Optical adhesive sheet

Abstract

To provide an optical adhesive sheet suitable for rollable display application.SOLUTION: An adhesive sheet 10 is an optical adhesive sheet. The adhesive sheet 10 has a peel strength F1 of 5 N / 20 mm or more in a low-speed peel test in which the adhesive sheet 10 is peeled from a glass plate at 25°C, a peel angle of 180°, and a tensile speed of 30 mm / min after the adhesive sheet 10 is stuck to the glass plate followed by heating / pressure treatment at 50°C, 0.5 MPa for 15 minutes. The adhesive sheet 10 has a tensile adhesive strength B1 of 0.9 N / mm2 or more in a low-speed tensile test in which a first glass plate and a second glass plate are pulled to opposite sides to each other in the thickness direction at 25°C and a tensile speed of 5 mm / min after the first glass plate and the second glass plate are joined in the thickness direction via the adhesive sheet 10 followed by the heating / pressure treatment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A display panel has a laminated structure that includes, for example, a pixel panel, a polarizing plate, a touch panel, and a cover film. In the manufacturing process of such a display panel, a transparent adhesive sheet for optical applications (optical adhesive sheet) is used to bond the elements included in the laminated structure together.

[0003] Meanwhile, development is progressing on foldable display panels, for example, 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 display panels, 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 Initiative] [Problems that the invention aims to solve]

[0005] Development of rollable display panels is also progressing as a flexible display panel. 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 such elements. When the rollable display panel is in a wound shape, the optical adhesive sheet that is joined to the wound element is continuously subjected to stress from that element. Such an optical adhesive sheet is required to be extremely resistant to peeling off from the element as the adherend when the display is in a wound shape.

[0006] This invention provides an optical adhesive sheet suitable for rollable display applications. [Means for solving the problem]

[0007] The present invention [1] relates to an optical adhesive sheet, wherein, after bonding the optical adhesive sheet to a glass plate and subsequently performing a heat and pressure treatment at 50°C, 0.5 MPa and 15 minutes, the optical adhesive sheet is peeled off the glass plate at 25°C, a peel angle of 180° and a tensile speed of 30 mm / min, and the peel strength F1 is 5 N / 20 mm or more. 2 This includes an optical adhesive sheet having the above-mentioned tensile adhesive strength B1.

[0008] The present invention [2] relates to the peel strength F1 (N / 20 mm) and the tensile adhesive strength B1 (N / mm 2 This includes the optical adhesive sheet described in [1] above, wherein F1 ≥ -1 / 3 × B1 + 7.

[0009] The present invention [3] provides a low-speed peel test in which, after bonding the optical adhesive sheet to a glass plate and the subsequent heat-pressure treatment, the optical adhesive sheet is peeled off the glass plate at 50°C, a peel angle of 180°, and a tensile speed of 30 mm / min, and a peel strength F2 of 4 N / 20 mm or more is achieved. Furthermore, in a low-speed tensile test in which, after bonding a first glass plate and a second glass plate in the thickness direction via the optical adhesive sheet and the subsequent heat-pressure treatment, the first and second glass plates are pulled in opposite directions in the thickness direction at 50°C and a tensile speed of 5 mm / min, the peel strength F2 is 0.9 N / mm 2 The optical adhesive sheet described in [1] or [2] above has a tensile adhesive strength B2 greater than or equal to the above.

[0010] The present invention [4] relates to the peel strength F2 (N / 20mm) and the tensile adhesive strength B2 (N / mm). 2 ), including the optical adhesive sheet described in [3] above, satisfying F2≧-1 / 3×B2+5.

[0011] The present invention [5] provides a low-speed peel test in which, after bonding the optical adhesive sheet to a glass plate and the subsequent heat-pressure treatment, the optical adhesive sheet is peeled off the glass plate at 80°C, a peel angle of 180°, and a tensile speed of 30 mm / min, and a peel strength F3 of 3 N / 20 mm or more is achieved. Furthermore, in a low-speed tensile test in which, after bonding a first glass plate and a second glass plate in the thickness direction via the optical adhesive sheet and the subsequent heat-pressure treatment, the first and second glass plates are pulled in opposite directions in the thickness direction at 80°C and a tensile speed of 5 mm / min, the peel strength F3 is 0.9 N / mm 2 The optical adhesive sheet includes any one of the above [1] to [4], having a tensile adhesive strength B3.

[0012] The present invention [6] includes the optical adhesive sheet according to any one of [1] to [5] above, in which the ratio of the peel strength F4 in a low-speed peel test where the optical adhesive sheet is peeled from the glass plate under the conditions of 95°C, a peel angle of 180°, and a tensile speed of 30 mm / min after bonding the optical adhesive sheet to the glass plate and then performing the heat and pressure treatment, to the peel strength F1 is 0.48 or less.

[0013] The present invention [7] includes the optical adhesive sheet according to any one of [1] to [6] above, in which the ratio of the peel strength F5 in a low-speed peel test where the optical adhesive sheet is peeled from the glass plate under the conditions of 65°C, a relative humidity of 90%, a peel angle of 180°, and a tensile speed of 30 mm / min after bonding the optical adhesive sheet to the glass plate and then performing the heat and pressure treatment, to the peel strength F1 is 0.45 or less.

Advantages of the Invention

[0014] The optical adhesive sheet of the present invention has a peel strength of 5 N / 20 mm or more in the above low-speed peel test at 25°C and a tensile adhesive strength of 0.9 N / mm or more in the above low-speed tensile test at 25°C. Such an optical adhesive sheet with strong adhesion measured in both low-speed tests is suitable for ensuring good adhesion to the adherend and suppressing peeling from the adherend when the adherend continues to receive stress from the adherend in a state where the adherend to which the adhesive sheet is attached is wound. Therefore, the optical adhesive sheet is suitable for rollable display applications. 2

Brief Description of the Drawings

[0015] [Figure 1] It is a schematic cross-sectional view of an embodiment of the optical adhesive sheet of the present invention. [Figure 2] It shows an example of the usage method of the optical adhesive sheet of the present invention. Fig. 2A shows the step of bonding the optical adhesive sheet to the first adherend, Fig. 2B shows the step of joining the first adherend and the second adherend through the optical adhesive sheet, and Fig. 2C shows the aging step.​ [Figure 3] This graph plots the tensile adhesive strength (horizontal axis) and peel strength (vertical axis) measurements taken for the optical adhesive sheets of the examples and comparative examples. [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 (surface direction). The adhesive sheet 10 has an adhesive surface 11 (first adhesive surface) on one side in the thickness direction H, and an adhesive surface 12 (second adhesive surface) 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.

