JP2023095066A - Optical pressure sensitive adhesive sheet - Google Patents

Abstract

To provide an optical pressure sensitive adhesive sheet suitable for a use in a flexible device.SOLUTION: A pressure sensitive adhesive sheet 10 is an optical pressure sensitive adhesive sheet. In the pressure sensitive adhesive sheet 10, an adhesive force F at a peeling speed 0 is 1 N/10 mm or more, obtained by an extrapolation method according to an adhesive force to a polyimide adherend in a first 180° peel test under a condition at 25°C with a peeling speed 300 mm/min., an adhesive force in a second 180° peel test under a condition at 25°C with a peeling speed 100 mm/min., and an adhesive force in a third 180° peel test under a condition at 25°C with a peeling speed 10 mm/min. In the pressure sensitive adhesive sheet 10, a distortion stress S200 is 15 N/cm2 or less at 200% elongation in a tensile test under a condition at 25°C with a peeling speed 300 mm/min.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. 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 have a high level of resistance to peeling from elements (adherends) when the display is bent.

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. Such an optical pressure-sensitive adhesive sheet is required at a very high level to be difficult to peel off from the element (adherend) when the display is rolled.

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, wherein the adhesive strength in the first 180 ° peel test at 25 ° C. and a tensile speed of 300 mm / min to the polyimide adherend and the adhesive strength at 25 ° C. and a tensile speed of 100 mm Determined by extrapolation based on the adhesion in the second 180 ° peel test at /min and the adhesion in the third 180 ° peel test at 25 ° C and a tensile speed of 10 mm / min , the adhesive force F at a tensile speed of 0 is 1 N/10 mm or more, and the strain stress _S200 at 200% elongation in a tensile test under the conditions of 25 ° C. and a tensile speed of 300 mm / min is 15 N/cm ² or less. , including an optical adhesive sheet.

The present invention [2] includes the optical pressure-sensitive adhesive sheet according to [1] above, which has an adhesive strength of 2 N/10 mm or more in the second 180° peel test.

The present invention [3] includes the optical pressure-sensitive adhesive sheet according to [1] or [2] above, wherein the strain stress _S500 at 500% elongation in the tensile test is 30 N/cm ² or less.

The present invention [4] is any one of [1] to [3] above, wherein the ratio of the strain stress _S500 at 500% elongation in the tensile test to the strain stress _S200 is 2.5 or less. including the optical adhesive sheet described in 1.

In the optical pressure-sensitive adhesive sheet of the present invention, as described above, the adhesive force F at a tensile speed of 0, which is obtained by extrapolation based on the three adhesive forces in the first to third 180° peel tests, is 1 N/10 mm. (This adhesive force F is an adhesive force acting on an adherend in a state in which the optical adhesive sheet continues to adhere to the adherend without relative displacement, and is an indicator of adhesive properties. one). In contrast, the optical pressure-sensitive adhesive sheet of the present invention has a low strain stress _S200 at 200% elongation in a tensile test under conditions of 25° C. and a tensile speed of 300 mm/min, ie, 15 N/cm ² or less. Such an optical pressure-sensitive adhesive sheet resists internal stress such as tensile stress generated in the optical pressure-sensitive adhesive sheet and continues to adhere to the adherend when the adherend to which the pressure-sensitive adhesive sheet is adhered is deformed. and therefore suitable for suppressing peeling of the optical pressure-sensitive adhesive sheet from the adherend. 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. For the adhesive sheet of Example 1, three adhesive strengths measured in the first to third 180° peel tests, and the adhesive strength at a tensile speed of 0, which is obtained by extrapolation based on these adhesive strengths, It is a plotted graph.

