Optical laminate and display device using the same

Abstract

Provided are an optical laminate having a layer configuration in which a low-reflection layer is layered on an antiglare layer, and a display device using the optical laminate, in which the reflectance of the surface layer is further reduced. An optical laminate is one in which an antiglare layer having a concavo-convex structure and a low-reflection layer are layered in this order on at least one surface of a transparent substrate, characterized in that the rate of change |ΔHz| in external haze before and after the low-reflection layer is layered is 40% or less, the rate of change |ΔRa| in arithmetic mean roughness before and after the low-reflection layer is layered is 21% or less, and the rate of change |ΔRv| in maximum valley depth before and after the low-reflection layer is layered is 41% or less.

Description

Technical Field

[0001] The present invention relates to an optical laminate for reducing the reflection of external light and a display device using the optical laminate. Background Technology

[0002] An optical film, such as an anti-glare (AG) film or a low-reflection (LR) film, is provided on the outermost surface of the display device. The anti-glare film has an anti-glare layer containing filler, and the reflected light is diffused by the irregularities formed by the filler on the surface of the anti-glare layer, reducing the reflection of external light. The low-reflection film reduces the reflection of external light by causing interference between light reflected at the interface between the low-reflection layer and the substrate film and light reflected on the surface of the low-reflection layer. Furthermore, an anti-glare low-reflection (AGLR) film, which combines both and has a low-reflection layer laminated on the surface of the anti-glare layer, is also known (see, for example, Patent Document 1).

[0003] In recent years, vehicles have been equipped with multiple central information displays (CID) and instrument cluster panels (MCP). For in-vehicle displays, which sometimes show safety-related information, it is essential to minimize external light exposure, prevent glare from reflected light, suppress glare characteristic of anti-glare films, and ensure clear image display.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2021 / 182424 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The aforementioned AGLR film is preferred as an optical film capable of both suppressing external light reflection and enhancing image sharpness. However, when a coating liquid for forming a low-reflection layer is applied to an anti-glare layer with uneven surfaces and allowed to dry, the coating liquid flows into the recesses along the inclined surfaces of the micro-undulations on the surface of the anti-glare layer, causing a deviation in the film thickness of the low-reflection layer. Therefore, when the film thickness of the low-reflection layer deviates from the designed thickness, there is a problem of reduced anti-reflection effect of the low-reflection layer and increased reflectivity of the film surface.

[0009] Therefore, the object of the present invention is to provide an optical laminate having a layer configuration in which a low-reflection layer is stacked on an anti-glare layer, further reducing the reflectivity of the outermost surface, and a display device using the optical laminate.

[0010] Methods for solving problems

[0011] An optical laminate is formed by sequentially stacking an anti-glare layer having an uneven surface and a low-reflection layer on at least one surface of a transparent substrate. The laminate is characterized in that the rate of change of external haze |ΔHz| before and after the low-reflection layer is stacked is less than 40%, the rate of change of the arithmetic mean roughness |ΔRa| before and after the low-reflection layer is stacked is less than 21%, and the rate of change of the maximum valley depth |ΔRv| before and after the low-reflection layer is stacked is less than 41%. in, |ΔHz| = |(External haze without a low-reflection layer - External haze with a low-reflection layer) / External haze without a low-reflection layer × 100| |ΔRa| = |(arithmetic mean roughness without a low-reflection layer - arithmetic mean roughness with a low-reflection layer) / arithmetic mean roughness without a low-reflection layer × 100| |ΔRv| = |(Maximum valley depth without a low-reflection layer - Maximum valley depth with a low-reflection layer) / Maximum valley depth without a low-reflection layer × 100|.

[0012] The display device of the present invention includes the above-described optical laminate.

[0013] The effects of the invention

[0014] According to the present invention, an optical laminate having a layer configuration in which a low-reflection layer is stacked on an anti-glare layer, further reducing the reflectivity of the outermost surface, and a display device using the optical laminate can be provided. Attached Figure Description

[0015] [ Figure 1 ] Figure 1 This is a schematic cross-sectional view showing the optical laminate according to the embodiment.

