Laminated optical film

Abstract

A layered optical film (X) according to the present invention comprises an optical film (10), optical films (21, 22), and adhesive layers (31, 32). The adhesive layer (31) is joined to the optical film (10), and is joined to the optical film (21). The adhesive layer (32) is joined to the optical film (10), and is joined to the optical film (22). The indentation modulus E1 at 25°C of the adhesive layer (31) and the indentation modulus E2 at 25°C of the adhesive layer (32) satisfy 0.3≤E2 / E1<1.

Description

Technical Field

[0001] The present invention relates to a laminated optical film.

Background Art

[0002] A display panel has a laminated structure including, for example, a pixel panel, a touch panel, a surface protection cover, etc. Various functional optical films having predetermined optical functions are also included in the laminated structure of the display panel. Examples of the functional optical film include a polarizer film and a retardation film. The functional optical film is incorporated into the laminated structure, for example, in a state where other optical films such as a protective film are joined via an adhesive to both surfaces of the film, that is, in the form of a laminated optical film. Such a laminated optical film is described, for example, in Patent Document 1 below.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For example, development is underway on foldable display panels for smartphones and tablet devices. In foldable display panels, each element in the laminated structure is manufactured to be repeatedly bendable. Furthermore, at the bending point of a foldable display panel, tensile stress is generated in the optical film on the outer side of the bend in the laminated optical film. Conventionally, this tensile stress causes a photoelastic effect in the outer optical film at the bending point, resulting in birefringence of light transmitted through the film. Birefringence of transmitted light is undesirable as it causes display unevenness in the image display of the display panel. In particular, when a foldable display panel is used by being repeatedly bent over a long period of time, display unevenness is likely to occur due to the birefringence caused by the hardness of the adhesive layer located on the outer side of the bend.

[0005] The present invention provides a laminated optical film suitable for suppressing display unevenness when a foldable display panel is folded. [Means for solving the problem]

[0006] The present invention [1] includes a laminated optical film comprising 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, the second adhesive layer is bonded to the second optical film and to the third optical film, and the indentation modulus E1 of the first adhesive layer at 25°C and the indentation modulus E2 of the second adhesive layer at 25°C satisfy 0.3 ≤ E2 / E1 < 1.

[0007] The present invention [2] includes the laminated optical film described in [1] above, wherein the indentation modulus E2 is 4 GPa or less.

[0008] The present invention [3] includes the laminated optical film described in [1] or [2] above, wherein the indentation modulus E2 is 0.4 GPa or greater.

[0009] The present invention [4] includes a laminated optical film according to any one of [1] to [3] above, wherein the indentation modulus E1 is 0.5 GPa or more.

[0010] The present invention [5] includes a laminated optical film according to any one of [1] to [4] above, wherein the indentation modulus E1 is 7 GPa or less.

[0011] The present invention [6] includes a laminated optical film according to any one of [1] to [5] above, wherein the second optical film is a polarizer film. [Effects of the Invention]

[0012] In the laminated optical film of the present invention, as described above, the indentation modulus E1 of the first adhesive layer and the indentation modulus E2 of the second adhesive layer satisfy the condition 0.3 ≤ E2 / E1 < 1. The second adhesive layer has a softness such that its indentation modulus E2 is small enough that its ratio (E2 / E1) is less than 1. Such a second adhesive layer is suitable for relieving the tensile stress generated in the third optical film at the bending point when the laminated optical film is bent so that the third optical film is on the outside of the bend. At the bending point of the third optical film, the photoelastic effect described above is reduced by the relief of tensile stress, and display unevenness in the image display of the display panel is suppressed. Furthermore, a second adhesive layer having an indentation modulus E2 that is large enough that its ratio (E2 / E1) is 0.3 or greater is suitable for ensuring the bonding strength between the second and third optical films at the bending point. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view of one embodiment of the laminated optical film of the present invention. [Figure 2] Figure 1 shows the laminated optical film in a folded state. [Modes for carrying out the invention]

[0014] As one embodiment of the laminated optical film of the present invention, the laminated optical film X comprises an optical film 10, optical films 21 and 22, and adhesive layers 31 and 32, as shown in Figure 1. Specifically, the laminated optical film X comprises 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 order along the thickness direction H. The laminated optical film X has a sheet shape of a predetermined thickness and extends in a direction perpendicular to the thickness direction H (surface direction). The adhesive layer 31 joins the optical films 10 and 21. The adhesive layer 32 joins the optical films 10 and 22. Furthermore, the laminated optical film X is a composite film incorporated into the laminated structure of a foldable display panel. The laminated optical film X is, for example, a laminated optical film disposed on the image display side surface of a display panel such as a foldable organic EL panel (OLED panel). In a foldable display panel, the laminated optical film X is folded so that the optical film 21 and adhesive layer 31 face inward, as shown in Figure 2. At folding point B, the optical film 21 and adhesive layer 31 are on the inward side (lower side in the figure) relative to the optical film 10, while the optical film 22 and adhesive layer 32 are on the outward side (upper side in the figure) relative to the optical film 10.

[0015] In this embodiment, the optical film 10 is a functional optical film. Examples of functional optical films include polarizer films and phase difference films.

[0016] Examples of polarizer films include hydrophilic polymer films that have undergone dyeing treatment with a dichroic substance followed by stretching. Examples of dichroic substances include iodine and dichroic dyes. Examples of hydrophilic polymer films include polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films. Polyene-oriented films can also be used as polarizer films. Examples of materials for polyene-oriented films include dehydrated PVA and dehydrochlorinated polyvinyl chloride. As polarizer films, PVA films that have undergone dyeing treatment with iodine followed by uniaxial stretching are preferred because they have excellent optical properties such as polarization characteristics.

