Optical adhesive sheet

Abstract

This invention provides an optical adhesive sheet suitable for use in rollable displays. The adhesive sheet 10 of this invention is an optical adhesive sheet. The adhesive sheet 10 exhibits a peel strength F1 of 5 N / 20 mm or higher in a low-speed peel test. This low-speed peel test is conducted after bonding the adhesive sheet 10 to a glass plate and subsequent heat and pressure treatment at 50°C, 0.5 MPa, and 15 minutes, followed by peeling the adhesive sheet 10 from the glass plate at 25°C, a peel angle of 180°, and a tensile speed of 30 mm / min. The adhesive sheet 10 exhibits a tensile adhesion strength B1 of 0.9 N / mm² or higher in the low-speed peel test. This low-speed peel test is conducted after bonding the first and second glass plates in the thickness direction of the adhesive sheet 10 between them and subsequent heat and pressure treatment, followed by stretching the first and second glass plates in opposite directions in the thickness direction at 25°C and a tensile speed of 5 mm / min.

Description

[Technical Field]

[0001] This invention relates to an optical adhesive sheet. [Previous Technology]

[0002] The display panel has a multilayer structure including, 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 purposes (optical adhesive sheet) is used to bond the components included in the multilayer structure to each other.

[0003] On the other hand, foldable display panels are being developed for use in, for example, smartphones and tablets. Specifically, foldable display panels can repeatedly deform between a curved shape and a flat, non-curved shape. The components in the laminated structure of such foldable display panels are manufactured to be repeatedly bent, and thin optical adhesive sheets are used to bond these components together. 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 Application Publication No. 2018-111754 [Summary of the Invention]

[0005] [The problem the invention aims to solve]

[0006] As a flexible display panel, the development of rollable (flexible) display panels is also continuously advancing. Rollable display panels, for example, can repeatedly deform between a rolled shape after being rolled up entirely or partially and a flat shape after being rolled out entirely. In the laminated structure of such a rollable display panel, each element is manufactured to be repeatedly deformable, and a thin optical adhesive sheet is used to bond these elements together. When the rollable display panel is in a rolled shape, the optical adhesive sheet bonded to the elements in the rolled shape is continuously subjected to stress from those elements. For this optical adhesive sheet, a very high level of requirement is required so that it does not easily peel off from the bonded elements when the display is in a rolled shape.

[0007] This invention provides an optical adhesive sheet suitable for use in rollable displays. [Technical Means for Solving the Problem]

[0008] The present invention [1] includes an optical adhesive sheet having a peel strength F1 of 5 N / 20 mm or more in a low-speed peel test. The low-speed peel test is performed after the optical adhesive sheet is bonded to a glass plate and then subjected to heat and pressure treatment at 50°C, 0.5 MPa and 15 minutes. The optical adhesive sheet is then peeled from the glass plate at 25°C, peel angle 180° and tensile speed 30 mm / min. The optical adhesive sheet also has a tensile bonding strength B1 of 0.9 N / mm2 or more in a low-speed tensile test. The low-speed tensile test is performed after the first glass plate and the second glass plate are bonded in the thickness direction of the optical adhesive sheet and then subjected to heat and pressure treatment. The first and second glass plates are stretched in opposite directions in the thickness direction at 25°C and tensile speed 5 mm / min.

[0009] The present invention [2] includes an optical adhesive sheet as described in [1] above, wherein the peel strength F1 (N / 20 mm) and the tensile bonding strength B1 (N / mm2) satisfy F1≧-1 / 3×B1+7.

[0010] The present invention [3] includes an optical adhesive sheet as described in [1] or [2] above, which has a peel strength F2 of 4 N / 20 mm or more in a low-speed peel test. The low-speed peel test is performed after the optical adhesive sheet is bonded to a glass plate and after the heat and pressure treatment thereafter, the optical adhesive sheet is peeled from the glass plate at 50°C, peel angle 180° and tensile speed 30 mm / min. The low-speed tensile test has a tensile adhesion strength B2 of 0.9 N / mm2 or more. The low-speed tensile test is performed after the first glass plate and the second glass plate are joined in the thickness direction of the optical adhesive sheet and after the heat and pressure treatment thereafter, the first and second glass plates are stretched in opposite directions in the thickness direction at 50°C and tensile speed 5 mm / min.

[0011] The present invention [4] includes an optical adhesive sheet as described in [3] above, wherein the peel strength F2 (N / 20 mm) and the tensile bonding strength B2 (N / mm2) satisfy F2≧-1 / 3×B2+5.

[0012] The present invention [5] includes an optical adhesive sheet as described in any one of [1] to [4] above, which has a peel strength F3 of 3 N / 20 mm or more in a low-speed peel test. The low-speed peel test is performed after the optical adhesive sheet is bonded to a glass plate and after the heat and pressure treatment thereafter, the optical adhesive sheet is peeled from the glass plate at 80°C, peel angle 180° and tensile speed 30 mm / min. The low-speed tensile test has a tensile adhesion strength B3 of 0.9 N / mm2 or more. The low-speed tensile test is performed after the first glass plate and the second glass plate are joined in the thickness direction of the optical adhesive sheet and after the heat and pressure treatment thereafter, the first and second glass plates are stretched in opposite directions in the thickness direction at 80°C and tensile speed 5 mm / min.

[0013] The present invention [6] includes an optical adhesive sheet as described in any one of [1] to [5] above, wherein the ratio of the peel strength F4 to the peel strength F1 in the low-speed peel test is 0.48 or less. The low-speed peel test is performed after the optical adhesive sheet is bonded to the glass plate and after the heat and pressure treatment thereafter, and the optical adhesive sheet is peeled from the glass plate at 95°C, peel angle 180° and tensile speed 30 mm / min.

[0014] The present invention [7] includes an optical adhesive sheet as described in any one of [1] to [6] above, wherein the ratio of the peel strength F5 to the peel strength F1 in a low-speed peel test is 0.45 or less. The low-speed peel test is performed after the optical adhesive sheet is bonded to a glass plate and subsequently subjected to the heat and pressure treatment, and the optical adhesive sheet is peeled from the glass plate under conditions of 65°C, 90% relative humidity, a peel angle of 180°, and a tensile speed of 30 mm / min. [Effects of the Invention]

[0015] The optical adhesive sheet of the present invention exhibits a peel strength of 5 N / 20 mm or more in the aforementioned low-speed peel test at 25°C, and a tensile adhesion strength of 0.9 N / mm² or more in the aforementioned low-speed tensile test at 25°C. This optical adhesive sheet, exhibiting strong adhesion in both aspects as measured in the low-speed test, is suitable for ensuring good adhesion to the adhered object and suppressing peeling from the adhered object when the adhered object is continuously subjected to stress from the adhered object while it is being rolled up. Therefore, the optical adhesive sheet is suitable for use in rollable displays.

Implementation Method

[0017] As shown in FIG1, the adhesive sheet 10, as one embodiment of the optical adhesive sheet of the present invention, has a sheet shape of a specific thickness and extends in a direction orthogonal 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. FIG1 shows, by way of example, the state in which release pads L1 and L2 are attached to the adhesive surfaces 11 and 12 of the adhesive sheet 10. The release pad L1 is disposed on the adhesive surface 11. The release pad L2 is disposed on the adhesive surface 12.

[0018] This adhesive sheet 10 is a transparent adhesive sheet (optical adhesive sheet) disposed in the light-passing portion of a rollable display panel. The rollable display panel, for example, has a laminated structure including a pixel panel, a polarizing plate (polarizing film), a touch panel, and a cover film. Examples of rollable display panels include smartphone display panels, automotive display panels, and indoor display panels. The adhesive sheet 10 can be used, for example, during the manufacturing process of the rollable display panel for bonding the elements included in the aforementioned laminated structure to each other.

