Laminated optical films

Abstract

The laminated optical film (X) of the present invention comprises an optical film (10), an optical film (21, 22), and an adhesive layer (31, 32), wherein the adhesive layer (31) is bonded to the optical film (10) and to the optical film (21), and the adhesive layer (32) is bonded to the optical film (10) and to the optical film (22), and the indentation elastic modulus E1 of the adhesive layer (31) at 25°C and the indentation elastic modulus E2 of the adhesive layer (32) at 25°C satisfy 0.3≤E2 / E1<1.

Description

Technical Field

[0001] The present invention relates to laminated optical films. Background Art

[0002] A display panel, for example, has a laminated structure comprising a pixel panel, a touch panel, a surface protection cover, and the like. The laminated structure of the display panel also includes various functional optical films having given optical functions. Examples of functional optical films include polarizer films and phase difference films. The functional optical film is incorporated into the laminated structure, for example, by being bonded to other optical films such as a protective film on both sides of the film via an adhesive, i.e., in the form of a laminated optical film. Such laminated optical films are described, for example, in Patent Document 1 below.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-147865 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] For example, in the use of smart phones and tablet terminals, the development of repeatedly bendable (foldable) display panels has made progress. In the foldable display panel, each element in the stacked structure is made to be repeatedly bendable. In addition, at the bending portion of the foldable display panel, the optical film located on the outer side of the bend in the stacked optical film will produce tensile stress. This tensile stress used to cause the above-mentioned optical film on the outer side of the bend to have a photoelastic effect at the bending portion, thereby causing birefringence of the light transmitted from the film. The birefringence of the transmitted light becomes the cause of uneven display of the image displayed on the display panel, which is undesirable. When the foldable display panel is repeatedly bent for a long time and used, it is particularly easy to produce uneven display due to the above-mentioned birefringence caused by the hardness of the adhesive layer arranged on the outer side of the bend.

[0008] The present invention provides a laminated optical film suitable for suppressing display unevenness when a foldable display panel is folded.

[0009] Solutions to the Problem

[0010] The present invention [1] includes a laminated optical film, which comprises a first optical film, a first adhesive layer, a second optical film, a second adhesive layer, and a third optical film in order in the thickness direction, wherein the first adhesive layer is bonded to the first optical film and to the second optical film, and the second adhesive layer is bonded to the second optical film and to the third optical film, and the indentation elastic modulus E1 of the first adhesive layer at 25°C and the indentation elastic modulus E2 of the second adhesive layer at 25°C satisfy 0.3≤E2 / E1<1.

[0011] The present invention [2] includes the laminated optical film described in [1] above, wherein the indentation elastic modulus E2 is 4 GPa or less.

[0012] The present invention [3] includes the laminated optical film described in [1] or [2] above, wherein the indentation elastic modulus E2 is 0.4 GPa or more.

[0013] The present invention [4] includes the laminated optical film according to any one of [1] to [3], wherein the indentation elastic modulus E1 is 0.5 GPa or more.

[0014] The present invention [5] includes the laminated optical film according to any one of [1] to [4], wherein the indentation elastic modulus E1 is 7 GPa or less.

[0015] The present invention [6] includes the laminated optical film according to any one of [1] to [5], wherein the second optical film is a polarizer film.

[0016] Effects of the Invention

[0017] In the laminated optical film of the present invention, as described above, the indentation elastic modulus E1 of the first adhesive layer and the indentation elastic modulus E2 of the second adhesive layer satisfy 0.3≤E2 / E1<1. The second adhesive layer has such a softness that its elastic modulus E2 is so small that the ratio (E2 / E1) is less than 1. Such a second adhesive layer is suitable for alleviating the tensile stress generated by the third optical film at the bent portion when the laminated optical film is bent with the third optical film as the outer side of the curve. At the bent portion of the third optical film, the above-mentioned photoelastic effect is reduced due to the relaxation of the tensile stress, which can suppress the uneven display of the image displayed on the display panel. In addition, the second adhesive layer having a large indentation elastic modulus E2 of a ratio (E2 / E1) of 0.3 or more is suitable for ensuring the bonding force between the second and third optical films at the above-mentioned bent portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic cross-sectional view of one embodiment of the laminated optical film of the present invention.

[0019] Figure 2 Show Figure 1 The laminated optical film is shown in a bent state.

[0020] Explanation of symbols

[0021] X-Laminated Optical Film

[0022] 10 Optical film (second optical film)

[0023] 21 Optical film (first optical film)

[0024] 22 Optical film (third optical film)

[0025] 31 Adhesive layer (first adhesive layer)

[0026] 32 Adhesive layer (second adhesive layer)

[0027] H thickness direction

[0028] B Bending part DETAILED DESCRIPTION

[0029] like Figure 1 As shown, a laminated optical film X, which is one embodiment of the laminated optical film of the present invention, comprises an optical film 10, optical films 21, 22, and adhesive layers 31, 32. Specifically, the laminated optical film X comprises, in order, an optical film 21 (first optical film), an adhesive layer 31 (first adhesive layer), an optical film 10 (second optical film), an adhesive layer 32 (second adhesive layer), and an optical film 22 (third optical film) in the thickness direction H. The laminated optical film X has a sheet shape of a given thickness and is unfolded in a direction (surface direction) perpendicular to the thickness direction H. The adhesive layer 31 joins the optical films 10 and 21 together. The adhesive layer 32 joins the optical films 10 and 22 together. In addition, the laminated optical film X is a composite film introduced into the laminated structure of a foldable display panel. The laminated optical film X is, for example, a laminated optical film arranged on the image display side surface of a display panel such as a foldable organic EL panel (OLED panel). In foldable display panels, laminated optical films such as Figure 2 At the bend portion B, the optical film 21 and the adhesive layer 31 are located on the inner side of the bend relative to the optical film 10 (the lower side in the figure), and the optical film 22 and the adhesive layer 32 are located on the outer side of the bend relative to the optical film 10 (the upper side in the figure).

[0030] In this embodiment, the optical film 10 is a functional optical film. Examples of the functional optical film include a polarizer film and a retardation film.

[0031] Examples of polarizer films include hydrophilic polymer films that have been dyed with a dichroic substance and subsequently stretched. Examples of dichroic substances include iodine and dichroic dyes. Examples of hydrophilic polymer films include polyvinyl alcohol (PVA) films, partially methylated PVA films, and partially saponified films of ethylene-vinyl acetate copolymers. Examples of polarizer films include polyene-oriented films. Examples of materials for polyene-oriented films include dehydrated PVA and dehydrochlorinated polyvinyl chloride. As polarizer films, PVA films that have been dyed with iodine and subsequently uniaxially stretched are preferred due to their excellent optical properties such as polarization properties.

