Optical laminate and display device using same

Abstract

Provided are: an optical laminate that has a layered structure in which a low-reflection layer is laminated on an anti-glare layer, and that exhibits further reduced reflectance on the outermost surface; and a display device using the same. The optical laminate is obtained by laminating an anti-glare layer, which has protrusions and recesses, and a low-reflection layer in this order on at least one surface of a transparent substrate. Said optical laminate being characterized in that the external haze change rate |ΔHz| before and after lamination of the low-reflection layer is 40% or less, the arithmetic average roughness change rate |ΔRa| before and after lamination of the low-reflection layer is 21% or less, and the maximum valley depth change rate |ΔRv| before and after lamination of the low-reflection layer is 41% or less.

Description

Optical laminate and display device using the same

[0001] The present invention relates to an optical laminate that reduces reflection of external light and a display device using the same.

[0002] An optical film such as an anti-glare (AG) film or a low-reflection (LR) film is provided on the outermost surface of a display device. An anti-glare film has an anti-glare layer containing a filler, and the unevenness formed on the surface of the anti-glare layer by the filler diffuses reflected light, reducing the glare of external light. A low-reflection film reduces the reflection of external light by canceling out light reflected at the interface between the low-reflection layer and the substrate film and light reflected at the surface of the low-reflection layer through interference. Also known is an anti-glare low-reflection (AGLR) film that combines both and has a configuration in which a low-reflection layer is laminated on the surface of an anti-glare layer (see, for example, Patent Document 1).

[0003] In recent years, vehicles have been equipped with multiple display devices such as center information displays (CIDs), meter cluster panels (MCPs), etc. In-vehicle display devices may display safety-related information, so they are required to have low reflection of external light, not dazzling reflected light, suppression of the glare that is characteristic of anti-glare films, and clear displayed images.

[0004] International Publication No. 2021 / 182424

[0005] The above-mentioned AGLR film is suitable as an optical film that can simultaneously suppress the reflection of external light and sharpen images. However, when a coating liquid for forming a low-reflection layer is applied to an uneven anti-glare layer and then dried, the coating liquid flows into the recesses along the inclined surfaces of the fine unevenness on the anti-glare layer surface, causing variations in the film thickness of the low-reflection layer. Therefore, if the film thickness of the low-reflection layer varies and deviates from the designed film thickness, the anti-reflection effect of the low-reflection layer is reduced, and the reflectance of the film surface increases, which is a problem.

[0006] Therefore, an object of the present invention is to provide an optical laminate having a layer structure in which a low-reflection layer is laminated on an anti-glare layer, and in which the reflectance of the outermost surface is further reduced, and a display device using the same.

[0007] An optical laminate comprising an antiglare layer having irregularities and a low-reflection layer laminated in this order on at least one surface of a transparent substrate, wherein the rate of change in external haze |ΔHz| before and after lamination of the low-reflection layer is 40% or less, the rate of change in arithmetic mean roughness |ΔRa| before and after lamination of the low-reflection layer is 21% or less, and the rate of change in maximum valley depth |ΔRv| before and after lamination of the low-reflection layer is 41% or less, wherein |ΔHz|=|(external haze without low-reflection layer−external haze with low-reflection layer) / external haze without low-reflection layer×100|, |ΔRa|=|(arithmetic mean roughness without low-reflection layer−arithmetic mean roughness with low-reflection layer) / arithmetic mean roughness without low-reflection layer×100|, |ΔRv|=|(maximum valley depth without low-reflection layer−maximum valley depth with low-reflection layer) / maximum valley depth without low-reflection layer×100|.

[0008] A display device according to the present invention includes the above optical laminate.

[0009] According to the present invention, it is possible to provide an optical laminate having a layer structure in which a low-reflection layer is laminated on an antiglare layer and in which the reflectance of the outermost surface is further reduced, and a display device using the same.

[0010] 1 is a schematic cross-sectional view showing an optical laminate according to an embodiment, and FIG 2 is a schematic cross-sectional view showing an optical laminate according to a comparative example.

[0011] FIG. 1 is a schematic cross-sectional view showing an optical laminate according to an embodiment.

