Optical adhesive sheet

Abstract

We provide optical adhesive sheets suitable for flexible device applications. [Solution] The adhesive sheet 10 is an optical adhesive sheet and has a shear storage modulus of 80 kPa or less at 25°C. The adhesive sheet 10 is used to determine the shear adhesive strength F1 (N / cm²) in a first shear test in which the first and second glass plates are pulled on opposite sides in a direction perpendicular to the thickness direction H under predetermined conditions after a predetermined heat treatment of the joint in which the first and second glass plates are joined in the thickness direction H via the adhesive sheet 10. 2 The adhesive sheet 10 has a tensile adhesive strength B1 (N / cm²) in a first tensile test in which the third and fourth glass plates are pulled in opposite directions in the thickness direction H under predetermined conditions after heat treatment of the joint in which the third and fourth glass plates are joined in the thickness direction H via the adhesive sheet 10 under predetermined conditions. 2 It has the following properties: The product of the shear adhesive strength F1 and the tensile adhesive strength B1 is 10,000 or more.

Description

[Technical Field]

[0001] This invention relates to an optical adhesive sheet. [Background technology]

[0002] A display panel has a laminated structure that includes 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, optically transparent adhesive sheets (optical adhesive sheets) are used to bond the elements included in the laminated structure together.

[0003] Meanwhile, development is progressing on foldable display panels for smartphones and tablet devices. Specifically, foldable display panels can be repeatedly deformed between a bent shape and a flat, unbendable shape. In such foldable display panels, each element in the laminated structure is manufactured to be repeatedly bendable, and a thin optical adhesive sheet is used to join these elements. Optical adhesive sheets for flexible devices such as foldable display panels are described, for example, in Patent Document 1 below. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-111754 [Overview of the project] [Problems that the invention aims to solve]

[0005] At the bending portion of a foldable display panel, conventionally, an optical adhesive sheet is likely to peel off from an element as an adherend. This is because when the display panel is bent, a relatively large tensile stress is locally generated in the bent portion of the optical adhesive sheet. In the bent portion of the optical adhesive sheet, the larger the tensile stress in, for example, the shear direction with respect to the element (adherend), the more likely peeling occurs between the optical adhesive sheet and the element. The occurrence of such peeling causes malfunction of the device, which is undesirable. For an optical adhesive sheet for a foldable display panel, it is highly required that it is difficult to peel off from the element (adherend) when the display is bent.

[0006] On the other hand, as a flexible device, the development of a rollable display panel is also progressing. A rollable display panel is, for example, repeatedly deformable between a wound shape after being partially or entirely wound and a flat shape after being entirely unwound. In such a rollable display panel, each element in the laminated structure is produced to be repeatedly deformable, and a thin optical adhesive sheet is used for joining between such elements. When the rollable display panel is in the wound shape, the optical adhesive sheet joined to the element in the wound shape continuously receives a tensile stress from the element. For such an optical adhesive sheet, it is highly required that it is difficult to peel off from the element (adherend) when the display is in the wound shape.

[0007] The present invention provides an optical adhesive sheet suitable for flexible device applications.

Means for Solving the Problems

[0008] The present invention [1] relates to an optical adhesive sheet having a shear storage modulus of 80 kPa or less at 25°C, and after heat treatment of a joined body in which a first glass plate and a second glass plate are joined in the thickness direction via the optical adhesive sheet under the conditions of 50°C, 0.5 MPa, and 15 minutes, in a first shear test in which the first and second glass plates are pulled in opposite directions in a direction orthogonal to the thickness direction under the conditions of 25°C and a tensile speed of 25 mm / min, the shear adhesion strength F1 (N / cm 2 ), and after the heat treatment of a joined body in which a third glass plate and a fourth glass plate are joined in the thickness direction via the optical adhesive sheet, in a first tensile test in which the third and fourth glass plates are pulled in opposite directions in the thickness direction under the conditions of 25°C and a tensile speed of 25 mm / min, the tensile adhesion strength B1 (N / cm 2 ), and the product of the shear adhesion strength F1 and the tensile adhesion strength B1 is 10,000 or more, and includes an optical adhesive sheet.