[0032] From the perspective of thinning, the thickness of the optical film 10 as a polarizer film is preferably 15 μm or less, more preferably 12 μm or less, even more preferably 10 μm or less, and particularly preferably 8 μm or less. Thin polarizer films have less thickness variation, resulting in excellent visibility. Furthermore, due to minimal dimensional change due to temperature fluctuations, they exhibit excellent durability against thermal shock. From the perspective of strength, the thickness of the optical film 10 as a polarizer film is preferably 3 μm or greater, more preferably 5 μm or greater.

[0033] As the phase difference film, for example, there can be mentioned: a λ / 2 wavelength film, a λ / 4 wavelength film, and a viewing angle compensation film. As the material of the phase difference film, for example, there can be mentioned a polymer film that has undergone birefringence by stretching treatment. As the polymer film, for example, there can be mentioned a cellulose film and a polyester film. As the cellulose film, for example, there can be mentioned a cellulose triacetate film. As the polyester film, for example, there can be mentioned a polyethylene terephthalate film and a polyethylene naphthalate film. The thickness of the optical film 10 as the phase difference film is, for example, not less than 20 μm, for example, not more than 150 μm. In addition, as the phase difference film, it is also preferable to use a film having a substrate such as a cellulose film and an orientation layer of a liquid crystal compound such as a liquid crystal polymer on the substrate.

[0034] The optical films 21 and 22 are transparent protective films, respectively. The transparent protective film is, for example, a flexible transparent resin film. Examples of the material of the transparent protective film include polyolefins, polyesters, polyamides, polyimides, polyvinyl chloride, polyvinylidene chloride, cellulose, modified cellulose, polystyrene, and polycarbonate. Examples of polyolefins include cycloolefin polymers (COP), polyethylene, polypropylene, ethylene-propylene copolymers, ethylene-vinyl acetate copolymers, and ethylene-vinyl alcohol copolymers. Examples of polyesters include polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate. Examples of polyamides include polyamide 6, polyamide 6,6, and partially aromatic polyamides. Examples of modified cellulose include cellulose triacetate. These materials may be used alone or in combination of two or more. From the perspective of cleanliness, polyolefins are preferably used as the material of the transparent protective film, and COP is more preferably used. In addition, the material of the optical film 21 may be the same as or different from the material of the optical film 22.

[0035] From the perspective of the strength of the laminated optical film X, the thickness of each of the optical films 21 and 22 is preferably 5 μm or greater, more preferably 10 μm or greater, and even more preferably 20 μm or greater. From the perspective of reducing the thickness of the laminated optical film X, the thickness of the optical film 21 is preferably 100 μm or less, more preferably 70 μm or less, and even more preferably 50 μm or less. The thickness of the optical film 21 and the thickness of the optical film 22 may be the same or different.

[0036] The adhesive layer 31 is a cured product of the first adhesive composition. The adhesive layer 31 is directly bonded to the optical film 10 and directly bonded to the optical film 21. The first adhesive composition contains a curable resin. The specific components of the first adhesive composition are described below.

[0037] From the perspective of the bonding strength between the optical films 10 and 21, the thickness T1 of the adhesive layer 31 is preferably 0.1 μm or greater, more preferably 0.4 μm or greater, further preferably 0.7 μm or greater, and particularly preferably 0.8 μm or greater. From the perspective of reducing the thickness of the laminated optical film X, the thickness T1 of the adhesive layer 31 is preferably 5 μm or less, more preferably 3 μm or less, further preferably 1.5 μm or less, and particularly preferably 1 μm or less.

[0038] The indentation elastic modulus E1 of the adhesive layer 31 at 25°C, as measured by nanoindentation, is preferably 0.5 GPa or greater, more preferably 1 GPa or greater, even more preferably 1.5 GPa or greater, and particularly preferably 2 GPa or greater. This configuration is preferred for ensuring the bonding strength between the optical films 10 and 21 at the folded portion B when the laminated optical film X is folded with the optical film 21 side facing inward. The indentation elastic modulus E1 is preferably 7 GPa or less, more preferably 6 GPa or less, and even more preferably 5.2 GPa or less. This configuration is preferred for alleviating the compressive stress acting on the adhesive layer 31 at the folded portion B. The relaxation of the compressive stress of the adhesive layer 31 at the folded portion B contributes to suppressing delamination between the optical films 10 and 21. Furthermore, this configuration related to the upper limit of the indentation elastic modulus E1 is preferred for ensuring low elasticity in the adhesive layer 31 (the adhesive layer on the inner side of the bend) at the bend portion B to achieve sufficient adhesion with the optical films 10 and 21. Therefore, it is suitable for suppressing buckling of the optical film 10 at the bend portion B. As a method for adjusting the indentation elastic modulus E1 of the adhesive layer 31, for example, a method of adjusting the composition of the first adhesive composition can be cited. Specifically, as a method for adjusting the indentation elastic modulus E1 of the adhesive layer 31, adjusting the number of functional groups of the polymerizable compound in the first adhesive composition, that is, adjusting the acrylic acid equivalent and epoxy equivalent of the polymerizable compound, as described later, is effective.

[0039] Nanoindentation is a technique for measuring various physical properties of a sample at nanoscale. In the present embodiment, nanoindentation is implemented based on ISO14577. In the nanoindentation, a process of pressing an indenter into a sample arranged on a stage (load application process) and a process of pulling the indenter out of the sample thereafter (load release process) are implemented. In a series of processes, the load acting between the indenter and the sample and the relative displacement of the indenter relative to the sample are measured (load-displacement measurement), thereby obtaining a load-displacement curve. According to the load-displacement curve, various physical properties can be obtained based on nanoscale measurement of the measured sample. The load-displacement measurement of the adhesive layer cross section using the nanoindentation method can, for example, use a nanoindenter (trade name "Triboindenter", manufactured by Hysitron), as described in detail in the examples below.

[0040] The adhesive layer 32 is a cured product of the second adhesive composition. The adhesive layer 32 is directly bonded to the optical film 10 and directly bonded to the optical film 22. The second adhesive composition contains a curable resin. The specific components of the second adhesive composition are described below.

[0041] From the perspective of the bonding force between the optical films 10 and 22, the thickness T2 of the adhesive layer 32 is preferably 0.1 μm or more, more preferably 0.4 μm or more, further preferably 0.7 μm or more, and particularly preferably 0.8 μm or more. From the perspective of thinning the laminated optical film X, the thickness T2 of the adhesive layer 32 is preferably 5 μm or less, more preferably 3 μm or less, further preferably 1.5 μm or less, and particularly preferably 1 μm or less. The thickness T2 of the adhesive layer 32 may be the same as or different from the thickness T1 of the adhesive layer 31 described above. In addition, the ratio of the thickness T2 to the thickness T1 (T2 / T1) is, for example, 0.5 or more, and, for example, 2 or less.

