Optical laminate and display device using the same

Abstract

To provide an optical laminate that employs a biaxially stretched polyethylene terephthalate film as a base material, exhibits bending resistance, and suppresses color unevenness, and an image display device using the same.SOLUTION: An optical laminate is used in an image display device, in which a surface arithmetic average roughness Ra of an optical functional layer is 0.070 μm or more and 0.536 μm or less, an average inclination angle θa of irregularities present on the surface of the optical functional layer is 0.59° or more and 4.58° or less, an internal haze is 3.1% or more and 31.5% or less, a total haze is 20.0% or more and 72.0% or less, and an in-plane retardation Re of a light-transmissive base material defined by Expression (1): Re=(nx-ny)×d is 2,000 nm or more and 7,500 nm or less. Here, nx denotes a refractive index in a slow axis direction, ny denotes a refractive index in an advance phase axis direction, and d denotes a thickness of the light-transmissive base material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical laminate provided on the front side of an image display panel, and a display device using the same. [Background technology]

[0002] Conventionally, triacetyl cellulose (TAC) film, which has no in-plane phase difference and excellent visibility, has been used as the substrate of the optical film placed on the surface of an image display device. However, TAC film has the problem of absorbing moisture in the air, causing warping of the image display device. For this reason, polyethylene terephthalate (PET) film, which absorbs less moisture, has attracted attention, and in recent years, ultra-high retardation (ultra-high Re) PET film has been used (see, for example, Patent Documents 1 and 2).

[0003] When an image display device is viewed through a polarizing plate such as polarized sunglasses, the vibration plane of light emitted from the image display device and the transmission axis of the polarizing plate such as polarized sunglasses are perpendicular to each other, causing a phenomenon known as blackout, in which the image display device appears dark. As a technique for solving this blackout, for example, Patent Document 3 describes a technique in which the angle between the slow axis of an optical laminate and the absorption axis of a polarizer used in a liquid crystal display device is set to 45°±15°. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5304939 [Patent Document 2] Patent No. 6256385 [Patent Document 3] Patent No. 6044118 Summary of the Invention [Problem to be solved by the invention]

[0005] When ultra-high RePET film is used as the substrate, it is possible to suppress blackout when wearing polarized sunglasses depending on the angle of the slow axis, but because it is a uniaxially stretched film, there is a problem of poor bending resistance.On the other hand, with biaxially stretched PET film, bending resistance is greatly improved and blackout can be suppressed regardless of the angle of the slow axis, but there is a problem of noticeable rainbow spots due to in-plane retardation.

[0006] Therefore, an object of the present invention is to provide an optical laminate that uses a biaxially stretched polyethylene terephthalate film as a substrate, has bending resistance, and has suppressed rainbow irregularities, and an image display device that uses the same. [Means for solving the problem]

[0007] The optical laminate of the present invention comprises a biaxially stretched polyethylene terephthalate film, a light-transmitting substrate having in-plane birefringence, and an optical functional layer provided on one side of the light-transmitting substrate, wherein the arithmetic mean roughness Ra of the surface of the optical functional layer is 0.070 μm or more and 0.536 μm or less, the average slope angle θa of the irregularities present on the surface of the optical functional layer is 0.59° or more and 4.58° or less, the internal haze is 3.1% or more and 31.5% or less, the total haze is 20.0% or more and 72.0% or less, and the in-plane retardation Re of the light-transmitting substrate defined by the following formula (1) is 2,000 nm or more and 7,500 nm or less. Re=(nx-ny)×d (1) where: nx: refractive index in the slow axis direction ny: refractive index in the fast axis direction d: Thickness of the light-transmitting substrate is.

[0008] An image display device according to the present invention includes an image display panel and the above-described optical laminate. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an optical laminate that uses a biaxially stretched polyethylene terephthalate film as a substrate, has bending resistance, and is suppressed from having rainbow irregularities, and an image display device using the same. [Brief explanation of the drawings]

[0010] [Figure 1] Schematic cross-sectional view showing an example of an optical laminate according to an embodiment. [Figure 2] Schematic cross-sectional view showing another example of an optical laminate according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0012] The optical laminate 10 includes a light-transmitting substrate 1 and an antiglare layer (AG layer) 2 laminated on one surface of the light-transmitting substrate 1. The optical laminate 10 is an optical film (also referred to as an "AG film") that scatters incident light using the fine unevenness on the surface of the antiglare layer 2 and particles inside the antiglare layer 2 to suppress reflections of external light. In the optical laminate 10 shown in FIG. 1, the antiglare layer 2 corresponds to the optical functional layer.

[0013] FIG. 2 is a schematic cross-sectional view showing another example of the optical film according to the embodiment.

[0014] The optical laminate 20 includes a light-transmitting substrate 1, an anti-glare layer 2 laminated on one side of the light-transmitting substrate 1, and a low refractive index layer (LR layer) 3 laminated on the surface of the anti-glare layer 2 and having a refractive index lower than that of the anti-glare layer 2. The optical laminate 20 is an optical film (also referred to as an "AGLR film") that suppresses glare and reflection of external light by utilizing scattering of incident light and optical interference caused by fine irregularities on the outermost surface and internal particles. In the optical laminate 20 shown in FIG. 2, the anti-glare layer 2 and the low refractive index layer 3 correspond to optically functional layers.