[0019] The adhesive sheet 10 exhibits a peel strength F1 of 5 N / 20 mm or more in a low-speed peel test (first low-speed peel test). This low-speed peel test is conducted after the adhesive sheet 10 is bonded to a glass plate and subsequently subjected to heat and pressure treatment at 50°C, 0.5 MPa, and 15 minutes. The adhesive sheet 10 is then peeled from the glass plate at 25°C, a peel angle of 180°, and a tensile speed of 30 mm / min. The peel strength F1 at 25°C is 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. The peel strength F1 is, for example, 30 N / 20 mm or less. Methods for adjusting the peel strength F1 include, for example, selecting the type of base polymer in the adhesive sheet 10, adjusting the molecular weight, and adjusting the formulation amount. The selection of the type of base polymer includes adjusting the composition of the monomers forming the base polymer. As an example of adjusting the peel strength F1, the selection of the types of components in the adhesive sheet 10 other than the base polymer, and the adjustment of the formulation amount of such components, can be cited. Examples of such components include crosslinking agents, silane coupling agents, and oligomers. The peel strength adjustment method described above is also applicable to the peel strengths F2 to F5 described below.

[0020] The adhesive sheet 10 exhibits a tensile bond strength B1 of 0.9 N / mm² or higher in a low-speed tensile test (first low-speed tensile test). This low-speed tensile test is conducted after the bonding of the adhesive sheet 10 between the first and second glass plates in the thickness direction, followed by heating and pressurizing at 50°C, 0.5 MPa, and 15 minutes. The first and second glass plates are then stretched at 25°C and a tensile speed of 5 mm / min, with the first and second glass plates facing opposite directions in the thickness direction. The tensile bond strength B1 at 25°C is preferably 1.2 N / mm² or higher, more preferably 1.5 N / mm² or higher, and even more preferably 1.8 N / mm² or higher, and particularly preferably 2 N / mm² or higher. The tensile bond strength B1 is, for example, 15 N / mm² or lower. Methods for adjusting the tensile bond strength B1 include, for example, selecting the type of base polymer in the adhesive sheet 10, adjusting the molecular weight, and adjusting the formulation amount. The selection of the base polymer includes adjusting the composition of the monomers that form the base polymer. As a method for adjusting tensile bond strength B1, examples include the selection of the types of components in the adhesive sheet 10 other than the base polymer, and the adjustment of the formulation amount of these components. Examples of these components include crosslinking agents, silane coupling agents, and oligomers. The above-described method for adjusting tensile bond strength also applies to the tensile bond strengths B2 and B3 described below.

[0021] As described above, the peel strength F1 of the adhesive sheet 10 in the first low-speed peel test is 5 N / 20 mm or more, 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 the tensile bond strength B1 in the first low-speed tensile test is 0.9 N / mm² or more, preferably 1.2 N / mm² or more, more preferably 1.5 N / mm² or more, even more preferably 1.8 N / mm² or more, and particularly preferably 2 N / mm² or more. Regarding the adhesive sheet, the combination of the peel strength measured in the 180° peel test and the tensile bond strength measured in the tensile test in the thickness direction of the adhesive sheet can be used as an indicator of the all-around adhesive strength (adhesive function) of the adhesive sheet. On the other hand, adhesive sheets for rollable displays (where the adhered object is rolled up) are required to have a high all-around adhesive function.

[0022] The adhesive sheet 10, which exhibits strong adhesion in both types as measured in the low-speed test, is suitable for ensuring good adhesion to the adhered body and suppressing peeling from the adhered body when the adhered body to which the adhesive sheet 10 is attached is continuously subjected to stress from the adhered body while it is being rolled up. Therefore, the adhesive sheet 10 is suitable for use in rollable displays.

[0023] The peel strength F1 (N / 20 mm) and tensile bond strength B1 (N / mm2) of the adhesive sheet 10 preferably satisfy F1 ≥ -1 / 3 × B1 + 7. This configuration is better for balancing peel strength F1 and tensile bond strength B1, for example, for obtaining good results regarding the adhesion of the adhesive sheet 10 to the adhered body when performing the winding retention test and bending retention test as described below at room temperature.

[0024] The peel strength F2 of the adhesive sheet 10 in the second low-speed peel test is preferably 4 N / 20 mm or more, more preferably 4.2 N / 20 mm or more, and even more preferably 4.5 N / 20 mm or more. The tensile bond strength B2 in the second low-speed tensile test is preferably 0.9 N / mm² or more, more preferably 1 N / mm² or more, even more preferably 1.1 N / mm² or more, and particularly preferably 1.2 N / mm² or more. The peel strength F2 is, for example, 30 N / 20 mm or less. The tensile bond strength B2 is, for example, 15 N / mm² or less. The second low-speed peel test is a peel test in which the adhesive sheet is peeled from the glass plate at 50°C, a peel angle of 180°, and a tensile speed of 30 mm / min after the adhesive sheet is bonded to the glass plate and subsequently subjected to heat and pressure treatment at 50°C, 0.5 MPa, and 15 minutes. The second low-speed tensile test is a tensile test conducted on the first and second glass plates in the thickness direction after the bonding of the interlayer adhesive sheet between the first and second glass plates and the subsequent heating and pressurization treatment under the conditions of 50°C, 0.5 MPa and 15 minutes. The first and second glass plates are stretched in opposite directions in the thickness direction at 50°C and a tensile speed of 5 mm / min.

[0025] This type of adhesive sheet 10 is better for ensuring good adhesion to the adhesive and suppressing peeling from the adhesive when the adhesive sheet 10 is continuously subjected to stress from the adhesive when it is wound up. It is better for this type of adhesive sheet 10 to ensure good adhesion to the adhesive and suppress peeling from the adhesive in a temperature range of 50°C and around.

[0026] The peel strength F2 (N / 20 mm) and tensile bond strength B2 (N / mm2) of the adhesive sheet 10 preferably satisfy F2 ≥ -1 / 3 × B2 + 5. This configuration is better for balancing peel strength F2 and tensile bond strength B2, for example, for obtaining good results regarding the adhesion of the adhesive sheet 10 to the adhered body in the winding retention test and bending retention test as described below under high temperature conditions.

[0027] The peel strength F3 of the adhesive sheet 10 in the third low-speed peel test is preferably 3 N / 20 mm or more, more preferably 3.1 N / 20 mm or more, and even more preferably 3.2 N / 20 mm or more. The tensile bond strength B3 in the third low-speed tensile test is preferably 0.9 N / mm² or more, more preferably 1 N / mm² or more, even more preferably 1.1 N / mm² or more, and particularly preferably 1.2 N / mm² or more. The peel strength F3 is, for example, 30 N / 20 mm or less. The tensile bond strength B3 is, for example, 15 N / mm² or less. The third low-speed peel test is a peel test in which the adhesive sheet is peeled from the glass plate at 80°C, a peel angle of 180°, and a tensile speed of 30 mm / min after the adhesive sheet is bonded to the glass plate and subsequently subjected to heat and pressure treatment at 50°C, 0.5 MPa, and 15 minutes. The third low-speed tensile test is a tensile test conducted on the first and second glass plates in the thickness direction after the bonding of the interlayer adhesive sheet 10 between the first and second glass plates and the subsequent heating and pressurization treatment under the conditions of 50°C, 0.5 MPa and 15 minutes. The first and second glass plates are stretched in opposite directions in the thickness direction at 80°C and a tensile speed of 5 mm / min.

[0028] This type of adhesive sheet 10 is better for ensuring good adhesion to the adhesive and suppressing peeling from the adhesive when the adhesive sheet 10 is continuously subjected to stress from the adhesive when it is wound up. It is better for this type of adhesive sheet 10 to ensure good adhesion to the adhesive and suppress peeling from the adhesive in a temperature range of 80°C and around.