[0042] The indentation elastic modulus E2 of the adhesive layer 32 at 25°C measured by the nanoindentation method is smaller than the indentation elastic modulus E1, and is preferably greater than 0.4 GPa, more preferably greater than 0.8 GPa, further preferably greater than 1.2 GPa, and particularly preferably greater than 1.8 GPa. The indentation elastic modulus E2 is smaller than the indentation elastic modulus E1, and is preferably less than 4 GPa, more preferably less than 3 GPa, and further preferably less than 2.5 GPa. These structures are preferred for ensuring the bonding force between the optical films 10 and 22. As a method for adjusting the indentation elastic modulus E2 of the adhesive layer 32, for example, a method of adjusting the composition of the second adhesive composition can be cited. Specifically, as a method for adjusting the indentation elastic modulus E2 of the adhesive layer 32, it is effective to adjust the number of functional groups of the polymerizable compound described later in the second adhesive composition, that is, to adjust the acrylic acid equivalent and epoxy equivalent of the polymerizable compound.

[0043] The indentation elastic modulus E1 of the adhesive layer 31 at 25° C. and the indentation elastic modulus E2 of the adhesive layer 32 at 25° C. satisfy 0.3≦E2 / E1<1.

[0044] The adhesive layer 32 has such a softness that its compression modulus E2 is so small that the ratio (E2 / E1) is less than 1. This adhesive layer 32 is suitable for alleviating the tensile stress generated in the optical film 22 at the bend portion B when the laminated optical film X is bent with the optical film 22 as the outer side of the bend. By alleviating the tensile stress at the bend portion of the optical film 22, the photoelastic effect is reduced, thereby suppressing display unevenness in the image displayed on the display panel. From this perspective, the ratio (E2 / E1) is preferably 0.97 or less, and more preferably 0.8 or less.

[0045] Furthermore, an adhesive layer 32 having a high indentation elastic modulus E2, with a ratio (E2 / E1) of approximately 0.3 or greater, is suitable for ensuring the bonding strength between the optical films 10 and 22 at the bend portion B. Furthermore, an adhesive layer 31 having a low indentation elastic modulus E1, with a ratio (E2 / E1) of approximately 0.3 or greater, is preferred because it ensures low elasticity in the adhesive layer 31 at the bend portion B (the adhesive layer on the inner side of the bend) to achieve sufficient adhesion with the optical films 10 and 21. This is therefore suitable for suppressing buckling of the optical film 10 at the bend portion B. From these viewpoints, the ratio (E2 / E1) is preferably 0.5 or greater, and more preferably 0.6 or greater.

[0046] Examples of methods for adjusting the ratio (E2 / E1) include adjusting the indentation elastic modulus E1 and adjusting the indentation elastic modulus E2.

[0047] In the laminated optical film X, the 90° peel strength F1 between the optical film 21 and the optical film 10 at 25°C is preferably 0.8 N / 15 mm or more, more preferably 1 N / 15 mm or more, further preferably 1.2 N / 15 mm or more, and particularly preferably 1.5 N / 15 mm or more. Such a structure is preferable for ensuring good bonding strength between the optical films 10 and 21, and is particularly preferable for ensuring bonding strength between the optical films 10 and 21 at the bent portion B when the laminated optical film X is bent. In addition, the 90° peel strength F1 is, for example, 10 N / 15 mm or less. The 90° peel strength F1 can be measured by the method described in the examples below. The peel strength between the optical film 21 and the optical film 10 is the force required to peel the optical film 21 from the optical film 10, and this peeling includes interfacial peeling between the optical film 10 and the adhesive layer 31, peeling caused by cohesive failure of the adhesive layer 31, interfacial peeling between the adhesive layer 31 and the optical film 21, and peeling based on a combination thereof. Furthermore, methods for adjusting the 90° peel strength F1 include, for example, adjusting the composition of the first adhesive composition. Specifically, methods for adjusting the 90° peel strength F1 include adjusting the number of functional groups of the polymerizable compound described below in the first adhesive composition, that is, adjusting the acrylic acid equivalent and epoxy equivalent of the polymerizable compound.

[0048] In the laminated optical film X, the 90° peel strength F2 between the optical film 22 and the optical film 10 at 25°C is preferably 0.8 N / 15 mm or more, more preferably 1 N / 15 mm or more, further preferably 1.2 N / 15 mm or more, and particularly preferably 1.5 N / 15 mm or more. Such a structure is preferable for ensuring good bonding strength between the optical films 10 and 22, and is particularly preferable for ensuring bonding strength between the optical films 10 and 22 at the bent portion B when the laminated optical film X is bent. In addition, the 90° peel strength F2 is, for example, 10 N / 15 mm or less. The 90° peel strength F2 can be measured by the method described in the examples below. The peel strength between the optical film 22 and the optical film 10 is the force required to peel the optical film 22 from the optical film 10, and this peeling includes interfacial peeling between the optical film 10 and the adhesive layer 32, peeling caused by cohesive failure of the adhesive layer 32, interfacial peeling between the adhesive layer 32 and the optical film 22, and peeling based on a combination thereof. Furthermore, as a method for adjusting the 90° peel strength F2, for example, a method of adjusting the composition of the second adhesive composition can be cited. Specifically, as a method for adjusting the 90° peel strength F2, an example is adjusting the number of functional groups of the polymerizable compound described below in the second adhesive composition, that is, adjusting the acrylic acid equivalent and epoxy equivalent of the polymerizable compound.

[0049] The adhesive layer 31 is, for example, a cured product of a first adhesive composition (first active-energy-ray-curable composition) containing an active-energy-ray-curable curable resin. Examples of the first active-energy-ray-curable composition include electron beam-curable compositions, ultraviolet-curable compositions, and visible-light-curable compositions. In this embodiment, the first active-energy-ray-curable composition is either a free-radical polymerizable composition or a cationically polymerizable composition, or both.

[0050] When the first active energy ray-curable composition is a free radical polymerizable composition, the composition contains a free radical polymerizable compound as a monomer. The free radical polymerizable compound is a compound having a free radical polymerizable functional group. As the free radical polymerizable functional group, for example, a group containing an ethylenically unsaturated bond can be mentioned. As the group containing an ethylenically unsaturated bond, for example, a (meth)acryloyl group, a vinyl group, and an allyl group can be mentioned. A (meth)acryloyl group refers to an acryloyl group and / or a methacryloyl group. From the viewpoint of the curability of the first active energy ray-curable composition, the first active energy ray-curable composition preferably contains a free radical polymerizable compound having a (meth)acryloyl group as a main component, and the main component refers to the component with the largest content in terms of mass ratio. The proportion of the free radical polymerizable compound containing a (meth)acryloyl group in the first active energy ray-curable composition is, for example, 50% by mass or more, preferably 70% by mass or more, and more preferably 80% by mass or more. Examples of the radical polymerizable compound include monofunctional radical polymerizable compounds and difunctional or higher polyfunctional radical polymerizable compounds.