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 an adhesive force F of 1 N/10 mm or more at a tensile speed of 0, which is obtained by extrapolation based on the adhesive forces f ₁ , f ₂ and f ₃ to the polyimide adherend. The adhesive force f ₁ is obtained by peeling the adhesive sheet 10 from the polyimide adherend under the conditions of 25 ° C., a peeling angle of 180 ° and a tensile speed of 300 mm / min after the adhesive sheet 10 is attached to the polyimide adherend. Adhesion measured in the test (first 180° peel test). The adhesive force f ₂ is obtained by peeling the adhesive sheet 10 from the polyimide adherend under the conditions of 25 ° C., a peeling angle of 180 ° and a tensile speed of 100 mm / min after the adhesive sheet 10 is attached to the polyimide adherend. Adhesion measured in the test (second 180° peel test). The adhesive force f ₃ is obtained by peeling the adhesive sheet 10 from the polyimide adherend under the conditions of 25 ° C., a peeling angle of 180 ° and a tensile speed of 10 mm / min after the adhesive sheet 10 is attached to the polyimide adherend. Adhesion measured in the test (third 180° peel test). The adhesive force F is the adhesive force acting on the adherend while the adhesive sheet 10 continues to adhere to the adherend without relative displacement, and is one of the indicators of the adhesive properties. be. The method of measuring the adhesive forces f ₁ , f ₂ , and f ₃ and the method of deriving the adhesive force F are specifically described later with regard to the examples.

Further, the adhesive sheet 10 has a strain stress _S200 of 15 N/cm ² or less at 200% elongation in a tensile test under conditions of 25° C. and a tensile speed of 300 mm/min. The method of measuring strain stress S ₂₀₀ and strain stresses S ₃₀₀ and S ₅₀₀ to be described later is specifically as described later with respect to the examples.

In the adhesive sheet 10, as described above, the adhesive force F at a tensile speed of 0, which is obtained by extrapolation based on the adhesive forces f ₁ , f ₂ , and f ₃ in the first to third 180° peel tests, is It is 1N/10mm or more. On the other hand, the adhesive sheet 10 has a strain stress _S200 of 15 N/cm ² or less at 200% elongation in a tensile test (25° C., tensile speed of 300 mm/min). The adhesive force F is as large as 1 N / 10 mm or more, and the strain stress S ₂₀₀ at 200% elongation is as small as 15 N / cm ² or less. It is suitable for the adhesive sheet 10 to continue sticking to the adherend against the internal stress such as tensile stress generated in the adhesive sheet 10 when deformed, and therefore the peeling of the adhesive sheet 10 from the adherend is suppressed. Suitable for Such an adhesive sheet 10 is suitable for use in flexible devices.

From the viewpoint of ensuring the strong adhesiveness of the adhesive sheet 10 and suppressing the peeling described above, the adhesive force F is preferably 1.5 N/10 mm or more, more preferably 1.8 N/10 mm or more, and still more preferably 2 N/10 mm. As mentioned above, it is more preferably 2.2 N/10 mm or more, still more preferably 2.4 N/10 mm or more, and particularly preferably 2.6 N/10 mm or more. The adhesive force F is, for example, 10 N/10 mm or less. Methods for adjusting the adhesive force F include, for example, selection of the type of base polymer in the adhesive sheet 10, adjustment of the molecular weight, and adjustment of the compounding amount. Selecting the type of base polymer involves adjusting the composition of the monomers forming the base polymer. Methods for adjusting the adhesive force F include selection of the types of components other than the base polymer in the adhesive sheet 10 and adjustment of the compounding amounts of the components. Such components include crosslinkers, silane coupling agents, and oligomers. The adhesive force adjusting method as described above also applies to the adhesive force described later.

From the viewpoint of suppressing the stress generated during deformation in the pressure-sensitive adhesive sheet 10 to suppress the above-described peeling, the strain stress _S200 at 200% elongation is preferably 14 N/cm ² or less, more preferably 12 N/cm ² or less, More preferably 10 N/cm ² or less, particularly preferably 6 N/cm ² or less. The strain stress S ₂₀₀ is, for example, 1 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 adjusting method is the same for strain stress described later.

From the viewpoint of ensuring the strong adhesiveness of the adhesive sheet 10 and suppressing the peeling described above, the adhesive force _f1 is preferably 2.5 N/10 mm or more, more preferably 3 N/10 mm or more, and still more preferably 3.5 N/10 mm or more. 10 mm or more, more preferably 4 N/10 mm or more, particularly preferably 4.5 N/10 cm ² or more. The adhesive force _f1 is, for example, 20 N/10 mm or less.

From the viewpoint of ensuring the strong adhesiveness of the adhesive sheet 10 and suppressing the above-described peeling, the adhesive force _f2 is preferably 2 N/10 mm or more, more preferably 2.5 N/10 mm or more, and still more preferably 3 N/10 mm or more. , more preferably 3.5 N/10 mm or more, particularly preferably 3.7 N/10 cm ² or more. The adhesive force _f2 is, for example, 15 N/10 mm or less.