[0017] From the viewpoint 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 excellent visibility due to less thickness unevenness and excellent durability against thermal shock due to small dimensional changes due to temperature changes. From the viewpoint of strength, the thickness of the optical film 10 as a polarizer film is preferably 3 μm or more, more preferably 5 μm or more.

[0018] Examples of phase difference films include λ / 2 wavelength films, λ / 4 wavelength films, and viewing angle compensation films. Examples of materials for the phase difference film include polymer films that have been birefred by stretching. Examples of polymer films include cellulose films and polyester films. Examples of cellulose films include triacetylcellulose films. Examples of polyester films include polyethylene terephthalate films and polyethylene naphthalate films. The thickness of the optical film 10 as a phase difference film is, for example, 20 μm or more and, for example, 150 μm or less. Furthermore, a film comprising a substrate such as a cellulose film and an alignment layer of a liquid crystal compound such as a liquid crystal polymer on the substrate can also be preferably used as a phase difference film.

[0019] Optical films 21 and 22 are transparent protective films. The transparent protective film is, for example, a flexible transparent resin film. Examples of materials for 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. An example of modified cellulose is triacetylcellulose. These materials may be used individually or in combination of two or more. From the viewpoint of cleanliness, polyolefins are preferably used as the material for the transparent protective film, and COP is more preferably used. Furthermore, the materials of optical film 21 and optical film 22 may be the same or different.

[0020] From the viewpoint 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 more, more preferably 10 μm or more, still more preferably 20 μm or more. From the viewpoint of thinning the laminated optical film X, the thickness of the optical film 21 is preferably 100 μm or less, more preferably 70 μm or less, still 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.

[0021] The adhesive layer 3ɪ is a cured product of the first adhesive composition. The adhesive layer 3ɪ is directly bonded to the optical film ɪ0 and directly bonded to the optical film 2ɪ. The first adhesive composition contains a curable resin. The components of the first adhesive composition are specifically as described below.

[0022] From the viewpoint of the bonding strength between the optical films ɪ0 and 2ɪ, the thickness Tɪ of the adhesive layer 3ɪ is preferably 0.ɪ μm or more, more preferably 0.4 μm or more, still more preferably 0.7 μm or more, particularly preferably 0.8 μm or more. From the viewpoint of thinning the laminated optical film X, the thickness Tɪ of the adhesive layer 3ɪ is preferably 5 μm or less, more preferably 3 μm or less, still more preferably ɪ.5 μm or less, particularly preferably ɪ μm or less.

[0023] It should be noted that there seems to be some inconsistent variable naming in the original text (such as "光学フィルム10" and "光学フィルム21" which should probably be more systematically named if this were a more formal document). I've translated it as presented while keeping the variable names as they are. Also, there might be a small error in the original where "3ɪ" and "ɪ0" and "2ɪ" are used which might need to be corrected in the source material for a more clear translation.The indentation modulus E1 of the adhesive layer 31 at 25°C, measured by nanoindentation, is preferably 0.5 GPa or higher, more preferably 1 GPa or higher, even more preferably 1.5 GPa or higher, and particularly preferably 2 GPa or higher. This configuration is preferable for ensuring bonding strength between optical films 10 and 21 at the bending point B when the laminated optical film X is bent so that the optical film 21 side faces inward. The indentation modulus E1 is preferably 7 GPa or lower, more preferably 6 GPa or lower, and even more preferably 5.2 GPa or lower. This configuration is preferable for relieving the compressive stress acting on the adhesive layer 31 at the bending point B. Relieving the compressive stress of the adhesive layer 31 at the bending point B helps suppress delamination between the optical films 10 and 21. Furthermore, this configuration regarding the upper limit of the indentation modulus E1 is preferable in that it ensures low elasticity in the adhesive layer 31 (the adhesive layer on the inside of the bend) at the bending point B, thereby obtaining sufficient adhesion to the optical films 10 and 21, and is therefore suitable for suppressing buckling of the optical film 10 at the bending point B. As a method for adjusting the indentation modulus E1 of the adhesive layer 31, for example, adjustment of the composition of the first adhesive composition can be mentioned. Specifically, adjusting the number of functional groups of the polymerizable compound described later in the first adhesive composition, that is, adjusting the acrylic equivalent or epoxy equivalent of the polymerizable compound, is an effective method for adjusting the indentation modulus E1 of the adhesive layer 31.

[0024] Nanoindentation is a technique for measuring various physical properties of a sample on a nanometer scale. In this embodiment, the nanoindentation method is performed in accordance with ISO 14577. In the nanoindentation method, a process of pressing an indenter into the sample set on a stage (load application process) and a subsequent process of withdrawing the indenter from the sample (unloading process) are performed. During this series of processes, the load acting between the indenter and the sample and the relative displacement of the indenter with respect to the sample are measured (load-displacement measurement). This makes it possible to obtain a load-displacement curve. From this load-displacement curve, it is possible to determine various physical properties of the sample based on nanometer-scale measurements. For measuring the load-displacement of the cross-section of an adhesive layer using the nanoindentation method, for example, a nanoindenter (product name "Triboindenter", manufactured by Hysitron) can be used. Specifically, the examples will be described later.

[0025] 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 also directly bonded to the optical film 22. The second adhesive composition contains a curable resin. The components of the second adhesive composition are specifically as described below.

[0026] The thickness T2 of the adhesive layer 32 is preferably 0.1 μm or more, more preferably 0.4 μm or more, even more preferably 0.7 μm or more, and particularly preferably 0.8 μm or more, from the viewpoint of bonding strength between the optical films 10 and 22. The thickness T2 of the adhesive layer 32 is preferably 5 μm or less, more preferably 3 μm or less, even more preferably 1.5 μm or less, and particularly preferably 1 μm or less, from the viewpoint of thinning the laminated optical film X. The thickness T2 of the adhesive layer 32 and the thickness T1 of the adhesive layer 31 described above may be the same or different. The ratio of thickness T2 to thickness T1 (T2 / T1) is, for example, 0.5 or more, and for example, 2 or less.