[0009] The present invention [2] includes the optical adhesive sheet according to [1] above, wherein the shear adhesion strength F1 is 60 N / cm 2 or more.

[0010] The present invention [3] includes the optical adhesive sheet according to [1] or [2] above, wherein the tensile adhesion strength B1 is 150 N / cm 2 or more.

[0011] The present invention [4] relates to a second shear test in which, after the heat treatment of a joined body in which a first glass plate and a second glass plate are joined in the thickness direction via the optical adhesive sheet, the first and second glass plates are pulled in opposite directions in a direction orthogonal to the thickness direction under the conditions of 60°C and a tensile speed of 25 mm / min, the shear adhesion strength F2 (N / cm 2 ), and after the heat treatment of a joined body in which a third glass plate and a fourth glass plate are joined in the thickness direction via the optical adhesive sheet, in a second tensile test in which the third and fourth glass plates are pulled in opposite directions in the thickness direction under the conditions of 60°C and a tensile speed of 25 mm / min, the tensile adhesion strength B2 (N / cm 2) and the product of the shear adhesion strength F2 and the tensile adhesion strength B2 is 1500 or more, and includes the optical adhesive sheet according to any one of [1] to [3] above.

[0012] In the present invention [5], the shear adhesion strength F2 is 12 N / cm 2 or more, and includes the optical adhesive sheet according to [4] above.

[0013] In the present invention [6], the tensile adhesion strength B2 is 80 N / cm 2 or more, and includes the optical adhesive sheet according to [4] or [5] above.

[0014] In the present invention [7], the ratio of the shear adhesion strength F1 to the shear adhesion strength F2 is 2 or less, and includes the optical adhesive sheet according to any one of [4] to [6] above.

[0015] In the present invention [8], the ratio of the tensile adhesion strength B1 to the tensile adhesion strength B2 is 5.5 or less, and includes the optical adhesive sheet according to any one of [4] to [7] above.

Advantages of the Invention

[0016] The optical adhesive sheet of the present invention has a shear storage modulus of not more than 80 kPa at 25°C as described above. An optical adhesive sheet having such a high degree of softness is likely to deform with a large curvature following the deformation of the adherend when the adherend to which the adhesive sheet is bonded is deformed with a relatively large curvature. Therefore, the optical adhesive sheet is suitable for realizing good repeated deformation of the flexible device in which the optical adhesive sheet is used. Further, the optical adhesive sheet of the present invention has a shear adhesion strength F1 (N / cm 2 ) in the above first shear test (25°C, tensile speed 25 mm / min), and a tensile adhesion strength B1 (N / cm 2The product of () is large, exceeding 10,000. Such optical adhesive sheets are suitable for resisting internal stresses such as tensile stress generated in the adherend when the adherend to which the adhesive sheet is bonded deforms, and thus are suitable for suppressing peeling of the optical adhesive sheet from the adherend. Such optical adhesive sheets are suitable for flexible device applications. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic cross-sectional view of one embodiment of the optical adhesive sheet of the present invention. [Figure 2] This diagram schematically represents the shear tests (first shear test, second shear test). [Figure 3] This diagram schematically represents the tensile tests (first tensile test, second tensile test). [Figure 4] This shows an example of how to use the optical adhesive sheet of the present invention. Figure 4A shows the step of attaching the optical adhesive sheet to a first adherend, Figure 4B shows the step of joining the first adherend and the second adherend via the optical adhesive sheet, and Figure 4C shows the aging step. [Modes for carrying out the invention]

[0018] 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.

[0019] 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.

[0020] The adhesive sheet 10 has a shear storage modulus of 80 kPa or less at 25°C, and in the first shear test, it has a shear adhesive strength F1 (N / cm²). 2 ) has a tensile adhesive strength B1 (N / cm²) in the first tensile test. 2 The material has a shear bond strength F1 and a tensile bond strength B1 product (F1 × B1) of 10,000 or more. The method for measuring the shear storage modulus is described later with respect to the examples.

