Decomposed optical thin films

Abstract

The present invention relates to providing a multilayer optical film suitable for suppressing uneven display in a foldable display panel when bent. The solution is as follows: The laminated optical thin film X of the present invention comprises an optical thin film 10, optical thin films 21 and 22, and adhesive layers 31 and 32. Adhesive layer 31 is bonded to optical thin film 10 and to optical thin film 21. Adhesive layer 32 is bonded to optical thin film 10 and to optical thin film 22. The indentation elastic modulus E1 of adhesive layer 31 at 25°C and the indentation elastic modulus E2 of adhesive layer 32 at 25°C satisfy 0.3 ≤ E2 / E1 < 1.

Description

Technical Field

[0001] This invention relates to a multilayer optical thin film. Prior Technology

[0002] The display panel has a multilayer structure, including, for example, a pixel panel, a touch panel, and a surface protective cover. The multilayer structure of the display panel also includes various functional optical films having predetermined optical functions. Examples of functional optical films include polarizing films and retardation films. The functional optical films are, for example, assembled into the multilayer structure in the form of multilayer optical films, with other optical films such as protective films bonded to both sides of the film through an adhesive. Such multilayer optical films are described, for example, in Patent Document 1 below. Previous technical documents Patent documents

[0003] Patent Document 1: Japanese Patent Application Publication No. 2019-147865 Summary of the Invention

[0004] The problem the invention aims to solve For example, in applications such as smartphones and tablet computers, there is ongoing development of repeatedly bendable (foldable) display panels. In foldable display panels, the components of the laminated structure are designed to be repeatedly bendable. Furthermore, at the bend in a foldable display panel, tensile stress is generated on the optical film located on the outer side of the flexure in the laminated optical film. It is known that this tensile stress causes a photoelastic effect on the aforementioned outer optical film at the bend, resulting in birefringence of the light transmitted through the film. This birefringence of transmitted light can cause uneven image display on the display panel, which is undesirable. When foldable display panels are used for extended periods of repeated bending, the aforementioned birefringence caused by the hardness of the adhesive layer located on the outer side of the flexure is particularly prone to causing uneven display.

[0005] The present invention provides a multilayer optical film suitable for suppressing uneven display when a foldable display panel is bent.

[0006] The means to solve the problem The present invention [1] includes a laminated optical thin film, which is provided in sequence in the thickness direction with a first optical thin film, a first adhesive layer, a second optical thin film, a second adhesive layer and a third optical thin film; the first adhesive layer is bonded to the first optical thin film and to the second optical thin film; the second adhesive layer is bonded to the second optical thin film and to the third optical thin 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.

[0007] The present invention [2] includes a multilayer optical thin film as described in [1] above, wherein the aforementioned indentation elastic modulus E2 is 4 GPa or less.

[0008] The present invention [3] includes a multilayer optical thin film as described in [1] or [2] above, wherein the aforementioned indentation elastic modulus E2 is 0.4 GPa or above.

[0009] The present invention [4] includes a multilayer optical thin film as described in any one of [1] to [3] above, wherein the aforementioned indentation elastic modulus E1 is 0.5 GPa or above.

[0010] The present invention [5] includes a multilayer optical thin film as described in any one of [1] to [4] above, wherein the aforementioned indentation elastic modulus E1 is 7 GPa or less.

[0011] The present invention [6] includes a multilayer optical thin film as described in any of [1] to [5] above, wherein the aforementioned second optical thin film is a polarizing film.

[0012] Invention Effects As described above, in the laminated optical thin film of the present invention, 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 a small indentation elastic modulus E2, such that the ratio (E2 / E1) is less than 1. When the laminated optical thin film is bent so that the third optical thin film becomes the flexed outer side, the second adhesive layer is suitable for mitigating the tensile stress generated in the third optical thin film at the bending point. By mitigating the tensile stress at the bending point of the third optical thin film, the aforementioned photoelastic effect can be reduced, and the unevenness of image display on the display panel can be suppressed. Furthermore, the second adhesive layer having a larger indentation elastic modulus E2, such that the ratio (E2 / E1) is 0.3 or more, is suitable for ensuring the bonding force between the second and third optical thin films at the aforementioned bending point. Simple Explanation of the Diagram

[0013] Figure 1 is a cross-sectional schematic diagram of one embodiment of the stacked optical thin film of the present invention. Figure 2 shows the bent state of the laminated optical film shown in Figure 1. Implementation

[0014] As shown in FIG1, the multilayer optical film X, one embodiment of the multilayer optical film of the present invention, comprises an optical film 10, optical films 21 and 22, and adhesive layers 31 and 32. Specifically, the multilayer optical film X comprises, in the thickness direction H, 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). The multilayer optical film X has a sheet shape of a predetermined thickness and extends in a direction orthogonal to the thickness direction H (plane direction). Adhesive layer 31 is bonded between optical films 10 and 21. Adhesive layer 32 is bonded between optical films 10 and 22. Furthermore, the multilayer optical film X is a composite film incorporated into the multilayer structure of a foldable display panel. The multilayer optical film X is, for example, a multilayer optical film disposed on the image display side surface of a display panel such as a foldable organic EL panel (OLED panel). In the foldable display panel, the laminated optical film X, as shown in Figure 2, is bent so that the sides of the optical film 21 and the adhesive layer 31 become the inside. At the bend B, the optical film 21 and the adhesive layer 31 are located on the flexed inner side (lower side in the figure) relative to the optical film 10, while the optical film 22 and the adhesive layer 32 are located on the flexed outer side (upper side in the figure) relative to the optical film 10.

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

[0016] Examples of polarizing films include hydrophilic polymer films that have undergone dyeing with dichroic substances and subsequent stretching treatment. 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 films of ethylene-vinyl acetate copolymers. Another example of a polarizing film is a polyene-oriented film. Examples of materials for polyene-oriented films include dehydrated PVA and dehydrochlorinated polyvinyl chloride. Considering the excellent optical properties such as polarization characteristics, a PVA film that has undergone dyeing with iodine and subsequent uniaxial stretching treatment is preferable for polarizing films.

