymer can be formed by polymerizing the above-mentioned monomer components. Examples of the polymerization method include solution polymerization, photopolymerization in the absence of a solvent (for example, UV polymerization), block polymerization, and emulsion polymerization. As a solvent for solution polymerization, ethyl acetate and toluene are used, for example. Moreover, as a polymerization initiator, a thermal polymerization initiator and a photoinitiator are used, for example. 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 or less, based on 100 parts by mass of the monomer component.

As a thermal polymerization initiator, an azo polymerization initiator and a peroxide polymerization initiator are mentioned, for example. Examples of the azo polymerization initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, and 2,2'-azobis(2-methylpropionic acid). ) dimethyl, 4,4'-azobis-4-cyanovalerian 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 and '-azobis(N,N'-dimethyleneisobutylamidine)dihydrochloride. As a peroxide polymerization initiator, dibenzoyl peroxide, t-butyl permaleate, and lauroyl peroxide are mentioned, for example.

Examples of the photopolymerization initiator include benzoin ether photopolymerization initiators, acetophenone photopolymerization initiators, α-ketol photopolymerization initiators, aromatic sulfonyl chloride photopolymerization initiators, photoactive oxime photopolymerization initiators, benzoin photopolymerization initiators, and benzyl photopolymerization initiators. initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxantone-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 even more preferably 500,000 or more, from the viewpoint of securing the cohesive force in the pressure-sensitive adhesive sheet 10. The weight average molecular weight of the base polymer is measured by a gel permeation chromatograph (GPC) and calculated in terms of polystyrene.

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

Regarding the glass transition temperature (Tg) of the base polymer, a glass transition temperature (theoretical value) obtained based on the following formula of Fox can be used. Fox's formula 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 Fox's formula below, Tg represents the glass transition temperature (° C.) of a polymer, Wi represents the weight fraction of monomer i constituting the polymer, and Tgi represents the glass transition temperature of a homopolymer formed of monomer i ( °C). Literature values can be used for the glass transition temperature of the homopolymer. For example, "Polymer Handbook" (fourth edition, John Wiley & Sons, Inc., 1999) and "New Polymer Library 7 Introduction to Synthetic Resins for Paint" (Written by Kyojo Kitaoka, Polymer Press, 1995) ), the glass transition temperatures of various homopolymers are exemplified. On the other hand, about the glass transition temperature of the homopolymer of a monomer, it is also possible to obtain|require by the method specifically described in Unexamined-Japanese-Patent No. 2007-51271.

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

The pressure-sensitive 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 part by mass or more, more preferably 0.2 part by mass or more with respect to 100 parts by mass of the base polymer. The copper content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less.

The adhesive composition may contain other components as needed. Examples of other components include solvents, tackifiers, plasticizers, softeners, antioxidants, fillers, colorants, ultraviolet absorbers, surfactants, and antistatic agents. Examples of the solvent include a polymerization solvent used as needed during polymerization of acrylic polymer and a solvent added to the polymerization reaction solution after polymerization. As the solvent, for example, ethyl acetate and toluene are used.

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

As the peeling liner L1, a plastic film having flexibility is exemplified. As the said plastic film, a polyethylene terephthalate film, a polyethylene film, a polypropylene film, and a polyester film are mentioned, for example. The thickness of the release liner L1 is, for example, 3 µm or more, and is, for example, 200 µm or less. The surface of the release liner L1 is preferably subjected to a release treatment.

As a method of applying the pressure-sensitive adhesive composition, for example, roll coating, kiss roll coating, gravure coating, reverse coating, roll brush, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and die coating. The drying temperature of the coating film is, for example, 50°C to 200°C. Drying time is 5 seconds - 20 minutes, for example.

You may laminate|stack the peeling liner L2 (2nd peeling liner) further on the adhesive sheet 10 on the peeling liner L1. The release liner L2 is preferably a flexible plastic film whose surface has been subjected to a release treatment. 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 faces 11 and 12 are covered and protected by the release liners L1 and L2 can be manufactured.

The thickness of the adhesive sheet 10 is preferably 10 μm or more, more preferably 15 μm or more, from the viewpoint of ensuring sufficient adhesion to the adherend and handling properties. 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 reducing the thickness of the flexible device.

The haze of the adhesive sheet 10 is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. The haze of the adhesive sheet 10 can be measured using a haze meter based on JIS K7136 (2000). As a haze meter, "NDH2000" by Nippon Denshoku Kogyo Co., Ltd. and "HM-150 type|mold" by Murakami Color Technology Laboratory Co., Ltd. are mentioned, for example.