[0021] In the first shear test, as shown in Figure 2, a joint W1 is prepared in which glass plate 51 (first glass plate) and glass plate 52 (second glass plate) are joined in the thickness direction H via an adhesive sheet 10 (the same applies to the second shear test described later). In the first shear test, after heat treatment of the joint W1 under the conditions of 50°C, 0.5 MPa and 15 minutes, the glass plates 51 and 52 are pulled in opposite directions in a direction perpendicular to the thickness direction H at a temperature of 25°C and a tensile speed of 25 mm / min. The method of the first shear test is specifically as shown in the following steps S11 to S13, and more specifically as described later with respect to the examples.

[0022] Step S11: Glass plate 51 and glass plate 52 are joined in the thickness direction H via an adhesive sheet 10 to obtain a joined body W1. Step S12: The bonded body W1 is heat-treated at 50°C, 0.5 MPa, and for 15 minutes. Step S13: The glass plates 51 and 52 in the joint W1 are pulled in opposite directions in a direction perpendicular to the thickness direction H, under conditions of 25° and a tensile speed of 25 mm / min.

[0023] In the first tensile test, as shown in Figure 3, a joint W2 is prepared in which glass plate 53 (third glass plate) and glass plate 54 (fourth glass plate) are joined in the thickness direction H via an adhesive sheet 10 (the same applies to the second tensile test described later). In the first tensile test, after heat treatment of the joint W2 under the conditions of 50°C, 0.5 MPa and 15 minutes, the glass plates 53 and 54 are pulled in opposite directions in the thickness direction H at 25°C and a tensile speed of 25 mm / min. The method for the first tensile test is specifically as described in the following steps S21 to S23, and more specifically as described later with respect to the examples.

[0024] Step S21: Glass plate 53 and glass plate 54 are joined in the thickness direction H via an adhesive sheet 10 to obtain a joined body W2. Step S22: The bonded body W2 is heat-treated at 50°C, 0.5 MPa, and for 15 minutes. Step S23: The glass plates 53 and 54 in the joint W2 are pulled in opposite directions in the thickness direction H at a temperature of 25° and a tensile speed of 25 mm / min.

[0025] As described above, the adhesive sheet 10 has a shear storage modulus of 80 kPa or less at 25°C. Because the adhesive sheet 10 possesses such a high degree of flexibility, it easily deforms with a large curvature, following the deformation of the adherend to which the adhesive sheet 10 is bonded when the adherend deforms with a relatively large curvature. Therefore, the adhesive sheet 10 is suitable for achieving good repeated deformation in flexible devices in which it is used.

[0026] Furthermore, the adhesive sheet 10 has a shear adhesive strength F1 (N / cm²) as described above. 2) and tensile adhesive strength B1 (N / cm 2 The product of (F1 × B1) with ) is large, at 10000 or more. Such an adhesive sheet 10 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 which the adhesive sheet 10 is bonded deforms, and therefore is suitable for suppressing the peeling of the adhesive sheet 10 from the adherend.

[0027] As described above, the adhesive sheet 10 is suitable for deforming with a large curvature in accordance with the deformation of the adherend, and is also suitable for suppressing peeling from the adherend. Therefore, the adhesive sheet 10 is suitable for flexible device applications.

[0028] From the viewpoint of ensuring good deformability in the adhesive sheet 10, the shear storage modulus of the adhesive sheet 10 is preferably 60 kPa or less, more preferably 50 kPa or less, even more preferably 45 kPa or less, and particularly preferably 40 kPa or less. The shear storage modulus is, for example, 5 kPa or more. Methods for adjusting the shear storage modulus of the adhesive sheet 10 include, for example, selecting the type of base polymer in the adhesive sheet 10, adjusting the molecular weight and the amount blended, and selecting the type of crosslinking agent that crosslinks the base polymer and adjusting the amount blended. The selection of the type of base polymer includes adjusting the composition of the monomers that form the base polymer. Methods for adjusting the shear storage modulus of the adhesive sheet 10 also include selecting the type and amount of functional groups in the base polymer.

[0029] From the viewpoint of ensuring strong adhesion of the adhesive sheet 10 and suppressing the peeling described above, the shear adhesive strength F1 (N / cm 2 ) and tensile adhesive strength B1 (N / cm 2The product (F1 × B1) of ) is preferably 12,000 or more, more preferably 13,000 or more, even more preferably 14,000 or more, and particularly preferably 15,000 or more. The product (F1 × B1) is, for example, 50,000 or less. Methods for adjusting the shear adhesive strength F1 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 shear adhesive strength F1 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 same adjustment methods described above also apply to the tensile adhesive strength B1, and the shear adhesive strength F2 and tensile adhesive strength B2 described below.