[0017] From the perspective of thinning, the thickness of the optical thin film 10, which serves as a polarizing element thin film, should preferably be 15µm or less, more preferably 12µm or less, even more preferably 10µm or less, and especially preferably 8µm or less. Thin polarizing thin films have excellent visibility due to their smaller thickness variations, and their dimensional changes due to temperature variations are small, resulting in excellent thermal shock resistance. From the perspective of strength, the thickness of the optical thin film 10, which serves as a polarizing element thin film, should preferably be 3µm or more, and more preferably 5µm or more.

[0018] Examples of phase retardation films include, for example, λ / 2 wavelength films, λ / 4 wavelength films, and viewing angle compensation films. Materials for phase retardation films include, for example, polymer films that have undergone birefringence through a stretching process. Examples of polymer films include cellulose films and polyester films. Examples of cellulose films include, for example, cellulose triacetate films. Examples of polyester films include, for example, polyethylene terephthalate films and polyethylene naphthalate films. The thickness of the optical film 10, as a phase retardation film, is, for example, 20 µm or more, and for example, 150 µm or less. Furthermore, phase retardation films can also be suitable films comprising a substrate such as a cellulose film and an alignment layer of a liquid crystal compound such as a liquid crystal polymer on that substrate.

[0019] Optical films 21 and 22 are transparent protective films. The transparent protective film is, for example, a flexible transparent resin film. Materials for the transparent protective film include, for example, polyolefins, polyesters, polyamides, polyimides, polyvinyl chloride, polyvinyl chloride, cellulose, modified cellulose, polystyrene, and polycarbonate. Examples of polyolefins include cyclic olefin 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 some aromatic polyamides. Examples of modified cellulose include cellulose triacetate. These materials can be used alone or in combination of two or more. From a cleanliness perspective, polyolefins are preferable for the transparent protective film, and COPs are more suitable. Furthermore, the materials of optical thin film 21 and optical thin film 22 can be the same or different.

[0020] From the perspective of the strength of the laminated optical thin film X, the thicknesses of optical thin films 21 and 22 should preferably be 5µm or more, preferably 10µm or more, and even more preferably 20µm or more. From the perspective of thinning the laminated optical thin film X, the thickness of optical thin film 21 should preferably be 100µm or less, preferably 70µm or less, and even more preferably 50µm or less. The thicknesses of optical thin film 21 and optical thin film 22 can be the same or different.

[0021] Adhesive layer 31 is a cured form of the first adhesive composition. Adhesive layer 31 is directly bonded to optical film 10 and optical film 21. The first adhesive composition contains a curable resin. The specific composition of the first adhesive composition is described below.

[0022] From the perspective of the bonding strength between optical thin films 10 and 21, the thickness T1 of the adhesive layer 31 should preferably be 0.1µm or more, preferably 0.4µm or more, more preferably 0.7µm or more, and especially preferably 0.8µm or more. From the perspective of thinning the laminated optical thin film X, the thickness T1 of the adhesive layer 31 should preferably be 5µm or less, preferably 3µm or less, more preferably 1.5µm or less, and especially preferably 1µm or less.

[0023] The indentation modulus E1 of the adhesive layer 31 at 25°C, measured using nanoindentation, is preferably 0.5 GPa or higher, more preferably 1 GPa or higher, more preferably 1.5 GPa or higher, and especially preferably 2 GPa or higher. When the laminated optical film X is bent so that the optical film 21 side becomes the inner side, this configuration is suitable for ensuring the bonding force between the optical films 10 and 21 at the bend B. The indentation modulus E1 is preferably 7 GPa or lower, more preferably 6 GPa or lower, and more preferably 5.2 GPa or lower. This configuration is suitable for mitigating the compressive stress acting on the adhesive layer 31 at the bend B. The mitigation of the compressive stress of the adhesive layer 31 at the bend B helps to suppress peeling between the optical films 10 and 21. Furthermore, regarding the upper limit of the indentation elastic modulus E1, this configuration is suitable for ensuring low elasticity in the adhesive layer 31 (the adhesive layer on the inner side of the bend) at the aforementioned bend B, thereby achieving sufficient adhesion to the optical films 10 and 21, and thus is suitable for suppressing the buckling of the optical film 10 at the bend B. A method for adjusting the indentation elastic modulus E1 of the adhesive layer 31 can be, for example, adjusting the composition of the first adhesive component. Specifically, an effective method for adjusting the indentation elastic modulus E1 of the adhesive layer 31 is to adjust the functional group of the polymeric compound described later in the first adhesive component, that is, to adjust the acrylonitrile equivalent or epoxy equivalent of the polymeric compound.

[0024] Nanoindentation is a method for determining the properties of a sample at the nanoscale. In this embodiment, nanoindentation is performed according to ISO 14577. Nanoindentation involves the following process: pressing an indenter into the sample mounted on a platform (load application process), and subsequently pulling the indenter out of the sample (unloading process), and measuring the load acting between the indenter and the sample and the relative displacement of the indenter relative to the sample during this series of processes (load-displacement measurement). This yields a load-displacement curve. From this load-displacement curve, the properties of the sample can be determined based on nanoscale measurements. The load-displacement measurement of the adhesive layer cross-section using nanoindentation can be performed, for example, using a nanoindenter (trade name "Triboindenter," manufactured by Hysitron). Specifically, as described later with reference to examples.

[0025] Adhesive layer 32 is a cured form of the second adhesive composition. Adhesive layer 32 is directly bonded to optical film 10 and optical film 22. The second adhesive composition contains a curable resin. The specific composition of the second adhesive composition is described below.

[0026] From the viewpoint of the bonding strength between optical films 10 and 22, the thickness T2 of adhesive layer 32 should preferably be 0.1µm or more, preferably 0.4µm or more, more preferably 0.7µm or more, and especially preferably 0.8µm or more. From the viewpoint of thinning the laminated optical film X, the thickness T2 of adhesive layer 32 should preferably be 5µm or less, preferably 3µm or less, more preferably 1.5µm or less, and especially preferably 1µm or less. The thickness T2 of adhesive layer 32 can be the same as or different from the thickness T1 of adhesive layer 31. Furthermore, 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, should preferably be 0.4 GPa or higher, more preferably 0.8 GPa or higher, more preferably 1.2 GPa or higher, and especially preferably 1.8 GPa or higher, provided it is less than the indentation modulus E1. The indentation modulus E2 should preferably be 4 GPa or lower, more preferably 3 GPa or lower, and more preferably 2.5 GPa or lower, provided it is less than the indentation modulus E1. This configuration is suitable for ensuring the adhesion between the optical films 10 and 22. The method for adjusting the indentation modulus E2 of the adhesive layer 32 can be, for example, by adjusting the composition of the second adhesive component. Specifically, an effective method for adjusting the indentation modulus E2 of the adhesive layer 32 is to adjust the functional groups of the polymeric compound described later in the second adhesive component, that is, to adjust the acrylonitrile equivalent or epoxy equivalent of the polymeric compound.

