CN116333613A - Optical adhesive sheet - Google Patents

Abstract

Provides optical adhesive sheets suitable for flexible device applications. The adhesive sheet (10) of the present invention is an optical adhesive sheet. The adhesive sheet (10) has an adhesive force F (N/10mm) as the adhesive force under the tensile speed 0, and the adhesive force under the tensile speed 0 is obtained as follows: based on the polyimide being adhered Adhesion in the first 180°peel test at 25°C and a tensile speed of 300mm/min, and the second 180°peel test at 25°C and a tensile speed of 100mm/min and the adhesive force in the third 180° peel test at 25°C and a tensile speed of 10 mm/min were obtained by extrapolation. The pressure-sensitive adhesive sheet 10 has a strain stress S ₂₀₀ (N/cm ² ) as a strain stress at 200% elongation in a tensile test under the conditions of 25° C. and a tensile speed of 300 mm/min. The ratio of the adhesive force F to the strain stress S ₂₀₀ is 0.3 or more.

Description

Optical adhesive sheet

Technical Field

The present invention relates to an optical adhesive sheet.

Background Art

The display panel has a laminated structure including, for example, a pixel panel, a polarizing plate, a touch panel, a cover film, etc. In the manufacturing process of such a display panel, an optically transparent adhesive sheet (optical adhesive sheet) is used to bond the elements included in the laminated structure.

On the other hand, for smartphones and tablet terminals, repeatedly bendable (foldable) display panels are being developed. Specifically, a 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 made in a repeatedly bendable manner, and a thin optical adhesive sheet is used to join such elements. Optical adhesive sheets for flexible devices such as foldable display panels are described, for example, in the following patent document 1.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Publication No. 2018-111754

Summary of the invention

Problem that the invention aims to solve

In the past, the optical adhesive sheet was easily peeled off from the element as the adherend at the bending part of the foldable display panel. This is because, when the display panel is bent, a large tensile stress will be locally generated in the bent part of the optical adhesive sheet. In the bent part of the optical adhesive sheet, the greater the tensile stress on the element (adherend), for example in the shear direction, the easier it is for the optical adhesive sheet to peel off from the element. The occurrence of this peeling will become a cause of malfunction of the equipment, which is not preferred. For the optical adhesive sheet used for the foldable display panel, a high level is required to be not easy to peel off from the element (adherend) when the display is bent.

On the other hand, as a flexible device, a rollable display panel is also being developed. The rollable display panel can, for example, be repeatedly deformed between a rolled-up shape after being rolled up as a whole or in part and a flat shape after being unwound as a whole. In such a rollable display panel, each element in the laminated structure is made in a repeatedly deformable manner, and a thin optical adhesive sheet is used in the bonding between such elements. When the rollable display panel is in a rolled-up shape, the optical adhesive sheet bonded to the rolled-up element is continuously subjected to tensile stress from the element. Such an optical adhesive sheet is required at a very high level to be difficult to peel off from the element (adherend) when in the rolled-up shape of the display.

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

Solutions for solving problems

The present invention [1] comprises an optical adhesive sheet having an adhesive force F (N/10 mm) as an adhesive force at a tensile speed of 0, the adhesive force at a tensile speed of 0 being obtained by extrapolating the adhesive force in a first 180° peel test at 25°C and a tensile speed of 300 mm/min, the adhesive force in a second 180° peel test at 25°C and a tensile speed of 100 mm/min, and the adhesive force in a third 180° peel test at 25°C and a tensile speed of 10 mm/min on a polyimide adherend, the optical adhesive sheet having a strain stress S ₂₀₀ (N/cm ² ) as a strain stress at 200% elongation in a tensile test at 25°C and a tensile speed of 300 mm/min, and a ratio of the adhesive force F to the strain stress S ₂₀₀ being 0.3 or more.

The present invention [2] comprises the optical adhesive sheet according to the above [1], wherein the ratio of the adhesive force F to the strain stress S ₅₀₀ (N/cm ² ) at 500% elongation in the tensile test is 0.2 or more.

The present invention [3] comprises the optical adhesive sheet according to [1] or [2], wherein the ratio of the strain stress S ₅₀₀ at 500% elongation in the tensile test to the strain stress S ₂₀₀ is 3 or less.

The present invention [4] comprises the optical adhesive sheet according to any one of [1] to [3] above, wherein the adhesive force F is 1 N/10 mm or more.

The present invention [5] comprises the optical adhesive sheet according to any one of [1] to [4], wherein the strain stress S ₂₀₀ is 20 N/cm ² or less.

The present invention [6] comprises the optical adhesive sheet according to any one of [1] to [5], wherein the strain stress S ₅₀₀ at 500% elongation in the tensile test is 30 N/cm ² or less.

Effects of the Invention

In the optical adhesive sheet of the present invention, as described above, the ratio (F/S 200 ) of the adhesive force F at a tensile speed of 0 obtained by extrapolation based on the three adhesive forces in the first to third 180° peeling tests to the strain stress S ₂₀₀ at 200% elongation in the tensile test (25°C, tensile speed 300mm/min) is greater than 0.3 (the adhesive force F is the adhesive force acting on the adherend in a state where the optical adhesive sheet is continuously bonded to the adherend without relative displacement, and is one of the indicators representing the adhesive properties). Such _an optical adhesive sheet is suitable for resisting the internal stress such as the tensile stress generated by the optical adhesive sheet when the adherend to which the adhesive sheet is bonded is deformed, so that the adhesive sheet continues to be bonded to the adherend, and is therefore suitable for inhibiting the peeling of the optical adhesive sheet from the adherend. Such an optical adhesive sheet is suitable for use in flexible devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of one embodiment of the optical adhesive sheet of the present invention.

Fig. 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 to a second adherend via the optical adhesive sheet, and Fig. 2C shows an aging step.

3 is a graph showing the three adhesive forces measured by the first to third 180° peel tests for the PSA sheet of Example 1 and the adhesive force at a tensile rate of 0 obtained by extrapolation based on these adhesive forces.