[0015] Each layer will be described in detail below.

[0016] The light-transmitting substrate is a transparent film that serves as the base of the optical laminate. As the light-transmitting substrate, a biaxially stretched polyethylene terephthalate film having birefringence and an in-plane retardation Re defined by the following formula (1) is used. Re=(nx-ny)×d (1) where: nx: refractive index in the slow axis direction (the direction with the largest refractive index) of the light-transmitting substrate ny: refractive index in the fast axis direction of the light-transmitting substrate d: Thickness of the light-transmitting substrate is.

[0017] If the in-plane retardation Re of the light-transmitting substrate is less than 2,000 nm, the thickness of the light-transmitting substrate becomes too thin, which is undesirable because it reduces handleability and may result in insufficient surface hardness when an optical laminate is formed.If the in-plane retardation Re of the light-transmitting substrate exceeds 7,500 nm, the thickness of the light-transmitting substrate becomes too thick, which is undesirable because it increases raw material costs and the total thickness when an optical laminate is formed.

[0018] It is preferable to use a light-transmitting substrate that satisfies the following condition (2). (nx-ny)<0.06 (2)

[0019] If the value of nx-ny is 0.06 or more, excessive stretching will undesirably reduce the mechanical properties, ie, resistance to tearing and breaking.

[0020] It is also preferable to use a light-transmitting substrate having a thickness direction retardation Rth' represented by the following formula (3) of 9,500 nm or more and 18,000 nm or less. Rth'=(nx-nz)×d (3) where: nz: Refractive index in the thickness direction is.

[0021] If the thickness direction retardation Rth' of the light-transmitting substrate is less than 9,500 nm, the thickness of the light-transmitting substrate becomes too thin, which is undesirable since the mechanical strength of the optical laminate formed therefrom may be insufficient. Also, if the thickness direction retardation Rth' of the light-transmitting substrate exceeds 18,000 nm, the thickness of the light-transmitting substrate becomes too large, which is undesirable since it is difficult to make the optical laminate thinner.

[0022] It is also preferable to use a light-transmitting substrate in which the ratio Nz' represented by the following formula (4) is 1.5 or more and 5.5 or less. Nz'=Rth' / Re (4)

[0023] When the ratio Nz' is within the above range, the birefringence and thickness of the light-transmitting substrate fall within appropriate ranges, and when an optical laminate is formed, it is possible to achieve both good mechanical strength and suppression of rainbow irregularities.

[0024] The thickness of the light-transmitting substrate 1 is not particularly limited, but is preferably 35 to 200 μm, and more preferably 35 to 125 μm. The surface of the light-transmitting substrate 1 may be subjected to a surface modification treatment to improve adhesion with other layers to be laminated. 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.

[0025] The antiglare layer 2 is a functional layer that forms the fine uneven shape on the outermost surface of the optical laminate 10 .

[0026] The antiglare layer 2 is formed by applying a coating liquid containing an active energy ray-curable compound and organic and / or inorganic fine particles (filler) to the light-transmitting substrate 1 and curing the coating film.

[0027] As the active energy ray-curable compound, 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.

[0028] 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 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,Examples include adamantane derivative mono(meth)acrylates such as adamantyl acrylate having a monovalent mono(meth)acrylate derived from adamantanediol.

[0029] Examples of bifunctional (meth)acrylates 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.

[0030] Examples of tri- or higher functional (meth)acrylates 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; Examples of the polyfunctional (meth)acrylate compound include tri- or higher functional polyfunctional (meth)acrylate compounds 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, as well as polyfunctional (meth)acrylate compounds in which a portion of these (meth)acrylates is substituted with an alkyl group or ε-caprolactone.

[0031] Urethane (meth)acrylates can also be used as polyfunctional monomers. 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.

[0032] 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.

[0033] The polyfunctional monomers may be used alone or in combination of two or more thereof. In addition, the polyfunctional monomers may be in the form of a monomer in the coating liquid, or may be in the form of a partially polymerized oligomer.

[0034] The organic fine particles are a material that mainly forms fine irregularities on the surface of the antiglare layer 2 and provides the function of diffusing external light. 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, or polyethylene fluoride resin can be used as the organic fine particles. Two or more types of resin particles with different materials (refractive indexes) may be mixed and used to adjust the refractive index and dispersion of the resin particles. The average particle size of the organic fine particles is preferably 0.5 to 10 μm.

[0035] The inorganic fine particles added to the composition for forming an antiglare layer are preferably nanoparticles having an average particle size of 10 to 200 nm.

