Optical laminate and display device using same

Abstract

Provided are: an optical laminate which uses a biaxially stretched polyethylene terephthalate film as a base material, has bending resistance, and in which iris irregularities are suppressed; and an image display device which uses the optical laminate. This optical laminate is used in an image display device, and is provided with: a light-transmitting base material which is formed from a biaxially stretched polyethylene terephthalate film and which has in-plane birefringence; and an optical functional layer provided on one surface of the light-transmitting substrate, the total haze of the optical laminate being 5% or more, and the in-plane retardation Re of the light-transmitting substrate defined by formula (1): Re = (nx-ny) * d being 2,000 nm to 7,500 nm (inclusive). Here, nx is the refractive index in the slow axis direction, ny is the refractive index in the in-phase axis direction, and d is the thickness of the translucent substrate.

Description

Technical Field

[0001] The present invention relates to an optical layered body provided on the front side of an image display panel and a display device using the optical layered body. Background Art

[0002] In the past, triacetylcellulose (TAC) films, which have no in-plane phase difference and excellent visibility, were used as substrates for optical films placed on the surface of image display devices. However, TAC films have the problem of warping the image display device due to absorption of moisture from the air. Therefore, polyethylene terephthalate (PET) films, which absorb less moisture, have attracted much attention. In recent years, ultra-high retardation (ultra-high Re) PET films have sometimes been used (for example, see Patent Documents 1 and 2).

[0003] When viewing an image display device through a polarizing plate, such as a pair of polarized sunglasses, the vibration plane of light emitted from the image display device is perpendicular to the transmission axis of the polarizing plate, resulting in a so-called blackout phenomenon in which the image display device appears dimly visible. Patent Document 3, for example, describes a technique for addressing this blackout phenomenon, which sets the angle between the slow axis of an optical laminate and the absorption axis of a polarizer used in a liquid crystal display device to 45°±15°.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 5304939

[0007] Patent Document 2: Japanese Patent No. 6256385

[0008] Patent Document 3: Japanese Patent No. 6044118 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] When using ultra-high RePET film as a substrate, while the occurrence of blackout during use of polarized sunglasses can be suppressed by adjusting the slow axis angle, it suffers from poor folding resistance due to uniaxial stretching. On the other hand, biaxially stretched PET film significantly improves folding resistance, suppressing blackout regardless of the slow axis angle. However, there is a problem with noticeable iris unevenness caused by in-plane retardation.

[0011] Therefore, an object of the present invention is to provide an optical layered body using a biaxially stretched polyethylene terephthalate film as a substrate, having bending resistance and suppressed iris unevenness, and an image display device using the optical layered body.

[0012] Means for solving problems

[0013] The optical laminate according to the present invention comprises: a light-transmitting substrate composed of a biaxially stretched polyethylene terephthalate film and having birefringence in a plane; and an optical functional layer arranged on one surface of the light-transmitting substrate, wherein the total haze of the optical laminate is greater than 5%, and the in-plane retardation Re of the light-transmitting substrate defined by the following formula (1) is greater than 2,000 nm and less than 7,500 nm.

[0014] Re=(nx-ny)×d (1)

[0015] here,

[0016] nx: refractive index in the direction of the slow axis

[0017] ny: refractive index in the direction of the leading axis

[0018] d: thickness of the light-transmitting substrate.

[0019] An image display device according to the present invention includes an image display panel and the above-mentioned optical layered body.

[0020] Effects of the Invention

[0021] According to the present invention, it is possible to provide an optical layered body using a biaxially stretched polyethylene terephthalate film as a substrate, having bending resistance and suppressed iris unevenness, and an image display device using the optical layered body. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] [ Figure 1 ] is a schematic cross-sectional view showing an example of an optical layered body involved in an embodiment.

[0023] [ Figure 2 ] is a schematic cross-sectional view showing another example of the optical layered body involved in the embodiment.

[0024] Explanation of symbols

[0025] 1. Translucent substrate

[0026] 2 anti-glare layer

[0027] 3 low refractive index layer

[0028] 10, 20 optical laminates DETAILED DESCRIPTION

[0029] Figure 1 This is a schematic cross-sectional view showing an example of the optical layered body according to the embodiment.