[0029] In the fourth low-speed peel test, the ratio (F4 / F1) of the peel strength F4 of the adhesive sheet 10 to the peel strength F1 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 peeled from the glass plate at 95°C, a peel angle of 180°, and a tensile speed of 30 mm / min after the adhesive sheet is bonded to the glass plate and subsequently subjected to heat and pressure treatment at 50°C, 0.5 MPa, and 15 minutes.

[0030] This configuration is preferable for balancing peel strength F1 and peel strength F4, for example, for obtaining good results regarding the adhesion of the adhesive sheet 10 to the adherend in the winding retention test and bending retention test as described below under high temperature conditions. The ratio (F4 / F1) satisfies the above range, and the peel strength F4 is preferably 1 N / 20 mm or more, more preferably 1.3 N / 20 mm or more, and even more preferably 1.5 N / 20 mm or more, and preferably 5 N / 20 mm or less, more preferably 4 N / 20 mm or less, and even more preferably 3 N / 20 mm or less.

[0031] In the fifth low-speed peel test, the ratio (F5 / F1) of the peel strength F5 to the peel strength F1 of the adhesive sheet 10 is preferably 0.45 or less, more preferably 0.42 or less, further 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 further preferably 0.15 or more. The fifth low-speed peel test is a peel test in which the adhesive sheet is peeled from the glass plate after the adhesive sheet is bonded to the glass plate and after heat and pressure treatment at 50°C, 0.5 MPa and 15 minutes, and then peeled from the glass plate at 65°C, 90% relative humidity, peel angle of 180° and tensile speed of 30 mm / min.

[0032] This configuration is preferable for balancing peel strength F1 and peel strength F5, for example, for obtaining good results regarding the adhesion of the adhesive sheet 10 to the adherend in the winding retention test and bending retention test as described below under high temperature conditions. The ratio (F5 / F1) satisfies the above range, and the peel strength F5 is preferably 1 N / 20 mm or more, more preferably 1.3 N / 20 mm or more, and even more preferably 1.5 N / 20 mm or more, and preferably 5 N / 20 mm or less, more preferably 4 N / 20 mm or less, and even more preferably 3 N / 20 mm or less.

[0033] 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). This peel test is conducted after the adhesive sheet 10 is bonded to the glass plate and subsequently subjected to heat and pressure treatment at 50°C, 0.5 MPa, and 15 minutes. The adhesive sheet 10 is then peeled from the glass plate at 25°C, a peel angle of 180°, and a tensile speed of 300 mm / min. 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. This configuration is preferable for ensuring good adhesion of the adhesive sheet 10 to the adhered body and suppressing peeling from the adhered body when the adhered body to which the adhesive sheet 10 is attached is wound at room temperature (dynamic deformation process). The peel strength F6 is, for example, 30 N / 20 mm or less.

[0034] 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). This peel test is conducted after the adhesive sheet 10 is bonded to the glass plate and subsequently subjected to heat and pressure treatment at 50°C, 0.5 MPa, and 15 minutes. The adhesive sheet 10 is then peeled from the glass plate at 95°C, a peel angle of 180°, and a tensile speed of 300 mm / min. 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. This configuration is preferable for ensuring good adhesion of the adhesive sheet 10 to the adhered body and suppressing peeling from the adhered body when the adhered body to which the adhesive sheet 10 is attached is wound in a high-temperature environment. The peel strength F7 is, for example, 30 N / 20 mm or less.

[0035] 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). This peel test is conducted after the adhesive sheet 10 is bonded to the glass plate and subsequently subjected to heat and pressure treatment at 50°C, 0.5 MPa, and 15 minutes. The adhesive sheet 10 is then peeled from the glass plate at 65°C, 90% relative humidity, a peel angle of 180°, and a tensile speed of 300 mm / min. 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. This configuration is preferable for ensuring good adhesion of the adhesive sheet 10 to the adhered body and suppressing peeling when the adhered body to which the adhesive sheet 10 is attached is wound in a high-temperature environment. The peel strength F8 is, for example, 30 N / 20 mm or less.

[0036] The adhesive sheet 10 is a pressure-sensitive adhesive layer formed from an adhesive composition. The adhesive sheet 10 contains at least a base polymer.

[0037] The base polymer is the adhesive component that exhibits adhesive properties in the adhesive sheet. Examples of base polymers include: acrylic polymers, silicone polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyethylene ether polymers, vinyl acetate / vinyl chloride copolymers, modified polyolefin polymers, epoxy polymers, fluoropolymers, and rubber polymers. The base polymer can be used alone or in combination of two or more. From the viewpoint of ensuring good transparency and adhesion in the adhesive sheet, acrylic polymers are preferred as the base polymer.

[0038] Acrylic polymers are copolymers containing monomeric components of alkyl (meth)acrylate at a ratio of 50% by mass or more. "(Meth)acrylate" means acrylic acid and / or methacrylic acid.

[0039] As an alkyl methacrylate, it is suitable to use an alkyl methacrylate having 1 to 20 carbon atoms in the alkyl group. The alkyl methacrylate may have straight-chain or branched alkyl groups, or cyclic alkyl groups such as alicyclic alkyl groups.

[0040] Examples of alkyl (meth)acrylates having straight-chain or branched alkyl groups include: methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, dibutyl (meth)acrylate, tributyl (meth)acrylate, pentyl (meth)acrylate, isoamyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and propylene (meth)acrylate. Nonyl acrylate, isononyl acrylate, decyl acrylate, isodecyl acrylate, undecyl acrylate, dodecyl acrylate (i.e., lauryl acrylate), isotridecyl acrylate, tetradecyl acrylate, isotetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptadecanyl acrylate, octadecyl acrylate, isooctadecyl acrylate, and nonadecanyl acrylate.

[0041] 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. Examples of meth)acrylates having a bicyclic aliphatic hydrocarbon ring include: isopropyl (meth)acrylate. Examples of meth)acrylates having three or more aliphatic hydrocarbon rings include: dicyclopentyl (meth)acrylate, dicyclopentoxyethyl (meth)acrylate, tricyclopentyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

[0042] As an alkyl acrylate (meth)acrylate, it is preferred to use an alkyl acrylate having 3 to 15 carbon atoms, and more preferably to use at least one selected from the group consisting of n-butyl acrylate, 2-ethylhexyl acrylate and dodecyl acrylate.

[0043] Regarding the ratio of (meth)acrylate alkyl esters in the monomer component, from the viewpoint of appropriately exhibiting basic properties such as adhesion in the adhesive sheet, it is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, and particularly preferably 94% by mass or more. This ratio is, for example, 99% by mass or less.

[0044] The monomer component may also include comonomers capable of copolymerizing with alkyl (meth)acrylates. Examples of comonomers include monomers with polar groups. Examples of monomers containing polar groups include hydroxyl-containing monomers, carboxyl-containing monomers, and monomers with nitrogen-containing rings. Monomers containing polar groups help to introduce crosslinking points into acrylic polymers and improve the cohesiveness of acrylic polymers.

[0045] Examples of hydroxyl-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-hydroxylaurate (meth)acrylate, and methyl (4-hydroxymethylcyclohexyl)methacrylate. Preferably, at least one selected from the group consisting of 4-hydroxybutyl acrylate and 2-hydroxyethyl acrylate is used as the hydroxyl-containing monomer.

[0046] Regarding the ratio of hydroxyl-containing monomers in the monomer component, from the viewpoint of introducing a cross-linking structure into the acrylic polymer and ensuring the cohesive force in the adhesive sheet, it 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 adjusting the polarity of the acrylic polymer (related to the compatibility of various additive components in the adhesive sheet with the acrylic polymer), this ratio is preferably 20% by mass or less, more preferably 10% by mass or less.

