Optical laminate and display device using same

Abstract

The present invention provides an optical laminate that uses a biaxially oriented polyethylene terephthalate film as a substrate, has bending resistance, and is suppressed from having rainbow irregularities, and an image display device using the same. [Solution] An optical laminate for use in an image display device, comprising a light-transmitting substrate made of a biaxially stretched polyethylene terephthalate film and having in-plane birefringence, and an optical functional layer provided on one surface of the light-transmitting substrate, the optical functional layer having a surface arithmetic mean roughness Ra of 0.04 μm or more, an average inclination angle θa of the irregularities present on the surface of the optical functional layer of 0.30° or more, and an in-plane retardation Re of the light-transmitting substrate defined by the formula (1): Re = (nx - ny) × d of 2,000 nm or more and 7,500 nm or less, where nx is the refractive index in the slow axis direction, ny is the refractive index in the fast axis direction, and d is the thickness of the light-transmitting substrate.

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 is excellent in visibility, has been used as the substrate of the optical film arranged on the surface of the image display device. However, TAC film has a problem in that it absorbs moisture in the air and causes warping of the image display device. For this reason, polyethylene terephthalate (PET) film, which absorbs less moisture, has been attracting attention, and in recent years, ultra-high retardation (ultra-high Re) PET film has been used in some cases (for example, see 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 is viewed as dark. As a technique for solving this blackout, for example, Patent Document 3 describes that 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 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, the occurrence of blackouts when using polarized sunglasses can be suppressed 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 blackouts 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 oriented polyethylene terephthalate film as a substrate, has bending resistance, and is suppressed from having rainbow irregularities, and an image display device using the same. [Means for solving the problem]

[0007] The optical laminate according to the present invention is made of a biaxially stretched polyethylene terephthalate film and includes a light-transmitting substrate having in-plane birefringence and an optical functional layer provided on one surface of the light-transmitting substrate, and the arithmetic mean roughness Ra of the surface of the optical functional layer is 0.070μm or more 0.536μm The average inclination angle θa of the irregularities on the surface of the optical functional layer is 0.59° or more and 4.58° or less and The maximum height Rz of irregularities present on the surface of the optical functional layer is 0.410 μm or more and 2.982 μm or less, and the internal haze of the optical laminate is 3.1% or more and 31.5% or less, 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 It is.

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

[0009] According to the present invention, it is possible to provide an optical laminate which 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 description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of an optical laminate according to an embodiment. [Diagram 2] FIG. 1 is a schematic cross-sectional view showing another example of an optical laminate according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 side of the light-transmitting substrate 1. The optical laminate 10 is an optical film (also called an "AG film") that scatters incident light by means of the fine unevenness on the surface of the antiglare layer 2 and particles inside the antiglare layer 2 to suppress reflection 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 antiglare 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 antiglare layer 2 and having a lower refractive index than the antiglare layer 2. The optical laminate 20 is an optical film that suppresses glare and reflection of external light by utilizing the scattering of incident light and optical interference caused by fine irregularities on the outermost surface and internal particles (also referred to as an "AGLR film"). In the optical laminate 20 shown in FIG. 2, the two layers of the antiglare layer 2 and the low refractive index layer 3 correspond to optical 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. The film 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 (the direction with the larger 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 It is.

[0017] When the in-plane retardation Re of the light-transmitting substrate is less than 2,000 nm, the thickness of the light-transmitting substrate becomes thin, which is undesirable because the handleability may decrease or the surface hardness may be insufficient when an optical laminate is formed.When the in-plane retardation Re of the light-transmitting substrate exceeds 7,500 nm, the thickness of the light-transmitting substrate becomes thick, which is undesirable because the raw material cost increases or the total thickness increases 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 undesirably reduces the mechanical properties, ie, resistance to tearing and breaking.

[0020] It is 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 It is.