[0036] The inorganic fine particles are primarily materials for controlling the sedimentation and aggregation of the organic fine particles in the antiglare layer 2. Examples of inorganic fine particles that can be used include silica fine particles, metal oxide fine particles, and various mineral fine particles. Examples of silica fine particles that can be used include colloidal silica and silica fine particles surface-modified with reactive functional groups such as (meth)acryloyl groups. Examples of metal oxide fine particles that can be used include alumina, zinc oxide, tin oxide, antimony oxide, indium oxide, titania, and zirconia. Examples of mineral fine particles that can be used 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. Among mineral fine particles, layered organic clay is more preferred. Layered organic clay refers to a swelling clay in which organic onium ions have been introduced between its layers. The organic onium ions are not limited 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 suitably used. Synthetic smectite has the function of increasing the viscosity of the antiglare layer-forming composition, suppressing the settling of resin particles and inorganic fine particles, and adjusting the uneven shape of the surface of the optical functional layer.

[0037] A polymerization initiator may be added to cure the antiglare layer-forming composition by ultraviolet irradiation. Polymerization initiators that generate radicals upon ultraviolet irradiation can be used. Radical polymerization initiators such as acetophenones, benzophenones, thioxanthones, benzoin, benzoin methyl ether, and acylphosphine oxides can be used as the polymerization initiator. Examples of polymerization initiators that can be used include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,2-diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-phenylacetophenone, dibenzoyl, benzoin, benzoin methyl ether, benzoin ethyl ether, p-chlorobenzophenone, p-methoxybenzophenone, Michler's ketone, acetophenone, and 2-chlorothioxanthone. One of these initiators may be used alone. Two or more types may be used in combination.

[0038] The antiglare layer-forming composition may also contain components for improving antifouling properties, such as an antifouling agent, a leveling agent, an oil repellent, a water repellent, or an antifingerprint agent. Fluorine-containing compounds and silicone compounds can be suitably used as these additives. Other additives, such as antistatic agents, antifoaming agents, antioxidants, ultraviolet absorbers, infrared absorbers, colorants, light stabilizers, polymerization inhibitors, and photosensitizers, may also be added as needed.

[0039] Furthermore, a solvent may be added to the antiglare layer-forming composition, if necessary. Examples of the solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, butanol, isopropyl alcohol, and isobutanol; 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, butyl acetate, and amyl acetate; ethers such as dimethyl ether and diethyl ether; and N-methylpyrrolidone and dimethylformamide, which may be used alone or in combination.

[0040] The low refractive index layer 3 has a refractive index lower than that of the underlying antiglare layer 2, and is a functional layer that suppresses reflection by optical interference.

[0041] The low refractive index layer 3 can be formed by applying a composition containing an active energy ray-curable compound to the surface of the antiglare layer 2 and curing the coating. The low refractive index layer 3 may contain low refractive index fine particles to adjust the refractive index.

[0042] Suitable low-refractive-index particles include, for example, particles of LiF, MgF, 3NaF·AlF, or AlF (all of which have a refractive index of 1.4), or Na3AlF6 (cryolite, refractive index of 1.33), as well as silica particles having internal voids. Silica particles having internal voids can have the refractive index of the voids (approximately 1) of air, which is advantageous for achieving a low refractive index for the low-refractive-index layer 3. Specifically, porous silica particles or silica particles with a shell structure can be used. Note that low-refractive-index particles are not necessarily required; if the refractive index of the active-energy-ray-curable compound after curing is lower than that of the anti-glare layer 2, the low-refractive-index particles may be omitted.

[0043] As the active energy ray-curable compound, the polymerizable compound described in the antiglare layer can be used. In addition, the above-mentioned polymerization initiator and solvent may be appropriately added to the composition for forming the low refractive index layer.

[0044] The composition for forming the low refractive index layer may contain components for improving antifouling properties, such as an antifouling agent, a leveling agent, an oil repellent, a water repellent, or an antifingerprint agent. As these additives, fluorine-containing compounds and silicone compounds can be suitably used. In addition, various additives such as antistatic agents, antifoaming agents, antioxidants, ultraviolet absorbers, infrared absorbers, colorants, light stabilizers, polymerization inhibitors, and photosensitizers may be added as needed.

[0045] Between the light-transmitting substrate 1 and the antiglare layer 2, one or more other functional layers such as a hard coat layer, a high refractive index layer, a medium refractive index layer, an antistatic layer, an electromagnetic wave blocking layer, an infrared absorbing layer, an ultraviolet absorbing layer, or a color correction layer may be laminated.

[0046] The method for applying the antiglare layer-forming composition and the low refractive index layer-forming composition is not particularly limited, and for example, they can be applied using a spin coater, a roll coater, a reverse roll coater, a gravure coater, a microgravure coater, a knife coater, a bar coater, a wire bar coater, a die coater, a dip coater, a spray coater, an applicator, or the like.

[0047] Here, the surface irregularities of the optical laminate according to this embodiment will be described in detail.

[0048] The total haze of the optical laminate according to the present invention is preferably 5% or more. When the total haze is 5% or more, external light is sufficiently diffused, and rainbow unevenness caused by the light-transmitting substrate can be suppressed. The total haze is more preferably 22.0 to 71.6%. When the total haze is within the more preferred range, rainbow unevenness can be suppressed.