[0017] Such an adhesive sheet 10 is a transparent adhesive sheet (optical adhesive sheet) placed in the light-transmitting area of ​​a rollable display panel. The rollable display panel has a laminated structure including, for example, a pixel panel, a polarizing plate, a touch panel, and a cover film. Examples of rollable display panels include smartphone display panels, automotive display panels, and interior display panels. The adhesive sheet 10 is used, for example, in the manufacturing process of the rollable display panel to bond elements included in the laminated structure together.

[0018] The adhesive sheet 10 has a peeling strength F1 of 5 N / 20 mm or more in a low-speed peeling test (first low-speed peeling test) in which the adhesive sheet 10 is peeled from the glass plate at 25°C, a peeling angle of 180°, and a tensile speed of 30 mm / min after the adhesion of the adhesive sheet 10 to the glass plate and subsequent heat and pressure treatment under the conditions of 50°C, 0.5 MPa, and 15 minutes. The peeling strength F1 at 25°C is preferably 5.5 N / 20 mm or more, more preferably 6 N / 20 mm or more, still more preferably 6.5 N / 20 mm or more. The peeling strength F1 is, for example, 30 N / 20 mm or less. Examples of the method for adjusting the peeling strength F1 include selection of the type of base polymer in the adhesive sheet 10, adjustment of the molecular weight, and adjustment of the blending amount. The selection of the type of base polymer includes adjustment of the composition of the monomers forming the base polymer. Examples of the method for adjusting the peeling strength F1 also include selection of the type of components other than the base polymer in the adhesive sheet 10 and adjustment of the blending amount of the components. Examples of such components include crosslinking agents, silane coupling agents, and oligomers. The above-described method for adjusting the peeling strength is the same for the peeling strengths F2 to F5 described below.

[0019] The adhesive sheet 10 is subjected to a low-speed tensile test (first low-speed tensile test) in which the first glass plate and the second glass plate are joined in the thickness direction via the adhesive sheet 10 and then heat and pressure treated under the conditions of 50°C, 0.5 MPa, and 15 minutes, and then the first and second glass plates are pulled in opposite directions in the thickness direction at 25°C and a tensile speed of 5 mm / min. 2 The adhesive sheet 10 has the above-described tensile adhesion strength B1 of 0.9 N / mm. The tensile adhesion strength B1 at 25°C is preferably 1.2 N / mm 2 or more, more preferably 1.5 N / mm 2 or more, still more preferably 1.8 N / mm 2 or more, particularly preferably 2 N / mm 2 or more. The tensile adhesion strength B1 is, for example, 15 N / mm 2The following are methods for adjusting the tensile adhesive strength B1. For example, this includes selecting the type of base polymer in the adhesive sheet 10, adjusting its molecular weight, and adjusting its blending amount. The selection of the type of base polymer includes adjusting the composition of the monomers that form the base polymer. Other methods for adjusting the tensile adhesive strength B1 include selecting the type of components other than the base polymer in the adhesive sheet 10 and adjusting the blending amount of these components. These components include crosslinking agents, silane coupling agents, and oligomers. The same methods for adjusting the tensile adhesive strength described above also apply to the tensile adhesive strengths B2 and B3 described later.

[0020] As described above, the adhesive sheet 10 has a peel strength F1 of 5 N / 20 mm or more in the first low-speed peel test, preferably 5.5 N / 20 mm or more, more preferably 6 N / 20 mm or more, and even more preferably 6.5 N / 20 mm or more, and a tensile adhesive strength B1 of 0.9 N / mm in the first low-speed tensile test. 2 The above is preferable, preferably 1.2 N / mm 2 More preferably 1.5 N / mm 2 More preferably 1.8 N / mm 2 The above is particularly preferably 2 N / mm 2 That concludes the explanation. For adhesive sheets, the combination of the peel strength measured in a 180° peel test and the tensile adhesive strength measured in a tensile test in the thickness direction of the adhesive sheet can be used as an indicator of the overall adhesive strength (adhesive function) of the adhesive sheet. On the other hand, for adhesive sheets used in rollable displays (where the adherend is wound), high adhesive function in all directions is required.

[0021] The adhesive sheet 10 described above, which exhibits strong adhesive strength in both types of tests measured at low speeds, is suitable for ensuring good adhesion to the adherend and suppressing peeling from the adherend when the adherend to which the adhesive sheet 10 is attached is continuously subjected to stress from the adherend while it is being wound. Therefore, the adhesive sheet 10 is suitable for rollable display applications.

[0022] The peel strength F1 (N / 20mm) and tensile adhesive strength B1 (N / mm) of the adhesive sheet 10. 2 Preferably, the equation F1 ≥ -1 / 3 × B1 + 7 is satisfied. Such a configuration is preferable for achieving both peel strength F1 and tensile adhesive strength B1, and is preferable for obtaining good results regarding the adhesion of the adhesive sheet 10 to the adherend when, for example, the winding retention test and bending retention test described below are performed in a room temperature environment.

