CN115537129A

CN115537129A - Optical adhesive layer and optical film with optical adhesive layer

Info

Publication number: CN115537129A
Application number: CN202210766204.0A
Authority: CN
Inventors: 荒井良介; 熊野隆史; 木村智之
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2021-06-30
Filing date: 2022-06-30
Publication date: 2022-12-30
Also published as: KR20230004282A; JP2023006451A; TW202311479A

Abstract

The present invention provides optical adhesive layers suitable for flexible device applications and optical films with optical adhesive layers. The optical adhesive layer (10A) of the present invention is provided with a high adhesive layer (11) and a low adhesive layer (12). The low-adhesive layer (12) has a 1 st surface (12 a) and a 2 nd surface (12 b) opposite to the 1 st surface (12 a). The high adhesive layer (11) is disposed on the 1 st surface (12 a), and has a high adhesive surface (11 a) on the side opposite to the low adhesive layer (12). The highly adhesive surface (11 a) has a peel adhesion to a polyimide film of 5N/25mm or more under predetermined conditions after 30 minutes at 23 ℃ from the time of bonding to the polyimide film. The ratio of the shear storage modulus at-20 ℃ of the low adhesive layer (12) to the shear storage modulus at-20 ℃ of the high adhesive layer (11) is less than 1.

Description

Optical adhesive layer and optical film with optical adhesive layer

Technical Field

The present invention relates to an optical adhesive layer and an optical film with the optical adhesive layer.

Background

The display panel has a laminated structure including elements such as a pixel panel, a touch panel, a polarizing plate, and a cover film. The elements in the laminated structure are bonded to each other, for example, by a transparent pressure-sensitive adhesive layer for optical use (optical pressure-sensitive adhesive layer). The optical adhesive layer is produced, for example, in the form of an optical adhesive sheet formed from an optical adhesive composition. The optical adhesive sheet is used for bonding elements to each other in a process of manufacturing a display panel. Alternatively, the optical adhesive layer is formed by coating the optical adhesive composition on the elements to be bonded in the process of manufacturing the display panel.

On the other hand, for example, for smart phone applications and flat panel terminal applications, a display panel that can be repeatedly folded (folded) has been developed. In a foldable display panel, each element in a laminated structure is made in the form of a film member that can be repeatedly bent, and such elements are joined by an optical adhesive layer. An optical adhesive layer for a flexible device such as a folding display panel is described in, for example, patent document 1 below.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2018-111754

Disclosure of Invention

Problems to be solved by the invention

Conventionally, the optical pressure-sensitive adhesive layer is easily peeled from an adherend (optical film) at a folded portion of the foldable display panel. This is because when the display panel is bent, stress such as shear stress locally acts on the optical adhesive layer at the bent portion. The occurrence of such peeling is not preferable because it causes a malfunction of the device. An optical pressure-sensitive adhesive layer for a folding display panel is required to satisfy both easy bending deformation together with an adherend when a display is bent and suppression of peeling from the adherend at a higher level.

As flexible devices, development of rollable (rollable) display panels is also proceeding. An optical pressure-sensitive adhesive layer for a rollable display panel is required to satisfy, at a very high level, both easy deformation (curl deformation) together with an adherend at the time of rolling up a display and suppression of peeling from the adherend.

The present invention provides an optical adhesive layer suitable for flexible device applications, and an optical film with an optical adhesive layer.

Means for solving the problems

The present invention [1] includes an optical adhesive layer comprising: a low adhesive layer having a 1 st surface and a 2 nd surface opposite to the 1 st surface; and a high adhesive layer disposed on the 1 st surface and having a high adhesive surface on the opposite side of the low adhesive layer, wherein the high adhesive surface has a peel adhesion of 5N/25mm or more to a polyimide film under conditions of a peel angle of 180 DEG and a peel speed of 300 mm/min after 30 minutes from the time of bonding to the polyimide film at 23 ℃, and a ratio of a shear storage modulus of the low adhesive layer at-20 ℃ to a shear storage modulus of the high adhesive layer at-20 ℃ is less than 1.

The invention [2] includes the optical adhesive layer according to [1], wherein a ratio of a thickness of the low adhesive layer to a thickness of the high adhesive layer is 1 or more.

The invention [3] includes the optical adhesive layer according to [1] or [2], wherein a ratio of a thickness of the low adhesive layer to a thickness of the high adhesive layer is 30 or less.

The invention [4] includes the optical adhesive layer according to [1], further comprising a high adhesive layer disposed on the 2 nd surface, the high adhesive layer having a high adhesive surface on the opposite side to the low adhesive layer.

The invention [5] includes the optical adhesive layer according to [4], wherein a ratio of a thickness of the low adhesive layer to a total of thicknesses of the high adhesive layers is 1 or more.

The invention [6] includes the optical adhesive layer according to [4] or [5], wherein a ratio of the thickness of the low adhesive layer to the total thickness of the high adhesive layers is 30 or less.

The invention [7] includes the optical adhesive layer according to any one of [1] to [6], which has a total thickness of 5 μm or more and 150 μm or less.

The invention [8] is an optical pressure-sensitive adhesive layer according to any one of the above [1] to [7], wherein the difference between the maximum thickness and the minimum thickness is 3 μm or less.

The invention [9] is an optical adhesive layer according to any one of the above [1] to [8], wherein the high adhesive layer has a shear storage modulus of 1000kPa or less at-20 ℃.

The present invention [10] includes an optical film with an optical adhesive layer, comprising: an optical film and an optical adhesive layer, wherein the optical adhesive layer is the optical adhesive layer according to any one of the above [1] to [3], and is bonded to the optical film through the 2 nd surface side.

ADVANTAGEOUS EFFECTS OF INVENTION

As described above, the optical adhesive layer of the present invention has the high adhesive layer having the high adhesive surface on the side opposite to the low adhesive layer, and the high adhesive surface has the peel adhesion of 5N/25mm or more under a predetermined condition. This configuration is suitable for ensuring good adhesion of the optical pressure-sensitive adhesive layer to the adherend via the high adhesion surface, and is therefore suitable for suppressing peeling of the optical pressure-sensitive adhesive layer from the adherend. In addition, in the optical adhesive layer, as described above, the ratio of the shear storage modulus at-20 ℃ of the low adhesive layer to the shear storage modulus at-20 ℃ of the high adhesive layer is less than 1. This constitution is suitable for ensuring the flexibility of the optical adhesive layer as a whole, thereby ensuring the bending deformability. When the adherend to which the pressure-sensitive adhesive layer is bonded is deformed with a large curvature (such as the above-described bending deformation and curling deformation) as the optical pressure-sensitive adhesive layer is more flexible, the optical pressure-sensitive adhesive layer is more likely to follow the deformation of the adherend and to be deformed with a large curvature. The optical adhesive layer is soft and easily deformed with a large curvature (bending deformability), and is suitable for realizing favorable repeated deformation (repeated bending deformation, curling deformation, and the like) of a flexible device using the optical adhesive layer. The optical pressure-sensitive adhesive layer having both the peeling inhibiting property and the bending deformation property described above and the optical film with the optical pressure-sensitive adhesive layer having the optical pressure-sensitive adhesive layer are suitable for use in a flexible device.

Drawings

Fig. 1 is a schematic cross-sectional view of embodiment 1 of the optical adhesive layer of the present invention.

Fig. 2 is a schematic cross-sectional view of embodiment 2 of the optical adhesive layer of the present invention.

Fig. 3A to 3C show an example of a method of using the optical pressure-sensitive adhesive layer of the present invention. Fig. 3A shows a step of bonding the optical pressure-sensitive adhesive layer to the 1 st adherend, fig. 3B shows a step of bonding the 1 st adherend and the 2 nd adherend via the optical pressure-sensitive adhesive layer, and fig. 3C shows a curing step.

FIG. 4 is a schematic cross-sectional view of one embodiment of an optical film with an optical adhesive layer of the present disclosure.

Description of the reference numerals

S optical adhesive sheet

10A, 10B optical adhesive layer

11. 11A, 11B high adhesive agent layer

11a high adhesion surface

12. Low adhesive layer

12a 1 st surface

12b side 2

H thickness direction

L1, L2 Release film

21. No. 1 component

22. The 2 nd member

X-ray optical film with optical adhesive layer

Detailed Description

The optical pressure-sensitive adhesive layer 10 (optical pressure-sensitive adhesive layer 10A) as embodiment 1 of the optical pressure-sensitive adhesive layer of the present invention has a sheet shape with a predetermined thickness as shown in fig. 1, and spreads in a direction (planar direction) orthogonal to the thickness direction H. The optical adhesive layer 10 has transparency (visible light transmittance). The optical adhesive layer 10A is a multilayer adhesive layer including a high adhesive layer 11 and a low adhesive layer 12 in this order in the thickness direction H. The high adhesive layer 11 is an adhesive layer having relatively strong surface adhesion, and the low adhesive layer 12 is an adhesive layer having relatively low surface adhesion. The low adhesive layer 12 has a 1 st surface 12a and a 2 nd surface 12b opposite to the 1 st surface 12 a. The high adhesive layer 11 is disposed on the 1 st surface 12 a. The high adhesive layer 11 has a high adhesive surface 11a on the opposite side to the low adhesive layer 12. The high adhesive surface 11a is one adhesive surface of the optical adhesive layer 10A. The 2 nd surface 12b of the low adhesive layer 12 is the other adhesive surface of the optical adhesive layer 10A. Fig. 1 exemplarily shows a state in which an optical pressure-sensitive adhesive layer 10A is produced in the form of an optical pressure-sensitive adhesive sheet S and peeling films L1 and L2 are bonded to both surfaces of the sheet.

