Optical adhesive sheet

Abstract

We provide optical adhesive sheets suitable for flexible device applications. [Solution] 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 at a tensile speed of 0, which is determined by extrapolation based on 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. The adhesive sheet 10 has a strain stress S as the strain stress at 200% elongation in a tensile test at 25°C and a tensile speed of 300 mm / min. 200 (N / cm 2 ) has strain stress S 200 The ratio of adhesive strength F to the given value is 0.3 or greater.

Description

Technical Field

[0001] The present invention relates to an optical adhesive sheet.

Background Art

[0002] A display panel has a laminated structure including elements such as a pixel panel, a polarizing plate, a touch panel, and a cover film. In the manufacturing process of such a display panel, an optically transparent adhesive sheet (optical adhesive sheet), for example, is used for joining the elements included in the laminated structure.

[0003] On the other hand, the development of foldable display panels for smartphones and tablet terminals is progressing. A foldable display panel is specifically 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 joining between such elements. An optical adhesive sheet for flexible devices such as a foldable display panel is described in, for example, Patent Document 1 below.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Conventionally, optical adhesive sheets tend to peel off from the adherend at the bending points of foldable display panels. This is because relatively large tensile stresses are locally generated at the bent portion of the optical adhesive sheet when the display panel is bent. At the bent portion of the optical adhesive sheet, the greater the tensile stress on the adherend (for example, in the shear direction), the more likely peeling will occur between the optical adhesive sheet and the adherend. Such peeling can cause malfunctions in the device and is undesirable. Optical adhesive sheets for foldable display panels are required to be highly resistant to peeling from the adherend (adherend) when the display is bent.

[0006] Meanwhile, as a flexible device, development is also progressing on rollable display panels. A rollable display panel can be repeatedly deformed between a wound shape, which is the shape after the whole or a part of it has been wound up, and a flat shape, which is the shape after the whole panel has been unwound. 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 to join these elements. When the rollable display panel is in a wound shape, the optical adhesive sheet joined to the wound element is continuously subjected to tensile stress from that element. Such an optical adhesive sheet is required to be extremely resistant to peeling off from the element (adhered object) when the display is in a wound shape.

[0007] This invention provides an optical adhesive sheet suitable for flexible device applications. [Means for solving the problem]

[0008] The present invention [1] is an optical adhesive sheet having an adhesive force F (N / 10 mm) as the adhesive force at a tensile speed of 0 obtained by extrapolation based on the adhesive force in the first 180° peel test under the conditions of 25°C and a tensile speed of 300 mm / min with respect to a polyimide adherend, the adhesive force in the second 180° peel test under the conditions of 25°C and a tensile speed of 100 mm / min, and the adhesive force in the third 180° peel test under the conditions of 25°C and a tensile speed of 10 mm / min, and having a strain stress S at 200% elongation in a tensile test under the conditions of 25°C and a tensile speed of 300 mm / min. 200 (N / cm 2 ) and includes an optical adhesive sheet in which the ratio of the adhesive force F to the strain stress S is 0.3 or more. 200

[0009] The present invention [2] includes the optical adhesive sheet according to [1] above, in which the ratio of the adhesive force F to the strain stress S at 500% elongation in the tensile test is 0.2 or more. 500 (N / cm 2 )

[0010] The present invention [3] includes the optical adhesive sheet according to [1] or [2] above, in which the ratio of the strain stress S at 500% elongation in the tensile test to the strain stress S is 3 or less. 500 200

[0011] The present invention [4] includes the optical adhesive sheet according to any one of [1] to [3] above, in which the adhesive force F is 1 N / 10 mm or more.

[0012] The present invention [5] is the optical adhesive sheet according to any one of [1] to [4] above, in which the strain stress S is 20 N / cm or less. 200 2

[0013] The present invention [6] includes the optical adhesive sheet according to any one of [1] to [5] above, in which the strain stress S at 500% elongation in the tensile test is 30 N / cm or less. 500 2 ​ [Effects of the Invention]

[0014] In the optical adhesive sheet of the present invention, the strain stress S at 200% elongation in a tensile test (25°C, tensile speed 300 mm / min) is determined by extrapolation based on the three adhesive forces in the first to third 180° peel tests as described above. 200 Ratio to (F / S 200 ) is large, at 0.3 or higher (adhesion force F is the adhesive force that acts on the adherend when the optical adhesive sheet remains attached to the adherend without relative displacement, and is one of the indicators of adhesive properties). Such an optical adhesive sheet is suitable for maintaining adhesion to the adherend against internal stresses such as tensile stress that occur in the adherend when the adherend to which the adhesive sheet is bonded deforms, and therefore is suitable for suppressing peeling of the optical adhesive sheet from the adherend. Such an optical adhesive sheet is suitable for flexible device applications. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic cross-sectional view of one embodiment of the optical adhesive sheet of the present invention. [Figure 2] This shows an example of how to use the optical adhesive sheet of the present invention. Figure 2A shows the step of attaching the optical adhesive sheet to a first adherend, Figure 2B shows the step of joining the first adherend and the second adherend via the optical adhesive sheet, and Figure 2C shows the aging step. [Figure 3] This graph plots the three adhesive strengths measured in the first to third 180° peel tests for the adhesive sheet of Example 1, and the adhesive strength at a tensile speed of 0, which is determined by extrapolation based on these adhesive strengths. [Modes for carrying out the invention]

[0016] As one embodiment of the optical adhesive sheet of the present invention, the adhesive sheet 10 has a sheet shape of a predetermined thickness, as shown in Figure 1, and extends in a direction perpendicular to the thickness direction H (surface direction). 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. Figure 1 illustrates the 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 placed on the adhesive surface 11. The release liner L2 is placed on the adhesive surface 12. The release liners L1 and L2 are peeled off at a predetermined timing when the adhesive sheet 10 is used.

[0017] The adhesive sheet 10 is an optically transparent adhesive sheet placed at the light-transmitting location in a flexible device. Examples of flexible devices include flexible display panels. Examples of flexible display panels include foldable display panels and rollable display panels. A flexible display panel has a laminated structure that includes elements such as a pixel panel, a polarizing plate, a touch panel, and a cover film. The adhesive sheet 10 is used, for example, in the manufacturing process of a flexible display panel to bond elements included in the laminated structure together.