[0023] The adhesive sheet 10 has a peel strength F2 in the second low-speed peel test, preferably 4N / 20mm or more, more preferably 4.2N / 20mm or more, and even more preferably 4.5N / 20mm or more, and a tensile adhesive strength B2 in the second low-speed tensile test, preferably 0.9N / mm 2 More preferably 1 N / mm 2 More preferably 1.1 N / mm 2 The above is particularly preferably 1.2 N / mm 2 That's all. The peel strength F2 is, for example, 30 N / 20 mm or less. The tensile adhesive strength B2 is, for example, 15 N / mm 2 The following applies: The second low-speed peel test involves bonding an adhesive sheet to a glass plate, followed by a heat and pressure treatment at 50°C, 0.5 MPa, and for 15 minutes. The adhesive sheet is then peeled off the glass plate at 50°C, a peel angle of 180°, and a tensile speed of 30 mm / min. The second low-speed tensile test involves bonding a first glass plate and a second glass plate in the thickness direction via an adhesive sheet, followed by a heat and pressure treatment at 50°C, 0.5 MPa, and for 15 minutes. The first and second glass plates are then pulled in opposite directions in the thickness direction at 50°C and a tensile speed of 5 mm / min.

[0024] Such an adhesive sheet 10 is preferable in the temperature range of 50°C and nearby, for ensuring good adhesion to the adherend and suppressing peeling from the adherend when the adherend to which the adhesive sheet 10 is attached is continuously subjected to stress from the adherend while the adherend is wound.

[0025] The peel strength F2 (N / 20mm) and tensile adhesive strength B2 (N / mm) of the adhesive sheet 10. 2 Preferably, F2 ≥ -1 / 3 × B2 + 5 is satisfied. Such a configuration is preferable for achieving both peel strength F2 and tensile adhesive strength B2, and is preferable for obtaining good results regarding the adhesion of the adhesive sheet 10 to the adherend in the winding retention test and bending retention test described later under high temperature environments.

[0026] The adhesive sheet 10 has a peel strength F3 in the third low-speed peel test, preferably 3N / 20mm or more, more preferably 3.1N / 20mm or more, and even more preferably 3.2N / 20mm or more, and a tensile adhesive strength B3 in the third low-speed tensile test, preferably 0.9N / mm 2 More preferably 1 N / mm 2 More preferably 1.1 N / mm 2 The above is particularly preferably 1.2 N / mm 2 That's all. The peel strength F3 is, for example, 30 N / 20 mm or less. The tensile adhesive strength B3 is, for example, 15 N / mm 2 The following applies: The third low-speed peel test involves bonding an adhesive sheet to a glass plate, followed by a heat and pressure treatment at 50°C, 0.5 MPa, and for 15 minutes, after which the adhesive sheet is peeled off the glass plate at 80°C, a peel angle of 180°, and a tensile speed of 30 mm / min. The third low-speed tensile test involves bonding a first glass plate and a second glass plate in the thickness direction via an adhesive sheet 10, followed by a heat and pressure treatment at 50°C, 0.5 MPa, and for 15 minutes, after which the first and second glass plates are pulled in opposite directions in the thickness direction at 80°C and a tensile speed of 5 mm / min.

[0027] Such an adhesive sheet 10 is preferable in the temperature range of 80°C and nearby, for ensuring good adhesion to the adherend to which the adhesive sheet 10 is attached, and for suppressing peeling from the adherend, when the adherend is continuously subjected to stress from the adherend while the adherend is wound.

[0028] The adhesive sheet 10 has a peel strength F4 ratio (F4 / F1) of peel strength F1 in the fourth low-speed peel test which is preferably 0.48 or less, more preferably 0.46 or less, and even more preferably 0.44 or less. The ratio (F4 / F1) is preferably 0.05 or more, more preferably 0.1 or more, and even more preferably 0.15 or more. The fourth low-speed peel test is a peel test in which the adhesive sheet is bonded to a glass plate, followed by a heat and pressure treatment at 50°C, 0.5 MPa and 15 minutes, and then the adhesive sheet is peeled off the glass plate at 95°C, a peel angle of 180° and a tensile speed of 30 mm / min.

[0029] Such a configuration is preferable for achieving both peel strength F1 and peel strength F4, and is preferable for obtaining good results regarding the adhesion of the adhesive sheet 10 to the adherend in the winding retention test and bending retention test described later under high temperature environments. While the ratio (F4 / F1) satisfies the above range, the peel strength F4 is preferably 1N / 20mm or more, more preferably 1.3N / 20mm or more, even more preferably 1.5N / 20mm or more, and also preferably 5N / 20mm or less, more preferably 4N / 20mm or less, and even more preferably 3N / 20mm or less.

[0030] The adhesive sheet 10 has a peel strength F5 ratio (F5 / F1) of peel strength F1 in the fifth low-speed peel test which is preferably 0.45 or less, more preferably 0.42 or less, even more preferably 0.4 or less, and particularly preferably 0.38 or less. The ratio (F5 / F1) is preferably 0.05 or more, more preferably 0.1 or more, and even more preferably 0.15 or more. The fifth low-speed peel test is a peel test in which the adhesive sheet is bonded to a glass plate, followed by a heat and pressure treatment at 50°C, 0.5 MPa and 15 minutes, and then the adhesive sheet is peeled off the glass plate at 65°C, 90% relative humidity, a peel angle of 180° and a tensile speed of 30 mm / min.

[0031] Such a configuration is preferable for achieving both peel strength F1 and peel strength F5, and is preferable for obtaining good results regarding the adhesion of the adhesive sheet 10 to the adherend in the winding retention test and bending retention test described later under high temperature environments. While the ratio (F5 / F1) satisfies the above range, the peel strength F5 is preferably 1N / 20mm or more, more preferably 1.3N / 20mm or more, even more preferably 1.5N / 20mm or more, and also preferably 5N / 20mm or less, more preferably 4N / 20mm or less, and even more preferably 3N / 20mm or less.

[0032] The adhesive sheet 10 has a peel strength F6 of 10 N / 20 mm or more in a peel test (first normal-speed peel test) in which the adhesive sheet 10 is peeled off the glass plate at 25°C, a peel angle of 180°, and a tensile speed of 300 mm / min, after bonding the adhesive sheet 10 to the glass plate and undergoing a subsequent heat and pressure treatment at 50°C, 0.5 MPa, and 15 minutes. The peel strength F6 is preferably 11 N / 20 mm or more, more preferably 12 N / 20 mm or more, and even more preferably 13 N / 20 mm or more. Such a configuration is preferable in that, when the adherend to which the adhesive sheet 10 is attached is wound up in a room temperature environment (dynamic deformation process), the adhesive sheet 10 ensures good adhesion to the adherend and suppresses peeling from the adherend. The peel strength F6 is, for example, 30 N / 20 mm or less.