[0049] The surface haze of the optical laminate according to the present invention is preferably 3% or more. When the surface haze is 3% or more, external light is sufficiently diffused, and rainbow irregularities originating from the light-transmitting substrate can be suppressed. The surface haze is more preferably 12.0 to 68.6%. When the surface haze is within the more preferred range, rainbow irregularities can be advantageously suppressed.

[0050] The internal haze of the optical laminate according to the present invention is preferably 2% or more. When the internal haze is 2% or more, external light is sufficiently diffused, and rainbow irregularities originating from the light-transmitting substrate can be suppressed. The internal haze is more preferably 3.1 to 55.6%. When the internal haze is within the more preferred range, rainbow irregularities are advantageously suppressed.

[0051] The total haze, surface haze and internal haze are values ​​measured in accordance with JIS K7136.

[0052] In the optical laminate according to the present invention, the value of Δn×total haze is preferably 0.2 or more (where Δn=nx−ny). If the value of Δn×total haze is 0.2 or more, it is advantageous in terms of suppressing rainbow irregularities in the optical laminate. From the viewpoint of suppressing rainbow irregularities in the optical laminate, within the above range, the value of Δn×total haze is more preferably 0.39 to 2.55, and even more preferably 0.78 to 2.55.

[0053] In the optical laminate according to the present invention, the value of Re × total haze is preferably 10,000 or more. When the value of Re × total haze is 10,000 or more, it is advantageous in terms of suppressing rainbow irregularities in the optical laminate. From the viewpoint of suppressing rainbow irregularities in the optical laminate, within the above range, the value of Re × total haze is more preferably 19,725 to 301,028, and even more preferably 58,679 to 301,028.

[0054] Furthermore, in the optical laminate according to the present invention, the value of Δn × surface haze is preferably 0.12 or more. When the value of Δn × surface haze is 0.12 or more, it is advantageous in terms of suppressing rainbow irregularities in the optical laminate. From the viewpoint of suppressing rainbow irregularities in the optical laminate, within the above range, the value of Δn × surface haze is more preferably 0.15 to 2.44, and even more preferably 0.37 to 2.44.

[0055] Furthermore, in the optical laminate according to the present invention, the Re×surface haze value is preferably 6,000 or more. When the Re×surface haze value is 6,000 or more, it is advantageous in terms of suppressing rainbow irregularities in the optical laminate. From the viewpoint of suppressing rainbow irregularities in the optical laminate, within the above range, the Re×surface haze value is more preferably 9,544 to 182,972, and even more preferably 32,007 to 182,972.

[0056] In addition, in the optical laminate according to the present invention, the value of Δn × internal haze is preferably 0.08 or more. When the value of Δn × internal haze is 0.08 or more, it is advantageous in terms of suppressing rainbow irregularities in the optical laminate. From the viewpoint of suppressing rainbow irregularities in the optical laminate, it is more preferable that the value of Δn × internal haze is 0.11 to 1.98 within the above range.

[0057] In addition, in the optical laminate according to the present invention, the value of Re × internal haze is preferably 4,000 or more. When the value of Re × internal haze is 4,000 or more, it is advantageous in terms of suppressing rainbow irregularities in the optical laminate. From the viewpoint of suppressing rainbow irregularities in the optical laminate, it is more preferable that the value of Re × internal haze is 8,268 to 207,991 within the above range.

[0058] In the optical laminate according to the present invention, it is preferable that the arithmetic mean roughness Ra of the surface of the optical functional layer is 0.04 μm or more, and the average slope angle θa of the irregularities present on the surface of the optical functional layer is 0.30° or more. When the arithmetic mean roughness Ra and the average slope angle θa are within the above ranges, external light is sufficiently diffused, and rainbow irregularities originating from the light-transmitting substrate can be suppressed. From the viewpoint of suppressing rainbow irregularities in the optical laminate, the arithmetic mean roughness Ra is preferably 0.070 to 0.391 μm, and the average slope angle θa is preferably 0.39 to 4.58° within the above ranges.

[0059] In the optical laminate according to the present invention, the maximum height Rz of the irregularities present on the surface of the optical functional layer is preferably 0.2 μm or more. When the maximum height Rz is 0.2 μm or more, external light is sufficiently diffused, and rainbow irregularities originating from the light-transmitting substrate can be suppressed. From the viewpoint of suppressing rainbow irregularities in the optical laminate, the maximum height Rz is more preferably 0.280 to 2.982 μm within the above range.

[0060] In addition, in the optical laminate according to the present invention, the value of Ra×Rsm is preferably 1.6 or more. Here, Rsm is the average length of the profile curve element. When the value of Ra×Rsm is 1.6 or more, it is advantageous in terms of suppressing rainbow unevenness in the optical laminate. From the viewpoint of suppressing rainbow unevenness in the optical laminate, the value of Ra×Rsm is more preferably 1.77 to 23.09 within the above range.

[0061] In addition, in the optical laminate according to the present invention, the value of Ra×θa is preferably 0.018 or more. When the value of Ra×θa is 0.018 or more, it is advantageous in terms of suppressing rainbow irregularities in the optical laminate. From the viewpoint of suppressing rainbow irregularities in the optical laminate, the value of Ra×θa is more preferably 0.027 to 2.457 within the above range.