The optical pressure-sensitive adhesive layer 10 (optical pressure-sensitive adhesive layer 10B) according to embodiment 2 of the present invention has a sheet shape with a predetermined thickness as shown in fig. 2, and spreads in a direction (planar direction) perpendicular to the thickness direction H. The optical adhesive layer 10B includes 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 including a high adhesive layer 11A, a low adhesive layer 12, and a high adhesive layer 11B in this order in the thickness direction H. The low adhesive layer 12 has a 1 st surface 12a and a 2 nd surface 12b opposite to the 1 st surface 12 a. The high adhesive layer 11A (one high adhesive layer 11) is disposed on the 1 st surface 12 a. The high adhesive layer 11A has a high adhesive surface 11A (1 st high adhesive surface) on the opposite side to the low adhesive layer 12. The high adhesive surface 11a is one adhesive surface of the optical adhesive layer 10A. The high adhesive layer 11B (another high adhesive layer 11) is disposed on the 2 nd surface 12B. The high adhesive layer 11B has a high adhesive surface 11a (2 nd high adhesive surface) on the opposite side to the low adhesive layer 12. The high adhesive surface 11a of the high adhesive layer 11B is the other adhesive surface of the optical adhesive layer 10A. The adhesive force of the high adhesive surface 11A of the high adhesive layer 11A and the adhesive force of the high adhesive surface 11B of the high adhesive layer 11B may be the same or different. Fig. 2 exemplarily shows a state in which the optical pressure-sensitive adhesive layer 10B is produced in the form of an optical pressure-sensitive adhesive sheet S and peeling films L1 and L2 are bonded to both surfaces of the sheet.

Such an optical adhesive layer 10 is a transparent adhesive layer disposed at a light-passing portion in the flexible device. As the flexible device, for example, a flexible display panel can be cited. The flexible display panel has a laminated structure including elements such as a pixel panel, a touch panel, a polarizing plate, and a cover film. Examples of the flexible display panel include a foldable display panel and a rollable display panel. The optical adhesive layer 10 is used for bonding elements included in the aforementioned laminated structure to each other, for example, in a manufacturing process of a flexible display panel.

The high-adhesion surface 11a of the optical adhesive layer 10A and the high-

adhesion surfaces

11a and 11B of the optical adhesive layer 10B each have a peel adhesion of 5N/25mm or more to a polyimide film under conditions of a peel angle of 180 ° and a peel speed of 300 mm/min after 30 minutes at 23 ℃ from the time of adhesion to the polyimide film. The optical adhesive layer 10 was attached to the polyimide film by applying a weight by reciprocating a 2kg roller 1 time in an environment of 23 ℃. The peel adhesion is preferably 7N/25mm or more, more preferably 9N/25mm or more, and even more preferably 11N/25mm or more, from the viewpoint of ensuring good adhesion to an adherend (an element contained in the laminated structure of a flexible device). The peel adhesion is, for example, 30N/25mm or less. Examples of the method for adjusting the peel adhesion on the surface of the pressure-sensitive adhesive layer include selection of the type of base polymer in the pressure-sensitive adhesive layer, adjustment of the molecular weight, and adjustment of the amount of the compound. Examples of the method for adjusting the peel adhesion of the surface of the pressure-sensitive adhesive layer include selection of the kind of components other than the base polymer in the pressure-sensitive adhesive layer and adjustment of the amount of the components to be blended. Examples of the component include a crosslinking agent, a silane coupling agent, and an oligomer.

In the optical adhesive layer 10 (optical adhesive layer 10A, optical adhesive layer 10B), the ratio (E2/E1) of the shear storage modulus (E2) at-20 ℃ of the low adhesive layer 12 to the shear storage modulus (E1) at-20 ℃ of the high adhesive layer 11 is less than 1. That is, the low adhesive layer 12 has a smaller shear storage modulus at-20 ℃ and a lower elasticity than 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 apparatus. In this measurement, the measurement mode was set to the shear mode, the measurement temperature range was set to-60 ℃ to 150 ℃, the temperature increase rate was set to 5 ℃/min, and the frequency was set to 1Hz. In particular, as described in the following description relating to the embodiments. Examples of the method for adjusting the shear storage modulus of the pressure-sensitive adhesive layer include selection of the type of the base polymer in the pressure-sensitive adhesive layer, adjustment of the molecular weight and adjustment of the amount of blending, and selection of the type of the crosslinking agent for crosslinking the base polymer and adjustment of the amount of blending. The selection of the kind of the base polymer includes the selection of the kind of the main chain in the base polymer, and the selection of the kind and the adjustment of the amount of the functional group.

As described above, the optical pressure-sensitive adhesive layer 10 has the high-adhesive-layer 11 having the high-adhesive surface 11a on the side opposite to the low-adhesive-layer 12, and the peel adhesion under the predetermined conditions of the high-adhesive surface 11a is 5N/25mm or more, preferably 7N/25mm or more, more preferably 9N/25mm or more, and further preferably 11N/25mm or more. This configuration is suitable for ensuring good adhesion of the optical pressure-sensitive adhesive layer 10 to an adherend via the high-adhesion surface 11a, and is therefore suitable for suppressing peeling of the optical pressure-sensitive adhesive layer 10 from the adherend.

In the optical adhesive layer 10, as described above, the ratio of the shear storage modulus at-20 ℃ of the low adhesive layer 12 to the shear storage modulus at-20 ℃ of the high adhesive layer 11 is less than 1, preferably 0.7 or less, more preferably 0.5 or less, still more preferably 0.3 or less, and particularly preferably 0.15 or less. This constitution is suitable for ensuring the flexibility of the optical adhesive layer 10 as a whole, thereby ensuring the bending deformability. The softer the optical pressure-sensitive adhesive layer 10, the more easily the adherend bonded with the optical pressure-sensitive adhesive layer 10 deforms with a large curvature following the deformation of the adherend. Examples of the deformation of the adherend under a large curvature include bending deformation of a foldable display and deformation (curling deformation) of a rollable display when rolled. The optical adhesive layer 10 is soft and easily deformed with a large curvature (bending deformability) and is suitable for realizing favorable repeated deformation (repeated bending deformation, curling deformation, and the like) of a flexible device using the optical adhesive layer 10.

The optical adhesive layer 10 suitable for both the peeling inhibition property and the bending deformation property as described above is suitable for the flexible device use by sharing the functions of the high adhesive layer 11 and the low adhesive layer 12.

From the viewpoint of ensuring flexibility and bendability suitable for a flexible device, the shear storage modulus of the optical adhesive layer 10 at-20 ℃ is preferably 180kPa or less, more preferably 150kPa or less, further preferably 130kPa or less, and particularly preferably 100kPa or less. From the viewpoint of ensuring the cohesive force of the optical adhesive layer 10, the shear storage modulus of the optical adhesive layer 10 at-20 ℃ is preferably 30kPa or more, more preferably 40kPa or more, still more preferably 50kPa or more, and particularly preferably 60kPa or more. By adjusting the shear storage modulus at-20 ℃ of each of the adhesive layers in the optical adhesive layer 10 and adjusting the thickness of each of the adhesive layers, the overall shear storage modulus at-20 ℃ of the optical adhesive layer 10 can be adjusted.

From the viewpoint of ensuring the above flexibility and bendability of the optical adhesive layer 10, the shear storage modulus E1 of the high adhesive layer 11 at-20 ℃ is preferably 1000kPa or less, more preferably 800kPa or less, and further preferably 700kPa or less. From the viewpoint of securing high adhesive force of the high adhesive surface 11a, the shear storage modulus E1 of the high adhesive layer 11 at-20 ℃ is preferably 100kPa or more, more preferably 200kPa or more, further preferably 300kPa or more, and particularly preferably 500kPa or more.

From the viewpoint of ensuring the above flexibility and bendability of the optical adhesive layer 10, the shear storage modulus E2 of the low adhesive layer 12 at-20 ℃ is preferably 150kPa or less, more preferably 110kPa or less, and further preferably 80kPa or less. From the viewpoint of securing the adhesive force at the 1 st face 12a and the 2 nd face 12b, the shear storage modulus E2 of the low adhesive layer 12 at-20 ℃ is preferably 10kPa or more, more preferably 20kPa or more, and further preferably 30kPa or more.

The ratio of the thickness H2 of the low adhesive layer 12 to the thickness H1 of the high adhesive layer 11 (the sum of the thicknesses of the plurality of high adhesive layers 11 when the optical adhesive layer 10 includes the plurality of high adhesive layers 11) is preferably 1 or more, more preferably 3 or more, still more preferably 6 or more, and particularly preferably 9 or more. Such a constitution is preferable for ensuring the above 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, more preferably 25 or less, and still more preferably 20 or less. Such a configuration is preferable for ensuring the rigidity of the optical pressure-sensitive adhesive layer 10 and ensuring good handleability.