[0030] The shear adhesive strength F1 is preferably 60 N / cm² in the adhesive sheet 10 attached to the adherend, from the viewpoint of suppressing the peeling described above against shear stress. 2 More preferably 68 N / cm 2 More preferably 80 N / cm 2 More preferably 90 N / cm 2 More preferably, 100 N / cm 2 The above is particularly preferably 110 N / cm 2 That concludes the explanation. The shear bond strength F1 is, for example, 200 N / cm². 2 The following applies:

[0031] The tensile adhesive strength B1 is preferably 150 N / cm² in the adhesive sheet 10 attached to the adherend, from the viewpoint of suppressing the peeling described above against tensile stress in the thickness direction. 2 More specifically, 165 N / cm² 2 More preferably 180 N / cm 2 More preferably, 190 N / cm² 2 More preferably, 200 N / cm 2 The above, particularly preferably 210 N / cm². 2That concludes the explanation. The tensile adhesive strength B1 is, for example, 300 N / cm². 2 The following applies:

[0032] The adhesive sheet 10 preferably has a shear adhesive strength F2 (N / cm²) in the second shear test. 2 ) has a tensile adhesive strength B2 (N / cm) in the second tensile test. 2 The adhesive sheet 10 has a product of shear adhesive strength F2 and tensile adhesive strength B2 (F2 × B2) of 1500 or more. The second shear test is the same as the first shear test described above, except that the temperature condition in step S13 is 60°C. The second tensile test is the same as the second tensile test described above, except that the temperature condition in step 23 is 60°C. Having a large product (F2 × B2) of 1500 or more in the adhesive sheet 10 is preferable for the adhesive sheet 10 to continue to adhere to the adherend against internal stresses such as tensile stress generated in the adhesive sheet 10 when the adherend to which the adhesive sheet 10 is bonded deforms under relatively high temperature conditions of 60°C or nearby. Such an adhesive sheet 10 is preferable for suppressing peeling of the adhesive sheet 10 from the adherend under relatively high temperature conditions.

[0033] From the viewpoint of ensuring strong adhesion of the adhesive sheet 10 under relatively high temperature conditions and suppressing the peeling described above, the product (F2 × B2) is more preferably 3000 or more, even more preferably 4000 or more, and particularly preferably 5000 or more. The equivalent product (F2 × B2) is, for example, 10000 or less.

[0034] The shear adhesive strength F2 is preferably 12 N / cm² in the adhesive sheet 10 attached to the adherend, from the viewpoint of suppressing the aforementioned peeling against shear stress under relatively high temperature conditions. 2 More preferably 15 N / cm 2 More preferably 30 N / cm 2 More preferably 40 N / cm 2 The above is particularly preferable at 45 N / cm². 2 That concludes the explanation. The shear bond strength F2 is, for example, 100 N / cm². 2 The following applies:

[0035] The ratio of shear adhesive strength F1 to shear adhesive strength F2 (F1 / F2) is preferably 2 or less, more preferably 1.8 or less, even more preferably 1.5 or less, even more preferably 1.4 or less, particularly preferably 1.3 or less, and also preferably 0.5 or more, more preferably 0.6 or more, even more preferably 0.7 or more, even more preferably 0.8 or more, particularly preferably 0.9 or more, from the viewpoint of stabilizing the adhesive properties of the adhesive sheet 10 by suppressing temperature dependence.