[0062] In addition, in the optical laminate according to the present invention, the value of Ra×Rsm×θa is preferably 1.6 or more. When the value of Ra×Rsm×θa is 1.6 or more, it is advantageous in terms of suppressing rainbow unevenness in the optical laminate. From the viewpoint of suppressing rainbow unevenness in the optical laminate, it is more preferable that the value of Ra×Rsm×θa is 1.79105.78 within the above range.

[0063] In addition, in the optical laminate according to the present invention, the value of Δn×Ra is preferably 0.002 to 0.02. When the value of Δn×Ra is 0.002 to 0.02, it is advantageous in terms of suppressing rainbow unevenness in the optical laminate. From the viewpoint of suppressing rainbow unevenness in the optical laminate, within the above range, the value of Δn×Ra is more preferably 0.0025 to 0.0191.

[0064] Furthermore, in the optical laminate according to the present invention, the Re×Ra value is preferably 140 to 1,500. When the Re×Ra value is 140 to 1,500, it is advantageous in terms of suppressing rainbow irregularities in the optical laminate. From the viewpoint of suppressing rainbow irregularities in the optical laminate, the Re×Ra value is more preferably 159 to 1,431 within the above range.

[0065] In addition, in the optical laminate according to the present invention, the value of Δn×θa is preferably 0.01 to 0.17. When the value of Δn×θa is 0.01 to 0.17, it is advantageous in terms of suppressing rainbow unevenness in the optical laminate. From the viewpoint of suppressing rainbow unevenness in the optical laminate, within the above range, the value of Δn×θa is more preferably 0.014 to 0.163.

[0066] Furthermore, in the optical laminate according to the present invention, the value of Re×θa is preferably 800 to 12,500. When the value of Re×θa is 800 to 12,500, it is advantageous in terms of suppressing rainbow irregularities in the optical laminate. From the viewpoint of suppressing rainbow irregularities in the optical laminate, within the above range, the value of Re×θa is more preferably 886 to 12,218.

[0067] The optical laminate according to this embodiment can be used to construct an image display device by being attached to the outermost surface of an image display panel such as a liquid crystal panel or an organic EL panel. A touch panel may be provided between the optical laminate and the image display panel. The optical laminate according to this embodiment has excellent moisture resistance and bending resistance because a biaxially stretched PET film is used as the light-transmitting substrate, and the light diffusion properties of the antiglare layer suppress the rainbow unevenness inherent in the biaxially stretched PET film, making it suitable as an optical film to be provided on the outermost surface of an image display device. Because the optical laminate has bending resistance, it can also be used as an optical film for use in a foldable image display device.

[0068] As described above, the optical laminate according to this embodiment includes a biaxially stretched PET film having an in-plane retardation Re of 2,000 to 7,500 nm as the light-transmitting substrate. When a biaxially stretched PET film is used, there is a problem of noticeable rainbow irregularities. However, by controlling the optical properties (anti-glare and anti-reflection properties) of the entire optical laminate using an optical functional layer, it is possible to suppress the occurrence of rainbow irregularities. When a biaxially stretched PET film having an in-plane retardation Re of less than 2,000 is used, the thickness of the light-transmitting substrate is reduced, which tends to reduce the surface hardness. However, in this embodiment, by using a biaxially stretched PET film having an in-plane retardation Re of 2,000 to 7,500 nm, it is possible to ensure the surface hardness required for the optical laminate. Furthermore, when a PET film known as an ultra-high Re PET film is used as the light-transmitting substrate, adjusting the angle of the slow axis of the light-transmitting substrate can eliminate blackout when using polarized sunglasses. However, because the ultra-high Re PET film is a uniaxially stretched film, it has the problem of poor bending resistance. In this embodiment, the light-transmitting substrate is a biaxially stretched PET film, which has good bending resistance and has the advantage that blackout can be eliminated without considering the angle of the slow axis of the light-transmitting substrate, even when used in applications where the image is viewed through a polarizing plate such as polarized sunglasses. In other words, the optical laminate according to this embodiment simultaneously solves the problems that arise when using a PET film with low in-plane retardation Re (less than 2,000 nm) and the problems that arise when using a PET film with high in-plane retardation Re (more than 7,500 nm), and is suitable for use in image display devices where the image is viewed through a polarizing plate such as polarized sunglasses. [Example]

[0069] Examples of specific implementations of the present invention will be described below.

[0070] First, a method for producing the light-transmitting substrate will be described.

[0071] <Unstretched film> The polyethylene terephthalate raw material was melted at 285°C and filtered through a stainless steel sintered filter material (nominal filtration accuracy: 95% cut of 10μm particles), laminated in a two-type, three-layer confluence block, extruded into a sheet from a die, and then wrapped around a casting drum with a surface temperature of 30°C using an electrostatic casting method, where it was cooled and solidified to obtain an unstretched film. At this time, the output of each extruder was adjusted so that the thickness ratio of the three layers was 10:80:10. Next, using the reverse roll method, a coating amount of 0.08g / m2 was applied to both sides of the unstretched PET film after drying. 2 After applying the adhesive property modifying coating liquid so as to obtain the above, the coating liquid was dried at 80°C for 20 seconds.