[0016] [ Figure 2 ] Figure 2 This is a schematic cross-sectional view showing the optical laminate involved in the comparative example. Detailed Implementation

[0017] Figure 1 This is a schematic cross-sectional view showing the optical laminate according to the embodiment.

[0018] The optical laminate 10 is an anti-reflective film disposed on the outermost surface of the display device, comprising 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.

[0019] The transparent substrate 1 is a film serving as the base of the optical laminate 10, and is formed from a material with excellent visible light transmittance. The transparent substrate 1 can be formed from 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; transparent resins such as polyimide, polyarylate, polycarbonate, triacetyl cellulose, polyacrylate, polyvinyl alcohol, polyvinyl chloride, cyclic olefin copolymers, norbornene-containing resins, polyethersulfone, and polysulfone, or inorganic glass. The thickness of the transparent substrate 1 is not particularly limited, but is preferably set to 10–200 μm.

[0020] To improve adhesion to the anti-glare layer 2, the surface of the transparent substrate 1 can be modified. Examples of surface modification treatments include alkali treatment, corona treatment, plasma treatment, sputtering treatment, coating with surfactants or silane coupling agents, and Si evaporation.

[0021] The anti-glare layer 2 contains fillers, which scatter external light and reduce its reflection by creating micro-unfolds on the surface. The anti-glare layer 2 is formed by applying an anti-glare layer forming liquid containing binder resin and fillers onto a transparent substrate 1 and then curing the coating.

[0022] As an adhesive resin, an active energy ray-curing resin that is cured by ionizing radiation or ultraviolet light can be used, such as monofunctional, difunctional, or trifunctional (meth)acrylate monomers. It should be noted that 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 groups.

[0023] 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, tert-butyl (meth)acrylate, glycidyl (meth)acrylate, acryloylmorpholine, N-vinylpyrrolidone, tetrahydrofurfuryl acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, and so on. Isodecanyl acrylate, lauryl acrylate, tridecyl acrylate, hexadecyl acrylate, octadecyl acrylate, benzyl acrylate, 2-ethoxyethyl acrylate, 3-methoxybutyl acrylate, ethyl carbitol acrylate, methacrylate, ethylene oxide modified methacrylate, phenoxy(meth)acrylate, ethylene oxide modified phenoxy(meth)acrylate, propylene 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 acrylate, hydrogenated 2-(meth)acryloyloxyethyl phthalate, hydrogenated 2-(meth)acryloyloxyethyl phthalate 2-(meth)acryloyloxypropyl ester, 2-(meth)acryloyloxypropyl hexahydrogenated phthalic acid, 2-(meth)acryloyloxypropyl tetrahydrogenated phthalic acid, dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, and adamantane derivatives of mono(meth)acrylates derived from 2-adamantane and adamantanediol, such as adamantane acrylate and other adamantane derivatives of mono(meth)acrylates.

[0024] Examples of difunctional (meth)acrylate compounds include: 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, hydroxypentyl acid neopentyl glycol di(meth)acrylate, and other di(meth)acrylates.

[0025] Examples of trifunctional or higher (meth)acrylate compounds include: trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, glycerol tri(meth)acrylate, etc.; and trifunctional (meth)acrylates such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and di(trimethylolpropane)acrylate. Acrylates; polyfunctional (meth)acrylates such as pentaerythritol tetra(meth)acrylate, di(trimethylolpropane)tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, di(trimethylolpropane) penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and di(trimethylolpropane) hexa(meth)acrylate; and polyfunctional (meth)acrylates such as those with three or more functions, wherein a portion of these (meth)acrylates is replaced by alkyl groups or ε-caprolactones.

[0026] Alternatively, urethane (meth)acrylates can also be used as active energy ray-curable resins. Examples of urethane (meth)acrylates include those obtained by reacting a product obtained by reacting an isocyanate monomer or prepolymer with a polyester polyol with a (meth)acrylate monomer having hydroxyl groups.

[0027] 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.

[0028] The aforementioned active energy ray-curable resin can be used in one or in combination of two or more types. Furthermore, the aforementioned active energy ray-curable resin in the coating solution can be a monomer or a partially polymerized oligomer.