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

[0029] The adhesive layer 32 has a small indentation modulus E2, such that the ratio (E2 / E1) is less than 1. When the laminated optical film X is bent so that the optical film 22 becomes the flexed outer side, the adhesive layer 32 is suitable for mitigating the tensile stress generated at the bending point B of the optical film 22. By mitigating the tensile stress at the bending point of the optical film 22, the photoelastic effect can be reduced, suppressing unevenness in the image display of the display panel. From the above perspective, the ratio (E2 / E1) should preferably be 0.97 or less, and more preferably 0.8 or less.

[0030] Furthermore, an adhesive layer 32 having a relatively large indentation modulus E2, such as a ratio (E2 / E1) of 0.3 or higher, is suitable for ensuring adhesion between the optical films 10 and 22 at the bend. Also, an adhesive layer 31 having a relatively small indentation modulus E1, such as a ratio (E2 / E1) of 0.3 or higher, is suitable for ensuring low elasticity in the adhesive layer 31 at the bend (the adhesive layer on the inside of the bend) to achieve sufficient adhesion to the optical films 10 and 21, thus effectively suppressing buckling of the optical film 10 at the bend. From these viewpoints, a ratio (E2 / E1) of 0.5 or higher is preferable, and more preferably 0.6 or higher.

[0031] The ratio (E2 / E1) can be adjusted by adjusting the indentation elastic modulus E1 and adjusting the indentation elastic modulus E2.

[0032] In the laminated optical film X, the 90° peel strength F1 of the optical film 21 against 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. This configuration is suitable for ensuring good adhesion between the optical films 10 and 21, and is particularly suitable for ensuring adhesion between the 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 reference to the embodiments. The peel strength of the optical film 21 to the optical film 10 is the force required to peel the optical film 21 from the optical film 10. This peeling includes: interfacial peeling between the optical film 10 and the adhesive layer 31, peeling due to aggregation and destruction 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, the method for adjusting the 90° peel strength F1 can be, for example, by adjusting the composition of the first adhesive component. Specifically, the method for adjusting the 90° peel strength F1 can be, for example, by adjusting the functional groups of the polymeric compound described later in the first adhesive component, that is, adjusting the acrylonitrile equivalent or epoxy equivalent of the polymeric compound.

[0033] In the laminated optical film X, the 90° peel strength F2 of the optical film 22 against 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. This configuration is suitable for ensuring good adhesion between the optical films 10 and 22, and is particularly suitable for ensuring adhesion between the optical films 10 and 22 at the bend 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 reference to the embodiments. The peel strength of the optical film 22 to the optical film 10 is the force required to peel the optical film 22 from the optical film 10. This peeling includes: interfacial peeling between the optical film 10 and the adhesive layer 32, peeling due to aggregation and destruction 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, the method for adjusting the 90° peel strength F2 can be, for example, by adjusting the composition of the second adhesive component. Specifically, the method for adjusting the 90° peel strength F2 can be, for example, by adjusting the number of functional groups of the polymeric compound described later in the second adhesive component, that is, adjusting the acrylonitrile equivalent or epoxy equivalent of the polymeric compound.

[0034] The adhesive layer 31 is, for example, a cured product containing a first adhesive composition (first active energy line curing composition) of an active energy line curing resin. Examples of the first active energy line curing composition include electron beam curing compositions, ultraviolet curing compositions, and visible light curing compositions. Furthermore, in this embodiment, the first active energy line curing composition is either a free radical polymerization composition or a cationic polymerization composition, or both.

[0035] When the first active energy line hardening type composition is a free radical polymer type composition, the composition contains a free radical polymerizable compound as a monomer. A free radical polymerizable compound is a compound having a free radical polymerizable functional group. Examples of free radical polymerizable functional groups include groups containing vinyl unsaturated bonds. Examples of groups containing vinyl unsaturated bonds include (meth)acryl, vinyl, and allyl. (Meth)acryl means acrylonitrile and / or methacryl. From the viewpoint of the hardening properties of the first active energy line hardening type composition, the first active energy line hardening type composition preferably contains a free radical polymerizable compound having a (meth)acryl group as a main component. A main component means the component with the highest mass percentage. The proportion of the free radical polymerizable compound containing a (meth)acryl group in the first active energy line hardening type 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 free radical polymers include monofunctional free radical polymers and polyfunctional free radical polymers with two or more functions.

[0036] Monofunctional free radical polymerizable compounds include, for example, (meth)acrylamide derivatives containing a (meth)acrylamide group. Examples of (meth)acrylamide derivatives include: (meth)acrylamide derivatives containing N-alkyl groups, (meth)acrylamide derivatives containing N-hydroxyalkyl groups, (meth)acrylamide derivatives containing N-aminealkyl groups, (meth)acrylamide derivatives containing N-alkoxy groups, and (meth)acrylamide derivatives containing N-mercaptoalkyl groups. Examples of (meth)acrylamide derivatives containing N-alkyl groups 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; N,N-diethylacrylamide is preferred. Examples of N-hydroxyalkyl (meth)acrylamide derivatives include: N-hydroxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, and N-hydroxymethyl-N-propane (meth)acrylamide. N-hydroxyethylacrylamide is preferred. (Methacrylamide)acrylamide derivatives may be used alone or in combination of two or more.

[0037] Examples of monofunctional free radical polymerizable compounds include (meth)acrylic acid derivatives having a (meth)acryloxy group. Examples of such (meth)acrylic acid derivatives include alkyl (meth)acrylates and other (meth)acrylic acid derivatives. (Methacryl)acrylic acid derivatives can be used alone or in combination of two or more.