The total light transmittance of the pressure-sensitive adhesive sheet 10 is preferably 60% or more, more preferably 80% or more, still more preferably 85% or more. 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 based on JIS K 7375 (2008).

2A to 2C show an example of a method of using the adhesive sheet 10.

In this method, first, as shown in FIG. 2A, the adhesive sheet 10 is bonded to one side of the thickness direction H of the first member 21 (adherent). The first member 21 is, for example, one element of a laminated structure of a flexible display panel. As the said element, a pixel panel, a film-like polarizing plate (polarizing film), a touchscreen, and a cover film are mentioned, for example (the same also applies to the 2nd member 22 mentioned later). According to this step, the adhesive sheet 10 for bonding with another member is provided on the first member 21 .

Next, as shown in FIG. 2B , the one side of the first member 21 in the thickness direction H and the second member 22 are formed by interposing the adhesive sheet 10 on the first member 21. The other side side of the thickness direction H of is bonded. 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. Aging time is 1 minute - 21 days, for example. In the case of autoclave treatment (heating and pressure treatment) 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 pressure-sensitive adhesive sheet 10 used in the manufacturing process of the flexible display panel, for example, 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, and therefore, the adhesive sheet from the adherend It is suitable for suppressing peeling of (10). Such an adhesive sheet 10 is suitable for flexible device applications.

Example

The present invention will be described concretely by showing examples below. However, this invention is not limited to an Example. In addition, the specific numerical values such as the compounding amount (content), physical property values, and parameters described below are the compounding amounts (content), physical property values, and parameters corresponding to them described in the above-mentioned “Specific Content for Carrying Out the Invention”. It can be substituted with the upper limit (numerical value defined as "below" or "less than") or the lower limit (numerical value defined as "greater than" or "exceeding") of the same.

[Example 1]

<Preparation of prepolymer composition>

In a flask, 60 parts by mass of n-octyl acrylate (NOAA), 30 parts by mass of n-butyl (BA) acrylate, 8 parts by mass of 4-hydroxybutyl acrylate (4HBA), and N-vinyl-2-pyrroly 0.05 mass of 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "Omnirad 651", manufactured by IGM Resins) as a first photopolymerization initiator to a monomer mixture containing 2 parts by mass of pig (NVP) and 0.05 part by mass of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad184", manufactured by IGM Resins) as a second photopolymerization initiator, and then irradiating the mixture with ultraviolet rays under a nitrogen atmosphere to obtain a monomer component in the mixture A part of was polymerized to obtain a first prepolymer composition (containing a monomer component that has not undergone a polymerization reaction) having a polymerization rate of about 10%.

<Preparation of pressure-sensitive adhesive composition>

100 parts by mass of the first prepolymer composition, 0.08 parts by mass of dipentaerythritol hexaacrylate (DPHA) as a crosslinking agent, and 2,2-dimethoxy-1,2-diphenylethane-1-one (product name) as a photopolymerization initiator "Omnirad651", manufactured by IGM Resins) 0.05 parts by mass and 0.3 parts by mass of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Industry) were mixed to obtain a first adhesive composition.

<Formation of pressure-sensitive adhesive layer>

On the peeling treated surface of the first peeling liner (product name “Diafoil MRF#38”, thickness 38 μm, manufactured by Mitsubishi Chemical Corporation) having a peeling treated surface on one side, a first pressure-sensitive adhesive composition was applied to form a coating film. Next, on the coating film on the first release liner, a release treatment surface of a second release liner (product name “Diafoil MRN#38”, thickness 38 μm, manufactured by Mitsubishi Chemical Corporation) having a release treatment surface on one side was bonded. Next, the coating film between the peeling liners was irradiated with ultraviolet rays, and the coating film was photocured to form an adhesive layer (thickness: 50 µm). In the ultraviolet irradiation, a black light was used as the irradiation light source, and the irradiation intensity was 5 mW/cm ² .

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

[Example 2]

In the preparation of the PSA composition, the PSA sheet of Example 2 was prepared in the same manner as in the PSA sheet of Example 1, except that the blending amount of the crosslinking agent was changed to 0.04 parts by mass instead of 0.08 parts by mass, and no photopolymerization initiator was added. did.