From the viewpoint of ensuring strong adhesiveness of the adhesive sheet 10 and suppressing the above-mentioned peeling, the adhesive force _f3 is preferably 1 N/10 mm or more, more preferably 1.5 N/10 mm or more, and still more preferably 2 N/10 mm or more. , more preferably 2.5 N/10 mm or more, particularly preferably 2.6 N/10 cm ² or more. The adhesive force _f3 is, for example, 12 N/10 mm or less.

From the viewpoint of suppressing the stress generated during deformation in the adhesive sheet 10 and suppressing the above-described peeling, the strain stress S ₃₀₀ at 300% elongation in the tensile test is preferably 20 N/cm ² or less, more preferably 17 N/cm cm ² or less, more preferably 14 N/cm ² or less, still more preferably 12 N/cm ² or less, even more preferably 10 N/cm ² or less, particularly preferably 8 N/cm ² or less. The strain stress S ₃₀₀ is, for example, 1 N/cm ² or more.

The ratio of strain stress S ₃₀₀ to strain stress S ₂₀₀ (S ₃₀₀ /S ₂₀₀ ) is preferably 1.4 or less, more preferably 1.4 or less, more preferably 1.4 or less, from the viewpoint of suppressing the difference in generated stress due to the degree of deformation of the adhesive sheet 10 . It is 3 or less, more preferably 1.2 or less, and particularly preferably 1.15 or less. The ratio (S ₃₀₀ /S ₂₀₀ ) is, for example, 1 or more.

From the viewpoint of suppressing the stress generated during deformation in the adhesive sheet 10 and suppressing the above-described peeling, the strain stress S ₅₀₀ at 500% elongation in the tensile test is preferably 30 N/cm ² or less, more preferably 25 N/cm cm ² or less, more preferably 20 N/cm ² or less, still more preferably 15 N/cm ² or less, even more preferably 12 N/cm ² or less, and particularly preferably 11 N/cm ² or less. The strain stress S ₃₀₀ is, for example, 1 N/cm ² or more.

The ratio of strain stress S ₅₀₀ to strain stress S ₂₀₀ (S ₅₀₀ /S ₂₀₀ ) is preferably 2.5 or less, more preferably 2 or less, from the viewpoint of suppressing the difference in generated stress due to the degree of deformation of the adhesive sheet 10. , more preferably 1.8 or less, particularly preferably 1.5 or less. The ratio (S ₅₀₀ /S ₂₀₀ ) is, for example, 1 or more.

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, n-hexyl (meth)acrylate, ( Heptyl methacrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, (meth)acrylic acid Decyl, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (that is, lauryl 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, 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 cohesive force in the pressure-sensitive adhesive sheet 10, and ensuring adhesion of the pressure-sensitive 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 ratio 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. A method (first method), and a polyfunctional monomer is included in the monomer component forming the base polymer, and a base polymer is formed in which a branched structure (crosslinked structure) is introduced into the polymer chain by polymerizing the monomer component. method (second method). 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) is 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 0.05 parts by mass or more, more preferably 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 polyfunctional monomer blended with respect to 100 parts by mass of the monofunctional monomer is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, more preferably 3 parts by mass. It is below.

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. Examples of the solvent include 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 (heating 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.

For example, the adhesive sheet 10 used in the manufacturing process of the flexible display panel as described above has an adhesive force F at a tensile speed of 0 (adhesive force f ₁ , (obtained by extrapolation based on f ₂ and f ₃ ) is 1 N / 10 mm or more, and the strain stress S ₂₀₀ at 200% elongation in a tensile test (25 ° C., tensile speed 300 mm / min) is 15 N / cm ² or less. Such a pressure-sensitive adhesive sheet 10 is suitable for continuing to adhere to an adherend against internal stress such as tensile stress generated in the pressure-sensitive adhesive sheet 10 when the adherend is deformed. It is suitable for suppressing peeling of the adhesive sheet 10 from.

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 adhesive composition, the adhesive sheet of Example 2 was prepared in the same manner as the adhesive sheet of Example 1, except that the amount of the photopolymerization initiator was changed to 0.1 part by mass instead of 0.05 part by mass. An adhesive sheet was produced.