[0029] In addition to the compounds with free radical polymerizable functional groups mentioned above, monomers, oligomers, and prepolymers with cationic polymerizable functional groups such as epoxy groups, vinyl ether groups, and oxetyl groups can also be used alone or in combination as active energy ray-curable resins. Examples of monomers include unsaturated polyesters, epoxy acrylates, tetramethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A diglycidyl ether, or various alicyclic epoxy compounds, 3-ethyl-3-hydroxymethyloxetane, 1,4-bis{[(3-ethyl-3-oxetyl)methoxy]methyl}benzene, and bis[1-ethyl(3-oxetyl)]methyl ether, etc., as oxetane compounds.

[0030] In addition to the aforementioned adhesive resin, it is preferable to incorporate a low-refractive-index resin into the coating liquid for forming the anti-glare layer. Adding a low-refractive-index resin to the coating liquid for forming the anti-glare layer facilitates the reduction of the refractive index of the anti-glare layer. The low-refractive-index resin can be any of monomers, oligomers, and polymers, and may also have functional groups capable of polymerizing with the aforementioned adhesive resin.

[0031] The aforementioned resin materials can be cured by ultraviolet irradiation with the addition of a photopolymerization initiator. As photopolymerization initiators, free radical polymerization initiators such as acetophenone-based, benzophenone-based, thioxanone-based, benzoin, and benzoin methyl ether can be used alone or in combination; cationic polymerization initiators such as aromatic diazonium salts, aromatic sulfonium salts, aromatic iodonium salts, and metallocene compounds can also be used.

[0032] The filler is mainly a material that forms micro-protrusions on the surface of the anti-glare layer 2 to give it the function of diffusing external light. As a filler, one or both of organic microparticles and inorganic microparticles can be used.

[0033] As organic microparticles, resin particles composed of light-transmitting resin materials such as acrylic resin, polystyrene resin, styrene-(meth)acrylate copolymer, polyethylene resin, epoxy resin, silicone resin, polyvinylidene fluoride, and polyvinyl fluoride-based resins can be used. To adjust the refractive index and the dispersion of the resin particles, two or more resin particles with different materials (refractive indices) can also be mixed and used.

[0034] The inorganic microparticles added to the coating liquid for forming the anti-glare layer are preferably nanoparticles with an average particle size of 10 to 200 nm.

[0035] As inorganic microparticles, silica microparticles, metal oxide microparticles, and various mineral microparticles can be used. Examples of silica microparticles include colloidal silica or silica microparticles surface-modified with reactive functional groups such as (meth)acryloyl groups. Examples of metal oxide microparticles include alumina, zinc oxide, tin oxide, antimony oxide, indium oxide, titanium dioxide, and zirconium oxide. Examples of mineral microparticles include mica, synthetic mica, vermiculite, montmorillonite, iron montmorillonite, bentonite, beidellite, saponite, hectorite, stevensite, nontronite, magadiite, illite, kanemite, layered titanate, smectite, and synthetic smectite. Mineral microparticles can be either natural or synthetic (including substituted products and derivatives), or a mixture of both. Mineral microparticles have the functions of increasing the viscosity of the coating liquid used to form the anti-glare layer, inhibiting the sedimentation of resin particles and inorganic microparticles, and adjusting the surface texture of the anti-glare layer. Among the mineral microparticles, layered organic clay is more preferred. Layered organic clay refers to a substance in which organic onium ions are introduced into the interlayer of bentonite. There are no restrictions on the organic onium ions as long as they can be organically converted using the cation exchange capacity of bentonite. When using layered organic clay minerals as mineral microparticles, the aforementioned synthetic montmorillonite is preferred.

[0036] Alternatively, a leveling agent can be added to the coating solution used to form the anti-glare layer. The leveling agent, by adjusting the surface orientation of the coating film during the drying process, can homogenize the surface tension of the coating film and reduce surface defects.

