CN116413948A

CN116413948A - Optical laminate

Info

Publication number: CN116413948A
Application number: CN202211651967.7A
Authority: CN
Inventors: 藤田昌邦
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2021-12-23
Filing date: 2022-12-21
Publication date: 2023-07-11
Also published as: TW202335329A; KR20230096891A; JP2023094579A

Abstract

An optical laminate suitable for suppressing degradation of optical characteristics after repeated bending is provided. The optical laminate (X) of the present invention comprises an optical member (11), an adhesive layer (21), an optical member (12), an adhesive layer (22), and an optical member (13) in that order in the thickness direction (H). The optical members (11, 12) are bonded together by an adhesive layer (21). The optical members (12, 13) are bonded together by an adhesive layer (22). After repeated bending test at 25 ℃ under the 1 st bending condition of 180 DEG bending angle, 4mm bending outer diameter, 60 rounds/min bending speed and 10000 bending times, the 1 st ratio of the maximum thickness to the minimum thickness of the repeatedly bent portion in the test is 1.2 or less.

Description

Optical laminate

Technical Field

The present invention relates to an optical laminate.

Background

The display panel has a laminated structure including optical members such as a pixel panel, a polarizing plate, and a surface cover. In the manufacturing process of the display panel, a transparent adhesive layer is used for bonding optical members included in the laminated structure to each other. In addition, in the manufacturing process of the display panel, for example, an optical laminate forming a part of the laminated structure is manufactured in advance. Such an optical laminate is used in a manufacturing line of a display panel.

On the other hand, in smart phone applications and tablet terminal applications, display panels that can be repeatedly folded (foldable) have been developed. The foldable display panel is in particular repeatedly deformable between a curved shape and a flat non-curved shape. In such a foldable display panel, each optical member in the laminated structure is made in the form of an optical member that can be repeatedly bent. In the bonding between optical members, a thin adhesive layer is used. For example, patent document 1 below describes an optical laminate for flexible devices such as a foldable display panel.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2021-91117

Disclosure of Invention

Problems to be solved by the invention

In a bending portion of a foldable display panel, optical characteristics have been reduced by bending a plurality of times. Examples of the cause of the decrease in optical characteristics include peeling between the optical member and the pressure-sensitive adhesive layer. The decrease in optical characteristics is not preferable because it causes image defects in the display panel.

The present invention provides an optical laminate suitable for suppressing degradation of optical characteristics after repeated bending.

Solution for solving the problem

The invention [1] comprises an optical laminate comprising, in order in the thickness direction, a 1 st optical member, a 1 st adhesive layer, a 2 nd optical member, a 2 nd adhesive layer, and a 3 rd optical member, wherein the 1 st and 2 nd optical members are bonded by the 1 st adhesive layer, and the 2 nd and 3 rd optical members are bonded by the 2 nd adhesive layer, and after a repeated bending test at 25 ℃ based on a 1 st bending condition of 180 DEG bending angle, 4mm bending outer diameter, 60 rounds/min bending speed, and 10000 bending times, the 1 st ratio of the maximum thickness to the minimum thickness of the portion subjected to repeated bending in the test is 1.2 or less.

The invention [2] comprises the optical laminate of [1] above, wherein after the repeated bending test at 85 ℃ based on the bending condition of [1], the 2 nd ratio of the maximum thickness to the minimum thickness of the portion subjected to repeated bending in the test is 1.5 or less.

The invention [3] includes the optical laminate of [2] above, wherein the ratio of the 2 nd ratio to the 1 st ratio is 0.95 or more and 1.3 or less.

The invention [4] comprises an optical laminate having a 3 rd ratio of a maximum thickness to a minimum thickness of a portion subjected to repeated bending in a repeated bending test at 25 ℃ under a 2 nd bending condition of 180 DEG bending angle, 4mm bending outer diameter, 60 rounds/min bending speed and 50000 bending times of 1.3 or less.

The invention [5] comprises the optical laminate of [4] above, wherein after the repeated bending test at 85 ℃ based on the bending condition of [ 2 ], the 4 th ratio of the maximum thickness to the minimum thickness of the portion subjected to repeated bending in the test is 1.6 or less.

The invention [6] includes the optical laminate of [5] above, wherein the ratio of the 4 th ratio to the 3 rd ratio is 0.95 or more and 1.3 or less.

The invention [7] comprises an optical laminate having a 5 th ratio of a maximum thickness to a minimum thickness of a portion subjected to repeated bending in a repeated bending test at 25 ℃ under a 3 rd bending condition of 180 DEG bending angle, 3mm bending outer diameter, 60 rounds/min bending speed and 50000 bending times of 1.4 or less.

The invention [8] comprises the optical laminate of [7] above, wherein after the repeated bending test at 85 ℃ based on the 3 rd bending condition, the 6 th ratio of the maximum thickness to the minimum thickness of the portion subjected to repeated bending in the test is 1.7 or less.

The invention [9] includes the optical laminate of [8], wherein the ratio of the 6 th ratio to the 5 th ratio is 0.95 or more and 1.3 or less.

ADVANTAGEOUS EFFECTS OF INVENTION

The optical laminate of the present invention has a ratio 1 (maximum thickness/minimum thickness) of 1.2 or less after repeated bending test at 25℃under the 1 st bending condition (bending angle 180 DEG, bending outer diameter 4mm, bending speed 60 rounds/min, bending number 10000). Alternatively, the optical laminate of the present invention has a ratio of 3 rd (maximum thickness/minimum thickness) of 1.3 or less after repeated bending test at 25℃under the 2 nd bending condition (bending angle 180 DEG, bending outer diameter 4mm, bending speed 60 rounds/min, number of times of bending 50000). Alternatively, the optical laminate of the present invention has a ratio of 5 th (maximum thickness/minimum thickness) of 1.4 or less after repeated bending test at 25 ℃ under the 3 rd bending condition (bending angle 180 °, bending outer diameter 3mm, bending speed 60 rounds/min, number of times of bending 50000). The thickness variation of the optical laminate of the present invention after such a number of 180 ° bends of 10000 or 50000 times is small to the extent described above. Such an optical laminate is suitable for suppressing a decrease in optical characteristics after repeated bending.

Drawings

Fig. 1 is a schematic cross-sectional view of one embodiment of an optical stack of the present invention.

In fig. 2, a in fig. 2 shows a state in which the test piece is flat in the repeated bending test, and B in fig. 2 shows a state in which the test piece is bent in the repeated bending test.

Description of the reference numerals

X-ray laminate

11 optical component (1 st optical component)

12 optical component (2 nd optical component)

13 optical component (3 rd optical component)

21 adhesive layer (adhesive layer 1)

22 adhesive layer (adhesive layer 2)

H thickness direction

Detailed Description

As shown in fig. 1, an optical laminate X, which is an embodiment of the optical laminate of the present invention, includes

optical members

11, 12, 13 and

adhesive layers

21, 22. Specifically, the optical laminate X includes, in order in the thickness direction H, an optical member 11 (1 st optical member), an adhesive layer 21 (1 st adhesive layer), an optical member 12 (2 nd optical member), an adhesive layer 22 (2 nd adhesive layer), and an optical member 13 (3 rd optical member). The optical laminate X has a sheet shape of a predetermined thickness, and extends in a direction (plane direction) orthogonal to the thickness direction H. The

optical members

11, 12 are bonded to each other by an adhesive layer 21. The

optical members

12, 13 are joined by an adhesive layer 22.