Description of Reference Numerals

10 Adhesive sheet (optical adhesive sheet)

11, 12 Adhesive surface

H thickness direction

L1, L2 release liner

21 Component 1

22 Component 2

DETAILED DESCRIPTION

As shown in FIG1 , an adhesive sheet 10 as one embodiment of the optical adhesive sheet of the present invention has a sheet shape of a predetermined thickness and extends in a direction (surface direction) orthogonal to the thickness direction H. The adhesive sheet 10 has an adhesive surface 11 on one side in the thickness direction H and an adhesive surface 12 on the other side in the thickness direction H. FIG1 exemplarily shows a state in which release liners L1 and L2 are attached to the adhesive surfaces 11 and 12 of the adhesive sheet 10. The release liner L1 is arranged on the adhesive surface 11. The release liner L2 is arranged on the adhesive surface 12. The release liners L1 and L2 are respectively peeled off at a predetermined timing when the adhesive sheet 10 is used.

The adhesive sheet 10 is an optically transparent adhesive sheet arranged at the light transmission part of the flexible device. As a flexible device, for example, a flexible display panel can be listed. As a flexible display panel, for example, a foldable display panel and a rollable display panel can be listed. The flexible display panel, for example, has a laminated structure including elements such as a pixel panel, a thin film polarizer (polarizing film), a touch panel and a cover film. The adhesive sheet 10 is used, for example, in the manufacturing process of the flexible display panel to bond the elements contained in the laminated structure to each other.

The adhesive sheet 10 has an adhesive force F as an adhesive force at a tensile speed of 0 obtained by extrapolation based on the adhesive forces f ₁ , f ₂ , and f ₃ to the polyimide adherend, has a strain stress S ₂₀₀ as a strain stress at 200% elongation in a tensile test under the conditions of 25° C. and a tensile speed of 300 mm/min, and a ratio (F/S ₂₀₀ ) of the adhesive force F to the strain stress S ₂₀₀ is 0.3 or more. The adhesive force f ₁ is an adhesive force measured by a peeling test (first 180° peeling test) in which the adhesive sheet 10 is peeled off 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 bonded to the polyimide adherend. Adhesive force _f2 is the adhesive force measured by a peeling test (second 180° peeling test) in which the adhesive sheet 10 is peeled off from the polyimide adherend at 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. Adhesive force _f3 is the adhesive force measured by a peeling test (third 180° peeling test) in which the adhesive sheet 10 is peeled off from the polyimide adherend at 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. Adhesive force F is the adhesive force acting on the adherend in a state where the adhesive sheet 10 is continuously attached to the adherend without relative displacement, and is one of the indicators representing adhesive properties. The methods for measuring adhesive forces _f1 , _f2 , and _f3 and the method for deriving adhesive force F are specifically described in the following examples. The method for measuring the strain stress S ₂₀₀ and the strain stress S ₃₀₀ and S ₅₀₀ described later is specifically described in the examples described later.

As described above, the ratio (F/S ₂₀₀ ) of the adhesive force F to the strain stress S ₂₀₀ of the adhesive sheet 10 is greater than 0.3. Such a configuration is suitable for resisting the internal stress such as the tensile stress generated by the adhesive sheet 10 when the adherend to which the adhesive sheet 10 is attached is deformed, so that the adhesive sheet 10 is continuously attached to the adherend, and therefore, it is suitable for suppressing the peeling of the adhesive sheet 10 from the adherend. Such an adhesive sheet 10 is suitable for flexible device applications.

From the viewpoint of suppressing the above-mentioned peeling, the ratio (F/S ₂₀₀ ) is preferably 0.4 or more, more preferably 0.5 or more, further preferably 0.6 or more, further preferably 0.7 or more, and particularly preferably 0.8 or more. The ratio (F/S ₂₀₀ ) is, for example, 5 or less, 3 or less, 2 or less, or 1 or less.

From the viewpoint of suppressing the above-mentioned peeling, the ratio (F/S 500 ) of the adhesive force F (N/10 mm) of the adhesive sheet 10 to the strain stress S ₅₀₀ (N/cm ² ) at 500% elongation in a tensile test (25° C., tensile speed 300 mm/min) is preferably 0.2 or more, more preferably 0.3 or more, further preferably 0.4 or more, and particularly preferably 0.5 or more. The ratio (F/S ₅₀₀ ) is _, for example, 5 or less, 3 or less, 2 or less, 1 or less, or 0.8 or less.

From the viewpoint of ensuring the strong adhesion of the adhesive sheet 10 and suppressing the above-mentioned peeling, the adhesive force F is preferably 1N/10mm or more, more preferably 1.5N/10mm or more, further preferably 1.8N/10mm or more, further preferably 2N/10mm or more, further preferably 2.2N/10mm or more, further preferably 2.4N/10mm or more, and particularly preferably 2.6N/10mm or more. The adhesive force F is, for example, 10N/10mm or less. As a method for adjusting the adhesive force F, for example, the selection of the type of the base polymer in the adhesive sheet 10, the adjustment of the molecular weight, and the adjustment of the blending amount can be listed. The selection of the type of the base polymer includes the adjustment of the monomer composition forming the base polymer. As a method for adjusting the adhesive force F, the selection of the type of the component other than the base polymer in the adhesive sheet 10 and the adjustment of the blending amount of the component can also be listed. As the component, a crosslinking agent, a silane coupling agent, and an oligomer can be listed. The above-mentioned adhesive force adjustment method is also the same for the adhesive force described later.

From the viewpoint of ensuring strong adhesion of the pressure-sensitive adhesive sheet 10 and suppressing the above-mentioned peeling, the pressure-sensitive adhesive force _f1 is preferably 2.5 N/10 mm or more, more preferably 3 N/10 mm or more, further preferably 3.5 N/10 mm or more, further preferably 4 N/10 mm or more, and particularly preferably 4.5 N/10 ^cm2 or more. The pressure-sensitive 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-mentioned peeling, the adhesive force _f2 is preferably 2 N/10 mm or more, more preferably 2.5 N/10 mm or more, further preferably 3 N/10 mm or more, further preferably 3.5 N/10 mm or more, and particularly preferably 3.7 N/10 ^cm2 or more. The adhesive force _f2 is, for example, 15 N/10 mm or less.

From the viewpoint of ensuring the 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, further preferably 2 N/10 mm or more, further preferably 2.5 N/10 mm or more, and particularly preferably 2.6 N/10 ^cm2 or more. The adhesive force _f3 is, for example, 12 N/10 mm or less.

