Optical adhesive layer and optical film with optical adhesive layer

Abstract

The present invention provides an optical adhesive layer suitable for use in flexible devices, and an optical film with the optical adhesive layer attached. The optical adhesive layer 10A of the present invention comprises a high-adhesion adhesive layer 11 and a low-adhesion adhesive layer 12. The low-adhesion adhesive layer 12 has a first surface 12a and a second surface 12b opposite to the first surface 12a. The high-adhesion adhesive layer 11 is disposed on the first surface 12a and has a high-adhesion surface 11a on the side opposite to the low-adhesion adhesive layer 12. After being bonded to a polyimide film and subjected to 30 minutes at 23°C, the high-adhesion surface 11a exhibits a peel adhesion of 5 N / 25 mm or more to the polyimide film under specific conditions. The ratio of the shear storage modulus of the low-adhesion adhesive layer 12 at -20°C to that of the high-adhesion adhesive layer 11 at -20°C is less than 1. The optical film X with an optical adhesive layer of the present invention comprises: an optical film 23, and an optical adhesive layer 10A attached to the optical film 23 on the second side 12b.

Description

Technical Field

[0001] This invention relates to an optical adhesive layer and an optical film with the optical adhesive layer attached. Prior Technology

[0002] Display panels, for example, have a laminated structure comprising elements such as a pixel panel, a touch panel, a polarizing plate, and a cover film. The elements in this laminated structure are bonded together, for example, by a transparent adhesive layer for optical purposes (optical adhesive layer). The optical adhesive layer is, for example, made into an optical adhesive sheet formed from an optical adhesive composition. Furthermore, this optical adhesive sheet is used for bonding the elements together during the manufacturing process of the display panel. Alternatively, the optical adhesive layer is formed during the manufacturing process of the display panel by coating the elements that are to be bonded with an optical adhesive composition, etc.

[0003] On the other hand, foldable display panels are currently being developed for use in devices such as smartphones and tablets. In foldable display panels, the elements of the laminated structure are fabricated as film components capable of repeated bending, and these elements are bonded together by an optical adhesive layer. Optical adhesive layers for flexible devices such as foldable display panels are described, for example, in Patent Document 1 below. [Previous Technical Documents] [Patent Literature]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-111754 Summary of the Invention

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

[0006] Previously, the optical adhesive layer was prone to peeling off from the substrate (optical film) at the bending points of foldable display panels. This was because when the display panel was bent, shear stress and other stresses were locally applied to the optical adhesive layer at the bending point. This peeling could lead to malfunctions in the device, which was undesirable. For optical adhesive layers used in foldable display panels, a higher level of performance is required to balance the ease with which the display can bend and deform along with the substrate when bent, and to suppress peeling off from the substrate.

[0007] As a flexible device, rollable (flexible) display panels are also being developed. For the optical adhesive layer used in rollable display panels, a very high level of balance is required to ensure that the display can easily deform along with the adhered body when rolled up (winding deformation) and to prevent peeling from the adhered body.

[0008] The present invention provides an optical adhesive layer suitable for use in flexible devices, and an optical film with the optical adhesive layer attached. [Technical means to solve the problem]

[0009] The present invention [1] includes an optical adhesive layer comprising: a low adhesive layer having a first surface and a second surface opposite to the first surface; and a high adhesive layer disposed on the first surface and having a high adhesive surface on the side opposite to the low adhesive layer; wherein the high adhesive surface, after being bonded to a polyimide film and subjected to a peel angle of 180° and a peel speed of 300 mm / min for 30 minutes at 23°C, has a peel adhesion of 5 N / 25 mm or more to the polyimide film, and the ratio of the shear storage modulus of the low adhesive layer at -20°C to the shear storage modulus of the high adhesive layer at -20°C is less than 1.

[0010] The present invention [2] includes an optical adhesive layer as described in [1] above, wherein the ratio of the thickness of the low adhesive layer to the thickness of the high adhesive layer is 1 or more.

[0011] The present invention [3] includes an optical adhesive layer as described in [1] or [2] above, wherein the ratio of the thickness of the low adhesive layer to the thickness of the high adhesive layer is 30 or less.

[0012] The present invention [4] includes an optical adhesive layer as described in [1] above, which further has a high adhesive layer disposed on the second surface and has a high adhesive surface on the side opposite to the low adhesive layer.

[0013] The present invention [5] includes an optical adhesive layer as described in [4] above, wherein the ratio of the thickness of the low adhesive layer to the total thickness of the high adhesive layer is 1 or more.

[0014] The present invention [6] includes an optical adhesive layer as described in [4] or [5] above, wherein the ratio of the thickness of the low adhesive layer to the total thickness of the high adhesive layer is 30 or less.

[0015] The present invention [7] comprises an optical adhesive layer as described in any one of [1] to [6] above, having a total thickness of 5 μm or more and 150 μm or less.

[0016] The present invention [8] includes an optical adhesive layer as described in any one of [1] to [7] above, wherein the difference between the maximum thickness and the minimum thickness is less than 3 μm.

[0017] The present invention [9] comprises an optical adhesive layer as described in any one of [1] to [8] above, wherein the high adhesive layer has a shear storage modulus of less than 1000 kPa at -20°C.

[0018] The present invention

[10] includes an optical film with an optical adhesive layer, comprising: an optical film; and an optical adhesive layer, the optical adhesive layer being the optical adhesive layer described in any one of [1] to [3] above, and being attached to the optical film with the second side thereon. [Effects of the Invention]

[0019] As described above, the optical adhesive layer of this invention has a high-adhesion surface on the side opposite to the low-adhesion layer, which exhibits a peel adhesion of 5 N / 25 mm or more under specific conditions. This configuration is suitable for ensuring good adhesion between the optical adhesive layer and the adherend through the high-adhesion surface, and therefore suitable for suppressing peeling of the optical adhesive layer from the adherend. Furthermore, as described above, the ratio of the shear storage modulus of the low-adhesion layer at -20°C to that of the high-adhesion layer at -20°C in the optical adhesive layer is less than 1. This configuration is suitable for ensuring the overall flexibility of the optical adhesive layer, thereby ensuring flexural deformability. The more flexible the optical adhesive layer, the easier it is for the optical adhesive layer to follow the deformation of the adherend with a larger curvature when the adherend to which the adhesive layer is attached deforms with a relatively large curvature (such as the aforementioned bending deformation and winding deformation). The optical adhesive layer is flexible and easily deformable with a large curvature (flexibility), which is suitable for achieving good repeated deformation (repeated bending deformation and winding deformation, etc.) in flexible devices using this optical adhesive layer. As described above, the optical adhesive layer that is suitable for balancing peel resistance and flexibility, and the optical film with such an optical adhesive layer described above, are suitable for use in flexible devices. Simple Explanation of the Diagram

[0020] Figure 1 is a cross-sectional schematic diagram of the first embodiment of the optical adhesive layer of the present invention. Figure 2 is a cross-sectional schematic diagram of the second embodiment of the optical adhesive layer of the present invention. Figure 3 illustrates an example of the method of using the optical adhesive layer of the present invention. Figure 3A shows the step of attaching the optical adhesive layer to the first adherend, Figure 3B shows the step of bonding the first adherend and the second adherend via the optical adhesive layer, and Figure 3C shows the curing step. Figure 4 is a cross-sectional schematic diagram of one embodiment of the optical film with an optical adhesive layer of the present invention. Implementation

[0021] As shown in FIG1, the optical adhesive layer 10 (optical adhesive layer 10A), which is a first embodiment of the optical adhesive layer of the present invention, is a sheet shape having a specific thickness and extends in a direction orthogonal to the thickness direction H (surface direction). The optical adhesive layer 10 is transparent (visible light transmittance). Furthermore, the optical adhesive layer 10A is a multilayer adhesive layer having a high adhesive layer 11 and a low adhesive layer 12 sequentially along the thickness direction H. The high adhesive layer 11 is an adhesive layer with relatively strong surface adhesion, and the low adhesive layer 12 is an adhesive layer with relatively low surface adhesion. The low adhesive layer 12 has a first surface 12a and a second surface 12b opposite to the first surface 12a. The high adhesive layer 11 is disposed on the first surface 12a. The high adhesive layer 11 has a high adhesion surface 11a on the side opposite to the low adhesive layer 12. The high-adhesion surface 11a is one of the adhesive surfaces of the optical adhesive layer 10A. The second surface 12b of the low-adhesion layer 12 is the other adhesive surface of the optical adhesive layer 10A. Figure 1 illustrates the following state: the optical adhesive layer 10A is made into an optical adhesive sheet S, and release films L1 and L2 are bonded to both sides of the sheet.

