JP2024073939A - Optical laminate and image display device - Google Patents

Abstract

To provide an optical laminate with improved reworkability.SOLUTION: Provided is an optical laminate in which a first optical film, a first adhesive sheet, a second optical film, and a second adhesive sheet are laminated in the stated order. When the adhesion between the first adhesive sheet and the second optical film at 23°C is defined as F (23°C), and, when the second adhesive sheet and no-alkali glass are bonded together and the initial adhesivity between the second adhesive sheet and the no-alkali glass at 23°C is defined as G0 (23°C), the optical laminate satisfies G0(23°C)/F(23°C)≤1.0.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical laminate and an image display device.

In recent years, image display devices such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices and inorganic EL display devices) have rapidly become popular. These various image display devices usually have a laminated structure of an image forming layer such as a liquid crystal layer or an EL light emitting layer, and an optical laminate including an optical film and an adhesive sheet. The adhesive sheet is mainly used for bonding between films included in the optical laminate, or for bonding between the image forming layer and the optical laminate. Examples of optical films are a polarizing plate, a retardation film, and a polarizing plate with a retardation film that is an integrated combination of a polarizing plate and a retardation film.

Patent document 1 describes a method for bonding an adhesive layer to a resin film, which is characterized in that the surfaces of the resin film and the adhesive layer to be bonded are subjected to a surface activation treatment before bonding.

JP 2005-213314 A

The image display device has a configuration in which, for example, an optical laminate and an image forming layer are bonded together via an adhesive sheet of the optical laminate. In addition, the optical laminate has an interlayer adhesive sheet arranged, for example, between a retardation film and a polarizing film together with this adhesive sheet. In the manufacture of such an image display device, a task called rework may be required in which the optical laminate attached to the adherend is peeled off from the adherend. When peeling the optical laminate from the adherend, it is possible to peel off the entire optical laminate from the adherend by peeling off a part of the end of the optical laminate from the adherend to form a peeled part, and by grasping and pulling this peeled part, the entire optical laminate is peeled off from the adherend. Note that this peeled part is the starting part of the peeling of the entire optical laminate, that is, it is a trigger or clue for peeling, so it may be simply referred to as the "trigger" hereinafter.

The present invention aims to provide an optical laminate with improved reworkability.

The present invention relates to
An optical laminate in which a first optical film, a first adhesive sheet, a second optical film, and a second adhesive sheet are laminated in this order,
The adhesion strength between the first pressure-sensitive adhesive sheet and the second optical film at 23° C. is defined as F(23° C.),
The present invention provides an optical laminate, which satisfies the following formula ( ₁ ), when the initial adhesive strength between the second adhesive sheet and the non-alkali glass at 23°C when the second adhesive sheet is bonded to the non-alkali glass is defined as G0 (23°C).
_G0 (23°C)/F(23°C)≦1.0 (1)

Furthermore, the present invention provides a method for producing a
The present invention provides an image display device comprising the above optical laminate and an image forming layer.

The present invention provides an optical laminate with improved reworkability.

FIG. 1 is a cross-sectional view that illustrates an example of the optical laminate of the present embodiment. FIG. 2 is a schematic cross-sectional view showing another example of the optical laminate. FIG. 3 is a schematic cross-sectional view showing an example of a substrate-attached optical laminate. FIG. 4 is a schematic cross-sectional view showing another example of a substrate-attached optical laminate. FIG. 5 is a schematic cross-sectional view showing another example of a substrate-attached optical laminate. FIG. 6 is a schematic cross-sectional view showing another example of a substrate-attached optical laminate. FIG. 7 is a schematic cross-sectional view showing an example of an image display device. FIG. 8 is a cross-sectional view illustrating a schematic diagram of another example of an image display device. FIG. 9 is a schematic cross-sectional view showing an example of an image display device in which a trigger is fabricated.

The optical laminate according to the first aspect of the present invention is
An optical laminate in which a first optical film, a first adhesive sheet, a second optical film, and a second adhesive sheet are laminated in this order,
The adhesion strength between the first pressure-sensitive adhesive sheet and the second optical film at 23° C. is defined as F(23° C.),
When the initial adhesive strength between the second adhesive sheet and the non-alkali glass at 23° C. when the second adhesive sheet is attached to the non-alkali glass is defined as G ₀ (23° C.), the following formula (1) is satisfied.
_G0 (23°C)/F(23°C)≦1.0 (1)

In the second aspect of the present invention, for example, in the optical laminate according to the first aspect, a surface modification treatment is performed on the surface of the first adhesive sheet on which the second optical film is laminated.

In the third aspect of the present invention, for example, in the optical laminate according to the second aspect, the surface modification treatment is a corona treatment.

In a fourth aspect of the present invention, for example, in an optical laminate according to any one of the first to third aspects, at least a portion of the end of the second adhesive sheet is located inside the side surface of the second optical film.

In a fifth aspect of the present invention, for example, in the optical laminate according to the fourth aspect, when observed from a direction perpendicular to the lamination direction of the optical laminate, the end of the second adhesive sheet has a curved surface that is curved so as to be convex inward.

In the sixth aspect of the present invention, for example, in the optical laminate according to the fourth aspect, the maximum distance L between the surface of the end of the second adhesive sheet and the side surface of the second optical film in a direction perpendicular to the lamination direction of the optical laminate is 2 μm to 100 μm.

In a seventh aspect of the present invention, for example, in the optical laminate according to any one of the first to sixth aspects, the second pressure-sensitive adhesive sheet has a thickness _T2 of 8 μm or more.

In an eighth aspect of the present invention, for example, in the optical laminate according to any one of the first to seventh aspects, the thickness _T2 of the second pressure-sensitive adhesive sheet and the thickness _T1 of the first pressure-sensitive adhesive sheet satisfy _T2 / _T1 ≧1.1.

In a ninth aspect of the present invention, for example in the optical laminate according to any one of the first to eighth aspects, the storage modulus G _A '(23°C) of the first pressure-sensitive adhesive sheet at 23°C and the storage modulus G _B '(23°C) of the second pressure-sensitive adhesive sheet at 23°C satisfy G _A '(23°C)/G _B '(23°C) ≧ 1.1.

In a tenth aspect of the present invention, for example, in an optical laminate according to any one of the first to ninth aspects, when the second adhesive sheet is bonded to alkali-free glass and left at 23°C for two weeks, the adhesive strength _G2 (23°C) at 23°C satisfies _G2 (23°C)/ _G0 (23°C)≦1.5.

An image display device according to an eleventh aspect of the present invention comprises:
The optical laminate according to any one of the first to tenth aspects and an image forming layer are included.

Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the embodiments shown below.

The optical laminate according to this embodiment has a first optical film, a first adhesive sheet, a second optical film, and a second adhesive sheet laminated in this order. The adhesion between the first adhesive sheet and the second optical film at 23°C is defined as F (23°C). The initial adhesion between the second adhesive sheet and the non-alkali glass at 23°C when the second adhesive sheet is attached to the non-alkali glass is defined as G ₀ (23°C). In this case, the optical laminate satisfies the following formula (1).
_G0 (23°C)/F(23°C)≦1.0 (1)

Figure 1 is a cross-sectional view showing a schematic example of an optical laminate of this embodiment. The optical laminate 10A includes a first optical film 1, a first adhesive sheet 2, a second optical film 3, and a second adhesive sheet 4. The optical laminate 10A has a structure in which the first optical film 1, the first adhesive sheet 2, the second optical film 3, and the second adhesive sheet 4 are laminated in this order.

The first optical film 1 is in contact with the first adhesive sheet 2. The first optical film 1 is disposed in contact with one of the main surfaces 2a of the first adhesive sheet 2. In FIG. 1, the first optical film 1 is in contact with the entire one of the main surfaces 2a of the first adhesive sheet. However, the first optical film 1 may be in contact with only a portion of the one of the main surfaces 2a of the first adhesive sheet 2. In this specification, "main surface" means the surface of the film or layer having the widest area.

The first adhesive sheet 2 is formed on the second optical film 3. The first adhesive sheet 2 is formed on one main surface 3a of the second optical film 3. In FIG. 1, the first adhesive sheet 2 is formed on the entire one main surface 3a of the second optical film 3. However, the first adhesive sheet 2 may be formed on only a portion of one main surface 3a of the second optical film 3.

The second adhesive sheet 4 is formed in contact with the second optical film 3. In detail, the second adhesive sheet 4 is formed on the main surface 3b of the second optical film 3 opposite the main surface 3a on which the first adhesive sheet 2 is formed. In FIG. 1, the second adhesive sheet 4 is formed on the entire one main surface 3b of the second optical film 3. However, the second adhesive sheet 4 may be formed on only a portion of the one main surface 3b of the second optical film 3.

In this embodiment, the value calculated by formula (1) may be 0.90 or less, 0.80 or less, 0.75 or less, 0.60 or less, 0.57 or less, 0.50 or less, 0.45 or less, 0.40 or less, 0.35 or less, or even 0.30 or less. The lower limit of the value calculated by formula (1) is, for example, 0.10.

(First adhesive sheet and second adhesive sheet)
(First adhesive sheet)
The adhesion force F (23°C) may be, for example, 5.0N/25mm or more, 6.0N/25mm or more, 7.0N/25mm or more, 8.0N/25mm or more, 10.0N/25mm or more, 14.0N/25mm or more, 15.0N/25mm or more, or even 20.0N/25mm or more. The upper limit of the adhesion force F (23°C) is, for example, 30.0N/25mm. The method for measuring the adhesion force F (23°C) is described in the Examples section.

The first adhesive sheet 2 has principal surfaces 2a and 2b facing each other. The principal surface 2a faces the first optical film 1. The principal surface 2a is the surface on which the first optical film 1 of the first adhesive sheet 2 is laminated. The principal surface 2b faces the second optical film 3. The principal surface 2b is the surface on which the second optical film 3 of the first adhesive sheet 2 is laminated. The principal surfaces 2a and 2b may be subjected to a surface modification treatment. By subjecting the principal surface 2b to a surface modification treatment, the above-mentioned adhesion force F can be further improved. The surface modification treatment may be applied to at least a part of the principal surfaces 2a and 2b of the first adhesive sheet 2. The surface modification treatment may be applied only to the ends of the principal surfaces 2a and 2b of the first adhesive sheet 2, or may be applied to the entire principal surfaces 2a and 2b. Examples of the surface modification treatment include corona treatment, plasma treatment, excimer treatment, and frame treatment. It is preferable that the principal surfaces 2a and 2b are subjected to a corona treatment as a surface modification treatment.

The condition of the corona treatment for the main surface 2b is, for example, 0.5 to 100 kJ/ ^m2 , expressed in terms of the discharge amount. The discharge amount may be 1 kJ/ ^m2 or more, 3 kJ/ ^m2 or more, 7 kJ/ ^m2 or more, or even 9 kJ/ ^m2 or more. The upper limit of the discharge amount may be 70 kJ/ ^m2 , 50 kJ/ ^m2 , 30 kJ/ ^m2 , 20 kJ/ ^m2 , or even 15 kJ/ ^m2 . If the discharge amount is too high, a fragile layer may be generated by decomposition of the organic matter on the main surface 2b of the first adhesive sheet 2, and the adhesive strength may decrease. On the other hand, if the discharge amount is too low, the surface modification effect may not be obtained and the adhesive strength may not increase.

The adhesion force at 23°C when the surface of the first adhesive sheet 2 on which the second optical film 3 is formed is subjected to a surface modification treatment is defined as adhesion force _F1 (23°C). The adhesion force _F1 (23°C) is, for example, 5.0 N/25 mm or more, 7.0 N/25 mm or more, 10.0 N/25 mm or more, 14.0 N/25 mm or more, 15.0 N/25 mm or more, 16.0 N/25 mm or more, 17.0 N/25 mm or more, or even 20.0 N/25 mm or more. The upper limit of the adhesion force _F1 (23°C) is, for example, 30.0 N/25 mm.

