Optical laminate and display device using the same

Abstract

To provide an optical laminate having a layer configuration in which a low-reflection layer is laminated on an antiglare layer, and whose reflectivity on the outermost layer is more reduced, and a display device using the optical laminate.SOLUTION: An optical laminate is configured such that an antiglare layer having irregularities and a low-reflection layer are laminated in this order on at least one surface of a transparent substrate, where a rate of change in external haze |ΔHz| before and after lamination of the low-reflection layer is 40% or less, a rate of change in arithmetic mean roughness |ΔRa| before and after lamination of the low-reflection layer is 21% or less, and a rate of change in maximum valley depth |ΔRv| before and after lamination of the low-reflection layer is 41% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] An optical film such as an antiglare (AG) film or a low reflection (LR) film is provided on the outermost surface of a display device. The antiglare film has an antiglare layer containing a filler, and the unevenness formed on the surface of the antiglare layer by the filler diffuses the reflected light to reduce the reflection of external light. The low reflection film reduces the reflection of external light by canceling out the light reflected at the interface between the low reflection layer and the base film and the light reflected on the surface of the low reflection layer by interference. Further, an antiglare low reflection (AGLR) film having a configuration in which a low reflection layer is laminated on the surface of the antiglare layer is also known (see, for example, Patent Document 1).

[0003] In recent years, vehicles are equipped with a plurality of display devices such as a center information display (CID) and a meter cluster panel (MCP). Since a display device for in-vehicle use may display information related to safety, it is required that there is little reflection of external light, the reflected light is not dazzling, the glare peculiar to the antiglare film is suppressed, and the display image is clear.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As an optical film capable of achieving both suppression of external light reflection and enhancement of image clarity, the above-described AGLR film is suitable. However, when applying and drying the coating liquid for forming the low-reflection layer on the antiglare layer with irregularities, the coating liquid flows into the recesses along the inclined surfaces of the fine irregularities on the surface of the antiglare layer, resulting in variations in the film thickness of the low-reflection layer. Therefore, when the film thickness of the low-reflection layer varies and deviates from the designed film thickness, there is a problem that the antireflection effect of the low-reflection layer is reduced and the reflectance of the film surface increases.

[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 antiglare layer and having a lower reflectance on the outermost surface, and a display device using the same.

Means for Solving the Problems

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

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

Effects of the Invention

[0009] According to the present invention, there can be provided an optical laminate having a layer structure in which a low-reflection layer is laminated on an antiglare layer, and having a reduced reflectance on the outermost surface, and a display device using the same.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

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

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

[0013] The transparent substrate 1 is a film serving as a base of the optical laminate 10, and is formed of a material having excellent visible light transmittance. As the material for forming the transparent substrate 1, 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, polyimide, polyarylate, polycarbonate, triacetyl cellulose, polyacrylate, polyvinyl alcohol, polyvinyl chloride, cycloolefin copolymer, norbornene-containing resin, polyethersulfone, polysulfone and other transparent resins or inorganic glass can be used. 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 the adhesion to the antiglare layer 2. Examples of the surface modification treatment include alkali treatment, corona treatment, plasma treatment, sputtering treatment, application of a surfactant or a silane coupling agent, Si vapor deposition, and the like.

[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 reflection of external light. The antiglare layer 2 is formed by applying a coating liquid for forming an antiglare layer 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 cures by irradiation with ionizing radiation or ultraviolet rays can be used. For example, a monofunctional, bifunctional, or trifunctional or higher (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, isobornyl (meth)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, phosphoric acid (meth)acrylate, ethylene oxide-modified phosphoric acid (meth)acrylate, 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, methoxypolythylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)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,Examples of adamantyl acrylate derivatives mono(meth)acrylates, etc. include adamantyl acrylate, etc. having a monovalent mono(meth)acrylate derived from adamantane diol.

[0018] Examples of bifunctional (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, hydroxypivalic acid neopentyl glycol di(meth)acrylate, and other di(meth)acrylates.

[0019] Examples of (meth)acrylate compounds having three or more functional groups 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; trifunctional (meth)acrylate compounds such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and ditrimethylolpropane tri(meth)acrylate; 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 part of these (meth)acrylates is substituted with an alkyl group or ε-caprolactone.