[0021] When the thickness direction retardation Rth' of the light-transmitting substrate is less than 9,500 nm, the thickness of the light-transmitting substrate becomes thin, which is undesirable since the mechanical strength of the optical laminate may be insufficient when the optical laminate is formed. Also, when the thickness direction retardation Rth' of the light-transmitting substrate is more than 18,000 nm, the thickness of the light-transmitting substrate becomes large, which is undesirable since it is disadvantageous for making the optical laminate thinner.

[0022] It is preferable to use a light-transmitting substrate having a ratio Nz' represented by the following formula (4) of 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 are in 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 in order to improve adhesion with other layers to be laminated thereon. Examples of the surface modification treatment 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 fine particles 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, bifunctional, 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 ethylene oxide modified phenoxy (meth)acrylate, nonylphenol (meth)acrylate, ethylene oxide modified nonylphenol (meth)acrylate, propylene oxide modified nonylphenol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, ) acryloyloxyethyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hexahydrohydrogen phthalate, 2-(meth)acryloyloxypropyl tetrahydrohydrogen phthalate, dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, 2-adamantane,Examples of the mono(meth)acrylate include adamantane derivative mono(meth)acrylates such as adamantyl acrylate having a monovalent mono(meth)acrylate derived from an 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 trifunctional or higher (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 trifunctional or higher 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] In addition, as the polyfunctional monomer, a urethane (meth)acrylate can also be used. Examples of the urethane (meth)acrylate 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, dipentaerythritol pentaacrylate isophorone diisocyanate urethane prepolymer, and the like.

[0033] The above-mentioned polyfunctional monomers may be used alone or in combination of two or more kinds. In addition, the above-mentioned polyfunctional monomers may be monomers in the coating liquid or may be partially polymerized oligomers.

[0034] The organic fine particles are a material that mainly forms fine irregularities on the surface of the antiglare layer 2 and imparts a function of diffusing external light. As the organic fine particles, 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, and polyethylene fluoride resin can be used. In order to adjust the refractive index and dispersion of the resin particles, two or more types of resin particles having different materials (refractive indexes) may be mixed and used. 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 a material for adjusting the precipitation and aggregation of the organic fine particles in the antiglare layer 2. 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 or silica fine particles surface-modified with a reactive functional group such as a (meth)acryloyl group 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, ilealite, kanemite, layered titanic acid, smectite, synthetic smectite, etc. can be used. The mineral fine particles may be either natural products or synthetic products (including substitution products and derivatives), or a mixture of both may be used. Among the mineral fine particles, layered organic clay is more preferable. The layered organic clay refers to a swelling clay having an organic onium ion introduced between layers. The organic onium ion is not limited as long as it can be made organic by utilizing the cation exchange property 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. The synthetic smectite has a function of increasing the viscosity of the composition for forming the antiglare layer, suppressing the sedimentation of the 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. As the polymerization initiator, a polymerization initiator that generates radicals by ultraviolet irradiation may be used. As the polymerization initiator, radical polymerization initiators such as acetophenone, benzophenone, thioxanthone, benzoin, benzoin methyl ether, and acylphosphine oxide may be used. As the polymerization initiator, for example, 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 may be used. One of these may be used alone, or two or more may be used in combination.

[0038] In addition, the composition for forming the antiglare layer may contain an antifouling agent, a leveling agent, an oil repellent, a water repellent, or an anti-fingerprint agent as a component for improving the antifouling property. As these additives, fluorine-containing compounds and silicone compounds can be preferably 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 necessary.

[0039] Furthermore, a solvent may be added to the composition for forming an antiglare layer as necessary. As the solvent, one or more of the following may be used in combination: 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; N-methylpyrrolidone, dimethylformamide, and the like.