The adhesion force at 23°C when the surface of the first adhesive sheet 2 on which the second optical film 3 is formed is not subjected to a surface modification treatment is defined as adhesion force F ₀ (23°C). The adhesion force F ₀ (23°C) is, for example, 5.0 N/25 mm or more, and may be 6.0 N/25 mm or more, 7.0 N/25 mm or more, 8.0 N/25 mm or more, 9.0 N/25 mm or more, 9.5 N/25 mm or more, or even 10.0 N/25 mm or more. The upper limit of the adhesion force F ₀ (23°C) is, for example, 20.0 N/25 mm.

The storage modulus G _A '(23°C) of the first adhesive sheet 2 at 23°C may be 0.01 MPa or more, 0.05 MPa or more, 0.08 MPa or more, 0.09 MPa or more, 0.10 MPa or more, 0.12 MPa or more, 0.15 MPa or more, 0.20 MPa or more, 0.5 MPa or more, or even 0.9 MPa or more. The upper limit of the storage modulus G _A '(23°C) of the first adhesive sheet 2 at 23°C is, for example, 3.0 MPa. By increasing the storage modulus G _A '(23°C) of the first adhesive sheet 2 to the above level, it becomes more difficult to insert the blade of the rework jig into the first adhesive sheet 2. That is, by increasing the storage modulus G _A '(23°C) of the first adhesive sheet 2 to the upper level, it becomes easier to insert the blade of the rework jig between the second adhesive sheet 4 and the adherend. As a result, the success rate of the trigger creation can be further improved.

The thickness _T1 of the first adhesive sheet 2 is, for example, 2 μm to 40 μm. The thickness _T1 of the first adhesive sheet 2 may be 3 μm to 30 μm, 4 μm to 20 μm, 5 μm to 15 μm, or 8 μm to 15 μm. When the thickness _T1 of the first adhesive sheet 2 is this thin, the blade of the rework jig is less likely to be inserted into the first adhesive sheet 2. That is, the blade of the rework jig is more likely to be inserted between the second adhesive sheet 4 and the adherend. As a result, the success rate of the trigger creation can be further improved.

(Second adhesive sheet)
The initial adhesive strength G ₀ (23° C.) may be, for example, 8.0 N/25 mm or less, 7.0 N/25 mm or less, 6.0 N/25 mm or less, 5.5 N/25 mm or less, or even 5.0 N/25 mm or less. The lower limit of the initial adhesive strength G ₀ (23° C.) is, for example, 1.0 N/25 mm. In measuring the initial adhesive strength G ₀ (23° C.), first, the second adhesive sheet 4 of the optical laminate 10A and the alkali-free glass are bonded together at 23° C., and then the second adhesive sheet 4 and the alkali-free glass are placed in an autoclave at 50° C. and 5 atm (absolute pressure) for 15 minutes to homogenize the bonding between the second adhesive sheet 4 and the alkali-free glass. This produces an optical laminate with glass. Next, the optical laminate with glass is taken out of the autoclave. The initial adhesive strength G ₀ (23° C.) is the adhesive strength between the second adhesive sheet 4 and the non-alkali glass at 23° C., measured when the glass-attached optical laminate is removed from the autoclave and allowed to stand for 20 minutes at 23° C. The non-alkali glass is, for example, plate-shaped and has a thickness of 0.5 mm or more.

The storage modulus G _B '(23°C) of the second pressure-sensitive adhesive sheet 4 at 23°C may be 0.01 MPa or more, 0.05 MPa or more, 0.08 MPa or more, 0.09 MPa or more, 0.10 MPa or more, 0.12 MPa or more, or even 0.15 MPa or more. The upper limit of the storage modulus G _B '(23°C) of the second pressure-sensitive adhesive sheet 4 at 23°C is, for example, 0.5 MPa.

G _A '(23°C) and G _B '(23°C) may satisfy G _A '(23°C)/G _B '(23°C)≧1.1. This can further improve the reworkability. G _A '(23°C)/G _B '(23°C) may be 2.0 or more, 3.0 or more, 4.0 or more, 5.0 or more, or 5.2 or more. The upper limit of G _A '(23°C)/G _B '(23°C) is, for example, 8.0.

The adhesive strength G ₂ (23° C.) means the adhesive strength between the second adhesive sheet 4 of the optical laminate 10A and the alkali-free glass at 23° C. after two weeks have passed since the second adhesive sheet 4 of the optical laminate 10A was bonded to the alkali-free glass. The adhesive strength G ₂ (23° C.) is, for example, 10.0 N/25 mm or less, and may be 8.0 N/25 mm or less, 7.0 N/25 mm or less, 6.0 N/25 mm or less, 5.8 N/25 mm or less, or even 5.2 N/25 mm or less. The lower limit of the adhesive strength G ₂ (23° C.) is, for example, 1.0 N/25 mm. In measuring the adhesive strength G ₂ (23° C.), the second adhesive sheet 4 of the optical laminate 10A is first bonded to the alkali-free glass at 23° C., and then the bond between the second adhesive sheet 4 and the alkali-free glass is homogenized by placing the second adhesive sheet 4 and the alkali-free glass in an autoclave at 50° C. and 5 atm (absolute pressure) for 15 minutes. This results in the production of an optical laminate with glass. After the production of the optical laminate with glass, it is left to stand under conditions of 23° C. and 55% RH. The adhesive strength G ₂ (23° C.) is the adhesive strength between the second adhesive sheet 4 and the non-alkali glass at 23° C., measured after two weeks in this state.

G ₀ (23° C.) and G ₂ (23° C.) may satisfy G ₂ (23° C.)/G ₀ (23° C.)≦1.5. After the optical laminate and the adherend are bonded together via the pressure-sensitive adhesive sheet, the optical laminate may be peeled off from the adherend after being left at room temperature for several days to about two weeks. The pressure-sensitive adhesive sheet generally has a property that the adhesive strength gradually increases after being bonded to the adherend. The optical laminate 10A according to this embodiment satisfies, for example, G ₂ (23° C.)/G ₀ (23° C.)≦1.5. This makes it possible to further improve the reworkability even when the optical laminate is attached to an adherend such as an image forming layer for a long period of time. G ₂ (23° C.)/G ₀ (23° C.) may be 1.3 or less, or may be 1.2 or less. The lower limit of G ₂ (23° C.)/G ₀ (23° C.) is, for example, 1.0.

The initial adhesive strength between the second adhesive sheet 4 and the alkali-free glass at 80°C is defined as G ₀ (80°C). The initial adhesive strength G ₀ (80°C) may be, for example, 0.1 N/25 mm or more, 0.5 N/25 mm or more, 1.0 N/25 mm or more, 1.5 N/25 mm or more, 2.0 N/25 mm or more, 3.0 N/25 mm or more, 4.0 N/25 mm or more, 4.5 N/25 mm or more, or even 5.0 N/25 mm or more. The upper limit of the initial adhesive strength G ₀ (80°C) may be 7.0 N/25 mm, 6.5 N/25 mm, or 6.0 N/25 mm. In the measurement of the initial adhesive strength G ₀ (80°C), the second adhesive sheet 4 of the optical laminate 10A and the alkali-free glass are first bonded together at 23°C, and then the second adhesive sheet 4 and the alkali-free glass are placed in an autoclave at 50°C and 5 atm (absolute pressure) for 15 minutes to homogenize the bonding between them. This produces an optical laminate with glass. Next, the optical laminate with glass is taken out of the autoclave and left to stand at 23°C for 20 minutes, and then immediately heated. The heating is performed by placing the optical laminate with glass on a hot plate set at 80°C for 15 seconds. The initial adhesive strength G ₀ (80°C) is the adhesive strength between the second adhesive sheet 4 and the alkali-free glass at 80°C, measured immediately after heating the optical laminate with glass by the above method.

The adhesive strength G ₂ (80° C.) means the adhesive strength between the second adhesive sheet 4 of the optical laminate 10A and the alkali-free glass at 80° C. when two weeks have passed since the second adhesive sheet 4 of the optical laminate 10A was bonded to the alkali-free glass. The adhesive strength G ₂ (80° C.) is, for example, 10.0 N/25 mm or less, and may be 8.0 N/25 mm or less, 5.0 N/25 mm or less, 4.0 N/25 mm or less, 3.5 N/25 mm or less, or even 3.0 N/25 mm or less. The lower limit of the adhesive strength G ₂ (80° C.) is, for example, 1.0 N/25 mm. In measuring the adhesive strength G ₂ (80° C.), first, the second adhesive sheet 4 of the optical laminate 10A is bonded to the alkali-free glass at 23° C., and then the bond between the second adhesive sheet 4 and the alkali-free glass is homogenized by placing it in an autoclave at 50° C. and 5 atm (absolute pressure) for 15 minutes. This produces a glass-attached optical laminate. After producing the glass-attached optical laminate, it is left to stand for two weeks under conditions of 23°C and 55% RH. After leaving the glass-attached optical laminate to stand for two weeks, it is heated. The heating is performed by placing the glass-attached optical laminate on a hot plate set at 80°C for 15 seconds. The adhesive strength _G2 (80°C) is the adhesive strength between the second adhesive sheet 4 and the alkali-free glass at 80°C, measured immediately after heating the glass-attached optical laminate by the above method.

_G2 (80°C) and _G0 (80°C) may satisfy _G2 (80°C)/ _G0 (80°C)≦1.5. This allows the reworkability to be further improved even after a long period of time has elapsed since the optical laminate was attached to an adherend such as an image forming layer. _G2 (80°C)/ _G0 (80°C) may be 1.3 or less, or 1.2 or less. The lower limit of _G2 (80°C)/ _G0 (80°C) is, for example, 1.0.

The thickness _T2 of the second adhesive sheet 4 is, for example, 8 μm or more. The thickness _T2 of the second adhesive sheet 4 may be 10 μm or more, 12 μm or more, 15 μm or more, or even 18 μm or more. The upper limit of the thickness _T2 of the second adhesive sheet 4 is, for example, 30 μm.

The thickness _T2 of the second adhesive sheet 4 and the thickness _T1 of the first adhesive sheet 2 may satisfy _T2 / _T1 ≧1.1. This can further improve the reworkability. _T2 / _T1 may be 1.2 or more, 1.3 or more, 1.4 or more, 1.7 or more, 2.0 or more, or even 2.5 or more. The upper limit of _T2 / _T1 is, for example, 5.0. By satisfying _T2 / _T1 ≧1.1, the blade of the rework jig is more easily inserted between the second adhesive sheet 4 and the adherend. As a result, the success rate of the trigger creation can be further improved.

The second adhesive sheet 4 has principal surfaces 4a and 4b that face each other. The principal surface 4a faces the second optical film 3. The principal surface 4b is exposed, for example, to the outside of the optical laminate 10A, and is the surface on which an adherend such as glass is laminated. The principal surface 4a of the second adhesive sheet 4 may be subjected to a surface modification treatment. The principal surface 4b of the second adhesive sheet 4 may not be subjected to a surface modification treatment. For the surface modification treatment, the surface modification treatment described above for the first adhesive sheet 2 can be used as appropriate.

[Adhesive composition (I)]
The first adhesive sheet 2 and the second adhesive sheet 4 are formed, for example, from an adhesive composition (I). Details of the adhesive composition (I) are described below. In the following description, the first adhesive sheet 2 and the second adhesive sheet 4 may be referred to as "adhesive sheets".