[0051] Examples of monofunctional free radical polymerizable compounds include (meth)acrylamide derivatives having a (meth)acrylamide group. Examples of (meth)acrylamide derivatives include N-alkyl (meth)acrylamide derivatives, N-hydroxyalkyl (meth)acrylamide derivatives, N-aminoalkyl (meth)acrylamide derivatives, N-alkoxy (meth)acrylamide derivatives, and N-mercaptoalkyl (meth)acrylamide derivatives. Examples of N-alkyl (meth)acrylamide derivatives include N-methyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-butyl (meth)acrylamide, and N-hexyl (meth)acrylamide, with N,N-diethylacrylamide being preferred. Examples of N-hydroxyalkyl (meth)acrylamide derivatives include N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, and N-methylol-N-propyl (meth)acrylamide, with N-hydroxyethyl acrylamide being preferred. (Meth)acrylamide derivatives may be used alone or in combination of two or more.

[0052] Examples of monofunctional free-radical polymerizable compounds include (meth)acrylic acid derivatives having a (meth)acryloyloxy group. Examples of such (meth)acrylic acid derivatives include alkyl (meth)acrylates and (meth)acrylic acid derivatives other than alkyl (meth)acrylates. The (meth)acrylic acid derivatives may be used alone or in combination of two or more.

[0053] Examples of the alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, 2,2-dimethylbutyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 4-methyl-2-propylpentyl (meth)acrylate, and n-octadecyl (meth)acrylate.

[0054] Examples of (meth)acrylic acid derivatives other than alkyl (meth)acrylates include cycloalkyl (meth)acrylates, aralkyl (meth)acrylates, hydroxyl group-containing (meth)acrylate derivatives, alkoxy group-containing (meth)acrylate derivatives, and phenoxy group-containing (meth)acrylate derivatives. Examples of cycloalkyl (meth)acrylates include cyclohexyl (meth)acrylate and cyclopentyl (meth)acrylate. Examples of aralkyl (meth)acrylates include benzyl (meth)acrylate and 3-phenoxybenzyl (meth)acrylate. Examples of hydroxyl group-containing (meth)acrylate derivatives include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, [4-(hydroxymethyl)cyclohexyl]methyl acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate. Examples of alkoxy group-containing (meth)acrylic acid derivatives include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, and 3-methoxybutyl (meth)acrylate. Examples of phenoxy group-containing (meth)acrylic acid derivatives include phenoxyethyl (meth)acrylate and phenoxydiethylene glycol (meth)acrylate. As a (meth)acrylic acid derivative other than an alkyl (meth)acrylate, it is preferred to use at least one selected from the group consisting of 3-phenoxybenzyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, and phenoxydiethylene glycol acrylate.

[0055] Examples of monofunctional free-radical polymerizable compounds include carboxyl group-containing monomers, such as (meth)acrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and methacrylic acid.

[0056] Examples of the monofunctional radical polymerizable compound include lactam-based vinyl monomers, such as N-vinyl-2-pyrrolidone, N-vinyl-ε-caprolactam, and methylvinylpyrrolidone.

[0057] As monofunctional free radical polymerizable compounds, vinyl monomers having nitrogen-containing heterocyclic rings can also be mentioned. Examples of such monomers include vinyl pyridine, vinyl piperidone, vinyl pyrimidine, vinyl piperazine, vinyl pyrazine, vinyl pyrrole, vinyl imidazole, vinyl oxazole, acryloylmorpholine, and vinylmorpholine.

[0058] As the polyfunctional radical polymerizable compound, for example, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol diacrylate, 2-ethyl-2-butylpropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, cyclotrimethylolpropane formal (meth)acrylate, dimethacrylate, Alkanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate, preferably tripropylene glycol diacrylate and hydroxypivalic acid neopentyl glycol acrylic acid adduct. As the multifunctional free radical polymerizable compound, at least one selected from tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, and hydroxypivalic acid neopentyl glycol acrylic acid adduct can be preferably used. The multifunctional free radical polymerizable compound can be used alone or in combination of two or more. The multifunctional free radical polymerizable compound functions as a crosslinking agent.

[0059] When the first active energy ray-curable composition is an ultraviolet-curable composition or a visible light-curable composition, the first active energy ray-curable composition preferably contains a photopolymerization initiator. Examples of the photopolymerization initiator include benzophenone compounds, benzoin ether compounds, and thioxanthone compounds. Examples of benzophenone compounds include dibenzoyl, benzophenone, benzoylbenzoic acid, and 3,3'-dimethyl-4-methoxybenzophenone. Examples of benzoin ether compounds include benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin butyl ether. Examples of thioxanthone compounds include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

[0060] When the first active energy ray-curable composition is a visible light-curable composition, it is preferred to use a photopolymerization initiator that is highly sensitive to light of 380 nm or longer. Examples of such photopolymerization initiators include 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropane-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholino)phenyl]-1-butanone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and bis(η5-2,4-cyclopentadien-1-yl)bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium.

[0061] As the photopolymerization initiator, 2,4-diethylthioxanthone and / or 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropane-1-one is preferably used.

[0062] In the first active energy ray-curable composition, the content of the photopolymerization initiator is preferably 0.1 parts by mass or more, more preferably 0.05 parts by mass or more, and further preferably 0.1 parts by mass or more, relative to 100 parts by mass of the curable component (free radical polymerizable compound). In addition, it is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass or less.

[0063] When the first active energy ray curable composition is a cationic polymerizable composition, the composition contains a cationic polymerizable compound as a monomer. A cationic polymerizable compound is a compound having a cationic polymerizable functional group, which includes a monofunctional cationic polymerizable compound having one cationic polymerizable functional group and a polyfunctional cationic polymerizable compound having two or more cationic polymerizable functional groups. The liquid viscosity of a monofunctional cationic polymerizable compound is relatively low. By adding such a monofunctional cationic polymerizable compound to a resin composition, the viscosity of the resin composition can be reduced. In addition, in most cases, a monofunctional cationic polymerizable compound has a functional group that exhibits various functions. By adding such a monofunctional cationic polymerizable compound to a resin composition, the resin composition and / or the cured product of the resin composition can exhibit various functions. On the other hand, by curing a resin composition with a polyfunctional cationic polymerizable compound, a cured product having a three-dimensional crosslinked portion can be obtained (the polyfunctional cationic polymerizable compound functions as a crosslinking agent). From this point of view, it is preferred to use a polyfunctional cationic polymerizable compound. When a monofunctional cationically polymerizable compound and a polyfunctional cationically polymerizable compound are used in combination, the amount of the polyfunctional cationically polymerizable compound relative to 100 parts by mass of the monofunctional cationically polymerizable compound is, for example, 10 parts by mass or more, and for example, 1000 parts by mass or less. Examples of cationically polymerizable functional groups include epoxy groups, oxetane groups, and vinyl ether groups. Examples of compounds having epoxy groups include aliphatic epoxy compounds, alicyclic epoxy compounds, and aromatic epoxy compounds. As compounds having epoxy groups, alicyclic epoxy compounds are preferably used from the viewpoint of the curability and adhesion of the cationically polymerizable composition. Examples of alicyclic epoxy compounds include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, or caprolactone-modified, trimethylcaprolactone-modified, and valerolactone-modified 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate. Examples of commercially available alicyclic epoxy compounds include CELLOXIDE 2021, CELLOXIDE 2021A, CELLOXIDE 2021P, CELLOXIDE 2081, CELLOXIDE 2083, and CELLOXIDE 2085 (all manufactured by Daicel Chemical Industries, Ltd.). Examples include Cyracure UVR-6105, Cyracure UVR-6107, Cyracure 30, and R-6110 (all manufactured by Dow Chemical Japan Ltd.). From the perspective of improving the curability and reducing the viscosity of the cationic polymerizable composition, it is preferred to use a compound having an oxetane group and / or a compound having a vinyl ether group.Examples of the compound having an oxetane group include 3-ethyl-3-hydroxymethyloxetane, 1,4-bis[(3-ethyl-3-oxetane)methoxymethyl]benzene, 3-ethyl-3-(phenoxymethyl)oxetane, di[(3-ethyl-3-oxetane)methyl]ether, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, and phenol novolac oxetane. Examples of commercially available compounds having an oxetane group include ARON OXETANE OXT-101, ARON OXETANE OXT-121, ARON OXETANE OXT-211, ARON OXETANE OXT-221, and ARON OXETANE OXT-212 (all manufactured by Toagosei Co., Ltd.). Examples of the compound having a vinyl ether group include 2-hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, triethylene glycol divinyl ether, cyclohexanedimethanol divinyl ether, cyclohexanedimethanol monovinyl ether, tricyclodecane vinyl ether, cyclohexyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, and pentaerythritol tetravinyl ether.