The thickness of the single high adhesive layer 11 is preferably 0.1 μm or more, more preferably 0.5 μm or more, and still more preferably 1 μm or more. This configuration is preferable for ensuring the cohesive force of the high adhesive agent layer 11 and ensuring the high adhesive force. The thickness of the single high adhesive layer 11 is, for example, 10 μm or less.

The thickness of the low adhesive layer 12 is preferably 3 μm or more, more preferably 10 μm or more, and still more preferably 15 μm or more. This configuration is preferable for ensuring the cohesive force of the high adhesive agent layer 11 and ensuring the high adhesive force. The thickness of the low adhesive layer 12 is preferably 70 μm or less, more preferably 50 μm or less, and still more preferably 30 μm or less. Such a configuration is preferable for ensuring the rigidity of the optical pressure-sensitive adhesive layer 10 and ensuring good handleability.

From the viewpoint of ensuring the cohesive force and the high adhesive force, the total thickness of the optical pressure-sensitive adhesive layer 10 is preferably 5 μm or more, more preferably 10 μm or more, and still more preferably 15 μm or more. From the viewpoint of ensuring good deformability (ease of deformation), the total thickness of the optical pressure-sensitive adhesive layer 10 is preferably 150 μm or less, more preferably 100 μm or less, and still more preferably 50 μm or less.

In the optical adhesive layer 10, the difference between the maximum thickness and the minimum thickness is preferably 3 μm or less, more preferably 2 μm or less, and further preferably 1 μm or less. Such a constitution is preferable for suppressing stress concentration in an adherend in contact with the optical pressure-sensitive adhesive layer 10 when the adherend is deformed. In addition, this configuration relating to the difference in thickness is also preferable from the viewpoint of visibility of a flexible device (optical device) having the optical adhesive layer 10 in a laminated structure.

The change in the transmittance of the optical adhesive layer 10 after 1 hour from the winding of the optical adhesive layer 10 around a core having a cross-sectional diameter of 20mm is preferably 5% or less, more preferably 4% or less, and still more preferably 3% or less. This constitution is suitable for ensuring transparency of the optical adhesive layer for use as a flexible device. The change in transmittance of the optical pressure-sensitive adhesive layer 10 can be measured specifically by the method described below in connection with examples.

The haze of the optical adhesive layer 10 is preferably 3% or less, more preferably 2% or less, and more preferably 1% or less. The haze of the optical adhesive layer 10 can be measured using a haze meter in accordance with JIS K7136 (2000). Examples of the haze meter include "NDH2000" manufactured by Nippon Denshoku industries and "HM-150" manufactured by Nippon Denshoku industries research institute.

The total light transmittance of the optical adhesive layer 10 is preferably 60% or more, more preferably 80% or more, and further 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 K7375 (2008).

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

The base polymer is an adhesive component that exhibits adhesiveness in the adhesive layers (the high adhesive layer 11 and the low adhesive layer 12). Examples of the base polymer include acrylic polymers, silicone polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyvinyl ether polymers, vinyl acetate/vinyl chloride copolymers, modified polyolefin polymers, epoxy polymers, fluoropolymers, and rubber polymers. The base polymer may be used alone, or two or more thereof may be used in combination. From the viewpoint of ensuring good transparency and adhesiveness of the pressure-sensitive adhesive layer, an acrylic polymer is preferably used as the base polymer.

The acrylic polymer is a copolymer containing a monomer component of an alkyl (meth) acrylate in a ratio of 50% by mass or more. "(meth) acrylic acid" means acrylic acid and/or methacrylic acid.

As the alkyl (meth) acrylate, an alkyl (meth) acrylate in which the carbon number of the alkyl group is 1 to 20 can be suitably used. The alkyl (meth) acrylate may have a linear or branched alkyl group, or may have a cyclic alkyl group such as an alicyclic alkyl group.

Examples of the alkyl (meth) acrylate having a linear or branched alkyl group include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, neopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate (i.e., lauryl (meth) acrylate), isotridecyl (meth) acrylate, tetradecyl (meth) acrylate, isotetradecyl (meth) acrylate, pentadecyl (meth) acrylate, cetyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, isostearyl (meth) acrylate, and nonadecyl (meth) acrylate.

Examples of the alkyl (meth) acrylate having an alicyclic alkyl group include cycloalkyl (meth) acrylates, (meth) acrylates having a bicyclic aliphatic hydrocarbon ring, and (meth) acrylates having a tricyclic or higher aliphatic hydrocarbon ring. Examples of the cycloalkyl (meth) acrylate include cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, and cyclooctyl (meth) acrylate. Examples of the (meth) acrylate having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth) acrylate. Examples of the (meth) acrylate having an aliphatic hydrocarbon ring having at least three rings include dicyclopentyl (meth) acrylate, dicyclopentyloxyethyl (meth) acrylate, tricyclopentyl (meth) acrylate, 1-adamantyl (meth) acrylate, 2-methyl-2-adamantyl (meth) acrylate, and 2-ethyl-2-adamantyl (meth) acrylate.

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

From the viewpoint of suitably exhibiting basic characteristics such as adhesiveness in the pressure-sensitive adhesive layer, the ratio of the alkyl (meth) acrylate in the monomer component is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass or more. This ratio is, for example, 99 mass% or less.

The monomer component may contain a copolymerizable monomer copolymerizable with the alkyl (meth) acrylate. Examples of the copolymerizable monomer include monomers having a polar group. Examples of the polar group-containing monomer include a monomer having a nitrogen atom-containing ring, a hydroxyl group-containing monomer, and a carboxyl group-containing monomer. The polar group-containing monomer contributes to modification of the acrylic polymer, such as introduction of a crosslinking point into the acrylic polymer and securing of cohesive force of the acrylic polymer.

Examples of the monomer having a ring containing a nitrogen atom include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N- (meth) acryloyl-2-pyrrolidone, N- (meth) acryloylpiperidine, N- (meth) acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1, 3-oxazin-2-one, N-vinyl-3, 5-morpholinodione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, and N-vinylisothiazole. As the monomer having a nitrogen atom-containing ring, N-vinyl-2-pyrrolidone is preferably used.

From the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive layer and the adhesive strength of the pressure-sensitive adhesive layer to an adherend, the ratio of the monomer having a nitrogen atom-containing ring in the monomer component is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and still 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 (in relation to the compatibility of various additive components in the pressure-sensitive adhesive layer and the acrylic polymer), the ratio is preferably 30% by mass or less, and more preferably 20% by mass or less.

Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, and (4-hydroxymethylcyclohexyl) methyl (meth) acrylate. As the hydroxyl group-containing monomer, 4-hydroxybutyl (meth) acrylate is preferably used, and 4-hydroxybutyl acrylate is more preferably used.

The ratio of the hydroxyl group-containing monomer in the monomer component is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 0.8% by mass or more, from the viewpoint of introducing a crosslinked structure into the acrylic polymer and securing the cohesive force of the pressure-sensitive adhesive layer. From the viewpoint of adjusting the polarity of the acrylic polymer (in relation to the compatibility between various additive components and the acrylic polymer in the pressure-sensitive adhesive layer), the ratio is preferably 20% by mass or less, and more preferably 10% by mass or less.

Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

The ratio of the carboxyl group-containing monomer in the monomer component is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more, from the viewpoints of introducing a crosslinked structure into the acrylic polymer, ensuring the cohesive force of the pressure-sensitive adhesive layer, and ensuring the adhesive force of the pressure-sensitive adhesive layer to an adherend. From the viewpoints of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend by an acid, the ratio is preferably 30% by mass or less, more preferably 20% by mass or less.

In order to prevent corrosion of metal elements such as electrodes in flexible devices due to acid components, the binder layer is preferably small in acid content. When the pressure-sensitive adhesive layer is used for bonding a polarizing plate, the pressure-sensitive adhesive layer preferably has a small acid content in order to suppress polyene formation of the polyvinyl alcohol-based polarizing material due to the acid component. In such an acid-free pressure-sensitive adhesive layer, the content of the organic acid monomer (e.g., (meth) acrylic acid and the carboxyl group-containing monomer) is preferably 100ppm or less, more preferably 70ppm or less, and still more preferably 50ppm or less. The organic acid monomer content of the adhesive layer was determined by the following method: the adhesive layer was immersed in pure water, and the acid monomer extracted into water by heating at 100 ℃ for 45 minutes was quantified by ion chromatography.

From the viewpoint of no acid, the base polymer in the pressure-sensitive adhesive layer preferably contains substantially no organic acid monomer as a monomer component. From the viewpoint of no acid, the ratio of the organic acid monomer in the monomer component is preferably 0.5% by mass or less, more preferably 0.1% by mass or less, further preferably 0.05% by mass, and ideally 0% by mass.

The monomer component may contain other copolymerizable monomers. Examples of the other copolymerizable monomer include an acid anhydride monomer, a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, an epoxy group-containing monomer, a cyano group-containing monomer, an alkoxy group-containing monomer, and an aromatic vinyl compound. These other copolymerizable monomers may be used alone or in combination of two or more.

The base polymer preferably has a crosslinked structure. Examples of the method for introducing a crosslinked structure into a base polymer include: a method of compounding a base polymer having a functional group capable of reacting with a crosslinking agent and a crosslinking agent in an adhesive composition to react the base polymer and the crosslinking agent in an adhesive layer (method 1); and a method (method 2) in which a polyfunctional monomer is contained in a monomer component forming the base polymer, and the base polymer having a branched structure (crosslinked structure) introduced into a polymer chain is formed by polymerization of the monomer component. These methods may be used in combination.