Examples of adhesives constituting the adhesive sheet include acrylic adhesives, rubber adhesives, vinyl alkyl ether adhesives, silicone adhesives, polyester adhesives, polyamide adhesives, urethane adhesives, fluorine adhesives, epoxy adhesives, polyether adhesives, etc. The adhesives constituting the adhesive sheet are used alone or in combination of two or more. However, from the standpoint of transparency, processability, durability, adhesion, etc., it is preferable to use an acrylic adhesive (composition) containing a (meth)acrylic polymer alone. In other words, it is preferable that the adhesive sheet contains a (meth)acrylic polymer. In this specification, "(meth)acrylic" means acrylic and methacrylic. Also, "(meth)acrylate" means acrylate and methacrylate.

[(Meth)acrylic polymer (A)]
The (meth)acrylic polymer (A) may have, as a main unit, a structural unit derived from a (meth)acrylic monomer having an alkyl group having 1 to 30 carbon atoms on the side chain. The alkyl group may be linear or branched. The (meth)acrylic polymer (A) may have one or more structural units derived from the (meth)acrylic monomer (A1). Examples of the (meth)acrylic monomer (A1) are methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate (lauryl (meth)acrylate), n-tridecyl (meth)acrylate and n-tetradecyl (meth)acrylate. In this specification, the term "main unit" means a unit that accounts for, for example, 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, particularly preferably 80% by weight or more, and even more preferably 90% by weight or more of all structural units contained in a polymer.

The (meth)acrylic polymer (A) may have a structural unit derived from a (meth)acrylic monomer (A1) that, when made into a homopolymer, has a glass transition temperature (Tg) in the range of -70 to -20°C. An example of the monomer (A1) is n-butyl acrylate.

The (meth)acrylic polymer (A) may have a structural unit other than the structural unit derived from the (meth)acrylic monomer (A1). The structural unit is derived from a monomer (A2) that is copolymerizable with the (meth)acrylic monomer (A1). The (meth)acrylic polymer (A) may have one or more types of the structural unit.

An example of the monomer (A2) is an aromatic ring-containing monomer. The aromatic ring-containing monomer may be an aromatic ring-containing (meth)acrylic monomer. Examples of aromatic ring-containing monomers are phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, ethylene oxide-modified nonylphenol (meth)acrylate, hydroxyethylated β-naphthol (meth)acrylate, and biphenyl (meth)acrylate. The content of the constituent unit derived from the aromatic ring-containing monomer in the (meth)acrylic polymer (A) is, for example, 0 to 50% by weight, and may be 1 to 30% by weight, 5 to 25% by weight, 8 to 20% by weight, 10 to 18% by weight, or even 12 to 16% by weight. When the amount of the crosslinking agent (B) in the pressure-sensitive adhesive composition (I) is increased, a self-polymer of the crosslinking agent (B) may be formed. The (meth)acrylic polymer (A) having a structural unit derived from an aromatic ring-containing monomer improves the compatibility of the (meth)acrylic polymer (A) with the crosslinking agent (B) and its self-polymer. The improved compatibility can contribute to improving the uniformity of the pressure-sensitive adhesive sheet, for example, by suppressing the precipitation of the self-polymer.

Another example of the monomer (A2) is a hydroxyl group-containing monomer. The hydroxyl group-containing monomer may be a hydroxyl group-containing (meth)acrylic monomer. Examples of the hydroxyl group-containing monomer are hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate, as well as (4-hydroxymethylcyclohexyl)-methyl acrylate.

When the first adhesive sheet 2 contains a (meth)acrylic polymer (A) and the (meth)acrylic polymer (A) has a constituent unit derived from a hydroxyl group-containing monomer, the content of the constituent unit derived from the hydroxyl group-containing monomer in the (meth)acrylic polymer (A) may be, for example, 0.01% by weight or more, 0.05% by weight or more, 0.1% by weight or more, 0.3% by weight or more, 0.35% by weight or more, 0.4% by weight or more, or even 0.45% by weight or more. The content may be 2% by weight or less, 1.5% by weight or less, 1.2% by weight or less, 1.0% by weight or less, 0.8% by weight or less, 0.7% by weight or less, or 0.6% by weight or less.

When the second adhesive sheet 4 contains a (meth)acrylic polymer (A) and the (meth)acrylic polymer (A) has a constituent unit derived from a hydroxyl group-containing monomer, the content of the constituent unit derived from the hydroxyl group-containing monomer in the (meth)acrylic polymer (A) is, for example, 0.01% by weight or more, and may be 0.05% by weight or more, 0.06% by weight or more, 0.07% by weight or more, 0.08% by weight or more, or even 0.09% by weight or more. The content is 1% by weight or less, and may be 0.8% by weight or less, 0.5% by weight or less, 0.3% by weight or less, or 0.2% by weight or less.

Monomer (A2) may be a carboxyl group-containing monomer, an amino group-containing monomer, or an amide group-containing monomer. Examples of carboxyl group-containing monomers are (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Examples of amino group-containing monomers are N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate. Examples of the amide group-containing monomer include acrylamide-based monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropylacrylamide, N-methyl(meth)acrylamide, N-butyl(meth)acrylamide, N-hexyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylol-N-propane(meth)acrylamide, aminomethyl(meth)acrylamide, aminoethyl(meth)acrylamide, mercaptomethyl(meth)acrylamide, and mercaptoethyl(meth)acrylamide; N-acryloyl heterocyclic monomers such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperidine, and N-(meth)acryloylpyrrolidine; and N-vinyl group-containing lactam-based monomers such as N-vinylpyrrolidone and N-vinyl-ε-caprolactam. By having the (meth)acrylic polymer (A) contain a structural unit derived from a carboxyl group-containing monomer, particularly acrylic acid, it is possible to enhance the self-polymerization of the crosslinking agent (B), for example. The improvement in the self-polymerization of the crosslinking agent (B) can contribute to suppressing peeling of the pressure-sensitive adhesive sheet, particularly in a humid environment, and to stabilizing the physical properties of the pressure-sensitive adhesive sheet in a system with a high content of the crosslinking agent (B).

Monomer (A2) may be a polyfunctional monomer. Examples of polyfunctional monomers are polyfunctional acrylates such as hexanediol di(meth)acrylate (1,6-hexanediol di(meth)acrylate), butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, epoxy acrylate, polyester acrylate, and urethane acrylate; and divinylbenzene. The polyfunctional acrylate is preferably 1,6-hexanediol diacrylate or dipentaerythritol hexa(meth)acrylate.

The total content of the structural units derived from the carboxyl group-containing monomer, the amino group-containing monomer, the amide group-containing monomer, and the polyfunctional monomer in the (meth)acrylic polymer (A) is preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 8% by weight or less. When the (meth)acrylic polymer (A) has such structural units, the total content is, for example, 0.01% by weight or more, and may be 0.05% by weight or more. The (meth)acrylic polymer (A) may not contain structural units derived from polyfunctional monomers.

Examples of other monomers (A2) are (meth)acrylic acid alkoxyalkyl esters such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, and 4-ethoxybutyl (meth)acrylate; epoxy group-containing monomers such as glycidyl (meth)acrylate and methyl glycidyl (meth)acrylate; sulfonic acid group-containing monomers such as sodium vinyl sulfonate; phosphoric acid group-containing monomers; (meth)acrylic acid esters having alicyclic hydrocarbon groups such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate; vinyl esters such as vinyl acetate and vinyl propionate; aromatic vinyl compounds such as styrene and vinyl toluene; olefins or dienes such as ethylene, propylene, butadiene, isoprene, and isobutylene; vinyl ethers such as vinyl alkyl ethers; and vinyl chloride.

The total content of the structural units derived from the other monomer (A2) in the (meth)acrylic polymer (A) is, for example, 30% by weight or less, and may be 10% by weight or less, or may be 0% by weight (not including the structural units).

The (meth)acrylic polymer (A) can be formed by polymerizing one or more of the above-mentioned monomers by a known method. A monomer and a partial polymer of the monomer may be polymerized. The polymerization can be carried out, for example, by solution polymerization, emulsion polymerization, bulk polymerization, thermal polymerization, or active energy ray polymerization. Since a pressure-sensitive adhesive sheet having excellent optical transparency can be formed, solution polymerization and active energy ray polymerization are preferred. The polymerization is preferably carried out while avoiding contact between the monomer and/or the partial polymer and oxygen. For this purpose, for example, polymerization in an inert gas atmosphere such as nitrogen or polymerization in a state where oxygen is blocked by a resin film or the like can be adopted. The (meth)acrylic polymer (A) formed may be any of a random copolymer, a block copolymer, a graft copolymer, and the like.

The polymerization system that forms the (meth)acrylic polymer (A) may contain one or more polymerization initiators. The type of polymerization initiator can be selected depending on the polymerization reaction, and may be, for example, a thermal polymerization initiator or a photopolymerization initiator.

Solvents used in solution polymerization include, for example, esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. However, the solvent is not limited to the above examples. The solvent may be a mixed solvent of two or more solvents.

The polymerization initiator used in the solution polymerization is, for example, an azo-based polymerization initiator, a peroxide-based polymerization initiator, or a redox-based polymerization initiator. Examples of the peroxide-based polymerization initiator are dibenzoyl peroxide and t-butyl permaleate. Among them, the azo-based polymerization initiator disclosed in JP-A-2002-69411 is preferable. Examples of the azo-based polymerization initiator are 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionate) dimethyl, and 4,4'-azobis-4-cyanovaleric acid. However, the polymerization initiator is not limited to the above examples. The amount of the azo-based polymerization initiator used is, for example, 0.05 to 0.5 parts by weight, or may be 0.1 to 0.3 parts by weight, based on 100 parts by weight of the total amount of the monomers.

The active energy rays used in the active energy ray polymerization are, for example, ionizing radiation such as α rays, β rays, γ rays, neutron rays, and electron beams, and ultraviolet rays. The active energy rays are preferably ultraviolet rays. Polymerization by irradiation with ultraviolet rays is also called photopolymerization. The polymerization system for the active energy ray polymerization typically contains a photopolymerization initiator. The polymerization conditions for the active energy polymerization are not limited as long as the (meth)acrylic polymer (A) is formed.

Examples of photopolymerization initiators include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, and thioxanthone-based photopolymerization initiators. However, the photopolymerization initiator is not limited to the above examples.

Examples of benzoin ether-based photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethane-1-one, and anisole methyl ether. Examples of acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of α-ketol-based photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of aromatic sulfonyl chloride-based photopolymerization initiators include 2-naphthalenesulfonyl chloride. An example of the photoactive oxime-based photopolymerization initiator is 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. An example of the benzoin-based photopolymerization initiator is benzoin. An example of the benzyl-based photopolymerization initiator is benzil. An example of the benzophenone-based photopolymerization initiator is benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, α-hydroxycyclohexylphenyl ketone. An example of the ketal-based photopolymerization initiator is benzyl dimethyl ketal. An example of the thioxanthone-based photopolymerization initiator is thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

The amount of photopolymerization initiator used is, for example, 0.01 to 1 part by weight per 100 parts by weight of the total amount of monomers, and may be 0.05 to 0.5 parts by weight.

The weight average molecular weight (Mw) of the (meth)acrylic polymer (A) is, for example, 1,000,000 to 2,800,000, and from the viewpoint of the durability and heat resistance of the pressure-sensitive adhesive sheet, may be 1,200,000 or more, or even 1,400,000 or more. The weight average molecular weights (Mw) of the polymers and oligomers in this specification are values (polystyrene equivalent) based on measurements by GPC (gel permeation chromatography).

The content of the (meth)acrylic polymer (A) in the pressure-sensitive adhesive composition (I) may be, for example, 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, or even 85% by weight or more, in terms of solid content. The upper limit of the content may be, for example, 99.5% by weight, 99% by weight, 97% by weight, 95% by weight, 93% by weight, or even 90% by weight.