[0022] As shown in FIG2, the optical adhesive layer 10 (optical adhesive layer 10B), which is a second embodiment of the optical adhesive layer of the present invention, has a sheet shape with a specific thickness and extends in a direction orthogonal to the thickness direction H (surface direction). The optical adhesive layer 10B has two high adhesive layers 11 (11A, 11B) and a low adhesive layer 12 between the high adhesive layers 11. Specifically, the optical adhesive layer 10B is a multilayer adhesive layer consisting of a high adhesive layer 11A, a low adhesive layer 12, and a high adhesive layer 11B arranged sequentially along the thickness direction H. The low adhesive layer 12 has a first surface 12a and a second surface 12b opposite to the first surface 12a. The high adhesive layer 11A (a high adhesive layer 11) is disposed on the first surface 12a. The high-adhesion layer 11A has a high-adhesion surface 11a (first high-adhesion surface) on the side opposite to the low-adhesion layer 12. The high-adhesion surface 11a is one of the adhesion surfaces of the optical adhesive layers 10A. A high-adhesion layer 11B (another high-adhesion layer 11) is disposed on the second surface 12b. The high-adhesion layer 11B has a high-adhesion surface 11a (second high-adhesion surface) on the side opposite to the low-adhesion layer 12. The high-adhesion surface 11a of the high-adhesion layer 11B is another adhesion surface of the optical adhesive layers 10A. The adhesion strength of the high-adhesion surface 11a of the high-adhesion layer 11A and the adhesion strength of the high-adhesion surface 11b of the high-adhesion layer 11B may be the same or different. Figure 2 illustrates the following state: the optical adhesive layer 10B is made into an optical adhesive sheet S, and release films L1 and L2 are bonded to both sides of the sheet.

[0023] This optical adhesive layer 10 is a transparent adhesive layer disposed in the light-passing portion of a flexible device. Examples of flexible devices include flexible display panels. Flexible display panels, for example, have a laminated structure including elements such as a pixel panel, a touch panel, a polarizing plate, and a cover film. Examples of flexible display panels include foldable display panels and rollable display panels. The optical adhesive layer 10 is used, for example, during the manufacturing process of the flexible display panel for bonding the elements included in the aforementioned laminated structure to each other.

[0024] The high-adhesion surfaces 11a and 11b of optical adhesive layer 10A and optical adhesive layer 10B, respectively, after being bonded to the polyimide film and subjected to 30 minutes at 23°C, exhibit a peel adhesion of 5 N / 25 mm or more to the polyimide film at a peel angle of 180° and a peel speed of 300 mm / min. The bonding of the optical adhesive layer 10 to the polyimide film is performed at 23°C using a 2 kg roller for one reciprocating cycle. From the viewpoint of ensuring good adhesion to the substrate (elements included in the laminated structure of the flexible device), the peel adhesion is preferably 7 N / 25 mm or more, more preferably 9 N / 25 mm or more, and even more preferably 11 N / 25 mm or more. For example, the peel adhesion is 30 N / 25 mm or less. Methods for adjusting the peel adhesion of the adhesive layer surface include, for example, selecting the type of base polymer in the adhesive layer, adjusting its molecular weight, and adjusting its formulation amount. Methods for adjusting the peel adhesion of the adhesive layer surface also include selecting the type of components in the adhesive layer other than the base polymer, and adjusting the formulation amount of those components. Examples of such components include crosslinking agents, silane coupling agents, and oligomers.

[0025] In the optical adhesive layers 10 (optical adhesive layers 10A and 10B), the ratio (E2 / E1) of the shear storage modulus (E2) of the low adhesive layer 12 at -20°C to the shear storage modulus (E1) of the high adhesive layer 11 at -20°C is less than 1. That is, the low adhesive layer 12 has a smaller shear storage modulus at -20°C and lower elasticity compared to the high adhesive layer 11. This ratio is preferably 0.7 or less, more preferably 0.5 or less, further preferably 0.3 or less, and particularly preferably 0.15 or less. This ratio (E2 / E1) is, for example, 0.05 or more. The shear storage modulus of the adhesive layer can be measured using a dynamic viscoelasticity measuring device. In this measurement, the measurement mode is set to shear mode, the measurement temperature range is set to -60°C to 150°C, the heating rate is set to 5°C / minute, and the frequency is set to 1 Hz. Specifically, as described below with reference to the embodiments, methods for adjusting the shear storage modulus of the adhesive layer include, for example, the selection of the type of base polymer in the adhesive layer, the adjustment of its molecular weight and dosage, and the selection of the type of crosslinking agent used to crosslink the base polymer and the adjustment of its dosage. The selection of the type of base polymer includes the selection of the type of main chain in the base polymer, and the selection and adjustment of the type and amount of functional groups.

[0026] In the optical adhesive layer 10, as described above, the high-adhesion layer 11 has a high-adhesion surface 11a on the side opposite to the low-adhesion layer 12. Under the specific conditions described above, the peel adhesion of the high-adhesion surface 11a is 5 N / 25 mm or more, preferably 7 N / 25 mm or more, more preferably 9 N / 25 mm or more, and even more preferably 11 N / 25 mm or more. This configuration is suitable for ensuring good adhesion between the optical adhesive layer 10 and the adherend through the high-adhesion surface 11a, and therefore is suitable for suppressing the peeling of the optical adhesive layer 10 from the adherend.

[0027] Furthermore, in the optical adhesive layer 10, as described above, the ratio of the shear storage modulus of the low adhesive layer 12 at -20°C to the shear storage modulus of the high adhesive layer 11 at -20°C is less than 1, preferably 0.7 or less, more preferably 0.5 or less, further preferably 0.3 or less, and even more preferably 0.15 or less. This configuration is suitable for ensuring the overall flexibility of the optical adhesive layer 10, thereby ensuring bending deformability. The more flexible the optical adhesive layer 10 is, the easier it is to follow the deformation of the adhered body with a relatively large curvature when the adhered body deforms with a relatively large curvature. Examples of deformation of the adhered body with a relatively large curvature include: the bending deformation of a foldable display and the deformation (winding deformation) when a rollable display is rolled up. The optical adhesive layer 10 is soft and easily deforms with a large curvature (flexibility), which is suitable for achieving good repeated deformation (repeated bending deformation and winding deformation, etc.) of flexible devices using the optical adhesive layer 10.

[0028] By sharing the functions of the high-adhesion layer 11 and the low-adhesion layer 12, the optical adhesive layer 10, as described above, is suitable for both peel resistance and flexural deformation resistance and is suitable for use in flexible devices.

[0029] Based on the consideration of ensuring flexibility and bendability suitable for flexible devices in the optical adhesive layer 10, the shear storage modulus of the optical adhesive layer 10 at -20°C is preferably 180 kPa or less, more preferably 150 kPa or less, further preferably 130 kPa or less, and especially preferably 100 kPa or less. Furthermore, based on the consideration of ensuring the cohesiveness of the optical adhesive layer 10, the shear storage modulus of the optical adhesive layer 10 at -20°C is preferably 30 kPa or more, more preferably 40 kPa or more, further preferably 50 kPa or more, and especially preferably 60 kPa or more. The overall shear storage modulus of the optical adhesive layer 10 at -20°C can be adjusted by adjusting the shear storage modulus of each adhesive layer in the optical adhesive layer 10 at -20°C and the thickness of each adhesive layer.