Examples of the crosslinking agent used in the method 1 include compounds that react with functional groups (hydroxyl groups, carboxyl groups, and the like) contained in the base polymer. Examples of such a crosslinking agent include an isocyanate crosslinking agent, a peroxide crosslinking agent, an epoxy crosslinking agent, an oxazoline crosslinking agent, an aziridine crosslinking agent, a carbodiimide crosslinking agent, and a metal chelate crosslinking agent. The crosslinking agent may be used alone, or two or more of them may be used in combination. As the crosslinking agent, an isocyanate crosslinking agent, a peroxide crosslinking agent, and an epoxy crosslinking agent are preferably used in view of high reactivity with hydroxyl groups and carboxyl groups in the base polymer and easiness of introduction of a crosslinked structure.

Examples of the isocyanate crosslinking agent include toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate. Further, as the isocyanate crosslinking agent, derivatives of these isocyanates can be also mentioned. Examples of the isocyanate derivative include isocyanurate modifications and polyol modifications. Examples of commercially available isocyanate crosslinking agents include Coronate L (trimethylolpropane adduct of toluene diisocyanate, manufactured by tokyo co., ltd.), coronate HL (trimethylolpropane adduct of hexamethylene diisocyanate, manufactured by tokyo co., ltd.), coronate HX (isocyanurate of hexamethylene diisocyanate, manufactured by tokyo co., ltd.), and Takenate D110N (trimethylolpropane adduct of xylylene diisocyanate, manufactured by mitsui chemical).

Examples of the peroxide crosslinking agent include dibenzoyl peroxide, di (2-ethylhexyl) peroxydicarbonate, di (4-tert-butylcyclohexyl) peroxydicarbonate, di-sec-butyl peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-hexyl peroxypivalate, and tert-butyl peroxypivalate.

Examples of the epoxy crosslinking agent include bisphenol a, epichlorohydrin type epoxy resins, ethylene glycol glycidyl ether, polyethylene glycol diglycidyl ether, glycerol triglycidyl ether, 1, 6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidyl amine, N' -tetraglycidyl m-xylylenediamine, and 1, 3-bis (N, N-diglycidylaminomethyl) cyclohexane.

The isocyanate crosslinking agent (particularly, a difunctional isocyanate crosslinking agent) and the peroxide crosslinking agent are preferable from the viewpoint of ensuring appropriate flexibility (bending property due to this) of the adhesive layer. An isocyanate crosslinking agent (in particular, a trifunctional isocyanate crosslinking agent) is preferable from the viewpoint of ensuring the durability of the adhesive layer. In the base polymer, the difunctional isocyanate crosslinker and the peroxide crosslinker will form softer two-dimensional crosslinks, while the trifunctional isocyanate crosslinker will form stronger three-dimensional crosslinks. From the viewpoint of achieving both durability and flexibility of the adhesive layer, it is preferable to use a trifunctional isocyanate crosslinking agent in combination with a peroxide crosslinking agent and/or a difunctional isocyanate crosslinking agent.

From the viewpoint of ensuring the cohesive force of the pressure-sensitive adhesive layer, the blending amount of the crosslinking agent is, for example, 0.01 part by mass or more, preferably 0.05 part by mass or more, and more preferably 0.07 part by mass or more, relative to 100 parts by mass of the base polymer. In the pressure-sensitive adhesive layer, the amount of the crosslinking agent to be blended 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, relative to 100 parts by mass of the base polymer, from the viewpoint of ensuring good tackiness.

In the method 2, the monomer components (including the polyfunctional monomer for introducing the crosslinking structure and other monomers) may be polymerized at once or in multiple stages. In the multistage polymerization method, first, a monofunctional monomer for forming a base polymer is polymerized (prepolymerized), thereby preparing a prepolymer composition containing a partial polymer (a mixture of a polymer having a low degree of polymerization and an unreacted monomer). Next, after the polyfunctional monomer is added to the prepolymer composition, a partial polymer and the polyfunctional monomer are polymerized (main polymerization).

Examples of the polyfunctional monomer include polyfunctional (meth) acrylates having 2 or more ethylenically unsaturated double bonds in 1 molecule. The polyfunctional monomer is preferably a polyfunctional acrylate from the viewpoint of being capable of introducing a crosslinked structure by active energy ray polymerization (photopolymerization).

Examples of the polyfunctional (meth) acrylate include difunctional (meth) acrylates, trifunctional (meth) acrylates, and tetrafunctional or higher polyfunctional (meth) acrylates.

Examples of the difunctional (meth) acrylate include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol dimethacrylate, 1, 6-hexanediol di (meth) acrylate, 1, 9-nonanediol di (meth) acrylate, glycerol di (meth) acrylate, neopentyl glycol di (meth) acrylate, stearic acid-modified pentaerythritol di (meth) acrylate, dicyclopentadienyl diacrylate, di (meth) acryloyl isocyanurate, and alkylene oxide-modified bisphenol di (meth) acrylate.

Examples of the trifunctional (meth) acrylate include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, and tris (acryloyloxyethyl) isocyanurate.

Examples of the tetrafunctional or higher polyfunctional (meth) acrylate include ditrimethylolpropane tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol monohydroxypenta (meth) acrylate, alkyl-modified dipentaerythritol pentaacrylate, and dipentaerythritol hexa (meth) acrylate.

The molecular weight of the polyfunctional monomer is preferably 1500 or less, more preferably 1000 or less. The polyfunctional monomer preferably has a functional group equivalent (g/eq) of 50 or more, more preferably 70 or more, and still more preferably 80 or more. The functional group equivalent is preferably 500 or less, more preferably 300 or less, and still more preferably 200 or less. These configurations are preferable from the viewpoint of appropriately adjusting viscoelasticity (for example, storage modulus G' and loss tangent tan δ) by introducing a crosslinked structure into the base polymer.

The acrylic polymer can be formed by polymerizing the monomer components. Examples of the polymerization method include solution polymerization, active energy ray polymerization (e.g., UV polymerization), bulk polymerization, and emulsion polymerization. From the viewpoints of transparency, water resistance and cost of the adhesive layer, solution polymerization and UV polymerization are preferable. As the solvent for the solution polymerization, for example, ethyl acetate and toluene can be used. As the polymerization initiator, for example, a thermal polymerization initiator and a photopolymerization initiator can be used. The amount of the polymerization initiator used is, for example, 0.05 parts by mass or more and 1 part by mass or less per 100 parts by mass of the monomer component.

Examples of the thermal polymerization initiator include an azo polymerization initiator and a peroxide polymerization initiator. Examples of the azo polymerization initiator include 2,2' -azobisisobutyronitrile, 2' -azobis-2-methylbutyronitrile, dimethyl 2,2' -azobis (2-methylpropionate), 4' -azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2' -azobis (2-amidinopropane) dihydrochloride, 2' -azobis [2- (5-methyl-2-imidazolin-2-yl) propane ] dihydrochloride, 2' -azobis (2-methylpropionamidine) disulfate, and 2,2' -azobis (N, N ' -dimethyleneisobutylamidine) dihydrochloride. Examples of the peroxide polymerization initiator include dibenzoyl peroxide, tert-butyl peroxymaleate, and lauroyl peroxide.

Examples of the photopolymerization initiator include benzoin ether type photopolymerization initiators, acetophenone type photopolymerization initiators, α -ketol type photopolymerization initiators, aromatic sulfonyl chloride type photopolymerization initiators, photoactive oxime type photopolymerization initiators, benzoin type photopolymerization initiators, benzil type photopolymerization initiators, benzophenone type photopolymerization initiators, ketal type photopolymerization initiators, thioxanthone type photopolymerization initiators, and acylphosphine oxide type photopolymerization initiators.

In the polymerization, a chain transfer agent and/or a polymerization inhibitor (polymerization retarder) may be used for the purpose of molecular weight adjustment or the like. Examples of the chain transfer agent include α -thioglycerol, lauryl mercaptan, glycidyl mercaptan, thioglycolic acid (Mercaptoacetic acid), 2-mercaptoethanol, thioglycolic acid (Thioglycolic acid), 2-ethylhexyl thioglycolate, 2, 3-dimercapto-1-propanol, and α -methylstyrene dimer.

The molecular weight of the base polymer can be adjusted by adjusting the kind and/or amount of the polymerization initiator. For example, in radical polymerization, the higher the amount of the polymerization initiator, the higher the radical concentration of the reaction system, and therefore the higher the density of the reaction initiation point, the smaller the molecular weight of the base polymer formed. On the other hand, the smaller the amount of the polymerization initiator, the lower the density at the reaction initiation point, and therefore the more easily the polymer chain is stretched, and the larger the molecular weight of the base polymer to be formed tends to be.

From the viewpoint of securing the cohesive force of the pressure-sensitive adhesive layer, the weight average molecular weight of the base polymer is preferably 10 ten thousand or more, more preferably 30 ten thousand or more, and further preferably 50 ten thousand or more. The weight average molecular weight is preferably 500 ten thousand or less, more preferably 300 ten thousand or less, and further preferably 200 ten thousand or less. The weight average molecular weight of the base polymer was measured by Gel Permeation Chromatography (GPC) and calculated in terms of polystyrene.