[Crosslinking agent (B)]
The crosslinking agent (B) is typically a polyfunctional crosslinking agent having two or more crosslinking reactive groups per molecule. The crosslinking agent (B) may be a trifunctional or higher crosslinking agent having three or more crosslinking reactive groups per molecule. The upper limit of the number of crosslinking reactive groups per molecule is, for example, 5.

The crosslinking agent (B) is, for example, an isocyanate-based crosslinking agent. The isocyanate-based crosslinking agent contains an isocyanate group as a crosslinking reactive group. The isocyanate-based crosslinking agent (B) may be an aromatic isocyanate compound, an alicyclic isocyanate compound, or an aliphatic isocyanate compound. An isocyanate-based crosslinking agent (especially a trifunctional isocyanate-based crosslinking agent) is preferred in terms of durability.

Examples of aromatic isocyanate compounds that can be used in the crosslinking agent (B) are phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-toluidine diisocyanate, 4,4'-diphenylether diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, and xylylene diisocyanate.

Examples of alicyclic isocyanate compounds that can be used in the crosslinking agent (B) are 1,3-cyclopentene diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated tetramethylxylylene diisocyanate.

Examples of aliphatic isocyanate compounds that can be used in the crosslinking agent (B) are trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

The crosslinking agent (B) may be a derivative of the above-mentioned isocyanate compound. Examples of derivatives include polymers (dimers, trimers, pentamers, etc.), adducts obtained by addition to polyhydric alcohols such as trimethylolpropane, urea-modified products, biuret-modified products, allophanate-modified products, isocyanurate-modified products, carbodiimide-modified products, and urethane prepolymers obtained by addition to polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, etc.

The crosslinking agent (B) is preferably an aromatic isocyanate compound and its derivatives, and more preferably tolylene diisocyanate and its derivatives (in other words, a tolylene diisocyanate-based (TDI-based) crosslinking agent). TDI-based crosslinking agents have better reaction uniformity than xylylene diisocyanate and its derivatives (in other words, a xylylene diisocyanate-based (XDI-based) crosslinking agent). An example of a TDI-based crosslinking agent is an adduct of tolylene diisocyanate and a polyfunctional alcohol, and a more specific example is a trimethylolpropane/tolylene diisocyanate trimer adduct.

Commercially available products can be used as the crosslinking agent (B). Examples of commercially available products include Millionate MT, Millionate MTL, Millionate MR-200, Millionate MR-400, Coronate L, Coronate HL and Coronate HX (all manufactured by Tosoh Corporation; all trade names), as well as Takenate D-102, Takenate D-103, Takenate D-110N, Takenate D-120N, Takenate D-140N, Takenate D-160N, Takenate D-165N, Takenate D-170HN, Takenate D-178N, Takenate 500 and Takenate 600 (all manufactured by Mitsui Chemicals; all trade names). As the crosslinking agent (B), Coronate L, Takenate D-102 and Takenate D-103 (all trimethylolpropane/tolylene diisocyanate trimer adducts) can be preferably used.

The isocyanate-based crosslinking agent may be used alone or in a mixture of two or more of the above-mentioned isocyanate-based crosslinking agents. The amount of the isocyanate-based crosslinking agent in the adhesive composition (I) may be, for example, 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, 0.5 parts by weight or more, 0.6 parts by weight or more, 1 part by weight or more, 2 parts by weight or more, 2.5 parts by weight or more, 3 parts by weight or more, 5 parts by weight or more, 6 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, 9 parts by weight or more, 10 parts by weight or more, more than 10 parts by weight, or even 11 parts by weight or more, based on 100 parts by weight of the (meth)acrylic polymer (A). The upper limit of the amount may be, for example, 30 parts by weight or less, 28 parts by weight or less, 25 parts by weight or less, 23 parts by weight or less, 20 parts by weight or less, 19 parts by weight or less, 18 parts by weight or less, or even 15 parts by weight or less.

The adhesive composition (I) may contain a crosslinking agent other than an isocyanate-based crosslinking agent. Examples of crosslinking agents other than an isocyanate-based crosslinking agent include a peroxide-based crosslinking agent, an epoxy-based crosslinking agent, an imine-based crosslinking agent, and a polyfunctional metal chelate. The amount of the crosslinking agent other than an isocyanate-based crosslinking agent may be, for example, 2 parts by weight or less, 1 part by weight or less, 0.5 parts by weight or less, 0.3 parts by weight or less, 0.28 parts by weight or less, 0.25 parts by weight or less, 0.2 parts by weight or less, or even 0.15 parts by weight or less, relative to 100 parts by weight of the (meth)acrylic polymer (A). The lower limit of the amount is, for example, 0 parts by weight. The crosslinking agent (B) may contain an isocyanate-based crosslinking agent and a peroxide-based crosslinking agent. From the viewpoint of durability of the adhesive sheet, the adhesive composition (I) may not substantially contain other crosslinking agents, particularly epoxy-based crosslinking agents.

[Additive]
The adhesive composition (I) may contain other additives. Examples of additives include silane coupling agents, polyfunctional alcohols, colorants such as pigments and dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, rework improvers, softeners, antioxidants, antiaging agents, light stabilizers, UV absorbers, polymerization inhibitors, antistatic agents (alkali metal salts, ionic liquids, ionic solids, etc., which are ionic compounds), inorganic fillers, organic fillers, powders such as metal powders, particles, and foil-like materials. The additives can be blended in an amount of, for example, 10 parts by weight or less, preferably 5 parts by weight or less, and more preferably 1.5 parts by weight or less, relative to 100 parts by weight of the (meth)acrylic polymer (A).

Examples of silane coupling agents include epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containing silane coupling agents such as 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and N-phenyl-γ-aminopropyltrimethoxysilane; (meth)acrylic group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane; and isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane.

When the pressure-sensitive adhesive composition (I) contains a silane coupling agent, the amount of the silane coupling agent is, for example, 5 parts by weight or less, and may be 3 parts by weight or less, 1 part by weight or less, 0.5 parts by weight or less, 0.2 parts by weight or less, 0.1 parts by weight or less, or even 0.05 parts by weight or less, per 100 parts by weight of the (meth)acrylic polymer (A). The pressure-sensitive adhesive composition (I) does not have to contain a silane coupling agent.

The adhesive composition (I) may contain a polyfunctional alcohol. The molecular weight of the polyfunctional alcohol is, for example, 240 or less, and may be 230 or less, 220 or less, 210 or less, 200 or less, 190 or less, 180 or less, 170 or less, 160 or less, or even 150 or less. The lower limit of the molecular weight is, for example, 60 or more, 80 or more, 90 or more, or even 100 or more.

Examples of polyfunctional alcohols are alkylene glycols such as ethylene glycol and propylene glycol and their polymers; ether glycols such as diethylene glycol and their polymers; trimethylolethane; trimethylolpropane; glycerin; and sugar alcohols such as pentaerythritol and sorbitol. The polyfunctional alcohol is preferably trimethylolpropane, glycerin, or diethylene glycol and its polymers, more preferably trimethylolpropane.

The polyfunctional alcohol may be trifunctional or more. Examples of trifunctional polyfunctional alcohols are trimethylolpropane and glycerin.

The polyfunctional alcohol may not have a reactive group other than the hydroxyl group that is reactive with the crosslinking agent (B). The reactive group is, for example, at least one selected from an amino group, a carboxyl group, and an epoxy group, and is particularly an amino group.

The amount of polyfunctional alcohol in the pressure-sensitive adhesive composition (I) is, for example, 0.5 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the (meth)acrylic polymer (A). The upper limit of the amount may be 15 parts by weight or less, 10 parts by weight or less, 8 parts by weight or less, 5 parts by weight or less, 4 parts by weight or less, or even 3 parts by weight or less.

The adhesive composition (I) may not contain a crosslinking accelerator such as a catalyst. Examples of crosslinking accelerators are polyethers, polyether polyols, and phosphate esters having reactive groups that are reactive with the crosslinking agent (B). The reactive groups are, for example, at least one selected from a hydroxyl group, an amino group, a carboxyl group, and an epoxy group, and are particularly hydroxyl groups or amino groups. The adhesive composition (I) may not contain a polyether polyol having an amino group, and may not contain a phosphate ester having a hydroxyl group.

The type of the adhesive composition (I) is, for example, an emulsion type, a solvent type (solution type), an active energy ray curable type (photocurable type), or a hot melt type. From the viewpoint of forming an adhesive sheet with superior durability, the adhesive composition (I) may be a solvent type. The solvent type adhesive composition (I) may not contain a photocuring agent such as an ultraviolet curing agent.

[Method of manufacturing the first adhesive sheet and the second adhesive sheet]
The first adhesive sheet 2 and the second adhesive sheet 4 are formed from a pressure-sensitive adhesive composition (I). The first adhesive sheet 2 and the second adhesive sheet 4 contain, for example, a crosslinked product of a (meth)acrylic polymer (A). The first adhesive sheet 2 and the second adhesive sheet 4 can be formed from the pressure-sensitive adhesive composition (I) by the following method. A method for forming the first adhesive sheet 2 from the pressure-sensitive adhesive composition (I) will be described below, but the second adhesive sheet 4 can be formed by a similar method.

The method for producing the first adhesive sheet 2 includes, for example, applying an adhesive composition (I) containing a (meth)acrylic polymer (A) and a crosslinking agent to a substrate to form a coating film, and drying the resulting coating film.

For example, a release film can be used as the substrate. The first adhesive sheet 2 formed on the release film can be transferred to, for example, an optical film. The substrate may be an optical film. In this case, the first adhesive sheet can be formed into an optical film, and an optical film with the first adhesive sheet can be obtained.

After the first adhesive sheet 2 is transferred to the optical film, the release film can be used as a separator until the first adhesive sheet 2 is put to practical use, simplifying the process.

Examples of materials that can be used to make the release film include suitable thin materials such as plastic film, paper, cloth, nonwoven fabric, and other porous materials, nets, foam sheets, metal foils, and laminates of these materials. However, plastic film is preferably used because of its excellent surface smoothness.

The plastic film is not particularly limited, and examples thereof include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polybutylene terephthalate film, polyurethane film, ethylene-vinyl acetate copolymer film, etc.

The thickness of the release film is usually 5 to 200 μm, and preferably about 5 to 100 μm. The release film is subjected to a release treatment, for example, a silicone-based, fluorine-based, or long-chain alkyl-based treatment. The release film may be subjected to a release and antifouling treatment using a fatty acid amide-based release agent, silica powder, or the like, or an antistatic treatment such as a coating type, kneading type, or deposition type.

A solution (adhesive solution) containing the adhesive composition (I) may be applied to the substrate. The solids concentration of the adhesive solution is, for example, 5 to 50% by weight, and preferably 10 to 40% by weight. The adhesive solution can be prepared by appropriately adding the same solvent as the polymerization solvent or a different solvent to the adhesive composition (I) depending on the polymerization form of the (meth)acrylic polymer (A).

Various methods can be used to apply the adhesive composition (I) to the substrate, including, for example, roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and extrusion coating using a die coater. The amount of adhesive composition (I) applied can be adjusted appropriately depending on the desired thickness of the first adhesive sheet 2.

By drying the coating film, the coating film hardens and the first adhesive sheet 2 is formed. The drying temperature of the coating film is not particularly limited, and is, for example, 130°C or less, preferably 125°C or less, more preferably 120°C or less, even more preferably 110°C or less, and particularly preferably 100°C or less. The drying temperature of the coating film may be 60°C or more, or 80°C or more. When the drying temperature is 60°C or more, for example, the reaction of the isocyanate-based crosslinking agent proceeds smoothly, the cohesive force of the first adhesive sheet 2 can be improved, and display unevenness of the image display device tends to be reduced. When the drying temperature is 130°C or less, for example, the reaction speed of the isocyanate-based crosslinking agent can be appropriately adjusted, and transparency tends to be ensured.