[0047] As a carboxyl-containing monomer, examples include: acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, butenoic acid, and isobutenoic acid.

[0048] Regarding the ratio of carboxyl-containing monomers in the monomer composition, from the viewpoint of introducing a cross-linking structure into the acrylic polymer, ensuring the cohesive force in the adhesive sheet, and ensuring the adhesion of the adhesive sheet to the adherend, it 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 adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend caused by acid, this ratio is preferably 30% by mass or less, more preferably 20% by mass or less.

[0049] To prevent corrosion of metal components such as electrodes in a rollable display by acid components, the adhesive sheet 10 preferably has a low acid content. Furthermore, when the adhesive sheet 10 is used for bonding polarizing plates, to suppress polyolefin formation in polyvinyl alcohol-based polarizing elements caused by acid components, the adhesive sheet 10 preferably has a low acid content. In this acid-free adhesive sheet 10, the content of organic acid monomers (e.g., (meth)acrylic acid and carboxyl-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 is determined by immersing the adhesive sheet in pure water and heating it at 100°C for 45 minutes, thereby extracting the acid monomers into the water, and quantifying the extracted acid monomers by ion chromatography.

[0050] From the viewpoint of being acid-free, it is preferable that the base polymer in the adhesive sheet 10 does not substantially contain organic acid monomers as monomer components. From the viewpoint of being acid-free, the ratio of organic acid monomers in the monomer components is preferably 0.5% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.05% by mass, ideally 0% by mass.

[0051] As a monomer having a ring containing a nitrogen atom, examples include: N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperidone, N-vinylpyrrole, N-vinylimidazol, N-vinylpyrazole, N-(meth)acryl-2-pyrrolidone, N-(meth)acrylpiperidine, N-(meth)acrylpyrrolidone, N-vinylpyrrolidone, N-vinylpyrrolidone, N-vinylpyrrolidone, N-vinylpyrrolidone, N-vinylpyrrolidone, N-vinylpyrrolidone, N-vinyl-3-pyrrolidone, N-vinyl-2-caprolactone, N-vinyl-1,3-pyrrolidone-2-one, N-vinyl-3,5-pyrrolidone, N-vinylpyrazole, N-vinylisopyrazole, N-vinylthiazole, N-vinylisothiazole. N-vinyl-2-pyrrolidone is preferred as a monomer having a ring containing nitrogen atoms.

[0052] Regarding the ratio of monomers containing nitrogen-containing rings in the monomer composition, from the viewpoint of ensuring the cohesive force in the adhesive sheet and the adhesion force of the adhesive sheet to the adhered body, it 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 adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (related to the compatibility between the various additive components in the adhesive sheet and the acrylic polymer), this ratio is preferably 30% by mass or less, more preferably 20% by mass or less.

[0053] The monomer component may also include other comonomers. Examples of other comonomers include: acid anhydride monomers, sulfonic acid monomers, phosphate monomers, epoxy monomers, cyano monomers, alkoxy monomers, and aromatic vinyl compounds. These other comonomers may be used alone or in combination of two or more.

[0054] Preferably, the base polymer has a cross-linked structure. Examples of methods for introducing a cross-linked structure into the base polymer include: a method in which a base polymer having functional groups capable of reacting with a cross-linking agent and a cross-linking agent are formulated into an adhesive composition, and the base polymer and cross-linking agent react in an adhesive sheet (Method 1); and a method in which a multifunctional monomer is included in the monomer component forming the base polymer, and a base polymer with a branched structure (cross-linked structure) is formed by polymerization of the monomer component (Method 2). These methods may also be used in combination.

[0055] Examples of crosslinking agents used in the first method described above include compounds that react with functional groups (hydroxyl and carboxyl groups, etc.) contained in the base polymer. Examples of such crosslinking agents include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents. Crosslinking agents can be used alone or in combination of two or more. Isocyanate crosslinking agents, peroxide crosslinking agents, and epoxy crosslinking agents are preferred for their high reactivity with hydroxyl and carboxyl groups in the base polymer, which facilitates the introduction of crosslinking structures.

[0056] Examples of isocyanate crosslinking agents include: toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, phenyl diisocyanate, hydrogenated phenyl diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylphenyl diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate. Furthermore, derivatives of these isocyanates can also be used as isocyanate crosslinking agents. Examples of such isocyanate derivatives include isocyanurate modified forms and polyol modified forms. Commercially available isocyanate crosslinking agents include, for example: Coronate L (trimethylolpropane adduct of toluene diisocyanate, manufactured by Tosoh), Coronate HL (trimethylolpropane adduct of hexamethylene diisocyanate, manufactured by Tosoh), Coronate HX (isocyanurate form of hexamethylene diisocyanate, manufactured by Tosoh), Takenate D110N (trimethylolpropane adduct of phenyl diisocyanate, manufactured by Mitsui Chemicals), and Takenate 600 (1,3-bis(isocyanomethyl)cyclohexane, manufactured by Mitsui Chemicals).

[0057] Examples of peroxide crosslinking agents include: benzoyl peroxide, di(2-ethylhexyl) peroxide dicarbonate, di(4-tert-butylcyclohexyl) peroxide dicarbonate, di-second butyl peroxide dicarbonate, tert-butyl peroxydecanoate, tert-hexyl peroxypentanoate, and tert-butyl peroxypentanoate.

[0058] Examples of epoxy crosslinking agents include: bisphenol A, epichlorohydrin type epoxy resin, ethylene glycol glycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl m-phenylenediamine, and 1,3-bis(N,N-diglycidylaminemethyl)cyclohexane.

[0059] From the viewpoint of ensuring the flexibility of the adhesive sheet 10, isocyanate crosslinking agents (especially difunctional isocyanate crosslinking agents) and peroxide crosslinking agents are preferred. From the viewpoint of ensuring the durability of the adhesive sheet 10, isocyanate crosslinking agents (especially trifunctional isocyanate crosslinking agents) are preferred. In the base polymer, difunctional isocyanate crosslinking agents and peroxide crosslinking agents form a softer two-dimensional crosslink, while trifunctional isocyanate crosslinking agents form a stronger three-dimensional crosslink. From the viewpoint of balancing the durability and flexibility of the adhesive sheet 10, a combination of trifunctional isocyanate crosslinking agents, peroxide crosslinking agents, and / or difunctional isocyanate crosslinking agents is preferred.

[0060] Regarding the amount of crosslinking agent, from the viewpoint of ensuring the cohesive force of the adhesive sheet 10, it is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.07 parts by mass or more, relative to 100 parts by mass of the base polymer. From the viewpoint of ensuring good adhesion in the adhesive sheet 10, the amount of crosslinking agent relative to 100 parts by mass of the base polymer is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 3 parts by mass or less.

[0061] In the second method described above, the monomer components (including multifunctional monomers and other monomers used to introduce the crosslinking structure) can be polymerized in one step or in multiple stages. In the multi-stage polymerization method, firstly, a prepolymer composition containing a portion of the polymer (a mixture of low-degree polymers and unreacted monomers) is prepared by polymerizing (prepolymerization) with monofunctional monomers to form the base polymer. Subsequently, after adding multifunctional monomers to the prepolymer composition, the portion of the polymer is polymerized with the multifunctional monomers (formal polymerization).

[0062] As a multifunctional monomer, an example is a multifunctional (meth)acrylate containing two or more vinyl unsaturated double bonds in one molecule. From the viewpoint that a cross-linked structure can be introduced by active energy line polymerization (photopolymerization), a multifunctional acrylate is preferred as a multifunctional monomer.