The glass transition temperature (Tg) of the base polymer is preferably 0 ℃ or lower, more preferably-10 ℃ or lower, and still more preferably-20 ℃ or lower. The glass transition temperature is, for example, at least-80 ℃.

As the glass transition temperature (Tg) of the base polymer, a glass transition temperature (theoretical value) obtained based on the following Fox formula can be used. The Fox formula is a relation between the glass transition temperature Tg of a polymer and the glass transition temperature Tgi of a homopolymer of a monomer constituting the polymer. In the following Fox formula, tg represents the glass transition temperature (. Degree. C.) of the polymer, wi represents the weight fraction of the monomer i constituting the polymer, and Tgi represents the glass transition temperature (. Degree. C.) of a homopolymer formed from the monomer i. As regards the glass transition temperature of the homopolymer, literature values can be used. The glass transition temperatures of the various homopolymers are listed, for example, in "Polymer Handbook" (4 th edition, john Wiley & Sons, inc., 1999) and "synthetic resin for coating of New Polymer library 7" (North John Co., ltd., polymer journal Ltd., 1995). On the other hand, the glass transition temperature of a homopolymer of a monomer can also be determined by a method specifically described in Japanese patent laid-open No. 2007-51271.

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

As a method for adjusting the peel adhesion and/or the shear storage modulus of each pressure-sensitive adhesive layer, for example, adjustment of the molecular weight, adjustment of the glass transition temperature, and adjustment of the crosslinking degree in the base polymer in the pressure-sensitive adhesive layer are effective. The larger the molecular weight of the base polymer, the higher the elastic modulus of the pressure-sensitive adhesive layer tends to be, and the higher the adhesive strength tends to be. The smaller the glass transition temperature of the base polymer, the lower the elastic modulus of the pressure-sensitive adhesive layer tends to be, and the lower the adhesion tends to be. The higher the degree of crosslinking of the base polymer, the higher the elastic modulus of the adhesive layer tends to be. The adhesive strength of the adhesive layer varies depending on the degree of crosslinking so as to have a maximum value at a predetermined degree of crosslinking in the base polymer. Specifically, the following is described. The higher the crosslinking degree of the base polymer, the higher the cohesive force inside the pressure-sensitive adhesive layer and the higher the adhesive force of the pressure-sensitive adhesive layer, to a certain degree of crosslinking. If the crosslinking degree exceeds the above-mentioned certain degree, the higher the crosslinking degree of the base polymer is, the more highly elastic the pressure-sensitive adhesive layer tends to be, and the lower the adhesion thereof tends to be.

The monomer component forming the base polymer contained in the high adhesive agent layer 11 preferably contains an alkyl acrylate having an alkyl group with 6 to 15 carbon atoms, a monomer having a nitrogen atom-containing ring, and a hydroxyl group-containing monomer, and more preferably contains 2-ethylhexyl acrylate (2 EHA), N-vinyl-2-pyrrolidone (NVP), and 4-hydroxybutyl acrylate (4 HBA).

The monomer component forming the base polymer contained in the low adhesive layer 12 preferably contains an alkyl acrylate having an alkyl group with 6 to 15 carbon atoms and a hydroxyl group-containing monomer, and more preferably contains 2-ethylhexyl acrylate (2 EHA), lauryl Acrylate (LA), and 4-hydroxybutyl acrylate (4 HBA).

The adhesive composition may contain one or two or more oligomers on the basis of the base polymer. When an acrylic polymer is used as the base polymer, an acrylic oligomer is preferably used as the oligomer. The acrylic oligomer is a copolymer containing a monomer component of an alkyl (meth) acrylate in a ratio of 50 mass% or more, and has a weight average molecular weight of 1000 to 30000, for example.

The glass transition temperature of the acrylic oligomer is preferably 60 ℃ or higher, more preferably 80 ℃ or higher, further preferably 100 ℃ or higher, and particularly preferably 110 ℃ or higher. The glass transition temperature of the acrylic oligomer is, for example, 200 ℃ or lower, preferably 180 ℃ or lower, and more preferably 160 ℃ or lower. The adhesive strength of the pressure-sensitive adhesive layer, particularly the adhesive strength at high temperatures, is improved by using a combination of a low Tg acrylic polymer (base polymer) having a crosslinked structure introduced therein and a high Tg acrylic oligomer. The glass transition temperature of the acrylic oligomer is calculated by the above-mentioned Fox formula.

The acrylic oligomer having a glass transition temperature of 60 ℃ or higher is preferably a polymer containing monomer components of an alkyl (meth) acrylate having a chain alkyl group (a chain alkyl (meth) acrylate) and an alkyl (meth) acrylate having an alicyclic alkyl group (an alicyclic alkyl (meth) acrylate). Specific examples of the alkyl (meth) acrylate include the alkyl (meth) acrylate mentioned above as a monomer component of the acrylic polymer.

The (meth) acrylic acid chain alkyl ester is preferably methyl methacrylate because of its high glass transition temperature and excellent compatibility with the base polymer. As the alicyclic alkyl (meth) acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferable. That is, the acrylic oligomer is preferably a polymer containing 1 or more monomer components selected from the group consisting of dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate.

The proportion of the alicyclic alkyl (meth) acrylate in the monomer component of the acrylic oligomer is preferably 10% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass or more.

The ratio is preferably 90% by mass or less, more preferably 80% by mass or less, and still more preferably 70% by mass or less. The ratio of the (meth) acrylic acid chain alkyl ester in the monomer component of the acrylic oligomer is preferably 90% by mass or less, more preferably 80% by mass or less, and still more preferably 70% by mass or less. The ratio is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass or more.

The weight average molecular weight of the acrylic oligomer is preferably 1000 or more, more preferably 1500 or more, and further preferably 2000 or more. The molecular weight is preferably 30000 or less, more preferably 10000 or less, and further preferably 8000 or less. The molecular weight range of the acrylic oligomer is preferable for securing the adhesive strength and adhesive holding power of the adhesive layer.

The acrylic oligomer is obtained by polymerizing a monomer component of the acrylic oligomer. Examples of the polymerization method include solution polymerization, active energy ray polymerization (e.g., UV polymerization), bulk polymerization, and emulsion polymerization. In the polymerization of the acrylic oligomer, a polymerization initiator may be used, or a chain transfer agent may be used for the purpose of adjusting the molecular weight.

In order to sufficiently improve the adhesive strength of the pressure-sensitive adhesive layer, the content of the acrylic oligomer in the pressure-sensitive adhesive layer is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, and still more preferably 1 part by mass or more, per 100 parts by mass of the base polymer. On the other hand, from the viewpoint of ensuring the transparency of the pressure-sensitive adhesive layer, the content of the acrylic oligomer in the pressure-sensitive adhesive layer is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and still more preferably 3 parts by mass or less, relative to 100 parts by mass of the base polymer. When the content of the acrylic oligomer in the pressure-sensitive adhesive layer is too large, the compatibility of the acrylic oligomer is lowered, and thus the haze tends to be increased and the transparency tends to be lowered.

The adhesive composition may contain a silane coupling agent. The content of the silane coupling agent in the adhesive composition is preferably 0.1 part by mass or more, and more preferably 0.2 part by mass or more, per 100 parts by mass of the base polymer. The content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less.

The adhesive composition may contain other components as necessary. Examples of the other components include a tackifier, a plasticizer, a softener, an antioxidant, a filler, a colorant, an ultraviolet absorber, an antioxidant, a surfactant, and an antistatic agent.

As a method for forming the optical adhesive layer 10 having a multilayer structure, a dry lamination method (dry lamination method), a wet lamination method, and a wet lamination method can be cited. In the dry lamination method, for example, a plurality of adhesive layers (the high adhesive layer 11 and the low adhesive layer 12) can be formed by applying and drying an adhesive composition to a release film, and then the plurality of adhesive layers are bonded to form a multilayer adhesive layer. In the wet lamination dry method, for example, a multi-layer adhesive layer may be formed by applying an adhesive composition to each adhesive layer on a release film and forming the dried adhesive layer. In the wet-on-wet method, for example, a plurality of pressure-sensitive adhesive compositions may be applied to a release film in multiple stages to form a multilayer coating film, and the multilayer coating film may be dried to form a multilayer pressure-sensitive adhesive layer.

When the 2-layer optical adhesive layer 10A is produced by a wet-on-wet method, it can be produced, for example, as follows (production method 1). First, a 1 st adhesive composition for forming the high adhesive layer 11 and a 2 nd adhesive composition for forming the low adhesive layer 12 are prepared. Next, the release-treated surface of the 1 st release film whose surface was subjected to the release treatment was coated with the 1 st adhesive composition (lower position) and the 2 nd adhesive composition (upper position). Specifically, a 1 st adhesive composition is applied to a 1 st release film to form a 1 st coating film, and a 2 nd adhesive composition is applied to the 1 st coating film to form a 2 nd coating film (formation of a multilayer coating film). Next, the multilayer coating film on the 1 st release film was dried by heating to form a multilayer pressure-sensitive adhesive layer. Next, the release-treated surface of the 2 nd release film, which was subjected to a release treatment on one side, was bonded to the multilayer pressure-sensitive adhesive layer on the 1 st release film. Then, if necessary, a curing treatment is performed to perform a crosslinking reaction in the pressure-sensitive adhesive layer. As described above, the optical pressure-sensitive adhesive layer 10A as the optical pressure-sensitive adhesive sheet S whose pressure-sensitive adhesive surface is covered with the release films L1 and L2 can be produced. The release films L1 and L2 are peeled from the optical adhesive sheet S as necessary when the optical adhesive sheet S is used.