[0038] Examples of alkyl methacrylates include: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, 2,2-dimethylbutyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, 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-containing (meth)acrylic acid derivatives, alkoxy-containing (meth)acrylic acid derivatives, and phenoxy-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-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]methacrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate. Examples of alkoxy-containing (meth)acrylate derivatives include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, and 3-methoxybutyl (meth)acrylate. Examples of phenoxy-containing (meth)acrylate derivatives include phenoxyethyl (meth)acrylate and phenoxydiethylene glycol (meth)acrylate. (Meth)acrylate derivatives other than alkyl (meth)acrylates may preferably be selected from at least one of the group consisting of 3-phenoxybenzyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, and phenoxydiethylene glycol acrylate.

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

[0041] Monofunctional free radical polymerizable compounds also include lactone-based vinyl monomers. Examples of lactone-based vinyl monomers include N-vinyl-2-pyrrolidone, N-vinyl-ε-caprolactone, and methylvinylpyrrolidone.

[0042] Monofunctional free radical polymerizable compounds may also include vinyl monomers having nitrogen-containing heterocycles. Examples of such monomers include: vinylpyridine, vinylpiperidinone, vinylpyrimidine, vinylpiperidine, vinylpyridine, vinylpyrrole, vinylimidazolium, vinylpyrazole, acrylamide, and vinylamide.

[0043] Polyfunctional free radical polymerizable compounds may include, 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-butylpropanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecanediethanol di(meth)acrylate, cyclic trimethylolpropane acetal (meth)acrylate, dialkyldiol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, neopentyltetrol tri(meth)acrylate, neopentyltetrol tetra(meth)acrylate, dinepentyltetrol penta(meth)acrylate, and dinepentyltetrol hexa(meth)acrylate, preferably tripropylene glycol diacrylate and hydroxytrimethylacetic acid neopentyl glycol acrylate adducts. Polyfunctional radical polymerizable compounds are preferably selected from at least one of the group consisting of adducts of tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, and neopentyl glycol acrylate of hydroxytrimethylacetic acid. Polyfunctional radical polymerizable compounds can be used alone or in combination of two or more. Polyfunctional radical polymerizable compounds can function as crosslinking agents.

[0044] When the first active energy line curing composition is an ultraviolet-curing composition or a visible light-curing composition, the first active energy line curing composition preferably contains a photopolymerization initiator. Examples of photopolymerization initiators include diphenyl ketone compounds, benzoin ether compounds, and 9-oxosulfuron. Compounds. Examples of diphenyl ketone compounds include benzyl, diphenyl ketone, benzoic acid, and 3,3'-dimethyl-4-methoxydiphenyl ketone. Examples of benzoin ether compounds include benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether. 9-Oxysulfuron Examples of compounds include: 9-oxosulfur 2-Chloro-9-oxysulfur 2-Methyl-9-oxosulfur 2,4-Dimethyl-9-oxosulfur Isopropyl 9-Oxysulfur 2,4-Dichloro-9-oxosulfur 2,4-Diethyl-9-oxosulfur 2,4-Diisopropyl-9-oxosulfuron and dodecyl 9-oxosulfur .

[0045] When the first active energy line-curing component is a visible light-curing component, a photopolymerization initiator with high sensitivity to light above 380nm should be used. Examples of photopolymerization initiators include: 2-methyl-1-(4-methylthiophenyl)-2-mofolinylprop-1-one, 2-benzyl-2-dimethylamino-1-(4-mofolinylphenyl)-but-1-one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-mofolinyl)phenyl]-1-butanone, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis(n5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrole-1-yl)-phenyl)titanium.

[0046] 2,4-Diethyl-9-oxosulfuron is a suitable photopolymerization initiator. And / or 2-methyl-1-(4-methylthiophenyl)-2-morphofolinylprop-1-one.

[0047] Relative to 100 parts by mass of the curing component (free radical polymerizable compound), the content of the photopolymerization initiator in the first active energy line curing composition should preferably be 0.1 parts by mass or more, more preferably 0.05 parts by mass or more, 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 more preferably 5 parts by mass or less.

[0048] When the first active energy line curing composition is a cationic polymer composition, the composition contains a cationic polymeric compound as a monomer. The cationic polymeric compound is a compound having a cationic polymeric functional group, including monofunctional cationic polymeric compounds having one cationic polymeric functional group and polyfunctional cationic polymeric compounds having two or more cationic polymeric functional groups. Monofunctional cationic polymeric compounds have relatively low liquid viscosity. By incorporating the monofunctional cationic polymeric compound into the resin composition, the viscosity of the resin composition can be reduced. Furthermore, monofunctional cationic polymeric compounds mostly possess functional groups capable of exhibiting various functions. By incorporating the monofunctional cationic polymeric compound into the resin composition, the resin composition and / or the cured resin composition can exhibit various functions. On the other hand, by curing a resin composition incorporating a polyfunctional cationic polymeric compound, a cured product with a 3D cross-linked portion can be obtained (the polyfunctional cationic polymeric compound functions as a cross-linking agent). From this perspective, it is preferable to utilize polyfunctional cationic polymeric compounds. When using both monofunctional cationic polymeric compounds and polyfunctional cationic polymeric compounds, the amount of the polyfunctional cationic polymeric compound is, for example, 10 parts by mass or more, and for example, 1000 parts by mass or less, relative to 100 parts by mass of the monofunctional cationic polymeric compound. Examples of cationic polymeric functional groups include epoxy groups, oxetyl groups, and vinyl ether groups. Examples of compounds containing epoxy groups include aliphatic epoxy compounds, alicyclic epoxy compounds, and aromatic epoxy compounds. From the viewpoint of the curability and adhesion of cationic polymeric compositions, alicyclic epoxy compounds are preferable to be used as epoxy groups. Examples of alicyclic epoxy compounds include: 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, or caprolactone-modified, trimethylcaprolactone-modified, and valproicone-modified versions of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate. Commercially available alicyclic epoxy compounds include, for example, CELLOXIDE 2021, CELLOXIDE 2021A, CELLOXIDE 2021P, CELLOXIDE 2081, CELLOXIDE 2083, and CELLOXIDE 2085 (all manufactured by DAICL Chemical Co., Ltd.), and Cyracure UVR-6105, Cyracure UVR-6107, Cyracure 30, and R-6110 (all manufactured by DOW CHEMICAL Japan Co., Ltd.). From the perspective of improved curability and reduced viscosity of cationic polymeric compositions, compounds containing oxetane groups and / or compounds containing vinyl ether groups are preferable.Examples of compounds containing oxetane 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 phenolic varnish oxetane. Commercially available examples of compounds containing oxetane 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 Toa Synthetic Co., Ltd.). Compounds containing a vinyl ether group include, for example: 2-hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, triethylene glycol divinyl ether, cyclohexanediethanol divinyl ether, cyclohexanediethanol monovinyl ether, tricyclodecane vinyl ether, cyclohexyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, and neopentyl tetravinyl ether.