The optical laminate X is an optically transparent laminate. The optical layered body X is disposed at a light passing portion of the flexible device. As the flexible device, for example, a flexible display panel can be cited. Examples of the flexible display panel include a foldable display panel and a rollable display panel. The

optical members

11, 12, 13 are optical members incorporated into the flexible device, respectively. The

optical members

11, 12, 13 are each a repeatedly bendable film-like optical member.

After the repeated bending test at 25 ℃ based on the 1 st bending condition, the ratio R1 (1 st ratio) of the maximum thickness to the minimum thickness of the portion (bent portion P described later) subjected to repeated bending in the test is 1.2 or less. The 1 st bending condition is a condition of a bending angle of 180 °, a bending outer diameter of 4mm, a bending speed of 60 rounds/min, and a bending number of 10000. In the repeated bending test, the optical laminate X is bent with the 1 st optical member side as the bending inner side or the bending outer side (the same applies to the repeated bending test under other conditions described later). The repeated bending test can be performed by, for example, a U-shaped expansion and contraction tester (manufactured by YUASASYSTEM co., ltd.).

Fig. 2 a and 2B schematically show a trial and error of bending at a bending angle of 180 °. In the repeated bending test, both ends of the test piece S of the optical laminate X were fixed to the grip portions C1 and C2 of the tester. In the repeated bending test, a series of processes including the 1 st process and the 2 nd process is referred to as 1 cycle (1 round trip). In the 1 st procedure, the test piece S was bent from a flat shape to a U-shape. In the 2 nd process, the test piece S was returned to the flat shape after the 1 st process. The bending outer diameter of the test piece can be adjusted by adjusting the distance between the two ends of the test piece S when the U-shape is formed. After the repeated bending test, the minimum thickness and the maximum thickness of the bent portion P (indicated by cross hatching) in which the repeated bending was performed in the test piece S were measured. The method of the repeated bending test is specifically described in examples described below.

The ratio R1 (maximum thickness/minimum thickness) of the bent portion P after a plurality of 180 ° bends of the optical laminate X10000 times as described above is suppressed to a range of 1.2 or less. Such an optical laminate X is suitable for suppressing a decrease in optical characteristics after repeated bending. Specifically, examples described below are shown. The ratio R1 is preferably 1.15 or less, more preferably 1.1 or less, from the viewpoint of suppressing the reduction of the optical characteristics of the optical laminate X after repeated bending. The ratio R1 is, for example, 0.9 or more, preferably 1.00 or more, more than 1.00 or 1.05 or more.

After the repeated bending test at 85 ℃ based on the 1 st bending condition, the ratio R2 (2 nd ratio) of the maximum thickness to the minimum thickness of the bent portion P subjected to repeated bending in the test is preferably 1.5 or less, more preferably 1.4 or less, still more preferably 1.3 or less, and particularly preferably 1.0 from the viewpoint of suppressing the decrease in optical characteristics after repeated bending of the optical laminate X in a high-temperature environment. The ratio R2 is, for example, 0.9 or more, preferably 1.00 or more, more than 1.00 or 1.05 or more. The ratio (R2/R1) of the ratio R2 to the ratio R1 is preferably 0.95 or more, more preferably 0.98 or more, and further preferably 1.3 or less, more preferably 1.2 or less, more preferably 1.1 or less, particularly preferably 1.0.

In the present embodiment, after the repeated bending test at 25 ℃ based on the 2 nd bending condition, the ratio R3 (3 rd ratio) of the maximum thickness to the minimum thickness of the bent portion P subjected to repeated bending in the test is 1.3 or less. The 2 nd bending condition is a condition of a bending angle of 180 °, a bending outer diameter of 4mm, a bending speed of 60 rounds/min, and a number of bending times of 50000. In the optical laminate X, the ratio R3 of the bent portion P after a plurality of 180 ° bends of 50000 times is suppressed to a range of 1.3 or less. Therefore, the optical laminate X is suitable for suppressing degradation of optical characteristics after repeated bending. Specifically, examples described below are shown. The ratio R3 is preferably 1.25 or less, more preferably 1.2 or less, from the viewpoint of suppressing the reduction of the optical characteristics after repeated bending of the optical laminate X. The ratio R3 is, for example, 0.9 or more, preferably 1.00 or more, more than 1.00 or 1.05 or more.

After the repeated bending test at 85 ℃ based on the 2 nd bending condition, the ratio R4 (4 th ratio) of the maximum thickness to the minimum thickness of the bent portion P subjected to repeated bending in the test is preferably 1.6 or less, more preferably 1.5 or less, and even more preferably 1.4 or less from the viewpoint of suppressing the decrease in optical characteristics after repeated bending of the optical laminate X in a high-temperature environment. The ratio R4 is, for example, 0.9 or more, preferably 1.00 or more, more than 1.00 or 1.05 or more. The ratio (R4/R3) of the ratio R4 to the ratio R3 is preferably 0.95 or more, more preferably 0.98 or more, and further preferably 1.3 or less, more preferably 1.2 or less, and further preferably 1.15 or less.

In the present embodiment, after the repeated bending test at 25 ℃ under the 3 rd bending condition, the ratio R5 (5 th ratio) of the maximum thickness to the minimum thickness of the bent portion P subjected to repeated bending in the test is 1.4 or less. The 3 rd bending condition is a condition of a bending angle of 180 °, a bending outer diameter of 3mm, a bending speed of 60 rounds/min, and a number of bending times of 50000. The ratio R5 of the bent portion P after 50000 times of 180 DEG bending (the bending outer diameter is 3 mm) of the optical laminate X is suppressed to a range of 1.4 or less. Therefore, the optical laminate X is suitable for suppressing degradation of optical characteristics after repeated bending. Specifically, the method is described in examples described later. The ratio R5 is preferably 1.3 or less, more preferably 1.2 or less, from the viewpoint of suppressing the reduction of the optical characteristics of the optical laminate X after repeated bending. The ratio R5 is, for example, 0.9 or more, preferably 1.00 or more, more than 1.00 or 1.05 or more.

After the repeated bending test at 85 ℃ based on the 3 rd bending condition, the ratio R6 (6 th ratio) of the maximum thickness to the minimum thickness of the bent portion P subjected to repeated bending in the test is preferably 1.7 or less, more preferably 1.6 or less, and even more preferably 1.5 or less, from the viewpoint of suppressing the decrease in optical characteristics after repeated bending of the optical laminate X in a high-temperature environment. The ratio R6 is, for example, 0.9 or more, preferably 1.00 or more, more than 1.00 or 1.05 or more. The ratio (R6/R5) of the ratio R6 to the ratio R5 is preferably 0.95 or more, more preferably 0.98 or more, and further preferably 1.3 or less, more preferably 1.25 or less, and further preferably 1.2 or less.