[0018] The adhesive sheet 10 has an adhesive strength F, which is determined by extrapolation based on the adhesive strengths f1, f2, and f3 to the polyimide adherend, and a strain stress S, which is the strain stress at 200% elongation in a tensile test under the conditions of 25°C and a tensile speed of 300 mm / min. 200 It has strain stress S 200 The ratio of adhesive strength F to (F / S) 200The adhesive strength f1 is measured in a peel test (first 180° peel test) in which the adhesive sheet 10 is peeled off the polyimide adherend at 25°C, a peel angle of 180°, and a tensile speed of 300 mm / min after the adhesive sheet 10 has been bonded to the polyimide adherend. The adhesive strength f2 is measured in a peel test (second 180° peel test) in which the adhesive sheet 10 is peeled off the polyimide adherend at 25°C, a peel angle of 180°, and a tensile speed of 100 mm / min after the adhesive sheet 10 has been bonded to the polyimide adherend. The adhesive strength f3 is measured in a peel test (third 180° peel test) in which the adhesive sheet 10 is peeled off the polyimide adherend at 25°C, a peel angle of 180°, and a tensile speed of 10 mm / min after the adhesive sheet 10 has been bonded to the polyimide adherend. The adhesive force F is the adhesive force that acts on the adherend while the adhesive sheet 10 remains attached to the adherend without relative displacement, and is one of the indicators of adhesive properties. The methods for measuring the adhesive forces f1, f2, and f3 and the method for deriving the adhesive force F are described in detail later with respect to the examples. Strain stress S 200 and the strain stress S described below 300 ,S 500 The measurement method is specifically described below with reference to the examples.

[0019] In the adhesive sheet 10, as described above, the strain stress S 200 The ratio of adhesive strength F to (F / S) 200 The ratio is large, at 0.3 or higher. This configuration is suitable for the adhesive sheet 10 to remain attached to the adherend against internal stresses such as tensile stress generated in the adhesive sheet 10 when the adherend to the adherend deforms, and therefore 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.

[0020] Ratio (F / S 200 The ratio (F / S) is preferably 0.4 or higher, more preferably 0.5 or higher, even more preferably 0.6 or higher, even more preferably 0.7 or higher, and particularly preferably 0.8 or higher, from the viewpoint of suppressing the peeling described above.200 For example, 5 or less, 3 or less, 2 or less, or 1 or less.

[0021] Strain stress S at 500% elongation during tensile test (25°C, tensile speed 300 mm / min) of adhesive sheet 10. 500 (N / cm 2 ) Ratio of adhesive strength F (N / 10mm) to (F / S 500 The ratio (F / S) is preferably 0.2 or higher, more preferably 0.3 or higher, even more preferably 0.4 or higher, and particularly preferably 0.5 or higher, from the viewpoint of suppressing the peeling described above. 500 For example, 5 or less, 3 or less, 2 or less, 1 or less, or 0.8 or less.

[0022] From the viewpoint of ensuring strong adhesion of the adhesive sheet 10 and suppressing the peeling described above, the adhesive strength F is preferably 1 N / 10 mm or more, more preferably 1.5 N / 10 mm or more, even more preferably 1.8 N / 10 mm or more, even more preferably 2 N / 10 mm or more, even more preferably 2.2 N / 10 mm or more, even more preferably 2.4 N / 10 mm or more, and particularly preferably 2.6 N / 10 mm or more. The adhesive strength F is, for example, 10 N / 10 mm or less. Methods for adjusting the adhesive strength F include, for example, selecting the type of base polymer in the adhesive sheet 10, adjusting the molecular weight, and adjusting the amount of blending. The selection of the type of base polymer includes adjusting the composition of the monomers that form the base polymer. Methods for adjusting the adhesive strength F also include selecting the type of components other than the base polymer in the adhesive sheet 10 and adjusting the amount of blending of such components. Examples of such components include crosslinking agents, silane coupling agents, and oligomers. The above methods for adjusting the adhesive strength are also applicable to the adhesive strength described later.

[0023] From the viewpoint of ensuring strong adhesion 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, even more preferably 3.5 N / 10 mm or more, even more preferably 4 N / 10 mm or more, and particularly preferably 4.5 N / 10 cm 2That's all. The adhesive strength f1 is, for example, 20 N / 10 mm or less.

[0024] From the viewpoint of ensuring strong adhesion of the adhesive sheet 10 and suppressing the peeling described above, the adhesive force f2 is preferably 2N / 10mm or more, more preferably 2.5N / 10mm or more, even more preferably 3N / 10mm or more, even more preferably 3.5N / 10mm or more, and particularly preferably 3.7N / 10cm 2 That's all. The adhesive strength f2 is, for example, 15 N / 10 mm or less.

[0025] From the viewpoint of ensuring strong adhesion of the adhesive sheet 10 and suppressing the peeling described above, the adhesive force f3 is preferably 1 N / 10 mm or more, more preferably 1.5 N / 10 mm or more, even more preferably 2 N / 10 mm or more, even more preferably 2.5 N / 10 mm or more, and particularly preferably 2.6 N / 10 cm 2 That's all. The adhesive strength f3 is, for example, 12 N / 10 mm or less.

[0026] From the viewpoint of suppressing the stress generated during deformation in the adhesive sheet 10 and thereby suppressing the peeling described above, the strain stress S at 200% elongation is considered. 200 Preferably, the pressure is 20 N / cm². 2 More preferably, 10 N / cm 2 More preferably 8 N / cm 2 Further, 6 N / cm is more preferable. 2 The following is particularly preferred: 5 N / cm 2 The following is the strain stress S. 200 For example, 1 N / cm 2 That concludes the explanation. Strain stress S 200 Methods for adjusting the strain stress 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 crosslinking. Such strain stress adjustment methods are described below as strain stress S 300 ,S 500 The same applies to this matter.