[0027] The indentation modulus E2 of the adhesive layer 32 at 25°C, measured by nanoindentation, is preferably 0.4 GPa or higher, more preferably 0.8 GPa or higher, even more preferably 1.2 GPa or higher, and particularly preferably 1.8 GPa or higher, as long as it is smaller than the indentation modulus E1. The indentation modulus E2 is preferably 4 GPa or lower, more preferably 3 GPa or lower, and even more preferably 2.5 GPa or lower, as long as it is smaller than the indentation modulus E1. These configurations are preferable for ensuring bonding strength between the optical films 10 and 22. As a method for adjusting the indentation modulus E2 of the adhesive layer 32, for example, adjustment of the composition of the second adhesive composition can be mentioned. Specifically, adjusting the number of functional groups of the polymerizable compound described later in the second adhesive composition, i.e., adjusting the acrylic equivalent or epoxy equivalent of the polymerizable compound, is an effective method for adjusting the indentation modulus E2 of the adhesive layer 32.

[0028] The indentation modulus E1 of adhesive layer 31 at 25°C and the indentation modulus E2 of adhesive layer 32 at 25°C satisfy 0.3 ≤ E2 / E1 < 1.

[0029] The adhesive layer 32 has a softness such that its indentation modulus E2 is small enough that its ratio (E2 / E1) is less than 1. Such an adhesive layer 32 is suitable for relieving the tensile stress generated in the optical film 22 at the bending point B when the laminated optical film X is bent so that the optical film 22 is on the outside of the bend. At the bending point of the optical film 22, the photoelastic effect is reduced by the relief of tensile stress, and display unevenness in the image display of the display panel is suppressed. From this viewpoint, the ratio (E2 / E1) is preferably 0.97 or less, more preferably 0.8 or less.

[0030] Furthermore, an adhesive layer 32 having a ratio (E2 / E1) of 0.3 or more and a sufficiently large indentation modulus E2 is suitable for ensuring bonding strength between optical films 10 and 22 at the bending point B. Conversely, an adhesive layer 31 having a ratio (E2 / E1) of 0.3 or more and a sufficiently small indentation modulus E1 is preferable in the adhesive layer 31 (the adhesive layer on the inside of the bend) at the bending point B to ensure low elasticity and obtain sufficient adhesion to the optical films 10 and 21, and therefore is suitable for suppressing buckling of the optical film 10 at the bending point B. From these viewpoints, the ratio (E2 / E1) is preferably 0.5 or more, more preferably 0.6 or more.

[0031] Methods for adjusting the ratio (E2 / E1) include adjusting the indentation modulus E1 and adjusting the indentation modulus E2.

[0032] In the laminated optical film X, the 90° peel strength F1 of optical film 21 relative to optical film 10 at 25°C is preferably 0.8 N / 15 mm or more, more preferably 1 N / 15 mm or more, even more preferably 1.2 N / 15 mm or more, and particularly preferably 1.5 N / 15 mm or more. Such a configuration is preferable for ensuring good bonding strength between optical films 10 and 21, and is particularly preferable for ensuring bonding strength between optical films 10 and 21 at the bending point B when the laminated optical film X is bent. Furthermore, 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 later with respect to the examples. The peel strength of the optical film 21 from 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 due to cohesive failure of the adhesive layer 31, interfacial peeling between the adhesive layer 31 and the optical film 21, and peeling due to a combination of these. Furthermore, a method for adjusting the 90° peel strength F1 is, for example, adjusting the composition of the first adhesive composition. Specifically, a method for adjusting the 90° peel strength F1 is to adjust the number of functional groups of the polymerizable compound described later in the first adhesive composition, that is, to adjust the acrylic equivalent and epoxy equivalent of the polymerizable compound.

[0033] In the laminated optical film X, the 90° peel strength F2 of the optical film 22 relative to the optical film 10 at 25°C is preferably 0.8 N / 15 mm or more, more preferably 1 N / 15 mm or more, even more preferably 1.2 N / 15 mm or more, and particularly preferably 1.5 N / 15 mm or more. Such a configuration 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 bending point B when the laminated optical film X is bent. Furthermore, 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 later with respect to the examples. The peel strength of the optical film 22 from 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 due to cohesive failure of the adhesive layer 32, interfacial peeling between the adhesive layer 32 and the optical film 22, and peeling due to a combination of these. Furthermore, a method for adjusting the 90° peel strength F2 is, for example, adjusting the composition of the second adhesive composition. Specifically, a method for adjusting the 90° peel strength F2 is to adjust the number of functional groups of the polymerizable compound described later in the second adhesive composition, that is, to adjust the acrylic equivalent and epoxy equivalent of the polymerizable compound.

[0034] 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 resin. Examples of the first active energy ray curable composition include an electron beam curable composition, an ultraviolet light curable composition, and a visible light curable composition. In this embodiment, the first active energy ray curable composition is either a radical polymerization composition or a cationic polymerization composition, or both.

[0035] When the first active energy ray-curable composition is a radical polymerization composition, the composition contains a radical polymerizable compound as a monomer. A radical polymerizable compound is a compound having a radical polymerizable functional group. Examples of radical polymerizable functional groups include ethylenically unsaturated bond-containing groups. Examples of ethylenically unsaturated bond-containing groups include (meth)acryloyl groups, vinyl groups, and allyl groups. (Meth)acryloyl groups mean acryloyl groups and / or methacryloyl groups. From the viewpoint of the curability of the first active energy ray-curable composition, it is preferable that the first active energy ray-curable composition contains a radical polymerizable compound having a (meth)acryloyl group as a main component. The main component means the component that is most abundant by mass. The proportion of the (meth)acryloyl group-containing radical polymerizable compound 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. Furthermore, examples of radical polymerizable compounds include monofunctional radical polymerizable compounds and polyfunctional radical polymerizable compounds with two or more functions.