[0049] When the first active energy line curing composition is an ultraviolet-curing or visible-light-curing composition, it contains a photocationic polymerization initiator. When irradiated by active energy lines (visible light, ultraviolet light, X-rays, electron beams, etc.), the photocationic polymerization initiator generates cationic species or Lewis acids, initiating the polymerization reaction of cationic polymerizable functional groups. Examples of photocationic polymerization initiators include photoacid generators and photobase generators; photoacid generators are preferred. When the first active energy line curing composition is a visible-light-curing composition, it is particularly advisable to use a photocationic polymerization initiator with high sensitivity to light above 380 nm. Furthermore, when using a photocationic polymerization initiator, it is advisable to also use a photosensitizer that exhibits maximum absorption to light with wavelengths longer than 380 nm. Photocationic polymerization initiators are generally compounds that exhibit maximum absorption in the wavelength region around 300 nm or shorter. Therefore, by using them in conjunction with photosensitizers that exhibit maximum absorption in wavelengths longer than 380 nm, the generation of cationic species or Lewis acids from the photocationic polymerization initiator can be effectively promoted using light with wavelengths longer than 380 nm. Examples of photosensitizers include anthracene compounds, pyrene compounds, carbonyl compounds, organosulfur compounds, persulfides, redox compounds, azo compounds, diazo compounds, halogen compounds, and photoreducing pigments. These can be used alone or in combination of two or more. Anthracene compounds are particularly ideal due to their excellent photosensitizing effect. 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 line curable composition may also contain oligomers. Examples of oligomers include acrylic oligomers, fluoro oligomers, and polysiloxane oligomers; acrylic oligomers are preferred. The blending of oligomers into the first active energy line curable composition helps suppress shrinkage during curing. Suppression of curing shrinkage in the first active energy line curable composition appropriately reduces the interfacial stress between the formed adhesive layer 31 and the optical films 10 and 21. Suppression of interfacial stress helps ensure adhesion between the optical films 10 and 21.

[0051] Examples of (meth)acrylic acid monomers that form acrylic acid oligomers include: alkyl (meth)acrylic acid esters with 1 to 20 carbon atoms, cycloalkyl (meth)acrylic acid esters, aralkyl (meth)acrylic acid esters, polycyclic (meth)acrylic acid esters, hydroxyl-containing (meth)acrylic acid esters, and halogen-containing (meth)acrylic acid esters. Examples of alkyl methacrylates include: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, 2-methyl-2-nitropropyl (meth)acrylate, n-butyl methacrylate, isobutyl methacrylate, S-butyl methacrylate, tributyl methacrylate, n-pentyl methacrylate, tripentyl methacrylate, 3-pentyl methacrylate, 2,2-dimethylbutyl (meth)acrylate, n-hexyl methacrylate, cetyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, 4-methyl-2-propylpentyl (meth)acrylate, and N-octadecyl (meth)acrylate. Examples of cycloalkyl methacrylates include cyclohexyl methacrylate and cyclopentyl methacrylate. Examples of aralkyl methacrylates include benzyl methacrylate. Examples of polycyclic (meth)acrylates include 2-isocamphene (meth)acrylate, 2-norcamphenylmethyl (meth)acrylate, 5-norcamphen-2-yl-methyl (meth)acrylate, and 3-methyl-2-norcamphenylmethyl (meth)acrylate. Examples of hydroxyl-containing (meth)acrylates include hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2,3-dihydroxypropylmethyl-butyl (meth)methacrylate. Examples of halogen-containing (meth)acrylates 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 can be used alone or in combination of two or more.

[0052] The weight average molecular weight (Mw) of acrylic oligomers should preferably be below 15,000, more preferably below 10,000, and even more preferably below 5,000. The Mw of acrylic oligomers should preferably be above 500, more preferably above 1,000, and even more preferably above 1,500.

[0053] The content of acrylic oligomer in the first active energy line hardening type composition should preferably be 2% by mass or more, more preferably 4% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less.

[0054] The first active energy line hardening composition may also contain other components. Other components may include silane coupling agents, leveling agents, surfactants, plasticizers, and ultraviolet absorbers. The amount of these other components should preferably be less than 10 parts by mass, more preferably less than 5 parts by mass, more preferably less than 3 parts by mass, and for example, more than 0.01 parts by mass.

[0055] From the perspective of coatability in the coating step described later, the viscosity of the first active energy line-curing composition at 25°C should preferably be 3 mPa·s or higher, more preferably 5 mPa·s or higher, more preferably 10 mPa·s or higher, and preferably 100 mPa·s or lower, more preferably 50 mPa·s or lower, and more preferably 30 mPa·s or lower. 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 containing a second adhesive composition of an active energy line curing resin (an active energy line curing composition). Examples of the second active energy line curing composition include electron beam curing compositions, ultraviolet curing compositions, and visible light curing compositions. In these cases, the second active energy line curing composition and the first active energy line curing composition may be of the same type or different types. Furthermore, in this embodiment, the second active energy line curing composition is a free radical polymerizable composition.

[0057] The components contained in the second active energy line hardening type composition may be the same as those contained in the first active energy line hardening type composition. The content range of the components in the second active energy line hardening type composition is the same as the content range of the components in the first active energy line hardening type composition. The composition of the second active energy line hardening type composition may be the same as or different from that of the first active energy line hardening type composition.