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

[0021] Examples of urethane (meth)acrylate 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, dipentaerythritol pentaacrylate isophorone diisocyanate urethane prepolymer, and the like.

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

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

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

[0025] The above-described resin material can be cured by irradiation with ultraviolet rays on the condition that a photoinitiator is added. As the photoinitiator, radical polymerization initiators such as acetophenone-based, benzophenone-based, thioxanthone-based, 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 mainly a material that forms fine irregularities on the surface of the antiglare layer 2 and imparts a function of diffusing external light. As the filler, one or both of organic fine particles and inorganic fine particles can be used.

[0027] As the organic fine particles, resin particles made of a light-transmitting resin material such as acrylic resin, polystyrene resin, styrene-(meth)acrylate copolymer, polyethylene resin, epoxy resin, silicone resin, polyvinylidene fluoride, and polyfluoroethylene-based resin can be used. In order to adjust the refractive index and the dispersion of the resin particles, two or more types of resin particles having different materials (refractive indices) 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] As the inorganic fine particles, silica fine particles, metal oxide fine particles, various mineral fine particles, etc. can be used. As the silica fine particles, for example, colloidal silica, silica fine particles surface-modified with reactive functional groups such as (meth)acryloyl groups, etc. can be used. As the metal oxide fine particles, for example, alumina, zinc oxide, tin oxide, antimony oxide, indium oxide, titania, zirconia, etc. can be used. As the mineral fine particles, for example, mica, synthetic mica, vermiculite, montmorillonite, iron montmorillonite, bentonite, beidellite, saponite, hectorite, stevensite, nontronite, magadiite, illite, kanemite, layered titanic acid, smectite, synthetic smectite, etc. can be used. The mineral fine particles may be either natural products or synthetic products (including substituents and derivatives), and a mixture of both may be used. The fine particles of preference have a function of increasing the viscosity of the coating liquid for forming the antiglare layer, suppressing the sedimentation of the resin particles and the inorganic fine particles, and adjusting the uneven shape of the surface of the antiglare layer. Among the mineral fine particles, layered organic clay is more preferable. The layered organic clay refers to a material in which organic onium ions are introduced between the layers of the swellable clay. The organic onium ions are not limited as long as they can be organicized by utilizing the cation exchangeability of the swellable clay. When using layered organic clay minerals as the mineral fine particles, the above-described synthetic smectite can be preferably used.

[0030] In addition, a leveling agent may be added to the coating liquid for forming the antiglare layer. The leveling agent has a function of orienting on the surface of the coating film during the drying process, equalizing the surface tension of the coating film, and reducing the surface defects of the coating film.

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

[0032] The low-reflection layer 3 is an optical functional layer that reduces the surface reflection of the optical laminate 10 by canceling out the light reflected on the surface of the low-reflection layer 3 through interference with the light reflected at the interface between the low-reflection layer 3 and the antiglare 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 (indicated by circles in Fig. 1) to the surface of the antiglare layer 2 and curing the coating film.

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

[0034] As the low refractive index fine particles, for example, fine particles such as LiF, MgF, 3NaF·AlF or AlF (all having a refractive index of 1.4), or Na3AlF6 (cryolite, refractive index 1.33), or silica fine particles having voids inside can be preferably used. Since the silica fine particles having voids inside can have the refractive index of the void part as about 1 (refractive index of air), they are free for reducing the refractive index of the low reflection layer 3. Specifically, porous silica particles or silica particles having a shell structure can be used.

[0035] In addition, solvents and various additives can be added to the coating liquid for forming the low reflection layer 3 as necessary. As the solvent, for example, those exemplified as the material of the antiglare layer 2 can be used. Examples of the additives include defoaming agents, leveling agents, antioxidants, ultraviolet absorbers, light stabilizers, polymerization inhibitors, photosensitizers, and the like.