[0037] In addition, an appropriate organic solvent may be added to the coating liquid for forming the anti-glare layer. One or more of the following may be used as organic solvents: alcohols such as methanol, ethanol, 1-propanol, 2-propanol, butanol, isopropanol, isobutanol, and tert-butanol; ketones such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone; ketols such as diacetone alcohol; aromatic hydrocarbons such as benzene, toluene, and xylene; diols such as ethylene glycol, propylene glycol, and hexanediol; diol 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, and water.

[0038] The low-reflection layer 3 is an optical functional layer as described below: it reduces surface reflection of the optical laminate 10 by interfering with light reflected at the interface between the low-reflection layer 3 and the anti-glare layer 2 to cancel out light reflected from the surface of the low-reflection layer 3. The low-reflection layer 3 can be formed by coating the surface of the anti-glare layer 2 with a binder resin and, if necessary, low-refractive-index microparticles. Figure 1 A coating liquid (represented by a circular mark in the middle) is applied and cured to form a coating film.

[0039] There are no particular limitations on the adhesive resin used to form the low-reflection layer 3, and compounds exemplified as materials for the anti-glare layer 2 can be used.

[0040] As low-refractive-index microparticles, LiF, MgF, 3NaF·AlF, or AlF (all with a refractive index of 1.4), or Na3AlF6 (cryolite with a refractive index of 1.33) microparticles, or silica microparticles with internal voids, are preferred. Silica microparticles with internal voids are advantageous for achieving a low refractive index in the low-reflection layer 3 because the void portion can be considered to have the refractive index of air (approximately 1). Specifically, porous silica particles or shell-structured silica particles can be used.

[0041] It should be noted that, as needed, solvents or various additives can be added to the coating liquid used to form the low-reflection layer 3. As a solvent, for example, the solvent exemplified as a material used in the anti-glare layer 2 can be used. As additives, examples include defoamers, leveling agents, antioxidants, ultraviolet absorbers, light stabilizers, polymerization inhibitors, and photosensitizers.

[0042] Furthermore, when the coating film of the coating liquid used to form the low-reflection layer is cured by ultraviolet irradiation, a photopolymerization initiator is added to the coating liquid. As the photopolymerization initiator, a photopolymerization initiator exemplified as a material for the anti-glare layer 2 can be used.

[0043] Figure 2 This is a schematic cross-sectional view showing the optical laminate involved in the comparative example.

[0044] The comparative example of the optical laminate 90 includes a transparent substrate 1, an anti-glare layer 2 laminated on one side of the transparent substrate 1, and a low-reflection layer 93 laminated on the anti-glare layer 2. Similar to the reflective layer 3 of the embodiment, the low-reflection layer 93 may contain low-refractive-index microparticles indicated by circular marks. However, in the comparative example, when the coating liquid for forming the low-reflection layer is applied, it flows into the recess, causing a large difference between the film thickness of the low-reflection layer 93 on the protrusion and the film thickness of the low-reflection layer 93 in the recess. As a whole, the film thickness of the low-reflection layer 93 deviates. When the film thickness of the low-reflection layer 93 is uneven and deviates from the designed film thickness, the problem arises that the cancellation of light reflected at the interface between the low-reflection layer 93 and the anti-glare layer 2 and the light reflected on the surface of the low-reflection layer 93 via interference becomes insufficient, and the reflectivity cannot be adequately reduced. Furthermore, the coating liquid used to form the low-reflection layer flows into the recesses, reducing their depth and making the surface nearly flat. As a result, the arithmetic mean roughness Ra of the surface of the optical laminate 90 decreases. Due to the reduction in the arithmetic mean roughness Ra, the scattering of external light decreases, thus leading to insufficient suppression of external light reflection.

[0045] In contrast, the optical laminate 10 of the present invention can suppress the reflection of external light onto the optical laminate 10 and the surface reflection by simultaneously satisfying the following conditions (1) to (3).

[0046] (1) The rate of change of external haze before and after the three layers of low reflectivity layer is less than 40% |ΔHz|.

[0047] (2) The rate of change of the arithmetic mean roughness |ΔRa| before and after the three layers of low reflectivity layer are less than 21%.

[0048] (3) The rate of change of the maximum valley depth before and after the three layers of low reflectivity layer, |ΔRv|, is less than 41%.