Examples of the method for adjusting the ratios R1 to R6 include adjustment of the adhesive force of the

adhesive layers

21 and 22, adjustment of the shear storage modulus, and adjustment of the thickness. Examples of the method for adjusting the adhesive force of the adhesive layer include selection of the type of the base polymer in the adhesive layer, adjustment of the molecular weight, and adjustment of the blending amount. The selection of the kind of the base polymer includes selection of the kind of the main chain of the base polymer, selection of the kind of the functional group, and adjustment of the amount. The method for adjusting the adhesive force of the adhesive layer includes selection of the types of components other than the base polymer in the adhesive layer and adjustment of the blending amount of the components. Examples of the component include a crosslinking agent, a silane coupling agent, and an oligomer. Examples of the method for adjusting the shear storage modulus of the pressure-sensitive adhesive layer include selection of the type of the base polymer in the pressure-sensitive adhesive layer, adjustment of the molecular weight, adjustment of the blending amount, selection of the type of the crosslinking agent for crosslinking the base polymer, and adjustment of the blending amount.

The optical member 11 is a base film in the present embodiment. Examples of the base film include a resin film, a glass film, and a metal film. Examples of the material of the resin film include polyester, polyolefin, polyimide (PI), polyamide, cellulose, modified cellulose, polystyrene, and polycarbonate. Examples of the polyester include polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate. Examples of the polyolefin include polyethylene, polypropylene, and cycloolefin polymer (COP). Examples of the polyamide include polyamide 6, and partially aromatic polyamide. As the modified cellulose, for example, cellulose Triacetate (TAC) is cited. These resin materials may be used alone or in combination of two or more. Examples of the material of the glass thin film include aluminosilicate glass, soda lime glass, borosilicate glass, and aluminoborosilicate glass. These glass materials may be used alone or in combination of two or more. Examples of the material of the metal thin film include stainless steel, iron, copper, aluminum, magnesium, nickel, zinc, chromium, and titanium. These metal materials may be used alone or in combination of two or more. The optical member 11 may be a base film that functions as a transparent cover film disposed on the visual recognition side of the display panel.

The thickness of the optical member 11 is preferably 10 μm or more, more preferably 20 μm or more, from the viewpoint of securing the supporting function by the optical member 11. The thickness of the optical member 11 is preferably 100 μm or less, more preferably 75 μm or less, from the viewpoint of thinning the optical laminate X.

The optical member 12 is a functional optical member in the present embodiment. Examples of the functional optical member include a polarizing plate (polarizing film) in the form of a film and a retardation plate. The functional optical member is preferably a film-like functional optical member. Examples of such an optical member include a polarizing plate (polarizing film) in a film form and a retardation film.

Examples of the polarizing film include a hydrophilic polymer film subjected to dyeing treatment with a dichroic substance and subsequent stretching treatment. Examples of the dichroic material include iodine and dichroic dyes. Examples of the hydrophilic polymer film include a polyvinyl alcohol (PVA) film, a partially formalized PVA film, and a partially saponified film of an ethylene-vinyl acetate copolymer. The polarizing film may be a polyene oriented film. Examples of the material of the polyene oriented film include a dehydrated product of PVA and a desalted product of polyvinyl chloride. The polarizing film may have a protective film bonded to one surface in the thickness direction and/or the other surface with an adhesive. The thickness of the optical member 12 as the polarizing film is preferably 1 μm or more, more preferably 5 μm or more from the viewpoint of securing the function and strength of the optical member 12. The thickness of the optical member 12 as the polarizing film is preferably 50 μm or less, more preferably 35 μm or less from the viewpoint of thinning the optical laminate X.

Examples of the retardation film include a λ/2 wavelength film, a λ/4 wavelength film, and a viewing angle compensation film. Examples of the material of the retardation film include a polymer film which is birefringent by stretching. Examples of the polymer film include a cellulose film and a polyester film. Examples of the cellulose film include cellulose triacetate film. Examples of the polyester film include polyethylene terephthalate film and polyethylene naphthalate film. As the retardation film, a film having a substrate such as a cellulose film and an alignment layer of a liquid crystal compound such as a liquid crystalline polymer on the substrate can be preferably used. The thickness of the optical member 12 as the retardation film is preferably 1 μm or more, more preferably 2 μm or more, from the viewpoint of securing the function and strength of the optical member 12. The thickness of the optical member 12 as the retardation film is preferably 50 μm or less, more preferably 40 μm or less, from the viewpoint of thinning the optical laminate X.

The optical member 13 is a thin film-like pixel panel in the present embodiment. Examples of the pixel panel include an organic EL panel and a liquid crystal panel. The thickness of the optical member 13 is preferably 10 μm or more, more preferably 20 μm or more, from the viewpoint of securing the function of the optical member 13. The thickness of the optical member 13 is preferably 150 μm or less, more preferably 100 μm or less, from the viewpoint of thinning the optical laminate X.

The adhesive layer 21 is a pressure-sensitive adhesive layer formed of the 1 st adhesive composition. The adhesive layer 21 is an optically transparent adhesive layer (optical adhesive layer). The 1 st adhesive composition contains at least a base polymer.

The base polymer is an adhesive component that causes the adhesive layer 21 to exhibit adhesiveness. Examples of the base polymer include acrylic polymers, silicone polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyvinyl ether polymers, vinyl acetate/vinyl chloride copolymers, modified polyolefin polymers, epoxy polymers, fluoropolymers, and rubber polymers. The base polymer may be used alone or in combination of two or more. From the viewpoint of ensuring good transparency and adhesion of the adhesive layer 21, an acrylic polymer is preferable as the base polymer.

The acrylic polymer is a copolymer containing a monomer component of a (meth) acrylic acid ester in a proportion of 50 mass% or more. "(meth) acrylic" refers to acrylic and/or methacrylic.

As the (meth) acrylic acid ester, an alkyl (meth) acrylate is preferably used, and an alkyl (meth) acrylate having an alkyl group of 1 to 20 carbon atoms is more preferably used. The alkyl (meth) acrylate may have a linear or branched alkyl group, or may have a cyclic alkyl group such as an alicyclic alkyl group.

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

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

From the viewpoint of obtaining the balance between the soft property and the adhesive force required for the adhesive layer for flexible device use in the adhesive layer 21, at least one selected from alkyl (meth) acrylates having an alkyl group having 3 to 15 carbon atoms is preferably used, more preferably an alkyl (meth) acrylate having a relatively small carbon number selected from alkyl (meth) acrylates having an alkyl group having 3 to 15 carbon atoms, and an alkyl (meth) acrylate having a relatively large carbon number selected from alkyl (1) (meth) acrylates having an alkyl group having 3 to 15 carbon atoms, and more preferably an alkyl (2) (meth) acrylate having an alkyl group having a relatively large carbon number, more preferably an alkyl (meth) acrylate having an alkyl group having 4 to 8 carbon atoms and an alkyl (meth) acrylate having an alkyl group having 9 to 13 carbon atoms, and even more preferably an alkyl (meth) acrylate having a linear alkyl group having a carbon number of 4 to 8.

The proportion of the alkyl (meth) acrylate in the monomer component is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more, from the viewpoint of appropriately exhibiting basic characteristics such as adhesiveness in the adhesive layer 21. The ratio is, for example, 99 mass% or less. When the 1 st and 2 nd alkyl (meth) acrylates are used in combination, the proportion of the 1 st alkyl (meth) acrylate in the monomer component is preferably 40% by mass or more, more preferably 50% by mass or more, and further preferably 70% by mass or less, more preferably 60% by mass or less, from the viewpoint of balance between the soft property and the adhesive force of the adhesive layer 21. The proportion of the 2 nd alkyl (meth) acrylate in the monomer component is preferably 20 mass% or more, more preferably 30 mass% or more, and further preferably 50 mass% or less, more preferably 45 mass% or less, from the viewpoint of balance between the soft nature of the adhesive layer 21 and the adhesive force.