[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] As the low refractive index fine particles, for example, fine particles such as LiF, MgF, 3NaF·AlF or AlF (all of which have a refractive index of 1.4), or Na3AlF6 (cryolite, a refractive index of 1.33), or silica fine particles having voids therein can be suitably used. Silica fine particles having voids therein can have the refractive index of the voids (about 1) of air, which is advantageous for lowering the refractive index of the low refractive index layer 3. Specifically, porous silica particles and silica particles having a shell structure can be used. The low refractive index fine particles are not necessarily required, and when the refractive index of the active energy ray curable compound after curing is lower than that of the antiglare layer 2, the low refractive index fine 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 an antifouling agent, a leveling agent, an oil repellent, a water repellent, or an anti-fingerprint agent as a component for improving antifouling properties. As these additives, fluorine-containing compounds and silicone compounds can be preferably used. In addition, various additives such as antistatic agents, defoamers, antioxidants, ultraviolet absorbers, infrared absorbers, colorants, light stabilizers, polymerization inhibitors, and photosensitizers may be added as necessary.

[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 above-mentioned composition for forming an antiglare layer and the composition for forming a low refractive index layer 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 spots originating from 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, it is advantageous in suppressing rainbow spots.

[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, it is advantageous in suppressing rainbow irregularities.

[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, it is advantageous in suppressing rainbow irregularities.

[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] In addition, 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] In addition, 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 inclination 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 inclination angle θa are within the above ranges, external light can be sufficiently diffused and rainbow irregularities originating from the light-transmitting substrate can be suppressed. From the viewpoint of suppressing rainbow irregularities on the optical laminate, within the above range, the arithmetic mean roughness Ra is 0.070 to 0.536 It is preferable that the average inclination angle θa is 0.39 to 4.58°.

[0059] In addition, 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 contour curve element. When the value of Ra×Rsm is 1.6 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 Ra×Rsm is more preferably 1.77 to 23.09.

[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 irregularities in the optical laminate. From the viewpoint of suppressing rainbow irregularities in the optical laminate, the value of Ra×Rsm×θa is preferably 1.79 or more within the above range. ~ 105.78 is more preferable.

[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 irregularities in the optical laminate. From the viewpoint of suppressing rainbow irregularities in the optical laminate, within the above range, the value of Δn×Ra is more preferably 0.0025 to 0.0191.

[0064] In addition, 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 irregularities in the optical laminate. From the viewpoint of suppressing rainbow irregularities in the optical laminate, within the above range, the value of Δn×θa is more preferably 0.014 to 0.163.

[0066] In addition, 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 the present embodiment can be used to form 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 the present embodiment is excellent in moisture resistance and bending resistance because a biaxially stretched PET film is used as a light-transmitting substrate, but the light diffusion property of the anti-glare layer suppresses the rainbow unevenness caused by the biaxially stretched PET film, making it suitable as an optical film to be provided on the outermost surface of an image display device. Since the optical laminate has bending resistance, it can also be used as an optical film to be used 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 a light-transmitting substrate. When a biaxially stretched PET film is used, there is a problem that rainbow irregularities are noticeable, but it is possible to suppress the occurrence of rainbow irregularities by controlling the optical properties (anti-glare property and anti-reflection property) of the entire optical laminate by the optical functional layer. When a biaxially stretched PET film having an in-plane retardation Re of less than 2000 is used, the thickness of the light-transmitting substrate becomes thin, and the surface hardness is likely to decrease, but in this embodiment, it is possible to ensure the surface hardness required for the optical laminate by using a biaxially stretched PET film having an in-plane retardation Re of 2,000 to 7,500 nm. In addition, when a PET film called an ultra-high RePET film is used as a light-transmitting substrate, blackouts when polarized sunglasses are used can be eliminated by adjusting the angle of the slow axis of the light-transmitting substrate, but the ultra-high RePET film has a problem of being weak in bending resistance because it is a uniaxially stretched film. In this embodiment, since the light-transmitting substrate is a biaxially stretched PET film, it 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 it is assumed that 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 of using a PET film with low in-plane retardation Re (less than 2,000 nm) and the problems of using a PET film with high in-plane retardation Re (more than 7,500 nm), and is suitable for use in image display devices viewed through polarizing plates such as polarized sunglasses. EXAMPLES

[0069] Examples of the present invention will now be described in detail.