[0064] When the first active energy ray curable composition is an ultraviolet curable composition or a visible light curable composition, the first active energy ray curable composition contains a photocationic polymerization initiator. The photocationic polymerization initiator is irradiated by active energy rays (visible light, ultraviolet rays, X-rays, electron beams, etc.) to generate cationic species or Lewis acids, thereby initiating a polymerization reaction of cationic polymerizable functional groups. As photocationic polymerization initiators, photoacid generators and photobase generators can be mentioned, and photoacid generators are preferably used. When the first active energy ray curable composition is set as a visible light curable composition, it is particularly preferred to use a photocationic polymerization initiator with high sensitivity to light of 380nm or more. In addition, when using a photocationic polymerization initiator, it is preferably used in combination with a photosensitizer that shows maximum absorption for light of a wavelength longer than 380nm. Photocationic polymerization initiators are compounds that generally exhibit maximum absorption in wavelength regions near or shorter than 300nm. Therefore, by combining the use of a photosensitizer that exhibits maximum absorption under light having a wavelength longer than 380nm, it is possible to effectively utilize light having a wavelength longer than 380nm to promote the generation of cationic species or Lewis acids from the photocationic polymerization initiator. As photosensitizers, for example, anthracene compounds, pyrene compounds, carbonyl compounds, organic sulfur compounds, persulfides, redox compounds, azo compounds, diazo compounds, halogen compounds, and photoreductive pigments can be mentioned. These can be used alone or in combination of two or more. In particular, anthracene compounds are preferred due to their excellent photosensitizing effect. As commercially available products of anthracene compounds used as photosensitizers, for example, Anthracure UVS-1331 and Anthracure UVS-1221 (manufactured by Kawasaki Chemicals, Ltd.) can be mentioned. The content of the photosensitizer in the composition is, for example, 0.1 to 5% by weight.

[0065] The first active energy ray-curable composition may contain an oligomer. Examples of the oligomer include acrylic oligomers, fluoro oligomers, and silicone oligomers, with acrylic oligomers being preferred. Adding an oligomer to the first active energy ray-curable composition helps suppress shrinkage of the composition during curing. Suppressing the curing shrinkage of the first active energy ray-curable composition is preferred for reducing the interfacial stress between the formed adhesive layer 31 and the optical films 10 and 21. Suppressing the interfacial stress helps ensure the bonding strength between the optical films 10 and 21.

[0066] Examples of the (meth)acrylic monomer forming the acrylic oligomer include alkyl (meth)acrylates having 1 to 20 carbon atoms, cycloalkyl (meth)acrylates, aralkyl (meth)acrylates, polycyclic (meth)acrylates, hydroxyl group-containing (meth)acrylates, and halogen-containing (meth)acrylates. Examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, 2-methyl-2-nitropropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, t-pentyl (meth)acrylate, 3-pentyl (meth)acrylate, 2,2-dimethylbutyl (meth)acrylate, n-hexyl (meth)acrylate, hexadecyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 4-methyl-2-propylpentyl (meth)acrylate, and n-octadecyl (meth)acrylate. Examples of the cycloalkyl (meth)acrylate include cyclohexyl (meth)acrylate and cyclopentyl (meth)acrylate. Examples of the aralkyl (meth)acrylate include benzyl (meth)acrylate. Examples of polycyclic (meth)acrylates include 2-isobornyl (meth)acrylate, 2-norbornyl methyl (meth)acrylate, 5-norbornyl-2-yl methyl (meth)acrylate, and 3-methyl-2-norbornyl methyl (meth)acrylate. Examples of hydroxyl-containing (meth)acrylates include hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2,3-dihydroxypropyl methylbutyl (meth)acrylate. Examples of halogen-containing (meth)acrylates include 2,2,2-trifluoroethyl (meth)acrylate, 2,2,2-trifluoroethyl ethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropentyl (meth)acrylate, and heptadecafluorodecyl (meth)acrylate. These (meth)acrylates may be used alone or in combination of two or more.

[0067] The weight average molecular weight (Mw) of the acrylic oligomer is preferably 15,000 or less, more preferably 10,000 or less, and even more preferably 5,000 or less. The Mw of the acrylic oligomer is preferably 500 or more, more preferably 1,000 or more, and even more preferably 1,500 or more.

[0068] The content of the acrylic oligomer in the first active energy ray-curable composition is preferably 2% by mass or more, more preferably 4% by mass or more, and is preferably 20% by mass or less, more preferably 15% by mass or less.

[0069] The first active energy ray-curable composition may contain other components. Examples of such other components include silane coupling agents, leveling agents, surfactants, plasticizers, and ultraviolet absorbers. The amount of such other components incorporated per 100 parts by mass of the curable component is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, and for example, 0.01 parts by mass or more.

[0070] From the perspective of coatability in the coating step described below, the viscosity of the first active energy ray-curable composition at 25°C is preferably 3 mPa·s or higher, more preferably 5 mPa·s or higher, and even more preferably 10 mPa·s or higher, and is preferably 100 mPa·s or lower, more preferably 50 mPa·s or lower, and even more preferably 30 mPa·s or lower. The viscosity of the composition is a value measured using an E-type viscometer (cone-plate viscometer).