[0036] Examples of monofunctional radical polymerizable compounds include (meth)acrylamide derivatives having a (meth)acrylamide group. Examples of (meth)acrylamide derivatives include N-alkyl group-containing (meth)acrylamide derivatives, N-hydroxyalkyl group-containing (meth)acrylamide derivatives, N-aminoalkyl group-containing (meth)acrylamide derivatives, N-alkoxy group-containing (meth)acrylamide derivatives, and N-mercaptoalkyl group-containing (meth)acrylamide derivatives. Examples of N-alkyl group-containing (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 group-containing (meth)acrylamide derivatives include N-methylol(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, and N-methylol-N-propane(meth)acrylamide, with N-hydroxyethylacrylamide being preferred. (Meth)acrylamide derivatives may be used alone or in combination of two or more types.

[0037] Examples of monofunctional 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. (Meth)acrylic acid derivatives may be used alone or in combination of two or more types.

[0038] Examples of 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.

[0039] Examples of (meth)acrylic acid derivatives other than alkyl (meth)acrylates include cycloalkyl (meth)acrylates, aralkyl (meth)acrylates, hydroxyl group-containing (meth)acrylic acid derivatives, alkoxy group-containing (meth)acrylic acid derivatives, and phenoxy group-containing (meth)acrylic acid 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)acrylic acid 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 alkyl (meth)acrylate, preferably at least one selected from the group consisting of 3-phenoxybenzyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, and phenoxydiethylene glycol acrylate is used.

[0040] Examples of monofunctional radical polymerizable compounds include carboxyl group-containing monomers. Examples of carboxyl group-containing monomers include (meth)acrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

[0041] Examples of monofunctional radical polymerizable compounds include lactam-based vinyl monomers. Examples of lactam-based vinyl monomers include N-vinyl-2-pyrrolidone, N-vinyl-ε-caprolactam, and methylvinylpyrrolidone.

[0042] Examples of monofunctional radical polymerizable compounds include vinyl monomers having nitrogen-containing heterocyclic rings. Examples of such monomers include vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylimidazole, vinyloxazole, acryloylmorpholine, and vinylmorpholine.

[0043] Examples of polyfunctional radical polymerizable compounds include 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-butylpropanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, and cyclic trimethylolpropane. Formal (meth)acrylate, dioxane glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate are used, preferably tripropylene glycol diacrylate and hydroxypivalate neopentyl glycol acrylic acid adduct. As the polyfunctional radical polymerizable compound, preferably at least one selected from the group consisting of tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, and hydroxypivalate neopentyl glycol acrylic acid adduct is used. The polyfunctional radical polymerizable compound may be used alone or in combination of two or more types. The polyfunctional radical polymerizable compound functions as a crosslinking agent.

[0044] 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 photopolymerization initiators include benzophenone compounds, benzoin ether compounds, and thioxanthone compounds. Examples of benzophenone compounds include benzyl, 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.

[0045] When the first active energy ray curable composition is a visible light curable composition, a photopolymerization initiator that is highly sensitive to light of 380 nm or higher is preferably used. Examples of such photopolymerization initiators include 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrole-1-yl)-phenyl)titanium.

[0046] Preferably, 2,4-diethylthioxanthone and / or 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one are used as photopolymerization initiators.

[0047] The content of the photopolymerization initiator in the first active energy ray curable composition is preferably 0.1 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, and preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the curable component (radical polymerizable compound).

[0048] When the first active energy ray curable composition is a cationic polymerization composition, the composition contains a cationic polymerizable compound as a monomer. The cationic polymerizable compound is a compound having a cationic polymerizable functional group, and includes monofunctional cationic polymerizable compounds having one cationic polymerizable functional group and polyfunctional cationic polymerizable compounds having two or more cationic polymerizable functional groups. Monofunctional cationic polymerizable compounds have relatively low liquid viscosity. By incorporating such a monofunctional cationic polymerizable compound into a resin composition, the viscosity of the resin composition can be reduced. Furthermore, monofunctional cationic polymerizable compounds often have functional groups that exhibit various functions. By incorporating such a monofunctional cationic polymerizable compound into a resin composition, various functions can be exhibited in the resin composition and / or in the cured product of the resin composition. On the other hand, curing a resin composition containing a polyfunctional cationic polymerizable compound yields a cured product having a three-dimensional crosslinked portion (the polyfunctional cationic polymerizable compound functions as a crosslinking agent). From this viewpoint, the use of polyfunctional cationic polymerizable compounds is preferred. When a monofunctional cationic polymerizable compound and a polyfunctional cationic polymerizable compound are used in combination, the amount of the polyfunctional cationic polymerizable compound per 100 parts by mass of the monofunctional cationic polymerizable compound is, for example, 10 parts by mass or more, and also, for example, 1000 parts by mass or less. Examples of cationic polymerizable functional groups include epoxy groups, oxetanyl groups, and vinyl ether groups. Examples of compounds having epoxy groups include aliphatic epoxy compounds, alicyclic epoxy compounds, and aromatic epoxy compounds. From the viewpoint of curability and adhesion of the cationic polymerized composition, alicyclic epoxy compounds are preferably used as the compounds having epoxy groups. Examples of alicyclic epoxy compounds include caprolactone-modified, trimethylcaprolactone-modified, and valerolactone-modified 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 Celoxide 2021, Celoxide 2021A, Celoxide 2021P, Celoxide 2081, Celoxide 2083, and Celoxide 2085 (all manufactured by Daicel Chemical Industries, Ltd.), as well as Cyracure UVR-6105, Cyracure UVR-6107, Cyracure 30, and R-6110 (all manufactured by Dow Chemical Japan). From the viewpoint of improving the curability and reducing the viscosity of cationic polymerization compositions, it is preferable to use compounds having an oxetanyl group and / or a vinyl ether group. Examples of compounds having an oxetanyl group include 3-ethyl-3-hydroxymethyloxetane, 1,4-bis[(3-ethyl-3-oxetanyl)methoxymethyl]benzene, 3-ethyl-3-(phenoxymethyl)oxetane, di[(3-ethyl-3-oxetanyl)methyl]ether, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, and phenol novolac oxetane. Examples of commercially available compounds having an oxetanyl group include Aronoxetane OXT-101, Aronoxetane OXT-121, Aronoxetane OXT-211, Aronoxetane OXT-221, and Aronoxetane OXT-212 (all manufactured by Toagosei Co., Ltd.). Examples of compounds 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-type tetravinyl ether.