[0063] Examples of polyfunctional (meth)acrylates include: difunctional (meth)acrylates, trifunctional (meth)acrylates, and polyfunctional (meth)acrylates with more than four functions.

[0064] Examples of difunctional (meth)acrylates include: ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, glycerol dimethacrylate, neopentyl glycol dimethacrylate, stearic acid modified pentaerythritol dimethacrylate, dicyclopentene dimethacrylate, dimethacrylamide isocyanurate, and epoxide-modified bisphenol dimethacrylate.

[0065] Examples of trifunctional (meth)acrylates include: trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tri(acryloxyethyl)isocyanurate.

[0066] Examples of polyfunctional (meth)acrylates with more than four functions include: di-trimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxy penta(meth)acrylate, alkyl-modified dipentaerythritol pentaacrylate, and dipentaerythritol hexa(meth)acrylate.

[0067] The molecular weight of the multifunctional monomer is preferably 1500 or less, more preferably 1000 or less. Furthermore, the functional group equivalent (g / eq) of the multifunctional monomer is preferably 50 or more, more preferably 70 or more, and even more preferably 80 or more. This functional group equivalent is preferably 500 or less, more preferably 300 or less, and even more preferably 200 or less. From the viewpoint of appropriately adjusting viscoelasticity (e.g., storage modulus and loss tangent) by introducing a crosslinking structure into the base polymer, these configurations are preferred.

[0068] Acrylic polymers can be formed by polymerizing the aforementioned monomer components. Examples of polymerization methods include solution polymerization, active energy line polymerization (e.g., UV (ultraviolet) 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. Examples of solvents used for solution polymerization include ethyl acetate and toluene. Furthermore, examples of initiators for polymerization include thermal polymerization initiators and photopolymerization initiators. The amount of polymerization initiator used relative to 100 parts by mass of the monomer component is, for example, 0.05 parts by mass or more, and for example, 1 part by mass or less.

[0069] 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 ester, 4,4'-azobis-4-cyanovaleric acid, azobisisovalerate, 2,2'-azobis(2-amidinylpropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(2-methylpropanediamine) disulfate, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine) dihydrochloride. Examples of peroxide polymerization initiators include benzoyl peroxide, tributyl maleate peroxide, and lauryl peroxide.

[0070] Examples of photopolymerization initiators include: benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-keto alcohol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, 9-oxosulfuron-based photopolymerization initiators, and acetylated phosphine oxide-based photopolymerization initiators.

[0071] 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 thiol, glycidyl thiol, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolic acid, 2,3-dimercapto-1-propanol, and α-methylstyrene dimer.

[0072] The molecular weight of the base polymer can be adjusted by changing the type and / or amount of the polymerization initiator. For example, in free radical polymerization, the more polymerization initiator used, the higher the concentration of free radicals in the reaction system, and therefore the higher the density of the reaction initiation point, resulting in a tendency for the molecular weight of the formed base polymer to be smaller. Conversely, the less polymerization initiator used, the lower the density of the reaction initiation point, and therefore the easier it is for the polymer chain to elongate, resulting in a tendency for the molecular weight of the formed base polymer to be larger.

[0073] Regarding the weight-average molecular weight of the base polymer, from the viewpoint of ensuring the cohesive force in the adhesive sheet 10, it is preferably 100,000 or more, more preferably 300,000 or more, and even more preferably 500,000 or more. This 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 can be determined using gel permeation chromatography (GPC) and calculated using polystyrene conversion.

[0074] The glass transition temperature (Tg) of the base polymer is preferably below 0°C, more preferably below -10°C, and even more preferably below -20°C. This glass transition temperature is, for example, above -80°C.

[0075] Regarding the glass transition temperature (Tg) of the basic polymer, the theoretical value of the glass transition temperature can be obtained based on the following Fox formula. The Fox formula is the relationship between the glass transition temperature Tg of the polymer and the glass transition temperature Tgi of the homopolymer of the monomers constituting the polymer. In the following Fox formula, 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. Regarding the glass transition temperature of the homopolymer, literature values ​​can be used. For example, the glass transition temperatures of various homopolymers are listed in "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) and "New Polymer Library 7: Introduction to Synthetic Resins for Coatings" (by Kyozo Kitaoka, Polymer Publishing Association, 1995). On the other hand, the glass transition temperature of the homopolymer of the monomer can also be determined by the method specifically described in Japanese Patent Application Publication No. 2007-51271.

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

[0077] The adhesive composition may contain one or more oligomers in addition to the base polymer. When using an acrylic polymer as the base polymer, it is preferable to use an acrylic oligomer. The acrylic oligomer is a copolymer containing a monomer component of alkyl (meth)acrylate at a ratio of 50% by mass or more, and has a weight average molecular weight, for example, of 1,000 to 30,000.

[0078] The glass transition temperature of the acrylic oligomer is preferably 60°C or higher, more preferably 80°C or higher, further 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 combining a low-Tg acrylic polymer (base polymer) with a cross-linked structure with a high-Tg acrylic oligomer, the adhesion of the adhesive sheet 10, especially at high temperatures, can be improved. The glass transition temperature of the acrylic oligomer is calculated using the aforementioned Fox formula.

[0079] The acrylic oligomer with a glass transition temperature of 60°C or higher is preferably a polymer containing monomer components of alkyl (meth)acrylates having chain alkyl groups ((meth)acrylate chain alkyl esters) and alkyl (meth)acrylates having alicyclic alkyl groups ((meth)acrylate alicyclic alkyl esters). Specific examples of such alkyl (meth)acrylates include, for instance, the alkyl (meth)acrylates described above as monomer components of the acrylic polymer.

[0080] As a (meth)acrylate chain alkyl ester, methyl methacrylate is preferred in terms of its high glass transition temperature and excellent compatibility with the base polymer. As a (meth)acrylate alicyclic alkyl ester, dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferred. That is, the acrylic oligomer is preferably a polymer comprising a monomer component including one or more monomers selected from the group consisting of dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate.

[0081] The proportion of alicyclic (meth)acrylate alkyl esters 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. This 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 (meth)acrylate chain alkyl esters 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. This proportion is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more.

[0082] 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. This molecular weight is preferably 30000 or less, more preferably 10000 or less, and even more preferably 8000 or less. This molecular weight range of the acrylic oligomer is preferable in order to ensure the adhesion and adhesion retention of the adhesive sheet 10.

[0083] Acrylic oligomers are obtained by polymerizing the monomer components of the acrylic oligomer. Examples of polymerization methods include solution polymerization, active energy line polymerization (e.g., UV polymerization), bulk polymerization, and emulsion polymerization. In the polymerization of acrylic oligomers, polymerization initiators and chain transfer agents can be used to adjust the molecular weight.

[0084] In order to sufficiently improve the adhesion of the adhesive sheet 10, the content of acrylic oligomer in the adhesive sheet 10 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, relative to 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 content of acrylic oligomer 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, relative to 100 parts by mass of the base polymer. When the content of acrylic oligomer in the adhesive sheet 10 is too high, there is a tendency for the haze to increase and the transparency to decrease due to the decreased compatibility of the acrylic oligomer.

[0085] The adhesive composition may also contain a silane coupling agent. The content of the silane coupling agent in the adhesive composition is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, relative to 100 parts by weight of the base polymer. This content is preferably 5 parts by weight or less, more preferably 3 parts by weight or less.

[0086] The adhesive composition may also contain other components as needed. Examples of other components include: solvents, adhesive agents, plasticizers, softeners, antioxidants, fillers, colorants, UV absorbers, antioxidants, 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.

[0087] The adhesive sheet 10 can be manufactured, for example, by applying the above adhesive composition onto the release liner L1 (first release liner) to form a coating film, and then drying the coating film.