[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 merging block, extruded from a die into a sheet, and then wrapped around a casting drum with a surface temperature of 30°C using an electrostatic casting method, cooled and solidified, to obtain an unstretched film. At this time, the discharge rate 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 the adhesiveness modifying coating liquid was applied so as to obtain the above-mentioned thickness, 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 ends of the film were held by clips, the film was introduced into a hot air zone at a temperature of 125° C. and stretched 4.0 times in the width direction. Next, while maintaining the width stretched in the width direction, the film was treated at a temperature of 225° C. for 30 seconds, and further subjected to a 3% relaxation treatment in the width direction to obtain a uniaxially stretched PET film with a film thickness of 80 μm.

[0073] <Biaxially oriented film> The unstretched film with the coating layer formed thereon was heated to 105°C using a heated roll group and an infrared heater, and then stretched 2.6 times in the running direction and 4.0 times in the width direction using a roll group with different peripheral speeds to obtain biaxially stretched PET films with thicknesses of 38, 50, 75, 125, and 188 μm. Also, it was stretched 1.4 times in the running direction and 4.0 times in the width direction to obtain a biaxially stretched PET film with a thickness 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 shown in Tables 1 to 4. The addition ratio of each component shown in Tables 1 to 4 is the ratio (mass%) to the total solid mass of the coating liquid. Here, the total solid content of the coating liquid for forming an optical functional layer refers to the components excluding the solvent. Therefore, the blending ratio (mass%) of the resin particles and inorganic fine particles in the total solid content of the coating liquid for forming an optical functional layer is equal to the content (mass%) of the resin particles and inorganic fine particles in the optical functional layer, which is the cured film of the coating liquid for forming an optical functional layer. In Table 1, "-" indicates that the corresponding material is 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 solution 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 solution 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) A coating solution for forming an antiglare layer having the composition shown in Tables 1 to 4 was prepared, and applied onto a biaxially stretched PET film shown in Table 5. The coating film was dried, and then irradiated with ultraviolet light to polymerize and harden the coating film to form an antiglare layer. Next, a coating solution for forming a low refractive index layer having the composition shown in Tables 1 to 4 was prepared, and applied onto the antiglare layer. The coating film was dried, and then irradiated with ultraviolet light to polymerize and harden the coating film to form a low refractive index layer. An optical laminate (AGLR film) was obtained by the above process.

[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, and the coating film was dried and then irradiated with ultraviolet light to polymerize and cure the coating film to form a hard coat layer. An optical laminate (HC film) was obtained by the above process.

[0085] Comparative Example 2 An optical laminate (HC film) was obtained in the same manner as in Comparative Example 1, except that the 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.) according to 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 on 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. As the transparent sheet with adhesive, a polyethylene terephthalate film (thickness 38 μm) coated with an acrylic adhesive (thickness 10 μm) was used. The surface haze was calculated by 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 film were measured using a retardation film / optical material inspection device (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°、40° Measurement wavelength range: 400nm to 800nm Average refractive index N of light-transmitting substrate: Value calculated from nx, ny, and nz using the formula N=(nx+ny+nz) / 3. In the case of PET film, N=1.660 The in-plane retardation Re and the retardation in the thickness direction Rth' are values ​​at a wavelength of 589 nm.

[0088] [Surface shape analysis] The uneven shape 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: Bertscan 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 inclination 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 the 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 the present invention.