[0012] The optical laminate 10 is an anti-reflection film provided on the outermost surface of a display device, and comprises a transparent substrate 1, an anti-glare layer 2 laminated on one side of the transparent substrate 1, and a low-reflection layer 3 laminated on the anti-glare layer 2.

[0013] The transparent substrate 1 is a film that serves as the base of the optical laminate 10, and is made of a material that has excellent transmittance to visible light. Examples of materials that can be used to form the transparent substrate 1 include polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polyacrylates such as polymethyl methacrylate, polyamides such as nylon 6 and nylon 66, polyimides, polyarylates, polycarbonates, triacetyl cellulose, polyacrylates, polyvinyl alcohol, polyvinyl chloride, cycloolefin copolymers, norbornene-containing resins, polyethersulfones, and transparent resins such as polysulfones, and inorganic glass. The thickness of the transparent substrate 1 is not particularly limited, but is preferably 10 to 200 μm.

[0014] The surface of the transparent substrate 1 may be subjected to a surface modification treatment in order to improve adhesion to the antiglare layer 2. Examples of surface modification treatments include alkali treatment, corona treatment, plasma treatment, sputtering treatment, application of a surfactant or a silane coupling agent, and Si vapor deposition.

[0015] The antiglare layer 2 contains a filler, and the fine irregularities formed on the surface by the filler scatter external light, thereby reducing the glare of external light. The antiglare layer 2 is formed by applying an antiglare layer-forming coating liquid containing a binder resin and a filler to the transparent substrate 1 and curing the coating film.

[0016] As the binder resin, an active energy ray-curable resin that is cured by irradiation with ionizing radiation or ultraviolet light can be used, and for example, a monofunctional, difunctional, trifunctional or higher functional (meth)acrylate monomer can be used. In this specification, "(meth)acrylate" is a general term for both acrylate and methacrylate, and "(meth)acryloyl" is a general term for both acryloyl and methacryloyl.

[0017] Examples of monofunctional (meth)acrylate compounds include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, glycidyl (meth)acrylate, acryloylmorpholine, N-vinylpyrrolidone, tetrahydrofurfuryl acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isobornyl (meth)acrylate. acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, benzyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, ethyl carbitol (meth)acrylate, phosphate (meth)acrylate, ethylene oxide-modified phosphate (meth)acrylate, phenoxy (meth)acrylate, ethylene oxide-modified phenoxy (meth)acrylate, propylene oxide ethylene oxide-modified phenoxy (meth)acrylate, nonylphenol (meth)acrylate, ethylene oxide-modified nonylphenol (meth)acrylate, propylene oxide-modified nonylphenol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, ) acryloyloxyethyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hexahydrohydrogen phthalate, 2-(meth)acryloyloxypropyl tetrahydrohydrogen phthalate, dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, 2-adamantane,adamantane derivative mono(meth)acrylates such as adamantyl acrylate having a monovalent mono(meth)acrylate derived from adamantanediol, etc.

[0018] Examples of bifunctional (meth)acrylate compounds include di(meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, ethoxylated hexanediol di(meth)acrylate, propoxylated hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and hydroxypivalic acid neopentyl glycol di(meth)acrylate.

[0019] Examples of trifunctional or higher functional (meth)acrylate compounds include tri(meth)acrylates such as trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, tris-2-hydroxyethyl isocyanurate tri(meth)acrylate, and glycerin tri(meth)acrylate, as well as trifunctional (meth)acrylate compounds such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and ditrimethylolpropane tri(meth)acrylate. and polyfunctional (meth)acrylate compounds having three or more functional groups such as pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, ditrimethylolpropane penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ditrimethylolpropane hexa(meth)acrylate; and polyfunctional (meth)acrylate compounds in which a portion of these (meth)acrylates is substituted with an alkyl group or ε-caprolactone.

[0020] Urethane (meth)acrylates can also be used as the active energy ray-curable resin. Examples of urethane (meth)acrylates include those obtained by reacting a polyester polyol with an isocyanate monomer or a prepolymer, and then reacting the resulting product with a (meth)acrylate monomer having a hydroxyl group.

[0021] Examples of urethane (meth)acrylates include pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer, and dipentaerythritol pentaacrylate isophorone diisocyanate urethane prepolymer.