When the 3-layer optical adhesive layer 10B is produced by a wet-on-wet method, it can be produced, for example, as follows (production method 2). First, the 1 st adhesive composition for forming the high adhesive layer 11A, the 2 nd adhesive composition for forming the low adhesive layer 12, and the 3 rd adhesive composition for forming the high adhesive layer 11B are prepared. Next, the release-treated surface of the 1 st release film whose surface was subjected to release treatment was coated with the 1 st adhesive composition (lower position), the 2 nd adhesive composition (middle position), and the 3 rd adhesive composition (upper position). Specifically, a 1 st pressure-sensitive adhesive composition is applied to a 1 st release film to form a 1 st coating film, a 2 nd pressure-sensitive adhesive composition is applied to the 1 st coating film to form a 2 nd coating film, and a 3 rd pressure-sensitive adhesive composition is applied to the 2 nd coating film to form a 3 rd coating film (formation of a multilayer coating film). Subsequently, the multilayer coating film on the 1 st release film was dried by heating to form a multilayer pressure-sensitive adhesive layer. Next, the release-treated surface of the 2 nd release film, which was subjected to a release treatment on one side, was bonded to the multilayer pressure-sensitive adhesive layer on the 1 st release film. Then, if necessary, a curing treatment is performed to perform a crosslinking reaction in the pressure-sensitive adhesive layer. As described above, the optical pressure-sensitive adhesive layer 10B as the optical pressure-sensitive adhesive sheet S whose pressure-sensitive adhesive surface is protected by the release films L1 and L2 can be produced. The release films L1 and L2 are peeled from the optical adhesive sheet S as necessary when the optical adhesive sheet S is used.

In the above-described production method, examples of the release film include a flexible plastic film. Examples of the plastic film include a polyethylene terephthalate film, a polyethylene film, a polypropylene film, and a polyester film. The thickness of the release film is, for example, 3 μm or more and 200 μm or less.

In the above-mentioned production method, examples of the method for coating the adhesive composition include roll coating, roll-to-roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, blade coating, air knife coating, curtain coating, lip coating, and die coating. The drying temperature of the coating film is, for example, 50 ℃ to 200 ℃. The drying time is, for example, 5 seconds to 20 minutes.

Fig. 3A to 3C show an example of a method of using the optical adhesive layer 10 (the multilayer structure of the optical adhesive layer 10 is not shown in fig. 3A to 3C).

In this method, first, as shown in fig. 3A, the optical pressure-sensitive adhesive layer 10 is bonded to one surface of the 1 st member 21 (adherend) in the thickness direction H. The 1 st member 21 is, for example, one element of a laminated 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 2 nd member 22 described later). In this step, the optical pressure-sensitive adhesive layer 10 for bonding to another member is provided on the 1 st member 21.

Next, as shown in fig. 3B, one surface side in the thickness direction H of the 1 st member 21 and the other surface side in the thickness direction H of the 2 nd member 22 are joined via the optical adhesive layer 10 on the 1 st member 21. The 2 nd member 22 is another element in the laminated structure of the flexible display panel, for example.

Next, as shown in fig. 3C, the optical adhesive layer 10 between the 1 st member 21 and the 2 nd member 22 is cured. By curing, a crosslinking reaction of the base polymer advances in the optical adhesive layer 10, and the joining force between the 1 st member 21 and the 2 nd member 22 is improved. The curing temperature is, for example, 20 ℃ to 160 ℃. The aging time is, for example, 1 minute to 21 days. When the autoclave treatment (heat and pressure treatment) is performed as the aging treatment, the temperature is, for example, 30 to 80 ℃, the pressure is, for example, 0.1 to 0.8MPa, and the treatment time is, for example, 15 minutes or more.

The optical adhesive layer 10 used as described above in the manufacturing process of the flexible device has the high adhesive surface 11a having a peel adhesion of 5N/25mm or more under a predetermined condition, and the ratio of the shear storage modulus of the low adhesive layer 12 at-20 ℃ to the shear storage modulus of the high adhesive layer 11 at-20 ℃ is less than 1, as described above. As described above, the optical adhesive layer 10 is suitable for both bending deformation and peeling inhibition, and is therefore suitable for flexible device applications.

Fig. 4 is a schematic cross-sectional view of an optical film X with an optical adhesive layer according to an embodiment of the optical film with an optical adhesive layer of the present invention. The optical film X with an optical pressure-sensitive adhesive layer includes an optical film 23 and the optical pressure-sensitive adhesive layer 10A in this order in the thickness direction H.

The optical film 23 has flexibility. The optical film 23 is a functional film or a base film incorporated in the laminated structure of the flexible display panel in this embodiment. Examples of the functional film include a polarizer film and a retardation film. Examples of the polarizer film include a hydrophilic polymer film subjected to a dyeing treatment with a dichroic substance and a subsequent stretching treatment. Examples of the dichroic substance include iodine and dichroic dyes. Examples of the hydrophilic polymer film include a polyvinyl alcohol (PVA) film, a partially formalized PVA film, and a partially saponified film of an ethylene-vinyl acetate copolymer. Examples of the retardation film include a λ/2 wavelength film, a λ/4 wavelength film, and a viewing angle compensating film. The thickness of the optical film 23 is, for example, 5 μm or more and 500 μm or less.

As described above, the optical adhesive layer 10A is a multilayer adhesive layer including the high adhesive layer 11 and the low adhesive layer 12 in this order in the thickness direction H. The optical adhesive layer 10A adheres the optical film 23 to the second surface 12b side of the low adhesive layer 12. In the present embodiment, the optical pressure-sensitive adhesive layer 10A is a multilayer pressure-sensitive adhesive layer formed on the optical film 23.

The optical film X with an optical adhesive layer can be manufactured by: after the 1 st adhesive composition for forming the high adhesive layer 11 and the 2 nd adhesive composition for forming the low adhesive layer 12 are prepared, they are manufactured by a dry-on-dry method, a wet-on-dry method, or a wet-on-wet method.

In the dry lamination method, first, the low adhesive layer 12 is formed by coating and drying the 2 nd adhesive composition on the optical film 23. On the other hand, the high adhesive layer 11 is formed by coating and drying the 1 st adhesive composition on the release film. Then, the high adhesive layer 11 is bonded to the low adhesive layer 12 on the optical film 23. For example, in this manner, the optical adhesive layer 10A can be formed on the optical film 23.

In the wet lamination method, first, the low adhesive layer 12 is formed by coating and drying the 2 nd adhesive composition on the optical film 23. Next, the high adhesive layer 11 is formed by coating and drying the 1 st adhesive composition on the low adhesive layer 12. For example, in this manner, the optical adhesive layer 10A can be formed on the optical film 23.

In the wet-on-wet method, first, the 2 nd adhesive composition (lower position) and the 1 st adhesive composition (upper position) are applied to the optical film 23. Specifically, the 2 nd pressure-sensitive adhesive composition is applied to the optical film 23 to form a coating film, and the 1 st pressure-sensitive adhesive composition is applied to the coating film to form a 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 manner, the optical adhesive layer 10A can be formed on the optical film 23.

When the low-viscosity adhesive layer 12 is formed as described above by applying and drying the 2 nd adhesive composition to the optical film 23 as an adherend, the low-viscosity adhesive layer 12 can apply a higher anchoring force to the surface of the optical film 23 than when the low-viscosity adhesive 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 an optical pressure-sensitive adhesive layer is suitable for ensuring good adhesion of the 2 nd surface 12b of the low pressure-sensitive adhesive layer 12 to the optical film 23.

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

In addition, as described above, the optical adhesive layer 10A has the high adhesive surface 11a having a peel adhesion of 5N/25mm or more under a predetermined condition, and the ratio of the shear storage modulus at-20 ℃ of the low adhesive layer 12 to the shear storage modulus at-20 ℃ of the high adhesive layer 11 is less than 1.

Such an optical adhesive layer 10A is suitable for having both bending deformability and peeling inhibition property by the high adhesive surface 11a as described above. Therefore, the optical film X with an optical pressure-sensitive adhesive layer provided with the optical pressure-sensitive adhesive layer 10A is suitable for having both bending deformation properties and peeling inhibition properties.

The optical film X with an optical adhesive layer may be a composite optical film in which the optical adhesive layer 10 and an additional optical film are alternately laminated on the opposite side of the optical adhesive layer 10A with respect to the optical film 23. Examples of the additional optical film include a pixel panel (such as an OLED panel), a touch panel, a polarizing plate, and a cover film, which are arranged in a predetermined order. The optical adhesive layer 10 may be the optical adhesive layer 10A or the optical adhesive layer 10B. In the optical film X with an optical pressure-sensitive adhesive layer as such a composite optical film, all pressure-sensitive adhesive layers to be bonded between elements are the optical pressure-sensitive adhesive layers 10 (10A, 10B). The composite optical film thus obtained may also be a folded display panel.