From the viewpoint of suppressing the stress generated when the adhesive sheet 10 is deformed and suppressing the above-mentioned peeling, the strain stress _S200 at 200% elongation is preferably 20N/cm2 ^or less, more preferably 10N/cm2 ^or less, further preferably 8N/cm2 or ^less , further preferably 6N/cm2 ^or less, and particularly preferably 5N/cm2 ^or less. The strain stress _S200 is, for example, 1N/ ^cm2 or more. As a method for adjusting the strain stress _S200 , for example, adjustment of the monomer composition of the base polymer in the adhesive sheet 10, adjustment of the molecular weight, adjustment of the compounding amount, and adjustment of the crosslinking degree can be cited. Such a strain stress adjustment method is also the same for the strain stress _S300 and _S500 described later.

From the viewpoint of suppressing the stress generated when the adhesive sheet 10 is deformed and suppressing the above-mentioned peeling, the strain stress _S300 at 300% elongation in the above-mentioned tensile test is preferably 20N/cm2 ^or less, more preferably 17N/cm2 ^or less, further preferably 14N/cm2 ^or less, further preferably 12N/cm2 ^or less, further preferably 10N/cm2 ^or less, and particularly preferably 8N/cm2 ^or less. The strain stress _S300 is, for example, 1N/cm2 ^or more.

From the viewpoint of suppressing the difference in stress generated due to the degree of deformation of the adhesive sheet 10, the ratio of the strain stress _S300 to the strain stress _S200 ( _S300 / _S200 ) is preferably 2 or less, more preferably 1.8 or less, further preferably 1.6 or less, and particularly preferably 1.4 or less. The ratio ( _S300 / _S200 ) is, for example, 1 or more.

From the viewpoint of suppressing the stress generated when the adhesive sheet 10 is deformed and suppressing the above-mentioned peeling, the strain stress _S500 at 500% elongation in the above-mentioned tensile test is preferably 30N/cm2 ^or less, more preferably 25N/cm2 ^or less, further preferably 20N/cm2 ^or less, further preferably 15N/cm2 ^or less, further preferably 12N/cm2 ^or less, and particularly preferably 11N/cm2 ^or less. The strain stress _S500 is, for example, 1N/ ^cm2 or more.

From the viewpoint of suppressing the difference in stress generated due to the degree of deformation of the pressure-sensitive adhesive sheet 10, the ratio of the strain stress _S500 to the strain stress _S200 ( _S500 / _S200 ) is preferably 3 or less, more preferably 2.5 or less, further preferably 2.2 or less, and particularly preferably 2 or less. The ratio ( _S500 / _S200 ) is, for example, 1 or more.

The pressure-sensitive adhesive sheet 10 is a sheet-shaped pressure-sensitive adhesive formed of a pressure-sensitive 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 exhibits adhesiveness in the adhesive sheet 10. As the base polymer, 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 can be cited. The base polymer can be used alone or in combination of two or more. From the viewpoint of ensuring good transparency and adhesiveness of the adhesive sheet 10, as the base polymer, an acrylic polymer is preferably used.

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

As the (meth)acrylate, an alkyl (meth)acrylate is preferably used, and more preferably an alkyl (meth)acrylate having an alkyl group with a carbon number of 1 to 20. The alkyl (meth)acrylate 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, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, n-hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, and tert-butyl (meth)acrylate. Nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (i.e., 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.

As the (meth) alkyl acrylate having an alicyclic alkyl group, for example, cycloalkyl (meth) acrylate, (meth) acrylate having a bicyclic aliphatic hydrocarbon ring, and (meth) acrylate having a tricyclic aliphatic hydrocarbon ring. As the cycloalkyl (meth) acrylate, for example, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, and cyclooctyl (meth) acrylate can be listed. As the (meth) acrylate having a bicyclic aliphatic hydrocarbon ring, for example, isobornyl (meth) acrylate can be listed. As the (meth) acrylate having a tricyclic aliphatic hydrocarbon ring, for example, dicyclopentyl (meth) acrylate, dicyclopentyloxyethyl (meth) acrylate, tricyclopentyl (meth) acrylate, 1-adamantyl (meth) acrylate, 2-methyl-2-adamantyl (meth) acrylate, and 2-ethyl-2-adamantyl (meth) acrylate can be listed.

As the alkyl (meth)acrylate, from the viewpoint of achieving a balance between softness and adhesive strength required for an adhesive sheet for use in flexible devices in the adhesive sheet 10, it is preferred to use at least one selected from alkyl (meth)acrylates having an alkyl group with 3 to 12 carbon atoms, more preferably a first alkyl (meth)acrylate having a relatively large alkyl group carbon number and a second alkyl (meth)acrylate having a relatively small alkyl group carbon number selected from alkyl (meth)acrylates having an alkyl group with 3 to 12 carbon atoms are used in combination, further preferably an alkyl (meth)acrylate having an alkyl group with 6 to 8 carbon atoms and an alkyl (meth)acrylate having an alkyl group with 5 or less carbon atoms are used in combination, and particularly preferably an alkyl (meth)acrylate having a linear alkyl group with 6 to 8 carbon atoms and an alkyl (meth)acrylate having an alkyl group with 5 or less carbon atoms are used in combination.

From the viewpoint of making the adhesive sheet 10 appropriately exhibit basic properties such as adhesiveness, the proportion of the (meth) alkyl acrylate in the monomer component is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 90% by mass or more, and particularly preferably 92% by mass or more. This proportion is, for example, 99% by mass or less. In the case of using the first and second (meth) alkyl acrylates in combination, from the viewpoint of the balance between the softness and adhesive force of the adhesive sheet 10, the proportion of the first (meth) alkyl acrylate in the monomer component is preferably 40% by mass or more, more preferably 50% by mass or more, further preferably 55% by mass or more, and particularly preferably 58% by mass or more, and preferably 80% by mass or less, more preferably 70% by mass or less, further preferably 65% by mass or less, and particularly preferably 62% by mass or less. From the viewpoint of the balance between the softness and the adhesive force of the adhesive sheet 10, the proportion of the second alkyl (meth)acrylate in the monomer component is preferably 20% by mass or more, more preferably 25% by mass or more, and further preferably 28% by mass or more, and is preferably 40% by mass or less, more preferably 35% by mass or less, and further preferably 32% by mass or less.