[0036] When the coating film of the coating liquid for forming the low reflection layer is cured by ultraviolet irradiation, a photoinitiator is added to the coating liquid. As the photoinitiator, those exemplified as the material of 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 surface side of the transparent substrate 1, and a low-reflection layer 93 laminated on the antiglare layer 2. Similar to the reflection layer 3 according to the embodiment, the low-reflection layer 93 may contain low-refractive-index fine particles indicated by circles. However, in the low-reflection layer 93 according to the comparative example, when the coating liquid for forming the low-reflection layer was applied, the coating liquid flowed into the concave portions, resulting in a large difference between the film thickness of the low-reflection layer 93 on the convex portions and the film thickness of the low-reflection layer 93 in the concave portions. As a whole, there is a 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, cancellation due to interference between the 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 the light reflected at the surface of the low-reflection layer 93 becomes insufficient, and there is a problem that the reflectance cannot be sufficiently reduced. Further, the coating liquid for forming the low-reflection layer flows into the concave portions and the depth of the concave portions decreases, and as the unevenness approaches flatness, the arithmetic mean roughness Ra of the surface of the optical laminate 90 decreases. Due to the decrease in the arithmetic mean roughness Ra, the scattering of external light decreases, and there is a problem that suppression of the reflection of external light is also insufficient.

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

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

[0041] Here, the "state without the low-reflection layer" includes both the state before laminating the antiglare layer 2 on the transparent substrate 1 and before laminating the low-reflection layer 3, and the state where the low-reflection layer 3 on the outermost surface of the optical laminate 10 is saponification-removed to expose the antiglare layer 2. As a result of investigations by the inventors of the present application, when only the antiglare layer 3 was laminated on the transparent substrate 1 and the antiglare layer 3 was subjected to saponification treatment, and the surface roughness parameters (Ra, Rv, and Rz) before and after lamination were measured and compared, it was confirmed that these surface roughness parameters hardly changed before and after the saponification treatment, and the surface uneven shape of the antiglare layer hardly changed. Therefore, the values of external haze, arithmetic mean roughness, and maximum valley depth measured in the state where the low-reflection layer 3 of the optical laminate 10 was saponification-removed afterwards can be used to substitute for the values of external haze, arithmetic mean roughness, and maximum valley depth before the lamination of the low-reflection layer 3, and there is no substantial difference in the calculated values of the change rates |ΔHz|, |ΔRa|, and |ΔRv| regardless of which of the above states the measured values are used.

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

[0043] When the above conditions (1) to (3) are satisfied, during the coating of the coating liquid for forming the low-reflection layer, the flow of the coating liquid into the concave portions is suppressed, and since the thickness of the low-reflection layer 3 is close to the designed film thickness over the whole, by the cancellation due to the interference between the light transmitted through the low-reflection layer 3 and reflected at the interface between the low-reflection layer 3 and the antiglare layer 2 and the light reflected at the surface of the low-reflection layer 3, the reflectance can be further reduced. Further, since the flow of the coating liquid for forming the low-reflection layer into the concave portions is suppressed, the decrease in the depth of the concave portions and the arithmetic mean roughness of the surface irregularities is suppressed. As a result, by scattering external light, the reflection of the 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 atmospheric temperature during the coating of the coating liquid for forming the low-reflection layer and the nonvolatile content concentration of the coating liquid for forming the low-reflection layer. The atmospheric temperature during the coating of the coating liquid for forming the low-reflection side is preferably 60 to 100°C. If the atmospheric temperature during the coating is within this range, the volatile components such as the solvent contained in the applied coating liquid for forming the low-reflection layer are quickly volatilized after the coating, and by reducing the fluidity of the coating film, the flow of the coating liquid for forming the low-reflection layer into the concave portions can be suppressed. Further, the nonvolatile content concentration of the coating liquid for forming the low-reflection layer is preferably 3.0 to 3.4%. When the nonvolatile content concentration of 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, and it becomes difficult to suppress the flow into the concave portions, which is not preferable. On the other hand, when the nonvolatile content concentration of the coating liquid for forming the low-reflection layer exceeds 3.4%, the fluidity of the coating liquid for forming the 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 the reflected light including the specularly 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 made 0.7%, and an optical laminate 10 excellent in low reflectivity can be realized.

[0046] The reflection spectrum of the optical laminate 10 is a curve with a minimum value at a specific wavelength. Hereinafter, in the visible light region, the wavelength 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 distance from the bottom wavelength increases. The bottom wavelength of the optical laminate 10 according to the present 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.

[0047] According to the present invention, by simultaneously satisfying the above conditions (1) to (3), an optical laminate 10 with less surrounding reflection and a further reduced reflectance of the outermost surface can be realized. Since the optical laminate according to the present invention reduces external light reflection and surface reflection, it is suitable as an optical film for an image display device, and in particular, it is suitable as an antireflection film for an in-vehicle display device that displays information related to safety.