[0071] The adhesive layer 32 is, for example, a cured product of a second adhesive composition containing an active energy ray-curable curable resin (active energy ray-curable composition). Examples of the second active energy ray-curable composition include electron beam-curable compositions, ultraviolet-curable compositions, and visible light-curable compositions. The second active energy ray-curable composition and the first active energy ray-curable composition may be of the same type or different types. In this embodiment, the second active energy ray-curable composition is a free radical polymerizable composition.

[0072] As the components contained in the second active-energy-ray-curable composition, the components described above as the components contained in the first active-energy-ray-curable composition can be used. The content ranges of the components in the second active-energy-ray-curable composition are the same as the content ranges of the components in the first active-energy-ray-curable composition described above. The composition of the second active-energy-ray-curable composition may be the same as or different from that of the first active-energy-ray-curable composition.

[0073] The laminated optical film X can be produced, for example, as follows.

[0074] First, a first active energy ray-curable composition is applied to a single surface (predetermined surface for bonding) of the optical film 21 to form a first coating film of the composition (first coating process). In addition, a second active energy ray-curable composition is applied to a single surface (predetermined surface for bonding) of the optical film 22 to form a second coating film of the composition (second coating process). Before each coating process, the surface of the optical film to be bonded may be subjected to a surface modification treatment. Examples of surface modification treatments include corona treatment, plasma treatment, excimer treatment, and flame treatment. Examples of coating methods in this process include reverse coating, gravure coating, rod reverse coating, roller coating, die coating, wire rod coating, and rod coating.

[0075] Next, the optical film 21 is laminated to one surface of the optical film 10 via the first coating film, and the optical film 22 is laminated to the other surface of the optical film 10 via the second coating film. For example, a roll laminator that performs two laminations simultaneously can be used for lamination.

[0076] Next, the first and second coating films are irradiated with active energy rays to cure the first coating film to form an adhesive layer 31, and the second coating film is cured to form an adhesive layer 32 (the adhesive layers 31 and 32 are not pressure-sensitive adhesive layers). Thus, the optical films 10 and 21 are bonded together via the adhesive layer 31, and the optical films 10 and 22 are bonded together via the adhesive layer 32.

[0077] In this process, from the viewpoint of suppressing the degradation of the optical film 10 as a functional optical film, it is preferred to irradiate the active energy ray for curing the first coating film from the optical film 21 side, and irradiate the active energy ray for curing the second coating film from the optical film 22 side. As active energy rays, electron beams, ultraviolet rays, and visible light can be used. As an electron beam irradiation device, an electron beam accelerator can be mentioned, for example. As light sources of ultraviolet rays and visible light, for example, LED lamps, metal halide lamps encapsulated with gallium, low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, xenon lamps, halogen lamps, and gallium lamps can be mentioned. In this process, a wavelength blocking filter for blocking light of a part of the wavelength range in the ultraviolet rays and / or visible light emitted from the light source can be used as needed.

[0078] The laminated optical film X can be produced, for example, as described above.

[0079] Example

[0080] The present invention will be described in detail below with reference to the following examples, but the present invention is not limited to the examples. In addition, the specific numerical values ​​such as the amount (content), physical property values, and parameters described below can be replaced with the upper limits (numerical values ​​defined as "below" or "less than") or lower limits (numerical values ​​defined as "above" or "exceeding") of the amount (content), physical property values, and parameters corresponding to them described in the above-mentioned "Detailed Description of the Invention".

[0081] [Example 1]

[0082] The following components were mixed at 25°C for 1 hour in the amounts shown in Table 1 (in terms of solid content) to prepare a first adhesive composition for the first adhesive layer (first preparation step). Separately, the following components were mixed at 25°C for 1 hour in the amounts shown in Table 1 (in terms of solid content) to prepare a second adhesive composition for the second adhesive layer (second preparation step). The amounts shown in Table 1 are expressed in relative "parts by mass."

[0083] LIGHT ACRYLATE POB-A (monomer): 3-phenoxybenzyl acrylate, manufactured by Kyoeisha Chemical Co., Ltd.

[0084] LIGHT ACRYLATE P2H-A (monomer): phenoxydiethylene glycol acrylate, manufactured by Kyoeisha Chemical Co., Ltd.

[0085] Aronix M-5700 (monomer): 2-hydroxy-3-phenoxypropyl acrylate, manufactured by Toagosei Co., Ltd.

[0086] Aronix M-220 (monomer): tripropylene glycol diacrylate, manufactured by Toagosei Co., Ltd.

[0087] HEAA (monomer): Hydroxyethyl acrylamide, manufactured by KJ Chemical Co., Ltd.

[0088] DEAA (monomer): diethylacrylamide, manufactured by KJ Chemical Co., Ltd.

[0089] OMINIRAD907 (photopolymerization initiator): 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, manufactured by IGM Resins

[0090] KAYACURE DETX-S (photopolymerization initiator): 2,4-diethylthioxanthone, manufactured by Nippon Kayaku Co., Ltd.

[0091] Arufon 1190 (acrylic oligomer): viscosity 6000 mPa·s (25°C), Mw 1700, Tg -50°C, manufactured by Toagosei Co., Ltd.

[0092] BYK-UV3505 (leveling agent): modified polydimethylsiloxane with acryloyl groups, manufactured by BYK

[0093] Next, a coating process is performed, as described below. A first adhesive composition is applied to a COP film (trade name "ZEONOR Film ZF14", manufactured by Zeonor Co., Ltd., Japan) having a thickness of 23 μm as a first transparent protective film to form a first adhesive coating film having a thickness of 1 μm. On the other hand, a second adhesive composition is applied to a COP film (trade name "ZEONOR Film ZF14", manufactured by Zeonor Co., Ltd., Japan) having a thickness of 23 μm as a second transparent protective film to form a second adhesive coating film having a thickness of 1 μm. Each coating was performed using an MCD coater (manufactured by Fuji Machinery Co., Ltd.) (a unit shape is a honeycomb, a gravure roller line number is 1000 lines / inch, and a rotation speed of 140% / to-line speed).

[0094] Next, the first transparent protective film with the first adhesive coating, the polarizer film, and the second transparent protective film with the second adhesive coating are laminated (lamination step). Specifically, a roll laminator is used to laminate the first adhesive coating side of the first transparent protective film to one side of the polarizer film, and the second adhesive coating side of the second transparent protective film to the other side of the polarizer film.

[0095] Next, the first adhesive coating film is irradiated with ultraviolet light from the first transparent protective film side, and the second adhesive coating film is irradiated with ultraviolet light from the second transparent protective film side, thereby curing the adhesive coating film between the films (curing step). Ultraviolet light irradiation is performed using an ultraviolet irradiation device (trade name "LightHAMMER10", valve: V valve, manufactured by Fusion UV Systems, Inc.) equipped with a gallium-enclosed metal halide lamp as a light source. During ultraviolet light irradiation, the peak illuminance is set to 1600 mW / cm 2 , set the cumulative irradiation dose to 1000mJ / cm 2 (Wavelength 380-440 nm) (Illuminance was measured using the "Sola-Check System" manufactured by Solatell.) Thus, the first transparent protective film and the polarizer film were bonded together via the first adhesive layer, and the second transparent protective film and the polarizer film were bonded together via the second adhesive layer, thereby obtaining a laminated optical film.