[Example 3]
A pressure-sensitive adhesive sheet of Example 3 was prepared in the same manner as the pressure-sensitive adhesive sheet of Example 1, except that the photopolymerization initiator was not blended in the preparation of the pressure-sensitive adhesive composition.

[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 0.035 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 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 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 6]
<Preparation of prepolymer composition>
In a flask, 80 parts by weight of n-hexyl acrylate (HxA), 10 parts by weight of butyl acrylate (BA), 8 parts by weight 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-hydroxy-cyclohexyl-phenyl-ketone (product name "Omnirad 184", manufactured by IGM Resins) as a second photopolymerization initiator, and then added to the mixture. A part of the monomer components in the mixture was polymerized by irradiating 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, 0.08 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) 0.1 parts by mass and 0.3 parts by mass of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) are mixed to form a second adhesive. A 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 Example 6 with a double-sided release liner was produced.

[Example 7]
In the preparation of the adhesive composition, the adhesive sheet of Example 7 was prepared in the same manner as the adhesive sheet of Example 6, except that the amount of the photopolymerization initiator was changed to 0.05 parts by mass instead of 0.1 part by mass. An adhesive sheet was produced.

[Example 8]
A pressure-sensitive adhesive sheet of Example 8 was prepared in the same manner as the pressure-sensitive adhesive sheet of Example 6, except that no photopolymerization initiator was added in the preparation of the pressure-sensitive adhesive composition.

[Comparative Example 1]
<Preparation of prepolymer composition>
A monomer mixture containing 78 parts by weight of 2-ethylhexyl acrylate (2EHA), 18 parts by weight of N-vinyl-2-pyrrolidone (NVP), and 4 parts by weight of 2-hydroxyethyl acrylate (2HEA) in a flask. 0.035 parts by mass of the first photopolymerization initiator (product name "Omnirad 651", manufactured by IGM Resins) and 0.035 parts by weight of the second photopolymerization initiator (product name "Omnirad 184", manufactured by IGM Resins) After adding, the mixture was irradiated with ultraviolet rays in a nitrogen atmosphere to polymerize a part of the monomer components in the mixture to obtain a third prepolymer composition with a polymerization rate of about 10%.

<Preparation of adhesive composition>
100 parts by mass of the third prepolymer composition, 0.29 parts by mass of DPHA as a cross-linking agent, and 0.353 parts by mass of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) are mixed, A third 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 third 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.

<180° Peeling Test>
The pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Example 1 were examined for their adhesive strength to adherends by a 180° peel test.

Specifically, first, a required number of measurement samples were prepared for each pressure-sensitive adhesive sheet. In preparing the measurement sample, first, the first release liner was peeled off from the adhesive sheet, and the exposed surface thus exposed was covered with a plasma-treated polyethylene terephthalate (PET) film (product name: Lumirror S10, thickness: 25 μm, manufactured by Toray) to obtain a laminate. In the 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 (the same applies to the plasma treatment described later. is). Next, a test piece (width 10 mm×length 100 mm) was cut out from the laminate (PET film/adhesive sheet/second release liner). Next, the second release liner was peeled off from the adhesive sheet of this test piece, and the exposed surface was covered with a plasma-treated polyimide (PI) film (product name “GV200”, thickness 80 μm, manufactured by Kolon Co., Ltd.). ). Next, the PI film with the adhesive sheet (test piece) was subjected to heat and pressure treatment under conditions of a temperature of 50° C. and a pressure of 0.5 MPa for 15 minutes. This caused the test piece to be crimped against the PI film. A measurement sample was prepared as described above.

Next, after the measurement sample was allowed to stand at room temperature for 30 minutes, a 180° peel test was performed in which the test piece was peeled from the PI film in the measurement sample, and the force required for peeling (peel strength) was measured (first 180° peel test). For this measurement, a tensile tester (product name “Autograph AG-50NX plus”, manufactured by Shimadzu Corporation) was used. In this measurement, the measurement temperature was 25 ° C., the relative humidity was 55%, the peeling angle of the test piece from the PI film was 180 °, the tensile speed of the test piece was 300 mm / min, and the peel length was 50 mm. . The average value of measured peel strength is shown in Table 1 as adhesive strength f ₁ (N/10 mm) at a tensile speed of 300 mm/min.