[0022] The active energy ray-curable resins described above may be used alone or in combination of two or more. In addition, the active energy ray-curable resins described above may be in the form of a monomer in the coating liquid or a partially polymerized oligomer.

[0023] Furthermore, as the active energy ray-curable resin, in addition to the compounds having the above-mentioned radically polymerizable functional groups, monomers, oligomers, and prepolymers having cationically polymerizable functional groups such as epoxy groups, vinyl ether groups, and oxetane groups can be used alone or in combination. Examples of the monomer include unsaturated polyesters, epoxy acrylates, epoxy compounds such as tetramethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A diglycidyl ether, and various alicyclic epoxies, and oxetane compounds such as 3-ethyl-3-hydroxymethyloxetane, 1,4-bis{[(3-ethyl-3-oxetanyl)methoxy]methyl}benzene, and di[1-ethyl(3-oxetanyl)]methyl ether.

[0024] Furthermore, it is preferable that a low refractive index resin be blended in the coating liquid for forming the antiglare layer in addition to the binder resin described above. Adding a low refractive index resin to the coating liquid for forming the antiglare layer is advantageous for lowering the refractive index of the antiglare layer. The low refractive index resin may be any of a monomer, oligomer, and polymer, and may have a functional group polymerizable with the binder resin described above.

[0025] The resin material described above can be cured by irradiation with ultraviolet light, provided that a photopolymerization initiator is added. As the photopolymerization initiator, radical polymerization initiators such as acetophenones, benzophenones, thioxanthones, benzoin, and benzoin methyl ether, and cationic polymerization initiators such as aromatic diazonium salts, aromatic sulfonium salts, aromatic iodonium salts, and metallocene compounds can be used alone or in combination.

[0026] The filler is a material that mainly provides a function of diffusing external light by forming fine irregularities on the surface of the antiglare layer 2. As the filler, either or both of organic fine particles and inorganic fine particles can be used.

[0027] The organic fine particles may be resin particles made of a light-transmitting resin material such as acrylic resin, polystyrene resin, styrene-(meth)acrylic acid ester copolymer, polyethylene resin, epoxy resin, silicone resin, polyvinylidene fluoride, polyethylene fluoride resin, etc. In order to adjust the refractive index and dispersion of the resin particles, two or more types of resin particles made of different materials (refractive indexes) may be mixed and used.

[0028] The inorganic fine particles added to the coating liquid for forming the antiglare layer are preferably nanoparticles having an average particle size of 10 to 200 nm.

[0029] Examples of inorganic fine particles include silica fine particles, metal oxide fine particles, and various mineral fine particles. Examples of silica fine particles include colloidal silica and silica fine particles surface-modified with reactive functional groups such as (meth)acryloyl groups. Examples of metal oxide fine particles include alumina, zinc oxide, tin oxide, antimony oxide, indium oxide, titania, and zirconia. Examples of mineral fine particles include mica, synthetic mica, vermiculite, montmorillonite, iron-montmorillonite, bentonite, beidellite, saponite, hectorite, stevensite, nontronite, magadiite, ilealite, kanemite, layered titanic acid, smectite, and synthetic smectite. The mineral fine particles may be natural or synthetic (including substituted or derivative) materials, or a mixture of both may be used. The inorganic fine particles have the function of increasing the viscosity of the coating liquid for forming the antiglare layer, suppressing the sedimentation of resin particles and inorganic fine particles, and adjusting the uneven shape of the surface of the antiglare layer. Among mineral fine particles, layered organic clay is more preferred. Layered organic clay refers to a swelling clay in which organic onium ions are introduced between the layers. There are no limitations on the organic onium ions as long as they can be organized by utilizing the cation exchange properties of the swelling clay. When a layered organic clay mineral is used as the mineral fine particles, the above-mentioned synthetic smectite can be preferably used.

[0030] A leveling agent may also be added to the coating solution for forming the antiglare layer. The leveling agent orients itself on the surface of the coating film during drying, thereby equalizing the surface tension of the coating film and reducing surface defects of the coating film.