[0036] The tensile adhesive strength B2 is preferably 80 N / cm² in the adhesive sheet 10 attached to the adherend, from the viewpoint of suppressing the peeling described above against tensile stress in the thickness direction under relatively high temperature conditions. 2 More preferably, 100 N / cm 2 More preferably, 115 N / cm 2 More preferably 130 N / cm² 2 More preferably, 140 N / cm² 2 In particular, 150 N / cm² is preferred. 2 That concludes the explanation. The tensile adhesive strength B2 is, for example, 200 N / cm². 2 The following applies:

[0037] The ratio of tensile adhesive strength B1 to tensile adhesive strength B2 (B1 / B2) is preferably 5.5 or less, more preferably 5.2 or less, even more preferably 4 or less, even more preferably 3 or less, particularly preferably 2 or less, and also preferably 0.5 or more, more preferably 0.6 or more, even more preferably 0.7 or more, even more preferably 0.8 or more, particularly preferably 0.9 or more, from the viewpoint of stabilizing the adhesive properties of the adhesive sheet 10 by suppressing temperature dependence.

[0038] 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.

[0039] 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.

[0040] Acrylic polymers are copolymers of monomer components containing 50% or more by mass of (meth)acrylic acid ester. "(Meth)acrylic" means acrylic and / or methacrylic.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] The proportion of alkyl (meth)acrylate in the monomer component is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% 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.

[0046] 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.

[0047] 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.

[0048] The proportion of hydroxyl group-containing monomers in the monomer components is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2% 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 20% by mass or less, and more preferably 10% by mass or less.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The proportion of monomers having nitrogen atom-containing rings 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, even more preferably 6% by mass or more, and particularly preferably 7% 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 30% by mass or less, more preferably 20% by mass or less, from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (related to the compatibility between various additive components in the adhesive sheet 10 and the acrylic polymer).

[0053] 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.

[0054] The monomer component preferably includes 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, from the viewpoint of achieving both adhesion in the adhesive sheet 10 and suppression of stress generation during deformation. The first alkyl (meth)acrylate is preferably an alkyl (meth)acrylate having an alkyl group with 6 to 8 carbon atoms, more preferably an alkyl (meth)acrylate having a linear alkyl group with 6 to 8 carbon atoms, and even more 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 preferably an alkyl (meth)acrylate having an alkyl group with 5 or fewer carbon atoms, and more preferably butyl acrylate (BA). The hydroxyl group-containing monomer is 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 adhesive sheet 10 to have a relatively high elastic modulus from room temperature to high temperatures, the monomer having a nitrogen atom-containing ring is preferably N-vinyl-2-pyrrolidone (NVP).

[0055] 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.

[0056] 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.

[0057] 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).

[0058] 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.

[0059] 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.

[0060] 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.

[0061] From the viewpoint of ensuring the cohesive force of the adhesive sheet 10, the amount of crosslinking agent blended in the first method 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 blended 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.

[0062] 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).

[0063] 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.

[0064] Examples of polyfunctional (meth)acrylates include difunctional (meth)acrylates, trifunctional (meth)acrylates, and polyfunctional (meth)acrylates with four or more functions.

[0065] 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.

[0066] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl) isocyanurate.

[0067] 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.

[0068] Preferably, a polyfunctional (meth)acrylate with four or more functions is used, and more preferably, dipentaerythritol hexaacrylate is used.

[0069] 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 3 parts by mass or less, more preferably 1 part by mass or less, even more preferably 0.5 parts by mass or less, even more preferably 0.2 parts by mass or less, and particularly preferably 0.1 parts by mass or less, per 100 parts by mass of monofunctional monomer.

[0070] 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 solvent polymerization, for example, ethyl acetate and toluene are used. For polymerization initiators, for example, thermal polymerization initiators and photopolymerization initiators are used. Polymerization initiators may be used alone or in combination of two or more types. The amount of polymerization initiator used is preferably 0.05 parts by mass or more, more preferably 0.08 parts by mass or more, even more preferably 0.1 parts by mass or more, and also preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, even more preferably 0.3 parts by mass or less, even more preferably 0.2 parts by mass or less, and particularly preferably 0.15 parts by mass or less, per 100 parts by mass of monomer components.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] Fox's formula 1 / (273+Tg)=Σ[Wi / (273+Tgi)]

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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).

[0087] Figures 4A to 4C show an example of how to use the adhesive sheet 10.

[0088] In this method, first, as shown in Figure 4A, 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.

[0089] Next, as shown in Figure 4B, 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.