[0048] Incidentally, 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 constitutes a display device together with the display panel. 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 characteristics can be exhibited. Further, one or more optical functional layers such as an antistatic layer, an antifouling layer, an infrared absorption layer, an ultraviolet absorption layer, and a color correction layer may be provided on the low reflection layer 3 of the optical laminate 10.

Examples

[0049] Hereinafter, examples of specifically implementing the antireflection film according to the embodiment will be described.

[0050] (Examples 1 to 4, Comparative Examples 1 to 4) As the transparent substrate, a TAC film with a thickness of 40 μm was used. A coating liquid for forming an antiglare layer containing a binder resin, a filler, a photoinitiator, and a solvent was prepared. The coating liquid for forming an antiglare layer was applied onto the transparent substrate so that the film thickness after curing would be 5 μm, and after drying, the coating film was polymerized and cured by ultraviolet irradiation to form an antiglare layer. Next, on the antiglare layer, a coating liquid for forming a low-reflection layer containing a binder resin, silica fine particles having voids inside, a leveling agent, a photoinitiator, and a solvent was prepared. The coating liquid for forming a low-reflection layer was applied onto the antiglare layer so that the film thickness after curing would be 0.1 μm, and after drying, the coating film was 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 ambient temperature during coating were set to the conditions shown in Table 1.

[0051] Using the optical laminate before the formation of the low-reflection layer (before coating the coating liquid for forming a low-reflection layer) and after the formation of the low-reflection layer, the external haze, arithmetic mean roughness Ra, and maximum valley depth Rv were measured. Also, the SCI reflectance of the optical laminate after the formation of the low-reflection layer was measured. The measurement methods are as follows.

[0052] [Haze] The 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 surface of the optical laminate on the transparent substrate side, 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 attaching the optical adhesive film. The external haze was calculated by subtracting the internal haze calculated from the haze of the optical laminate before attaching the optical adhesive film. The external haze was calculated for each of the optical laminates before and after the formation of the low-reflection layer, and the change rate |ΔHz| of the external haze before and after the lamination of the low-reflection layer was calculated using the above-described formula.

[0053] [Arithmetic mean roughness Ra, maximum valley depth Rv] The uneven shape of the surface of the low refractive index layer of the optical laminate according to the examples and comparative examples was measured by an optical interference method using a non-contact surface / layer cross-sectional shape measurement system (measurement device: Bertscanner R3300FL-Lite-AC, analysis software: VS-Viewer6, manufactured by Hitachi High-Tech Corporation). The measurement data was analyzed using the particle analysis software of the device, and the arithmetic mean roughness Ra and the maximum valley depth Rv of the surface of the low refractive index layer were measured.

[0054] In the present invention, average unevenness is generated under the analysis conditions in the cross-sectional profile (multi-line) of VS-Viewer. In the cross-sectional profile (multi-line), the arithmetic mean roughness Ra and the maximum valley depth Rv obtained from the cross-section obtained by averaging the cross-sectional profiles of 6 set measurement cursors are defined as the arithmetic mean roughness Ra and the maximum valley depth Rv of the unevenness of the present invention.

[0055] Measurement was performed under the following conditions using the measurement software of the device, and an image file as the measurement result of the surface unevenness was obtained. ·Optical conditions Camera: HR-50 1 / 3 inch, manufactured by Sony Objective lens: 10XDI (10 times) Imaging lens (lens barrel): 0.5 times Zoom lens: 1 time Light source / wavelength filter: 520 nm ND filter: Not used A-Stop (aperture stop): Not used (fully open) F-Stop (field stop): Not used (fully open) ·Measurement conditions Measurement device: Piezo Measurement mode: Phase Scan speed: 4 μm / sec Scan range: -10 to 10 μm Effective pixel number: 50% Measurement area: 704.192 μm × 938.923 μm

[0056] The obtained image file was analyzed under the following conditions using the analysis software of the device. ·Analysis Conditions (VS-Viewer6) Surface Correction: 4th order S Filter: Automatic L Filter: Not used ·Particle Analysis Conditions (VS-Viewer6) Analysis Type: Impact Analysis Image Correction: None Height Threshold: 0.1 μm Particle Shaping: None

[0057] [Calculation Method of Ra and Rv] In the acquired image to which surface correction (4th order) and S filter were applied, 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 (a total of 6 positions including 3 cross-sections parallel to the X direction and 3 cross-sections parallel to the Y direction) automatically calculated by the cross-section profile of VS-Viewer were acquired, and the average value (arithmetic mean) of the acquired values was used as the measurement result.