[0030] The optical laminate 10 includes a light-transmitting substrate 1 and an anti-glare 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 by fine concavo-convex shapes on the surface of the anti-glare layer 2 or particles inside, thereby suppressing the entry of external light. Figure 1 In the described optical layered body 10 , the anti-glare layer 2 corresponds to the optical functional layer.

[0031] Figure 2 This is a schematic cross-sectional view showing another example of the optical film according to the embodiment.

[0032] The optical laminate 20 comprises a light-transmitting substrate 1, an anti-glare layer 2 laminated on one surface 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 lower refractive index than the anti-glare layer 2. The optical laminate 20 is an optical film (also called an "AGLR film") that suppresses the entry and reflection of external light by scattering and optical interference of incident light caused by fine concave-convex portions on the outermost surface or particles inside. Figure 2 In the described optical layered body 20 , the two layers of the anti-glare layer 2 and the low-refractive index layer 3 correspond to the optical functional layer.

[0033] The following describes each layer in detail.

[0034] The light-transmitting substrate is a transparent film serving as a base of the optical laminate. A biaxially stretched polyethylene terephthalate film having birefringence and having an in-plane retardation Re defined by the following formula (1) of 2,000 nm to 7,500 nm is used as the light-transmitting substrate.

[0035] Re=(nx-ny)×d (1)

[0036] here,

[0037] nx: The refractive index of the light-transmitting substrate in the slow axis direction (the direction with the largest refractive index)

[0038] ny: refractive index of the light-transmitting substrate in the direction of the leading axis

[0039] d: thickness of the light-transmitting substrate.

[0040] 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 thinner, which may reduce the handleability or the surface hardness of the optical layered body may be insufficient, which is not preferred. When the in-plane retardation Re of the light-transmitting substrate exceeds 7,500 nm, the thickness of the light-transmitting substrate becomes thicker, which increases the raw material cost or increases the total thickness of the optical layered body, which is not preferred.

[0041] As the light-transmitting substrate, it is preferable to use a substrate that satisfies the following condition (2).

[0042] (nx-ny)<0.06 (2)

[0043] When the value of nx-ny is 0.06 or more, mechanical properties, that is, resistance to cracks and ruptures, are reduced due to excessive stretching, which is not preferable.

[0044] As the light-transmitting substrate, it is preferable to use a light-transmitting substrate represented by the following formula (3) having a thickness-direction retardation Rth′ of 9,500 nm to 18,000 nm.

[0045] Rth'=(nx-nz)×d (3)

[0046] here,

[0047] nz: refractive index in the thickness direction.

[0048] 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 thinner, and the mechanical strength of the optical layered body may be insufficient, which is not preferred. Furthermore, when the thickness-direction retardation Rth' of the light-transmitting substrate exceeds 18,000 nm, the thickness of the light-transmitting substrate becomes larger, which is not conducive to thinning the optical layered body, which is not preferred.

[0049] Furthermore, as the light-transmitting substrate, it is preferable to use a substrate having a ratio Nz' represented by the following formula (4) of 1.5 or more and 5.5 or less.

[0050] Nz'=Rth' / Re (4)

[0051] When the ratio Nz' is within the above range, the birefringence and thickness of the light-transmitting substrate are within appropriate ranges, and both mechanical strength and suppression of iris unevenness can be achieved when configuring an optical layered body.

[0052] The thickness of the light-transmitting substrate 1 is not particularly limited, but is preferably 35 to 200 μm, more preferably 35 to 125 μm. To improve adhesion with other laminated layers, the surface of the light-transmitting substrate 1 may be subjected to a surface modification treatment. Examples of surface modification treatments include alkali treatment, corona treatment, plasma treatment, sputtering treatment, application of a surfactant or silane coupling agent, and Si vapor deposition.

[0053] The anti-glare layer 2 is a functional layer that forms the fine concavo-convex shape of the outermost surface of the optical layered body 10 .