[0090] Next, as shown in Figure 4C, the adhesive sheet 10 between the first member 21 and the second member 22 is aged. Aging promotes the crosslinking reaction of the base polymer in the adhesive sheet 10, increasing the bonding strength between the first member 21 and the second member 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 (heat treatment) 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 treatment time is, for example, 15 minutes or more.

[0091] The adhesive sheet 10 is used, for example, in the manufacturing process of a flexible display panel as described above. As mentioned above, the adhesive sheet 10 has a shear storage modulus of 80 kPa or less at 25°C. The adhesive sheet 10 has a high degree of flexibility. Therefore, when the adherend to which the adhesive sheet 10 is bonded deforms with a relatively large curvature, the adhesive sheet 10 easily deforms with a large curvature, following the deformation of the adherend. Furthermore, as described above, the adhesive sheet 10 has a shear adhesive strength F1 (N / cm 2 ) and tensile adhesive strength B1 (N / cm 2 The product of (F1 × B1) is large, exceeding 10,000. Such an adhesive sheet 10 is suitable for maintaining adhesion to the adherend against internal stresses such as tensile stress generated in the adhesive sheet 10 when the adherend to which the adhesive sheet 10 is bonded deforms, and is therefore suitable for suppressing the peeling of the adhesive sheet 10 from the adherend. Such an adhesive sheet 10 is suitable for flexible device applications. [Examples]

[0092] 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.

[0093] [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), 2 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 8 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%.

[0094] <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.).

[0095] <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.

[0096] As described above, an adhesive sheet (thickness 50 μm) with a double-sided release liner was prepared according to Example 1. The composition of the adhesive sheet of Example 1 is shown in Table 1 in parts by mass (the same applies to the examples and comparative examples described later).

[0097] [Example 2] The adhesive sheet of Example 2 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.

[0098] [Example 3] The adhesive sheet of Example 3 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 crosslinking agent was changed from 0.08 parts by mass to 0.04 parts by mass, and no photopolymerization initiator was added.

[0099] [Example 4] The adhesive sheet of Example 4 was prepared in the same manner as the adhesive sheet of Example 1, except that the amount of crosslinking agent (DPHA) was changed from 0.08 parts by mass to 0.04 parts by mass in the preparation of the adhesive composition.

[0100] [Comparative Example 1] <Preparation of prepolymer composition> In a flask, a monomer mixture containing 57 parts by mass of butyl acrylate (BA), 12 parts by mass of cyclohexyl acrylate (CHA), and 31 parts by mass of 4-hydroxybutyl acrylate (2HBA) was mixed with 0.09 parts by mass of a first photopolymerization initiator (product name "Omnirad651," manufactured by IGM Resins) and 0.09 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 second prepolymer composition with a polymerization rate of approximately 10%.

[0101] <Preparation of adhesive composition> A second adhesive composition was obtained by mixing 100 parts by mass of the second prepolymer composition, 0.12 parts by mass of DPHA as a crosslinking agent, and 0.3 parts by mass of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.).

[0102] <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.

[0103] As described above, an adhesive sheet (thickness 50 μm) of Comparative Example 1 with a double-sided release liner was prepared.

[0104] [Comparative Example 2] <Preparation of prepolymer composition> In a flask, a monomer mixture containing 60 parts by mass of 2-ethylhexyl acrylate (2EHA), 34 parts by mass of lauryl acrylate (LA), and 6 parts by mass of 4-hydroxybutyl acrylate (4HEA) was mixed with 0.05 parts by mass of a first photopolymerization initiator (product name "Omnirad651," manufactured by IGM Resins) and 0.05 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%.

[0105] <Preparation of adhesive composition> A third adhesive composition was obtained by mixing 100 parts by mass of the third prepolymer composition, 0.01 parts by mass of DPHA as a crosslinking agent, and 0.3 parts by mass of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.).

[0106] <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.

[0107] As described above, an adhesive sheet (50 μm thick) of Comparative Example 2 with a double-sided release liner was prepared.

[0108] <Shear storage modulus> The dynamic viscoelasticity of each adhesive sheet in Examples 1-4 and Comparative Examples 1 and 2 was measured.

[0109] First, a sample for measurement was prepared for each adhesive sheet. Specifically, several pieces of adhesive sheet cut from the original sheet were glued together to create a sample sheet approximately 1.5 mm thick. Next, this sheet was punched out to obtain cylindrical pellets (7.9 mm in diameter), which were to be used as measurement samples.