[0049] The change rate of external haze |ΔHz|, the change rate of arithmetic mean roughness |ΔRa|, and the change rate of maximum valley depth |ΔRv| are calculated using the following formulas.

[0050] |ΔHz| = |(External haze without a low-reflection layer - External haze with a low-reflection layer) / External haze without a low-reflection layer × 100|

[0051] |ΔRa| = |(arithmetic mean roughness without a low-reflection layer - arithmetic mean roughness with a low-reflection layer) / arithmetic mean roughness without a low-reflection layer × 100|

[0052] |ΔRv| = |(Maximum valley depth without a low-reflection layer - Maximum valley depth with a low-reflection layer) / Maximum valley depth without a low-reflection layer × 100|

[0053] Here, "the state without a low-reflection layer" includes two states: the state before the anti-glare layer 2 is stacked on the transparent substrate 1 and the state after the low-reflection layer 3 is stacked, and the state after the low-reflection layer 3 on the outermost surface of the optical laminate 10 is removed by saponification, exposing the anti-glare layer 2. The inventors of this application conducted research and confirmed that when the anti-glare layer 3 is stacked only on the transparent substrate 1, and the surface roughness parameters (Ra, Rv, and Rz) before and after stacking are measured and compared after saponification, these surface roughness parameters remain essentially unchanged before and after saponification, and the surface unevenness of the anti-glare layer hardly changes. Therefore, the values ​​of 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 subsequent saponification can be used instead of the values ​​of external haze, arithmetic mean roughness, and maximum valley depth before the low-reflection layer 3 is stacked. Even if the values ​​measured in either of the above states are used, the calculated values ​​of the rates of change |ΔHz|, |ΔRa|, and |ΔRv| will not produce substantial differences.

[0054] It should be noted that the arithmetic mean roughness (Ra) and maximum valley depth (Rv) for both the state without and with the low-reflection layer 3 are values ​​measured according to JIS-B-0601:2013. The arithmetic mean roughness Ra is the average of the mountain heights (distances from the average height) along the reference length of the profile curve, and the maximum valley depth Rv is the depth of the deepest valley along the reference length of the profile curve, located from the average line. Figure 1 and Figure 2 The average line and the maximum valley depth Rv are simply shown in the diagram.

[0055] When conditions (1) to (3) above are met, the inflow into the recesses is suppressed during the application of the coating liquid for forming the low-reflection layer, and the thickness of the low-reflection layer 3 is close to the designed film thickness overall. Therefore, by causing the light reflected at the interface between the low-reflection layer 3 and the anti-glare layer 2 that passes through the low-reflection layer 3 to interfere and cancel out the light reflected on the surface of the low-reflection layer 3, the reflectivity can be further reduced. In addition, by suppressing the inflow of the coating liquid for forming the low-reflection layer into the recesses, the reduction in the depth of the recesses and the arithmetic mean roughness of the surface unevenness can be suppressed. As a result, by scattering external light, the reflection of external light can be further reduced.

[0056] The film thickness of the low-reflection layer 3 that satisfies the above conditions (1) to (3) can be controlled, for example, by the ambient temperature during the application of the coating liquid for forming the low-reflection layer and the concentration of non-volatile components in the coating liquid for forming the low-reflection layer. The ambient temperature during the application of the coating liquid for forming the low-reflection layer is preferably 60 to 100°C. If the ambient temperature during application is within this range, the volatile components such as solvents contained in the coating liquid for forming the low-reflection layer will evaporate rapidly after application, reducing the fluidity of the coating film and thereby suppressing the inflow of the coating liquid for forming the low-reflection layer into the recesses. Furthermore, the concentration of non-volatile components in the coating liquid for forming the low-reflection layer is preferably 3.0 to 3.4%. When the concentration of non-volatile components in the coating liquid for forming the low-reflection layer is less than 3.0%, the fluidity of the coating liquid for forming the low-reflection layer is high, making it difficult to suppress the inflow into the recesses, and therefore this is not preferred. On the other hand, when the concentration of non-volatile components in the coating liquid for forming a low-reflection layer exceeds 3.4%, the coating liquid for forming a low-reflection layer has low fluidity and the solid components are prone to localization, so it is not preferred.