[0031] Furthermore, an organic solvent may be added to the coating liquid for forming the antiglare layer as appropriate. Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, butanol, isopropyl alcohol, isobutanol, and t-butyl alcohol; ketones such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone; ketone alcohols such as diacetone alcohol; aromatic hydrocarbons such as benzene, toluene, and xylene; glycols such as ethylene glycol, propylene glycol, and hexylene glycol; glycol ethers such as ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, diethyl cellosolve, diethyl carbitol, and propylene glycol monomethyl ether; esters such as methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, and amyl acetate; ethers such as dimethyl ether and diethyl ether; N-methylpyrrolidone, dimethylformamide, water, and the like, and a mixture of two or more of these can be used.

[0032] The low-reflection layer 3 is an optically functional layer that reduces the surface reflection of the optical laminate 10 by canceling out light reflected on the surface of the low-reflection layer 3 through interference with light reflected on the interface between the low-reflection layer 3 and the anti-glare layer 2. The low-reflection layer 3 can be formed by applying a coating liquid containing a binder resin and, if necessary, low-refractive-index fine particles (shown by circles in FIG. 1 ) to the surface of the anti-glare layer 2 and curing the coating film.

[0033] The binder resin used to form the low reflection layer 3 is not particularly limited, and the compounds exemplified as the material for the antiglare layer 2 can be used.

[0034] Examples of low refractive index particles include LiF, MgF, 3NaF·AlF, and AlF (each having a refractive index of 1.4), and Na ３ AlF ６Fine particles such as cryolite (refractive index 1.33) and silica fine particles having voids therein can be suitably used. Silica fine particles having voids therein can have the refractive index of the voids (approximately 1) of air, and are therefore useful for lowering the refractive index of the low-reflection layer 3. Specifically, porous silica particles and silica particles with a shell structure can be used.

[0035] If necessary, a solvent or various additives may be added to the coating liquid for forming the low-reflection layer 3. As the solvent, for example, those exemplified as the materials for the antiglare layer 2 may be used. Furthermore, as the additive, for example, an antifoaming agent, a leveling agent, an antioxidant, an ultraviolet absorber, a light stabilizer, a polymerization inhibitor, a photosensitizer, etc. may be used.

[0036] When the coating film of the coating liquid for forming the low-reflection layer is cured by ultraviolet irradiation, a photopolymerization initiator is added to the coating liquid. As the photopolymerization initiator, those exemplified as the materials for the antiglare layer 2 can be used.

[0037] FIG. 2 is a schematic cross-sectional view showing an optical laminate according to a comparative example.

[0038] The optical laminate 90 according to the comparative example includes a transparent substrate 1, an antiglare layer 2 laminated on one side of the transparent substrate 1, and a low-reflection layer 93 laminated on the antiglare layer 2. The low-reflection layer 93 may contain low-refractive-index fine particles, indicated by circles, similar to the reflective layer 3 according to the embodiment. However, in the low-reflection layer 93 according to the comparative example, the coating liquid for forming the low-reflection layer flows into the recesses during application of the coating liquid, resulting in a large difference between the film thickness of the low-reflection layer 93 on the protrusions and the film thickness of the low-reflection layer 93 in the recesses, resulting in overall variation in the film thickness of the low-reflection layer 93. When the film thickness of the low-reflection layer 93 varies and deviates from the designed film thickness, there is insufficient interference between light transmitted through the low-reflection layer 93 and reflected at the interface between the low-reflection layer 93 and the antiglare layer 2 and light reflected at the surface of the low-reflection layer 93, resulting in an insufficient reduction in reflectance. Furthermore, the coating liquid for forming a low-reflection layer flows into the recesses, reducing the depth of the recesses and making the unevenness closer to flat, thereby reducing the arithmetic mean roughness Ra of the surface of the optical laminate 90. The reduction in arithmetic mean roughness Ra reduces scattering of external light, which has led to the problem of insufficient suppression of reflection of external light.

[0039] In contrast, the optical laminate 10 according to the present invention can suppress the glare of external light and surface reflection on the optical laminate 10 by simultaneously satisfying the following conditions (1) to (3): (1) The rate of change |ΔHz| in external haze before and after lamination of the low-reflection layer 3 is 40% or less. (2) The rate of change |ΔRa| in arithmetic mean roughness before and after lamination of the low-reflection layer 3 is 21% or less. (3) The rate of change |ΔRv| in maximum valley depth before and after lamination of the low-reflection layer 3 is 41% or less.