[0072] <Uniaxially stretched film> The unstretched film with the coating layer formed thereon was introduced into a tenter stretching machine, and while the edges of the film were held with clips, it was introduced into a hot air zone at 125°C and stretched 4.0 times in the width direction. Next, while maintaining the stretched width in the width direction, it was treated at 225°C for 30 seconds and further relaxed by 3% in the width direction to obtain a uniaxially stretched PET film with a thickness of 80 μm.

[0073] <Biaxially stretched film> The unstretched film with the coating layer formed thereon was heated to 105°C using a group of heated rolls and an infrared heater, and then stretched 2.6 times in the running direction and 4.0 times in the width direction using a group of rolls with different peripheral speeds to obtain biaxially stretched PET films with thicknesses of 38, 50, 75, 125, and 188 μm. It was also stretched 1.4 times in the running direction and 4.0 times in the width direction to obtain biaxially stretched PET films with thicknesses of 23 μm.

[0074] Tables 1 to 4 below show the compositions of the coating liquid for forming an antiglare layer and the coating liquid for forming a low refractive index layer used in the examples and comparative examples. Each coating liquid was diluted to a concentration suitable for coating using the solvents listed in Tables 1 to 4. The proportion of each component added in Tables 1 to 4 is the proportion (mass%) of the total solids in the coating liquid. Here, the total solids in the coating liquid for forming an optical functional layer refers to the components excluding the solvent. Therefore, the blending proportion (mass%) of resin particles and inorganic fine particles in the total solids in the coating liquid for forming an optical functional layer is equal to the content (mass%) of resin particles and inorganic fine particles in the optical functional layer, which is a cured film of the coating liquid for forming an optical functional layer. In Table 1, "-" indicates that the corresponding material was not blended.

[0075] [Table 1]

[0076] [Table 2]

[0077] [Table 3]

[0078] [Table 4]

[0079] The materials used in Tables 1 to 4 are as follows:

[0080] <Coating liquid for forming anti-glare layer (hard coat layer)> ·UV / EB curable resin Light Acrylate PE-3A (pentaerythritol triacrylate), manufactured by Kyoeisha Chemical Co., Ltd. Photopolymerization initiator Omnirad® 184 (1-hydroxycyclohexyl-phenyl ketone), IGM Resins BV Resin particles (organic spherical filler) (1) Acrylic-styrene copolymer, average particle size 3.5 μm, n=1.515 (2) Acrylic-styrene copolymer, average particle size 3.5 μm, n=1.565 (3) Acrylic-styrene copolymer, average particle size 3.5 μm, n=1.555 (4) Polystyrene, average particle size 3.5 μm, n=1.595 (5) Acrylic-styrene copolymer, average particle size 2.0 μm, n=1.595 Irregular silica particles Average particle size 2.7 μm, n=1.45, Fuji Silysia Ltd. Leveling agent F565, DIC Corporation Nanoparticles (organosilica sol) MEK-ST-40, Nissan Chemical Co., Ltd.

[0081] <Coating liquid for forming low refractive index layer> Binder resin Light Acrylate PE-3A (Pentaerythritol Triacrylate), Kyoeisha Chemical Co., Ltd. Photopolymerization initiator Omnirad® 184 (1-hydroxycyclohexyl-phenyl ketone) ), IGM Resins BV Hollow silica (porous silica microparticle dispersion) (1) Average particle diameter 60nm (2) Average particle diameter 75nm Leveling agent RS-75, DIC Corporation

[0082] (Examples 1, 2, 7, 8, 11, Comparative Example 3) An antiglare layer-forming coating solution having the composition shown in Tables 1 to 4 was prepared and applied to a biaxially stretched PET film shown in Table 5. The coating film was dried and then polymerized and cured by irradiating with ultraviolet light to form an antiglare layer. Next, a low refractive index layer-forming coating solution having the composition shown in Tables 1 to 4 was prepared and applied to the antiglare layer. The coating film was dried and then polymerized and cured by irradiating with ultraviolet light to form a low refractive index layer. An optical laminate (AGLR film) was obtained by the above steps.

[0083] (Examples 3 to 6, 9, 10, 12 to 16, Comparative Examples 4 and 5) An optical laminate (AG film) was obtained in the same manner as in Example 1, except that a low refractive index layer was not formed on the antiglare layer.

[0084] (Comparative Example 1) A coating solution for forming a hard coat layer having the composition shown in Table 4 was prepared and applied to a uniaxially stretched PET film shown in Table 5 so that the film thickness after curing would be 5 μm. The coating film was dried and then irradiated with ultraviolet light to polymerize and cure the coating film, thereby forming a hard coat layer. An optical laminate (HC film) was obtained by the above steps.

[0085] (Comparative Example 2) An optical laminate (HC film) was obtained in the same manner as in Comparative Example 1, except that a biaxially stretched PET film shown in Table 5 was used as the light-transmitting substrate.