[0027] From the viewpoint of suppressing the stress generated during deformation in the adhesive sheet 10 and thereby suppressing the peeling described above, the strain stress S at 300% elongation in the tensile test described above is...300 Preferably, the pressure is 20 N / cm². 2 More preferably, 17 N / cm 2 More preferably, 14 N / cm 2 Further, a more preferable value is 12 N / cm². 2 More preferably, the following is 10 N / cm 2 The following is particularly preferred: 8 N / cm 2 The following is the strain stress S. 300 For example, 1 N / cm 2 That's all.

[0028] Strain stress S 200 Total strain stress S 300 The ratio (S 300 / S 200 From the viewpoint of suppressing differences in stress generation due to the degree of deformation of the adhesive sheet 10, the value is preferably 2 or less, more preferably 1.8 or less, even more preferably 1.6 or less, and particularly preferably 1.4 or less. Ratio (S 300 / S 200 ) is, for example, 1 or greater.

[0029] From the viewpoint of suppressing the stress generated during deformation in the adhesive sheet 10 and thereby suppressing the peeling described above, the strain stress S at 500% elongation in the tensile test described above is... 500 Preferably, 30 N / cm 2 More preferably, 25 N / cm 2 More preferably, 20 N / cm 2 Further, a more preferable value is 15 N / cm². 2 More preferably, the following is 12 N / cm 2 The following is particularly preferred: 11 N / cm 2 The following is the strain stress S. 300 For example, 1 N / cm 2 That's all.

[0030] Strain stress S 200 Total strain stress S 500 The ratio (S 500 / S 200The ratio (S) is preferably 3 or less, more preferably 2.5 or less, even more preferably 2.2 or less, and particularly preferably 2 or less, from the viewpoint of suppressing differences in stress generation due to the degree of deformation of the adhesive sheet 10. 500 / S 200 ) is, for example, 1 or greater.

[0031] 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.

[0032] The base polymer is an adhesive component that provides tackiness to the adhesive sheet 10. Examples of base polymers include 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 types. From the viewpoint of ensuring good transparency and tackiness in the adhesive sheet 10, an acrylic polymer is preferably used as the base polymer.

[0033] Acrylic polymers are copolymers of monomer components containing (meth)acrylic acid esters in a proportion of 50% by mass or more. "(Meth)acrylic" means acrylic and / or methacrylic.

[0034] Preferably, an alkyl (meth)acrylate ester is used as the (meth)acrylic acid ester, and more preferably, an alkyl (meth)acrylate ester having 1 to 20 carbon atoms in the alkyl group. The alkyl (meth)acrylate ester may have a linear or branched alkyl group, or a cyclic alkyl group such as an alicyclic alkyl group.

[0035] Examples of alkyl (meth)acrylates having linear or branched alkyl groups include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 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 (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, and isooctyl (meth)acrylate. Examples include (meth)acrylate nonyl, (meth)acrylate isononyl, (meth)acrylate decyl, (meth)acrylate isodecyl, (meth)acrylate undecyl, (meth)acrylate dodecyl (i.e., lauryl acrylate), (meth)acrylate isotridecyl, (meth)acrylate tetradecyl, (meth)acrylate isotetradecyl, (meth)acrylate pentadecyl, (meth)acrylate cetyl, (meth)acrylate heptadecyl, (meth)acrylate octadecyl, (meth)acrylate isooctadecyl, and (meth)acrylate nonadecyl.

[0036] Examples of alkyl (meth)acrylates having an alicyclic alkyl group include cycloalkyl (meth)acrylates, (meth)acrylates having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylates having three or more aliphatic hydrocarbon rings. Examples of cycloalkyl (meth)acrylates include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. An example of a (meth)acrylate ester having a bicyclic aliphatic hydrocarbon ring is isobornyl (meth)acrylate. Examples of (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings include 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.

[0037] As for the alkyl (meth)acrylate ester, in the adhesive sheet 10, from the viewpoint of balancing the flexibility and adhesive strength required for adhesive sheets for flexible device applications, preferably at least one selected from alkyl (meth)acrylate esters having an alkyl group with 3 to 12 carbon atoms is used. More preferably, a first alkyl (meth)acrylate ester with a relatively large number of carbon atoms in the alkyl group and a second alkyl (meth)acrylate ester with a relatively small number of carbon atoms in the alkyl group are used in combination, selected from alkyl (meth)acrylate esters having an alkyl group with 3 to 12 carbon atoms. Even more preferably, an alkyl (meth)acrylate ester having an alkyl group with 6 to 8 carbon atoms and an alkyl (meth)acrylate ester having an alkyl group with 5 or fewer carbon atoms are used in combination. Particularly preferably, an alkyl (meth)acrylate ester having a linear alkyl group with 6 to 8 carbon atoms and an alkyl (meth)acrylate ester having an alkyl group with 5 or fewer carbon atoms are used in combination.

[0038] The proportion of alkyl (meth)acrylate in the monomer component is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 92% by mass or more, from the viewpoint of appropriately exhibiting basic properties such as tackiness in the adhesive sheet 10. This proportion is, for example, 99% by mass or less. When the first and second alkyl (meth)acrylates are used in combination, the proportion of the first alkyl (meth)acrylate in the monomer component is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, particularly preferably 58% by mass or more, and also preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 65% ​​by mass or less, and particularly preferably 62% by mass or less, from the viewpoint of balancing the flexibility and tackiness 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, even more preferably 28% by mass or more, and also preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 32% by mass or less, from the viewpoint of balancing the flexibility and adhesive strength of the adhesive sheet 10.

[0039] The monomer component may include copolymerizable monomers that can copolymerize with alkyl (meth)acrylate esters. Examples of copolymerizable monomers include monomers having polar groups. Examples of polar group-containing monomers include monomers containing hydroxyl groups, monomers containing carboxyl groups, and monomers having nitrogen atom-containing rings. Polar group-containing monomers are useful for modifying acrylic polymers, such as introducing crosslinking sites into acrylic polymers and ensuring the cohesive strength of acrylic polymers.

[0040] Examples of monomers containing a hydroxyl group 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.