[0040] Here, the rate of change in external haze |ΔHz|, the rate of change in arithmetic mean roughness |ΔRa|, and the rate of change in maximum valley depth |ΔRv| are values ​​calculated by the following formulas, respectively: |ΔHz|=|(external haze without low-reflection layer−external haze with low-reflection layer) / external haze without low-reflection layer×100|, |ΔRa|=|(arithmetic mean roughness without low-reflection layer−arithmetic mean roughness with low-reflection layer) / arithmetic mean roughness without low-reflection layer×100|, |ΔRv|=|(maximum valley depth without low-reflection layer−maximum valley depth with low-reflection layer) / maximum valley depth without low-reflection layer×100|

[0041] Here, "a state without a low-reflection layer" includes both a state in which the anti-glare layer 2 is laminated on the transparent substrate 1 and before the low-reflection layer 3 is laminated, and a state in which the low-reflection layer 3 on the outermost surface of the optical laminate 10 is removed by saponification to expose the anti-glare layer 2. The inventors of the present application conducted studies in which only the anti-glare layer 3 was laminated on the transparent substrate 1, and then subjected the anti-glare layer 3 to a saponification treatment, and measured and compared the surface roughness parameters (Ra, Rv, and Rz) before and after lamination. It was confirmed that these surface roughness parameters remained almost unchanged before and after the saponification treatment, and that the surface irregularity shape of the anti-glare layer remained almost unchanged. Therefore, the values ​​of the external haze, arithmetic mean roughness and maximum valley depth measured after the low-reflection layer 3 of the optical laminate 10 has been removed by saponification can be used to replace the values ​​of the external haze, arithmetic mean roughness and maximum valley depth before the low-reflection layer 3 is laminated, and no substantial difference occurs in the calculated values ​​of the change rates |ΔHz|, |ΔRa| and |ΔRv| regardless of which of the above-mentioned measured values ​​is used.

[0042] The arithmetic mean roughness (Ra) and maximum valley depth (Rv) in the state without the low-reflection layer 3 and in the state with the low-reflection layer 3 are both values ​​measured in accordance with JIS-B-0601:2013. The arithmetic mean roughness Ra is the average of the heights (distances from the average height) of the peaks in the reference length of the profile curve, and the maximum valley depth Rv is the depth of the deepest valley from the average line in the reference length of the profile curve. The average line and maximum valley depth Rv are shown in Figures 1 and 2 for convenience.

[0043] When the above conditions (1) to (3) are satisfied, the flow of the low-reflection layer-forming coating liquid into the recesses during coating is suppressed, and the thickness of the low-reflection layer 3 is close to the designed film thickness throughout, so that the reflectance can be further reduced by interference and cancellation between light that has passed through the low-reflection layer 3 and is reflected at the interface between the low-reflection layer 3 and the antiglare layer 2 and light that is reflected at the surface of the low-reflection layer 3. Furthermore, suppressing the flow of the low-reflection layer-forming coating liquid into the recesses suppresses a decrease in the depth of the recesses and the arithmetic mean roughness of the surface irregularities. As a result, external light is scattered, and the reflection of external light can be further reduced.

[0044] The film thickness of the low-reflection layer 3 satisfying the above conditions (1) to (3) can be controlled, for example, by the ambient temperature during application of the low-reflection layer-forming coating liquid and the non-volatile content of the low-reflection layer-forming coating liquid. The ambient temperature during application of the low-reflection side-forming coating liquid is preferably 60 to 100°C. If the ambient temperature during application is within this range, volatile components such as solvents contained in the applied low-reflection layer-forming coating liquid are quickly volatilized after application, reducing the fluidity of the coating film and thereby preventing the low-reflection layer-forming coating liquid from flowing into recesses. Furthermore, the non-volatile content of the low-reflection layer-forming coating liquid is preferably 3.0 to 3.4%. If the non-volatile content of the low-reflection layer-forming coating liquid is less than 3.0%, the fluidity of the low-reflection layer-forming coating liquid is high, making it difficult to prevent the low-reflection layer-forming coating liquid from flowing into recesses, which is not preferred. On the other hand, if the nonvolatile content of the coating liquid for forming a low reflection layer exceeds 3.4%, the fluidity of the coating liquid for forming a low reflection layer is low and the solid content is likely to be localized, which is not preferable.