[0110] Then, dynamic viscoelasticity measurements were performed on the sample using a dynamic viscoelasticity measuring device (product name "Advanced Rheometric Expansion System (ARES)", manufactured by Rheometric Scientific) after fixing it to a 7.9 mm diameter parallel plate jig. In this measurement, the measurement mode was set to shear mode, the measurement temperature range to -40°C to 100°C, the heating rate to 5°C / min, and the frequency to 1 Hz. The shear storage modulus (kPa) at 25°C was read from the measurement results. The values ​​are shown in Table 1.

[0111] <Shear Test> The shear adhesive strength in shear tests (first shear tests) was investigated for each adhesive sheet in Examples 1-4 and Comparative Examples 1 and 2. Specifically, the results are as follows:

[0112] First, two glass plates (30mm x 30mm x 5mm) were prepared. Next, the first release liner was peeled off a piece of adhesive sheet (10mm x 10mm) cut from an adhesive sheet, and the exposed surface of the adhesive sheet was bonded to one of the glass plates (first glass plate). For this bonding, the adhesive sheet piece was pressed against the glass plate by running a 2kg hand roller back and forth once in an environment of 25°C (the conditions for bonding described later were the same). Next, the second release liner was peeled off the adhesive sheet piece on the glass plate, and the exposed surface of the adhesive sheet was bonded to the other glass plate (second glass plate). This resulted in obtaining a first joint in which the first glass plate and the second glass plate were joined in the thickness direction via an adhesive sheet (Step S11). Next, the first joint was heat-treated at a temperature of 50°C, a pressure of 0.5 MPa, and for 15 minutes, pressing pieces of the adhesive sheet against both glass plates (Step S12). In this manner, a sample for measurement (first glass plate / adhesive sheet / second glass plate) was prepared.

[0113] Next, the sample was left in a 25°C environment for 30 minutes. Then, in a 25°C environment, the two glass plates of the sample were pulled in opposite directions perpendicular to the thickness direction while measuring the tensile force (Step S13). For this measurement, a tensile testing machine (product name "Autograph AG-50NX plus", manufactured by Shimadzu Corporation) was used, with a measurement temperature of 25°C, a relative humidity of 55%, and a tensile speed of 25 mm / min. The maximum force measured was used to determine the shear bond strength F1 (N / cm²). 2 ) are shown in Table 1.

[0114] The shear test was conducted in the same manner as the first shear test, except that the temperature condition in step S13 above was changed to 60°C, and the shear bond strength F2 (N / cm) at 60°C was obtained. 2 The second shear test measured the shear bond strength F1. The results are shown in Table 1. The ratio of shear bond strength F1 to shear bond strength F2 is also shown in Table 1.

[0115] <Tensile Test> The tensile adhesive strength (first tensile test) was investigated for each adhesive sheet in Examples 1-4 and Comparative Examples 1 and 2. Specifically, the results are as follows:

[0116] First, a sample for measurement was prepared for each adhesive sheet. In preparing the sample for measurement, two glass plates supported on a metal block were first prepared. The metal block-supported glass plate was prepared by attaching a glass plate (30mm x 30mm x 5mm) to one side of a metal block (a cubic block made of SUS304 measuring 30mm x 30mm x 30mm) using adhesive. Next, the first release liner was peeled off an adhesive sheet piece (10mm x 10mm) cut from the adhesive sheet, and the exposed surface was attached to the exposed glass surface of one of the metal block-supported glass plates (third glass plate). Next, the second release liner was peeled off from the adhesive sheet piece on the glass plate, and the exposed surface was attached to the exposed glass surface of the other metal block-supported glass plate (fourth glass plate), thereby joining the glass plates together. This resulted in a second joined body in which the third glass plate and the fourth glass plate were joined in the thickness direction via the adhesive sheet piece (step S21). Next, the second bond was heat-treated at a temperature of 50°C, a pressure of 0.5 MPa, and for 15 minutes, and the adhesive sheet piece was pressed onto both glass plates (step S22). In this manner, a sample for measurement (metal block / third glass plate / adhesive sheet piece / fourth glass plate / metal block) was prepared.