[0041] The proportion of hydroxyl group-containing monomers in the monomer components is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and particularly preferably 7% by mass or more, from the viewpoint of introducing a crosslinked structure into the acrylic polymer and ensuring cohesive force in the adhesive sheet 10. From the viewpoint of adjusting the polarity of the acrylic polymer (which is related to the compatibility between the various additive components in the adhesive sheet 10 and the acrylic polymer), the proportion is preferably 30% by mass or less, and more preferably 20% by mass or less.

[0042] Examples of monomers containing a carboxyl group include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

[0043] The proportion of carboxyl group-containing monomers in the monomer component is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more, from the viewpoint of introducing a crosslinked structure into the acrylic polymer, ensuring cohesive force in the adhesive sheet 10, and ensuring adhesion force to the adherend in the adhesive sheet 10. The same proportion is preferably 10% by mass or less, more preferably 5% by mass or less, from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend by acid.

[0044] 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-morpholindione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, and N-vinylisothiazole.

[0045] The proportion of monomers having nitrogen atom-containing rings in the monomer components is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 1.5% by mass or more, from the viewpoint of ensuring cohesive force in the adhesive sheet 10 and ensuring adhesion force to the adherend in the adhesive sheet 10. The same proportion is preferably 20% by mass or less, more preferably 10% 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 (which is related to the compatibility between the various additive components in the adhesive sheet 10 and the acrylic polymer).

[0046] The monomer component may also contain other copolymerizable monomers. Examples of other copolymerizable monomers include acid anhydride monomers, sulfonic acid group-containing monomers, phosphate group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, alkoxy group-containing monomers, and aromatic vinyl compounds. These other copolymerizable monomers may be used individually or in combination of two or more types.

[0047] The monomer component preferably includes, from the viewpoint of achieving both adhesion in the adhesive sheet 10 and suppression of stress generated during deformation, a first alkyl (meth)acrylate (with a relatively large number of carbon atoms in the alkyl group), a second alkyl (meth)acrylate (with a relatively small number of carbon atoms in the alkyl group), a hydroxyl group-containing monomer, and a monomer having a nitrogen atom-containing ring. The first alkyl (meth)acrylate is more preferably an alkyl (meth)acrylate having an alkyl group having 6 to 8 carbon atoms, even more preferably an alkyl (meth)acrylate having a linear alkyl group having 6 to 8 carbon atoms, and particularly preferably at least one selected from the group consisting of n-octyl acrylate (NOAA) and n-hexyl acrylate (HxA). The second alkyl (meth)acrylate is more preferably an alkyl (meth)acrylate having an alkyl group having 5 or fewer carbon atoms, and even more preferably butyl acrylate (BA). The hydroxyl group-containing monomer is more preferably at least one selected from the group consisting of 4-hydroxybutyl acrylate (4HBA) and 2-hydroxyethyl acrylate (2HEA). The monomer having a nitrogen atom-containing ring is more preferably N-vinyl-2-pyrrolidone (NVP) from the viewpoint of designing the elastic modulus of the adhesive sheet 10 to be relatively high from room temperature to high temperature.

[0048] The base polymer preferably has a crosslinked structure. Methods for introducing a crosslinked structure to the base polymer include a first method in which a base polymer having a functional group reactive with a crosslinking agent and a crosslinking agent are blended into an adhesive composition and the base polymer and crosslinking agent are reacted in an adhesive sheet, and a second method in which a polyfunctional monomer as a crosslinking agent is included in the monomer component that forms the base polymer, and a base polymer in which a branched structure (crosslinked structure) is introduced into the polymer chain is formed by polymerization of the monomer component. These methods may be used in combination.

[0049] Examples of crosslinking agents used in the first method described above include compounds that react with functional groups (such as hydroxyl groups and carboxyl groups) contained in the base polymer. Examples of such crosslinking agents include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents. The crosslinking agent may be used alone or in combination of two or more types. As crosslinking agents, isocyanate crosslinking agents, peroxide crosslinking agents, and epoxy crosslinking agents are preferably used because they have high reactivity with hydroxyl groups and carboxyl groups in the base polymer and facilitate the introduction of crosslinked structures.

[0050] Examples of isocyanate crosslinking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethyl xylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate. Derivatives of these isocyanates can also be used as isocyanate crosslinking agents. Examples of such isocyanate derivatives include isocyanurate-modified and polyol-modified derivatives. Examples of commercially available isocyanate crosslinking agents include Coronate L (trimethylolpropane adduct of tolylene diisocyanate, manufactured by Tosoh Corporation), Coronate HL (trimethylolpropane adduct of hexamethylene diisocyanate, manufactured by Tosoh Corporation), Coronate HX (isocyanurate of hexamethylene diisocyanate, manufactured by Tosoh Corporation), Takenate D110N (trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals Corporation), and Takenate 600 (1,3-bis(isocyanatomethyl)cyclohexane, manufactured by Mitsui Chemicals Corporation).

[0051] Examples of peroxide crosslinking agents include dibenzoyl peroxide, di(2-ethylhexyl)peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t-butylperoxyneodecanoate, t-hexylperoxypivalate, and t-butylperoxypivalate.

[0052] Examples of epoxy crosslinking agents include bisphenol A, epichlorohydrin-type epoxy resins, 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.

[0053] Isocyanate crosslinking agents (especially 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 (especially 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 more flexible two-dimensional crosslinks, while trifunctional isocyanate crosslinking agents form stronger three-dimensional crosslinks. From the viewpoint of achieving both durability and flexibility of the adhesive sheet 10, a combination of a trifunctional isocyanate crosslinking agent and a peroxide crosslinking agent and / or a difunctional isocyanate crosslinking agent is preferred.

[0054] From the viewpoint of ensuring the cohesive force of the adhesive sheet 10, the amount of crosslinking agent 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, per 100 parts by mass of the base polymer. From the viewpoint of ensuring good tackiness in the adhesive sheet 10, the amount of crosslinking agent per 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.

[0055] In the second method described above, the monomer components (including polyfunctional monomers and other monomers for introducing a crosslinking structure) may be polymerized in a single step or in multiple steps. In the multi-step polymerization method, first, monofunctional monomers for forming the base polymer are polymerized (prepolymerization), thereby preparing a prepolymer composition containing a partially polymerized product (a mixture of a low-degree polymerized product and unreacted monomers). Next, a polyfunctional monomer as a crosslinking agent is added to the prepolymer composition, and then the partially polymerized product and the polyfunctional monomer are polymerized (main polymerization).