[0045] The SCI reflectance of the optical laminate 10 is preferably 0.7% or less. The SCI reflectance is the reflectance of all reflected light, including specular reflected light, measured by the SCI (Specular Component Include) method, and can be measured in accordance with JIS Z 8722. When the above conditions (1) to (3) are satisfied, the SCI reflectance of the optical laminate 10 can be set to 0.7% or less, and an optical laminate 10 with excellent low reflectance can be realized.

[0046] The reflection spectrum of the optical laminate 10 is a curve with a minimum value at a specific wavelength. Hereinafter, the wavelength in the visible light region at which the reflectance is minimum is referred to as the "bottom wavelength." The reflectance of the optical laminate 10 is minimum at the bottom wavelength and increases as the wavelength moves away from the bottom wavelength. The bottom wavelength of the optical laminate 10 according to this embodiment is preferably 520 to 580 nm. When the bottom wavelength is in this range, reflection of light in the visible light region can be effectively reduced.

[0047] According to the present invention, by simultaneously satisfying the above conditions (1) to (3), it is possible to realize an optical laminate 10 in which the reflection of surroundings is reduced and the reflectance of the outermost surface is further reduced. Since the optical laminate according to the present invention reduces the reflection of external light and surface reflection, it is suitable as an optical film to be used in image display devices, and is particularly suitable as an anti-reflection film for in-vehicle display devices that display safety information and the like.

[0048] The optical laminate 10 according to the present invention is typically provided on the outermost surface of a display panel such as an organic EL panel or a liquid crystal panel, and together with the display panel, constitutes a display device. A touch panel may be provided between the optical laminate and the display panel. However, the lamination position of the optical laminate 10 is not particularly limited as long as the desired optical properties can be exhibited. Furthermore, one or more optical functional layers such as an antistatic layer, an antifouling layer, an infrared absorbing layer, an ultraviolet absorbing layer, or a color correction layer may be provided on the low-reflectivity layer 3 of the optical laminate 10.

[0049] Examples in which the anti-reflection film according to the embodiment was specifically implemented will be described below.

[0050] (Examples 1 to 4, Comparative Examples 1 to 4) A 40 μm thick TAC film was used as the transparent substrate. A coating liquid for forming an antiglare layer was prepared, containing a binder resin, a filler, a photopolymerization initiator, and a solvent. The coating liquid for forming an antiglare layer was applied to the transparent substrate so that the film thickness after curing would be 5 μm, dried, and then polymerized and cured by ultraviolet irradiation to form an antiglare layer. Next, a coating liquid for forming a low-reflection layer was prepared on the antiglare layer, containing a binder resin, silica microparticles having internal voids, a leveling agent, a photopolymerization initiator, and a solvent. The coating liquid for forming a low-reflection layer was applied to the antiglare layer so that the film thickness after curing would be 0.1 μm, dried, and then polymerized and cured by ultraviolet irradiation to form a low-reflection layer. The nonvolatile content concentration of the coating liquid for forming a low-reflection layer and the atmospheric temperature during coating were as shown in Table 1.

[0051] The external haze, arithmetic mean roughness Ra, and maximum valley depth Rv were measured using the optical laminate before forming the low-reflection layer (before applying the coating liquid for forming the low-reflection layer) and after forming the low-reflection layer. In addition, the SCI reflectance of the optical laminate after forming the low-reflection layer was measured. The measurement method is as follows.

[0052] [Haze] Haze was measured in accordance with JIS K 7136:2000 using a haze meter (NDH-4000, manufactured by Nippon Denshoku Industries Co., Ltd.). First, the total haze of the optical laminate was measured. Next, a sample was prepared by laminating an optical adhesive film on the transparent substrate side of the optical laminate, and the haze (total haze) of this sample was measured. The internal haze of the optical laminate was calculated by subtracting the haze of the optical adhesive film alone from the haze of the sample after the optical adhesive film was attached. The external haze was calculated by subtracting the internal haze calculated from the haze of the optical laminate before the optical adhesive film was attached. The external haze was calculated for each of the optical laminates before and after the formation of the low-reflection layer, and the rate of change |ΔHz| in external haze before and after lamination of the low-reflection layer was calculated using the above formula.