[0033] The adhesive sheet 10 has a peel strength F7 of 8 N / 20 mm or more in a peel test (second normal-speed peel test) in which the adhesive sheet 10 is peeled off the glass plate at 95°C, a peel angle of 180°, and a tensile speed of 300 mm / min, after being bonded to the glass plate and subsequently subjected to a heat and pressure treatment at 50°C, 0.5 MPa, and for 15 minutes. The peel strength F7 is preferably 9 N / 20 mm or more, more preferably 10 N / 20 mm or more, and even more preferably 11 N / 20 mm or more. Such a configuration is preferable in that, when the adherend to which the adhesive sheet 10 is attached is wound in a high-temperature environment, the adhesive sheet 10 ensures good adhesion to the adherend and suppresses peeling from the adherend. The peel strength F7 is, for example, 30 N / 20 mm or less.

[0034] The adhesive sheet 10 has a peel strength F8 of 8 N / 20 mm or more in a peel test (third normal speed peel test) in which the adhesive sheet 10 is peeled off the glass plate under the conditions of 65°C, relative humidity 90%, peel angle 180°, and tensile speed 300 mm / min, after bonding the adhesive sheet 10 to the glass plate and subsequent heat and pressure treatment at 50°C, 0.5 MPa, and for 15 minutes. The peel strength F8 is preferably 9 N / 20 mm or more, more preferably 10 N / 20 mm or more, and even more preferably 11 N / 20 mm or more. Such a configuration is preferable in that, when the adherend to which the adhesive sheet 10 is attached is wound in a high humidity environment, the adhesive sheet 10 ensures good adhesion to the adherend and suppresses peeling from the adherend. The peel strength F8 is, for example, 30 N / 20 mm or less.

[0035] The adhesive sheet 10 is a pressure-sensitive adhesive layer formed from an adhesive composition. The adhesive sheet 10 includes at least a base polymer.

[0036] The base polymer is the adhesive component that provides tackiness in the adhesive sheet. 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, acrylic polymers are preferably used as the base polymer.

[0037] Acrylic polymers are copolymers of monomer components containing 50% or more by mass of alkyl (meth)acrylate. "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid.

[0038] As the alkyl (meth)acrylate ester, an alkyl (meth)acrylate ester having 1 to 20 carbon atoms in the alkyl group is preferably used. The alkyl (meth)acrylate ester may have a linear or branched alkyl group, or a cyclic alkyl group such as an alicyclic alkyl group.

[0039] 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, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, Examples include nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (i.e., lauryl acrylate), isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, and nonadecyl (meth)acrylate.

[0040] 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.

[0041] Preferably, an alkyl acrylate having an alkyl group with 3 to 15 carbon atoms is used as the (meth)acrylate, and more preferably, at least one selected from the group consisting of n-butyl acrylate, 2-ethylhexyl acrylate, and dodecyl acrylate is used.

[0042] 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 94% by mass or more, from the viewpoint of appropriately exhibiting basic properties such as tackiness in the adhesive sheet. This proportion is, for example, 99% by mass or less.

[0043] 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.

[0044] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. Preferably, at least one selected from the group consisting of 4-hydroxybutyl acrylate and 2-hydroxyethyl acrylate is used as the hydroxyl group-containing monomer.

[0045] The proportion of hydroxyl group-containing monomers in the monomer components 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 and ensuring cohesive force in the adhesive sheet. From the viewpoint of adjusting the polarity of the acrylic polymer (related to the compatibility between various additive components in the adhesive sheet and the acrylic polymer), the proportion is preferably 20% by mass or less, and more preferably 10% by mass or less.

[0046] 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.

[0047] 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, and ensuring adhesion force to the adherend in the adhesive sheet. 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 avoiding the risk of corrosion of the adherend by acid.

[0048] To prevent corrosion of metal elements such as electrodes in a rollable display by acidic components, it is preferable that the adhesive sheet 10 has a low acid content. Furthermore, when the adhesive sheet 10 is used to bond polarizing plates, it is preferable that the adhesive sheet 10 has a low acid content to suppress polyene formation of polyvinyl alcohol-based polarizers by acidic components. In such an acid-free adhesive sheet 10, the content of organic acid monomers (e.g., (meth)acrylic acid and carboxyl group-containing monomers) is preferably 100 ppm or less, more preferably 70 ppm or less, and even more preferably 50 ppm or less. The organic acid monomer content of the adhesive sheet can be determined by immersing the adhesive sheet in pure water and heating it at 100°C for 45 minutes, then quantifying the acid monomers extracted into the water using ion chromatography.

[0049] From an acid-free viewpoint, it is preferable that the base polymer in the adhesive sheet 10 substantially does not contain organic acid monomers as monomer components. From an acid-free viewpoint, the proportion of organic acid monomers in the monomer components is preferably 0.5% by mass or less, more preferably 0.1% by mass or less, even more preferably 0.05% by mass, and ideally 0% by mass.

[0050] 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. N-vinyl-2-pyrrolidone is preferably used as the monomer having a nitrogen atom-containing ring.

[0051] The proportion of monomers having nitrogen atom-containing rings in the monomer components is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.55% by mass or more, from the viewpoint of ensuring cohesive force in the adhesive sheet and ensuring adhesion force to the adherend in the adhesive sheet. 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 (which is related to the compatibility between various additive components in the adhesive sheet and the acrylic polymer).

[0052] 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.

[0053] 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 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.

[0054] 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.

[0055] 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).

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] In the second method described above, the monomer components (including polyfunctional monomers and other monomers for introducing crosslinking structures) 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, polyfunctional monomers are added to the prepolymer composition, and then the partially polymerized product and the polyfunctional monomer are polymerized (main polymerization).

[0061] 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.