[0056] Examples of polyfunctional monomers include polyfunctional (meth)acrylates containing two or more ethylenically unsaturated double bonds in one molecule. From the viewpoint of being able to introduce crosslinked structures by active energy ray polymerization (photopolymerization), polyfunctional acrylates are preferred as polyfunctional monomers.

[0057] Examples of polyfunctional (meth)acrylates include difunctional (meth)acrylates, trifunctional (meth)acrylates, and polyfunctional (meth)acrylates with four or more functions.

[0058] Examples of difunctional (meth)acrylates 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, glycerin 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.

[0059] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl) isocyanurate.

[0060] Examples of polyfunctional (meth)acrylates with four or more functions include ditrimethylolpropanetetra(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0061] Preferably, a polyfunctional (meth)acrylate with four or more functions is used, and more preferably, dipentaerythritol hexaacrylate is used.

[0062] From the viewpoint of ensuring the cohesive force of the adhesive sheet 10, the amount of polyfunctional monomer used 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, per 100 parts by mass of monofunctional monomer. From the viewpoint of ensuring good tackiness in the adhesive sheet 10, the amount of polyfunctional monomer used 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, per 100 parts by mass of monofunctional monomer.

[0063] Acrylic polymers can be formed by polymerizing the monomer components described above. Polymerization methods include, for example, solution polymerization, solvent-free photopolymerization (e.g., UV polymerization), bulk polymerization, and emulsion polymerization. For solution polymerization, for example, ethyl acetate and toluene are used as solvents. For example, thermal polymerization initiators and photopolymerization initiators are used as polymerization initiators. The amount of polymerization initiator used is, for example, 0.05 parts by mass or more, preferably 0.08 parts by mass or more, and for example, 1 part by mass or less, preferably 0.5 parts by mass or less, per 100 parts by mass of monomer components.

[0064] Examples of thermal polymerization initiators include 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-methylpropionic acid)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'-dimethyleneisobutylamidine)dihydrochloride. Examples of peroxide polymerization initiators include dibenzoyl peroxide, t-butyl permaleate, and lauroyl peroxide.

[0065] 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, 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.

[0066] 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 cohesive force in the adhesive sheet 10. The weight-average molecular weight of the base polymer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene equivalent.

[0067] 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.

[0068] For the glass transition temperature (Tg) of the base polymer, the theoretical glass transition temperature (Tg) can be obtained based on Fox's equation below. Fox's equation is a relationship between the glass transition temperature Tg of a polymer and the glass transition temperature Tgi of the homopolymer of the monomers constituting the polymer. In Fox's equation below, Tg represents the glass transition temperature (°C) of the polymer, Wi represents the weight fraction of monomer i constituting the polymer, and Tgi represents the glass transition temperature (°C) of the homopolymer formed from monomer i. For the glass transition temperature of the homopolymer, literature values ​​can be used. For example, "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) and "New Polymer Library 7: Introduction to Synthetic Resins for Coatings" (by Kyozo Kitaoka, Polymer Publication Association, 1995) list the glass transition temperatures of various homopolymers. On the other hand, the glass transition temperature of the monomer homopolymer can also be determined by the method specifically described in Japanese Patent Publication No. 2007-51271.

[0069] Fox's formula 1 / (273+Tg)=Σ[Wi / (273+Tgi)]

[0070] The adhesive composition may 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, per 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.

[0071] The adhesive composition may contain other components as needed. Examples of other components include solvents, tackifiers, plasticizers, softeners, antioxidants, fillers, colorants, UV absorbers, surfactants, and antistatic agents. Examples of solvents include polymerization solvents used as needed during the polymerization of acrylic polymers, and solvents added to the polymerization reaction solution after polymerization. Examples of such solvents include ethyl acetate and toluene.

[0072] The adhesive sheet 10 can be manufactured, for example, by applying the above-described adhesive composition onto a release liner L1 (first release liner) to form a coating film, and then drying the coating film.

[0073] Examples of the release liner L1 include a flexible plastic film. Examples of such plastic films 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 treated to release the coating.

[0074] Methods for applying the adhesive composition include, for example, 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, 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.

[0075] A second release liner (L2) may be laminated on top of the adhesive sheet 10 on the release liner L1. Preferably, the release liner L2 is a flexible plastic film with a peel-off surface treatment. As the release liner L2, the plastic film described above with respect to the release liner L1 can be used.

[0076] In this manner, an adhesive sheet 10 can be manufactured in which the adhesive surfaces 11 and 12 are covered and protected by the release liners L1 and L2.

[0077] The thickness of the adhesive sheet 10 is preferably 10 μm or more, more preferably 15 μm or more, from the viewpoint of ensuring sufficient adhesion to the adherend and ease of handling. From the viewpoint of making the flexible device thinner, the thickness of the adhesive sheet 10 is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less.

[0078] 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 in accordance with JIS K7136 (2000). Examples of haze meters include the "NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. and the "HM-150" manufactured by Murakami Color Technology Laboratory Co., Ltd.

[0079] 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).

[0080] Figures 2A to 2C show an example of how to use the adhesive sheet 10.

[0081] In this method, first, as shown in Figure 2A, the adhesive sheet 10 is attached to one side of the first member 21 (adhered object) in the thickness direction H. The first member 21 is, for example, one element in the laminated structure of a 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). Through this step, an adhesive sheet 10 for bonding with other members is provided on the first member 21.

[0082] Next, as shown in Figure 2B, one side of the first member 21 in the thickness direction H is joined to the other side of the second member 22 in the thickness direction H via an adhesive sheet 10 on the first member 21. The second member 22 is, for example, another element in the laminated structure of a flexible display panel.

[0083] Next, as shown in Figure 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 autoclaving (heating and pressurizing) is used for aging, the temperature is, for example, 30°C to 80°C, the pressure is, for example, 0.1 to 0.8 MPa, and the processing time is, for example, 15 minutes or more.