[0053] [Arithmetic mean roughness Ra, maximum valley depth Rv] The uneven shapes of the low refractive index layer surfaces of the optical laminates according to the examples and comparative examples were measured by optical interference using a non-contact surface / layer cross-sectional shape measurement system (measuring device: Vertscan R3300FL-Lite-AC, analysis software: VS-Viewer 6, manufactured by Hitachi High-Technologies Corporation). The measurement data was analyzed using the particle analysis software of the device, and the arithmetic mean roughness Ra and maximum valley depth Rv of the low refractive index layer surfaces were measured.

[0054] In the present invention, average irregularities are generated under the analysis conditions for the cross-sectional profile (multi-line) of VS-Viewer. In the cross-sectional profile (multi-line), the arithmetic mean roughness Ra and maximum valley depth Rv obtained from a cross section obtained by averaging the cross-sectional profiles of the six set measurement cursors are defined as the arithmetic mean roughness Ra and maximum valley depth Rv of the irregularities in the present invention.

[0055] Measurements were carried out under the following conditions using the device's measurement software, and image files showing the surface unevenness measurement results were obtained. Optical conditions Camera: Sony HR-50 1 / 3 inch Objective lens: 10XDI (10x) Imaging lens (lens barrel): 0.5x Zoom lens: 1x Light source / wavelength filter: 520nm ND filter: not used A-Stop (aperture diaphragm): not used (fully open) F-Stop (field diaphragm): not used (fully open) Measurement conditions Measurement device: Piezo Measurement mode: Phase Scan speed: 4μm / sec Scan range: -10 to 10μm Number of effective pixels: 50% Measurement area: 704.192μm x 938.923μm

[0056] The acquired image files were analyzed using the device's analysis software under the following conditions: Analysis conditions (VS-Viewer 6) Surface correction: 4th order S filter: automatic L filter: not used Particle analysis conditions (VS-Viewer 6) Analysis type: protrusion analysis Image correction: none Height threshold: 0.1 μm Particle shaping: none

[0057] [Method of calculating Ra and Rv] In the acquired image to which surface correction (fourth order) and an S filter were applied, the measurement cursors were set at positions of 200 μm, 500 μm, and 800 μm in the vertical direction (X direction) and 200 μm, 400 μm, and 600 μm in the horizontal direction (Y direction). The Ra and Rv values ​​at each cursor position (three cross sections parallel to the X direction and three cross sections parallel to the Y direction, a total of six positions) automatically calculated using the cross-sectional profile of VS-Viewer were acquired, and the average value (arithmetic mean) of the acquired values ​​was used as the measurement result.

[0058] The Ra and Rv were calculated for each of the optical laminates before and after the formation of the low-reflection layer, and the rate of change |ΔRa| of the arithmetic mean roughness before and after the lamination of the low-reflection layer and the rate of change |ΔRv| of the maximum valley depth before and after the lamination of the low-reflection layer were calculated using the above-mentioned formula.

[0059] [SCI Reflectance Y] SCI reflectance Y was measured in accordance with JIS Z 8722 using a spectrophotometer (CM-2600d, manufactured by Konica Minolta Japan, Inc.). The measurement conditions were a measurement diameter / illumination diameter of 8 mm / 11 mm, a 10° field of view for observation, and a D65 observation light source. Measurement with a measurement diameter (8 mm) allows areas with relatively high and low reflectance due to coating unevenness to be captured within a single field of view, thereby enabling the measurement of an average SCI reflectance. Furthermore, a 10° field of view corresponds to viewing an area with a diameter of 8.8 cm at a distance of 50 cm. However, in the case of in-vehicle applications, a relatively large area of ​​the image display device is often viewed at a close distance, making measurement with a 10° field of view more appropriate. D65 is the average noon light in Europe / Northern Europe as defined by the International Commission on Illumination, and is suitable for measurement because it has a wavelength distribution similar to that of ambient light. An SCI reflectance of 0.7 or less was determined to indicate that reflectance was sufficiently suppressed.