[0062] Examples of polyfunctional (meth)acrylates include difunctional (meth)acrylates, trifunctional (meth)acrylates, and polyfunctional (meth)acrylates with four or more functions.

[0063] Examples of difunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol dimethacrylate, 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 diacrylate, di(meth)acryloyl isocyanurate, and alkylene oxide-modified bisphenol di(meth)acrylate.

[0064] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl) isocyanurate.

[0065] Examples of polyfunctional (meth)acrylates with four or more functions include ditrimethylolpropanetetra(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol pentaacrylate, and dipentaerythritol hexa(meth)acrylate.

[0066] The molecular weight of the polyfunctional monomer is preferably 1500 or less, more preferably 1000 or less. The functional group equivalent (g / eq) of the polyfunctional monomer is preferably 50 or more, more preferably 70 or more, and even more preferably 80 or more. The functional group equivalent is preferably 500 or less, more preferably 300 or less, and even more preferably 200 or less. These configurations are preferred from the viewpoint of appropriately adjusting the viscoelasticity (e.g., storage modulus and loss tangent) by introducing a crosslinking structure in the base polymer.

[0067] Acrylic polymers can be formed by polymerizing the monomer components described above. Polymerization methods include, for example, solution polymerization, active energy ray polymerization (e.g., UV polymerization), bulk polymerization, and emulsion polymerization. From the viewpoint of transparency, water resistance, and cost of the adhesive sheet 10, solution polymerization and UV polymerization are preferred. For example, ethyl acetate and toluene are used as solvents for solution polymerization. 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, and for example, 1 part by mass or less, per 100 parts by mass of monomer components.

[0068] 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.

[0069] 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.

[0070] In polymerization, chain transfer agents and / or polymerization inhibitors (polymerization retarders) may be used for purposes such as molecular weight adjustment. Examples of chain transfer agents include α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, and α-methylstyrene dimers.

[0071] The molecular weight of the base polymer can be adjusted by controlling the type and / or amount of polymerization initiator. For example, in radical polymerization, a larger amount of polymerization initiator leads to a higher radical concentration in the reaction system, resulting in a higher density of reaction initiator sites and a tendency for the formed base polymer to have a smaller molecular weight. Conversely, a smaller amount of polymerization initiator leads to a lower density of reaction initiator sites, allowing the polymer chain to elongate more easily and resulting in a tendency for the formed base polymer to have a larger molecular weight.

[0072] 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 same weight-average molecular weight is preferably 5 million or less, more preferably 3 million or less, and even more preferably 2 million or less. The weight-average molecular weight of the base polymer is measured by gel permeation chromatography (GPC) and calculated on a polystyrene basis.

[0073] 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.

[0074] 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.

[0075] Fox's formula 1 / (273+Tg)=Σ[Wi / (273+Tgi)]

[0076] The adhesive composition may contain one or more oligomers in addition to the base polymer. When an acrylic polymer is used as the base polymer, an acrylic oligomer is preferably used as the oligomer. The acrylic oligomer is a copolymer of monomer components containing 50% by mass or more of alkyl (meth)acrylate, and has a weight-average molecular weight of, for example, 1,000 to 30,000.

[0077] The glass transition temperature of the acrylic oligomer is preferably 60°C or higher, more preferably 80°C or higher, even more preferably 100°C or higher, and particularly preferably 110°C or higher. The glass transition temperature of the acrylic oligomer is, for example, 200°C or lower, preferably 180°C or lower, and more preferably 160°C or lower. By using a low-Tg acrylic polymer (base polymer) with a crosslinked structure in combination with a high-Tg acrylic oligomer, the adhesive strength of the adhesive sheet 10, especially the adhesive strength at high temperatures, can be increased. The glass transition temperature of the acrylic oligomer is calculated using the Fox formula described above.

[0078] Acrylic oligomers with a glass transition temperature of 60°C or higher are preferably polymers of monomer components containing a (meth)acrylate (linear alkyl(meth)acrylate) having a chain-like alkyl group and an (meth)acrylate (alicyclic alkyl(meth)acrylate) having an alicyclic alkyl group. Specific examples of these (meth)acrylate alkyl esters include, for example, the above-mentioned (meth)acrylate alkyl esters used as monomer components in acrylic polymers.

[0079] As the linear alkyl (meth)acrylate, methyl methacrylate is preferred due to its high glass transition temperature and excellent compatibility with the base polymer. As the alicyclic alkyl (meth)acrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferred. In other words, the acrylic oligomer is preferably a polymer of monomer components containing one or more selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate.

[0080] The proportion of alicyclic alkyl (meth)acrylate in the monomer component of the acrylic oligomer is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. The same proportion is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. The proportion of linear alkyl (meth)acrylate in the monomer component of the acrylic oligomer is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. The same proportion is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more.

[0081] The weight-average molecular weight of the acrylic oligomer is preferably 1000 or more, more preferably 1500 or more, and even more preferably 2000 or more. The molecular weight is preferably 30000 or less, more preferably 10000 or less, and even more preferably 8000 or less. Such a molecular weight range for the acrylic oligomer is preferable for ensuring the adhesive strength and adhesive retention of the adhesive sheet 10.

[0082] Acrylic oligomers are obtained by polymerizing the monomer components of the acrylic oligomer. Examples of polymerization methods include solution polymerization, active energy ray polymerization (e.g., UV polymerization), bulk polymerization, and emulsion polymerization. In the polymerization of acrylic oligomers, polymerization initiators may be used, and chain transfer agents may be used for the purpose of adjusting the molecular weight.

[0083] To sufficiently enhance the adhesive strength of the adhesive sheet 10, the acrylic oligomer content is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of the base polymer. On the other hand, from the viewpoint of ensuring the transparency of the adhesive sheet 10, the acrylic oligomer content in the adhesive sheet 10 is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of the base polymer. In the adhesive sheet 10, if the acrylic oligomer content is too high, the haze tends to increase and the transparency tends to decrease due to a decrease in the compatibility of the acrylic oligomer.

[0084] 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.

[0085] 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 acrylic polymer polymerization, and solvents added to the polymerization reaction solution after polymerization. Examples of such solvents include ethyl acetate and toluene.