[0086] (Hayes) The haze value was measured using a haze meter (NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136. Here, the haze value of the optical laminate was taken as the total haze. The haze value measured by laminating a transparent sheet with adhesive to the surface of the optical functional layer of the optical laminate and subtracting the haze value of the transparent sheet with adhesive was taken as the internal haze of the optical laminate. The transparent sheet with adhesive used was a polyethylene terephthalate film (thickness 38 μm) coated with an acrylic adhesive (thickness 10 μm). The surface haze was calculated using the following formula. Surface haze (%) = Total haze (%) - Internal haze (%)

[0087] (retardation) The in-plane retardation and thickness direction retardation of the prepared uniaxially or biaxially stretched PET films were measured using a retardation film and optical material tester (RETS-100, manufactured by Otsuka Electronics Co., Ltd.) under the following measurement conditions: [Measurement conditions] Retardation measurement method: Rotating analyzer method Measurement spot diameter: φ5mm Tilt angle range: 0° Measurement wavelength range: 400nm to 800nm Average refractive index N of the light-transmitting substrate: N = (nx + ny + nz) based on nx, ny, and nz / 3. For PET film, N=1.660 The in-plane retardation Re and the thickness direction retardation Rth' are values ​​at a wavelength of 589 nm.

[0088] [Surface shape analysis] The unevenness of the surface of the optical functional layer of the optical laminate according to each example and comparative example was measured by optical interference using a non-contact surface / layer cross-sectional shape measurement system (measuring device: Vertscan R3300FL-Lite-AC, analysis software: VS-Viewer6, manufactured by Ryoka Systems Co., Ltd.). The measurement data was analyzed using the particle analysis software of the device, and the arithmetic mean roughness Ra, maximum height Rz, average length Rsm of curved elements, and average slope angle θa of the low refractive index layer surface were measured.

[0089] The average unevenness is generated under the analysis conditions for the cross-sectional profile (multi-line) of VS-Viewer. The arithmetic mean roughness Ra, maximum height Rz, average length Rsm of curved elements, and average inclination angle θa obtained from the cross-section obtained by averaging the cross-sectional profiles of the six measurement cursors set are defined as the arithmetic mean roughness Ra, maximum height Rz, average length Rsm of curved elements, and average inclination angle θa of the unevenness of this invention.

[0090] Measurement was carried out under the following conditions using the measurement software of the device, and an image file showing the measurement results of the surface unevenness was obtained. ·Optical conditions Camera: Sony HR-50 1 / 3 inch Objective lens: 10XDI (10x magnification) Imaging lens (barrel): 0.5x Zoom lens: 1x Light source / wavelength filter: 520 nm ND filter: Not used A-Stop (Aperture Stop): Not used (fully open) F-Stop (field aperture): Not used (fully open) Measurement conditions Measuring device: Piezo Measurement mode: Phase Scan speed: 4 μm / sec Scan range: -10 to 10 μm Effective pixels: 50% Measurement area: 704.192μm×938.923μm

[0091] The acquired image files were analyzed using the analysis software of the device under the following conditions. ·Analysis conditions (VS-Viewer6) Surface correction: 4th order S filter: Automatic L filter: Not used ·Particle analysis conditions (VS-Viewer6) Analysis type: sudden analysis Image correction: None Height threshold: 0.1 μm Particle shaping: None

[0092] (Calculation method for Ra, Rz, Rsm and θa) In the acquired image with surface correction (4th order) and S filter 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, Rz, Rsm, and θa values ​​at each cursor position (6 positions in total, 3 positions on the cross section parallel to the X direction and 3 positions on the cross section parallel to the Y direction), which were automatically calculated using the cross-sectional profile of VS-Viewer, were obtained, and the average (arithmetic mean) of the obtained values ​​was used as the measurement result.

[0093] (Nijimura's review) Observation of the rainbow smear, assuming the use of polarized sunglasses, was carried out as follows: Backlight (brightness 5,000 cd / m 2 An observation sample was prepared by arranging a first polarizer, an optical laminate of an example or comparative example, and a second polarizer (simulating polarized sunglasses) in this order on a display equipped with a polarizer (approximately 1 / 4"). The first polarizer was arranged so that its absorption axis was perpendicular to the vertical direction of the display, and the second polarizer was arranged so that its absorption axis was perpendicular to the absorption axis of the first polarizer. Furthermore, the optical laminate was rotated 45° clockwise and then another 45° (a rotation position 90° from the standard rotation position) from a reference rotation position (0°) in which the vertical direction of the display and the slow axis of the light-transmitting substrate of the optical laminate are parallel, and rainbow irregularities were visually observed at each orientation. The observer observed the display from a position 50 to 60 cm from the front and from a position 50 to 60 cm from the display, tilted 45° to the left or right with respect to the normal direction when viewed from the front. The rainbow irregularities were evaluated based on the observation results using the following criteria. -: Blackout occurs and it is not possible to judge the rainbow pattern (not practical) ×: Rainbow spots occur, not practical △: Rainbow spots occur, but there is no practical problem. 〇: Slight rainbow marks occur, but this does not cause any problems in practical use. ◎: No rainbow spots (very good)

[0094] (bending resistance) A sheet-shaped no-load U-shaped expansion / contraction test jig (DMX-FS) was attached to a tabletop durability tester (manufactured by Yuasa System Co., Ltd.), and each sample was attached flat. Continuous bending was performed with the optical functional layer facing outward so that the distance between the opposing surfaces was 2 mm. After 50,000 and 200,000 consecutive bending operations, the presence or absence of fractures at the bent portions was visually confirmed and evaluated according to the following criteria. ◯: No breakage occurred at the bent portion in any of the consecutive folding tests. ×: Breakage occurred at the bent portion in any of the continuous folding tests.