[0060] Table 1 also shows the low-reflection layer formation conditions (non-volatile content [mass%] of the coating solution for forming the low-reflection layer, atmospheric temperature during coating), the change rate of external haze |ΔHz|, the change rate of arithmetic mean roughness |ΔRa|, the change rate of maximum valley depth |ΔRv|, and the measurement results of SCI reflectivity in each example and each comparative example.

[0061]

[0062] The optical laminates of Examples 1 to 4 had the external haze change rate |ΔHz|, the arithmetic mean roughness change rate |ΔRa|, and the maximum valley depth change rate |ΔRv| all satisfying the above-mentioned conditions, and were excellent in low reflectivity.

[0063] In contrast, the optical laminates according to Comparative Examples 1 to 4 did not satisfy the above-mentioned conditions in terms of the rate of change in external haze |ΔHz|, the rate of change in arithmetic mean roughness |ΔRa|, or the rate of change in maximum valley depth |ΔRv|, and had higher SCI reflectance than the examples.

[0064] From the above, it was confirmed that the present invention can further reduce the reflectance of the outermost surface in an optical laminate having a layer structure of transparent substrate / antiglare layer / low-reflection layer.

[0065] As described above, when the low refractive index layer was saponified and peeled off from the optical laminate, the surface of the antiglare layer was thought to dissolve slightly due to saponification, but the surface irregularities of the antiglare layer did not change significantly. As an example, an optical laminate in which only the antiglare layer was laminated on a transparent substrate was immersed in a 10% sodium hydroxide aqueous solution at 55°C for 10 minutes for saponification, and the Ra, Rv, and Rz of the antiglare layer surface before and after saponification were measured. The results were Ra (before saponification: 0.092, after saponification: 0.099), Rv (before saponification: -0.232, after saponification: -0.216), and Rz (before saponification: 0.456, after saponification: 0.448), and the difference in the measured values ​​before and after saponification was slight. The surface condition of the antiglare layer before and after saponification may be measured by averaging values ​​from a total of three points: two at the ends and one at the center when the film on which the antiglare layer was laminated is divided into thirds in the width direction. The measurement methods for Ra and Rv may be the same as those used in the Examples and Comparative Examples. As with Ra and Rv, the measurement method for Rz may involve obtaining values ​​at each cursor position (a total of six positions, three positions on a cross section parallel to the X direction and three positions on a cross section parallel to the Y direction) that are automatically calculated using the cross-sectional profile of VS-Viewer, and then averaging the obtained values ​​(arithmetic mean). Because the antiglare layer remains almost unchanged before and after saponification, the surface state (|ΔHz|, |ΔRa|, and |ΔRv|) of the antiglare layer under the above conditions can be easily confirmed using the external haze, arithmetic mean roughness, and maximum valley depth measured in a state in which the low refractive index layer is saponified and peeled from the optical laminate.

[0066] The present invention can be used as an anti-reflection film for an image display device.

[0067] 1 Transparent base material 2 Anti-glare layer 3 Low reflection layer

Claims

1. An optical laminate comprising an antiglare layer having irregularities and a low-reflection layer laminated in this order on at least one surface of a transparent substrate, characterized in that the rate of change in external haze |ΔHz| before and after lamination of the low-reflection layer is 40% or less, the rate of change in arithmetic mean roughness |ΔRa| before and after lamination of the low-reflection layer is 21% or less, and the rate of change in maximum valley depth |ΔRv| before and after lamination of the low-reflection layer is 41% or less, wherein |ΔHz|=|(external haze without low-reflection layer−external haze with low-reflection layer) / external haze without low-reflection layer×100|, |ΔRa|=|(arithmetic mean roughness before lamination without low-reflection layer−arithmetic mean roughness with low-reflection layer) / arithmetic mean roughness without low-reflection layer×100| |ΔRv|=|(maximum valley depth without low reflective layer−maximum valley depth with low reflective layer) / maximum valley depth without low reflective layer×100|.

2. The optical laminate according to claim 1, wherein the low reflection layer contains an acrylic resin, a low refractive index resin, and hollow silica particles.

3. The optical laminate according to claim 1, wherein the bottom wavelength, which is the wavelength at which the reflectance is minimum in the visible light region, is within the range of 520 to 580 nm.

4. A display device comprising the optical laminate according to any one of claims 1 to 3.

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