[0090] Measurements were performed under the following conditions using the measurement software of the device, and image files showing the measurement results of the surface unevenness were obtained. ·Optical conditions Camera: Sony HR-50 1 / 3 inch Objective lens: 10XDI (10x) Imaging lens (lens tube): 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: 4μm / sec Scan range: -10~10μm 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 Grain Shaping: None

[0092] (Calculation method of Ra, Rz, Rsm and θa) In the acquired image to which surface correction (4th order) and S filter were applied, the measurement cursors were set at positions of 200 μm, 500 μm, and 800 μm in the vertical direction (X direction) and 200 μm, 400 μm, and 600 μm in the horizontal direction (Y direction). The values ​​of Ra, Rz, Rsm, and θa 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) were automatically calculated using the cross-sectional profile of VS-Viewer, and the average value (arithmetic mean) of the acquired values ​​was used as the measurement result.

[0093] (Nijimura's review) Observation of the nijimurae, assuming the use of polarized sunglasses, was carried out as follows. Backlight (brightness 5,000 cd / m 2 A sample for observation was prepared by arranging a first polarizer, an optical laminate of an embodiment or comparative example, and a second polarizer (assuming polarized sunglasses) in this order on a display equipped with a 300 mm diameter (approximately 1.5 mm thick). At this time, the absorption axis of the first polarizer was perpendicular to the vertical direction of the display, and the absorption axis of the second polarizer was perpendicular to the absorption axis of the first polarizer. In addition, the optical laminate was rotated 45° clockwise and then 45° (a rotation position of 90° from the reference rotation position) with the orientation in which the vertical direction of the display and the slow axis of the light-transmitting substrate of the optical laminate are parallel to each other as a reference rotation position (0°), and the rainbow marks at each orientation were visually observed. The observer observed the display from a position in front of the display 50 to 60 cm away and from a position obliquely inclined 45° to the left and right with respect to the normal direction when viewed from the front. The rainbow marks were evaluated based on the observation results according to the following criteria. -: The screen goes black, making it impossible to judge the rainbow pattern (not practical) ×: Rainbow spots occur, not practical △: Rainbow spots are observed, but not to the extent that they cause practical problems. ○: A small amount of rainbow spots are observed, but this does not affect the practical use. ◎: No rainbow marks (very good)

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

[0095] (Pencil hardness) The pencil hardness was evaluated according to 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 the change in appearance due to scratches was visually observed. The maximum hardness at which no scratches were observed was taken 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 of the examples and comparative examples, 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 respective examples and comparative examples.

[0099] [Table 6]

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

[0101] [Table 7]

[0102] Table 8 shows the evaluation results of the rainbow irregularities, bending resistance, and pencil hardness of the optical laminates according to each of the Examples and Comparative Examples.

[0103] [Table 8] The optical laminates according to Examples 1 to 16 all use a biaxially stretched PET film with an in-plane retardation Re of 2,000 to 7,500 nm as a light-transmitting substrate. Therefore, even when using polarized sunglasses, no blackout occurs regardless of the slow axis direction of the light-transmitting substrate, and rainbow irregularities are suppressed by the optical functional layer. In addition, since the optical laminates according to Examples 1 to 16 all use a biaxially stretched PET film, they have 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 a light-transmitting substrate, and therefore blackout occurs depending on the slow axis direction of the light-transmitting substrate, making it unsuitable for applications assuming the use of polarized sunglasses.

[0105] Moreover, both of the optical laminates according to Comparative Examples 2 and 3 were unable to suppress rainbow irregularities, and were not suitable for applications envisaged 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-transmissive substrate 2 Anti-glare layer 3 Low refractive index layer 10, 20 Optical laminate

Claims

1. An optical laminate for use in an image display device, A light-transmitting substrate made of a biaxially oriented polyethylene terephthalate film and having in-plane birefringence; 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, and 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 maximum height Rz of irregularities present on the surface of the optical functional layer is 0.410 μm or more and 2.982 μm or less, The internal haze of the optical laminate is 3.1% or more and 31.5% or less, The 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 light-transmitting substrate It 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 It 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 member according to claim 1, wherein the optical member is folded 180 degrees with the optical functional layer facing outward so that the distance between the opposing surfaces is 2 mm, and the folding test is repeated 200,000 times without breakage. Laminate.

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

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