The drying time of the coating film can be adjusted appropriately depending on the composition of the adhesive composition (I), and is preferably 30 to 300 seconds, more preferably 40 to 240 seconds, and particularly preferably 60 to 180 seconds.

[Optical film]
The first optical film 1 has principal surfaces 1a and 1b facing each other. The principal surface 1a is exposed to the outside of the optical laminate 10A, for example. The principal surface 1b faces the first adhesive sheet 2. The surface of the first optical film 1 on which the first adhesive sheet 2 is laminated, i.e., the principal surface 1b of the first optical film 1, may be subjected to a surface modification treatment. The principal surface 1b subjected to the surface modification treatment can further improve the adhesion between the first optical film 1 and the first adhesive sheet 2. The surface modification treatment may be appropriately selected from the surface modification treatments described above for the first adhesive sheet 2. The principal surface 1b may be subjected to a corona treatment as the surface modification treatment. When the principal surface 1b is subjected to a corona treatment, the conditions such as the discharge amount can be appropriately adjusted within the range described above for the first adhesive sheet 2, for example.

The second optical film 3 has principal surfaces 3a and 3b facing each other. The principal surface 3a faces the first adhesive sheet 2. The principal surface 3a is the surface on which the first adhesive sheet 2 of the second optical film 3 is laminated. The principal surface 3b faces the second adhesive sheet 4. The principal surface 3b is the surface on which the second adhesive sheet 4 of the second optical film 3 is laminated. The principal surfaces 3a and 3b may be subjected to a surface modification treatment. By subjecting the principal surface 3a to a surface modification treatment, the above-mentioned adhesion force F can be further improved. By subjecting the principal surface 3b to a surface modification treatment, the adhesive force between the second optical film 3 and the second adhesive sheet 4 can be further improved. The surface modification treatment may be applied to at least a part of the principal surfaces 3a and 3b of the second optical film 3. The surface modification treatment may be applied only to the ends of the principal surfaces 3a and 3b of the second optical film 3, or may be applied to the entire principal surfaces 3a and 3b. The surface modification treatment may be any of the surface modification treatments described above for the first adhesive sheet 2. The principal surfaces 3a and 3b may be subjected to a corona treatment as the surface modification treatment. When the principal surfaces 3a and 3b are subjected to a corona treatment, the conditions such as the discharge amount can be appropriately adjusted within the range described above for the first adhesive sheet 2, for example.

The first optical film 1 and the second optical film 3 each include, for example, at least one selected from the group consisting of a polarizing film and a retardation film. The first optical film 1 may include a polarizing film. The second optical film 3 may include a retardation film. The first optical film 1 and the second optical film 3 may be a laminated film including a polarizing film and/or a retardation film. The first optical film 1 and the second optical film 3 may include a glass film.

The polarizing film includes a polarizer. The polarizing film typically includes a polarizer and a protective film (transparent protective film). The protective film is, for example, disposed in contact with the main surface of the polarizer. The polarizer may be disposed between two protective films. The protective film may be disposed on at least one surface of the polarizer.

The polarizer is not particularly limited, and examples thereof include hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and partially saponified ethylene-vinyl acetate copolymer films, which are uniaxially stretched after adsorbing dichroic substances such as iodine and dichroic dyes; and polyene-based oriented films such as dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride. Polarizers are typically made of polyvinyl alcohol films (polyvinyl alcohol films include partially saponified ethylene-vinyl acetate copolymer films) and dichroic substances such as iodine.

The thickness of the polarizer is not particularly limited, and may be, for example, 80 μm or less, 50 μm or less, 30 μm or less, 25 μm or less, or even 20 μm or less. The lower limit of the thickness of the polarizer is not particularly limited, and may be, for example, 1 μm or more, 5 μm or more, 10 μm or more, or even 15 μm or more. A thin polarizer (for example, a thickness of 20 μm or less) suppresses dimensional changes and can contribute to improving the durability of the optical laminate, particularly the durability at high temperatures.

As the material of the protective film, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture blocking property, isotropy, etc. is used. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, cyclic polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. The material of the protective film may be a thermosetting resin or an ultraviolet-curing resin such as a (meth)acrylic, urethane, acrylic urethane, epoxy, or silicone. When the polarizing film has two protective films, the materials of the two protective films may be the same or different from each other. For example, a protective film made of a thermoplastic resin may be bonded to one main surface of the polarizer via an adhesive, and a protective film made of a thermosetting resin or an ultraviolet-curing resin may be bonded to the other main surface of the polarizer. The protective film may contain one or more types of optional additives. Examples of additives include ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, color inhibitors, flame retardants, nucleating agents, antistatic agents, pigments, and colorants.

Films containing (meth)acrylic resins tend to have low adhesive strength with adhesive sheets. However, in this embodiment, by performing a surface modification treatment on the main surface 3a of the second optical film 3, the above-mentioned adhesion force F can be adjusted to a sufficiently high value even when the surface of the protective film containing (meth)acrylic resin corresponds to the main surface 3a of the second optical film 3.

The thickness of the protective film can be determined as appropriate, but is generally about 10 to 200 μm, taking into consideration strength, ease of handling, thinness, etc.

The polarizer and the protective film are usually adhered to each other via a water-based adhesive or the like. Examples of water-based adhesives include isocyanate-based adhesives, polyvinyl alcohol-based adhesives, gelatin-based adhesives, vinyl latex, water-based polyurethane, water-based polyester, and the like. Examples of adhesives other than the above-mentioned adhesives include ultraviolet-curable adhesives and electron beam-curable adhesives. Electron beam-curable polarizing plate adhesives exhibit suitable adhesion to various protective films. The adhesive may contain a metal compound filler.

In polarizing films, instead of a protective film, a retardation film or the like can be formed on the polarizer. Another protective film can be further provided on the protective film, or a retardation film or the like can be provided.

The protective film may have a hard coat layer on the surface opposite to the surface attached to the polarizer, and may also be treated for the purposes of anti-reflection, anti-sticking, diffusion, anti-glare, etc.

The polarizing film may be a circular polarizing film.

The retardation film may be one obtained by stretching a polymer film or one obtained by aligning and fixing a liquid crystal material. The retardation film has birefringence, for example, in the in-plane and/or thickness direction.

Examples of retardation films include anti-reflection retardation films (see JP 2012-133303 A [0221], [0222], [0228]), viewing angle compensation retardation films (see JP 2012-133303 A [0225], [0226]), and tilted orientation retardation films for viewing angle compensation (see JP 2012-133303 A [0227]).

As the retardation film, as long as it has substantially the above-mentioned functions, there are no particular limitations on, for example, the retardation value, arrangement angle, three-dimensional birefringence, whether it is a single layer or a multilayer, and any known retardation film can be used.

The thickness of the retardation film is preferably 20 μm or less, more preferably 10 μm or less, even more preferably 1 to 9 μm, and particularly preferably 3 to 8 μm.

The retardation film is composed of two layers, for example a quarter-wave plate and a half-wave plate, in which liquid crystal material is oriented and fixed.

Figure 2 is a schematic cross-sectional view showing another example of an optical laminate. The optical laminate 10B in Figure 2 has a laminated structure in which a second adhesive sheet 4, a retardation film 3A, a first adhesive sheet 2, a polarizing film 1A, and a protective film 5 are laminated in this order.

The protective film 5 has a function of protecting the polarizing film 1A, which is the outermost layer, during distribution and storage of the optical laminate 10B and when the optical laminate 10B is incorporated into an image display device. The protective film 5 may also be a protective film that functions as a window to the external space when incorporated into an image display device. The protective film 5 is typically a resin film. The resin constituting the protective film 5 is, for example, polyester such as PET, polyolefin such as polyethylene and polypropylene, acrylic, cycloolefin, polyimide, and polyamide, and polyester is preferable. However, the protective film 5 is not limited to the above examples. The protective film 5 may be a glass film or a laminated film including a glass film. The protective film 5 may be subjected to surface treatment such as anti-glare, anti-reflection, and anti-static.

The protective film 5 may be bonded to the polarizing film 1A by any adhesive. Bonding by the first adhesive sheet 2 or the second adhesive sheet 4 is also possible.

The optical laminate may have any configuration as long as it includes an adhesive sheet formed by the above-mentioned method for producing an adhesive sheet.

The optical laminate of this embodiment is typically used in image display devices. Image display devices are, for example, EL displays such as liquid crystal displays, organic EL displays, and inorganic EL displays.

[Shape of second adhesive sheet]
At least a part of the end of the second adhesive sheet 4 may be located inside the side surface of the second optical film 3. This makes it easier for the tip of the blade of the rework jig to be inserted between the second adhesive sheet 4 and the adherend. As a result, the reworkability can be further improved.

Figure 3 is a schematic cross-sectional view showing an example of an optical laminate with a substrate. As shown in Figure 3, the optical laminate with a substrate 11A includes an optical laminate 10C and a substrate 8. In detail, the optical laminate with a substrate 11A has a configuration in which a first optical film 1, a first adhesive sheet 2, a second optical film 3, a second adhesive sheet 4A, and a substrate 8 are laminated in this order. As the substrate 8, for example, a release film can be used. The substrate 8 may be an optical film or an image forming layer 6 described later. The substrate 8 can be used, for example, as a separator in the optical laminate 10C until the second adhesive sheet 4 is put to practical use.

The material of the release film used for the substrate 8 may be, for example, plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester film; porous materials such as paper, cloth, and nonwoven fabric; nets, foam sheets, metal foils, and laminates of these; and other suitable thin materials. However, plastic films are preferably used because of their excellent surface smoothness.

The plastic film is not particularly limited as long as it is a film capable of protecting the second adhesive sheet 4A, and examples include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polybutylene terephthalate film, polyurethane film, ethylene-vinyl acetate copolymer film, etc.

The thickness of the release film that can be used for the substrate 8 is usually 5 to 200 μm, and preferably about 5 to 100 μm. If necessary, the release film may be subjected to a release and antifouling treatment using a silicone-based, fluorine-based, long-chain alkyl-based or fatty acid amide-based release agent, silica powder, etc., or an antistatic treatment such as a coating type, kneading type or deposition type. In particular, by appropriately performing a release treatment such as silicone treatment, long-chain alkyl treatment or fluorine treatment on the surface of the release film, the releasability from the second adhesive sheet 4A can be further improved.

The release film used when producing the second adhesive sheet 4A may also be used as the substrate 8.

In the optical laminate 10C, the second adhesive sheet 4A is formed on a part of one of the main surfaces 3b of the second optical film 3. The area of the main surface of the second adhesive sheet 4A may be smaller than the area of the main surface 3b of the second optical film 3. That is, the optical laminate 11A with the substrate may have a predetermined distance between the end of the second adhesive sheet 4A and the side of the second optical film 3. In the direction perpendicular to the stacking direction of the optical laminate 10C, all of the ends of the second adhesive sheet 4A may be located on the inside. That is, in the direction perpendicular to the stacking direction of the optical laminate 10C, all of the side surfaces 4s of the second adhesive sheet 4A may be located on the inside of the side surface 11a of the optical laminate 11A with the substrate.