[0058] The laminated optical thin film X can be manufactured, for example, in the following manner.

[0059] First, a first active energy line-curing composition is coated on one side (the bonding predetermined surface) of the optical thin film 21 to form a first coating film of the composition (first active coating step). Then, a second active energy line-curing composition is coated on one side (the bonding predetermined surface) of the optical thin film 22 to form a second coating film of the composition (second active coating step). Before each coating step, the bonding predetermined surface of the optical thin film may also undergo surface modification treatment. Surface modification treatments may include corona treatment, plasma treatment, excimer laser treatment, and flame treatment. The coating method in this step may include, for example, a reverse coating machine, a gravure coating machine, a bar reverse coating machine, a roll coating machine, a die coating machine, a bar coating machine, and a rod coating machine.

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

[0061] Next, the first coating and the second coating are irradiated with active energy lines, causing the first coating to harden and form an adhesive layer 31, and the second coating to harden and form an adhesive layer 32 (adhesive layers 31 and 32 are not pressure-sensitive adhesive layers). In this way, optical films 10 and 21 are bonded together through adhesive layer 31, and optical films 10 and 22 are bonded together through adhesive layer 32.

[0062] From the viewpoint of suppressing the degradation of the optical thin film 10, which is a functional optical thin film, in this step, it is advisable to irradiate the active energy line for curing the first coating from the optical thin film 21 side and the active energy line for curing the second coating from the optical thin film 22 side. The active energy line can be an electron beam, ultraviolet light, or visible light. An electron beam irradiation mechanism can be, for example, an electron beam accelerator. Examples of sources of ultraviolet and visible light include: 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 step, a wavelength cutoff filter can also be used as needed to cut off a portion of the wavelength range of ultraviolet and / or visible light emitted from the light source.

[0063] The laminated optical thin film X can be manufactured, for example, in the manner described above.

[0064] Example The following examples illustrate the present invention. The present invention is not limited to the examples. Furthermore, the specific values ​​of blending amount (content), physical property value, parameters, etc., described below can be replaced by the upper limit (values ​​defined as "below" or "less than") or lower limit (values ​​defined as "above" or "greater than") of the blending amount (content), physical property value, parameters, etc., corresponding to those described in the above "Forms for Implementing the Invention".

[0065] [Example 1] A first adhesive composition for the first adhesive layer is prepared by mixing the following components at the amounts shown in Table 1 (based on solid content) at 25°C for 1 hour (first preparation step). A second adhesive composition for the second adhesive layer is prepared by mixing the following components at the amounts shown in Table 1 (based on solid content) at 25°C for 1 hour (second preparation step). The mixing amounts shown in Table 1 are in parts by mass.

[0066] LIGHT ACRYLATE POB-A (monomer): 3-phenoxybenzyl acrylate, manufactured by Kyoei Chemical Co., Ltd. LIGHT ACRYLATE P2H-A (monomer): Phenoxy diethylene glycol acrylate, manufactured by Kyoei Chemical Co., Ltd. ARONIX M-5700 (monomer): 2-hydroxy-3-phenoxypropyl acrylate, manufactured by Dong-A Synthetic Co., Ltd. ARONIX M-220 (monomer): Tripropylene glycol diacrylate, manufactured by Dong-A Synthetic Co., Ltd. HEAA (monomer): Hydroxyethyl acrylamide, manufactured by KJ Chemicals Corporation DEAA (monomer): Diethylacrylamide, manufactured by KJ Chemicals Corporation OMINIRAD907 (photopolymerization initiator): 2-Methyl-1-(4-methylthiophenyl)-2-morphofolinylprop-1-one, manufactured by IGM Resins. KAYACURE DETX-S (Photopolymerization Initiator): 2,4-Diethyl-9-oxosulfur Nippon Kayaku Co., Ltd. ARUFON 1190 (acrylic oligomer): viscosity 6000 mPa·s (25℃), Mw 1700, Tg -50℃, manufactured by Toa Synthetic Co., Ltd. BYK-UV3505 (Leveling Agent): Acrylic-modified polydimethylsiloxane, manufactured by BYK Corporation.

[0067] Next, the coating process is performed. Specifically, the first adhesive composition is coated onto a 23µm thick COP film (brand name "ZeonorFilm ZF14", manufactured by ZEON Corporation, Japan), serving as the first transparent protective film, to form a 1µm thick first adhesive coating. Conversely, a second adhesive composition is coated onto a 23µm thick COP film (brand name "ZeonorFilm ZF14", manufactured by ZEON Corporation, Japan), serving as the second transparent protective film, to form a 1µm thick second adhesive coating. Each coating process utilizes an MCD coating machine (manufactured by Fuji Machinery Co., Ltd., with a honeycomb groove shape, 1000 lines / inch gravure roller, and a rotational speed of 140% / line speed).

[0068] Next, a first transparent protective film with a first adhesive coating, a polarizing film, and a second transparent protective film with a second adhesive coating are laminated (lamination step). Specifically, using a roll laminator, the first adhesive coating side of the first transparent protective film is laminated to one side of the polarizing film, and the second adhesive coating side of the second transparent protective film is laminated to the other side of the polarizing film.

[0069] Next, ultraviolet light is irradiated onto the first adhesive coating from the first transparent protective film side, and simultaneously onto the second adhesive coating from the second transparent protective film side, thereby hardening the adhesive coating between the films (hardening step). During ultraviolet irradiation, an ultraviolet irradiation device equipped with a gallium-filled metal halide lamp (brand name "Light HAMMER10", bulb: V bulb, manufactured by Fusion UV Systems, Inc.) is used as the light source. During ultraviolet irradiation, the peak illuminance is 1600 mW / cm², and the cumulative irradiance is set to 1000 mJ / cm² (wavelength 380~440 nm) (illuminance is measured using the "Sola-Check system" manufactured by Solatell). In this way, a laminated optical film is obtained by bonding the first transparent protective film and the polarizing film with the first adhesive layer, and by bonding the second transparent protective film and the polarizing film with the second adhesive layer.

[0070] The multilayer optical film of Example 1 was fabricated in the manner described above. The multilayer optical film of Example 1 has, in the thickness direction, a first transparent protective film (thickness 23µm), a first adhesive layer, a polarizing film (thickness 5µm), a second adhesive layer, and a second transparent protective film (thickness 23µm).