The monomer component may also contain a copolymerizable monomer copolymerizable with the (meth) alkyl acrylate. Examples of the copolymerizable monomer include monomers having polar groups. Examples of the polar group-containing monomer include hydroxyl-containing monomers, carboxyl-containing monomers, and monomers having nitrogen atom-containing rings. The polar group-containing monomer contributes to the modification of the acrylic polymer, such as the introduction of crosslinking points into the acrylic polymer and the securing of the cohesive force of the acrylic polymer.

Examples of the hydroxyl group-containing monomer 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 hydroxyl-containing monomer in the monomer component is preferably 1% by mass or more, more preferably 3% by mass or more, further preferably 5% by mass or more, and particularly preferably 7% by mass or more, from the viewpoint of introduction of the cross-linked structure into the acrylic polymer and ensuring the cohesive force of the adhesive sheet 10. The 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 the compatibility of various additive components in the adhesive sheet 10 and the acrylic polymer).

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.

From the viewpoint of introduction of the crosslinked structure into the acrylic polymer, ensuring the cohesive force of the adhesive sheet 10, and ensuring the adhesion of the adhesive sheet 10 to the adherend, the proportion of the carboxyl group-containing monomer in the monomer component is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and further preferably 0.8% by mass or more. From the viewpoint of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend caused by acid, the proportion is preferably 10% by mass or less, and more preferably 5% by mass or less.

Examples of the monomer 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-(methyl)acryloyl-2-pyrrolidone, N-(methyl)acryloylpiperidine, N-(methyl)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.

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

The monomer component may also contain other copolymerizable monomers. As other copolymerizable monomers, for example, 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 may be listed. These other copolymerizable monomers may be used alone or in combination of two or more.

From the perspective of both ensuring the adhesive force of the adhesive sheet 10 and suppressing the stress generated during deformation, the monomer component preferably includes a first (meth) alkyl ester (the carbon number of the alkyl group is relatively large), a second (meth) alkyl ester (the carbon number of the alkyl group is relatively small), a hydroxyl-containing monomer, and a monomer having a nitrogen atom ring. The first (meth) alkyl ester is more preferably an alkyl (meth) acrylate having an alkyl group with a carbon number of 6 to 8, and is further preferably an alkyl (meth) acrylate having a linear alkyl group with a carbon number of 6 to 8, and is particularly preferably at least one selected from the group consisting of n-butyl acrylate (NOAA) and n-hexyl acrylate (HxA). The second (meth) alkyl ester is more preferably an alkyl (meth) acrylate having an alkyl group with a carbon number of 5 or less, and is further preferably n-butyl acrylate (BA). The hydroxyl-containing monomer is more preferably at least one selected from the group consisting of 4-hydroxybutyl acrylate (4HBA) and 2-hydroxyethyl acrylate (2HEA). From the viewpoint of designing the elastic modulus of the pressure-sensitive adhesive sheet 10 to be high at room temperature to high temperatures, the monomer having a nitrogen atom-containing ring is more preferably N-vinyl-2-pyrrolidone (NVP).

The base polymer preferably has a cross-linked structure. As a method for introducing a cross-linked structure into the base polymer, the following methods can be cited: a method of mixing a base polymer having a functional group that can react with a cross-linking agent and a cross-linking agent into an adhesive composition, and reacting the base polymer and the cross-linking agent in an adhesive sheet (the first method); and a method of including a multifunctional monomer as a cross-linking agent in the monomer component used to form the base polymer, and forming a base polymer having a branched structure (cross-linked structure) introduced into the polymer chain through polymerization of the monomer component (the second method). These methods can also be used in combination.

As the cross-linking agent used in the above-mentioned first method, for example, compounds reacting with the functional groups (hydroxyl and carboxyl etc.) contained in the base polymer can be listed. As such a cross-linking agent, for example, isocyanate cross-linking agents, peroxide cross-linking agents, epoxy cross-linking agents, oxazoline cross-linking agents, aziridine cross-linking agents, carbodiimide cross-linking agents, and metal chelate cross-linking agents can be listed. The cross-linking agent can be used alone or in combination of two or more. As a cross-linking agent, due to the high reactivity with the hydroxyl and carboxyl in the base polymer and the cross-linked structure is easily introduced, therefore preferably isocyanate cross-linking agents, peroxide cross-linking agents, and epoxy cross-linking agents are used.

As the isocyanate crosslinking agent, for example, toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate can be listed. In addition, as the isocyanate crosslinking agent, derivatives of these isocyanates can also be listed. As the isocyanate derivative, for example, isocyanurate modified bodies and polyol modified bodies can be listed. Examples of commercially available isocyanate crosslinking agents include Coronate L (trimethylolpropane adduct of toluene diisocyanate, manufactured by Tosoh), Coronate HL (trimethylolpropane adduct of hexamethylene diisocyanate, manufactured by Tosoh), Coronate HX (isocyanurate of hexamethylene diisocyanate, manufactured by Tosoh), Takenate 110N (trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals), and Takenate 600 (1,3-bis(isocyanatomethyl)cyclohexane, manufactured by Mitsui Chemicals).

Examples of the peroxide crosslinking agent include dibenzoyl peroxide, bis(2-ethylhexyl) peroxydicarbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, di-sec-butyl peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-hexyl peroxypivalate, and tert-butyl peroxypivalate.

Examples of the epoxy crosslinking agent include bisphenol A, epichlorohydrin-type epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl meta-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

Isocyanate crosslinking agents (particularly difunctional isocyanate crosslinking agents) and peroxide crosslinking agents are preferred from the viewpoint of ensuring the flexibility of the adhesive sheet 10. Isocyanate crosslinking agents (particularly trifunctional isocyanate crosslinking agents) are preferred from the viewpoint of ensuring the durability of the adhesive sheet 10. In the base polymer, difunctional isocyanate crosslinking agents and peroxide crosslinking agents form softer two-dimensional crosslinking, while trifunctional isocyanate crosslinking agents form stronger three-dimensional crosslinking. From the viewpoint of taking into account the durability and flexibility of the adhesive sheet 10, it is preferred to use a trifunctional isocyanate crosslinking agent in combination with a peroxide crosslinking agent and/or a difunctional isocyanate crosslinking agent.