In the substrate-attached optical laminate 11A, the second adhesive sheet 4A may be provided so that its end is located inside the side surface 11a of the substrate-attached optical laminate 11A by (i) designing the second adhesive sheet 4A to be formed in a predetermined amount inside the end of the punched optical film during application or transfer, and (ii) applying the adhesive composition (I) for forming the second adhesive sheet 4A to form an adhesive sheet, and then removing a part of the adhesive sheet. Alternatively, (iii) the substrate-attached optical laminate 11A may be prepared by forming an adhesive sheet on a substrate such as a release film having a smaller main surface area than the second optical film 3 to prepare an adhesive sheet with a substrate, and laminating the adhesive sheet with a substrate to the second optical film 3.

Another example of the method of providing the second adhesive sheet 4A in the substrate-attached optical laminate 11A so that the end of the second adhesive sheet 4A is located inside the side surface 11a of the substrate-attached optical laminate 11A is (iv) a method by end treatment. In the method by end treatment, first, the substrate-attached optical laminate is pressurized from its stacking direction. For pressurization, for example, a jig such as a clamp is used to pressurize from both sides of the substrate-attached optical laminate. Alternatively, one side of the substrate-attached optical laminate may be fixed and pressurized from the other side to pressurize the substrate-attached optical laminate in the stacking direction. By pressurizing the substrate-attached optical laminate, the end of the adhesive sheet can be made to protrude from the edge of the substrate-attached optical laminate, specifically, from the side surface of the second optical film. Next, the protruding end of the adhesive sheet is cut or cut. Thereafter, the pressure applied to the substrate-attached optical laminate is released, so that the second adhesive sheet 4 can be produced so that the end of the second adhesive sheet 4A is located inside the side surface of the second optical film 3. In addition, in the cutting or cutting, only the protruding end of the adhesive sheet may be cut or cut, or the entire end of the optical laminate may be cut or cut. In the method of edge treatment, for example, the shape of the end of the second adhesive sheet and the distance between the end of the second adhesive sheet and the side of the second optical film can be adjusted by adjusting the amount of cutting or cutting, adjusting the pressure applied to the optical laminate with the substrate, and/or adjusting the elastic modulus (storage elastic modulus) of the adhesive sheet.

In the substrate-attached optical laminate 11A, the second adhesive sheet 4A may be produced by pulling the substrate-attached optical laminate from one or both sides outward in the thickness direction of the adhesive sheet so that the end of the second adhesive sheet 4A is positioned inside the side surface 11a of the substrate-attached optical laminate 11A.

In the substrate-attached optical laminate 11A, at least a portion of the end of the second adhesive sheet 4A may be located inside the side surface 11a of the substrate-attached optical laminate 11A. The end of the second adhesive sheet 4 located inside the side surface 11a of the substrate-attached optical laminate 11A may be formed to be 1/2 or more of the entire perimeter of the second optical film 3, or may be formed to be 3/4 or more of the entire perimeter.

Other examples of shapes that the end of the second adhesive sheet may have are shown in Figures 4 to 6. Figure 4 is a schematic cross-sectional view showing another example of a substrate-attached optical laminate. As shown in Figure 4, substrate-attached optical laminate 11B includes optical laminate 10D and substrate 8. Substrate-attached optical laminate 11B has a configuration in which substrate 8 is laminated to second adhesive sheet 4B of optical laminate 10D. In substrate-attached optical laminate 11B, when observed from a direction perpendicular to the stacking direction of optical laminate 10D, the end of second adhesive sheet 4B has a curved surface 4t that is curved so as to be convex inward.

Figure 5 is a schematic cross-sectional view showing another example of a substrate-attached optical laminate. As shown in Figure 5, the substrate-attached optical laminate 11C includes an optical laminate 10E and a substrate 8. The substrate-attached optical laminate 11C has a configuration in which the substrate 8 is laminated to the second adhesive sheet 4C of the optical laminate 10E. The length of the second adhesive sheet 4C in a direction perpendicular to the stacking direction of the optical laminate 10E increases from the second optical film 3 toward the substrate 8. That is, in a direction perpendicular to the stacking direction of the optical laminate 10E, the distance between the side 11c of the substrate-attached optical laminate 11C and the side 4u of the second adhesive sheet 4C decreases from the second optical film 3 toward the substrate 8.

Figure 6 is a schematic cross-sectional view showing another example of a substrate-attached optical laminate. As shown in Figure 6, substrate-attached optical laminate 11D includes optical laminate 10F and substrate 8. Substrate-attached optical laminate 11D has a configuration in which substrate 8 is laminated to second adhesive sheet 4D of optical laminate 10F. The length of second adhesive sheet 4D in a direction perpendicular to the stacking direction of optical laminate 10F decreases from second optical film 3 toward substrate 8. That is, in a direction perpendicular to the stacking direction of optical laminate 10F, the distance between side 11d of substrate-attached optical laminate 11D and side 4v of second adhesive sheet 4D increases from second optical film 3 toward substrate 8.

In Figures 4 to 6, at least a portion of the end of the second adhesive sheet 4B to 4D is located inside the side surfaces 11b to 11d of the optical laminates 10D to 10F. In the substrate-attached optical laminates 11B to 11D, at least a portion of the end of the second adhesive sheet 4B to 4D may be in contact with the side surfaces 11b to 11d of the optical laminates 10D to 10F, or may be located outside the side surfaces 11b to 11d of the optical laminates 10D to 10F in a direction perpendicular to the stacking direction of the optical laminates.

In a direction perpendicular to the lamination direction of the optical laminate, all of the ends of the first adhesive sheet 2 may be located on the inside. At least a portion of the ends of the first adhesive sheet 2 may be located on the inside of the side surface of the second optical film 3. In addition, in these substrate-attached optical laminates 11A to 11D, the shape of the ends of the first adhesive sheet and the shape of the ends of the second adhesive sheet may be the same or different.

In Figures 3 to 6, the maximum distance L between the surface of the end of the second pressure-sensitive adhesive sheet and the side of the second optical film may be, for example, 2 μm or more, 4 μm or more, 5 μm or more, or even 7 μm or more. The upper limit of the maximum distance L may be 100 μm, 50 μm, 30 μm, 20 μm, or 15 μm. The maximum distance L means the maximum value of the distance between the side of the second pressure-sensitive adhesive sheet and the side of the second optical film in the direction perpendicular to the lamination direction of the optical laminate. By appropriately adjusting the maximum distance L, the reworkability can be further improved. The maximum distance L can be adjusted by adjusting conditions such as the thickness T ₂ of the second pressure-sensitive adhesive sheet, the storage modulus of the second pressure-sensitive adhesive sheet, the presence or absence of an oligomer contained in the pressure-sensitive adhesive composition (I), and the pressure when pressing the optical laminate.

[Image display device]
7 is a schematic cross-sectional view showing an example of an image display device. The image display device 20A in FIG. 7 includes a substrate 7, an image forming layer (for example, an organic EL layer or a liquid crystal layer) 6, and an optical laminate 10A. In detail, the image display device 20A has a laminated structure in which the substrate 7, the image forming layer 6, the second adhesive sheet 4, the second optical film 3, the first adhesive sheet 2, and the first optical film 1 are laminated in this order. The image display device 20A may have the optical laminates 10B to 10F shown in FIGS. 2 to 6 instead of the optical laminate 10A. The substrate 7 and the image forming layer 6 may have the same configuration as the substrate and the image forming layer of a known image display device, respectively.

The image display device 20A in FIG. 7 may be an organic EL display or a liquid crystal display. However, the image display device 11 is not limited to this example. The image display device 11 may be an electroluminescence (EL) display, a plasma display (PD), a field emission display (FED), or the like. The image display device 11 may be used for home appliance applications, in-vehicle applications, public information display (PID) applications, and the like.

The image display device may have any configuration as long as it includes the above-mentioned pressure-sensitive adhesive sheet and/or the above-mentioned optical laminate.

The image display device may be a narrow-frame image display device. An example of such an image display device is shown in FIG. 8. FIG. 8 is a cross-sectional view showing a schematic diagram of another example of an image display device. The image display device 20B in FIG. 8 has a laminated structure in which a substrate 7, an image forming layer 6, and an optical laminate 10A are laminated in this order. In detail, the image display device 20B has a laminated structure in which a substrate 7, an image forming layer 6, a second adhesive sheet 4, a second optical film 3, a first adhesive sheet 2, and a first optical film 1 are laminated in this order. As shown in FIG. 8, the image display device 20B has a similar configuration to the image display device 20A, except that there is a distance W between the side of the image forming layer 6 and the side of the optical laminate 10A. The image display device 20B may have the optical laminates 10B to 10F shown in FIG. 2 to FIG. 6 instead of the optical laminate 10A.

In the image display device 20B, the distance W between the side surface 6s of the image forming layer 6 and the side surface 10s of the optical laminate 10A is, for example, 5.0 mm or less, and may be 3.0 mm or less, 2.0 mm or less, 1.0 mm or less, 0.7 mm or less, 0.5 mm or less, 0.3 mm or less, 0.2 mm or less, or even 0.1 mm or less. The lower limit of the distance W is, for example, 0 mm. According to the image display device of this embodiment, since the image display device 20B includes the optical laminate 10A, it is possible to peel off the optical laminate 10A from the image forming layer 6 even when the frame is narrowed.

[Method for peeling off optical laminate]
Next, a method for peeling off the optical laminate from the image forming layer in the image display device will be described.

As described above, the image display device 20A has a structure in which, for example, the optical laminate 10A is laminated on the image forming layer 6. In the image display device 20A, peeling the optical laminate 10A from the image forming layer 6 includes, for example, (i) creating a trigger, and (ii) peeling the optical laminate 10A from the image forming layer 6 by manually pulling the trigger.

In step (i), the trigger is prepared, for example, by peeling the end of the optical laminate 10A from the image-forming layer 6. The trigger is prepared, for example, by inserting the tip of the blade of a rework jig such as a cutter knife or scraper between the optical laminate 10A and the image-forming layer 6. The preparation of the trigger is carried out, for example, at room temperature.

In step (ii), the optical laminate 10A is peeled off from the image-forming layer 6. The optical laminate 10A is peeled off from the image-forming layer 6 at, for example, room temperature.

9 is a schematic cross-sectional view showing an example of an image display device in which a trigger is created. As shown in FIG. 9, in the image display device 20C, when the tip of the blade of the rework jig is inserted between the optical laminate 10A and the image forming layer 6, a trigger 30a is created. In detail, when the tip of the blade of the rework jig is inserted between the second adhesive sheet 4 and the image forming layer 6, the end of the second adhesive sheet 4 is peeled off from the image forming layer 6, and the trigger 30a is created. The trigger 30a includes, for example, the end of the first optical film 1, the end of the first adhesive sheet 2, the end of the second optical film 3, and the end of the second adhesive sheet 4. Then, while holding the trigger 30a by hand, for example, by pulling the trigger 30a at an angle of 180° to the image forming layer 6, the optical laminate 10A can be peeled off from the image forming layer 6.

Note that in FIG. 9, a method for peeling off the optical laminate from the image forming layer is described for the image display device 20C in which the optical laminate 10A is laminated on the image forming layer 6, but a similar method can also be applied to image display devices in which the optical laminates 10B to 10F are laminated.

The present invention will be described in more detail below with reference to examples. The present invention is not limited to the examples shown below.

The correspondence between the abbreviations or names and the compounds shown in the following explanation is as follows.
BA: n-butyl acrylate BzA: benzyl acrylate PEA: phenoxyethyl acrylate AA: acrylate HBA: 4-hydroxybutyl acrylate ACMO: N-acryloylmorpholine AIBN: 2,2'-azobisisobutyronitrile C/L: trimethylolpropane/tolylene diisocyanate trimer adduct (isocyanate-based crosslinking agent, manufactured by Tosoh Corporation, Coronate L)
Peroxide: Benzoyl peroxide (Niper BMT, manufactured by NOF Corporation)
KBM-403: 3-glycidoxypropyltrimethoxysilane (a silane coupling agent having an epoxy group at the end, manufactured by Shin-Etsu Chemical Co., Ltd.)
SAT-10: polyether compound having a reactive silyl group (Kaneka Corporation, Silyl SAT10)

[Retardation film R1]
The retardation film R1 was a polycarbonate resin film (a stretched resin film, PureAce RM, manufactured by Teijin Ltd.) Both sides of the retardation film R1 had been subjected to a corona treatment in advance.