[0071] [Table 1]

[0072] [Example 2] Except for the following, the multilayer optical film of Example 2 (first transparent protective film / first adhesive layer / polarizing film / second adhesive layer / second transparent protective film) was manufactured in the same manner as the multilayer optical film of Example 1.

[0073] In the first preparation step, "LIGHT ACRYLATE POB-A", "LIGHT ACRYLATE P2H-A" and "ARONIX M-220" are not used. Instead, 40 parts by weight of "LIGHT ACRYLATE 1.9ND-A" (1,9-nonanediol diacrylate) manufactured by Kyoeisha Chemical Co., Ltd. and 9 parts by weight of "LIGHT ACRYLATE HPP-A" (hydroxytrimethylacetic acid neopentyl glycol acrylate adduct) manufactured by Kyoeisha Chemical Co., Ltd. are used. The blending amount of "ARONIX M-5700" is set to 22 parts by weight, the blending amount of "HEAA" is set to 12.5 parts by weight, the blending amount of "DEAA" is set to 6 parts by weight, the blending amount of "HEAA" is set to 12.5 parts by weight, and the blending amount of "ARUFON 1190" is set to 10 parts by weight. Furthermore, in the coating step, the thickness of the first adhesive layer coating to be formed on the first transparent protective film is set to 1.1µm, and the thickness of the second adhesive layer coating to be formed on the second transparent protective film is set to 1.2µm.

[0074] [Example 3] Except for the following, the multilayer optical film of Example 3 (first transparent protective film / first adhesive layer / polarizing film / second adhesive layer / second transparent protective film) was manufactured in the same manner as the multilayer optical film of Example 1.

[0075] In the first preparation step, "LIGHT ACRYLATE POB-A", "ARONIX M-220", "ARONIX M-5700", "DEAA" and "ARUFON 1190" are not used. Instead, 27 parts by weight of "LIGHT ACRYLATE 1.9ND-A" (1,9-nonanediol diacrylate) manufactured by Kyoei Chemical Co., Ltd. and 59 parts by weight of "ACMO-LI" (acryloylmorpholine) manufactured by KJ Chemicals Corporation are used. The blending amount of "LIGHT ACRYLATE P2H-A" is set to 10 parts by weight and the blending amount of "HEAA" is set to 3 parts by weight. In the second preparation step, the blending amount of "LIGHT ACRYLATE POB-A" is set to 43 parts by mass, the blending amount of "LIGHT ACRYLATE P2H-A" is set to 29 parts by mass, the blending amount of "ARONIX M-220" is set to 3 parts by mass, and the blending amount of "ARONIX M-5700" is set to 10 parts by mass. Furthermore, in the coating step, the thickness of the first adhesive layer coating to be formed on the first transparent protective film is set to 1.2 µm, and the thickness of the second adhesive layer coating to be formed on the second transparent protective film is set to 0.9 µm.

[0076] [Comparative Example 1] Except for the following, the composite optical film of Comparative Example 1 (first transparent protective film / first adhesive layer / polarizing film / second adhesive layer / second transparent protective film) was produced in the same manner as the composite optical film of Example 1.

[0077] In the first preparation step, a composition identical to the second adhesive composition in Example 1 was prepared. In the second preparation step, "LIGHT ACRYLATE POB-A", "ARONIX M-220", "ARONIX M-5700", "DEAA" and "ARUFON 1190" were not used, and 23 parts by weight of "LIGHT ACRYLATE 1.9ND-A" (1,9-nonanediol diacrylate) manufactured by Kyoei Chemical Co., Ltd. and 60 parts by weight of "ACMO-LI" (acryloylmorphofrin) manufactured by KJ Chemicals Corporation were used. The blending amount of "LIGHT ACRYLATE P2H-A" was set to 13 parts by weight, and the blending amount of "HEAA" was set to 3 parts by weight. Furthermore, in the coating step, the thickness of the first adhesive layer coating to be formed on the first transparent protective film is set to 1.0 µm, and the thickness of the second adhesive layer coating to be formed on the second transparent protective film is set to 1.2 µm.

[0078] <Adhesive layer thickness> 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 5mm × 10mm film sheet (laminated optical film) was cut from the laminated optical film. Next, the laminated optical film was cut using a freeze-cutting method. Specifically, after cooling the laminated optical film to -30°C, it was cut along the thickness direction of the film with a hard cutter, and then restored to room temperature. This yielded a laminated optical film with a cut surface, and then a conductive treatment of less than 5nm was performed on the cut surface. This yielded an observation sample. 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) 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 accelerating voltage was set to 3.0 kV, the current to 10 µA, the working distance to 8 mm, the magnification to 100,000 times, 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 polarizing film in each of Examples 1-3 and Comparative Example 1 was measured (first measurement) as follows. 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 multilayer optical film. The first side is the side extending along the extension direction of the polarizing film. The second side is the side extending in a direction orthogonal to the aforementioned extension direction. Next, the second transparent protective film side of the first sample film was attached to a glass plate using a strong adhesive. Then, the 90° peel strength (N / 15 mm) of the first transparent protective film peeling from the polarizing film was measured using a TENSILON universal testing machine (product name "RTC", manufactured by A&D Company, Limited). In this test, the first clamp of the TENSILON universal testing machine gripped the polarizing film from the glass plate and the first sample film on the glass plate, while the second clamp of the testing machine gripped the first transparent protective film of the first sample film. Furthermore, in this test, the test temperature was set to 25°C, the peel angle to 90°, and the peel speed to 1000 mm / min. The 90° peel strength F1 (N / 15mm) of peeling the first transparent protective film from the polarizing film in this peel test is shown in Table 2.