[0057] 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 positively reflected light, measured by the SCI (Specular Component Include) method, and can be measured according to JIS Z8722. When the above conditions (1) to (3) are met, the SCI reflectance of the optical laminate 10 can be made to be 0.7% or less, thereby realizing an optical laminate 10 with excellent low reflectance.

[0058] The reflectance spectrum of the optical stack 10 is a curve with a minimum value at a specific wavelength. Hereinafter, the wavelength with the lowest reflectance in the visible light region will be referred to as the "bottom wavelength". The reflectance of the optical stack 10 is minimum at the bottom wavelength and increases with increasing distance from the bottom wavelength. The bottom wavelength of the optical stack 10 according to this embodiment is preferably 520 to 580 nm. When the bottom wavelength is within this range, the reflection of light in the visible light region can be effectively reduced.

[0059] According to the present invention, by simultaneously satisfying the above conditions (1) to (3), an optical laminate 10 with less ambient irradiation and further reduced surface reflectivity can be achieved. The optical laminate of the present invention is suitable as an optical film for use in image display devices due to its reduced external light irradiation and surface reflection, and is particularly suitable as an anti-reflective film for vehicle-mounted display devices displaying safety-related information.

[0060] It should be noted that the optical laminate 10 of the present invention is typically disposed 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. Sometimes a touch panel is also disposed between the optical laminate and the display panel. However, the stacking position of the optical laminate 10 is not particularly limited as long as the desired optical characteristics can be achieved. In addition, one or more optical functional layers such as an antistatic layer, an anti-fouling layer, an infrared absorption layer, an ultraviolet absorption layer, and a color correction layer may be disposed on the low-reflection layer 3 of the optical laminate 10.

[0061] Example

[0062] The following describes embodiments of the antireflective film involved in specific implementation methods.

[0063] (Examples 1-4, Comparative Examples 1-4)

[0064] A 40 μm thick TAC film was used as the transparent substrate. A coating solution for forming an anti-glare layer, containing binder resin, filler, photopolymerization initiator, and solvent, was prepared. The anti-glare layer coating solution was applied to the transparent substrate to achieve a cured film thickness of 5 μm. After drying, the coating was polymerized and cured by ultraviolet irradiation, thus forming the anti-glare layer. Next, a low-reflection layer coating solution containing binder resin, porous silica particles, a leveling agent, a photopolymerization initiator, and solvent was prepared on the anti-glare layer. The low-reflection layer coating solution was applied to the anti-glare layer to achieve a cured film thickness of 0.1 μm. After drying, the coating was polymerized and cured by ultraviolet irradiation, thus forming the low-reflection layer. The concentration of non-volatile components in the low-reflection layer coating solution and the ambient temperature during coating were set as shown in Table 1.

[0065] Using optical laminates before and after the formation of the low-reflection layer, the external haze, arithmetic mean roughness Ra, and maximum valley depth Rv were measured. Additionally, the SCI reflectance of the optical laminate after the formation of the low-reflection layer was measured. The measurement methods are as follows.

[0066] [Haze]

[0067] According to JIS K 7136:2000, haze was measured using a haze meter (NDH-4000, manufactured by Nippon Denshoku Kogyo Co., Ltd.). First, the total haze of the optical laminate was measured. Next, a sample with an optical adhesive film laminated on the transparent substrate side of the optical laminate was prepared, 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 individual optical adhesive film particles from the haze of the sample after the optical adhesive film was applied. The external haze was calculated by subtracting the calculated internal haze from the haze of the optical laminate before the optical adhesive film was applied. The external haze was calculated separately for the optical laminate before and after the formation of the low-reflection layer, and the rate of change of external haze |ΔHz| before and after the low-reflection layer was laminated was calculated using the above formula.