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

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

The proportion of the hydroxyl group-containing monomer in the monomer component is preferably 0.1% by mass or more, more preferably 1% by mass or more, and still more preferably 2% by mass or more, from the viewpoints of introduction of the crosslinked structure into the acrylic polymer and securing of cohesive force of the adhesive layer 21. The proportion is preferably 20 mass% or less, more preferably 10 mass% or less, from the viewpoint of adjustment of the polarity of the acrylic polymer (regarding compatibility of various additive components in the adhesive layer 21 and the acrylic polymer).

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

The proportion of the carboxyl group-containing monomer in the monomer component is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and still more preferably 0.8 mass% or more from the viewpoints of introduction of the crosslinked structure into the acrylic polymer, securing of the cohesive force of the adhesive layer 21, and securing of the adhesion force of the adhesive layer 21 to the adherend. The ratio is preferably 10 mass% or less, more preferably 5 mass% or less, from the viewpoint of adjustment of the glass transition temperature of the acrylic polymer and avoidance of corrosion risk of the adherend by acid.

Examples of the monomer having a nitrogen atom-containing ring include: n-vinyl-2-pyrrolidone, N-methyl vinyl pyrrolidone, N-vinyl pyridine, N-vinyl piperidone, N-vinyl pyrimidine, N-vinyl piperazine, N-vinyl pyrazine, N-vinyl pyrrole, N-vinyl imidazole, N-vinyl oxazole, N- (meth) acryl-2-pyrrolidone, N- (meth) acryl piperidine, N- (meth) acryl pyrrolidine, N-vinyl morpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1, 3-oxazin-2-one, N-vinyl-3, 5-morpholinedione, N-vinyl pyrazole, N-vinyl isoxazole, N-vinyl thiazole, and N-vinyl isothiazole.

The proportion of the monomer having a nitrogen atom-containing ring in the monomer component is preferably 1% by mass or more, more preferably 3% by mass or more, and still more preferably 5% by mass or more, from the viewpoints of ensuring the cohesive force of the adhesive layer 21 and ensuring the adhesion force of the adhesive layer 21 to the adherend. The ratio is preferably 30 mass% or less, more preferably 20 mass% or less, from the viewpoints of adjustment of the glass transition temperature of the acrylic polymer and adjustment of the polarity of the acrylic polymer (regarding compatibility of various additive components in the adhesive layer 21 and the acrylic polymer).

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

The monomer component preferably contains an alkyl (meth) acrylate 1 (alkyl group having a relatively small carbon number), an alkyl (meth) acrylate 2 (alkyl group having a relatively large carbon number), a hydroxyl group-containing monomer, and a monomer having a nitrogen atom-containing ring, from the viewpoint of both securing the adhesive force of the adhesive layer 21 and suppressing the occurrence of stress during deformation. The 1 st alkyl (meth) acrylate is preferably an alkyl (meth) acrylate having an alkyl group having 4 to 8 carbon atoms, more preferably an alkyl (meth) acrylate having a linear alkyl group having 4 to 8 carbon atoms, and still more preferably at least one selected from the group consisting of 2-ethylhexyl acrylate (2 EHA) and n-Butyl Acrylate (BA). The 2 nd alkyl (meth) acrylate is preferably an alkyl (meth) acrylate having an alkyl group of 9 or more carbon atoms, and more preferably Lauryl Acrylate (LA). The hydroxyl group-containing monomer is preferably at least one selected from the group consisting of 4-hydroxybutyl acrylate (4 HBA) and 2-hydroxyethyl acrylate (2 HEA). The monomer having a nitrogen atom-containing ring is preferably N-vinyl-2-pyrrolidone (NVP).

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

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

Examples of the isocyanate crosslinking agent include toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate. Further, as the isocyanate crosslinking agent, derivatives of these isocyanates can be mentioned. Examples of the isocyanate derivative include isocyanurate modified products and polyol modified products. Examples of the commercial products of the isocyanate crosslinking agent include CORONATE L (trimethylolpropane adduct of toluene diisocyanate, east Cao Zhizao), CORONATE HL (trimethylolpropane adduct of hexamethylene diisocyanate, east Cao Zhizao), CORONATE HX (isocyanurate of hexamethylene diisocyanate, east Cao Zhizao), TAKENATE D N (trimethylolpropane adduct of xylylene diisocyanate, manufactured by three-well chemical), and TAKENATE 600 (1, 3-bis (isocyanatomethyl) cyclohexane, manufactured by three-well chemical).

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

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

Isocyanate crosslinking agents (particularly difunctional isocyanate crosslinking agents) and peroxide crosslinking agents are preferable from the viewpoint of ensuring the flexibility of the adhesive layer 21. The isocyanate crosslinking agent (particularly, trifunctional isocyanate crosslinking agent) is preferable from the viewpoint of securing durability of the adhesive layer 21. In the base polymer, the difunctional isocyanate crosslinker and the peroxide crosslinker form softer two-dimensional crosslinks, while the trifunctional isocyanate crosslinker forms stronger three-dimensional crosslinks. From the viewpoint of achieving both durability and flexibility of the adhesive layer 21, it is preferable to use a trifunctional isocyanate crosslinking agent in combination with a peroxide crosslinking agent and/or a difunctional isocyanate crosslinking agent.

The amount of the crosslinking agent blended in the method 1 is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and still more preferably 0.2 parts by mass or more, relative to 100 parts by mass of the base polymer, from the viewpoint of securing cohesive force of the adhesive layer 21. From the viewpoint of ensuring good tackiness of the adhesive layer 21, the amount of the crosslinking agent to be blended is, for example, 5 parts by mass or less, preferably 3 parts by mass or less, and more preferably 2 parts by mass or less, per 100 parts by mass of the base polymer.

In the method 2, the monomer component (including a monofunctional monomer and a polyfunctional monomer for introducing a crosslinked structure) may be polymerized at one time or in multiple stages. In the multistage polymerization method, first, a monofunctional monomer is polymerized (prepolymerized), thereby producing a prepolymer composition containing a part of a polymer (a mixture of a polymer having a low degree of polymerization and an unreacted monomer). Next, after adding a polyfunctional monomer as a crosslinking agent to the prepolymer composition, a part of the polymer is polymerized with the polyfunctional monomer (main polymerization).

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

Examples of the multifunctional (meth) acrylate include difunctional (meth) acrylate, trifunctional (meth) acrylate, and multifunctional (meth) acrylate having four or more functions.

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

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

Examples of the polyfunctional (meth) acrylate having four or more functions include di (trimethylolpropane) tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol monohydroxypenta (meth) acrylate, alkyl-modified dipentaerythritol penta (meth) acrylate, and dipentaerythritol hexa (meth) acrylate.

For the polyfunctional (meth) acrylate as the crosslinking agent, a difunctional (meth) acrylate is preferably used, more preferably 1, 6-hexanediol di (meth) acrylate, and further preferably 1, 6-hexanediol dimethacrylate.

The blending amount of the polyfunctional monomer as the crosslinking agent in method 2 in the monomer component is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.07 parts by mass or more relative to 100 parts by mass of the monofunctional monomer from the viewpoint of securing the cohesive force of the adhesive layer 21. The blending amount of the polyfunctional monomer is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and still more preferably 1 part by mass or less relative to 100 parts by mass of the monofunctional monomer, from the viewpoint of securing good tackiness of the pressure-sensitive adhesive layer 21.