[Retardation film R2]
The retardation film R2 was prepared as follows.

(Preparation of First Retardation Film)
26.2 parts by weight of isosorbide (ISB), 100.5 parts by weight of 9,9-[4-(2-hydroxyethoxy)phenyl]fluorene (BHEPF), 10.7 parts by weight of 1,4-cyclohexanedimethanol (1,4-CHDM), 105.1 parts by weight of diphenyl carbonate (DPC), and 0.591 parts by weight of cesium carbonate (0.2% by weight aqueous solution) as a catalyst were charged into a reaction vessel and dissolved under a nitrogen atmosphere (about 15 minutes). At this time, the heat medium temperature of the reaction vessel was set to 150°C, and stirring was performed as necessary. Next, the pressure in the reaction vessel was reduced to 13.3 kPa, and the heat medium temperature was raised to 190°C in 1 hour. Phenol generated with the rise in the heat medium temperature was extracted outside the reaction vessel (hereinafter the same). Next, the temperature in the reaction vessel was held at 190 ° C. for 15 minutes, and then the pressure in the reaction vessel was changed to 6.67 kPa, and the heat medium temperature was raised to 230 ° C. in 15 minutes. When the stirring torque of the stirrer equipped in the reaction vessel increased, the heat medium temperature was raised to 250 ° C. in 8 minutes, and the pressure in the reaction vessel was set to 0.200 kPa or less. After reaching a predetermined stirring torque, the reaction was terminated, and the reaction product was extruded into water and pelletized. In this way, a polycarbonate resin having a composition of BHEPF / ISB / 1,4-CHDM = 47.4 mol% / 37.1 mol% / 15.5 mol% was obtained. The glass transition temperature of the obtained polycarbonate resin was 136.6 ° C., and the reduced viscosity was 0.395 dL / g.

The prepared polycarbonate resin pellets were vacuum-dried at 80°C for 5 hours, and then a long resin film with a thickness of 120 μm was obtained using a film-making device equipped with a single-screw extruder (manufactured by Isuzu Chemical Engineering Co., Ltd., screw diameter 25 mm, cylinder set temperature 220°C), a T-die (width 200 mm, set temperature 220°C), a chill roll (set temperature 120-130°C) and a winder. Next, the obtained resin film was stretched in the width direction by a tenter stretching machine at a stretching temperature of 137-139°C and a stretch ratio of 2.5 times to obtain a first retardation film.

(Preparation of Second Retardation Film)
20 parts by weight of a side-chain liquid crystal polymer (weight average molecular weight 5000) represented by the following chemical formula (I) (wherein 65 and 35 are the mol% of each constituent unit), 80 parts by weight of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF, trade name "Paliocolor LC242"), and 5 parts by weight of a photopolymerization initiator (manufactured by Ciba Specialty Chemicals, trade name "Irgacure 907") were dissolved in 200 parts by weight of cyclopentanone to prepare a liquid crystal coating solution. Next, the prepared liquid crystal coating solution was applied to the surface of a norbornene-based resin film (manufactured by Nippon Zeon, trade name "Zeonex"), which is a substrate film, using a bar coater, and then heated and dried at 80°C for 4 minutes to orient the liquid crystal contained in the coating film. Next, the coating film was cured by irradiation with ultraviolet light to form a liquid crystal solidified layer (thickness 0.58 μm) which is a second retardation film on the substrate film. The in-plane retardation Re of the liquid crystal solidified layer for light with a wavelength of 550 nm was 0 nm, and the retardation Rth in the thickness direction was −71 nm (nx=1.5326, ny=1.5326, nz=1.6550), and the liquid crystal solidified layer exhibited refractive index characteristics of nz>nx=ny.

(Preparation of Retardation Film R2)
One side of the first retardation film prepared above and the liquid crystal solidified layer of the second retardation film were bonded together via an adhesive to prepare a retardation film R2. In addition, in Examples 5A and 5B, the first adhesive sheet, the retardation film R2, and the second adhesive sheet were laminated in this order. That is, in Examples 5A and 5B, the first adhesive sheet, the first retardation film, the adhesive, the second retardation film, and the second adhesive sheet were laminated in this order. The surface of the first retardation film on which the first adhesive sheet was laminated had been subjected to a corona treatment in advance. The surface of the second retardation film on which the second adhesive sheet was laminated had not been subjected to a corona treatment.

The following describes the evaluation methods for the (meth)acrylic polymer, first adhesive sheet, second adhesive sheet, and optical laminate produced in the examples and comparative examples.

[Weight average molecular weight (Mw)]
The weight average molecular weight (Mw) of the (meth)acrylic polymer was evaluated by GPC under the following conditions.
Analytical device: Waters, Acquity APC
Column: Tosoh Corporation, G7000H _XL + GMH _XL + GMH _XL
Column temperature: 40°C
Eluent: Tetrahydrofuran (with added acid)
Flow rate: 0.8 mL/min Injection volume: 100 μL
Detector: differential refractometer (RI)
Standard sample: Polystyrene (PS) manufactured by Agilent

[Storage modulus G _A '(23°C)]
The storage modulus G _A '(23°C) of the first adhesive sheet at 23°C was evaluated by the following method. First, a measurement sample was prepared. The measurement sample was a disc-shaped punched out laminate in which a plurality of first adhesive sheets were laminated. The diameter of the bottom surface of the measurement sample was 8 mm, and the thickness of the measurement sample was 1 mm. Next, dynamic viscoelasticity measurement was performed on the measurement sample. ARES-G2 manufactured by TA Instruments was used for the dynamic viscoelasticity measurement. From the results of the dynamic viscoelasticity measurement, the storage modulus G _A ' of the first adhesive sheet at 23°C was determined. The conditions for the dynamic viscoelasticity measurement were as follows.
Measurement conditions Frequency: 1Hz
Deformation mode: Torsion Measurement temperature: -70℃ to 150℃
Heating rate: 5° C./min

[Storage modulus G _B ' (23°C)]
The storage modulus G _B ' at 23°C of the second PSA sheet was evaluated by the following method. First, a measurement sample was prepared. The measurement sample was a disc-shaped punched out laminate in which a plurality of second PSA sheets were laminated. The diameter of the bottom surface of the measurement sample was 8 mm, and the thickness of the measurement sample was 1 mm. Except for using this measurement sample, the storage modulus G _B ' (23°C) at 23°C of the second PSA sheet was determined by the same method as the above [Storage modulus G _A ' (23°C)].

[Measurement of Adhesion Strength F]
_F1 (23°C) and _F0 (23°C)
The optical laminates with release film according to the examples and comparative examples were cut to a size of 25 mm in width and 100 mm in length, the release film was peeled off, and the laminates were fixed to a soda glass plate (S200423, manufactured by Matsunami Glass Co., Ltd.) via double-sided tape (No. 500, manufactured by Nitto Denko Corporation) to produce optical laminate A with glass.

Next, a cutter blade was inserted between the first adhesive sheet and the second optical film (retardation film) in the glass-attached optical laminate A to create a trigger. After creating the trigger, the 90° peel adhesion was measured immediately. The 90° peel adhesion was measured using a tensile tester (device name: precision universal testing machine, Autograph AG-IS, manufactured by Shimadzu Corporation) at a peel angle of 90° and a tensile speed of 300 mm/min.

[Measurement of adhesive strength G]
・_G0 (23°C)
The optical laminate with the release film according to the examples and comparative examples was cut to a size of 25 mm wide and 100 mm long, the release film was peeled off, and the laminate was fixed to an alkali-free glass plate (Corning, EagleXG) to prepare an optical laminate with glass B. The glass-attached optical laminate B was placed in an autoclave at 50° C. and 5 atm (absolute pressure) for 15 minutes to homogenize the bonding between the second adhesive sheet and the alkali-free glass plate. The glass-attached optical laminate B was removed from the autoclave and allowed to stand for 20 minutes under conditions of 23° C. Thereafter, a cutter blade was immediately inserted between the second adhesive sheet and the alkali-free glass plate to prepare a trigger. After preparing the trigger, the 90° peel adhesion was measured immediately. The measurement conditions for the 90° peel adhesion were as described above.

・_G2 (23℃)
G ₂ (23° C.) was measured in the same manner as in the measurement of G ₀ (23° C.) above, except that the glass-attached optical laminate B was taken out of the autoclave and allowed to stand for 2 weeks under conditions of 23° C. and 55% RH.

_G0 (80°C)
The glass-attached optical laminate B was placed in an autoclave at 50° C. and 5 atm (absolute pressure) for 15 minutes to homogenize the bonding between the second adhesive sheet and the alkali-free glass plate. The glass-attached optical laminate B was removed from the autoclave and left to stand for 20 minutes under a condition of 23° C. Thereafter, the glass-attached optical laminate B was immediately placed on a hot plate set at 80° C. for 15 seconds so that the glass side of the glass-attached optical laminate B was in contact with the hot plate. Then, a cutter blade was immediately inserted between the second adhesive sheet and the alkali-free glass plate to prepare a trigger. After preparing the trigger, the 90° peel adhesion was measured immediately. The measurement conditions for the 90° peel adhesion were as described above.

_G2 (80°C)
G ₂ (80° C.) was measured in the same manner as G ₀ (80° C.), except that the glass-attached optical laminate B was taken out of the autoclave and allowed to stand for 2 weeks under conditions of 23° C. and 55% RH.

[Film thickness]
The thickness of the first adhesive sheet and the thickness of the second adhesive sheet were measured using a dial gauge (manufactured by Mitutoyo Corporation).

[Rework success rate at room temperature]
The reworkability (success rate of rework at room temperature) of the glass-attached optical laminate according to each Example and Comparative Example was evaluated by the following method. First, at room temperature (23°C), a part of the end of the optical laminate between the optical laminate and the glass was peeled off to prepare a trigger. In detail, the end of the optical laminate was peeled off from the glass between the second adhesive sheet and the glass to prepare a trigger. Next, for this glass-attached optical laminate, an attempt was made to peel the optical laminate from the glass by pulling the trigger at an angle of 180° to the glass while holding the trigger by hand at room temperature. At this time, the case where the second adhesive sheet did not remain on the glass and the optical laminate could be peeled off from the glass was evaluated as "success". The above evaluation was performed 10 times for each Example and Comparative Example, and the reworkability was evaluated as follows.
A: 100% success rate of rework at room temperature
B: The success rate of rework at room temperature is 80% or more and 90% or less. C: The success rate of rework at room temperature is 50% or more and 70% or less. D: The success rate of rework at room temperature is 40% or less.

[Success rate of creating an opportunity]
The success rate of the trigger creation in the glass-attached optical laminate was evaluated by the following method. At room temperature (23°C), the blade of a rework jig was inserted from the side of the glass-attached optical laminate to attempt the creation of a trigger. At this time, the case where the trigger was created by peeling the optical laminate from the glass at the end of the optical laminate between the second adhesive sheet and the glass was evaluated as "success". The above evaluation was performed 10 times for each example and comparative example, and the success rate of the trigger creation was evaluated as follows.
A: The success rate of creating a trigger is 80% or more. B: The success rate of creating a trigger is 60% to 70%. C: The success rate of creating a trigger is 40% to 50%. D: The success rate of creating a trigger is 30% or less.