On the other hand, a 180° peel test was conducted under the same conditions as the first 180° peel test except that the tensile speed was changed to 100 mm/min (second 180° peel test). The measurement results are shown in Table 1 as adhesive strength f ₂ (N/10 mm) at a tensile speed of 100 mm/min. A 180° peel test was also conducted under the same conditions as the first 180° peel test except that the tensile speed was changed to 10 mm/min (third 180° peel test). The measurement results are shown in Table 1 as adhesive strength f ₃ (N/10 mm) at a tensile speed of 10 mm/min.

Then _, as exemplified by _the straight line (solid line) in the graph of FIG _. A force F (N/10 mm) was obtained. Specifically, a regression line (straight line) is obtained by the method of least squares from the x-coordinate and y-coordinate of three plots (white plots in the graph of FIG. 3) relating to the adhesive strengths f ₁ to f ₃ , and the straight line is used. Adhesive force F at a tensile speed of 0 was determined by extrapolation. The values are shown in Table 1. In the graph of FIG. 3, the horizontal axis represents the tensile speed (mm/min) in the 180° peel test, and the vertical axis represents the adhesive strength (N/10 mm).

On the other hand, a 180° peel test was conducted under the same conditions as the first 180° peel test except that the adherend in the process of preparing the measurement sample was replaced with a polarizing film (thickness: 51 µm, manufactured by Nitto Denko). . The measurement results are shown in Table 1 as adhesive strength f′ ₁ (N/10 mm) at a tensile speed of 300 mm/min. A 180° peel test was conducted under the same conditions as the second 180° peel test except that the polarizing film was used as the adherend in the process of preparing the measurement sample. The measurement results are shown in Table 1 as adhesive strength f′ ₂ (N/10 mm) at a tensile speed of 100 mm/min. A 180° peel test was also conducted under the same conditions as the third 180° peel test except that the polarizing film was used as the adherend in the process of preparing the measurement sample. The measurement results are shown in Table 1 as adhesive strength f' ₃ (N/10 mm) at a tensile speed of 10 mm/min. Then _, as exemplified by the straight line (dotted line) in _the graph of FIG _. The adhesive force F' (N/10 mm) was obtained. Specifically, from the x-coordinate and y-coordinate of three plots (solid black plots in the graph of FIG. 3) relating to the adhesive forces f′ ₁ to f′ ₃ , a regression line (straight line) is obtained by the method of least squares, and the straight line Adhesive force F' at a tensile speed of 0 was determined by extrapolation using . The values are shown in Table 1.

<Tensile test>
The pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Example 1 were examined for strain stress generated in a 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 a relative humidity of 50%. The tensile stress produced during the pulling process was measured. 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 speed was 300 mm/min. Strain stress S ₂₀₀ (N/cm 2 ) at 200% elongation, S 300 (N/cm ² ) at 300% elongation, and S ₅₀₀ (N/cm ² ) at ₅₀₀ % elongation in such a tensile test N/cm ² ) are shown in Table 1. Also shown in Table 1 are the ratio _of strain stress S ₃₀₀ to strain stress S ₂₀₀ and the ratio of strain stress S ₅₀₀ to strain stress S 200 .

<Bending retention test>
The pressure-sensitive adhesive sheets of Examples 1 to 8 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 (4)

An optical adhesive sheet,
Adhesion to the polyimide adherend in the first 180 ° peel test at 25 ° C. and a tensile speed of 300 mm / min, and the second 180 ° peel test at 25 ° C. and a tensile speed of 100 mm / min Based on the adhesive strength and the adhesive strength in the third 180 ° peel test under the conditions of 25 ° C. and a tensile speed of 10 mm / min, the adhesive strength F at a tensile speed of 0 obtained by extrapolation is 1 N / 10 mm and
An optical pressure-sensitive adhesive sheet having a strain stress _S200 at 200% elongation of 15 N/cm ² or less in a tensile test under conditions of 25°C and a tensile speed of 300 mm/min. 2. The optical pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive strength in the second 180[deg.] peel test is 2N/10mm or more. The optical pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the strain stress _S500 at 500% elongation in the tensile test is 30 N/ ^cm2 or less. The optical pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the ratio of the strain stress _S500 at 500% elongation in the tensile test to the strain stress _S200 is 2.5 or less.

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