[0030] From the viewpoint of ensuring the aforementioned flexibility and bendability of the optical adhesive layer 10, the shear storage modulus E1 of the high adhesive layer 11 at -20°C is preferably 1000 kPa or less, more preferably 800 kPa or less, and even more preferably 700 kPa or less. From the viewpoint of ensuring the high adhesion of the high adhesion surface 11a, the shear storage modulus E1 of the high adhesive layer 11 at -20°C is preferably 100 kPa or more, more preferably 200 kPa or more, even more preferably 300 kPa or more, and particularly preferably 500 kPa or more.

[0031] From the viewpoint of ensuring the aforementioned flexibility and bendability of the optical adhesive layer 10, the shear storage modulus E2 of the low adhesive layer 12 at -20°C is preferably 150 kPa or less, more preferably 110 kPa or less, and even more preferably 80 kPa or less. From the viewpoint of ensuring the adhesion of the first surface 12a and the second surface 12b, the shear storage modulus E2 of the low adhesive layer 12 at -20°C is preferably 10 kPa or more, more preferably 20 kPa or more, and even more preferably 30 kPa or more.

[0032] The ratio of the thickness H2 of the low-adhesive layer 12 to the thickness H1 of the high-adhesive layer 11 (or the total thickness of the multiple high-adhesive layers 11 when the optical adhesive layer 10 has multiple high-adhesive layers 11) is preferably 1 or more, more preferably 3 or more, further preferably 6 or more, and especially preferably 9 or more. This configuration is better for ensuring the aforementioned flexibility and bendability of the optical adhesive layer 10. The ratio of the thickness H2 of the low-adhesive layer 12 to the thickness H1 of the high-adhesive layer 11 is preferably 30 or less, further preferably 25 or less, and more preferably 20 or less. This configuration is better for ensuring the plasticity of the optical adhesive layer 10, thereby ensuring good operability.

[0033] The thickness of the single high-adhesion layer 11 is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. This configuration is better for ensuring the cohesive force of the high-adhesion layer 11, thereby ensuring high adhesion. The thickness of the single high-adhesion layer 11 is, for example, 10 μm or less.

[0034] The thickness of the low-adhesion layer 12 is preferably 3 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. This configuration is better for ensuring the cohesive force of the high-adhesion layer 11, thereby ensuring high adhesion. The thickness of the low-adhesion layer 12 is preferably 70 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. This configuration is better for ensuring the plasticity of the optical adhesive layer 10, thereby ensuring good workability.

[0035] From the perspective of ensuring cohesiveness and thus high adhesion, the total thickness of the optical adhesive layer 10 is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. From the perspective of ensuring good deformability (ease of deformation), the total thickness of the optical adhesive layer 10 is preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less.

[0036] In the optical adhesive layer 10, the difference between the maximum and minimum thickness is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less. This configuration is better for suppressing stress concentration in the adhered body when the adhered body in contact with the optical adhesive layer 10 deforms. Furthermore, this thickness difference configuration is also better from the perspective of the visibility of the flexible device (optical device) with the optical adhesive layer 10 in the laminated structure.

[0037] After the optical adhesive layer 10 is wound onto a core with a cross-sectional diameter of 20 mm, the change in transmittance of the optical adhesive layer 10 after 1 hour is preferably 5% or less, more preferably 4% or less, and even more preferably 3% or less. This configuration is suitable for ensuring the transparency of the optical adhesive layer used in flexible devices. Specifically, the aforementioned change in transmittance of the optical adhesive layer 10 can be measured by the method described below with reference to the embodiments.

[0038] The haze of the optical adhesive layer 10 is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. The haze of the optical adhesive layer 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.

[0039] The total light transmittance of the optical adhesive layer 10 is preferably 60% or more, more preferably 80% or more, and even more preferably 85% or more. The total light transmittance of the optical adhesive layer 10 is, for example, 100% or less. The total light transmittance of the optical adhesive layer 10 can be measured according to JIS K 7375 (2008).

[0040] The high-adhesion layer 11 and low-adhesion layer 12 of the optical adhesive layer 10 are transparent pressure-sensitive adhesive layers formed from adhesive compositions. As described above, the low-adhesion layer 12 has lower elasticity than the high-adhesion layer 11 and has a different composition. The high-adhesion layer 11A and high-adhesion layer 11B in the optical adhesive layer 10B may have the same composition or different compositions. Each adhesive layer contains at least a base polymer.

[0041] The base polymer is the adhesive component that exhibits adhesive properties in the adhesive layers (high adhesive layer 11, low adhesive layer 12). 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 of the adhesive layer, it is preferable to use an acrylic polymer as the base polymer.

[0042] Acrylic polymers are copolymers containing monomeric components of alkyl (meth)acrylate at a ratio of 50% or more by mass. "(Meth)acrylate" means acrylic acid and / or methacrylic acid.

[0043] Alkyl methacrylates with 1 to 20 carbon atoms are suitable as alkyl methacrylates. Alkyl methacrylates may have straight-chain or branched alkyl groups, or cyclic alkyl groups such as alicyclic alkyl groups.

[0044] 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 methacrylic acid. 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.

[0045] 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-adamantane (meth)acrylate, 2-methyl-2-adamantane (meth)acrylate, and 2-ethyl-2-adamantane (meth)acrylate.

[0046] As an alkyl methacrylate, it is preferred to use an alkyl acrylate having an alkyl group 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.

[0047] Based on the viewpoint of appropriately exhibiting basic properties such as adhesion in the adhesive layer, the proportion of (meth)acrylate alkyl ester in the monomer component is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. This proportion is, for example, 99% by mass or less.

[0048] 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 monomers with nitrogen-containing rings, hydroxyl-containing monomers, and carboxyl-containing monomers. Monomers containing polar groups help to introduce crosslinking points into acrylic polymers and ensure the cohesiveness of acrylic polymers, thus modifying the acrylic polymers.

[0049] Examples of monomers having a nitrogen-containing ring include: N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperidone, N-vinylpyrrole, N-vinylimidazol, N-vinylpyrazole, N-(meth)propenyl-2-pyrrolidone, N-(meth)propenylpiperidone, N-(meth)propenylpyrrolidone, 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, and N-vinylisothiazole. It is preferable to use N-vinyl-2-pyrrolidone as a monomer with a nitrogen-containing ring.

[0050] From the perspective of ensuring the cohesive force of the adhesive layer and the adhesion between the adhesive layer and the adherend, the proportion of monomers with nitrogen-containing atomic rings in the monomer component 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 perspective of adjusting the glass transfer temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (which relates to the compatibility between the various additive components in the adhesive layer and the acrylic polymer), this proportion is preferably 30% by mass or less, more preferably 20% by mass or less.

[0051] 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-hydroxylauryl (meth)acrylate, and methyl (4-hydroxymethylcyclohexyl)methacrylate. 4-hydroxybutyl (meth)acrylate is preferred as the hydroxyl-containing monomer, and more preferably 4-hydroxybutyl acrylate.

[0052] From the perspective of introducing cross-linking structures into acrylic polymers and ensuring the cohesive force of adhesive layers, the proportion of hydroxyl-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 perspective of adjusting the polarity of acrylic polymers (which relates to the compatibility of various additive components in the adhesive layer with acrylic polymers), this proportion is preferably 20% by mass or less, and more preferably 10% by mass or less.

[0053] Examples of carboxyl-containing monomers include: acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, methylene succinic acid, maleic acid, trans-butenedioic acid, butenoic acid, and isobutenoic acid.

[0054] Based on the consideration of introducing a cross-linking structure into the acrylic polymer, ensuring the cohesive force of the adhesive layer, and ensuring the adhesion of the adhesive layer to the adherend, the proportion of carboxyl-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. Based on the consideration of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend caused by acid, this proportion is preferably 30% by mass or less, more preferably 20% by mass or less.