The acrylic polymer can be formed by polymerizing the above monomer components. Examples of the polymerization method include solution polymerization, photopolymerization in the absence of a solvent (for example, UV polymerization), bulk polymerization, and emulsion polymerization. As the solvent for the solution polymerization, for example, ethyl acetate and toluene are used. As the initiator for polymerization, for example, a thermal polymerization initiator and a photopolymerization initiator are used. The polymerization initiator may be used alone or in combination of two or more. The amount of the polymerization initiator to be used is preferably 0.05 parts by mass or more, more preferably 0.08 parts by mass or more, still more preferably 0.1 parts by mass or more, and further preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, still more preferably 0.3 parts by mass or less, based on 100 parts by mass of the monomer component.

Examples of the thermal polymerization initiator include azo polymerization initiators and peroxide polymerization initiators. Examples of the azo polymerization initiator include 2,2' -Azobisisobutyronitrile (AIBN), 2' -azobis-2-methylbutyronitrile, dimethyl 2,2' -azobis (2-methylpropionate), 4' -azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2' -azobis (2-amidinopropane) dihydrochloride, 2' -azobis [2- (5-methyl-2-imidazolin-2-yl) propane ] dihydrochloride, 2' -azobis (2-methylpropionamidine) disulfate, and 2,2' -azobis (N, N ' -dimethyleneisobutyl amidine) dihydrochloride. Examples of the peroxide polymerization initiator include dibenzoyl peroxide, t-butyl peroxymaleate, and lauroyl peroxide.

Examples of the photopolymerization initiator 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, benzil-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators.

The weight average molecular weight of the base polymer is preferably 10 ten thousand or more, more preferably 30 ten thousand or more, and still more preferably 50 ten thousand or more from the viewpoint of securing cohesive force of the adhesive layer 21. The weight average molecular weight of the base polymer is preferably 300 ten thousand or less, more preferably 250 ten thousand or less, and further preferably 200 ten thousand or less from the viewpoint of securing flexibility of the adhesive layer 21. The weight average molecular weight of the base polymer was measured by Gel Permeation Chromatography (GPC) and calculated by conversion to polystyrene.

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

As the glass transition temperature (Tg) of the base polymer, a glass transition temperature (theoretical value) obtained based on the following Fox formula can be used. The Fox formula is a relation between the glass transition temperature Tg of the polymer and the glass transition temperature Tgi of the homopolymer of the monomers constituting the polymer. In the following Fox formula, tg represents the glass transition temperature (. Degree. C.) of the polymer, wi represents the weight fraction of the monomer i constituting the polymer, tgi represents the glass transition temperature (. Degree. C.) of the homopolymer formed from the monomer i. For the glass transition temperature of the homopolymer, literature values can be used. For example, glass transition temperatures of various homopolymers are listed in "Polymer Handbook" (4 th edition, john Wiley & Sons, inc., 1999) and "synthetic resin entrance to New Polymer library 7 paint" (North Korea, polymer journal, congress, 1995). On the other hand, the glass transition temperature of a homopolymer of a monomer can be obtained by a method specifically described in JP-A2007-51271.

Fox 1/(273+tg) =Σ [ Wi/(273+tgi) ]

The adhesive composition may comprise an oligomer on the basis of a base polymer. When an acrylic polymer is used as the base polymer, an acrylic oligomer is preferably used as the oligomer. The oligomers may be used alone or in combination of two or more.

The acrylic oligomer is a copolymer containing a monomer component of an alkyl (meth) acrylate in a proportion of 50 mass% or more. The monomer component may contain a copolymerizable monomer copolymerizable with the alkyl (meth) acrylate. Examples of the alkyl (meth) acrylate include the alkyl (meth) acrylates described above for the acrylic polymer. Examples of the copolymerizable monomer include the copolymerizable monomers (polar group-containing monomers and the like) described above for the acrylic polymer. The acrylic oligomer is preferably a copolymer of an alkyl (meth) acrylate having 3 to 8 carbon atoms as an alkyl group and a polar group-containing monomer. The alkyl (meth) acrylate is more preferably n-butyl (meth) acrylate, and still more preferably n-butyl acrylate. The polar group-containing monomer is preferably a carboxyl group-containing monomer, more preferably acrylic acid. The proportion of the alkyl (meth) acrylate in the monomer component of the acrylic oligomer is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more. The ratio is, for example, 99 mass% or less.

The acrylic oligomer may be formed by polymerizing the monomer components of the acrylic oligomer. Examples of the polymerization method include solution polymerization, photopolymerization in the absence of a solvent (for example, UV polymerization), bulk polymerization, and emulsion polymerization. As the solvent for the solution polymerization, for example, ethyl acetate and toluene are used. In the polymerization of the acrylic oligomer, a polymerization initiator may be used, or a chain transfer agent may be used for the purpose of adjusting the molecular weight. As the initiator for polymerization, for example, a thermal polymerization initiator and a photopolymerization initiator are used. The amount of the polymerization initiator to be used is preferably 0.05 parts by mass or more, more preferably 0.08 parts by mass or more, and further preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, based on 100 parts by mass of the monomer component.

The weight average molecular weight of the acrylic oligomer is preferably 1000 or more, more preferably 1500 or more, and even more preferably 2000 or more from the viewpoint of securing cohesive force of the adhesive layer 21. The molecular weight is preferably 30000 or less, more preferably 10000 or less, and further preferably 8000 or less, from the viewpoint of securing flexibility of the adhesive layer 21.

The content of the acrylic oligomer in the 1 st adhesive composition is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and still more preferably 35 parts by mass or more, based on 100 parts by mass of the base polymer, in order to sufficiently improve the adhesive force of the adhesive layer 21. On the other hand, from the viewpoint of ensuring transparency of the adhesive layer 21, the content of the acrylic oligomer in the adhesive layer 21 is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, relative to 100 parts by mass of the base polymer. When the content of the acrylic oligomer in the pressure-sensitive adhesive layer 21 is too large, the compatibility of the acrylic oligomer decreases, and haze increases and transparency tends to decrease.

The 1 st adhesive composition may contain other components as needed. Examples of the other component include a silane coupling agent, a solvent, a thickener, a plasticizer, a softener, an antioxidant, a filler, a colorant, an ultraviolet absorber, a surfactant, and an antistatic agent. Examples of the solvent include a polymerization solvent used when polymerizing an acrylic polymer or an acrylic oligomer, and a solvent added to a polymerization reaction solution after polymerization. As such a solvent, for example, ethyl acetate and toluene are used.

The thickness of the pressure-sensitive adhesive layer 21 is preferably 10 μm or more, more preferably 15 μm or more, from the viewpoint of securing sufficient adhesion to the

optical members

11, 12. The thickness of the pressure-sensitive adhesive layer 21 is preferably 300 μm or less, more preferably 200 μm or less, still more preferably 100 μm or less, and particularly preferably 50 μm or less, from the viewpoint of thinning the flexible device.

The haze of the pressure-sensitive adhesive layer 21 is preferably 3% or less, more preferably 2% or less, and still more preferably 1% or less. The haze of the adhesive layer 21 can be measured using a haze meter based on JIS K7136 (year 2000). Examples of the haze meter include "NDH2000" manufactured by Nippon electric color industry Co., ltd., and "HM-150" manufactured by Toku Kogyo Co., ltd.