[0086] 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.

[0087] Examples of the release liner 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 is, for example, 3 μm or more, and for example, 200 μm or less. The surface of the release liner is preferably treated to release the adhesive.

[0088] 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.

[0089] A second release liner (L2) may be laminated on top of the adhesive sheet 10 on the first release liner L1. The second release liner is a flexible plastic film that has undergone a surface release treatment, and the same type as described above for the first release liner can be used.

[0090] In this manner, an adhesive sheet 10 can be manufactured in which the adhesive surfaces 11 and 12 are covered and protected by release liners L1 and L2. The release liners L1 and L2 are peeled off from the adhesive sheet 10 as needed when using the adhesive sheet 10.

[0091] From the viewpoint of ensuring sufficient adhesion to the adherend, the thickness of the adhesive sheet 10 is preferably 10 μm or more, more preferably 15 μm or more. From the viewpoint of handling the adhesive sheet 10, 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.

[0092] 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.

[0093] 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).

[0094] Figures 2A to 2C show an example of how to use the adhesive sheet 10.

[0095] In this method, first, as shown in Figure 2A, the adhesive sheet 10 is attached to one side of the first member 21 (adhered body) in the thickness direction H. The first member 21 is, for example, one element in the laminated structure of a rollable 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.

[0096] 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 rollable display panel.

[0097] Next, as shown in Figure 2C, 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 aging is performed by autoclave treatment (heat and pressure treatment), 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.

[0098] The adhesive sheet 10 used in the manufacturing process of the rollable display panel as described above has a peel strength F1 of 5 N / 20 mm or more in the first low-speed peel test, and a tensile adhesive strength B1 of 0.9 N / mm in the first low-speed tensile test. 2 This concludes the explanation. Such an adhesive sheet 10, in which both types of adhesive strength measured in low-speed tests are strong, is suitable for ensuring good adhesion to the adherend to which the adhesive sheet 10 is attached and suppressing peeling from the adherend when the adherend is continuously subjected to stress from the adherend while the adherend is wound. Therefore, the adhesive sheet 10 is suitable for rollable display applications. [Examples]

[0099] 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.

[0100] [Example 1] <Preparation of adhesive composition> In a flask, a monomer mixture containing 75 parts by mass of 2-ethylhexyl acrylate (2EHA), 5 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 20 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 "Irgacure 651", manufactured by Ciba Japan Co., Ltd.) as a first photopolymerization initiator and 0.05 parts by mass of 1-hydroxycyclohexyl-phenyl-ketone (product name "Irgacure 184", manufactured by Ciba Japan Co., Ltd.) 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, thereby obtaining a first prepolymer composition with a polymerization rate of 12% (containing monomer components that had not undergone the polymerization reaction). Then, 100 parts by mass of the first prepolymer composition, 0.3 parts by mass of hexamethylenediol diacrylate (HDDA) as a crosslinking agent, and 0.3 parts by mass of a silane coupling agent (product name "KBM403", manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed to obtain the first adhesive composition.

[0101] <Formation of the adhesive layer> A first adhesive composition was applied to the release surface of a first release liner (product name "Diafoil MRF", 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", 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 metal halide lamp was used as the light source, and the illuminance was set to 4 mW / cm². 2 The integrated irradiation light dose is 1200 mJ / cm². 2 That's what I decided.

[0102] As described above, an optical adhesive sheet (thickness 50 μm) with a double-sided release liner was prepared according to Example 1.

[0103] [Example 2] <Preparation of adhesive composition> In a flask, a monomer mixture containing 80 parts by mass of butyl acrylate (BA), 10 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 10 parts by mass of cyclohexyl acrylate was mixed with 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenyl-1-one (product name "Irgacure 651", manufactured by Ciba Japan Co., Ltd.) as a first photopolymerization initiator and 0.05 parts by mass of 1-hydroxycyclohexyl-phenyl-ketone (product name "Irgacure 184", manufactured by Ciba Japan Co., Ltd.) 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, thereby obtaining a second prepolymer composition with a polymerization rate of 10% (containing monomer components that had not undergone the polymerization reaction). Then, 100 parts by mass of the second prepolymer composition, 0.01 parts by mass of dipentaerythritol hexaacrylate (DPHA) as a crosslinking agent, and 0.3 parts by mass of a silane coupling agent (product name "KBM403", manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed to obtain the second adhesive composition.

[0104] <Formation of the adhesive layer> A first adhesive composition was applied to the release surface of a first release liner (product name "Diafoil MRF", 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", 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 metal halide lamp was used as the light source, and the illuminance was set to 4 mW / cm². 2 The integrated irradiation light dose is 1200 mJ / cm². 2 That's what I decided.

[0105] As described above, an optical adhesive sheet (thickness 50 μm) with a double-sided release liner was prepared according to Example 2.

[0106] [Comparative Example 1] In preparing the adhesive composition, the optical adhesive sheet with a double-sided peel-off liner (50 μm) of Comparative Example 1 was prepared in the same manner as the optical adhesive sheet with a double-sided peel-off liner of Example 2, except that the amount of DPHA was changed from 0.01 parts by mass to 0.1 parts by mass.

[0107] <Slow-speed peeling test> The peel strength of each optical adhesive sheet in Examples 1 and 2 and Comparative Example 1 was investigated in a low-speed peel test.

[0108] Specifically, first, the required number of measurement samples were prepared for each optical adhesive sheet. In preparing the measurement samples, the first release liner was peeled off the optical 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. Next, a test piece (width 20 mm x length 100 mm) was cut from this laminate (PET film / optical adhesive sheet / second release liner). Next, the second release liner was peeled off the optical adhesive sheet of this test piece, and the exposed surface was bonded to a glass plate (product name "Slide Glass S2004U8", manufactured by Matsunami Glass Industry Co., Ltd.). Next, the glass plate with the adhesive sheet (test piece) 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 piece against the glass plate. Measurement samples were prepared in the manner described above.