[0055] To prevent corrosion of metallic components such as electrodes in flexible devices by acid components, the adhesive layer preferably has a low acid content. Furthermore, when the adhesive layer is used for bonding polarizing plates, to suppress polyolefin formation in polyvinyl alcohol-based polarizing elements caused by acid components, the adhesive layer preferably has a low acid content. In this acid-free adhesive layer, 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 layer is determined by immersing the adhesive layer in pure water and heating it at 100°C for 45 minutes to extract the acid monomers into the water, and then quantifying the acid monomers using an ion chromatography system.

[0056] From an acid-free perspective, it is preferable that the base polymer in the adhesive layer does not substantially contain organic acid monomers as monomer components. From an acid-free perspective, the ratio of organic acid monomers in the monomer component 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.

[0057] 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.

[0058] The base polymer preferably 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 the cross-linking agent react in the adhesive layer (method 1); and a method in which a monomer component forming the base polymer contains a multifunctional monomer, and a base polymer with a branched structure (cross-linked structure) introduced into the polymer chain is formed by the polymerization of the monomer component (method 2). These methods can also be used in combination.

[0059] As a crosslinking agent used in the first method described above, examples include compounds that react with the 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. The crosslinking agent can be used alone or in combination of two or more. Considering the high reactivity with the hydroxyl and carboxyl groups in the base polymer and the ease with which crosslinking structures can be introduced, isocyanate crosslinking agents, peroxide crosslinking agents, and epoxy crosslinking agents are preferred as crosslinking agents.

[0060] 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 cited as isocyanate crosslinking agents. Examples of such isocyanate derivatives include isocyanurate-modified compounds and polyol-modified compounds. 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 of hexamethylene diisocyanate, manufactured by Tosoh), and Takenate D110N (trimethylolpropane adduct of phenyl diisocyanate, manufactured by Mitsui Chemicals).

[0061] 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.

[0062] Examples of epoxy crosslinking agents include: bisphenol A, epichlorohydrin type epoxy resin, ethylene 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-diglycidylaminomethyl)cyclohexane.

[0063] From the perspective of ensuring adequate flexibility (bendability) of the adhesive layer, isocyanate crosslinking agents (especially difunctional isocyanate crosslinking agents) and peroxide crosslinking agents are preferred. From the perspective of ensuring the durability of the adhesive layer, 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 perspective of balancing the durability and flexibility of the adhesive layer, it is preferable to use a combination of trifunctional isocyanate crosslinking agents, peroxide crosslinking agents, and / or difunctional isocyanate crosslinking agents.

[0064] From the viewpoint of ensuring the cohesive force of the adhesive layer, the amount of crosslinking agent relative to 100 parts by weight of the base polymer is, for example, 0.01 parts by weight or more, preferably 0.05 parts by weight or more, and more preferably 0.07 parts by weight or more. From the viewpoint of ensuring good adhesion in the adhesive layer, the amount of crosslinking agent relative to 100 parts by weight of the base polymer is, for example, 10 parts by weight or less, preferably 5 parts by weight or less, and more preferably 3 parts by weight or less.

[0065] In the second method described above, the monomer components (including multifunctional monomers and other monomers used to introduce the crosslinking structure) can undergo either single-stage polymerization or multi-stage polymerization. In the multi-stage polymerization method, firstly, the monofunctional monomers used to form the base polymer are polymerized (prepolymerization), thereby preparing a prepolymer composition containing a portion of the polymer (a mixture of low-degree polymers and unreacted monomers). Then, after adding the multifunctional monomers to the prepolymer composition, the portion of the polymer is polymerized with the multifunctional monomers (formal polymerization).

[0066] As a multifunctional monomer, an example is a multifunctional (meth)acrylate containing two or more vinyl unsaturated double bonds in one molecule. Considering that a cross-linked structure can be introduced through active energy line polymerization (photopolymerization), multifunctional monomers are preferred.

[0067] Examples of polyfunctional (meth)acrylates include: difunctional (meth)acrylates, trifunctional (meth)acrylates, and polyfunctional (meth)acrylates with four or more functions.

[0068] 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, dicyclopentenyl diacrylate, dimethacrylate isocyanurate, and epoxide-modified bisphenol dimethacrylate.

[0069] Examples of trifunctional (meth)acrylates include: trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tri(acryloxyethyl) isocyanurate.

[0070] Examples of polyfunctional (meth)acrylates with four or more 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.

[0071] 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. These configurations are preferred from the viewpoint of appropriately adjusting the viscoelasticity (e.g., storage modulus G' and loss tangent tanδ) in the base polymer by introducing crosslinking structures.

[0072] 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. Solution polymerization and UV polymerization are preferred from the perspectives of adhesive layer transparency, water resistance, and cost. For example, ethyl acetate and toluene are used as solvents for solution polymerization. Furthermore, thermal polymerization initiators and photopolymerization initiators are used as polymerization 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.

[0073] 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) disulfide, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine) dihydrochloride. Examples of peroxide polymerization initiators include benzoyl peroxide, tributyl maleate peroxide, and lauryl peroxide.

[0074] 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, diphenylethylene glycol-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, and 9-oxosulfuron-methyl-2-ethylhexylene ... It is a photopolymerization initiator and a phosphine oxide photopolymerization initiator.

[0075] In polymerization, chain transfer agents and / or polymerization inhibitors (polymerization retarders) may also 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.

[0076] 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, thus tending to result in a higher density of reaction initiation points and a smaller molecular weight of the formed base polymer. Conversely, the less polymerization initiator used, the lower the density of reaction initiation points, thus tending to result in easier polymer chain elongation and a larger molecular weight of the formed base polymer.

[0077] From the perspective of ensuring the cohesive strength of the adhesive layer, the weight-average molecular weight of the base polymer is preferably 100,000 or higher, more preferably 300,000 or higher, and even more preferably 500,000 or higher. This weight-average molecular weight is preferably 5 million or lower, more preferably 3 million or lower, and even more preferably 2 million or lower. The weight-average molecular weight of the base polymer was determined using gel permeation chromatography (GPC) and calculated using polystyrene.

[0078] 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.

[0079] The glass transition temperature (Tg) of the basic polymer can be obtained using the theoretical value 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 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. The glass transition temperature of the homopolymer can be obtained from literature. 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). Alternatively, the glass transition temperature of the homopolymer of the monomer can also be obtained using the method specifically described in Japanese Patent Application Publication No. 2007-51271.

[0080] Fox formula 1 / (273+Tg)=Σ[Wi / (273+Tgi)]

[0081] As a method for adjusting the peel adhesion and / or shear storage modulus of each adhesive layer, adjusting the molecular weight of the base polymer, the glass transfer temperature, and the degree of crosslinking within the adhesive layer is relatively effective. A larger molecular weight of the base polymer tends to result in a higher elastic modulus and, consequently, a higher adhesion. A lower glass transfer temperature of the base polymer tends to result in a lower elastic modulus and, consequently, a lower adhesion. A higher degree of crosslinking of the base polymer tends to result in a higher elastic modulus of the adhesive layer. Furthermore, the adhesion of the adhesive layer varies according to the degree of crosslinking, reaching a maximum value at a specific degree of crosslinking of the base polymer. Specifically, as described below: A higher degree of crosslinking of the base polymer tends to result in higher cohesive force within the adhesive layer and higher adhesion before reaching a certain degree of crosslinking. When the aforementioned certain degree of crosslinking is exceeded, a higher degree of crosslinking of the base polymer tends to result in excessive elasticity of the adhesive layer and lower adhesion.

[0082] The monomer components of the basic polymer contained in the high-adhesion layer 11 are preferably alkyl acrylates having alkyl groups having 6 to 15 carbon atoms, monomers having nitrogen-containing rings, and hydroxyl-containing monomers, and more preferably 2-ethylhexyl acrylate (2EHA), N-vinyl-2-pyrrolidone (NVP), and 4-hydroxybutyl acrylate (4HBA).

[0083] The monomer components of the basic polymer contained in the low-adhesion layer 12 are preferably alkyl acrylates containing alkyl groups having 6 to 15 carbon atoms and hydroxyl-containing monomers, and more preferably 2-ethylhexyl acrylate (2EHA), lauryl acrylate (LA), and 4-hydroxybutyl acrylate (4HBA).