The total light transmittance of the adhesive layer 21 is preferably 60% or more, more preferably 80% or more, and still more preferably 85% or more. The total light transmittance of the adhesive layer 21 is, for example, 100% or less. The total light transmittance of the adhesive layer 21 can be measured based on JIS K7375 (2008).

The adhesive layer 22 is a pressure-sensitive adhesive layer formed of the 2 nd adhesive composition. The adhesive layer 22 is an optical adhesive layer. The 2 nd adhesive composition contains at least a base polymer. The base polymer contained in the 2 nd adhesive composition includes, for example, the base polymer described above for the 1 st adhesive composition. The base polymer in the 1 st adhesive composition may be the same as or different from the base polymer in the 2 nd adhesive composition. The 2 nd adhesive composition may also contain components other than the base polymer. Examples of the component contained in the 2 nd adhesive composition include components other than the base polymer described above for the 1 st adhesive composition. The composition of the 1 st adhesive composition and the composition of the 2 nd adhesive composition may be the same or different.

The thickness of the adhesive layer 22 is preferably 10 μm or more, more preferably 15 μm or more, from the viewpoint of ensuring sufficient adhesion to the

optical members

12, 13. The thickness of the pressure-sensitive adhesive layer 22 is preferably 300 μm or less, more preferably 200 μm or less, still more preferably 100 μm or less, and particularly preferably 50 μm or less, from the viewpoint of thinning the flexible device.

The haze of the adhesive layer 22 is preferably 3% or less, more preferably 2% or less, and further preferably 1% or less. The total light transmittance of the adhesive layer 22 is preferably 60% or more, more preferably 80% or more, and still more preferably 85% or more. The total light transmittance of the adhesive layer 22 is, for example, 100% or less.

The optical laminate X can be manufactured, for example, as follows.

First, the

optical members

11, 12, 13 and the

adhesive layers

21, 22 are prepared.

The adhesive layer 21 may be prepared, for example, in the form of a release liner-attached adhesive layer 21. The release liner-attached adhesive layer 21 can be formed by coating the 1 st adhesive composition (varnish) on a release liner to form a coating film, and then drying the coating film. Examples of the method for applying the 1 st adhesive composition include roll coating, contact roll (kiss roll) coating, gravure coating, reverse coating, roll brush, spray coating, dip roll coating, bar coating, doctor blade coating, air knife coating, curtain coating, lip coating, and die coating (the same applies to the method for applying other adhesive compositions described later). Other release liners may be further laminated on the adhesive layer 21 on the release liner.

The adhesive layer 22 may be prepared, for example, in the form of a release liner-attached adhesive layer 22. The release liner-attached adhesive layer 22 may be formed by coating the 2 nd adhesive composition (varnish) on the release liner to form a coating film, and then drying the coating film. Other release liners may be further laminated on the release liner-bearing adhesive layer 22.

Next, the optical member 11 is bonded to the optical member 12 by the adhesive layer 21. For example, first, the pressure-sensitive adhesive layer 21 is bonded to one surface (lower surface in fig. 1) of the optical member 12 in the thickness direction. Before bonding, the surface of the optical member 12 is preferably subjected to corona treatment or plasma treatment, and more preferably the surface of the adhesive layer 21 is also subjected to corona treatment or plasma treatment (the same applies to bonding between the optical member and the adhesive layer, which will be described later). After that, the release liner is peeled from the adhesive layer 21 on the optical member 12. Then, the optical member 11 is bonded to the exposed surface of the pressure-sensitive adhesive layer 21 exposed by the peeling.

Next, the optical member 12 is bonded to the optical member 13 by the adhesive layer 22. For example, first, the adhesive layer 22 is bonded to the other surface (upper surface in fig. 1) of the optical member 12 in the thickness direction. Thereafter, the release liner is peeled from the adhesive layer 22 on the optical member 12. Then, the optical member 13 is bonded to the exposed surface of the pressure-sensitive adhesive layer 22 exposed by the peeling.

As described above, the optical laminate X can be manufactured.

Examples

The present invention will be specifically described with reference to the following examples. However, the present invention is not limited to the examples. Specific numerical values such as the compounding amount (content), physical property value, and parameter described below may be replaced with upper limits (numerical values defined as "below" or "less" or lower limits (numerical values defined as "above" or "exceeding") of the compounding amount (content), physical property value, and parameter described in the above-described "specific embodiment".

[ example 1 ]

Preparation of base Polymer

A1 st mixture (solid content concentration 47% by mass) comprising 53 parts by mass of 2-ethylhexyl acrylate (2 EHA), 40 parts by mass of Lauryl Acrylate (LA), 5 parts by mass of N-vinyl-2-pyrrolidone (NVP), 2 parts by mass of 4-hydroxybutyl acrylate (4 HBA), 0.1 part by mass of 2,2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator and ethyl acetate as a solvent was stirred under a nitrogen atmosphere at 56℃for 6 hours in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet pipe (polymerization reaction). Thus, a 1 st polymer solution containing an acrylic polymer was obtained. The weight average molecular weight of the acrylic polymer in the polymer solution 1 was about 180 ten thousand. The solid content concentration of the 1 st mixture was adjusted by adjusting the amount of the solvent.

Preparation of adhesive composition

To 100 parts by mass of an acrylic polymer (base polymer) in the polymer solution, 0.03 parts by mass of a 1 st crosslinking agent (trade name "TAKENATE D110N", trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui chemical Co., ltd.) and 0.4 parts by mass of a 2 nd crosslinking agent (trade name "Nyber BMT", dibenzoyl peroxide, manufactured by Japanese oil and fat Co., ltd.) were added and mixed to prepare a 1 st adhesive composition.

Formation of adhesive layer

A release liner (trade name "Diasol MRF#38", thickness 38 μm, manufactured by Mitsubishi chemical corporation) having a release treated surface on one side was coated with the 1 st adhesive composition on the release treated surface to form a coating film. Then, the mixture was heated at 100℃for 1 minute and then at 150℃for 3 minutesThe coating film on the release liner was dried to form a transparent adhesive layer (adhesive layer A) having a thickness of 50. Mu.m ₁ ). In the above manner, 2 1 st adhesive sheets (thickness: 50 μm) with release liners were produced.