[0068] [Arithmetic mean roughness Ra, maximum valley depth Rv]

[0069] The surface roughness of the low-refractive-index layer of the optical laminates involved in the examples and comparative examples was measured by optical interferometry using a non-contact surface / layer profile shape measurement system (measurement device: VertScanR3300FL-Lite-AC, analysis software: VS-Viewer6, manufactured by Hitachi High-Tech Corporation). The measurement data were analyzed using the device's particle analysis software to measure the arithmetic mean roughness Ra and maximum valley depth Rv of the low-refractive-index layer surface.

[0070] It should be noted that in this invention, the average roughness is generated using the analysis conditions in the VS-Viewer's profile (multi-line). In the profile (multi-line), the arithmetic mean roughness Ra and maximum valley depth Rv obtained from the following profile are defined as the arithmetic mean roughness Ra and maximum valley depth Rv of the roughness of this invention. The profile is obtained by averaging the profiles of the six set measurement cursors.

[0071] The measurement software of the device is used to perform measurements under the following conditions to obtain image files as measurement results of surface unevenness.

[0072] Optical conditions

[0073] Camera: Sony HR-50 1 / 3-inch

[0074] Objective lens: 10XDI (10x)

[0075] Imaging lens (lens tube): 0.5x

[0076] Zoom lens: 1x

[0077] Light source / wavelength filter: 520nm

[0078] ND filter: Not used

[0079] A-Stop (Aperture Stop): Not in use (fully open)

[0080] F-Stop (Field of View Aperture): Not in use (fully open)

[0081] • Measurement conditions

[0082] Measuring equipment: piezoelectric

[0083] Measurement mode: Phase

[0084] Scan speed: 4μm / sec

[0085] Scan range: -10 to 10 μm

[0086] Effective pixel count: 50%

[0087] Measurement area: 704.192 μm × 938.923 μm

[0088] The acquired image files are analyzed using the device's analysis software under the following conditions.

[0089] • Analysis conditions (VS-Viewer6)

[0090] Surface correction: 4 times

[0091] S-filter: Automatic

[0092] L-filter: Not used

[0093] • Particle analysis conditions (VS-Viewer6)

[0094] Analysis type: Protrusion analysis

[0095] Image correction: None

[0096] Height threshold: 0.1μm

[0097] Particle shaping: None

[0098] [Calculation methods for Ra and Rv]

[0099] In the acquired image after applying area correction (four times) and an S-filter, the measurement cursor was set at positions of 200μm, 500μm, and 800μm in the longitudinal (X direction) and 200μm, 400μm, and 600μm in the transverse (Y direction). The Ra and Rv values ​​of each cursor position (3 points parallel to the X direction and 3 points parallel to the Y direction, for a total of 6 points) were obtained automatically calculated by the VS-Viewer's profile contour. The average (arithmetic mean) of the obtained values ​​was taken as the measurement result.

[0100] For the optical stack before and after the formation of the low-reflection layer, Ra and Rv are calculated respectively. Using the above formula, the rate of change of the arithmetic mean roughness before and after the low-reflection layer is stacked, |ΔRa|, and the rate of change of the maximum valley depth before and after the low-reflection layer is stacked, |ΔRv|, are calculated.

[0101] [SCI reflectance Y]

[0102] SCI reflectance Y was measured using a spectrophotometer (CM-2600d, manufactured by Konica Minolta Japan, Inc.) according to JIS Z 8722. Measurement conditions were set as follows: measurement diameter / illumination diameter Φ8mm / Φ11mm, observation field of view 10°, and observation light source D65. When measuring with a measurement diameter of 8mm, the uneven coating allows for the inclusion of relatively high and low reflectance areas within a single field of view, thus providing an average SCI reflectance measurement value. Furthermore, a 10° field of view corresponds to viewing an area with a diameter of 8.8cm at a distance of 50cm; however, in automotive applications, the larger area of ​​the image display device is typically viewed at close range, making a 10° field of view suitable for measurement. D65 is the average midday light in Europe / Northern Europe as defined by the International Commission on Illumination, exhibiting a wavelength distribution close to external light, making it suitable for measurement. If the SCI reflectance is below 0.7, it is considered that reflectance is sufficiently suppressed.