[0084] The adhesive composition may also 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 as the 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, between 1,000 and 30,000.

[0085] The glass transition temperature of acrylic oligomers is preferably above 60°C, more preferably above 80°C, further preferably above 100°C, and even more preferably above 110°C. The glass transition temperature of acrylic oligomers is, for example, below 200°C, preferably below 180°C, and more preferably below 160°C. By using a low-Tg acrylic polymer (base polymer) with a cross-linked structure and a high-Tg acrylic oligomer, the adhesion of the adhesive layer, especially at high temperatures, can be improved. The glass transition temperature of the acrylic oligomer is calculated using the Fox formula described above.

[0086] Acrylic oligomers with a glass transition temperature of 60°C or higher are preferably polymers comprising 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 acrylic polymers.

[0087] Considering the high glass transition temperature and excellent compatibility with the base polymer, methyl methacrylate is preferred among (meth)acrylate chain alkyl esters. Dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferred among (meth)acrylate alicyclic alkyl esters. That is, the acrylic oligomer is preferably a polymer comprising one or more monomers selected from the group consisting of dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate.

[0088] The proportion of (meth)acrylate cycloalkyl 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.

[0089] 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 range of molecular weights for the acrylic oligomer is advantageous for ensuring the adhesion and retention of the adhesive layer.

[0090] Acrylic oligomers are obtained by polymerizing the monomeric 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 can be used, and chain transfer agents can be used for molecular weight adjustment purposes.

[0091] To fully enhance the adhesion of the adhesive layer, the content of acrylic oligomer in the adhesive layer 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 layer, the content of acrylic oligomer in the adhesive layer 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 layer is excessive, the compatibility of the acrylic oligomer decreases, which tends to lead to increased haze and decreased transparency.

[0092] 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.

[0093] The adhesive composition may also contain other components as needed. Examples of other components include, for instance, adhesive agents, plasticizers, softeners, antioxidants, fillers, colorants, UV absorbers, antioxidants, surfactants, and antistatic agents.

[0094] Methods for forming the multilayer optical adhesive layer 10 include: dry-on-dry (dry lamination), wet-on-dry, and wet-on-wet methods. In the dry-on-dry method, for example, the multilayer adhesive layer can be formed by coating an adhesive composition onto a release film and drying it to form multiple adhesive layers (high adhesive layer 11, low adhesive layer 12), and then bonding the multiple adhesive layers together. In the wet-on-dry method, for example, the multilayer adhesive layer can be formed by coating an adhesive composition onto the release film and drying it to form an adhesive layer for each adhesive layer. In the wet-on-wet method, for example, the multilayer adhesive layer can be formed by coating multiple layers of adhesive composition onto the release film in multiple stages to form a multilayer coating, and then drying the multilayer coating.

[0095] If a wet-on-wet method is used, the aforementioned optical adhesive layer 10A with a two-layer structure can be manufactured, for example, by the following method (first manufacturing method). First, a first adhesive composition for forming a high-adhesion layer 11 and a second adhesive composition for forming a low-adhesion layer 12 are prepared. Then, the first adhesive composition (lower position) and the second adhesive composition (upper position) are coated on the peel-treated surface of a first release film whose surface has been peeled. Specifically, the first adhesive composition is coated on the first release film to form a first coating film, and the second adhesive composition is coated on the first coating film to form a second coating film (formation of a multilayer coating film). Then, the multilayer coating film on the first release film is dried by heating to form a multilayer adhesive layer. Then, the peel-treated surface of the second release film, which has been peeled on one side, is bonded to the multilayer adhesive layer on the first release film. Subsequently, a cross-linking reaction is carried out in the adhesive layer as needed, and a curing treatment is performed. In the manner described above, an optical adhesive layer 10A, which serves as an optical adhesive sheet S, can be manufactured with the adhesive surface covered and protected by release films L1 and L2. When using the optical adhesive sheet S, the release films L1 and L2 are peeled off from the optical adhesive sheet S as needed.

[0096] If a wet-on-wet process is used, the aforementioned three-layer optical adhesive layer 10B can be manufactured, for example, by the following method (second manufacturing method). First, a first adhesive composition for forming a high-adhesion layer 11A, a second adhesive composition for forming a low-adhesion layer 12, and a third adhesive composition for forming a high-adhesion layer 11B are prepared. Then, the first adhesive composition (lower position), the second adhesive composition (middle position), and the third adhesive composition (upper position) are coated on the peeled surface of the first release film, which has undergone a surface peeling treatment. Specifically, the first adhesive composition is coated on the first release film to form a first coating film, and the second adhesive composition is coated on the first coating film to form a second coating film. Furthermore, the third adhesive composition is coated on the second coating film to form a third coating film (formation of a multilayer coating film). Subsequently, the multilayer coating on the first release film is dried by heating to form a multilayer adhesive layer. Then, the release-treated surface of the second release film, which has undergone a single-sided release treatment, is adhered to the multilayer adhesive layer on the first release film. Afterward, a curing treatment is performed as needed to conduct a crosslinking reaction in the adhesive layer. In the manner described above, an optical adhesive layer 10B, with its adhesive surfaces protected by release films L1 and L2, serving as an optical adhesive sheet S, can be manufactured. When using the optical adhesive sheet S, the release films L1 and L2 are peeled off from the optical adhesive sheet S as needed.

[0097] In the above manufacturing method, a flexible plastic film can be used as a release film. Examples of such plastic films include polyethylene terephthalate film, polyethylene film, polypropylene film, and polyester film. The thickness of the release film is, for example, 3 μm or more, and also, for example, 200 μm or less.

[0098] In the above manufacturing methods, the coating method for the adhesive composition can be exemplified by, for example, 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.

[0099] Figures 3A to 3C show an example of how the optical adhesive layer 10 is used (the multilayer structure of the optical adhesive layer 10 is omitted in Figures 3A to 3C).

[0100] In this method, firstly, as shown in FIG3A, an optical adhesive layer 10 is bonded to one side of the first component 21 (the adherend) in the thickness direction H. The first component 21 is, for example, an element in the multilayer structure of a flexible display panel. Examples of such elements include: a pixel panel, a touch panel, a polarizing plate, and a cover film (the same applies to the second component 22 described later). Through this step, an optical adhesive layer 10 for bonding with other components is provided on the first component 21.

[0101] Subsequently, as shown in FIG3B, the optical adhesive layer 10 on the first member 21 is used to bond 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 flexible display panel.

[0102] Subsequently, as shown in Figure 3C, the optical adhesive layer 10 between the first component 21 and the second component 22 is cured. Through curing, the optical adhesive layer 10 undergoes a cross-linking reaction of the basic polymer, thereby enhancing the bonding force between the first component 21 and the second component 22. The curing temperature is, for example, 20°C to 160°C. The curing time is, for example, 1 minute to 21 days. When curing is performed by autoclaving (heating and pressurizing), 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.

[0103] The optical adhesive layer 10 used in the manufacturing process of flexible devices as described above has, under specific conditions, a high-adhesion surface 11a with a peel adhesion of 5 N / 25 mm or more, and the ratio of the shear storage modulus of the low-adhesion layer 12 at -20°C to that of the high-adhesion layer 11 at -20°C is less than 1. This optical adhesive layer 10, as described above, is suitable for balancing flexural deformation resistance and peel inhibition, and is therefore suitable for use in flexible devices.

[0104] Figure 4 is a cross-sectional schematic diagram of an optical film X with an optical adhesive layer, which is one embodiment of the optical film with an optical adhesive layer according to the present invention. The optical film X with an optical adhesive layer has an optical film 23 and the aforementioned optical adhesive layer 10A sequentially arranged along the thickness direction H.