[0109] Next, after allowing the sample to stand at room temperature for 30 minutes, a slow peel test was performed to peel the test piece from the glass plate of the sample, and the peel strength was measured (Test 1). 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 glass plate to 180°, the tensile speed of the test piece to 30 mm / min, and the peel length to 50 mm. The average value of the measured peel strength is shown in Table 1 as the peel strength F1 (N / 20 mm).

[0110] A slow peel test was conducted under the same conditions as the first test, except that the measurement temperature was changed to 50°C, and the peel strength F2 at 50°C was measured. A slow peel test was conducted under the same conditions as the first test, except that the measurement temperature was changed to 80°C, and the peel strength F3 at 80°C was measured. A slow peel test was conducted under the same conditions as the first test, except that the measurement temperature was changed to 95°C, and the peel strength F4 at 95°C was measured. A slow peel test was conducted under the same conditions as the first test, except that the measurement temperature was changed to 65°C and the relative humidity was set to 90%, and the peel strength F5 at 65°C and 90% relative humidity was measured. The peel strengths F2 to F5, the ratio of peel strength F4 to peel strength F1 (F4 / F1), and the ratio of peel strength F5 to peel strength F1 (F5 / F1) are also shown in Table 1.

[0111] <Low-speed tensile test> The tensile adhesive strength of each optical adhesive sheet in Examples 1 and 2 and Comparative Example 1 was investigated in a low-speed tensile test. Specifically, the results are as follows:

[0112] First, a sample for measurement was prepared for each optical adhesive sheet. In preparing the sample for measurement, two glass plates supported by a metal block were first prepared. The metal block-supported glass plate was prepared by attaching a glass plate (3cm x 3cm x 0.5cm) to one side of a metal block (a cubic block made of SUS304 measuring 3cm x 3cm x 3cm) using adhesive. Next, the first release liner was peeled off a piece of optical adhesive sheet (1cm x 1cm) cut from the optical adhesive sheet, and the exposed surface was attached to the exposed glass surface of one of the metal block-supported glass plates (first glass plate). Next, the second release liner was peeled off from the optical 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 (second glass plate), thereby joining the glass plates together (joining the first glass plate and the second glass plate in the thickness direction via the optical adhesive sheet). Next, the optical adhesive sheet test pieces were pressed onto both glass plates by heating and pressurizing under the conditions of 50°C, 0.5 MPa, and for 15 minutes. In this manner, the measurement sample (metal block / glass plate / optical adhesive sheet / glass plate / metal block) was prepared.

[0113] Next, a test was performed in which two metal-supported glass plates in the measurement sample were pulled in opposite directions in the thickness direction (low-speed tensile test), and the force required to separate the glass plates was measured (second 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%, and the tensile speed to 5 mm / min. The maximum value of the measured force is shown in Table 1 as the tensile adhesive strength B1 (N / 20 mm).

[0114] A low-speed tensile test was conducted under the same conditions as the second test, except that the measurement temperature was changed to 50°C, and the tensile adhesive strength B2 at 50°C was measured. A low-speed tensile test was conducted under the same conditions as the second test, except that the measurement temperature was changed to 80°C, and the tensile adhesive strength B3 at 80°C was measured. These values ​​are also shown in Table 1.

[0115] Furthermore, the measurement results of the peel strength and tensile adhesive strength for each optical adhesive sheet in Examples 1 and 2 and Comparative Example 1 are shown in the graph in Figure 3. In the graph in Figure 3, the horizontal axis is the tensile adhesive strength (N / mm²) in the low-speed tensile test described above. 2 The vertical axis represents the peel strength (N / 20mm) in the low-speed peel test described above. In Figure 3, plot E1 represents the measurement results in Example 1, plot E2 represents the measurement results in Example 2, and plot C1 represents the measurement results in Comparative Example 1. The dotted line R1 represents the tensile adhesive strength B = 0.9 N / mm 2 The lines are shown. The dashed line R2 indicates the peel strength F = -1 / 3 × tensile adhesive strength B + 7. The dashed line R3 indicates the peel strength F = -1 / 3 × tensile adhesive strength B + 5. The optical adhesive sheets of Examples 1 and 2 have peel strength F (N / 20mm) and tensile adhesive strength B (N / mm) at 25°C. 2 The bond satisfies F≧-1 / 3×B+7, and at 50℃, the peel strength F(N / 20mm) and tensile adhesive strength B(N / mm) 2 The equation F≧-1 / 3×B+5 is satisfied. The optical adhesive sheets of Examples 1 and 2 showed good results in the winding retention test described below, and also showed good results in the bending retention test described below.

[0116] <Wrap-around retention test> The following winding and retention tests were performed on each optical adhesive sheet in Examples 1 and 2 and Comparative Example 1.

[0117] A first laminate was fabricated by peeling off the first release liner from the optical adhesive sheet and laminating a first PET film (product name "Lumirror S10", thickness 100 μm, manufactured by Toray) with a plasma-treated surface onto the exposed surface. Next, a second laminate was fabricated by peeling off the release liner from the adhesive layer of a polarizing plate with an adhesive (PSA) layer (thickness 66 μm, with a peelable release liner on the outer surface of the adhesive layer and a peelable protective film on the outer surface of the polarizing plate, manufactured by Nitto Denko Corporation) and laminating a second PET film (product name "Lumirror S10", thickness 188 μm, manufactured by Toray) with a plasma-treated surface onto the exposed surface. Next, the second release liner was peeled from the optical adhesive sheet in the first laminate, and the protective film was peeled from the polarizing plate in the second laminate. The exposed surfaces were then bonded together, and a third laminate (first PET film / optical adhesive sheet / polarizing plate / PSA on polarizing plate / second PET film) was fabricated after pressurized heating treatment at 50°C, 0.5 MPa, and for 15 minutes. Next, a test specimen (25 mm wide x 150 mm long) was cut from this third laminate. This test specimen has a first end at one end in the longitudinal direction and a second end at the other end.