[0088] As a release liner, a flexible plastic film can be cited as an example. 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 with a release coating.

[0089] Examples of coating methods for the adhesive composition include: roller coating, contact roller coating, gravure coating, reverse coating, roller brush coating, spraying, dip roller coating, rod coating, doctor blade coating, air knife coating, curtain coating, die lip coating, and die nozzle 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.

[0090] Alternatively, a release liner L2 (second release liner) may be laminated onto the adhesive sheet 10 on the first release liner L1. The second release liner is a flexible plastic film with a surface release treatment, and the same type as described above regarding the first release liner may be used.

[0091] The adhesive sheet 10 can be manufactured as described above, wherein the adhesive sheet 10 is formed by covering and protecting the adhesive surfaces 11 and 12 with release liner L1 and L2. When using the adhesive sheet 10, the release liner L1 and L2 can be peeled off from the adhesive sheet 10 as needed.

[0092] From the viewpoint of ensuring sufficient adhesion to the adhered object, the thickness of the adhesive sheet 10 is preferably 10 μm or more, more preferably 15 μm or more. From the viewpoint of the physical properties of the adhesive sheet 10, the thickness of the adhesive sheet 10 is preferably 300 μm or less, more preferably 200 μm or less, further preferably 100 μm or less, and particularly preferably 50 μm or less.

[0093] The haze of the adhesive sheet 10 is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. The haze of the adhesive sheet 10 can be measured using a haze meter according to JIS K7136 (2000). Examples of haze meters include the "NDH2000" manufactured by Nippon Denshoku Kogyo Co., Ltd., and the "HM-150" manufactured by Murakami Color Technology Research Institute Co., Ltd.

[0094] 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 according to JIS K 7375 (2008).

[0095] Figures 2A to 2C show one example of the method of using the adhesive sheet 10.

[0096] In this method, firstly, as shown in FIG2A, the adhesive sheet 10 is attached to one side of the first member 21 (the adhered body) in the thickness direction H. The first member 21 is, for example, a component in a laminated structure of a rollable display surface. Examples of such components include: a pixel panel, a polarizing plate (polarizing film), a touch panel, and a cover film (the same applies to the second member 22 described below). Through this step, the adhesive sheet 10 for bonding with other components is provided on the first member 21.

[0097] Subsequently, as shown in FIG2B, the adhesive sheet 10 on the first member 21 is used to join one side of the first member 21 in the thickness direction H to the other side of the second member 22 in the thickness direction H. The second member 22 is, for example, another element in the laminated structure of a rollable display panel.

[0098] Subsequently, as shown in FIG2C, the adhesive sheet 10 between the first component 21 and the second component 22 is aged. Aging allows the cross-linking reaction of the base polymer in the adhesive sheet 10 to occur, thereby increasing the bonding strength between the first component 21 and the second component 22. The aging temperature is, for example, 20°C to 160°C. The aging time is, for example, 1 minute to 21 days. When autoclaving (heating and pressurizing) is performed as aging, the temperature is, for example, 30°C to 80°C, the pressure is, for example, 0.1 to 0.8 MPa, and the processing time is, for example, 15 minutes or more.

[0099] The adhesive sheet 10 used in the manufacturing process of the rollable display panel as described above exhibits a peel strength F1 of 5 N / 20 mm or more in the first low-speed peel test and a tensile adhesion strength B1 of 0.9 N / mm² or more in the first low-speed tensile test. This adhesive sheet 10, which exhibits strong adhesion in both types of tests as measured in the low-speed test, is suitable for ensuring good adhesion to the adhered body and suppressing peeling when the adhered body to which the adhesive sheet 10 is attached is continuously subjected to stress from the adhered body while it is rolled up. Therefore, the adhesive sheet 10 is suitable for use in rollable displays. [Example]

[0100] Hereinafter, embodiments will be shown to specifically describe the present invention. However, the present invention is not limited to the embodiments. Furthermore, the specific values ​​of dosage (content), physical property values, parameters, etc., described below can be replaced with the upper limit (defined as "below" or "not reached") or lower limit (defined as "above" or "exceeding") of the dosage (content), physical property values, parameters, etc., corresponding to those described in the above "Embodiments".

[0101] [Example 1] <Preparation of Adhesive Composition> In a flask, 0.05 parts by weight of 2,2-dimethoxy-1,2-diphenyl-1-one (product name "Irgacure 651", manufactured by Ciba Japan) as the first photopolymerization initiator and 0.05 parts by weight of 1-hydroxy-cyclohexyl-phenyl-one (product name "Irgacure 184", manufactured by Ciba Japan) as the second photopolymerization initiator were added to a monomer mixture containing 75 parts by weight of 2-ethylhexyl acrylate (2EHA), 5 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 20 parts by weight of N-vinyl-2-pyrrolidone (NVP). The mixture was then irradiated with ultraviolet light under a nitrogen atmosphere, thereby partially polymerizing one of the monomer components in the mixture to obtain a first prepolymer composition (containing monomer components that have not undergone polymerization reaction) with a polymerization rate of 12%. Then, 100 parts by weight of the first prepolymer composition, 0.3 parts by weight of hexane diacrylate (HDDA) as a crosslinking agent, and 0.3 parts by weight of silane coupling agent (product name "KBM403", manufactured by Shin-Etsu Chemical Industry) are mixed to obtain the first adhesive composition.

[0102] <Formation of Adhesive Layer> A first adhesive composition is applied to the release-treated surface of a first release liner (product name "DIAFOIL MRF", thickness 38 μm, manufactured by Mitsubishi Chemical Co., Ltd.), which has a release-treated surface on one side, to form a coating film. Then, the release-treated surface of a second release liner (product name "DIAFOIL MRN", thickness 38 μm, manufactured by Mitsubishi Chemical Co., Ltd.), which also has a release-treated surface on one side, is adhered to the coating film on the first release liner. Next, the coating film between the release liners is irradiated with ultraviolet light to photocur the coating film and form an adhesive layer (thickness 50 μm). When irradiating with ultraviolet light, a metal halide lamp is used as the light source, the illuminance is set to 4 mW / cm², and the cumulative irradiation dose is set to 1200 mJ / cm².

[0103] An optical adhesive sheet (50 μm thick) of Example 1 with double-sided release liner was prepared as described above.

[0104] [Example 2] <Preparation of Adhesive Composition> In a flask, 0.05 parts by weight of 2,2-dimethoxy-1,2-diphenyl-1-one (product name "Irgacure 651", manufactured by Ciba Japan) as the first photopolymerization initiator and 0.05 parts by weight of 1-hydroxy-cyclohexyl-phenyl-one (product name "Irgacure 184", manufactured by Ciba Japan) as the second photopolymerization initiator were added to a monomer mixture containing 80 parts by weight of butyl acrylate (BA), 10 parts by weight of 4-hydroxybutyl acrylate (4HBA) and 10 parts by weight of cyclohexyl acrylate. The mixture was then irradiated with ultraviolet light under a nitrogen atmosphere to partially polymerize one of the monomer components in the mixture, thereby obtaining a second prepolymer composition (containing monomer components that have not undergone polymerization reaction) with a polymerization rate of 10%. Then, 100 parts by weight of the second prepolymer composition, 0.01 parts by weight of dipentaerythritol hexaacrylate (DPHA) as a crosslinking agent, and 0.3 parts by weight of silane coupling agent (product name "KBM403", manufactured by Shin-Etsu Chemical Industry) are mixed to obtain the second adhesive composition.