[0105] The optical film 23 is flexible. In this embodiment, the optical film 23 is a functional film or substrate film assembled into the multilayer structure of the flexible display panel. Examples of functional films include polarizing element films and retardation films. Examples of polarizing element films include hydrophilic polymer films that have undergone dyeing treatment using dichroic substances and subsequent stretching treatment. Examples of dichroic substances include iodine and dichroic dyes. Examples of hydrophilic polymer films include polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified films of ethylene-vinyl acetate copolymers. Examples of retardation films include λ / 2 wavelength films, λ / 4 wavelength films, and viewing angle compensation films. The thickness of the optical film 23 is, for example, 5 μm or more, and, for example, 500 μm or less.

[0106] As described above, the optical adhesive layer 10A is a multilayer adhesive layer consisting of a high-adhesion layer 11 and a low-adhesion layer 12 sequentially arranged along the thickness direction H. The optical adhesive layer 10A is attached to the optical film 23 with the second surface 12b side of the low-adhesion layer 12 attached. Furthermore, in this embodiment, the optical adhesive layer 10A is a multilayer adhesive layer formed on the optical film 23.

[0107] The optical film X with the optical adhesive layer can be manufactured by dry-on-dry method, wet-on-dry method, or wet-on-wet method after preparing the first adhesive composition for forming the high adhesive layer 11 and the second adhesive composition for forming the low adhesive layer 12.

[0108] In the dry-on-dry process, firstly, a low-adhesion layer 12 is formed by coating a second adhesive composition onto the optical film 23 and allowing it to dry. On the other hand, a high-adhesion layer 11 is formed by coating a first adhesive composition onto a release film and allowing it to dry. Then, the high-adhesion layer 11 is bonded to the low-adhesion layer 12 on the optical film 23. For example, this allows an optical adhesive layer 10A to be formed on the optical film 23.

[0109] In the wet-on-dry process, firstly, a low-adhesion layer 12 is formed by coating a second adhesive composition onto the optical film 23 and allowing it to dry. Then, a high-adhesion layer 11 is formed by coating a first adhesive composition onto the low-adhesion layer 12 and allowing it to dry. For example, this allows an optical adhesive layer 10A to be formed on the optical film 23.

[0110] In the wet-on-wet process, firstly, a second adhesive composition (lower layer) and a first adhesive composition (upper layer) are coated onto the optical film 23. Specifically, the second adhesive composition is coated onto the optical film 23 to form a coating film, and the first adhesive composition is coated onto the coating film to form another coating film (formation of a multilayer coating film). Subsequently, the multilayer coating film on the optical film 23 is dried by heating. For example, in this way, an optical adhesive layer 10A can be formed on the optical film 23.

[0111] When a low-adhesion layer 12 is formed as described above by coating the optical film 23, which serves as the adherend, with the second adhesive composition and allowing it to dry, the low-adhesion layer 12 can exert a higher adhesion force on the surface of the optical film 23 compared to the case where a low-adhesion layer 12 temporarily formed on a substrate such as a release film is bonded to the optical film 23. Therefore, the optical film X with the attached optical adhesive layer is suitable for ensuring good adhesion of the second surface 12b of the low-adhesion layer 12 to the optical film 23.

[0112] The optical adhesive layer 10A can also be a multilayer adhesive layer formed on a specific substrate, with the low-adhesion layer 12 side bonded to the optical film 23. In this case, it is preferable to ensure the adhesion between the optical film 23 and the optical adhesive layer 10A by performing plasma treatment on the surface of the optical film 23 (the predetermined bonding surface) before bonding the low-adhesion layer 12 side of the optical adhesive layer 10A to the optical film 23.

[0113] Furthermore, as described above, the optical adhesive layer 10A has a high adhesion surface 11a with a peel adhesion of 5 N / 25 mm or more under certain conditions, and the ratio of the shear storage modulus of the low adhesive layer 12 at -20°C to the shear storage modulus of the high adhesive layer 11 at -20°C is less than 1. As described above, this optical adhesive layer 10A is suitable for balancing flexural deformability and peel resistance using the high-adhesion surface 11a. Therefore, the optical film X with the optical adhesive layer 10A is suitable for balancing flexural deformability and peel resistance.

[0114] The optical film X with the attached optical adhesive layer can also be a composite optical film on the side of the optical film 23 opposite to the optical adhesive layer 10A, where the optical adhesive layer 10 and additional optical films are alternately deposited. Examples of additional optical films include pixel panels (OLED (organic light emitting diode) panels), touch panels, polarizing plates, and cover films, arranged in a specific order. The optical adhesive layer 10 can be either the aforementioned optical adhesive layer 10A or optical adhesive layer 10B. In this type of composite optical film with attached optical adhesive layers, the adhesive layers that bind the elements together are all optical adhesive layers 10 (10A, 10B). The composite optical film obtained in this way can also be a foldable display panel. [Example]

[0115] The present invention will be specifically described below with reference to the embodiments shown. However, the present invention is not limited to the embodiments. Furthermore, the specific values ​​of the dosage (content), physical property value, parameters, etc., described below can replace the upper limit (defined as "below" or "not reached") or lower limit (defined as "above" or "exceeded") of the dosage (content), physical property value, parameters, etc., corresponding to those described in the above "Embodiment".

[0116] <Preparation of Polymer P1> In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet, a mixture containing 89 parts by mass of 2-ethylhexyl acrylate (2EHA), 10 parts by mass of N-vinyl-2-pyrrolidone (NVP), 1 part by mass of 4-hydroxybutyl acrylate (4HBA), 0.1 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and ethyl acetate and toluene as solvents (solid content concentration 50% by mass, toluene ratio in solvent 5% by mass) was stirred at 55°C under a nitrogen atmosphere for 6 hours (polymerization reaction). This yielded a solution containing an acrylic polymer (polymer P1). Subsequently, ethyl acetate was added to this solution to adjust the polymer concentration to 30% by mass, thereby obtaining a first polymer solution containing the acrylic polymer (polymer P1). The weight average molecular weight of the acrylic polymer in the first polymer solution was 2.19 million.

[0117] <Preparation of Polymer P2> In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet, a mixture (solid content concentration of 33% by mass) comprising 56 parts by mass of 2-ethylhexyl acrylate (2EHA), 39 parts by mass of lauryl acrylate (LA), 5 parts by mass of 4-hydroxybutyl acrylate (4HBA), 0.1 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and ethyl acetate as a solvent was stirred at 58°C under a nitrogen atmosphere for 5 hours (polymerization reaction). This yielded a solution containing acrylic polymer (polymer P2). Subsequently, ethyl acetate was added to this solution to adjust the polymer concentration to 30% by mass, thereby obtaining a second polymer solution containing acrylic polymer (polymer P2). The weight average molecular weight of the acrylic polymer in the second polymer solution was 830,000.

[0118] <Preparation of Polymer P3> In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet, a mixture containing 97.3 parts by mass of 2-ethylhexyl acrylate (2EHA), 1.7 parts by mass of N-vinyl-2-pyrrolidone (NVP), 1.0 part by mass of 4-hydroxybutyl acrylate (4HBA), 0.1 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and ethyl acetate and toluene as solvents (solid content concentration of 50% by mass, toluene ratio in solvent of 5% by mass) was stirred at 55°C under a nitrogen atmosphere for 6 hours (polymerization reaction). This yielded a solution containing an acrylic polymer (polymer P1). Subsequently, ethyl acetate was added to this solution to adjust the polymer concentration to 30% by mass. This yielded a third polymer solution containing an acrylic polymer (polymer P4). The acrylic polymer in the third polymer solution had a weight average molecular weight of 2 million.

[0119] [Example 1] <Preparation of the First Adhesive Composition> Ethyl acetate was added to the first polymer solution to adjust the solid content concentration to 10% by mass, thus obtaining the first adhesive composition.

[0120] <Preparation of the Second Adhesive Composition> In the second polymer solution, for every 100 parts by weight of the acrylic polymer (polymer P2), 0.5 parts by weight of a crosslinking agent (product name "Nyper BMT 40SV", benzoyl peroxide, manufactured by Nippon Oils & Fats Co., Ltd.) is added and mixed. Then, ethyl acetate is added to adjust the concentration of solids to 23% by weight to obtain the second adhesive composition.