From the viewpoint of ensuring the cohesive force of the adhesive sheet 10, the amount of the crosslinking agent blended is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.07 parts by mass or more, relative to 100 parts by mass of the base polymer. From the viewpoint of ensuring good adhesion of the adhesive sheet 10, the amount of the crosslinking agent blended 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, relative to 100 parts by mass of the base polymer.

In the second method, the monomer components (including the multifunctional monomer and other monomers for introducing the crosslinking structure) can be polymerized at once or in multiple stages. In the multistage polymerization method, first, the monofunctional monomer for forming the base polymer is polymerized (prepolymerization) to prepare a prepolymer composition containing a partial polymer (a mixture of a polymer with a low degree of polymerization and unreacted monomers). Next, after adding a multifunctional monomer as a crosslinking agent to the prepolymer composition, the partial polymer and the multifunctional monomer are polymerized (main polymerization).

Examples of the polyfunctional monomer include polyfunctional (meth)acrylates having two or more ethylenically unsaturated double bonds in one molecule. Polyfunctional acrylates are preferred because they can introduce a crosslinked structure by active energy ray polymerization (photopolymerization).

Examples of the polyfunctional (meth)acrylate include difunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional or higher polyfunctional (meth)acrylates.

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

As a trifunctional (meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate are mentioned, for example.

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

As the polyfunctional (meth)acrylate, it is preferred to use a tetrafunctional or higher-functional (meth)acrylate, and it is more preferred to use dipentaerythritol hexaacrylate.

From the viewpoint of ensuring the cohesive force of the adhesive sheet 10, the amount of the multifunctional monomer as a crosslinking agent in the monomer component is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.07 parts by mass or more, relative to 100 parts by mass of the monofunctional monomer. From the viewpoint of ensuring good adhesion of the adhesive sheet 10, the amount of the multifunctional monomer 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, relative to 100 parts by mass of the monofunctional monomer.

The acrylic polymer can be formed by polymerizing the above-mentioned monomer components. As the polymerization method, for example, solution polymerization, photopolymerization (for example, UV polymerization) under a solvent-free state, bulk polymerization, and emulsion polymerization can be listed. As the solvent for solution polymerization, for example, ethyl acetate and toluene are used. In addition, as the initiator for polymerization, for example, a thermal polymerization initiator and a photopolymerization initiator are used. The amount of the polymerization initiator used is, for example, 0.05 mass parts or more, preferably 0.08 mass parts or more, and, for example, 1 mass part or less, preferably 0.5 mass part or less, relative to 100 mass parts of the monomer components.

As thermal polymerization initiators, for example, azo polymerization initiators and peroxide polymerization initiators can be listed. As azo polymerization initiators, for example, 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid) dimethyl ester, 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'-dimethyleneisobutylamidine) dihydrochloride can be listed. As peroxide polymerization initiators, for example, dibenzoyl peroxide, tert-butyl peroxymaleate, and lauroyl peroxide can be listed.

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, benzyl photopolymerization initiators, benzophenone photopolymerization initiators, ketal photopolymerization initiators, thioxanthone photopolymerization initiators, and acylphosphine oxide 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 ensuring the cohesive force of the pressure-sensitive 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 further preferably -20° C. or lower. The glass transition temperature is, for example, -80° C. or higher.

For 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 formula is a relationship between the glass transition temperature Tg of a polymer and the glass transition temperature Tgi of a homopolymer of a monomer constituting the polymer. In the following Fox formula, 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 temperature (°C) of the homopolymer formed by monomer i. For the glass transition temperature of a homopolymer, a literature value can be used. For example, the glass transition temperatures of various homopolymers are listed in "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) and "New Polymer Library 7 Introduction to Synthetic Resins for Coatings" (written by Kyozo Kitaoka, Polymer Publishing Association, 1995). On the other hand, the glass transition temperature of a homopolymer of a monomer can also be obtained by the method specifically described in Japanese Patent Publication No. 2007-51271.

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

The adhesive composition may also contain a silane coupling agent. The content of the silane coupling agent in the 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 adhesive composition may also contain other components as required. As other components, for example, solvents, tackifiers, plasticizers, softeners, antioxidants, fillers, colorants, ultraviolet absorbers, antioxidants, surfactants, and antistatic agents can be listed. As solvents, for example, polymerization solvents used as required during the polymerization of acrylic polymers and solvents added to the polymerization reaction solution after polymerization can be listed. As the solvent, for example, ethyl acetate and toluene are used.

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

As the release liner L1, for example, a flexible plastic film can be cited. As the plastic film, for example, a polyethylene terephthalate film, a polyethylene film, a polypropylene film, and a polyester film can be cited. The thickness of the release liner L1 is, for example, not less than 3 μm, and, for example, not more than 200 μm. The surface of the release liner L1 is preferably subjected to a release treatment.

Examples of the coating method of the adhesive composition include roll coating, kiss roll coating, gravure coating, reverse coating, roller brushing, spray coating, dip roll coating, rod coating, blade 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. The drying time is, for example, 5 seconds to 20 minutes.

A release liner L2 (second release liner) may be further laminated on the pressure-sensitive adhesive sheet 10 on the release liner L1. The release liner L2 is preferably a flexible plastic film with a release-treated surface. The plastic films described above with respect to the release liner L1 can be used as the release liner L2.

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

From the perspective of ensuring sufficient adhesion to the adherend and handling properties, the thickness of the adhesive sheet 10 is preferably 10 μm or more, more preferably 15 μm or more. From the perspective of thinning flexible devices, the thickness of the adhesive sheet 10 is preferably 300 μm or less, more preferably 200 μm or less, further preferably 100 μm or less, and particularly preferably 50 μm or less.

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 based on JIS K7136 (2000). Examples of the haze meter include "NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. and "HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd.

The total light transmittance of the adhesive sheet 10 is preferably 60% or more, more preferably 80% or more, and even 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 in accordance with JIS K 7375 (2008).

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

In this method, first, as shown in A of FIG. 2 , an adhesive sheet 10 is attached to one side of the thickness direction H of the first member 21 (adherend). The first member 21 is, for example, an element in the laminated structure of a flexible display panel. As such an element, for example, a pixel panel, a film-shaped polarizing film (polarizing film), a touch panel, and a cover film (the same is true for the second member 22 described later) can be cited. In this process, an adhesive sheet 10 for bonding with other members is provided on the first member 21.