[0105] <Formation of Adhesive Layer> A first adhesive composition is applied to the release-treated surface of a first release liner (product name "DIAFOIL MRF", thickness 38 μm, manufactured by Mitsubishi Chemical Co., Ltd.), which has a release-treated surface on one side, to form a coating film. Then, the release-treated surface of a second release liner (product name "DIAFOIL MRN", thickness 38 μm, manufactured by Mitsubishi Chemical Co., Ltd.), which also has a release-treated surface on one side, is adhered to the coating film on the first release liner. Next, the coating film between the release liners is irradiated with ultraviolet light to photocur the coating film and form an adhesive layer (thickness 50 μm). When irradiating with ultraviolet light, a metal halide lamp is used as the light source, the illuminance is set to 4 mW / cm², and the cumulative irradiation dose is set to 1200 mJ / cm².

[0106] An optical adhesive sheet (50 μm thick) of Example 2 with double-sided release liner was prepared as described above.

[0107] [Comparative Example 1] When preparing the adhesive composition, the amount of DPHA was replaced from 0.01 parts by mass to 0.1 parts by mass. Otherwise, the optical adhesive sheet with double-sided release liner (50 μm) of Comparative Example 1 was prepared in the same manner as the optical adhesive sheet with double-sided release liner on both sides of Example 2.

[0108] <Low-speed peel test> The peel strength in the low-speed peel test was investigated for each optical adhesive sheet of Examples 1, 2 and Comparative Example 1.

[0109] Specifically, firstly, a required number of test samples are prepared for each optical adhesive sheet. When preparing the test samples, firstly, the first release liner is peeled from the optical adhesive sheet, and the exposed surface is bonded to a plasma-treated polyethylene terephthalate (PET) film (product name "Lumirror S10", thickness 50 μm, manufactured by Toray Industries) to obtain a laminate. Then, a test piece (20 mm wide × 100 mm long) is cut from this laminate (PET film / optical adhesive sheet / second release liner). Next, the second release liner is peeled from the optical adhesive sheet in the test piece, and the exposed surface is bonded to a glass plate (product name "Slide Glass S2004U8", manufactured by Matsunami Glass Industries Co., Ltd.). Subsequently, the glass plate with the attached sheet (sample) was subjected to heating and pressurization at 50°C and 0.5 MPa for 15 minutes. This pressed the sample onto the glass plate. The test specimen was prepared in the above manner.

[0110] Subsequently, after the test specimen was left to stand at room temperature for 30 minutes, a low-speed peel test was performed, in which the specimen was peeled from the glass plate of the test specimen, and the peel strength was measured (Test 1). In this test, a tensile testing machine (product name "Autograph AG-50NX plus"), manufactured by Shimadzu Corporation, was used. In this test, the test temperature was set to 25°C, the relative humidity was set to 55%, the peel angle of the specimen from the glass plate was set to 180°, the tensile speed of the specimen was set to 30 mm / min, and the peel length was set to 50 mm. The average value of the measured peel strength is set as peel strength F1 (N / 20 mm) and is shown in Table 1.

[0111] Except that the measurement temperature was changed to 50°C, a low-speed peel test was performed under the same conditions as in the first test, and the peel strength F2 at 50°C was measured. Except that the measurement temperature was changed to 80°C, a low-speed peel test was performed under the same conditions as in the first test, and the peel strength F3 at 80°C was measured. Except that the measurement temperature was changed to 95°C, a low-speed peel test was performed under the same conditions as in the first test, and the peel strength F4 at 95°C was measured. Except that the measurement temperature was changed to 65°C and the relative humidity was set to 90%, a low-speed peel test was performed under the same conditions as in the first test, 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.

[0112] <Low-speed tensile test> The tensile bond strength in the low-speed tensile test was investigated for each optical adhesive sheet of Examples 1, 2 and Comparative Example 1. Specifically, it is described below.

[0113] First, test specimens for each optical adhesive sheet are prepared. When preparing the test specimens, first, two glass plates supported by metal blocks are prepared. The metal block-supported glass plates are prepared by attaching a glass plate (3 cm × 3 cm × 0.5 cm) to one side of a metal block (a 3 cm × 3 cm × 3 cm SUS (Steel Use Stainless) 304 cubic block). Then, the first release liner of an optical adhesive sheet (1 cm × 1 cm) cut from the optical adhesive sheet is peeled off, and the exposed surface is then bonded to the exposed glass surface of a metal block-supported glass plate (the first glass plate). Next, the second release liner is peeled off from the optical adhesive sheet on the glass plate, and the exposed surface is then adhered to the exposed glass surface of another metal block supporting the glass plate (the second glass plate), thus joining the glass plates together (the first and second glass plates are joined across the thickness direction of the aforementioned optical adhesive sheet). Subsequently, the optical adhesive sheet specimen is pressed onto the two glass plates by subjecting it to a heating and pressurizing treatment at 50°C and 0.5 MPa for 15 minutes. The test specimen (metal block / glass plate / optical adhesive sheet / glass plate / metal block) is prepared in the above manner.

[0114] Next, a test was conducted in which two metal-supported glass plates in the test specimen were stretched towards opposite sides in the thickness direction (low-speed tensile test), and the force required to pull the glass plates apart was measured (Test 2). In this test, a tensile testing machine (product name "Autograph AG-1 / 350NX plus"), manufactured by Shimadzu Corporation, was used. In this test, the test temperature was set to 25°C, the relative humidity was set to 55%, and the tensile speed was set to 5 mm / min. The maximum value of the measured force is set as the tensile bonding strength B1 (N / mm2) and is shown in Table 1.

[0115] Except that the measurement temperature was changed to 50°C, a low-speed tensile test was performed under the same conditions as in Test 2, and the tensile bond strength B2 at 50°C was measured. Except that the measurement temperature was changed to 80°C, a low-speed tensile test was performed under the same conditions as in Test 2, and the tensile bond strength B3 at 80°C was measured. The values ​​of these tests are also shown in Table 1.

[0116] Furthermore, the results of the above-mentioned peel strength and tensile bond strength measurements of the optical adhesive sheets of Examples 1, 2 and Comparative Example 1 are shown in the graphs of Figure 3. In the graphs of Figure 3, the horizontal axis represents the tensile bond strength (N / mm2) in the above-mentioned low-speed tensile test, and the vertical axis represents the peel strength (N / 20 mm) in the above-mentioned low-speed peel test. In Figure 3, curve E1 represents the measurement results in Example 1, curve E2 represents the measurement results in Example 2, and curve C1 represents the measurement results in Comparative Example 1. Furthermore, the dotted line R1 represents the line with tensile bond strength B = 0.9 N / mm2. The single-point chain line R2 represents the line with peel strength F = -1 / 3 × tensile bond strength B + 7. The two-point chain line R3 represents the line with peel strength F = -1 / 3 × tensile bond strength B + 5. The optical adhesive sheets of Examples 1 and 2 exhibit peel strength F (N / 20 mm) and tensile bond strength B (N / mm²) at 25°C satisfying F≧-1 / 3×B+7, and peel strength F (N / 20 mm) and tensile bond strength B (N / mm²) at 50°C satisfying F≧-1 / 3×B+5. These optical adhesive sheets of Examples 1 and 2 demonstrate good results in the following winding retention test and the following bending retention test.

[0117] <Wrap-up Retention Test> A wrap-up retention test was performed on each of the optical adhesive sheets of Examples 1, 2 and Comparative Example 1 in the following manner.

[0118] The first release liner is peeled off from the optical adhesive sheet, and a first PET film (product name "Lumirror S10", thickness 100 μm, manufactured by Toray Industries) with plasma-treated exposed bonding surface is used to form a first laminate. Then, the release liner is peeled off from the adhesive layer of the polarizing plate with 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 a second laminate is formed on the exposed bonding surface of a second PET film (product name "Lumirror S10", thickness 188 μm, manufactured by Toray Industries) with plasma-treated exposed bonding surface. Next, the second release liner is peeled from the optical adhesive sheet in the first laminate, and the protective film is peeled from the polarizing plate in the second laminate. The exposed surfaces are then bonded together, and the third laminate (first PET film / optical adhesive sheet / polarizing plate / PSA on polarizing plate / second PET film) is fabricated by pressurizing and heating at 50°C, 0.5 MPa, and 15 minutes. A test piece (25 mm wide × 150 mm long) is then cut from the third laminate. This test piece has a first end at one end along its length and a second end at the other end.