[Example 3]

A PSA sheet of Example 3 was produced in the same manner as the PSA sheet of Example 1 except for the following. In the preparation of the prepolymer composition, the compounding amount of the first photopolymerization initiator (product name "Omnirad651") is 0.035 parts by mass instead of 0.05 parts by mass, and the compounding amount of the second photopolymerization initiator (product name "Omnirad184") is 0.05 parts by mass instead of to 0.035 parts by mass. Preparation of the adhesive composition WHEREIN: The compounding quantity of a crosslinking agent was made into 0.02 mass part instead of 0.08 mass part, and the photoinitiator was not added.

[Example 4]

A PSA sheet of Example 4 was produced in the same manner as the PSA sheet of Example 1 except for the following. In the preparation of the prepolymer composition, the compounding amount of the first photopolymerization initiator (product name "Omnirad651") is 0.07 parts by mass instead of 0.05 parts by mass, and the compounding amount of the second photopolymerization initiator (product name "Omnirad184") is 0.05 parts by mass instead of to 0.07 parts by mass. Preparation of the adhesive composition WHEREIN: The compounding quantity of a crosslinking agent was made into 0.04 mass part instead of 0.08 mass part, and the photoinitiator was not added.

[Example 5]

A PSA sheet of Example 5 was produced in the same manner as the PSA sheet of Example 1 except for the following. In preparation of the prepolymer composition, the blending amount of NOAA was 70 parts by mass instead of 60 parts by mass, and the blending amount of BA was 20 parts by mass instead of 30 parts by mass. Preparation of the adhesive composition WHEREIN: The compounding quantity of the crosslinking agent was made into 0.05 mass part instead of 0.08 mass part.

[Example 6]

A PSA sheet of Example 6 was produced in the same manner as the PSA sheet of Example 1 except for the following. Preparation of the adhesive composition WHEREIN: The compounding quantity of the crosslinking agent was made into 0.05 mass part instead of 0.08 mass part.

[Comparative Example 1]

<Preparation of prepolymer composition>

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

<Preparation of pressure-sensitive adhesive composition>

100 parts by mass of the second prepolymer composition, 0.12 parts by mass of DPHA as a crosslinking agent, and 0.3 parts by mass of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Industry) were mixed to obtain a second adhesive composition.

<Formation of pressure-sensitive adhesive layer>

Except having used the 2nd adhesive composition instead of the 1st adhesive composition, it carried out similarly to formation of the adhesive layer in Example 1 (including ultraviolet ray irradiation), and the adhesive layer (thickness) clamped by the 1st and 2nd peeling liner 50 μm) were formed.

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

<Tensile test>

For each of the pressure-sensitive adhesive sheets of Examples 1 to 6 and Comparative Example 1, strain stress generated in the first tensile test and the second tensile test described below was investigated.

Specifically, first, the required number of samples for measurement were produced for each adhesive sheet. In preparation of the sample for measurement, first, a pressure-sensitive adhesive sheet piece (width: 30 mm x length: 100 mm) with a double-sided release liner was cut out from the pressure-sensitive adhesive sheet with a release liner on both sides. Next, after peeling one release liner from the same sheet piece, the pressure-sensitive adhesive sheet piece was wound on the other release liner in the longitudinal direction so as not to contain air bubbles to form a columnar shape (cylinder height: 30 mm). In this way, a columnar pressure-sensitive adhesive sheet piece as a sample for measurement was obtained. Next, with respect to the sample for measurement, a tensile test was performed using a tensilon type tensile tester (product name "Autograph AG-50NX plus", manufactured by Shimadzu Corporation) under an environment of 25 ° C. and 50% relative humidity, Tensile stress generated in the process was measured (first tensile test). In this way, a stress-strain curve (load-elongation curve) was obtained. In this tensile test, the initial distance between chucks was set to 10 mm, and the sample for measurement (a columnar pressure-sensitive adhesive sheet piece) was pulled in the columnar height direction, and the tensile speed was set to 50 mm/min. As the measurement results in the 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 the strain stress S ₅₀₀ (N/cm ² ) at 1000% elongation The deformation stress S ₁₀₀₀ (N/cm ² ) at the time is shown in Table 1 (the pressure-sensitive adhesive sheet of Comparative Example 1 broke prior to 1000% elongation in the first tensile test). Table 1 also shows the ratio of the strain stress S ₅₀₀ to the strain stress S ₂₀₀ .