[0049] 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 generates a cationic species or Lewis acid upon irradiation with active energy rays (visible light, ultraviolet light, X-rays, electron beams, etc.) and initiates the polymerization reaction of cationic polymerizable functional groups. Examples of photocationic polymerization initiators include photoacid generators and photobase generators, with photoacid generators being preferred. When the first active energy ray-curable composition is a visible light-curable composition, it is particularly preferable to use a photocationic polymerization initiator that is highly sensitive to light of 380 nm or longer. Furthermore, when using a photocationic polymerization initiator, it is preferable to use in combination a photosensitizer that exhibits maximum absorption for light with wavelengths longer than 380 nm. Since photocationic polymerization initiators are generally compounds that exhibit maximum absorption around 300 nm or shorter wavelengths, by using them in combination with photosensitizers that exhibit maximum absorption at wavelengths longer than 380 nm, it is possible to effectively utilize light at wavelengths longer than 380 nm to promote the generation of cationic species or Lewis acids from the photocationic polymerization initiator. Examples of photosensitizers include anthracene compounds, pyrene compounds, carbonyl compounds, organosulfur compounds, persulfides, redox compounds, azo compounds, diazo compounds, halogen compounds, and photoreducing dyes. These may be used alone or in combination of two or more. Anthracene compounds are particularly preferred due to their excellent photosensitizing effect. Examples of commercially available anthracene compounds as photosensitizers include Anthracure UVS-1331 and Anthracure UVS-1221 (manufactured by Kawasaki Chemical Co., Ltd.). The content of the photosensitizer in the composition is, for example, 0.1 to 5% by weight.

[0050] The first active energy ray-curable composition may contain an oligomer. Examples of oligomers include acrylic oligomers, fluorine oligomers, and silicone oligomers, with acrylic oligomers being preferred. The incorporation of an oligomer into the first active energy ray-curable composition helps suppress shrinkage during curing. Suppressing the curing shrinkage of the first active energy ray-curable composition is preferable for reducing interfacial stress between the formed adhesive layer 31 and the optical films 10 and 21. Suppressing interfacial stress helps ensure bonding strength between the optical films 10 and 21.

[0051] Examples of (meth)acrylic monomers that form acrylic oligomers 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 alkyl (meth)acrylates 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, S-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, cetyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 4-methyl-2-propylpentyl (meth)acrylate, and N-octadecyl (meth)acrylate. Examples of cycloalkyl (meth)acrylates include cyclohexyl (meth)acrylate and cyclopentyl (meth)acrylate. Examples of aralkyl (meth)acrylates include benzyl (meth)acrylate. Examples of polycyclic (meth)acrylates include 2-isobornyl (meth)acrylate, 2-norbornylmethyl (meth)acrylate, 5-norbornen-2-ylmethyl (meth)acrylate, and 3-methyl-2-norbornylmethyl (meth)acrylate. Examples of hydroxyl-containing (meth)acrylic acid esters include hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2,3-dihydroxypropylmethyl-butyl (meth)methacrylate.Examples of halogen-containing (meth)acrylic acid esters include 2,2,2-trifluoroethyl (meth)acrylate, 2,2,2-trifluoroethylethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropentyl (meth)acrylate, and heptadecafluorodecyl (meth)acrylate. These (meth)acrylates may be used individually or in combination of two or more types.

[0052] 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.

[0053] The content of 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 also preferably 20% by mass or less, more preferably 15% by mass or less.

[0054] The first active energy ray curable composition may contain other components. Examples of other components include silane coupling agents, leveling agents, surfactants, plasticizers, and ultraviolet absorbers. The amount of these other components is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, and also, for example, 0.01 parts by mass or more, per 100 parts by mass of the curable component.

[0055] The viscosity of the first active energy ray-curable composition at 25°C is preferably 3 mPa·s or more, more preferably 5 mPa·s or more, even more preferably 10 mPa·s or more, and also preferably 100 mPa·s or less, more preferably 50 mPa·s or less, and even more preferably 30 mPa·s or less, from the viewpoint of coatability in the coating process described later. The viscosity of the composition is measured using an E-type viscometer (cone plate viscometer).

[0056] The adhesive layer 32 is, for example, a cured product of a second adhesive composition containing an active energy ray-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. Of these, the second active energy ray-curable composition and the first active energy ray-curable composition may be the same type of composition or different types of compositions. In this embodiment, the second active energy ray-curable composition is a radical polymerization type composition.

[0057] The components of the second active energy ray curable composition may be the same as those listed above for the first active energy ray curable composition. The range of component content in the second active energy ray curable composition is the same as that listed above for the component content in the first active energy ray curable composition. The composition of the second active energy ray curable composition and the composition of the first active energy ray curable composition may be the same or different.