[0119] Next, the test piece is wound around a cylindrical metal rod (made of SUS304) with a cross-sectional diameter of 30 mm in the circumferential direction of the metal rod along its length as follows: First, the first PET film side of the first end of the test piece is attached to the metal rod via double-sided adhesive tape. Then, with the first PET film side of the test piece positioned on the inside of the winding, the test piece is stretched along its length while being wound around the metal rod. Specifically, the test piece is wound around the metal rod in such a way that there is no gap between the metal rod and the test piece, and there is also no gap between the test pieces in the radial direction of the metal rod. Then, the second end of the test piece wound around the metal rod is fixed by adhesive tape.

[0120] Subsequently, the metal rod with the test piece prepared as described above was placed in an environment of 60°C and 95% relative humidity for 250 hours (winding and holding test). Then, regarding the adhesion of the optical adhesive sheet to the adherend in this winding and holding test, the case in which no defects such as bubbles and peeling in the adhesive layer (optical adhesive sheet) or cracking of the polarizing plate occurred was rated as "good", and the case in which any defect occurred was rated as "poor". The results are shown in Table 1.

[0121] <Bending Retention Test> A bending retention test was performed on each of the optical adhesive sheets of Examples 1, 2 and Comparative Example 1 in the following manner.

[0122] First, a test piece identical to the one described above for the winding and holding test is prepared (25 mm wide × 150 mm long, laminated as follows: 1st PET film / optical adhesive sheet / polarizing plate / PSA on the polarizing plate / 2nd PET film). Then, the test piece is bent from a flat shape into a U-shape, and this deformed state is held in place by a specific holder. Specifically, the deformed test piece is bent along its length at the center (the distance between opposing ends is approximately 20 mm) so that the 1st PET film side of the first end of the test piece faces the 1st PET film side of the second end. Subsequently, the deformed test piece is placed at 60°C and 95% relative humidity for 250 hours (bending and holding test). Then, regarding the adhesion of the optical adhesive sheet to the adherend in this bending retention test, a case where no defects such as air bubbles and peeling in the adhesive layer (optical adhesive sheet) or cracking of the polarizing plate occurred was rated as "good," and a case where any defect occurred was rated as "poor." The results are shown in Table 1.

[0123] [Table 1] Example 1 Example 2 Comparative Example 1 Thickness (μm) 50 50 50 Peel strength in low-speed peel test (N / 20 mm) F1 (25℃) 6.9 6.3 3.8 F2 (50℃) 4.9 4.3 3.0 F3 (80℃) 3.1 3.3 1.9 F4 (95℃) 1.8 2.9 1.9 F5 (65℃, 90%RH) 1.3 2.5 1.8 F4 / F1 0.26 0.46 0.50 F5 / F1 0.19 0.40 0.46 Tensile bond strength in low-speed tensile tests (N / mm 2 ) B1 (25℃) 1.8 3.6 1.7 B2 (50℃) 1.1 3.0 1.0 B3 (80℃) 1.0 1.7 0.8 Evaluation in winding retention test 25℃ good good bad 65℃, 90%RH good good bad 85℃ good good bad Evaluation in flexural retention test 25℃ good good bad 65℃, 90%RH good good bad 85℃ good good bad [Simplified Explanation of the Diagram]

[0016] Figure 1 is a cross-sectional schematic diagram of one embodiment of the optical adhesive sheet of the present invention. Figures 2A to 2C show an example of a method of using the optical adhesive sheet of the present invention. Figure 2A shows the step of attaching the optical adhesive sheet to a first substrate, Figure 2B shows the step of bonding the first substrate and a second substrate together by means of the optical adhesive sheet, and Figure 2C shows the aging step. Figure 3 is a graph showing the measured results of tensile adhesion strength (horizontal axis) and peel strength (vertical axis) of the optical adhesive sheets of the embodiments and comparative examples.

Claims

1. An optical adhesive sheet comprising a base polymer, wherein the base polymer is a copolymer comprising a monomeric component of alkyl (meth)acrylate, and a cross-linking structure is introduced through a multifunctional (meth)acrylate; wherein the optical adhesive sheet exhibits a peel strength F1 of 5 N / 20 mm or more in a low-speed peel test; wherein the low-speed peel test is performed after the optical adhesive sheet is bonded to a glass plate and subsequently subjected to heat and pressure treatment at 50°C, 0.5 MPa, and 15 minutes, and the optical adhesive sheet is peeled from the glass plate at 25°C, a peel angle of 180°, and a tensile speed of 30 mm / min; and wherein the optical adhesive sheet exhibits a tensile adhesion strength B1 of 0.9 N / mm² or more in a low-speed tensile test; wherein the low-speed tensile test is performed after the first glass plate and the second glass plate are bonded together in the thickness direction of the optical adhesive sheet and subsequently subjected to heat and pressure treatment, and the first and second glass plates are held opposite each other in the thickness direction at 25°C and a tensile speed of 5 mm / min. Stretching is performed under conditions of mm / min.

2. The optical adhesive sheet of claim 1, wherein the peel strength F1 (N / 20 mm) and the tensile bonding strength B1 (N / mm2) satisfy F1 ≥ -1 / 3 × B1 + 7.

3. The optical adhesive sheet of claim 1, having a peel strength F2 of 4 N / 20 mm or more in a low-speed peel test, wherein the low-speed peel test is performed after the optical adhesive sheet is bonded to the glass plate and after the heat and pressure treatment thereafter, peeling the optical adhesive sheet from the glass plate at 50°C, peel angle 180° and tensile speed 30 mm / min, and having a tensile bond strength B2 of 0.9 N / mm2 or more in a low-speed tensile test, wherein the low-speed tensile test is performed after the first glass plate and the second glass plate are joined in the thickness direction of the optical adhesive sheet and after the heat and pressure treatment thereafter, stretching the first and second glass plates in opposite directions in the thickness direction at 50°C and tensile speed 5 mm / min.

4. The optical adhesive sheet as claimed in claim 3, wherein the peel strength F2 (N / 20 mm) and the tensile bonding strength B2 (N / mm2) satisfy F2≧-1 / 3×B2+5.

5. The optical adhesive sheet of claim 1, having a peel strength F3 of 3 N / 20 mm or more in a low-speed peel test, wherein the low-speed peel test is performed after the optical adhesive sheet is bonded to the glass plate and after the heat and pressure treatment thereafter, peeling the optical adhesive sheet from the glass plate at 80°C, peel angle 180° and tensile speed 30 mm / min, and having a tensile bond strength B3 of 0.9 N / mm2 or more in a low-speed tensile test, wherein the low-speed tensile test is performed after the first glass plate and the second glass plate are joined in the thickness direction of the optical adhesive sheet and after the heat and pressure treatment thereafter, stretching the first and second glass plates in opposite directions in the thickness direction at 80°C and tensile speed 5 mm / min.

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

7. The optical adhesive sheet of any one of claims 1 to 5 has a peel strength F5 in a low-speed peel test with a ratio of peel strength F1 of 0.45 or less. The low-speed peel test is conducted after the optical adhesive sheet is bonded to the glass plate and after the heat and pressure treatment thereafter, and the optical adhesive sheet is peeled from the glass plate at 65°C, relative humidity 90%, peel angle 180° and tensile speed 30 mm / min.

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