[0103] Table 1 shows the low-reflection layer formation conditions (concentration of non-volatile components of the coating liquid for low-reflection layer formation [mass %], atmosphere temperature during coating), external haze change rate |ΔHz|, arithmetic mean roughness change rate |ΔRa|, maximum valley depth change rate |ΔRv|, and SCI reflectance measurement results for each embodiment and comparative example.

[0104]

[0105] The rate of change of external haze |ΔHz|, the rate of change of arithmetic mean roughness |ΔRa|, and the rate of change of maximum valley depth |ΔRv| of the optical laminates involved in Examples 1 to 4 all meet the above conditions, and have excellent low reflectivity.

[0106] In contrast, the optical laminates involved in Comparative Examples 1 to 4 do not satisfy any of the above conditions, such as the rate of change of external haze |ΔHz|, the rate of change of arithmetic mean roughness |ΔRa|, and the rate of change of maximum valley depth |ΔRv|. Compared with the embodiments, the SCI reflectivity is higher.

[0107] In summary, according to the present invention, it can be confirmed that in an optical laminate consisting of a transparent substrate / anti-glare layer / low-reflection layer, the reflectivity of the outermost surface can be further reduced.

[0108] It should be noted that, as mentioned above, when the low-refractive-index layer is saponified and peeled off from the optical laminate, the surface of the anti-glare layer can be considered to dissolve slightly due to saponification, but the surface irregularity of the anti-glare layer does not change significantly. As an example, an optical laminate with only the anti-glare layer stacked on a transparent substrate was subjected to a saponification treatment by immersing it in a 10% sodium hydroxide aqueous solution at 55°C for 10 minutes. The Ra, Rv, and Rz values ​​of the anti-glare 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). The difference between the measured values ​​before and after saponification was very small. The surface state of the anti-glare layer before and after saponification can be measured by averaging the values ​​of three points: two points at the ends and one point at the center, when the film with the anti-glare layer is divided into three equal parts in the width direction. The methods for measuring Ra and Rv are the same as those used in the examples and comparative examples. The method for measuring Rz is similar to that for Ra and Rv; the values ​​at each cursor position (3 points parallel to the X direction and 3 points parallel to the Y direction, totaling 6 points) automatically calculated from the cross-sectional profile of the VS-Viewer are obtained, and the average (arithmetic mean) of the obtained values ​​is used. Since the anti-glare layer remains essentially unchanged before and after saponification, the surface condition (|ΔHz|, |ΔRa|, and |ΔRv|) of the anti-glare layer under the above conditions can be easily confirmed using the external haze, arithmetic mean roughness, and maximum valley depth measured in the state where the low-refractive-index layer has been saponified and peeled off from the optical laminate.

[0109] Industrial applicability

[0110] This invention can be used as an anti-reflective film in image display devices.

[0111] Explanation of symbols

[0112] 1 Transparent substrate

[0113] 2 Anti-glare layer

[0114] 3. Low-reflectivity layer

Claims

1. An optical laminate, comprising an anti-glare layer and a low-reflection layer having an uneven surface sequentially laminated on at least one surface of a transparent substrate, characterized in that, The rate of change of external haze |ΔHz| before and after the low-reflection layer is stacked is less than 40%. The rate of change of the arithmetic mean roughness |ΔRa| before and after the low-reflection layer is stacked is less than 21%. The rate of change of the maximum valley depth, |ΔRv|, before and after the low-reflectivity layer is stacked is less than 41%. in, |ΔHz| = |(External haze without a low-reflection layer - External haze with a low-reflection layer) / External haze without a low-reflection layer × 100| |ΔRa| = |(Arithmetic mean roughness before stacking without a low-reflection layer - Arithmetic mean roughness with a low-reflection layer) / Arithmetic mean roughness without a low-reflection layer × 100| |ΔRv| = |(Maximum valley depth without a low-reflection layer - Maximum valley depth with a low-reflection layer) / Maximum valley depth without a low-reflection layer × 100|.

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

3. The optical laminate according to claim 1, wherein, The wavelength with the lowest reflectivity in the visible light region, i.e., the bottom wavelength, is in the range of 520–580 nm.

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

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