[0096] As described above, a laminated optical film of Example 1 was produced. The laminated optical film of Example 1 comprises, in order of thickness, a first transparent protective film (thickness 23 μm), a first adhesive layer, a polarizer film (thickness 5 μm), a second adhesive layer, and a second transparent protective film (thickness 23 μm).

[0097] Table 1

[0098]

[0099] [Example 2]

[0100] A laminated optical film of Example 2 (first transparent protective film / first adhesive layer / polarizer film / second adhesive layer / second transparent protective film) was produced in the same manner as the laminated optical film of Example 1 except for the following operations.

[0101] In the first preparation step, instead of using "LIGHT ACRYLATE POB-A", "LIGHT ACRYLATE P2H-A" and "Aronix M-220", 40 parts by mass of "LIGHT ACRYLATE 1.9ND-A" (1,9-nonanediol diacrylate) manufactured by Kyoeisha Chemical Co., Ltd. and 9 parts by mass of "LIGHT ACRYLATE HPP-A" (hydroxypivalate neopentyl glycol acrylic acid adduct) manufactured by Kyoeisha Chemical Co., Ltd. were used. The blending amount of "Aronix M-5700" was 22 parts by mass, the blending amount of "HEAA" was 12.5 parts by mass, the blending amount of "DEAA" was 6 parts by mass, the blending amount of "HEAA" was 12.5 parts by mass, and the blending amount of "Arufon 1190" was 10 parts by mass. In the coating step, the thickness of the first adhesive layer formed on the first transparent protective film was set to 1.1 μm, and the thickness of the second adhesive layer formed on the second transparent protective film was set to 1.2 μm.

[0102] [Example 3]

[0103] A laminated optical film of Example 3 (first transparent protective film / first adhesive layer / polarizer film / second adhesive layer / second transparent protective film) was produced in the same manner as the laminated optical film of Example 1 except for the following operations.

[0104] In the first preparation step, instead of using "LIGHT ACRYLATE POB-A", "Aronix M-220", "Aronix M-5700", "DEAA" and "Arufon 1190", 27 parts by mass of "LIGHT ACRYLATE 1.9ND-A" (1,9-nonanediol diacrylate) manufactured by Kyoeisha Chemical Co., Ltd. and 59 parts by mass of "ACMO-LI" (acryloylmorpholine) manufactured by KJ Chemical Co., Ltd. were used. The blending amount of "LIGHT ACRYLATE P2H-A" was set to 10 parts by mass, and the blending amount of "HEAA" was set to 3 parts by mass. In the second preparation step, the blending amount of "LIGHT ACRYLATE POB-A" was set to 43 parts by mass, the blending amount of "LIGHT ACRYLATE P2H-A" was set to 29 parts by mass, the blending amount of "Aronix M-220" was set to 3 parts by mass, and the blending amount of "Aronix M-5700" was set to 10 parts by mass. Furthermore, in the coating step, the thickness of the first adhesive layer formed on the first transparent protective film was set to 1.2 μm, and the thickness of the second adhesive layer formed on the second transparent protective film was set to 0.9 μm.

[0105] [Comparative Example 1]

[0106] A laminated optical film of Comparative Example 1 (first transparent protective film / first adhesive layer / polarizer film / second adhesive layer / second transparent protective film) was produced in the same manner as the laminated optical film of Example 1 except for the following operations.

[0107] In the first preparation step, a composition identical to the second adhesive composition in Example 1 was prepared. In the second preparation step, instead of using "LIGHT ACRYLATE POB-A," "Aronix M-220," "Aronix M-5700," "DEAA," and "Arufon 1190," 23 parts by mass of "LIGHT ACRYLATE 1.9ND-A" (1,9-nonanediol diacrylate) manufactured by Kyoeisha Chemical Co., Ltd. and 60 parts by mass of "ACMO-LI" (acryloylmorpholine) manufactured by KJ Chemical Co., Ltd. were used. The blending amount of "LIGHT ACRYLATE P2H-A" was set to 13 parts by mass, and the blending amount of "HEAA" was set to 3 parts by mass. Furthermore, in the coating step, the thickness of the first adhesive layer formed on the first transparent protective film was set to 1.0 μm, and the thickness of the second adhesive layer formed on the second transparent protective film was set to 1.2 μm.

[0108] <Thickness of adhesive layer>

[0109] The thickness T of each adhesive layer in each laminated optical film of Examples 1 to 3 and Comparative Example 1 was measured as follows. First, a 5 mm × 10 mm film piece (laminated optical film) was cut out from the laminated optical film. Next, the laminated optical film was cut by a cryosection method. Specifically, the laminated optical film was cooled to -30°C, and then cut with a hard knife along the thickness direction of the film, and then returned to room temperature. The cut surface of the laminated optical film thus formed was subjected to a conductive treatment with a thickness of less than 5 nm, thereby obtaining an observation sample. Next, the thickness of the adhesive layer was measured by SEM observation of the observation sample. Specifically, a scanning electron microscope (trade name "REGULUS8220", manufactured by HITACHI Corporation) was used to observe and photograph the secondary electron image of the above-mentioned cut surface in the observation sample, and the thickness of each adhesive layer was measured. In this observation, the acceleration voltage was set to 3.0 kV, the current was set to 10 μA, the working distance was set to 8 mm, the magnification was set to 100,000 times, and the detection mode was set to Upper + Lower mode. The thickness T1 (μm) of the first adhesive layer and the thickness T2 (μm) of the second adhesive layer are shown in Table 2, as is the ratio of thickness T2 to thickness T1 (T2 / T1).

[0110] <Peel Strength>

[0111] The 90° peel strength between the first transparent protective film and the polarizer film in each laminated optical film of Examples 1 to 3 and Comparative Example 1 was measured as described below (first measurement). First, a first sample film having a size of 200 mm on the first side and 15 mm on the second side was cut out from the laminated optical film. The first side is a side extending in the stretching direction of the polarizer film, and the second side is a side extending in a direction orthogonal to the above-mentioned stretching direction. Next, the second transparent protective film side of the first sample film was adhered to a glass plate via a strong adhesive. Next, the 90° peel strength (N / 15mm) of the first transparent protective film from the polarizer film was measured using a Tensilon universal testing machine (trade name "RTC", manufactured by A&D). In this measurement, the first chuck of the Tensilon universal testing machine was used to hold the glass plate and the first sample film on the glass plate from the glass plate to the polarizer film, and the second chuck of the testing machine was used to hold the first transparent protective film of the first sample film. In this measurement, the measurement temperature was set to 25°C, the peeling angle was set to 90°, and the peeling speed was set to 1000 mm / min. Table 2 shows the 90° peel strength F1 (N / 15 mm) in this peeling test in which the first transparent protective film was peeled from the polarizer film.