Production of optical laminate

First, plasma treatment was performed on both surfaces of a polarizing film (thickness: 32 μm) having a liquid crystal retardation layer on one surface (the surface on the liquid crystal retardation layer side of the polarizing film was designated as the 1 st surface, and the surface on the opposite side was designated as the 2 nd surface). In each plasma treatment, a plasma irradiation apparatus (trade name "AP-TO5", manufactured by water industry Co., ltd.) was used, the voltage was set TO 160V, the frequency was set TO 10kHz, and the treatment speed was set TO 5000 mm/min (the same applies TO the plasma treatment described later). Then, the exposed surfaces of the 2 1 st adhesive sheets were bonded to the 1 st and 2 nd surfaces of the polarizing films. In this bonding, the 1 st adhesive sheet with a release liner was pressed against the polarizing film by a 2kg roller to and fro 1 time under an environment of 25 ℃ (the same applies to the bonding described later). Then, the release liner was peeled off from the 1 st adhesive sheet on the 1 st face of the polarizing film. Then, the exposed surface of the 1 st adhesive sheet exposed by the peeling is subjected to plasma treatment. On the other hand, a polyethylene terephthalate (PET) film (trade name "diasol", thickness 125 μm, manufactured by mitsubishi chemical corporation) as the 3 rd optical member was also subjected to plasma treatment. Then, the exposed surface of the 1 st adhesive sheet on the 1 st surface of the polarizing film was bonded to the plasma-treated surface of the PET film. Then, the release liner was peeled off from the 1 st adhesive sheet on the 2 nd side of the polarizing film. Then, the exposed surface of the 1 st adhesive sheet exposed by the peeling is subjected to plasma treatment. On the other hand, a Polyimide (PI) film (trade name "Kapton 300V", thickness 75 μm, manufactured by dori dupont) as the 1 st optical member was also subjected to plasma treatment. Then, the exposed surface of the 1 st adhesive sheet on the 2 nd surface of the polarizing film was bonded to the plasma-treated surface of the polyimide film.

In the above manner, the optical laminate of example 1 was produced. The optical laminate of example 1 was provided with the 1 st light as the 1 st light in the order of thickness directionPI film (thickness 75 μm) of chemical component, adhesive layer a as 1 st adhesive layer ₁ (thickness 50 μm), polarizing film (thickness 32 μm) as the 2 nd optical member, adhesive layer A as the 2 nd adhesive layer ₁ (thickness 50 μm) and a PET film (thickness 125 μm) as the 3 rd optical member. The PET film in this laminated structure is an element simulating the above-described film-like pixel panel (the same applies to examples and comparative examples described later).

[ example 2 ]

Preparation of base Polymer

A2 nd mixture (solid content concentration 47% by mass) comprising 98 parts by mass of n-Butyl Acrylate (BA), 2 parts by mass of 4-hydroxybutyl acrylate (4 HBA), 0.1 part by mass of 2,2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator and ethyl acetate as a solvent was stirred at 56℃under a nitrogen atmosphere for 6 hours (polymerization reaction) in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube. Thus, a 2 nd polymer solution containing an acrylic polymer was obtained. The weight average molecular weight of the acrylic polymer in the polymer solution 2 was about 170 ten thousand. The solid content concentration of the 2 nd mixture was adjusted by adjusting the amount of the solvent.

Preparation of oligomers

In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, a 3 rd mixture (solid content concentration 40% by mass) comprising 95 parts by mass of n-Butyl Acrylate (BA), 5 parts by mass of Acrylic Acid (AA), 3 parts by mass of 2-mercaptoethanol, 0.1 part by mass of 2,2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and toluene as a solvent was stirred at 70 ℃ under a nitrogen atmosphere for 8 hours (polymerization reaction). Thus, an oligomer solution containing an oligomer having a weight average molecular weight of 5000 was obtained. The solid content concentration of the 3 rd mixture was adjusted by adjusting the amount of the solvent.

Preparation of adhesive composition

To 100 parts by mass of an acrylic polymer (base polymer) in the polymer solution, 0.03 parts by mass of a 1 st crosslinking agent (trade name "TAKENATE D110N", manufactured by three-well chemical Co., ltd.), 1.5 parts by mass of a 2 nd crosslinking agent (trade name "Nyber BMT", manufactured by Japanese fat & oil Co., ltd.) and 40 parts by mass of the oligomer were added and mixed to prepare a 2 nd adhesive composition.

Formation of adhesive layer

A release liner-equipped 2 nd adhesive sheet (adhesive layer a having a thickness of 50 μm) was produced in the same manner as in the release liner-equipped 1 st adhesive sheet of example 1 except that the 2 nd adhesive composition was used instead of the 1 st adhesive composition ₂ )。

Production of optical laminate

An optical laminate of example 2 was produced in the same manner as the optical laminate of example 1, except that the release liner-carrying adhesive sheet 2 was used instead of the release liner-carrying adhesive sheet 1. The optical laminate of example 2 was provided with a PI film (thickness 75 μm) as the 1 st optical member and an adhesive layer a as the 1 st adhesive layer in this order in the thickness direction ₂ (thickness 50 μm), polarizing film (thickness 32 μm) as the 2 nd optical member, adhesive layer A as the 2 nd adhesive layer ₂ (thickness 50 μm) and a PET film (thickness 125 μm) as the 3 rd optical member.

Comparative example 1

Preparation of adhesive composition

To 100 parts by mass of an acrylic polymer (base polymer) in the polymer solution, 0.2 parts by mass of a 1 st crosslinking agent (trade name "TAKENATE D110N", manufactured by three-well chemical Co., ltd.) and 0.2 parts by mass of a 2 nd crosslinking agent (trade name "Nyber BMT", manufactured by Japanese fat & oil Co., ltd.) were added and mixed, to prepare a 3 rd adhesive composition.

Formation of adhesive layer

A release liner-equipped 3 rd adhesive sheet (adhesive layer a having a thickness of 50 μm) was produced in the same manner as in the release liner-equipped 1 st adhesive sheet of example 1 except that the 3 rd adhesive composition was used instead of the 1 st adhesive composition ₃ )。

Production of optical laminate

An optical laminate of comparative example 1 was produced in the same manner as the optical laminate of example 1, except that the release liner-carrying 3 rd adhesive sheet was used instead of the release liner-carrying 1 st adhesive sheet. The optical laminate of comparative example 1 was provided with a PI film (thickness 75 μm) as the 1 st optical member and an adhesive layer a as the 1 st adhesive layer in this order in the thickness direction ₃ (thickness 50 μm), polarizing film (thickness 32 μm) as the 2 nd optical member, adhesive layer A as the 2 nd adhesive layer ₃ (thickness 50 μm) and a PET film (thickness 125 μm) as the 3 rd optical member.

Repeated bending test, thickness measurement and reliability evaluation

For each of the optical laminates of examples 1 and 2 and comparative example 1, repeated bending test, thickness measurement, and reliability evaluation were performed as follows.

First, test pieces (25 mm wide. Times. 100mm long) were cut out from the optical laminate. For each of the optical laminates of examples 1 and 2 and comparative example 1, 5 test pieces were prepared. Next, the thickness of a portion of the test piece to be subjected to bending in the repeated bending test was measured by a scanning electron microscope (trade name "JSM-7100F", manufactured by japan electronics corporation). The thickness was the same (322 μm) (the same applies to a test piece described later before the repeated bending test). Next, as shown in a of fig. 2, both ends of the test piece S were fixed to the holding portions C1, C2 of a U-shaped expansion and contraction tester (manufactured by YUASASYSTEM co., ltd.). Then, the test machine was used to perform a repeated bending test (bending test 1) under conditions of a bending angle of 180 °, a bending outer diameter of 4mm, a bending speed of 60 rounds/min, and a bending number of 10000 (bending condition 1) in an environment having a temperature of 25 ℃ and a relative humidity of 55%. In the repeated bending test, a series of processes including the 1 st process and the 2 nd process was repeated as 1 cycle (1 round trip) a plurality of times (number of bending times) of the 1 cycle. In the 1 st step, the test piece S was bent from a flat shape (a in fig. 2) to a U-shape (B in fig. 2) with the PI film side as the inside of the bend. In the 2 nd process, the test piece S is returned to the flat shape after the 1 st process (a of fig. 2).