[0121] <Formation of Optical Adhesive Layer> On the release-treated surface of a first release film (product name "JT-50Wa", polyester film, 50 μm thick, manufactured by Nitto Denko Corporation) that has undergone silicone release treatment on one side, a first adhesive composition (lower position) and a second adhesive composition (upper position) are applied by a wet-on-wet method. Specifically, the first adhesive composition is applied to the first release film to form a coating film (2 μm thick after drying), and the second adhesive composition is applied to the coating film to form a coating film (23 μm thick after drying) (formation of a multilayer coating film). Subsequently, the multilayer coating film on the first release film is dried by heating at 155°C for 2 minutes to form a multilayer adhesive layer with a thickness of 25 μm. Subsequently, the peeled side of a second release film (product name "MRQ25T100J", polyester film, 25 μm thick, manufactured by Mitsubishi Chemical Co., Ltd.), which has undergone silicone peeling treatment on one side, is bonded to a multilayer adhesive layer on the first release film. Then, a curing treatment is performed at 50°C for 48 hours to allow a crosslinking reaction to occur in the adhesive layer. The optical adhesive sheet (optical adhesive layer) of Example 1 is produced as described above. The optical adhesive sheet of Example 1 has a two-layer structure: a first layer (2 μm thick) formed from the first adhesive composition as a high-adhesion layer, and a second layer (23 μm thick) formed from the second adhesive composition as a low-adhesion layer. The monomer composition of the polymer and the composition of the adhesive layer in the optical adhesive sheet of Example 1 are shown in Table 1, with units set to parts by mass (the same applies to the examples and comparative examples described later).

[0122] [Example 2] Except as described below, the optical adhesive sheet of Example 2 was prepared in the same manner as the optical adhesive sheet of Example 1. When preparing the second adhesive composition, the amount of crosslinking agent (product name "Nyper BMT 40SV") was set to 1.0 parts by weight instead of 0.5 parts by weight.

[0123] The optical adhesive sheet of Example 2 has a two-layer structure consisting of a first layer (2 μm thick) formed by a first adhesive composition as a high-adhesion layer, and a second layer (23 μm thick) formed by a second adhesive composition as a low-adhesion layer. The optical adhesive sheet of Example 2 differs from that of Example 2 in the degree of crosslinking of the polymer components in the first and second adhesive layers. As a result, the optical adhesive sheets of Examples 1 and 2 exhibit differences in peel adhesion F, which will be described later. This is because, during the wet-on-wet process in the manufacturing of the optical adhesive sheet, a portion of the crosslinking agent diffuses from the second adhesive composition (upper layer) coated on the first adhesive composition (lower layer) into the first adhesive composition.

[0124] [Comparative Example 1] In the first polymer solution described above, for every 100 parts by weight of the acrylic polymer (polymer P1), 0.5 parts by weight of a crosslinking agent (product name "Nyper BMT 40SV", benzoyl peroxide, manufactured by Nippon Yushu Co., Ltd.) was added and mixed. Then, ethyl acetate was added to adjust the solid content concentration to 15% by weight to obtain the third adhesive composition. Subsequently, the third adhesive composition was coated onto the release-treated surface of the first release film (product name "JT-50Wa", polyester film, 50 μm thick, manufactured by Nitto Denko Co., Ltd.), which had undergone silicone release treatment on one side, to form a coating film (25 μm thick after drying). Then, the coating film on the first release film was dried by heating at 155°C for 2 minutes to form an adhesive layer with a thickness of 25 μm. Subsequently, the peeled side of a second release film (product name "MRQ25T100J", polyester film, 25 μm thick, manufactured by Mitsubishi Chemical Co., Ltd.), which has undergone silicone peeling treatment on one side, is bonded to the adhesive layer on the first release film. Then, it is cured at 50°C for 48 hours to induce a crosslinking reaction in the adhesive layer. Comparative Example 1's optical adhesive sheet (a single-layer optical adhesive layer) is produced in the manner described above.

[0125] [Comparative Example 2] In the formation of the optical adhesive layer, the second adhesive composition described above was used instead of the third adhesive composition. Otherwise, the optical adhesive sheet of Comparative Example 2 (single-layer optical adhesive layer) was made in the same manner as the optical adhesive sheet of Comparative Example 1.

[0126] [Comparative Example 3] Ethyl acetate was added to the third polymer solution to adjust the solid content concentration to 10% by mass, thus obtaining the fourth adhesive composition. Subsequently, in the formation of the optical adhesive layer, the fourth adhesive composition was used instead of the first adhesive composition. Otherwise, the optical adhesive sheet of Comparative Example 3 was prepared in the same manner as the optical adhesive sheet of Example 1. The optical adhesive sheet of Comparative Example 3 has a two-layer structure: a first layer (2 μm thick) formed by the fourth adhesive composition as a high-adhesion layer, and a second layer (23 μm thick) formed by the second adhesive composition as a low-adhesion layer.

[0127] <Thickness of Adhesive Layer> The thickness of each optical adhesive sheet in Examples 1 and 2 and Comparative Examples 1-3 was investigated. Specifically, firstly, adhesive sheets (25 mm short side × 100 mm long side) were cut from the optical adhesive sheets. Then, the thickness at five measurement points on the adhesive sheet was measured using a pin gauge. The five measurement points were five points dividing the width direction of the adhesive sheet into six equal parts along its long side. The maximum thickness T1 (μm) and the minimum thickness T2 (μm) among the thickness measurements at the five measurement points are shown in Table 1. The difference between the maximum and minimum thickness (T1 - T2) is also shown in Table 1.

[0128] <Peeling Adhesion> For each optical adhesive sheet of Examples 1, 2 and Comparative Examples 1-3, the peel adhesion was investigated by peel test.

[0129] First, test samples were prepared for each optical adhesive sheet. In the preparation of the test samples for each optical adhesive sheet in Examples 1 and 2, firstly, the second release film was peeled off from the optical adhesive sheet, and a plasma-treated polyimide substrate (product name "Upilex 25RN", thickness 25 μm, manufactured by Ube Industries, Ltd.) was bonded to the exposed surface to obtain a laminate. Next, a test piece (25 mm wide × 100 mm long) was cut from this laminate (polyimide substrate / adhesive layer / first release film). Then, the first release film was peeled off from the adhesive layer of the test piece, and a polyimide film (product name "Upilex 50S", thickness 50 μm, manufactured by Ube Industries, Ltd.) was bonded to the exposed surface (the first layer side surface in the multilayer adhesive layers). The bonding system was performed at 23°C by pressing the test piece onto the polyimide film using a 2 kg hand roller that moved back and forth once. Test samples for the optical adhesive sheets of Examples 1, 2, and Comparative Example 3 were prepared in the manner described above. For the test samples for the optical adhesive sheets of Comparative Examples 1 and 2, a polyimide substrate without plasma treatment (product name "Upilex 25RN", thickness 25 μm, manufactured by Ube Industries, Ltd.) was used instead of the aforementioned polyimide substrate with plasma treatment. Otherwise, the samples were prepared in the same manner as the test samples in Examples 1, 2, and Comparative Example 3.

[0130] Subsequently, after the test specimens were allowed to stand at room temperature for 30 minutes, a peel test was performed to separate the specimen from the polyimide film in the test specimens, and the peel strength was measured. In the test specimens of Examples 1, 2, and Comparative Example 3, the peel strength of the first layer surface from the polyimide film surface was measured. This measurement was performed using a tensile testing machine (product name "Autograph AG-50NX plus", manufactured by Shimadzu Corporation). In this measurement, the test temperature was set to 25°C, the peel angle of the specimen from the polyimide film was set to 180°, the tensile speed of the specimen was set to 300 mm / min, and the peel length was set to 50 mm. The average value of the measured peel strengths is shown in Table 1 as the peel adhesion F (N / 25 mm). The peel adhesion F of the adhesive layer in the multilayer structure (the first layer as a high-adhesion layer / the second layer as a low-adhesion layer) is the adhesion of the exposed surface of the first layer.