Examples

The present invention will be specifically explained below with reference to examples. However, the present invention is not limited to the examples. In addition, specific numerical values of the blending amount (content), the physical property value, the parameter, and the like described below may be substituted for the upper limit (numerical value defined as "lower" or "less than") or the lower limit (numerical value defined as "upper" or "more than") of the blending amount (content), the physical property value, the parameter, and the like described in the above-mentioned "specific embodiment" corresponding thereto.

Production of Polymer P1

In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas introduction tube, a mixture containing 89 parts by mass of 2-ethylhexyl acrylate (2 EHA), 10 parts by mass of N-vinyl-2-pyrrolidone (NVP), 1 part by mass of 4-hydroxybutyl acrylate (4 HBA), 0.1 part by mass of 2,2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator and ethyl acetate and toluene as a solvent (solid content concentration 50% by mass, ratio of toluene in the solvent 5% by mass) was stirred at 55 ℃ for 6 hours under a nitrogen atmosphere (polymerization reaction). Thus, a solution containing the acrylic polymer (polymer P1) was obtained. Then, ethyl acetate was added to the solution to adjust the polymer concentration of the solution to 30 mass%. Thereby, the 1 st polymer solution containing the acrylic polymer (polymer P1) was obtained. The weight average molecular weight of the acrylic polymer in the 1 st polymer solution was 219 ten thousand.

Production of Polymer P2

In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas introduction tube, a mixture (solid content concentration 33 mass%) containing 56 parts by mass of 2-ethylhexyl acrylate (2 EHA), 39 parts by mass of Lauryl Acrylate (LA), 5 parts by mass of 4-hydroxybutyl acrylate (4 HBA), 0.1 part by mass of 2,2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator and ethyl acetate as a solvent was stirred at 58 ℃ for 5 hours under a nitrogen atmosphere (polymerization reaction). Thus, a solution containing the acrylic polymer (polymer P2) was obtained. Then, ethyl acetate was added to the solution to adjust the polymer concentration of the solution to 30 mass%. Thereby, a 2 nd polymer solution containing an acrylic polymer (polymer P2) was obtained. The weight average molecular weight of the acrylic polymer in the 2 nd polymer solution was 83 ten thousand.

Preparation of Polymer P3

In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas introduction tube, a mixture (solid content concentration 50 mass%, ratio of toluene in solvent 5 mass%) of 2-ethylhexyl acrylate (2 EHA) 97.3 mass parts, N-vinyl-2-pyrrolidone (NVP) 1.7 mass parts, 4-hydroxybutyl acrylate (4 HBA) 1.0 mass part, 2' -Azobisisobutyronitrile (AIBN) 0.1 mass part as a thermal polymerization initiator and ethyl acetate and toluene as a solvent was stirred at 55 ℃ under nitrogen atmosphere for 6 hours (polymerization reaction). Thus, a solution containing the acrylic polymer (polymer P3) was obtained. Then, ethyl acetate was added to the solution to adjust the polymer concentration of the solution to 30 mass%. Thus, a 3 rd polymer solution containing an acrylic polymer (polymer P3) was obtained. The weight average molecular weight of the acrylic polymer in the 3 rd polymer solution was 200 ten thousand.

[ example 1]

Preparation of adhesive composition No. 1

Ethyl acetate was added to the 1 st polymer solution to adjust the solid content concentration to 10 mass% and obtain the 1 st adhesive composition.

Preparation of adhesive composition (2)

To the 2 nd polymer solution, 0.5 part by mass of a crosslinking agent (trade name "NYPER BMT 40SV", dibenzoyl peroxide, manufactured by japan grease co., ltd.) was added and mixed with respect to 100 parts by mass of the acrylic polymer (polymer P2) in the polymer solution, and then ethyl acetate was added to adjust the solid content concentration to 23% by mass, to obtain a 2 nd adhesive composition.

Formation of optical adhesive layer

The 1 st adhesive composition (lower position) and the 2 nd adhesive composition (upper position) were applied by wet-on-wet method to the release-treated surface of the 1 st release film (trade name "JT-50Wa", polyester film, thickness 50 μm, manufactured by ritto electrical corporation) having one surface subjected to silicone release treatment. Specifically, the 1 st release film was coated with the 1 st pressure-sensitive adhesive composition to form a coating film (thickness after drying 2 μm), and the 2 nd pressure-sensitive adhesive composition was coated on the coating film to form a coating film (thickness after drying 23 μm) (formation of a multilayer coating film). Subsequently, the multilayer coating film on the 1 st release film was dried by heating at 155 ℃ for 2 minutes to form a multilayer pressure-sensitive adhesive layer having a thickness of 25 μm. Next, a release-treated surface of a 2 nd release film (product name: MRQ25T100J, polyester film, thickness: 25 μm, manufactured by Mitsubishi chemical) having a silicone release treatment on one side was bonded to the multi-layer pressure-sensitive adhesive layer on the 1 st release film. Then, the cured product was cured at 50 ℃ for 48 hours to allow the crosslinking reaction in the adhesive layer to proceed. The optical adhesive sheet (optical adhesive layer) of example 1 was produced in the manner described above. The optical adhesive sheet of example 1 had a 2-layer structure of a 1 st layer (thickness 2 μm) as a high adhesive layer formed from the 1 st adhesive composition and a 2 nd layer (thickness 23 μm) as a low adhesive layer formed from the 2 nd adhesive composition. The monomer composition and the pressure-sensitive adhesive layer composition of the polymer of the optical pressure-sensitive adhesive sheet of example 1 are shown in table 1 (the same applies to examples and comparative examples described below) with respect to the parts by mass per unit.

[ example 2]

An optical adhesive sheet of example 2 was produced in the same manner as the optical adhesive sheet of example 1, except for the following. In the preparation of the 2 nd adhesive composition, the compounding amount of the crosslinking agent (trade name "NYPER BMT 40 SV") was set to 1.0 part by mass instead of 0.5 part by mass.

The optical adhesive sheet of example 2 had a 2-layer structure of a 1 st layer (thickness 2 μm) as a high adhesive layer formed from the 1 st adhesive composition and a 2 nd layer (thickness 23 μm) as a low adhesive layer formed from the 2 nd adhesive composition. In the optical adhesive sheet of example 1 and the optical adhesive sheet of example 2, a difference was generated in the degree of crosslinking of the polymer components in the 1 st adhesive layer and the 2 nd adhesive layer. As a result, a difference in peel adhesion force F described later was generated between the optical pressure-sensitive adhesive sheets of examples 1 and 2. This is because, in the above wet-on-wet method in the production process of the optical adhesive sheet, a part of the crosslinking agent diffuses from the 2 nd adhesive composition (upper position) coated on the 1 st adhesive composition (lower position) to the 1 st adhesive composition.

[ comparative example 1]

To the 1 st polymer solution, 0.5 parts by mass of a crosslinking agent (trade name "NYPER BMT 40SV", dibenzoyl peroxide, manufactured by japan grease co., ltd.) was added and mixed with respect to 100 parts by mass of the acrylic polymer (polymer P1) in the polymer solution, and then ethyl acetate was added to adjust the solid content concentration to 15% by mass, to obtain a 3 rd adhesive composition. Next, a coating film (thickness after drying: 25 μm) was formed by applying the 3 rd pressure-sensitive adhesive composition to the release-treated surface of the 1 st release film (trade name "JT-50Wa", polyester film, thickness 50 μm, manufactured by Nindon electric Co., ltd.) having silicone release treatment on one surface thereof. Subsequently, the coating film on the 1 st release film was dried by heating at 155 ℃ for 2 minutes to form a pressure-sensitive adhesive layer having a thickness of 25 μm. Subsequently, a release-treated surface of a 2 nd release film (trade name "MRQ25T100J", polyester film, thickness 25 μm, manufactured by Mitsubishi chemical corporation) having a silicone release treatment on one side was bonded to the pressure-sensitive adhesive layer on the 1 st release film. Then, the mixture was cured at 50 ℃ for 48 hours to allow the crosslinking reaction in the adhesive layer to proceed. The optical adhesive sheet (optical adhesive layer having a single-layer structure) of comparative example 1 was produced in the same manner as described above.

[ comparative example 2]

An optical adhesive sheet (single-layer optical adhesive layer) of comparative example 2 was produced in the same manner as in comparative example 1, except that the 2 nd adhesive composition was used instead of the 3 rd adhesive composition in forming the optical adhesive layer.

[ comparative example 3]

Ethyl acetate was added to the 3 rd polymer solution to adjust the solid content concentration to 10 mass%, thereby obtaining a 4 th adhesive composition. An optical adhesive sheet of comparative example 3 was produced in the same manner as the optical adhesive sheet of example 1, except that the 4 th adhesive composition was used instead of the 1 st adhesive composition in forming the optical adhesive layer. The optical adhesive sheet of comparative example 3 had a 2-layer structure of the 1 st layer (thickness 2 μm) formed of the 4 th adhesive composition as a high adhesive layer and the 2 nd layer (thickness 23 μm) formed of the 2 nd adhesive composition as a low adhesive layer.