[End processing]
An end-processing laminate was prepared by stacking 100 optical laminates with release films according to the examples and comparative examples. The end-processing laminate was fixed from above and below in the stacking direction of the end-processing laminate with a vice-like jig. In a state where the second adhesive sheet was pressed so as to protrude from the end edge of the end-processing laminate, the end-processing laminate was cut together with the second adhesive sheet by using a rotary blade 1.0 mm inward from the end edge of the end-processing laminate in a direction perpendicular to the stacking direction of the end-processing laminate. In this way, an optical laminate with a release film (hereinafter referred to as an "end-processed optical laminate") with the end processed was prepared. In Tables 3 to 5, "Y" indicates that end processing was performed, and "N" indicates that end processing was not performed.

[Measurement of maximum distance L]
The optical laminate with the end treatment was cut in a direction perpendicular to the lamination direction of the optical laminate, 1 cm inward from the end of the optical laminate and 5 cm wide to prepare a test piece for measurement. The test piece for measurement was placed on a stage so that the end faces vertically upward. The end was observed with a Keyence Corporation shape measuring laser microscope (VK9510) to measure the maximum distance L. In Example 9, the maximum distance L was measured by the above-mentioned method using an optical laminate with a release film that was not end-treated.

[Preparation of (meth)acrylic polymer A1]
A monomer mixture containing 79.9 parts by weight of butyl acrylate (BA), 15 parts by weight of benzyl acrylate (BzA), 5 parts by weight of acrylic acid (AA), and 0.1 parts by weight of 4-hydroxybutyl acrylate (HBA) was charged into a four-neck flask equipped with a stirring blade, a thermometer, a nitrogen gas introduction tube, and a cooler. Furthermore, 0.1 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) was charged together with ethyl acetate as a polymerization initiator for 100 parts by weight of the monomer mixture to prepare a reaction solution. After introducing nitrogen gas to replace the reaction solution with nitrogen while gently stirring it, the liquid temperature in the flask was kept at around 55°C and a polymerization reaction was carried out for 7 hours. Ethyl acetate was added to the solution after the polymerization reaction to adjust the solid content concentration to 30%, and a solution of (meth)acrylic polymer A1 was obtained.

[(Meth)acrylic polymers A2 and A3]
Solutions of (meth)acrylic polymers A2 and A3 were prepared in the same manner as for (meth)acrylic polymer A1, except that the monomers used were changed as shown in Table 1.

[Preparation of Pressure-Sensitive Adhesive Compositions B1 to B6]
Solvent-based pressure-sensitive adhesive compositions B1 to B6 were obtained by mixing a (meth)acrylic polymer, a crosslinking agent, and additives so as to obtain the compositions shown in Table 2. In Table 2, the units of blend amounts are parts by mass. The drying temperature indicates the drying temperature when a pressure-sensitive adhesive sheet is formed from the pressure-sensitive adhesive composition.

[Preparation of Polarizing Plate P1]
In the preparation of the polarizing plate P1, a polarizer was first prepared as follows. A long polyvinyl alcohol (PVA) resin film (manufactured by Kuraray Co., Ltd., product name "PE3000", thickness 30 μm) was uniaxially stretched in the longitudinal direction (total stretching ratio 5.9 times) using a roll stretching machine, and at the same time, the resin film was subjected to each treatment of swelling, dyeing, crosslinking, washing and drying in order to prepare a polarizer having a thickness of 12 μm. In the swelling treatment, the resin film was stretched 2.2 times while being treated with pure water at 20 ° C. In the dyeing treatment, the resin film was stretched 1.4 times while being treated with an aqueous solution at 30 ° C. containing iodine and potassium iodide in a weight ratio of 1:7. The iodine concentration in the aqueous solution was adjusted so that the single transmittance of the polarizer to be prepared was 45.0%. A two-stage process was adopted for the crosslinking treatment. In the first crosslinking treatment, the resin film was stretched 1.2 times while being treated with an aqueous solution at 40° C. in which boric acid and potassium iodide were dissolved. The aqueous solution used in the first crosslinking treatment had a boric acid content of 5.0% by weight and a potassium iodide content of 3.0% by weight. In the second crosslinking treatment, the resin film was stretched 1.6 times while being treated with an aqueous solution at 65° C. in which boric acid and potassium iodide were dissolved. The aqueous solution used in the second crosslinking treatment had a boric acid content of 4.3% by weight and a potassium iodide content of 5.0% by weight. A potassium iodide aqueous solution at 20° C. was used for the cleaning treatment. The potassium iodide content of the aqueous solution used in the cleaning treatment was 2.6% by weight. The drying treatment was performed under drying conditions of 70° C. and 5 minutes.

A triacetyl cellulose (TAC) film (Konica Minolta, product name "KC2UA", thickness 25 μm) was attached to each of the main surfaces of the polarizer prepared above using a polyvinyl alcohol-based adhesive. However, the TAC film attached to one of the main surfaces had a hard coat (thickness 7 μm) formed on the main surface opposite the polarizer side. In this way, a polarizing plate P1 was obtained that has a configuration of protective layer with hard coat/polarizer/protective layer (without hard coat).

[Preparation of optical laminate]
Example 1A
The adhesive composition B1 prepared above was applied to the release surface of a 38 μm thick polyethylene terephthalate (PET) film (Mitsubishi Chemical Polyester Film Corporation, MRF38), which is a release film with a silicone treatment applied to the release surface, so that the layer thickness after drying would be 12 μm, and the coating was dried at 155° C. for 1 minute to form a first adhesive sheet on the surface of the release film.

Next, the first adhesive sheet formed on the surface of the release film was transferred to the polarizing plate P1, and a polarizing plate with a first adhesive sheet was produced in which the release film, the first adhesive sheet, and the polarizing plate were laminated in this order. The release film was peeled off from the polarizing plate with the first adhesive sheet a to expose the first adhesive sheet. Then, a corona treatment was performed on the surface of the first adhesive sheet on which the polarizing plate was not formed, to produce a polarizing plate with a first adhesive sheet b. The corona output was 10 kJ/ ^m2 .

Separately, the adhesive composition B2 prepared above was applied to the release surface of a 38 μm thick polyethylene terephthalate (PET) film (Mitsubishi Chemical Polyester Film Corporation, MRF38), a release film with a silicone-treated release surface, so that the thickness of the layer after drying would be 15 μm, and the film was dried at 155° C. for 1 minute to form a second adhesive sheet on the surface of the release film.

Next, the second adhesive sheet formed on the surface of the release film was transferred to the retardation film R1 to produce a retardation film a with a second adhesive sheet, in which the release film, the second adhesive sheet, and the retardation film R1 were laminated in this order. Before transferring the second adhesive sheet to the retardation film R1, a corona treatment was performed on the surface of the retardation film R1 on which the second adhesive sheet was to be formed.

In the retardation film a with the second adhesive sheet, a corona treatment was performed on the surface (back surface) of the retardation film R1 on which the second adhesive sheet was not formed, to prepare a retardation film b with the second adhesive sheet. The corona output was 7 kJ/ ^m2 .

Then, the polarizing plate b with the first adhesive sheet and the retardation film b with the second adhesive sheet were combined so that the polarizing plate, the first adhesive sheet, the retardation film R1, the second adhesive sheet, and the release film were laminated in this order to prepare an optical laminate with a release film. After that, the release film was peeled off from the optical laminate with the release film to expose the second adhesive sheet, and an optical laminate according to Example 1A was obtained. Then, glass (alkali-free glass plate, Corning, EAGLE XG) was laminated on the surface of the second adhesive sheet on which the retardation film R1 was not laminated. The second adhesive sheet and the glass were bonded together by moving a 2 kg roller back and forth once. Next, the optical laminate with the glass bonded thereto was placed in an autoclave at 50° C. and 5 atm (absolute pressure) for 15 minutes to homogenize the bonding between the second adhesive sheet 4 and the alkali-free glass. In this way, an optical laminate with glass according to Example 1A was prepared. Note that in the optical laminate with glass according to Example 1A, the distance between the side of the glass and the side of the retardation film was within 0.5 mm.

(Examples 2A to 8A, 1B to 8B, Example 9, and Comparative Example 1)
Glass-attached optical laminates according to each of the examples and comparative examples were produced in the same manner as in Example 1A, using the first adhesive sheet, retardation film, and second adhesive sheet shown in the following Tables 3 to 5. However, in Examples 1B to 8B, Example 9, and Comparative Example 1, the corona treatment was not performed on the side of the first adhesive sheet on which the retardation film was not formed.

In Tables 9 to 11, "Rework" refers to the evaluation results of the above-mentioned [Success rate of rework at room temperature], and "Trigger" refers to the evaluation results of the above-mentioned [Success rate of trigger creation].

As shown in Tables 9 and 10, in each Example, an optical laminate with improved reworkability was obtained compared to the Comparative Examples. In addition, in each Example, the retardation film and polarizing plate did not break after the optical laminate was peeled off from the glass. On the other hand, in Comparative Example 1, the retardation film and polarizing plate broke after the optical laminate was peeled off from the glass.

The optical laminate of the present invention can be used, for example, in an image display device.

REFERENCE SIGNS LIST 1 First optical film 2 First adhesive sheet 3 Second optical film 4 Second adhesive sheet 5 Protective film 6 Image forming layer 7 Substrate 8 Base material 10A, 10B, 10C, 10D, 10E, 10F Optical laminate 11A, 11B, 11C, 11D Base material-attached optical laminate 20A, 20B, 20C Image display device 30a Start

Claims (11)

An optical laminate in which a first optical film, a first adhesive sheet, a second optical film, and a second adhesive sheet are laminated in this order,
The adhesion strength between the first pressure-sensitive adhesive sheet and the second optical film at 23° C. is defined as F(23° C.),
An optical laminate, wherein the initial adhesive strength between the second adhesive sheet and the non-alkali glass at 23° C. when the second adhesive sheet is attached to the non-alkali glass is defined as G ₀ (23° C.), and the following formula (1) is satisfied:
_G0 (23°C)/F(23°C)≦1.0 (1) The optical laminate according to claim 1, wherein a surface modification treatment is performed on the surface of the first adhesive sheet on which the second optical film is laminated. The optical laminate according to claim 2, wherein the surface modification treatment is a corona treatment. The optical laminate according to claim 1, wherein at least a portion of the end of the second adhesive sheet is located inside the side of the second optical film. The optical laminate according to claim 4, wherein the end of the second adhesive sheet has a curved surface that is convex inward when observed from a direction perpendicular to the lamination direction of the optical laminate. The optical laminate according to claim 4, wherein the maximum distance L between the surface of the end of the second adhesive sheet and the side surface of the second optical film in a direction perpendicular to the lamination direction of the optical laminate is 2 μm to 100 μm. The optical laminate according to claim 1 , wherein the thickness _T2 of the second adhesive sheet is 8 μm or more. The optical laminate according to claim 1 , wherein a thickness _T2 of the second pressure-sensitive adhesive sheet and a thickness _T1 of the first pressure-sensitive adhesive sheet satisfy _T2 / _T1 ≧1.1. The optical laminate according to claim 1, wherein the storage modulus G _A '(23°C) of the first pressure-sensitive adhesive sheet at 23°C and the storage modulus G _B '(23°C) of the second pressure-sensitive adhesive sheet at 23°C satisfy G _A '(23°C)/G _B '(23°C) ≧ 1.1. The optical laminate of claim 1, wherein when the second adhesive sheet is attached to alkali-free glass and left at 23°C for two weeks, the adhesive strength _G2 (23°C) at 23°C satisfies _G2 (23°C)/ _G0 (23°C)≦1.5. An image display device comprising the optical laminate according to any one of claims 1 to 10 and an image forming layer.

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