[0058] The laminated optical film X can be manufactured, for example, as follows:

[0059] First, a first active energy ray-curable composition is applied to one side (the side to be bonded) of the optical film 21 to form a first coating film of the composition (first coating step). Then, a second active energy ray-curable composition is applied to one side (the side to be bonded) of the optical film 22 to form a second coating film of the composition (second coating step). Before each coating step, the side to be bonded of the optical film 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 step include a reverse coater, gravure coater, bar reverse coater, roll coater, die coater, bar coater, and rod coater.

[0060] Next, optical film 21 is laminated to one side of optical film 10 via a first coating, and optical film 22 is laminated to the other side of optical film 10 via a second coating. For lamination, for example, a roll laminator that performs both laminations simultaneously can be used.

[0061] Next, the first and second coating films are irradiated with active energy rays to cure the first coating film and form an adhesive layer 31, and to cure the second coating film and form an adhesive layer 32 (adhesive layers 31 and 32 are not pressure-sensitive adhesive layers). As a result, the optical films 10 and 21 are joined together via adhesive layer 31, and the optical films 10 and 22 are joined together via adhesive layer 32.

[0062] In this process, from the viewpoint of suppressing the degradation of the optical film 10 as a functional optical film, it is preferable to irradiate the optical film 21 side with an active energy ray for curing the first coating film and the optical film 22 side with an active energy ray for curing the second coating film. As the active energy ray, electron beams, ultraviolet rays, and visible light can be used. An electron beam irradiation means is, for example, an electron beam accelerator. Examples of light sources for ultraviolet rays and visible light are LED lights, gallium-filled metal halide lamps, low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, xenon lamps, halogen lamps, and gallium lamps. In this process, a wavelength cut filter may be used as needed to cut out some wavelength ranges in the ultraviolet rays and / or visible light emitted from the light source.

[0063] The laminated optical film X can be manufactured, for example, as described above. [Examples]

[0064] The present invention will be specifically described below with reference to examples. The present invention is not limited to these examples. Furthermore, the specific numerical values ​​such as the amounts (content), physical properties, and parameters described below can be substituted with the upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to" or "greater than") of the corresponding amounts (content), physical properties, and parameters described in the "Modes for Carrying Out the Invention" above.

[0065] [Example 1] The first adhesive composition for the first adhesive layer was prepared by mixing the following components in the amounts (solid content) shown in Table 1 at 25°C for 1 hour (first preparation step). The second adhesive composition for the second adhesive layer was also prepared by mixing the following components in the amounts (solid content) shown in Table 1 at 25°C for 1 hour (second preparation step). The units of the amounts shown in Table 1 are relative "parts by mass".

[0066] Light acrylate POB-A (monomer): 3-phenoxybenzyl acrylate, manufactured by Kyoeisha Chemical Co., Ltd. Light Acrylate P2H-A (Monomer): Phenoxydiethylene glycol acrylate, manufactured by Kyoeisha Chemical Co., Ltd. Aronix M-5700 (monomer): 2-hydroxy-3-phenoxypropyl acrylate, manufactured by Toagosei Co., Ltd. Aronix M-220 (Monomer): Tripropylene glycol diacrylate, manufactured by Toagosei Co., Ltd. HEAA (monomer): Hydroxyethylacrylamide, manufactured by KJ Chemicals. DEAA (monomer): Diethylacrylamide, manufactured by KJ Chemicals Co., Ltd. OMINIRAD907 (Photopolymerization Initiator): 2-Methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, manufactured by IGM Resins. KAYACURE DETX-S (photopolymerization initiator): 2,4-diethylthioxanthone, manufactured by Nippon Kayaku Co., Ltd. Alphon 1190 (acrylic oligomer): Viscosity 6000 mPa·s (25℃), Mw 1700, Tg -50℃, manufactured by Toagosei Co., Ltd. BYK-UV3505 (Leveling agent): Modified polydimethylsiloxane with acrylic groups, manufactured by BYK.

[0067] Next, the coating process was carried out. Specifically, it was as follows: A first adhesive composition was applied to a 23 μm thick COP film (product name "Zeonor Film ZF14", manufactured by Nippon Zeon Co., Ltd.) as the first transparent protective film to form a 1 μm thick first adhesive coating. Meanwhile, a second adhesive composition was applied to a 23 μm thick COP film (product name "Zeonor Film ZF14", manufactured by Nippon Zeon Co., Ltd.) as the second transparent protective film to form a 1 μm thick second adhesive coating. An MCD coater (manufactured by Fuji Machinery Co., Ltd., cell shape is honeycomb, gravure roll line count 1000 lines / inch, rotation speed 140% / line speed) was used for each coating.

[0068] 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 were bonded together (bonding process). Specifically, using a roll laminator, the adhesive coating side of the first transparent protective film was bonded to one side of the polarizer film, while the adhesive coating side of the second transparent protective film was bonded to the other side of the polarizer film.

[0069] Next, the adhesive coating between the films was cured by irradiating the first adhesive coating with ultraviolet light from the first transparent protective film side, while simultaneously irradiating the second adhesive coating with ultraviolet light from the second transparent protective film side (curing process). For ultraviolet irradiation, an ultraviolet irradiation device (product name "Light HAMMER10", bulb: V-bulb, manufactured by Fusion UV Systems, Inc.) equipped with a gallium-filled metal halide lamp as the light source was used. The peak illuminance during ultraviolet irradiation was 1600 mW / cm². 2 The cumulative irradiation dose is 1000 mJ / cm². 2(Wavelength 380-440 nm) was used (illuminance was measured using Solatell's "Sola-Check system"). This resulted in a laminated optical film being obtained by bonding the first transparent protective film and the polarizer film with a first adhesive layer, and then bonding the second transparent protective film and the polarizer film with a second adhesive layer.

[0070] The laminated optical film of Example 1 was fabricated as described above. The laminated optical film of Example 1 comprises 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) in this order in the thickness direction.