On the other hand, with respect to the sample for measurement, a tensile test was performed in the same manner as in the first tensile test except that the tensile speed was set to 600 mm/min, and the tensile stress generated in the tensile process was measured (second tensile test). In this way, a stress-strain curve (load-elongation curve) was obtained. As the measurement results in this second 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 The strain stress S' ₁₀₀₀ (N/cm ² ) at the time of % elongation is shown in Table 1 (the pressure-sensitive adhesive sheet of Comparative Example 1 broke prior to 1000% elongation in the second tensile test). In addition, 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 (S' ₅₀₀ /S' ₂₀₀ ) are also shown in Table 1. indicate

<Flex hold test>

Each of the PSA sheets of Examples 1 to 6 and Comparative Example 1 was subjected to a bending holding test as follows.

First, the second release liner was peeled from the pressure-sensitive adhesive sheet with double-sided release liner, and the exposed surface exposed by this was subjected to plasma treatment. On the other hand, both surfaces (1st surface, 2nd surface) of the 51 micrometer-thick polarizing film were also plasma-processed. In addition, the surface of the 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 subjected to plasma treatment. In each plasma treatment, a plasma irradiation device (product name "AP-TO5", manufactured by Sekisui Kogyo) was used, the voltage was 160 V, the frequency was 10 kHz, and the processing speed was 5000 mm/min. And the said exposed surface of the adhesive sheet and the 1st surface of the polarizing film were bonded together. In this pasting, the pressure-sensitive adhesive sheet with the first peeling liner and the polarizing film were crimped by an operation in which a 2-kg roller was reciprocated once in a 23°C environment. Next, after peeling the 1st peeling liner from the PSA sheet with a polarizing film, the said transparent polyimide film was bonded to the exposed surface of the PSA sheet thus exposed. Next, the PET film was bonded to the second surface of the polarizing film with a 15 µm-thick adhesive foil sheet interposed therebetween. In this pasting, the polarizing film and the PET film were crimped by an operation in which a 2 kg roller was reciprocated once in a 23°C environment. Thus, a laminate having a laminate configuration of a PET film (thickness: 125 μm), a thin adhesive sheet (thickness: 15 μm), a polarizing film (thickness: 51 μm), an adhesive sheet (thickness: 50 μm), and a transparent polyimide film (thickness: 80 μm). got the film

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

Next, the sample was subjected to a bending test using a planar body unloaded U-shaped stretching tester (manufactured by Yuasa System Equipment). In this test, for each of both ends in the long side direction of the sample, a bending jig was attached to a range of 20 mm from the edge of the sample, and the sample was fixed to the testing machine (the central region of 60 mm in the long side direction of the sample was fixed in a non-existent 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 subjected to 200,000 cycles at a bending speed of 60 rpm between a bent form and a non-curved form in which the surface on the PET film side becomes the inner side. , and repeatedly deformed (bent). The bending form in this test is, specifically, a form in which the axial direction of the bending moment acting on the sample and the absorption axis direction of the polarizing film are orthogonal. In the bending form, the sample had a bending radius of 1.3 mm and a bending angle of 180°. Regarding the adhesiveness of the adhesive sheet to the adherend in such a bending test, "good" was obtained when no peeling occurred between the adhesive sheet and the adherend (transparent polyimide film, polarizing film). was evaluated, and the case where peeling occurred was evaluated as "defective". The evaluation results are shown in Table 1.

10: adhesive sheet (optical adhesive sheet)
11, 12: adhesive surface
H: thickness direction
L1, L2: release liner
21: first member
22: second member

Claims (9)

As an optical adhesive sheet,
As the 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 S ₂₀₀ (N / cm ² ),
As the strain stress at 200% elongation in the second tensile test under conditions of 25 ° C. and a tensile speed of 600 mm / min, it has a strain stress S ' ₂₀₀ (N / cm ² ),
The optical adhesive sheet, wherein the ratio of the strain stress S ₂₀₀ to the strain stress S' ₂₀₀ is 0.8 or less. According to claim 1,
The optical adhesive sheet, 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. According to claim 1,
The optical adhesive sheet having a strain stress S ₁₀₀₀ at 1000% elongation in the first tensile test of 18 N/cm ² or less. According to claim 2,
The optical adhesive sheet having a strain stress S ₁₀₀₀ at 1000% elongation in the first tensile test of 18 N/cm ² or less. According to claim 1,
The optical adhesive sheet, 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. According to claim 2,
The optical adhesive sheet, 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. According to claim 3,
The optical adhesive sheet, 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. According to claim 4,
The optical adhesive sheet, 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. According to any one of claims 1 to 8,
The optical adhesive sheet having a strain stress S' ₁₀₀₀ at 1000% elongation in the second tensile test of 25 N/cm ² or less.

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