2B , one side of the first member 21 in the thickness direction H is bonded to the other side of the second member 22 in the thickness direction H via the adhesive sheet 10 on the first member 21. The second member 22 is, for example, another element in the laminated structure of the flexible display panel.

Next, as shown in C of FIG. 2 , the adhesive sheet 10 between the first component 21 and the second component 22 is aged. The bonding force between the adhesive sheet 10 and the components 21 and 22 is improved by the aging. The aging temperature is, for example, 20° C. to 160° C. The aging time is, for example, 1 minute to 21 days. When an autoclave treatment (heating and pressure treatment) is performed as the 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, more than 15 minutes.

In the manufacturing process of the flexible display panel, for example, the adhesive sheet 10 used in the above operation has a ratio (F/S ₂₀₀ ) of adhesive force F to strain stress S ₂₀₀ of 0.3 or more, which is large. Such a structure is suitable for resisting internal stress such as tensile stress generated in the adhesive sheet 10 when the adherend is deformed, so that the adhesive sheet 10 continues to be attached to the adherend, and therefore, is suitable for suppressing the peeling of the adhesive sheet 10 from the adherend.

Example

The present invention is specifically described below with reference to the following embodiments. However, the present invention is not limited to the embodiments. In addition, the specific numerical values of the compounding amount (content), physical property values, parameters, etc. described below can be replaced by the upper limit (defined as the numerical value of "below" or "less than") or the lower limit (defined as the numerical value of "above" or "exceeding") of the compounding amount (content), physical property values, parameters, etc. corresponding to them described in the above-mentioned "Specific Implementation Methods".

[Example 1]

<Preparation of prepolymer composition>

In a flask, 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name "Omnirad651", manufactured by IGM Resins) as a first photopolymerization initiator and 0.05 parts by mass of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad184", manufactured by IGM Resins) as a second photopolymerization initiator were added to a monomer mixture containing 60 parts by mass of n-octyl acrylate (NOAA), 30 parts by mass of n-butyl acrylate (BA), 8 parts by mass of 4-hydroxybutyl acrylate (4HBA) and 2 parts by mass of N-vinyl-2-pyrrolidone (NVP). The mixture was then irradiated with ultraviolet rays in a nitrogen atmosphere to polymerize a portion of the monomer components in the mixture, thereby obtaining a first prepolymer composition (containing monomer components that have not yet been polymerized) having 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 crosslinking agent, 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name "Omnirad651", manufactured by IGM Resins) as a photopolymerization initiator, and 0.3 parts by mass of a silane coupling agent (trade name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed to obtain a first adhesive composition.

<Formation of Adhesive Layer>

The first adhesive composition was applied to the release-treated surface of the first release liner (trade name "Diafol MRF#38", thickness 38 μm, manufactured by Mitsubishi Chemical Corporation) having a release-treated surface on one side to form a coating film. Next, the release-treated surface of the second release liner (trade name "Diafol MRN#38", thickness 38 μm, manufactured by Mitsubishi Chemical Corporation) having a release-treated surface on one side was attached to the coating film on the first release liner. Then, the coating film between the release liners was irradiated with ultraviolet rays to photocure the coating film to form an adhesive layer (thickness 50 μm). In the ultraviolet irradiation, a black light lamp was used as the irradiation light source, and the irradiation intensity was set to 5 mW/cm ² .

As described above, a PSA sheet (thickness 50 μm) with release liners on both sides of Example 1 was prepared. The composition of the PSA sheet of Example 1 is shown in parts by mass in Table 1 (the same applies to Examples and Comparative Examples described below).

[Example 2]

In the preparation of the pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet of Example 2 was produced in the same manner as in the pressure-sensitive adhesive sheet of Example 1, except that the amount of the photopolymerization initiator added was changed from 0.05 parts by mass to 0.1 parts by mass.

[Example 3]

In the preparation of the pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet of Example 3 was prepared in the same manner as in Example 1, except that the amount of the crosslinking agent was changed from 0.08 parts by mass to 0.04 parts by mass and no photopolymerization initiator was added.

[Example 4]

A pressure-sensitive adhesive sheet of Example 4 was produced in the same manner as in Example 1, except that a photopolymerization initiator was not blended in the preparation of the pressure-sensitive adhesive composition.

[Example 5]

The adhesive sheet of Example 5 was prepared in the same manner as the adhesive sheet of Example 1 except for the following contents. In the preparation of the prepolymer composition, the blending amount of the first photopolymerization initiator (trade name "Omnirad 651") was replaced from 0.05 mass parts to 0.035 mass parts, and the blending amount of the second photopolymerization initiator (trade name "Omnirad 184") was replaced from 0.05 mass parts to 0.035 mass parts. In the preparation of the adhesive composition, the blending amount of the crosslinking agent was replaced from 0.08 mass parts to 0.02 mass parts, and no photopolymerization initiator was added.

[Example 6]

The adhesive sheet of Example 6 was prepared in the same manner as the adhesive sheet of Example 1 except for the following contents. In the preparation of the prepolymer composition, the blending amount of the first photopolymerization initiator (trade name "Omnirad 651") was replaced from 0.05 mass parts to 0.07 mass parts, and the blending amount of the second photopolymerization initiator (trade name "Omnirad 184") was replaced from 0.05 mass parts to 0.07 mass parts. In the preparation of the adhesive composition, the blending amount of the crosslinking agent was replaced from 0.08 mass parts to 0.04 mass parts, and no photopolymerization initiator was added.

[Example 7]

<Preparation of prepolymer composition>

In a flask, 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name "Omnirad651", manufactured by IGM Resins) as a first photopolymerization initiator and 0.05 parts by mass of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad184", manufactured by IGM Resins) as a second photopolymerization initiator were added to a monomer mixture containing 80 parts by mass of n-hexyl acrylate (HxA), 10 parts by mass of n-butyl acrylate (BA), 8 parts by mass of 4-hydroxybutyl acrylate (4HBA) and 2 parts by mass of N-vinyl-2-pyrrolidone (NVP). The mixture was irradiated with ultraviolet rays in a nitrogen atmosphere to polymerize a part of the monomer components in the mixture, thereby obtaining a second prepolymer composition with a polymerization rate of about 10%.