After repeated bending test, a scanning electron microscope (trade name"JSM-7100F", manufactured by Japanese electronics company), the minimum thickness and the maximum thickness (thickness measurement) of the bent portion P (cross-hatched in A of FIG. 2 and B of FIG. 2) of the test piece S, which was repeatedly bent, were measured. The result is taken as the minimum thickness h after the test ₁₁ Maximum thickness h ₁₂ Shown in Table 1. Maximum thickness h ₁₂ And minimum thickness h ₁₁ The ratio R1 (ratio 1) of (2) is also shown in Table 1.

Further, the appearance of the bent portion P of the test piece S was observed. In addition, the joining reliability between the optical members in the optical laminate was evaluated as "excellent" when the surface of the bent portion P was flat and the appearance was not changed in all of the 5 test pieces, the surface of the bent portion P was flat and the appearance was not changed in 3 or 4 test pieces (i.e., when a small amount of irregularities were observed on the surface of the bent portion P in 1 or 2 test pieces), the surface of the bent portion P was evaluated as "good", and the surface of the bent portion P was observed as "irregular in all of the 5 test pieces (reliability evaluation). The results are shown in Table 1.

The same repeated bending test, thickness measurement and reliability evaluation as described above were performed except that the 2 nd bending test was performed as the repeated bending test instead of the 1 st bending test for the other test pieces (width 25 mm. Times.length 100 mm) cut out from the optical laminate. The 2 nd bending test was performed under the above 1 st bending condition at a temperature of 85℃and in a dry environment. Minimum thickness h of the bent portion P after test ₂₁ And a maximum thickness h ₂₂ Maximum thickness h ₂₂ And minimum thickness h ₂₁ The ratio R2 (ratio 2) of (2) and the ratio (R2/R1) of the above ratio R2 to the ratio R1 are shown in Table 1. The results of the reliability evaluation are also shown in table 1.

The same repeated bending test, thickness measurement and reliability evaluation as described above were performed except that the 3 rd bending test was performed as the repeated bending test instead of the 1 st bending test for the other test pieces (width 25 mm. Times.length 100 mm) cut out from the optical laminate. 3 rd bending test under the conditions of a temperature of 25 ℃ and a relative humidity of 55% at a bending angle of 180 DEG, a bending outer diameter of 4mm, a bending speed of 60 round trips/min,And the number of bending times 50000 (bending condition 2). Minimum thickness h of the bent portion P after test ₃₁ And a maximum thickness h ₃₂ And maximum thickness h ₃₂ And minimum thickness h ₃₁ The ratio R3 (ratio 3) of (3) is shown in Table 1. The results of the reliability evaluation are also shown in table 1.

The same repeated bending test, thickness measurement and reliability evaluation as described above were performed except that the 4 th bending test was performed as the repeated bending test instead of the 1 st bending test for the other test pieces (width 25 mm. Times.length 100 mm) cut out from the optical laminate. The 4 th bending test was performed under the 2 nd bending condition described above at a temperature of 85℃in a dry environment. Minimum thickness h of the bent portion P after test ₄₁ And a maximum thickness h ₄₂ Maximum thickness h ₄₂ And minimum thickness h ₄₁ The ratio R4 (ratio 4) of (2) and the ratio (R4/R3) of the above ratio R4 to the ratio R3 are shown in Table 1. The results of the reliability evaluation are also shown in table 1.

The same repeated bending test, thickness measurement and reliability evaluation as described above were performed except that the 5 th bending test was performed as the repeated bending test instead of the 1 st bending test for the other test pieces (width 25 mm. Times.length 100 mm) cut out from the optical laminate. The 5 th bending test was conducted under conditions of a bending angle of 180 °, a bending outer diameter of 3mm, a bending speed of 60 round trips/min, and a bending number of 50000 (3 rd bending condition) in an environment of a temperature of 25 ℃ and a relative humidity of 55%. Minimum thickness h of the bent portion P after test ₅₁ And a maximum thickness h ₅₂ And maximum thickness h ₅₂ And minimum thickness h ₅₁ The ratio R5 (ratio 5) of (2) is shown in Table 1. The results of the reliability evaluation are also shown in table 1.

The same repeated bending test, thickness measurement and reliability evaluation as described above were performed except that the 6 th bending test was performed as the repeated bending test instead of the 1 st bending test for the other test pieces (width 25 mm. Times.length 100 mm) cut out from the optical laminate. The 6 th bending test was performed under the above 3 rd bending condition at a temperature of 85℃in a dry environment. Minimum thickness h of the bent portion P after test ₆₁ And a maximum thickness h ₆₂ Maximum thickness h ₆₂ And minimum thickness h ₆₁ The ratio R6 (ratio 6) of (2) and the ratio (R6/R5) of the above ratio R6 to the ratio R5 are shown in Table 1. The results of the reliability evaluation are also shown in table 1.

TABLE 1

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Claims

1. An optical laminate comprising, in order in the thickness direction, a 1 st optical member, a 1 st adhesive layer, a 2 nd optical member, a 2 nd adhesive layer, and a 3 rd optical member, wherein the 1 st and 2 nd optical members are bonded by the 1 st adhesive layer, the 2 nd and 3 rd optical members are bonded by the 2 nd adhesive layer,

after a repeated bending test at 25 ℃ based on the 1 st bending condition of 180 DEG bending angle, 4mm bending outer diameter, 60 rounds/min bending speed and 10000 bending times, the 1 st ratio of the maximum thickness to the minimum thickness of the portion subjected to repeated bending in the test is 1.2 or less.

2. The optical laminate according to claim 1, wherein after a repeated bending test at 85 ℃ based on the 1 st bending condition, a 2 nd ratio of a maximum thickness to a minimum thickness of a portion subjected to repeated bending in the test is 1.5 or less.

3. The optical stack according to claim 2, wherein the ratio of the 2 nd ratio to the 1 st ratio is 0.95 or more and 1.3 or less.

4. An optical laminate having a 3 rd ratio of a maximum thickness to a minimum thickness of a portion subjected to repeated bending in a repeated bending test at 25 ℃ under a 2 nd bending condition of 180 DEG bending angle, 4mm bending outer diameter, 60 rounds/min bending speed and 50000 bending times, of 1.3 or less.

5. The optical laminate according to claim 4, wherein after the repeated bending test at 85 ℃ based on the 2 nd bending condition, a 4 th ratio of a maximum thickness to a minimum thickness of a portion subjected to repeated bending in the test is 1.6 or less.

6. The optical laminate according to claim 5, wherein a ratio of the 4 th ratio to the 3 rd ratio is 0.95 or more and 1.3 or less.

7. An optical laminate having a 5 th ratio of a maximum thickness to a minimum thickness of a portion subjected to repeated bending in a repeated bending test at 25 ℃ under a 3 rd bending condition of 180 DEG bending angle, 3mm bending outer diameter, 60 rounds/min bending speed and 50000 bending times of 1.4 or less.

8. The optical laminate according to claim 7, wherein after the repeated bending test at 85 ℃ based on the 3 rd bending condition, a 6 th ratio of a maximum thickness to a minimum thickness of a portion subjected to repeated bending in the test is 1.7 or less.

9. The optical stack according to claim 8, wherein the ratio of the 6 th ratio to the 5 th ratio is 0.95 or more and 1.3 or less.