Thickness of adhesive layer

The thickness of each of the optical adhesive sheets of examples 1 and 2 and comparative examples 1 to 3 was examined. Specifically, first, the adhesive sheet (short side 25mm × long side 100 mm) was cut out from the optical adhesive sheet. Next, the thickness of each of the 5 measurement points in the adhesive sheet was measured with a dial gauge. The 5 measurement points are 5 points obtained by equally dividing the widthwise center of the adhesive sheet along the longitudinal direction 6. The maximum thickness T of the thickness measured values at 5 measured points ₁ (mum) and minimum thickness T ₂ (. Mu.m) are shown in Table 1. In addition, the difference (T) between the maximum thickness and the minimum thickness ₁ -T ₂ ) Also shown in table 1.

Peel adhesion force

The peel adhesion of each of the optical adhesive sheets of examples 1 and 2 and comparative examples 1 to 3 was examined by a peel test.

First, a sample for measurement was prepared for each optical adhesive sheet. In the production of the measurement samples of the optical adhesive sheets of examples 1 and 2, first, the 2 nd release film was peeled off from the optical adhesive sheet, and a polyimide substrate (product name "Upilex25RN" having a thickness of 25 μm, manufactured by yuken corporation) having a plasma-treated exposed surface was bonded to the exposed surface, thereby obtaining a laminate. Then, a test piece (width 25 mm. Times. Length 100 mm) was cut out from the laminate (polyimide substrate/adhesive layer/No. 1 release film). Then, the 1 st release film was peeled from the pressure-sensitive adhesive layer of the test piece, and a polyimide film (trade name "Upilex50S", thickness 50 μm, product of yu seiko co., ltd.) was bonded to the exposed surface (the 1 st layer side surface in the multilayer pressure-sensitive adhesive layer) exposed by the peeling. In this bonding, a test piece was pressed against a polyimide film by 1-time reciprocating a 2kg hand roller in an environment of 23 ℃. As described above, measurement samples of the optical adhesive sheets of examples 1 and 2 and comparative example 3 were prepared. The samples for measurement of the optical adhesive sheets of comparative examples 1 and 2 were prepared in the same manner as the samples for measurement in examples 1 and 2 and comparative example 3, except that a polyimide substrate (trade name "Upilex25RN", thickness 25 μm, product of yu ken co., ltd.) which had not been subjected to plasma treatment was used instead of the above-mentioned polyimide substrate having been subjected to plasma treatment on the surface.

Next, the measurement sample was allowed to stand at room temperature for 30 minutes, and then a peel test was performed to peel the test piece from the polyimide film in the measurement sample, and the peel strength was measured. In the measurement samples of examples 1 and 2 and comparative example 3, the peel strength of the surface of the 1 st layer from the polyimide film surface was measured. In this measurement, a tensile tester (trade name "Autograph AG-50NX plus", manufactured by Shimadzu corporation) was used. In this measurement, the measurement temperature was set to 25 ℃, the peel angle of the test piece from the polyimide film was set to 180 °, the tensile speed of the test piece was set to 300 mm/min, and the peel length was set to 50mm. The average value of the peel strengths measured is shown in Table 1 as peel adhesion force F (N/25 mm). The peel adhesion force F of the adhesive layer of the multilayer structure (1 st layer as a high adhesive layer/2 nd layer as a low adhesive layer) is the adhesion force of the exposed surface of the 1 st layer.

Modulus of shear storage

For each of the optical adhesive sheets (optical adhesive layers) of examples 1 and 2 and comparative examples 1 to 3, the shear storage modulus was measured as follows.

First, a measurement sample is prepared. In the preparation of the measurement samples of comparative examples 1 and 2, a plurality of adhesive layer sheets cut out from an optical adhesive sheet were bonded to prepare an adhesive sheet having a thickness of about 1mm, and then the sheet was punched out to obtain cylindrical pellets (diameter 9 mm) as a measurement sample. The measurement samples of examples 1 and 2 and comparative example 3 were prepared in the same manner as the measurement samples of comparative examples 1 and 2 except that an optical adhesive sheet was prepared for each adhesive layer (high adhesive layer, low adhesive layer) and then used. An optical adhesive sheet having a high adhesive layer (layer 1) in example 1 was produced in the same manner as the optical adhesive sheet having a multilayer structure in example 1 except that the adhesive composition 2 was not applied to the adhesive composition 1 on the release film 1 (as a result, a low adhesive layer was not formed). An optical adhesive sheet having a low adhesive layer (layer 2) in example 1 was produced in the same manner as the optical adhesive sheet having a multilayer structure in example 1, except that the adhesive composition 1 was not applied to the release film 1 (as a result, a high adhesive layer was not formed). An optical adhesive sheet having a high adhesive layer (layer 1) in example 2 was produced in the same manner as the optical adhesive sheet having a multilayer structure in example 2, except that the adhesive composition 2 was not applied to the adhesive composition 1 on the release film 1 (as a result, a low adhesive layer was not formed). An optical adhesive sheet having a low adhesive layer (layer 2) in example 2 was produced in the same manner as the optical adhesive sheet having a multilayer structure in example 2, except that the adhesive composition 1 was not applied to the release film 1 (as a result, a high adhesive layer was not formed).

Then, the sample for measurement was fixed to a jig of a parallel plate having a diameter of 8mm using a dynamic viscoelasticity measuring apparatus (trade name "ARES-G2", manufactured by TA Instruments Co., ltd.) and then subjected to dynamic viscoelasticity measurement. In this measurement, the measurement mode was set to the shear mode, the measurement temperature range was-60 ℃ to 150 ℃, the temperature rise rate was 5 ℃/min, and the frequency was 1Hz. According to the measurement results, the shear storage modulus (kPa) at-20 ℃ was read. The results are shown in table 1. Also shown in table 1 is the ratio of the shear storage modulus E2 (kPa) at-20 ℃ of the low adhesive layer relative to the shear storage modulus E1 (kPa) at-20 ℃ of the high adhesive layer.

Change in transmittance

For each of the optical adhesive sheets (optical adhesive layers) of examples 1 and 2 and comparative examples 1 to 3, the change in transmittance was examined as follows.

First, a sample for measurement is prepared. Specifically, after the 2 nd release film was peeled from the optical adhesive sheet, the adhesive layer side exposed therefrom was bonded to a PET substrate (trade name "T100C50", thickness 50 μm, manufactured by mitsubishi chemical corporation). Subsequently, the 1 st release film was peeled off from the optical adhesive sheet (adhesive layer), and the exposed surface of the adhesive layer was bonded to a PET substrate (trade name "T100C50", thickness 50 μm, manufactured by Mitsubishi chemical corporation). In this way, a laminate having a laminated structure of PET substrate/optical adhesive layer/PET substrate was obtained. Then, a measurement sample having a width of 25mm × a length of 100mm was cut out from the laminate.

Next, the transmittance (T1) of light having a wavelength of 550nm was measured with respect to the measurement sample (No. 1 transmittance measurement). For the measurement, a transmittance measuring apparatus (trade name "spectrophotometer model U4100", manufactured by Hitachi High-Tech Corporation) was used.

Next, the measurement sample subjected to the 1 st transmittance measurement was wound around a core having a diameter of 20mm such that the longitudinal direction of the sample was along the circumferential direction of the core (about 1.6 circles around the core). Next, the sample wound around the core was stored at 23 ℃ for 1 hour. Then, the transmittance (T2) of light having a wavelength of 550nm was measured with respect to the stored measurement sample in the same manner as in the 1 st transmittance measurement (2 nd transmittance measurement).

Then, the change rate of the transmittance T2 with respect to the transmittance T1 was obtained based on the following formula. The values are shown in table 1.

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

[ Table 1]

Claims

1. An optical adhesive layer comprising:

a low adhesive layer having a 1 st surface and a 2 nd surface opposite to the 1 st surface; and

a high adhesive layer disposed on the 1 st surface and having a high adhesive surface on the opposite side of the low adhesive layer,

the high adhesive surface has a peel adhesion of 5N/25mm or more to the polyimide film under the conditions of a peel angle of 180 DEG and a peel speed of 300 mm/min after 30 minutes at 23 ℃ from the time of bonding to the polyimide film,

the ratio of the shear storage modulus at-20 ℃ of the low adhesive layer to the shear storage modulus at-20 ℃ of the high adhesive layer is less than 1.

2. An optical adhesive layer according to claim 1, wherein a ratio of the thickness of the low adhesive layer to the thickness of the high adhesive layer is 1 or more.

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

4. The optical adhesive layer of claim 1, further having a high adhesive layer disposed on the 2 nd side, the high adhesive layer having a high adhesive side on an opposite side from the low adhesive layer.

5. An optical adhesive layer according to claim 4, wherein a ratio of the thickness of the low adhesive layer to the sum of the thicknesses of the high adhesive layers is 1 or more.

6. An optical adhesive layer according to claim 4 or 5, wherein a ratio of the thickness of the low adhesive layer to the sum of the thicknesses of the high adhesive layers is 30 or less.

7. The optical adhesive layer according to claim 1, which has a total thickness of 5 μ ι η or more and 150 μ ι η or less.

8. The optical adhesive layer according to claim 1, having a difference between the maximum thickness and the minimum thickness of 3 μm or less.

9. An optical adhesive layer according to claim 1, wherein the high adhesive layer has a shear storage modulus at-20 ℃ of 1000kPa or less.

10. An optical film with an optical adhesive layer, comprising:

an optical film; and

an optical adhesive layer according to any one of claims 1 to 3, which is attached to the optical film via the 2 nd surface side.