[0080] Furthermore, the 90° peel strength between the second transparent protective film and the polarizing film in each of Examples 1-3 and Comparative Example 1 was measured (Second Measurement) in the following manner. First, a second sample film identical to the first sample film was cut from the multilayer optical film. Next, the first transparent protective film side of the second sample film was adhered to a glass plate using a strong adhesive. Then, the 90° peel strength (N / 15mm) of the second transparent protective film peeling from the polarizing film was measured using a TENSILON universal testing machine (product name "RTC", manufactured by A&D Company, Limited). In this measurement, the first clamp of the TENSILON universal testing machine held the glass plate from the glass plate and the second sample film on the glass plate to the polarizing film, and the second clamp of the testing machine held the second transparent protective film of the second sample film. The measurement conditions in the Second Measurement were the same as those in the First Measurement. The 90° peel strength F2 (N / 15mm) of the second transparent protective film peeled from the polarizing film in this peel test is shown in Table 2.

[0081] <Indentation modulus> The indentation modulus of the first adhesive layer in each of the laminated optical films of Examples 1-3 and Comparative Example 1 was determined by nanoindentation. Specifically, a 5mm × 10mm film sheet (laminated optical film) was first cut from the laminated optical film. Then, the laminated optical film was cut using the freeze-cutting method. Specifically, after cooling the laminated optical film to -30°C, it was cut along the thickness direction of the film with a hard cutter, and then restored to room temperature. This yielded the test sample. Next, using a nanoindentation testing machine (product name "TI950 Triboindenter", manufactured by Hysitron Corporation), the exposed surface of the adhesive layer in the test sample was subjected to load-displacement measurement in accordance with JISZ 2255:2003 to obtain the load-displacement curve. In this measurement, the measurement mode was set to single indentation measurement, the measurement temperature was set to 25℃, and a Berkovich (triangular pyramidal) diamond indenter was used. During load application, the maximum indentation depth (maximum displacement hmax) of the indenter on the test sample was set to 50 nm, the indentation speed was set to 10 nm / s, and the pull-out speed of the indenter from the test sample during unloading was set to 10 nm / s. The measurement data were then processed using the dedicated analysis software (Ver. 9.4.0.1) of the "TI950 Triboindenter". Specifically, based on the obtained load (f)-displacement (h) curve, the following were obtained: maximum load fmax (the load acting on the indenter with the maximum displacement hmax), contact projection area S (the projected area of ​​the contact region between the indenter and the sample at maximum load), and the slope D of the tangent line of the load-displacement curve at the start of unloading. Then, the indentation elastic modulus of the first adhesive layer is calculated from the slope D and the contact projected area S (=(π 1 / 2D) / (2S 1 / 2)). This value is shown as the indentation elastic modulus E1 (GPa) in Table 2.

[0082] Furthermore, the indentation elastic modulus of the second adhesive layer in each of the laminated optical films of Examples 1-3 and Comparative Example 1 was measured in the same manner as the indentation elastic modulus E1 of the first adhesive layer. 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.

[0083] <Uneven display> This investigation investigated whether there was any display unevenness when the display panel was bent while each of the multilayer optical films of Examples 1-3 and Comparative Example 1 was mounted on it. The display panel was an organic EL panel (OLED panel) taken from a commercially available smartphone. The multilayer optical film was disposed on the image display side surface of the display panel. Specifically, the second transparent protective film side of the multilayer optical film was adhered to the image display side surface of the display panel using an adhesive. Then, with the image displayed on the display panel, the display panel was bent 90° and the image at the bend was observed with the naked eye. The situation where no display unevenness (tone change) was observed in the image at the bend was evaluated as "good", and the situation where display unevenness was observed was evaluated as "bad". The results are shown in Table 2.

[0084] High Temperature and High Humidity Flexural Test High temperature and high humidity flexural tests were conducted on each of the laminated optical films of Examples 1-3 and Comparative Example 1 in the following manner.

[0085] First, evaluation samples were cut from the laminated optical film. Specifically, rectangular samples of 25 mm × 100 mm were cut from the laminated film such that the absorption axis of the polarizing film in the sample to be cut was parallel to the long side direction. Next, a flexural test was performed on the sample using a planar unloaded U-shaped stretching tester (manufactured by YUASA SYSTEM). In this test, flexural fixtures were installed at both ends of the sample along the long side direction within a range of 20 mm from the edge of the sample, and the sample was fixed in the tester (the central 60 mm area along the long side direction of the sample was not fixed). Furthermore, in this test, the sample was repeatedly deformed (flexed) 80,000 times between a flexed shape with the surface of the first transparent protective film side facing inward and a non-flexed shape at a flexural speed of 60 rpm in a constant temperature and humidity chamber at a temperature of 60°C and a relative humidity of 90%. In this experiment, the flexural morphology specifically refers to the morphology where the axis of the bending moment acting on the sample is orthogonal to the absorption axis of the polarizing film. In this flexural morphology, the bending radius of the sample was set to 3 mm, and the bending angle was set to 180°. Then, regarding the peeling inhibition between the films (first transparent protective film, polarizing film, and second transparent protective film) in the flexural test, a case where no peeling occurred between the films after 80,000 flexes was evaluated as "good," and a case where peeling occurred after fewer than 80,000 flexes was evaluated as "poor." The evaluation results are shown in Table 1.

[0086] [Table 2]

[0087] X: Multilayer optical thin film 10: Optical Thin Films (First Optical Thin Film) 21: Optical Thin Film (Second Optical Thin Film) 22: Optical Thin Film (3rd Optical Thin Film) 31: Adhesive layer (first adhesive layer) 32: Adhesive layer (second adhesive layer) B: Bend H: Thickness direction

Claims

1. A laminated optical thin film, comprising, in a thickness direction, a first optical thin film, a first adhesive layer, a second optical thin film, a second adhesive layer, and a third optical thin film sequentially thereon; wherein the first adhesive layer is bonded to the first optical thin film and to the second optical thin film; wherein the second adhesive layer is bonded to the second optical thin film and to the third optical thin film; wherein 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.

2. The laminated optical thin film of claim 1, wherein the aforementioned indentation elastic modulus E2 is 4 GPa or less.

3. The laminated optical thin film of claim 1, wherein the aforementioned indentation elastic modulus E2 is 0.4 GPa or higher.

4. The laminated optical thin film of claim 1, wherein the aforementioned indentation elastic modulus E1 is 0.5 GPa or higher.

5. The laminated optical thin film of claim 1, wherein the aforementioned indentation elastic modulus E1 is 7 GPa or less.

6. The laminated optical film of any one of claims 1 to 5, wherein the aforementioned second optical film is a polarizing film.

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