[0084] In the adhesive sheet 10 used, for example, in the manufacturing process of a flexible display panel as described above, the strain stress S is as described above. 200 The ratio of adhesive strength F to (F / S) 200 The ratio is large, at 0.3 or more. This configuration is suitable for the adhesive sheet 10 to continue adhering to the adherend against internal stresses such as tensile stress generated in the adhesive sheet 10 when the adherend is deformed, and therefore is suitable for suppressing the peeling of the adhesive sheet 10 from the adherend. [Examples]

[0085] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. Furthermore, the specific numerical values ​​such as the amounts (contents), physical properties, and parameters described below can be substituted with the upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to" or "greater than") of the corresponding amounts (contents), physical properties, and parameters described in the "Modes for Carrying Out the Invention" above.

[0086] [Example 1] <Preparation of prepolymer composition> In a flask, a monomer mixture containing 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 2 parts by mass of N-vinyl-2-pyrrolidone (NVP) was mixed with 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenyl-1-one (product name "Omnirad651", manufactured by IGM Resins) as a first photopolymerization initiator and 0.05 parts by mass of 1-hydroxycyclohexylphenyl ketone (product name "Omnirad184", manufactured by IGM Resins) as a second photopolymerization initiator. The mixture was then irradiated with ultraviolet light under a nitrogen atmosphere to polymerize a portion of the monomer components in the mixture, obtaining a first prepolymer composition (containing monomer components that had not undergone polymerization) with a polymerization rate of approximately 10%.

[0087] <Preparation of adhesive composition> A first adhesive composition was obtained by mixing 100 parts by mass of the first prepolymer composition with 0.08 parts by mass of dipentaerythritol hexaacrylate (DPHA) as a crosslinking agent, 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenyl-1-one (product name "Omnirad651", manufactured by IGM Resins) as a photopolymerization initiator, and 0.3 parts by mass of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.).

[0088] <Formation of the adhesive layer> A first adhesive composition was applied to the release surface of a first release liner (product name "Diafoil MRF#38", thickness 38 μm, manufactured by Mitsubishi Chemical Corporation), which has a release surface on one side, to form a coating film. Next, the release surface of a second release liner (product name "Diafoil MRN#38", thickness 38 μm, manufactured by Mitsubishi Chemical Corporation), which also has a release surface on one side, was bonded onto the coating film on the first release liner. Then, ultraviolet light was irradiated onto the coating film between the release liners to photocur the coating film and form an adhesive layer (thickness 50 μm). For ultraviolet irradiation, a black light was used as the light source, and the irradiation intensity was set to 5 mW / cm². 2 That's what I decided.

[0089] As described above, an adhesive sheet (50 μm thick) with a double-sided release liner was prepared for Example 1. The composition of the adhesive sheet for Example 1 is shown in Table 1 in parts by mass (the same applies to the examples and comparative examples described later).

[0090] [Example 2] The adhesive sheet of Example 2 was prepared in the same manner as the adhesive sheet of Example 1, except that the amount of photopolymerization initiator was changed from 0.05 parts by mass to 0.1 parts by mass in the preparation of the adhesive composition.

[0091] [Example 3] The adhesive sheet of Example 3 was prepared in the same manner as the adhesive sheet of Example 1, except that the amount of crosslinking agent was changed from 0.08 parts by mass to 0.04 parts by mass, and no photopolymerization initiator was added.

[0092] [Example 4] The adhesive sheet of Example 4 was prepared in the same manner as the adhesive sheet of Example 1, except that a photopolymerization initiator was not included in the preparation of the adhesive composition.

[0093] [Example 5] The adhesive sheet of Example 5 was prepared in the same manner as the adhesive sheet of Example 1, except as follows: In the preparation of the prepolymer composition, the amount of the first photopolymerization initiator (product name "Omnirad651") was changed from 0.05 parts by mass to 0.035 parts by mass, and the amount of the second photopolymerization initiator (product name "Omnirad184") was changed from 0.05 parts by mass to 0.035 parts by mass. In the preparation of the adhesive composition, the amount of the crosslinking agent was changed from 0.08 parts by mass to 0.02 parts by mass, and no photopolymerization initiator was added.

[0094] [Example 6] The adhesive sheet of Example 6 was prepared in the same manner as the adhesive sheet of Example 1, except as follows: In the preparation of the prepolymer composition, the amount of the first photopolymerization initiator (product name "Omnirad651") was changed from 0.05 parts by mass to 0.07 parts by mass, and the amount of the second photopolymerization initiator (product name "Omnirad184") was changed from 0.05 parts by mass to 0.07 parts by mass. In the preparation of the adhesive composition, 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.

[0095] [Example 7] <Preparation of prepolymer composition> In a flask, a monomer mixture containing 80 parts by mass of n-hexyl acrylate (HxA), 10 parts by mass of butyl acrylate (BA), 8 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 2 parts by mass of N-vinyl-2-pyrrolidone (NVP) was mixed with 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenyl-1-one (product name "Omnirad651", manufactured by IGM Resins) as a first photopolymerization initiator and 0.05 parts by mass of 1-hydroxycyclohexyl phenyl ketone (product name "Omnirad184", manufactured by IGM Resins) as a second photopolymerization initiator. The mixture was then irradiated with ultraviolet light under a nitrogen atmosphere to polymerize a portion of the monomer components in the mixture, obtaining a second prepolymer composition with a polymerization rate of approximately 10%.

[0096] <Preparation of adhesive composition> A second adhesive composition was obtained by mixing 100 parts by mass of the second prepolymer composition, 0.08 parts by mass of dipentaerythritol hexaacrylate (DPHA) as a crosslinking agent, 0.1 parts by mass of 2,2-dimethoxy-1,2-diphenyl-1-one (product name "Omnirad651", manufactured by IGM Resins) as a photopolymerization initiator, and 0.3 parts by mass of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.).

[0097] <Formation of the adhesive layer> An adhesive layer (50 μm thick) sandwiched between the first and second release liners was formed in the same manner as in Example 1 (including UV irradiation), except that the second adhesive composition was used instead of the first adhesive composition.

[0098] As described above, an adhesive sheet (50 μm thick) with a double-sided release liner was prepared according to Example 7.