[0071] [Table 1]

[0072] [Example 2] The laminated optical film of Example 2 (first transparent protective film / first adhesive layer / polarizer film / second adhesive layer / second transparent protective film) was prepared in the same manner as the laminated optical film of Example 1, except for the following:

[0073] In the first preparation step, instead of using "Light Acrylate POB-A", "Light Acrylate P2H-A", and "Arronix 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, with the amount of "Arronix M-5700" being 22 parts by mass, the amount of "HEAA" being 12.5 parts by mass, the amount of "DEAA" being 6 parts by mass, the amount of "HEAA" being 12.5 parts by mass, and the amount of "Alphon 1190" being 10 parts by mass. Furthermore, in the coating step, the thickness of the first adhesive layer coating film formed on the first transparent protective film was 1.1 μm, and the thickness of the second adhesive layer coating film formed on the second transparent protective film was 1.2 μm.

[0074] [Example 3] The laminated optical film of Example 3 (first transparent protective film / first adhesive layer / polarizer film / second adhesive layer / second transparent protective film) was prepared in the same manner as the laminated optical film of Example 1, except for the following:

[0075] In the first preparation step, instead of using "Light Acrylate POB-A", "Aronics M-220", "Aronics M-5700", "DEAA", and "Alphon 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" (acryloyl morpholine) manufactured by KJ Chemicals Co., Ltd. were used, with the amount of "Light Acrylate P2H-A" being 10 parts by mass and the amount of "HEAA" being 3 parts by mass. In the second preparation step, the amount of "Light Acrylate POB-A" was 43 parts by mass, the amount of "Light Acrylate P2H-A" was 29 parts by mass, the amount of "Aronics M-220" was 3 parts by mass, and the amount of "Aronics M-5700" was 10 parts by mass. Furthermore, in the coating process, the thickness of the first adhesive layer coating film formed on the first transparent protective film was set to 1.2 μm, and the thickness of the second adhesive layer coating film formed on the second transparent protective film was set to 0.9 μm.

[0076] [Comparative Example 1] A laminated optical film for Comparative Example 1 (first transparent protective film / first adhesive layer / polarizer film / second adhesive layer / second transparent protective film) was prepared in the same manner as the laminated optical film for Example 1, except for the following:

[0077] In the first preparation step, the same composition as the second adhesive composition in Example 1 was prepared. In the second preparation step, instead of using "Light Acrylate POB-A", "Aronics M-220", "Aronics M-5700", "DEAA", and "Alphon 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" (acryloyl morpholine) manufactured by KJ Chemicals Co., Ltd. were used, with the amount of "Light Acrylate P2H-A" being 13 parts by mass and the amount of "HEAA" being 3 parts by mass. Furthermore, in the coating step, the thickness of the first adhesive layer coating film formed on the first transparent protective film was set to 1.0 μm, and the thickness of the second adhesive layer coating film formed on the second transparent protective film was set to 1.2 μm.

[0078] <Thickness of the adhesive layer> The thickness T of each adhesive layer in each laminated optical film of Examples 1-3 and Comparative Example 1 was measured as follows. First, a 5 mm × 10 mm film piece (laminated optical film) was cut from the laminated optical film. Next, the laminated optical film was cut using the cryomicrotome method. Specifically, the laminated optical film was cooled to -30°C, cut in the thickness direction of the film with a hard knife, and then returned to room temperature. The cut surface of the laminated optical film thus formed was subjected to a conductive treatment of 5 nm thickness or less. This obtained a sample for observation. Next, the thickness of the adhesive layer was measured by SEM observation of the observation sample. Specifically, a scanning electron microscope (product name "REGULUS8220", manufactured by HITACHI Corporation) was used to observe and capture secondary electron images of the cut surface of 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 to 10 μA, the working distance to 8 mm, the magnification to 100,000x, and the detection mode to Upper + Lower mode. The thicknesses T1 (μm) of the first adhesive layer and T2 (μm) of the second adhesive layer are shown in Table 2. The ratio of thickness T2 to thickness T1 (T2 / T1) is also shown in Table 2.

[0079] <Peel strength> The 90° peel strength between the first transparent protective film and the polarizer film in each of the laminated optical films in Examples 1-3 and Comparative Example 1 was measured as follows (first measurement). First, a first sample film with dimensions of 200 mm on the first side and 15 mm on the second side was cut from the laminated optical film. The first side is the side extending in the stretching direction of the polarizer film. The second side is the side extending in a direction perpendicular to the stretching direction. Next, the second transparent protective film side of the first sample film was bonded to a glass plate using a strong adhesive. Then, the 90° peel strength (N / 15 mm) of the first transparent protective film from the polarizer film was measured using a Tensilon universal tester (product name "RTC", manufactured by A&D Company, Limited). In this measurement, the first chuck of the Tensilon universal testing machine was used to grip the glass plate and the first sample film on the glass plate, from the glass plate to the polarizer film, while the second chuck of the same testing machine was used to grip the first transparent protective film of the first sample film. In this measurement, the measurement temperature was set to 25°C, the peeling angle to 90°, and the peeling speed to 1000 mm / min. The 90° peel strength F1 (N / 15mm) in this peeling test, in which the first transparent protective film was peeled from the polarizer film, is shown in Table 2.

[0080] Furthermore, the 90° peel strength between the second transparent protective film and the polarizer film in each laminated optical film of Examples 1-3 and Comparative Example 1 was measured as follows (second measurement). First, a second sample film similar to the first sample film was cut from the laminated optical film. Next, the first transparent protective film side of the second sample film was bonded to a glass plate via a strong adhesive. Then, the 90° peel strength (N / 15mm) of the second transparent protective film from the polarizer film was measured using a Tensilon universal tester (product name "RTC", manufactured by A&D Company, Limited). In this measurement, the first chuck of the Tensilon universal tester gripped the glass plate and the second sample film on the glass plate, from the glass plate to the polarizer film, and the second transparent protective film of the second sample film was gripped by the second chuck of the same tester. The measurement conditions for the second measurement were the same as those for the first measurement. Table 2 shows the 90° peel strength F2 (N / 15mm) in the peel test in which the second transparent protective film is peeled from the polarizer film.