[0118] Next, the test specimen was wrapped around a cylindrical metal rod (made of SUS304) with a cross-sectional diameter of 30 mm, such that the length of the test specimen aligned with the circumference of the metal rod, as follows: First, the first PET film side of the first end of the test specimen was attached to the metal rod via double-sided tape. Next, the test specimen was wrapped around the metal rod while being pulled in the length direction, such that the first PET film side of the test specimen was positioned on the inside of the wrapped portion. Specifically, the test specimen was wrapped around the metal rod without any gaps between the metal rod and the test specimen, and without any gaps between the test specimens in the diameter direction of the metal rod. Next, the second end of the test specimen wrapped around the metal rod was fixed with adhesive tape.

[0119] Next, the metal rods with test specimens prepared as described above were left standing for 250 hours in an environment of 60°C and 95% relative humidity (wrapping and retention test). In this wrapping and retention test, the adhesion of the optical adhesive sheet to the adherend was evaluated as "good" if no defects such as air bubbles or peeling in the adhesive layer (optical adhesive sheet) or cracking of the polarizing plate occurred, and as "poor" if any of these defects occurred. The results are shown in Table 1.

[0120] <Flexibility test> The following bending and holding tests were performed on each optical adhesive sheet in Examples 1 and 2 and Comparative Example 1.

[0121] First, a test specimen similar to the one described above (width 25 mm x length 150 mm, laminate configuration: first PET film / optical adhesive sheet / polarizing plate / PSA on polarizing plate / second PET film) was prepared for the winding retention test. Next, this test specimen was bent from a flat shape to a U-shape, and the deformed test specimen was held in this state with a predetermined holder. Specifically, the deformed test specimen was curved in the longitudinal direction of the specimen so that the first PET film side of the first end and the first PET film side of the second end of the specimen faced each other (the distance between the opposing ends was approximately 20 mm). After this, this deformed test specimen was left to stand for 250 hours in an environment of 60°C and 95% relative humidity (bending retention test). The adhesion of the optical adhesive sheet to the adherend in this bending retention test was evaluated as "good" if no defects such as air bubbles and peeling in the adhesive layer (optical adhesive sheet) and cracking of the polarizing plate occurred, and as "poor" if any of these defects occurred. The results are shown in Table 1.

[0122] [Table 1] [Explanation of symbols]

[0123] 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. An optical adhesive sheet containing a base polymer, The base polymer is a copolymer of monomer components including an alkyl (meth)acrylate and a hydroxyl group-containing monomer. The aforementioned base polymer has a cross-linked structure introduced by a polyfunctional (meth)acrylate. The proportion of the alkyl (meth)acrylate in the monomer component is 50% by mass or more. The proportion of the hydroxyl group-containing monomer in the monomer component is 20% by mass or less. The (meth)acrylate alkyl ester includes an (meth)acrylate alkyl ester having an alicyclic alkyl group, In a low-speed peel test in which the optical adhesive sheet is bonded to a glass plate, followed by a heat and pressure treatment at 50°C, 0.5 MPa, and 15 minutes, and then peeled off the optical adhesive sheet from the glass plate at 25°C, a peel angle of 180°, and a tensile speed of 30 mm / min, the peel strength F1 is 5 N / 20 mm or more. In a low-speed tensile test in which the first and second glass plates are joined in the thickness direction via the optical adhesive sheet, and after the subsequent heat and pressure treatment, the first and second glass plates are pulled in opposite directions in the thickness direction at 25°C and a tensile speed of 5 mm / min, the result was 0.9 N / mm ２ An optical adhesive sheet having the above tensile adhesive strength B1.

2. The peel strength F1 (N / 20 mm) and the tensile adhesive strength B1 (N / mm) ２ The optical adhesive sheet according to claim 1, wherein F1 ≥ -1 / 3 × B1 + 7.

3. In a low-speed peel test in which the optical adhesive sheet is peeled off the glass plate at 50°C, a peel angle of 180°, and a tensile speed of 30 mm / min after bonding the optical adhesive sheet to the glass plate and the subsequent heat and pressure treatment, the peel strength F2 is 4 N / 20 mm or more. In a low-speed tensile test in which the first and second glass plates are joined in the thickness direction via the optical adhesive sheet, and after the subsequent heat and pressure treatment, the first and second glass plates are pulled in opposite directions in the thickness direction at 50°C and a tensile speed of 5 mm / min, the result was 0.9 N / mm ２ An optical adhesive sheet according to claim 1 or 2, having the above tensile adhesive strength B2.

4. The peel strength F2 (N / 20 mm) and the tensile adhesive strength B2 (N / mm) ２ The optical adhesive sheet according to claim 3, wherein F2 ≥ -1 / 3 × B2 + 5.

5. In a low-speed peel test in which the optical adhesive sheet is peeled off the glass plate at 80°C, a peel angle of 180°, and a tensile speed of 30 mm / min after bonding the optical adhesive sheet to the glass plate and the subsequent heat and pressure treatment, the peel strength F3 of 3 N / 20 mm or more is observed. In a low-speed tensile test in which the first and second glass plates are joined in the thickness direction via the optical adhesive sheet, and after the subsequent heat and pressure treatment, the first and second glass plates are pulled in opposite directions in the thickness direction at 80°C and a tensile speed of 5 mm / min, the result was 0.9 N / mm ２ An optical adhesive sheet according to any one of claims 1 to 4, having the above tensile adhesive strength B3.

6. The optical adhesive sheet according to any one of claims 1 to 5, wherein the ratio of the peel strength F4 to the peel strength F1 in a low-speed peel test in which the optical adhesive sheet is peeled off the glass plate at 95°C, a peel angle of 180°, and a tensile speed of 30 mm / min after lamination of the optical adhesive sheet to the glass plate and subsequent heat and pressure treatment is 0.48 or less.

7. The optical adhesive sheet according to any one of claims 1 to 6, wherein, after bonding the optical adhesive sheet to a glass plate and the subsequent heat and pressure treatment, the optical adhesive sheet is peeled off the glass plate under the conditions of 65°C, 90% relative humidity, a peel angle of 180°C, and a tensile speed of 30 mm / min, and the ratio of the peel strength F5 to the peel strength F1 is 0.45 or less.

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