[0112] In addition, the 90° peel strength between the second transparent protective film and the polarizer film in each of the laminated optical films of Examples 1 to 3 and Comparative Example 1 was measured as described below (second measurement). First, a second sample film identical to the first sample film was cut out from the laminated optical film. Next, the first transparent protective film side of the second sample film was adhered to a glass plate via a strong adhesive. Next, the 90° peel strength (N / 15mm) between the second transparent protective film and the polarizer film was measured using a Tensilon universal testing machine (trade name "RTC", manufactured by A&D). In this measurement, the glass plate and the second sample film on the glass plate were gripped from the glass plate to the polarizer film, and the second transparent protective film of the second sample film was gripped using the second chuck of the testing machine. The measurement conditions in the second measurement are the same as the above-mentioned measurement conditions in the first measurement. Table 2 shows the 90° peel strength F2 (N / 15 mm) in the peeling test in which the second transparent protective film was peeled from the polarizer film.

[0113] 〈Indentation elastic modulus〉

[0114] The indentation modulus of the first adhesive layer in each of the laminated optical films of Examples 1 to 3 and Comparative Example 1 was measured using nanoindentation. Specifically, a 5 mm x 10 mm film piece (laminated optical film) was cut from the laminated optical film. Next, the laminated optical film was sliced ​​using a cryosectioning method. Specifically, the laminated optical film was cooled to -30°C, then sliced ​​along the film's thickness with a hard knife, and then returned to room temperature to obtain a sample for measurement. Next, a load-displacement measurement was performed on the exposed surface of the adhesive layer of the measurement sample using a nanoindenter (trade name "TI950 Triboindenter," manufactured by Hysitron) in accordance with JIS Z2255:2003, generating a load-displacement curve. In this measurement, the measurement mode was set to a single indentation measurement, the measurement temperature was set to 25°C, the indenter used was set to a Berkovich (triangular pyramid) type diamond indenter, the maximum indentation depth (maximum displacement hmax) of the indenter into the measurement sample during the load application process was set to 50 nm, the indentation speed of the indenter was set to 10 nm / second, and the withdrawal speed of the indenter from the measurement sample during the load release process was set to 10 nm / second. Then, the obtained measurement data was processed by the dedicated analysis software (Ver.9.4.0.1) of "TI950 Triboindenter". Specifically, based on the obtained load (f)-displacement (h) curve, the maximum load fmax (the load acting on the indenter at the maximum displacement hmax), the contact projection area S (the projection area of ​​the contact area between the indenter and the sample at the maximum load), and the slope D of the tangent of the load-displacement curve at the beginning of the load release process were obtained. Then, based on the slope D and the contact projection area S, the indentation elastic modulus (= (π 1 / 2 D) / (2S 1 / 2 )), and its value is shown in Table 2 as the indentation elastic modulus E1 (GPa).

[0115] In addition, the indentation elastic modulus of the second adhesive layer in each laminated optical film of Examples 1 to 3 and Comparative Example 1 was measured in the same manner as the above-mentioned indentation elastic modulus E1 of the first adhesive layer, and this value is shown in Table 2 as the indentation elastic modulus E2 (GPa). The ratio of the indentation elastic modulus E2 to the indentation elastic modulus E1 (E2 / E1) is also shown in Table 2.

[0116] Uneven display

[0117] When each of the laminated optical films of Examples 1 to 3 and Comparative Example 1 is installed on a display panel, the presence or absence of display unevenness when the display panel is bent is investigated. As a display panel, an organic EL panel (OLED panel) taken out from a commercially available foldable smartphone is used. The laminated optical film is arranged on the image display side surface of the display panel. Specifically, the second transparent protective film side of the laminated optical film is adhered to the image display side surface of the display panel via an adhesive, and then, in a state where an image is displayed on the display panel, the display panel is bent 90°, and the image at the bent portion is observed with the naked eye. The case where no display unevenness (change in color tone) is confirmed in the image at the bent portion is evaluated as "good", and the case where the display unevenness is confirmed is evaluated as "poor", and the results are shown in Table 2.

[0118] <High temperature and high humidity bending test>

[0119] The high-temperature and high-humidity bending test was performed on each of the laminated optical films of Examples 1 to 3 and Comparative Example 1 as described below.

[0120] First, a sample for evaluation was cut out from the laminated optical film. Specifically, a rectangular sample of 25 mm × 100 mm was cut out from the laminated film, and the absorption axis of the polarizer film in the cut sample was parallel to the long side direction. Next, a bending test was performed on the sample using a planar unloaded U-shaped stretch tester (manufactured by YUASA SYSTEM Co., Ltd.). In this test, bending fixtures were installed at both ends of the long side of the sample within a range of 20 mm from the edge of the sample end, and the sample was fixed to the tester (the central 60 mm area of ​​the long side of the sample was in an unfixed state). In addition, in this test, in a constant temperature and humidity chamber at a temperature of 60°C and a relative humidity of 90%, the sample was repeatedly deformed (bent) 80,000 times at a bending speed of 60 rpm between a bent form in which the surface on the first transparent protective film side was on the inner side and a non-bent form. The bent form in this test specifically refers to a form in which the axial direction of the bending thrust acting on the sample is orthogonal to the absorption axis of the polarizer film. In this bending state, the sample was bent at a radius of 3 mm and a bend angle of 180°. The resistance to peeling between the films (first transparent protective film, polarizer film, and second transparent protective film) during this bending test was evaluated as "good" if no peeling occurred after 80,000 bends, and as "poor" if peeling occurred after less than 80,000 bends. The evaluation results are shown in Table 1.

[0121]

[0122] Industrial Applicability

[0123] The laminated optical film of the present invention can be used as an element included in the laminated structure of a display panel such as a foldable display panel, for example.

Claims

1. A laminated optical film comprising, in order in the thickness direction, a first optical film, a first adhesive layer, a second optical film, a second adhesive layer, and a third optical film, The first adhesive layer is bonded to the first optical film and to the second optical film. The second adhesive layer is bonded to the second optical film and to the third optical film. The indentation elastic modulus E1 of the first adhesive layer at 25° C. and the indentation elastic modulus E2 of the second adhesive layer at 25° C. satisfy 0.3≦E2 / E1<1.

2. The laminated optical film according to claim 1, wherein The indentation elastic modulus E2 is 4 GPa or less.

3. The laminated optical film according to claim 1, wherein The indentation elastic modulus E2 is 0.4 GPa or more.

4. The laminated optical film according to claim 1, wherein The indentation elastic modulus E1 is 0.5 GPa or more.

5. The laminated optical film according to claim 1, wherein The indentation elastic modulus E1 is 7 GPa or less.

6. The laminated optical film according to any one of claims 1 to 5, wherein The second optical film is a polarizer film.

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