[0131] <Cut Storage Modulus> For each adhesive layer of the optical adhesive sheets of Examples 1, 2 and Comparative Examples 1-3, the shear storage modulus was measured in the manner described below.

[0132] First, test samples were prepared. In the preparation of test samples for Comparative Examples 1 and 2, multiple adhesive layers cut from optical adhesive sheets were laminated to form an adhesive sheet with a thickness of approximately 1 mm. This sheet was then punched to obtain cylindrical particles (9 mm in diameter) that served as test samples. In the preparation of test samples for Examples 1, 2, and Comparative Example 3, optical adhesive sheets were prepared for each adhesive layer (high adhesive layer and low adhesive layer), and then these optical adhesive sheets were used. Otherwise, the preparation was carried out in the same manner as the test samples for Comparative Examples 1 and 2. The optical adhesive sheet of the high adhesive layer (first layer) of Example 1 was prepared in the same manner as the multilayer optical adhesive sheet of Example 1, except that the second adhesive composition was not coated on the first adhesive composition on the first release film (resulting in no low adhesive layer being formed). The optical adhesive sheet of Example 1 with a low-adhesion layer (second layer) was manufactured in the same manner as the optical adhesive sheet of Example 1, except that the first adhesive composition was not coated on the first release film (resulting in no high-adhesion layer being formed). The optical adhesive sheet of Example 2 with a high-adhesion layer (first layer) was manufactured in the same manner as the optical adhesive sheet of Example 2, except that the second adhesive composition was not coated on the first adhesive composition on the first release film (resulting in no low-adhesion layer being formed). The optical adhesive sheet of Example 2 with a low-adhesion layer (second layer) was manufactured in the same manner as the optical adhesive sheet of Example 2, except that the first adhesive composition was not coated on the first release film (resulting in no high-adhesion layer being formed).

[0133] Subsequently, for the test samples, dynamic viscoelasticity measurements were performed by fixing them to a fixture with a parallel plate of 8 mm diameter using a dynamic viscoelasticity measuring device (product name "ARES-G2", manufactured by TA Instruments). In this measurement, the measurement mode was set to shear mode, the measurement temperature range was set to -60℃ to 150℃, the heating rate was set to 5℃ / min, and the frequency was set to 1 Hz. The shear storage modulus (kPa) at -20℃ was read from the measurement results. The results are shown in Table 1. Table 1 also shows the ratio of the shear storage modulus E2 (kPa) of the low-adhesive layer at -20℃ to the shear storage modulus E1 (kPa) of the high-adhesive layer at -20℃.

[0134] <Changes in Transmission Rate> For each optical adhesive sheet (optical adhesive layer) of Examples 1, 2 and Comparative Examples 1-3, the transmittance variation was investigated in the manner described below.

[0135] First, a sample for testing is prepared. Specifically, after the second release film is peeled off from the optical adhesive sheet, the exposed adhesive layer is bonded to a PET substrate (product name "T100C50", thickness 50 μm, manufactured by Mitsubishi Chemical Co., Ltd.). Next, after the first release film is peeled off from the optical adhesive sheet (adhesive layer), the exposed adhesive layer surface is bonded to the PET substrate (product name "T100C50", thickness 50 μm, manufactured by Mitsubishi Chemical Co., Ltd.). This yields a laminate consisting of a PET substrate / optical adhesive layer / PET substrate. Then, a sample for testing, with dimensions of 25 mm width × 100 mm length, is cut from this laminate.

[0136] Next, the transmittance (T1) of light at a wavelength of 550 nm was measured on the sample (first transmittance measurement). The measurement was performed using a transmittance measuring device (product name "U4100 spectrophotometer", manufactured by Hitachi High-Technologies).

[0137] Next, the sample used for the first transmittance measurement was wound along the circumference of the core in the length direction of the sample onto a 20 mm diameter core (approximately 1.6 turns). The sample wound in this manner was then stored at 23°C for 1 hour. Subsequently, the transmittance (T2) of light at a wavelength of 550 nm was measured on the stored sample using the same method as the first transmittance measurement (second transmittance measurement).

[0138] Furthermore, the rate of change of transmittance T2 relative to transmittance T1 is calculated based on the following formula. Its value is shown in Table 1.

[0139] Rate of change of transmittance (%) = [(T2-T1) / T] × 100

[0140] [Table 1] Table 1 Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Level 1 2nd floor Level 1 2nd floor Level 1 2nd floor acrylic acid polymer 2EHA 89 56 89 56 89 56 97.3 56 LA - 39 - 39 - 39 - 39 BA - - - - - - - - 4HBA 1.0 5.0 1.0 5.0 1.0 5.0 1.0 5.0 NVP 10 - 10 - 10 - 1.7 - Crosslinking agent (Nyper BMT 40SV) - 0.5 - 1.0 0.5 0.5 - 0.5 Thickness (μm) (H1)2 (H2)23 (H1)2 (H2)23 25 25 (H1)2 (H2)23 H2 / H1 11.5 11.5 - - 11.5 Maximum thickness T1 (μm) 26 26 25 25 25 Minimum thickness T 2 (μm) twenty four twenty four 25 25 25 T1-T2(μm) 2 2 0 0 0 Peel adhesion force (N / 25 mm) 11.5 - 5.2 - 20 2.4 3.9 - Shear storage modulus (kPa) at -20℃ (E1)614 (E2)78 (E1)614 (E2)78 614 73 (E1)151 (E2)78 E2 / E1 0.13 0.13 - - 0.52 Change in transmittance (%) -0.05 -0.06 0.03 -0.06 0.15

[0141] 10: Optical adhesive layer 10A: Optical adhesive layer 10B: Optical adhesive layer 11: High Adhesive Layer 11A: High Adhesive Layer 11B: High Adhesion Layer 11a: High adhesion surface 12: Low adhesive layer 12a: Page 1 12b: Page 2 21: Component 1 22: Component 2 23: Optical film H: Thickness direction L1: Peel-off membrane L2: Peel-off membrane S: Optical adhesive sheet X: Optical film with attached optical adhesive layer

Claims

1. An optical adhesive layer comprising: a low-adhesion layer having a first surface and a second surface opposite to the first surface; and a high-adhesion layer disposed on the first surface and having a high-adhesion surface opposite to the low-adhesion layer; wherein the high-adhesion surface, after being bonded to a polyimide film and subjected to 30 minutes at 23°C, exhibits a peel adhesion of 5 N / 25 mm or more to the polyimide film at a peel angle of 180° and a peel speed of 300 mm / min, and the ratio of the shear storage modulus of the low-adhesion layer at -20°C to the shear storage modulus of the high-adhesion layer at -20°C is 0.05 or more and 0.5 or less, and the ratio of the thickness of the low-adhesion layer to the thickness of the high-adhesion layer is 3 or more.

2. The optical adhesive layer of claim 1, wherein the ratio of the thickness of the low adhesive layer to the thickness of the high adhesive layer is 30 or less.

3. The optical adhesive layer of claim 1, further comprising a high adhesive layer disposed on the second surface and having a high adhesive surface on the side opposite to the low adhesive layer.

4. The optical adhesive layer of claim 3, wherein the ratio of the thickness of the low adhesive layer to the total thickness of the high adhesive layers is 1 or more.

5. The optical adhesive layer as claimed in claim 3 or 4, wherein the ratio of the thickness of the low adhesive layer to the total thickness of the high adhesive layers is 30 or less.

6. The optical adhesive layer of claim 1 has a total thickness of 5 μm to 150 μm.

7. The difference between the maximum and minimum thickness of the optical adhesive layer, as requested in item 1, is less than 3 μm.

8. The optical adhesive layer of claim 1, wherein the high adhesive layer has a shear storage modulus of less than 1000 kPa at -20°C.

9. An optical film with an optical adhesive layer, comprising: an optical film; and an optical adhesive layer, which is the optical adhesive layer as claimed in claim 1 or 2, and is attached to the optical film on the second side.

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