<Preparation of Adhesive Composition>

100 parts by mass of the second prepolymer composition, 0.07 parts by mass of dipentaerythritol hexaacrylate (DPHA) as a crosslinking agent, 0.1 parts by mass of 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name "Omnirad651", manufactured by IGM Resins) as a photopolymerization initiator, and 0.3 parts by mass of a silane coupling agent (trade name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed to obtain a second adhesive composition.

<Formation of Adhesive Layer>

A PSA layer (thickness 50 μm) sandwiched between the first and second release liners was formed in the same manner as in Example 1 except that the second PSA composition was used instead of the first PSA composition.

As described above, a pressure-sensitive adhesive sheet (thickness 50 μm) of Example 7 having release liners on both sides was prepared.

[Example 8]

In the preparation of the pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet of Example 8 was produced in the same manner as in the pressure-sensitive adhesive sheet of Example 7, except that the amount of the photopolymerization initiator added was changed from 0.1 parts by mass to 0.05 parts by mass.

[Example 9]

A pressure-sensitive adhesive sheet of Example 9 was produced in the same manner as in Example 7, except that a photopolymerization initiator was not blended in the preparation of the pressure-sensitive adhesive composition.

[Comparative Example 1]

<Preparation of prepolymer composition>

In a flask, 0.035 parts by mass of a first photopolymerization initiator (trade name "Omnirad 651", manufactured by IGM Resins) and 0.035 parts by mass of a second photopolymerization initiator (trade name "Omnirad 184", manufactured by IGM Resins) were added to a monomer mixture containing 78 parts by mass of 2-ethylhexyl acrylate (2EHA), 18 parts by mass of N-vinyl-2-pyrrolidone (NVP) and 4 parts by mass of 2-hydroxyethyl acrylate (2HEA). The mixture was then irradiated with ultraviolet rays under a nitrogen atmosphere to polymerize a portion of the monomer components in the mixture, thereby obtaining a third prepolymer composition having 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 crosslinking agent, and 0.353 parts by mass of a silane coupling agent (trade name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed to obtain a third adhesive composition.

<Formation of Adhesive Layer>

A PSA layer (thickness 50 μm) sandwiched between the first and second release liners was formed in the same manner as in Example 1 (including ultraviolet irradiation), except that the third PSA composition was used instead of the first PSA composition.

As described above, a pressure-sensitive adhesive sheet (thickness 50 μm) of Comparative Example 1 having release liners on both sides was prepared.

<180° peel test>

The adhesive strength of each of the PSA sheets of Examples 1 to 9 and Comparative Example 1 to an adherend was examined by a 180° peel test.

Specifically, first, a necessary number of test specimens are prepared for each adhesive sheet. In the preparation of the test specimen, first, the first release liner is peeled off from the adhesive sheet, and the exposed surface thus exposed is bonded to a polyethylene terephthalate (PET) film (trade name "lumirror S10", thickness 50 μm, manufactured by Toray) whose surface has been plasma-treated to obtain a laminate. In the plasma treatment, a plasma irradiation device (trade name "AP-TO5", manufactured by Sekisui Industries) is used, and the voltage is set to 160 V, the frequency is set to 10 kHz, and the processing speed is set to 5000 mm/minute (the same is true in the plasma treatment described later). Next, a test piece (width 10 mm × length 100 mm) is cut out from the laminate (PET film/adhesive sheet/second release liner). Next, the second release liner was peeled off from the adhesive sheet in the test piece, and the exposed surface was bonded to a polyimide (PI) film (trade name "GV200", thickness 80 μm, manufactured by KOLON) with a plasma-treated surface. Then, the PI film with the adhesive sheet (test piece) was subjected to a heating and pressure treatment at a temperature of 50°C and a pressure of 0.5 MPa for 15 minutes. Thus, the test piece was pressed against the PI film. As above, a sample for measurement was prepared.

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

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

Then, as exemplarily shown by the straight line (solid line) in the graph of FIG3 for the PSA sheet of Example 1, the adhesive force F (N/10 mm) at a tensile speed of 0 was obtained by the extrapolation method based on the adhesive forces f ₁ , f ₂ , and f _3. Specifically, a regression line (straight line) was obtained by the least square method from the x-coordinates and y-coordinates of the three plotted points (white plotted points in the graph of FIG3 ) regarding the adhesive forces f ₁ to f ₃ , and the adhesive force F at a tensile speed of 0 was obtained by the extrapolation method using the straight line. The values are shown in Table 1. In the graph of FIG3 , the horizontal axis represents the tensile speed (mm/min) in the 180° peel test, and the vertical axis represents the adhesive force (N/10 mm).

On the other hand, the adherend in the process of making the measuring sample was replaced with a polarizing film (thickness 51 μm, manufactured by Nitto Denko Corporation), and a 180° peel test was performed under the same conditions as the first 180° peel test. The results of its measurement are shown in Table 1 as the adhesive force _f'1 (N/10mm) at a tensile speed of 300 mm/minute. The adherend in the process of making the measuring sample was replaced with the above-mentioned polarizing film, and a 180° peel test was performed under the same conditions as the second 180° peel test. The results of its measurement are shown in Table 1 as the adhesive force _f'2 (N/10mm) at a tensile speed of 100 mm/minute. In addition, the adherend in the process of making the measuring sample was replaced with the above-mentioned polarizing film, and a 180° peel test was performed under the same conditions as the third 180° peel test. The results of its measurement are shown in Table 1 as the adhesive force _f'3 (N/10mm) at a tensile speed of 10 mm/minute. Then, as exemplarily shown by the straight line (dashed line) in the graph of FIG3 for the PSA sheet of Example 1, the adhesive force F' (N/10 mm) at a tensile speed of 0 was obtained by the extrapolation method based on the adhesive forces f' ₁ , f' ₂ , and f' _3. Specifically, a regression line (straight line) was obtained by the least square method from the x-coordinates and y-coordinates of the three plotted points (solid black plotted points in the graph of FIG3 ) regarding the adhesive forces f' ₁ to f' ₃ , and the adhesive force F' at a tensile speed of 0 was obtained by the extrapolation method using the straight line. The values are shown in Table 1.

〈Tensile test〉

For each of the PSA sheets of Examples 1 to 9 and Comparative Example 1, strain stress generated in a tensile test was examined.