[0095] (Pencil hardness) The pencil hardness was evaluated in accordance with JIS K5400-1900. The pencil hardness of the protective layer surface was measured using a pencil (uni, Mitsubishi Pencil Co., Ltd.) and a Clemens scratch tester (HA-301, Tester Sangyo Co., Ltd.). The test was repeated while changing the pencil hardness, and changes in appearance due to scratches were visually observed. The maximum hardness at which no scratches were observed was used as the evaluation value. A pencil hardness of H or higher was considered to be acceptable.

[0096] Table 5 shows the type, thickness, and optical property values ​​such as retardation of the light-transmitting substrate according to each example and comparative example, together with the layer structure of the optical laminate.

[0097] [Table 5]

[0098] Table 6 shows the measured values ​​for the surface roughness of the optical laminates according to the examples and comparative examples.

[0099] [Table 6]

[0100] Table 7 shows the measured values ​​for the haze of the optical laminates according to the examples and comparative examples.

[0101] [Table 7]

[0102] Table 8 shows the rainbow unevenness, bending resistance and pencil hardness of the optical laminates according to each Example and Comparative Example. The evaluation results are shown below.

[0103] [Table 8] The optical laminates according to Examples 1 to 16 all used a biaxially stretched PET film with an in-plane retardation Re of 2,000 to 7,500 nm as the light-transmitting substrate. Therefore, even when using polarized sunglasses, blackout did not occur regardless of the slow axis direction of the light-transmitting substrate, and rainbow irregularities were suppressed by the optical functional layer. Furthermore, because the optical laminates according to Examples 1 to 16 all used a biaxially stretched PET film, they had good surface hardness and bending resistance.

[0104] In contrast, the optical laminate of Comparative Example 1 uses a uniaxially stretched PET film with high in-plane retardation Re as the light-transmitting substrate, and therefore blackout occurs depending on the direction of the slow axis of the light-transmitting substrate, making it unsuitable for applications intended for use with polarized sunglasses.

[0105] Furthermore, neither of the optical laminates according to Comparative Examples 2 and 3 was able to suppress rainbow unevenness, and were not suitable for applications envisioned for use with polarized sunglasses.

[0106] The optical laminate according to Comparative Example 4 used a biaxially stretched PET film with an in-plane retardation Re of less than 2,000 nm, and therefore had reduced rainbow irregularities but insufficient pencil hardness. [Industrial Applicability]

[0107] The present invention can be used as an optical laminate provided on the front side of an image display panel. [Explanation of symbols]

[0108] 1 Light-transmitting substrate 2 Anti-glare layer 3 Low refractive index layer 10, 20 optical layered bodies

Claims

1. An optical laminate used in an image display device, A biaxially stretched polyethylene terephthalate film with in-plane birefringence. a permeable substrate; an optical functional layer provided on one surface of the light-transmitting substrate, The arithmetic mean roughness Ra of the surface of the optical functional layer is 0.070 μm or more and 0.536 μm or less, the average inclination angle θa of the irregularities present on the surface of the optical functional layer is 0.59° or more and 4.58° or less; The internal haze is 3.1% or more and 31.5% or less, a total haze of 20.0% or more and 72.0% or less; An optical laminate, wherein the in-plane retardation Re of the light-transmitting substrate defined by the following formula (1) is 2,000 nm or more and 7,500 nm or less. Re=(nx-ny)×d (1) where: nx: refractive index in the slow axis direction ny: refractive index in the fast axis direction d: Thickness of the light-transmitting substrate is.

2. The optical laminate according to claim 1, which satisfies the following condition (2): (nx-ny)<0.06 (2)

3. 2. The optical laminate according to claim 1, wherein the thickness direction retardation Rth' of the light-transmitting substrate represented by the following formula (3) is 9,500 nm or more and 18,000 nm or less. Rth'=(nx-nz)×d (3) where: nz: refractive index in the thickness direction is.

4. The optical laminate according to claim 1, wherein the ratio Nz' represented by the following formula (4) is 1.5 or more and 5.5 or less. Nz'=Rth' / Re (4)

5. 2. The optical laminate according to claim 1, wherein no breakage occurs when a folding test is repeated 200,000 times in which the optical functional layer is on the outside and the laminate is folded 180° so that the distance between the opposing surfaces is 2 mm.

6. an image display panel; An image display device comprising the optical laminate according to any one of claims 1 to 5 provided on the front surface of the image display panel.

Images