[0117] Next, a test was conducted in which two metal-supported glass plates in the measurement sample were pulled in opposite directions in the thickness direction, and the force required to separate the glass plates was measured (Step S23). 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%, and the tensile speed to 25 mm / min. The maximum value of the measured force was used to determine the tensile adhesive strength B1 (N / cm). 2 The product of the tensile adhesive strength B1 and the shear adhesive strength F1 is also shown in Table 1.

[0118] The tensile test was performed in the same manner as the first tensile test, except that the temperature condition in step S23 above was changed to 60°C, and the tensile adhesive strength B2 at 60°C was measured. The maximum value of the measured force was defined as the tensile adhesive strength B2 (N / cm²). 2Table 1 shows the results. The product of the tensile adhesive strength B2 and the shear adhesive strength F2, and the ratio of the tensile adhesive strength B1 to the tensile adhesive strength B2 are also shown in Table 1.

[0119] <Flexibility test> The following bending and holding tests were performed on each adhesive sheet in Examples 1-4 and Comparative Examples 1 and 2.

[0120] 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).

[0121] 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.

[0122] 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.

[0123] [Table 1] [Explanation of Symbols]

[0124] 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, The optical adhesive sheet contains an acrylic polymer, The acrylic polymer is a copolymer of monomer components comprising an alkyl (meth)acrylate having an alkyl group having 6 to 8 carbon atoms and an alkyl (meth)acrylate having an alkyl group having 5 or fewer carbon atoms. It has a shear storage modulus of 80 kPa or less at 25°C. In a first shear test in which a joint formed by bonding a first glass plate and a second glass plate in the thickness direction via the optical adhesive sheet is subjected to heat treatment at 50°C, 0.5 MPa, and 15 minutes, the first and second glass plates are pulled in opposite directions in a direction perpendicular to the thickness direction at 25°C and a tensile speed of 25 mm / min, and the shear bond strength F1 (N / cm²) is obtained. ２ ) has, In a first tensile test in which the third and fourth glass plates are joined in the thickness direction via the optical adhesive sheet, after the heat treatment of the joint, the third and fourth glass plates are pulled in opposite directions in the thickness direction at 25°C and a tensile speed of 25 mm / min, the tensile adhesive strength B1 (N / cm) is ２ ) has, An optical adhesive sheet in which the product of the shear adhesive strength F1 and the tensile adhesive strength B1 is 10,000 or more.

2. The aforementioned shear bond strength F1 is 60 N / cm ２ The optical adhesive sheet according to claim 1.

3. The aforementioned tensile adhesive strength B1 is 150 N / cm ２ The optical adhesive sheet according to claim 1 or 2.

4. After the heat treatment of the joint in which the first glass plate and the second glass plate are joined in the thickness direction via the optical adhesive sheet, in a second shear test in which the first and second glass plates are pulled in opposite directions in a direction perpendicular to the thickness direction at 60°C and a tensile speed of 25 mm / min, the shear adhesive strength F2 (N / cm) ２ ) has, In a second tensile test, after the heat treatment of the joint in which the third glass plate and the fourth glass plate are joined in the thickness direction via the optical adhesive sheet, the third and fourth glass plates are pulled in opposite directions in the thickness direction at 60°C and a tensile speed of 25 mm / min, Tensile adhesive strength B2 (N / cm) ２ ) has, The optical adhesive sheet according to any one of claims 1 to 3, wherein the product of the shear adhesive strength F2 and the tensile adhesive strength B2 is 1500 or more.

5. The aforementioned shear bond strength F2 is 12 N / cm ２ The optical adhesive sheet according to claim 4.

6. The aforementioned tensile adhesive strength B2 is 80 N / cm ２ The optical adhesive sheet according to claim 4 or 5.

7. The optical adhesive sheet according to any one of claims 4 to 6, wherein the ratio of the shear adhesive strength F1 to the shear adhesive strength F2 is 2 or less.

8. The ratio of the tensile adhesive strength B1 to the tensile adhesive strength B2 is 5.5 or less. The optical adhesive sheet according to any one of claims 4 to 7.

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