Specifically, first, a necessary number of test specimens are made for each adhesive sheet. In the production of the test specimen, first, a small piece of adhesive sheet (width 30mm × length 100mm) with a release liner on both sides is cut out from the adhesive sheet with a release liner on both sides. Then, after peeling off a release liner from the small piece of adhesive sheet, the small piece of adhesive sheet is wound along the length direction on another release liner in a manner that does not enter bubbles to form a cylindrical shape (cylinder height 30mm). Thus, a cylindrical adhesive sheet small piece as a test specimen is obtained. Then, for the test specimen, under an environment of 25°C and a relative humidity of 50%, a tensile tester (trade name "Autograph AG-50NX plus", manufactured by Shimadzu Corporation) of the Tensilon type is used to perform a tensile test to measure the tensile stress generated during the stretching process. Thus, a stress-strain curve (load-elongation curve) is obtained. In this tensile test, the initial distance between the clamps was set to 10 mm, the test sample (cylindrical PSA sheet piece) was stretched in the height direction of the cylinder, and the stretching speed was set to 300 mm/min. The strain stress _S200 (N/ ^cm2 ) at 200% elongation, the strain stress _S300 (N/ ^cm2 ) at 300% elongation, and the strain stress _S500 (N/ ^cm2 ) at 500% elongation in such a tensile test are shown in Table 1. In addition, the ratio of the strain stress _S300 to the strain stress _S200 , and the ratio of the strain stress _S500 to the strain stress _S200 are also shown in Table 1.

〈Bend retention test〉

For each of the PSA sheets of Examples 1 to 9 and Comparative Example 1, a bending retention test was performed as follows.

First, the second release liner is peeled off from the adhesive sheet with release liner on both sides, and the exposed surface thus exposed is subjected to plasma treatment. On the other hand, both sides (the first side, the second side) of the polarizing film with a thickness of 51 μm are also subjected to plasma treatment. In addition, the surface of the transparent polyimide film with a thickness of 80 μm and the surface of the polyethylene terephthalate (PET) film with a thickness of 125 μm are also subjected to plasma treatment. In each plasma treatment, a plasma irradiation device (trade name "AP-TO5", manufactured by Sekisui Industries) is used, and the voltage is set to 160V, the frequency is set to 10kHz, and the processing speed is set to 5000mm/minute. Then, the above-mentioned exposed surface of the adhesive sheet is bonded to the first side of the polarizing film. In this bonding, under an environment of 23°C, the adhesive sheet with the first release liner is crimped to the polarizing film by making a 2kg roller go back and forth once. Then, the first release liner is peeled off from the adhesive sheet with polarizing film, and then the above-mentioned transparent polyimide film is laminated on the exposed surface of the adhesive sheet thus exposed. Next, the above-mentioned PET film is laminated on the second surface of the polarizing film with the help of a thin adhesive sheet with a thickness of 15 μm. In this lamination, the polarizing film and the PET film are crimped under an environment of 23°C by making a 2kg roller go back and forth once. Thus, a laminated film having a laminated structure 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) is obtained.

Then, 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 laminated film in such a way that the absorption axis of the polarizing film in the cut sample was parallel to the long side direction. Next, the sample was autoclaved at 35°C and 0.50 MPa for 15 minutes.

Next, for this sample, a bending test was performed using a planar unloaded U-shaped telescopic testing machine (manufactured by YUASA SYSTEM Co., Ltd.). In this test, for both ends of the long side direction of the sample, bending jigs were installed at a range of 20 mm from the end edge of the sample, and the sample was fixed to the testing machine (the central 60 mm area in the long side direction of the sample was in an unfixed state). In addition, in this test, in a constant temperature and humidity chamber at a temperature of 60°C and a relative humidity of 95%, the sample was repeatedly deformed (bent) 200,000 times at a bending speed of 60 rpm between the inner curved form and the non-curved form on the surface of the PET film side. Specifically, the curved 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 axial direction of the polarizing film. In this curved form, the bending radius of the sample is set to 1.3 mm and the bending angle is set to 180°. In addition, regarding the adhesion of the adhesive sheet to the adherend in such a bending test, the case where no peeling occurred between the adhesive sheet and its adherend (transparent polyimide film, polarizing film) was evaluated as "not good", and the case where peeling occurred was evaluated as "poor". The evaluation results are shown in Table 1.

[Table 1]

Claims (10)

1. An optical adhesive sheet, which has an adhesive force F (N/10mm) as the adhesive force under the tensile speed 0, and the adhesive force under the tensile speed 0 is obtained as follows: based on the polyamide Adhesion of imine adherends in the first 180° peel test at 25°C and a tensile speed of 300mm/min, the second 180° at 25°C and a tensile speed of 100mm/min The adhesive force in the °peel test and the adhesive force in the third 180° peel test at 25°C and a tensile speed of 10mm/min were obtained by extrapolation, The optical adhesive sheet has a strain stress S ₂₀₀ (N/cm ² ) as a strain stress at 200% elongation in a tensile test at 25° C. and a tensile speed of 300 mm/min, A ratio of the adhesive force F to the strain stress S ₂₀₀ is 0.3 or more. 2. The optical adhesive sheet according to claim 1, wherein the ratio of the adhesive force F to the strain stress S ₅₀₀ (N/cm ² ) at 500% elongation in the tensile test is 0.2 above. 3 . The optical adhesive sheet according to claim 1 , wherein a ratio of the strain stress S ₅₀₀ at 500% elongation in the tensile test to the strain stress S ₂₀₀ is 3 or less. 4 . 4 . The optical adhesive sheet according to claim 2 , wherein a ratio of the strain stress S ₅₀₀ at 500% elongation in the tensile test to the strain stress S ₂₀₀ is 3 or less. 5. The optical adhesive sheet according to claim 1, wherein the adhesive force F is 1 N/10 mm or more. 6. The optical adhesive sheet according to claim 2, wherein the adhesive force F is 1 N/10 mm or more. 7. The optical adhesive sheet according to claim 1, wherein the strain stress S ₂₀₀ is 20 N/cm ² or less. 8 . The optical adhesive sheet according to claim 2 , wherein the strain stress S ₂₀₀ is 20 N/cm ² or less. 9 . The optical adhesive sheet according to claim 3 , wherein the strain stress S ₂₀₀ is 20 N/cm ² or less. 10 . The optical adhesive sheet according to claim 1 , wherein the strain stress S ₅₀₀ at 500% elongation in the tensile test is 30 N/cm ² or less. 11 .

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