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

[0059] [SCI Reflectance Y] The 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 φ8 mm / φ11 mm, an observation condition of a 10° field of view, and an observation light source of D65. When measuring with a measurement diameter of 8 mm, since it is possible to include both a relatively high reflectance part and a low reflectance part due to coating unevenness within one field of view, an average measured value of the SCI reflectance can be obtained. Also, a 10° field of view corresponds to visually recognizing a range with a diameter of 8.8 cm at a distance of 50 cm. However, in the case of in-vehicle applications, since it is often necessary to visually recognize a relatively large area of an image display device at a short distance, measurement with a 10° field of view is suitable. D65 is the average midday light in Europe / Nordic defined by the International Commission on Illumination and has a wavelength distribution close to that of external light, so it is suitable for measurement. If the SCI reflectance was 0.7 or less, it was determined that the reflectance was sufficiently suppressed.

[0060] Table 1 shows together the low-reflection layer formation conditions (nonvolatile content concentration [mass%] of the coating liquid for forming the low-reflection layer, ambient temperature during coating), the change rate |ΔHz| of external haze, the change rate |ΔRa| of arithmetic mean roughness, the change rate |ΔRv| of maximum valley depth, and the measurement results of SCI reflectance for each example and each comparative example.

[0061]

Table 1

[0062] For the optical laminates according to Examples 1 to 4, the change rate |ΔHz| of external haze, the change rate |ΔRa| of arithmetic mean roughness, and the change rate |ΔRv| of maximum valley depth all satisfied the above-described conditions, and they were excellent in low reflectance.

[0063] On the other hand, for the optical laminates according to Comparative Examples 1 to 4, any of the change rate |ΔHz| of external haze, the change rate |ΔRa| of arithmetic mean roughness, and the change rate |ΔRv| of maximum valley depth did not satisfy the above-described conditions, and the SCI reflectance was higher than that of the examples.

[0064] As described above, according to the present invention, it was confirmed that in the optical laminate having the layer structure of the transparent substrate / antiglare layer / low reflection layer, the reflectance of the outermost surface can be further reduced.

[0065] In addition, as described above, when the low refractive index layer is saponified and peeled off from the optical laminate, it is considered that the surface of the antiglare layer is slightly melted by saponification, but the surface uneven shape of the antiglare layer did not change significantly. As an example, an optical laminate having only an antiglare layer laminated on a transparent substrate was subjected to a saponification treatment of immersing it in a 10% sodium hydroxide aqueous solution at 55°C for 10 minutes, and Ra, Rv, and Rz of the antiglare layer surface before and after saponification were measured. As a result, Ra (before saponification: 0.092, after saponification: 0.099), Rv (before saponification: -0.232, after saponification: -0.216), Rz (before saponification: 0.456, after saponification: 0.448), and the difference in the measured values before and after the saponification treatment was slight. The measurement of the surface state of the antiglare layer before and after saponification may be the average value of a total of three points, namely, two end points and one central point, when the film on which the antiglare layer is laminated is divided into three in the width direction. The measurement methods of Ra and Rv may be the same as those in the examples and comparative examples. The measurement method of Rz may be, similar to Ra and Rv, the average value (arithmetic mean) of the values at each cursor position (a total of six positions, three cross-sections parallel to the X direction and three cross-sections parallel to the Y direction) automatically calculated by the cross-section profile of the VS-Viewer. Since the antiglare layer hardly changes substantially before and after saponification, the surface state (|ΔHz|, |ΔRa|, and |ΔRv|) of the antiglare layer under the above conditions can be simply confirmed using the external haze, arithmetic mean roughness, and maximum valley depth measured in the state where the low refractive index layer is saponified and peeled off from the optical laminate.

Industrial Applicability

[0066] The present invention can be used as an antireflection film used in an image display device.

Explanation of Symbols

[0067] 1 Transparent substrate 2 Antiglare layer 3 Low reflection layer

Claims

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

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 minimized in the visible light region, is in the range of 520 to 580 nm.

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

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