[0099] [Example 8] The adhesive sheet of Example 8 was prepared in the same manner as the adhesive sheet of Example 7, except that the amount of photopolymerization initiator was changed from 0.1 parts by mass to 0.05 parts by mass in the preparation of the adhesive composition.

[0100] [Example 9] The adhesive sheet of Example 9 was prepared in the same manner as the adhesive sheet of Example 7, except that a photopolymerization initiator was not included in the preparation of the adhesive composition.

[0101] [Comparative Example 1] <Preparation of prepolymer composition> In a flask, 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) was mixed with 0.035 parts by mass of a first photopolymerization initiator (product name "Omnirad651," manufactured by IGM Resins) and 0.035 parts by mass of a second photopolymerization initiator (product name "Omnirad184," manufactured by IGM Resins). The mixture was then irradiated with ultraviolet light under a nitrogen atmosphere to polymerize a portion of the monomer components in the mixture, thereby obtaining a third prepolymer composition with a polymerization rate of approximately 10%.

[0102] <Preparation of adhesive composition> A third adhesive composition was obtained by mixing 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 (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.).

[0103] <Formation of the adhesive layer> An adhesive layer (50 μm thick) sandwiched between the first and second release liners was formed in the same manner as in Example 1 (including UV irradiation), except that the third adhesive composition was used instead of the first adhesive composition.

[0104] As described above, an adhesive sheet (thickness 50 μm) of Comparative Example 1 with a double-sided release liner was prepared.

[0105] <180° peel test> The adhesive strength of each adhesive sheet in Examples 1-9 and Comparative Example 1 was investigated by a 180° peel test.

[0106] Specifically, first, the required number of measurement samples were prepared for each adhesive sheet. In preparing the measurement samples, the first release liner was peeled off from the adhesive sheet, and the exposed surface was bonded to a plasma-treated polyethylene terephthalate (PET) film (product name "Lumirror S10", thickness 50 μm, manufactured by Toray) to obtain a laminate. For the plasma treatment, a plasma irradiation device (product name "AP-TO5", manufactured by Sekisui Co., Ltd.) was used, with a voltage of 160 V, a frequency of 10 kHz, and a processing speed of 5000 mm / min (the same was used for the plasma treatment described later). Next, test pieces (width 10 mm x length 100 mm) were cut from the laminate (PET film / adhesive sheet / second release liner). Next, the second release liner was peeled off the adhesive sheet of the test specimen, and the exposed surface was bonded to a plasma-treated polyimide (PI) film (product name "GV200", thickness 80 μm, manufactured by Kolon). Then, the PI film with the adhesive sheet (test specimen) attached was heated and pressurized at a temperature of 50°C, a pressure of 0.5 MPa, and for 15 minutes. This pressed the test specimen onto the PI film. In this manner, a sample for measurement was prepared.

[0107] Next, after allowing the sample to stand at room temperature for 30 minutes, a 180° peel test was performed to peel the test piece from the PI film on the sample, and the force required for peeling (peel strength) was measured (first 180° peel test). A tensile testing machine (product name "Autograph AG-50NX plus", manufactured by Shimadzu Corporation) was used for this measurement. In this measurement, the measurement temperature was set to 25°C, the relative humidity to 55%, the peel angle of the test piece from the PI film to 180°, the tensile speed of the test piece to 300 mm / min, and the peel length to 50 mm. The average value of the measured peel strength is shown in Table 1 as the adhesive force f1 (N / 10 mm) at a tensile speed of 300 mm / min.

[0108] 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 the adhesive strength f2 (N / 10 mm) at a tensile speed of 100 mm / min. Furthermore, a 180° peel test was 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 the adhesive strength f3 (N / 10 mm) at a tensile speed of 10 mm / min.

[0109] Then, for the adhesive sheet of Example 1, as exemplified by the straight line (solid line) in the graph of Figure 3, the adhesive force F (N / 10mm) at a tensile speed of 0 was determined by extrapolation based on the adhesive forces f1, f2, and f3. Specifically, a regression line (straight line) was obtained from the x and y coordinates of three plots (white plots in the graph of Figure 3) related to adhesive forces f1 to f3 using the least squares method, and the adhesive force F at a tensile speed of 0 was determined by extrapolation using that straight line. The values ​​are shown in Table 1. In the graph of Figure 3, the horizontal axis represents the tensile speed (mm / min) in the 180° peel test, and the vertical axis represents the adhesive force (N / 10mm).

[0110] On the other hand, a 180° peel test was conducted under the same conditions as the first 180° peel test, except that the adherend used in the sample preparation process was replaced with a polarizing film (51 μm thick, manufactured by Nitto Denko Corporation). The measurement results are shown in Table 1 as the 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 adherend used in the sample preparation process was replaced with the above-mentioned polarizing film. The measurement results are shown in Table 1 as the adhesive strength f'2 (N / 10 mm) at a tensile speed of 100 mm / min. Furthermore, a 180° peel test was conducted under the same conditions as the third 180° peel test, except that the adherend used in the sample preparation process was replaced with the above-mentioned polarizing film. The measurement results are shown in Table 1 as the adhesive strength f'3 (N / 10 mm) at a tensile speed of 10 mm / min. Then, for the adhesive sheet of Example 1, as exemplified by the straight line (dotted line) in the graph of Figure 3, the adhesive force F' (N / 10mm) at a tensile speed of 0 was determined by extrapolation based on the adhesive forces f'1, f'2, and f'3. Specifically, a regression line (straight line) was obtained from the x and y coordinates of three plots (solid black plots in the graph of Figure 3) relating to the adhesive forces f'1 to f'3 using the least squares method, and the adhesive force F' at a tensile speed of 0 was determined by extrapolation using that straight line. The values ​​are shown in Table 1.

[0111] <Tensile Test> The strain stress generated during tensile testing was investigated for each adhesive sheet in Examples 1-9 and Comparative Example 1.