[0081] <Indentation modulus> The indentation modulus of the first adhesive layer in each of the laminated optical films in Examples 1-3 and Comparative Example 1 was measured by nanoindentation. Specifically, first, a 5mm x 10mm film piece (laminated optical film) was cut from the laminated optical film. Next, the laminated optical film was cut using a cryomicrotome. Specifically, the laminated optical film was cooled to -30°C, cut in the thickness direction of the film with a hard knife, and then returned to room temperature. This obtained a sample for measurement. Next, using a nanoindenter (product name "TI950 Triboindenter", manufactured by Hysitron), load-displacement measurements were performed on the exposed surface of the adhesive layer in the measurement sample in accordance with JIS Z 2255:2003, and a load-displacement curve was obtained. In this measurement, the measurement mode was single-indentation measurement, the measurement temperature was 25°C, the indenter used was a Berkovich (triangular pyramidal) type diamond indenter, the maximum indentation depth (maximum displacement hmax) of the indenter into the measurement sample during the load application process was 50 nm, the indentation speed of the indenter was 10 nm / second, and the withdrawal speed of the indenter from the measurement sample during the unloading process was 10 nm / second. The obtained measurement data was then processed using 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 (load acting on the indenter at maximum displacement hmax), the contact projection area S (projected area of ​​the contact region between the indenter and the sample at maximum load), and the slope D of the tangent to the load-displacement curve at the start of the unloading process were obtained. Then, from the slope D and the contact projection area S, the indentation modulus of the first adhesive layer was calculated (=π 1 / 2 D) / (2S 1 / 2 The indentation modulus E1 (GPa) was calculated. This value is shown in Table 2.

[0082] Furthermore, the indentation modulus of the second adhesive layer in each laminated optical film of Examples 1-3 and Comparative Example 1 was measured in the same manner as the indentation modulus E1 of the first adhesive layer described above. This value is shown in Table 2 as the indentation modulus E2 (GPa). The ratio of the indentation modulus E2 to the indentation modulus E1 (E2 / E1) is also shown in Table 2.

[0083] <Display inconsistencies> The presence or absence of display unevenness when the display panel was bent after each of the laminated optical films in Examples 1-3 and Comparative Example 1 was mounted on the display panel was investigated. An organic EL panel (OLED panel) taken from a commercially available foldable smartphone was used as the display panel. The laminated optical film was placed on the image display side surface of the display panel. Specifically, the second transparent protective film side of the laminated optical film was attached to the image display side surface of the display panel via an adhesive. Then, with an image displayed on this display panel, the display panel was bent 90° and the image at the bend was observed visually. If no display unevenness (change in color) was observed in the image at the bend, it was evaluated as "good," and if display unevenness was observed, it was evaluated as "poor." The results are shown in Table 2.

[0084] <High-temperature, high-humidity bending test> High-temperature, high-humidity bending tests were performed on each of the laminated optical films in Examples 1-3 and Comparative Example 1 as follows.

[0085] First, evaluation samples were cut from the laminated optical film. Specifically, a rectangular sample measuring 25 mm x 100 mm was cut from the laminated film so that the absorption axis direction of the polarizer film was parallel to the long side direction of the sample. Next, a bending test was performed on the sample using a planar unloaded U-shaped stretch test machine (manufactured by Yuasa System Equipment). In this test, bending fixtures were attached to each end of the long side of the sample, within a range of 20 mm from the edge of the sample, and the sample was fixed to the test machine (the central 60 mm area of ​​the long side of the sample was not fixed). In this test, the sample was repeatedly deformed (bent) 80,000 times at a bending speed of 60 rpm in a constant temperature and humidity chamber under conditions of 60°C and 90% relative humidity, between a bent state where the side with the first transparent protective film was facing inward and an unbent state. Specifically, the bent state in this test is the state in which the axis direction of the bending moment acting on the sample and the absorption axis direction of the polarizer film are perpendicular to each other. In the bending configuration described, the bending radius of the sample was set to 3 mm and the bending angle to 180°. The delamination resistance between the films (first transparent protective film, polarizer film, second transparent protective film) in this bending test was evaluated as "good" if no delamination occurred between the films up to 80,000 bending cycles, and as "poor" if delamination occurred before 80,000 bending cycles. The evaluation results are shown in Table 1.

[0086] [Table 2] [Industrial applicability]

[0087] The laminated optical film of the present invention can be used, for example, as an element included in the laminated structure of a display panel, such as a foldable display panel. [Explanation of Symbols]

[0088] X Laminated Optical Film 10. Optical film (second optical film) 21 Optical film (first optical film) 22 Optical film (third optical film) 31 Adhesive layer (first adhesive layer) 32 Adhesive layer (second adhesive layer) H thickness direction B Folding point

Claims

1. A laminated optical film comprising 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 optical film and the first adhesive layer are bendable so that they face inward, 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 modulus E1 of the first adhesive layer at 25°C and the indentation modulus E2 of the second adhesive layer satisfy 0.3 ≤ E2 / E1 < 1. The indentation modulus E1 is the indentation modulus of the first adhesive layer when the maximum indentation depth of a triangular pyramidal diamond indenter is 50 nm. The indentation modulus E2 is the indentation modulus of the second adhesive layer when the maximum indentation depth of a triangular pyramidal diamond indenter is 50 nm, in a laminated optical film.

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

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

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

5. The laminated optical film according to claim 1, wherein the indentation 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.

Images