[0112] Specifically, first, the required number of measurement samples were prepared for each adhesive sheet. In preparing the measurement samples, first, a piece of adhesive sheet with a double-sided release liner (width 30 mm x length 100 mm) was cut from the adhesive sheet with a double-sided release liner. Next, after peeling off one side of the release liner from the sheet piece, the adhesive sheet piece was rolled lengthwise on the other side of the release liner, taking care not to introduce air bubbles, to form a cylindrical shape (cylinder height 30 mm). In this way, a cylindrical adhesive sheet piece for measurement was obtained. Next, the measurement samples were subjected to tensile testing using a Tensilon-type tensile testing machine (product name "Autograph AG-50NX plus", manufactured by Shimadzu Corporation) in an environment of 25°C and 50% relative humidity, and the tensile stress generated during the pulling process was measured. This resulted in obtaining a stress-strain curve (load-elongation curve). In this tensile test, the initial chuck distance was set to 10 mm, and the test sample (cylindrical adhesive sheet piece) was pulled in the vertical direction of the cylinder, with a tensile speed of 300 mm / min. The strain stress S at 200% elongation in such a tensile test is... 200 (N / cm 2 ) and the strain stress S at 300% elongation 300 (N / cm 2 ) and the strain stress S at 500% elongation 500 (N / cm 2 ) and are shown in Table 1. Also, the strain stress S 200 Total strain stress S 300 The ratio of and strain stress S 200 Total strain stress S 500 The ratios are also shown in Table 1.

[0113] <Flexibility test> For each adhesive sheet in Examples 1-9 and Comparative Example 1, a bending and retention test was performed as follows.

[0114] First, the second release liner was peeled off the adhesive sheet with a double-sided release liner, and the exposed surface was plasma-treated. Meanwhile, both sides (first and second surfaces) of a 51 μm thick polarizing film were also plasma-treated. Furthermore, the surface of an 80 μm thick transparent polyimide film and the surface of a 125 μm thick polyethylene terephthalate (PET) film were also plasma-treated. For each plasma treatment, a plasma irradiation device (product name "AP-TO5", manufactured by Sekisui Co., Ltd.) was used, with a voltage of 160 V, a frequency of 10 kHz, and a processing speed of 5000 mm / min. Then, the exposed surface of the adhesive sheet and the first surface of the polarizing film were bonded together. This bonding was performed in a 23°C environment by pressing a 2 kg roller back and forth once to bond the adhesive sheet with the first release liner and the polarizing film. Next, the first release liner was peeled off the adhesive sheet with the polarizing film, and the transparent polyimide film was laminated to the exposed surface of the adhesive sheet. Then, the PET film was laminated to the second surface of the polarizing film via a thin adhesive sheet with a thickness of 15 μm. In this lamination process, the polarizing film and the PET film were pressed together by running a 2 kg roller back and forth once in an environment of 23°C. As a result, a laminated film was obtained having a laminated structure of PET film (thickness 125 μm), thin adhesive sheet (thickness 15 μm), polarizing film (thickness 51 μm), adhesive sheet (thickness 50 μm), and transparent polyimide film (thickness 80 μm).

[0115] Next, evaluation samples were cut from the laminated film prepared in this manner. Specifically, a rectangular sample measuring 35 mm × 100 mm was cut from the laminated film so that the absorption axis direction of the polarizing film in the cut sample was parallel to the direction of the long side. Next, the sample was autoclaved for 15 minutes at 35°C and 0.50 MPa.

[0116] Next, a bending test was performed on the sample using a planar unloaded U-shaped stretch tester (manufactured by Yuasa System Equipment). In this test, bending fixtures were attached to each end of the long side of the sample, within a range of 20 mm from the edge of the sample, and the sample was fixed to the tester (the central 60 mm area of ​​the long side of the sample was not fixed). In this test, the sample was repeatedly deformed (bent) 200,000 times at a bending speed of 60 rpm in a constant temperature and humidity chamber under conditions of 60°C and 95% relative humidity, between a bent state with the PET film side facing inward and an unbent state. Specifically, the bent state in this test is the state in which the axis of the bending moment acting on the sample and the absorption axis of the polarizing film are perpendicular. In this bent state, the bending radius of the sample was set to 1.3 mm and the bending angle to 180°. In this bending test, the adhesion of the adhesive sheet to the substrate was evaluated as "good" if no peeling occurred between the adhesive sheet and the substrate (transparent polyimide film, polarizing film), and as "poor" if peeling occurred. The evaluation results are shown in Table 1.

[0117] [Table 1] [Explanation of Symbols]

[0118] 10 Adhesive sheets (optical adhesive sheets) 11,12 Adhesive surface H thickness direction L1, L2 peel-off liner 21 First Member 22 Second Member

Claims

1. It is an optical adhesive sheet, Based on the adhesive strength in the first 180° peel test at 25°C and a tensile speed of 300 mm / min, the adhesive strength in the second 180° peel test at 25°C and a tensile speed of 100 mm / min, and the adhesive strength in the third 180° peel test at 25°C and a tensile speed of 10 mm / min, the adhesive strength at a tensile speed of 0, determined by extrapolation, has an adhesive strength F (N / 10 mm). Strain stress S is defined as the strain stress at 200% elongation in a tensile test conducted at 25°C and a tensile speed of 300 mm / min. ２００ (N / cm ２ ) has, The aforementioned strain stress S ２００ An optical adhesive sheet in which the ratio of the adhesive strength F to the given value is 0.3 or greater.

2. The strain stress S at 500% elongation in the aforementioned tensile test ５００ (N / cm ２ The optical adhesive sheet according to claim 1, wherein the ratio of the adhesive strength F to ) is 0.2 or more.

3. The strain stress S at 500% elongation in the aforementioned tensile test ５００ The aforementioned strain stress S ２００ The optical adhesive sheet according to claim 1 or 2, wherein the ratio to is 3 or less.

4. The optical adhesive sheet according to any one of claims 1 to 3, wherein the adhesive strength F is 1 N / 10 mm or more.

5. The distortion stress S ２００ is 20 N / cm ２ or less. The optical adhesive sheet according to any one of claims 1 to 4

6. The strain stress S at 500% elongation in the aforementioned tensile test ５００ 30 N / cm ２ The optical adhesive sheet according to any one of claims 1 to 4, as follows:

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