[0054] The anti-glare layer 2 is formed by coating a coating liquid containing an active energy ray-curable compound and organic fine particles and / or inorganic fine particles (filler) on the light-transmitting substrate 1 and curing the coating film.

[0055] As the active energy ray-curable compound, for example, a monofunctional, bifunctional, or trifunctional or higher-functional (meth)acrylate monomer can be used. It should be noted that in this specification, "(meth)acrylate" is a general term for both acrylate and methacrylate, and "(meth)acryloyl" is a general term for both acryloyl and methacryloyl.

[0056] Examples of the monofunctional (meth)acrylate compound include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, glycidyl (meth)acrylate, acryloylmorpholine, N-vinylpyrrolidone, tetrahydrofurfuryl acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, and propylene glycol. Isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, hexadecyl (meth)acrylate, octadecyl (meth)acrylate, benzyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, ethyl carbitol (meth)acrylate, phosphoric acid (meth)acrylate, ethylene oxide modified phosphoric acid (meth)acrylate, phenoxy (meth)acrylate, ethylene oxide modified phenoxy (meth)acrylate, propylene oxide modified phenoxy (meth)acrylate 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 hydrogenated phthalate, 2-(meth)acryloyloxyethyl hydrogenated phthalate adamantane derivative mono(meth)acrylates such as 2-(meth)acryloyloxypropyl hexahydrophthalate, 2-(meth)acryloyloxypropyl tetrahydrophthalate, dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, and adamantane acrylate having a monovalent mono(meth)acrylate derived from 2-adamantane or adamantanediol.

[0057] Examples of bifunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, ethoxylated hexanediol di(meth)acrylate, propoxylated hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and di(meth)acrylates such as hydroxypivalate neopentyl glycol di(meth)acrylate.

[0058] Examples of trifunctional or higher-functional (meth)acrylates include trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, tris-2-hydroxyethyl isocyanurate tri(meth)acrylate, glycerol tri(meth)acrylate, and the like; trifunctional (meth)acrylates such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, ditrimethylolpropane tri(meth)acrylate, and the like. Acid ester compounds; polyfunctional (meth)acrylate compounds having three or more functions, such as pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, ditrimethylolpropane penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ditrimethylolpropane hexa(meth)acrylate; and polyfunctional (meth)acrylate compounds in which a part of these (meth)acrylates is substituted with an alkyl group or ε-caprolactone, etc.

[0059] In addition, urethane (meth)acrylates can also be used as polyfunctional monomers. Examples of urethane (meth)acrylates include urethane (meth)acrylates obtained by reacting an isocyanate monomer or prepolymer with a polyester polyol with a (meth)acrylate monomer having a hydroxyl group.

[0060] 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.

[0061] The polyfunctional monomers may be used alone or in combination of two or more. In addition, the polyfunctional monomers may be present in the coating solution as monomers or as partially polymerized oligomers.

[0062] Organic particles are materials that primarily form fine concavo-convex surfaces on the surface of the anti-glare layer 2, imparting the ability to diffuse external light. Resin particles made of light-transmitting resin materials such as acrylic resins, polystyrene resins, styrene-(meth)acrylate copolymers, polyethylene resins, epoxy resins, silicone resins, polyvinylidene fluoride, and polyvinyl fluoride resins can be used as organic particles. To adjust the refractive index or dispersion of the resin particles, two or more resin particles having different materials (refractive indices) can also be mixed and used. The average particle size of the organic particles is preferably 0.5 to 10 μm.

[0063] The inorganic fine particles added to the anti-glare layer-forming composition are preferably nanoparticles having an average particle diameter of 10 to 200 nm.

[0064] Inorganic particles are materials mainly used to regulate the sedimentation or aggregation of organic particles in the anti-glare layer 2. As inorganic particles, silica particles, metal oxide particles, various mineral particles, etc. can be used. As silica particles, for example, colloidal silica or silica particles surface-modified with reactive functional groups such as (meth) acryloyl groups can be used. As metal oxide particles, for example, aluminum oxide, zinc oxide, tin oxide, antimony oxide, indium oxide, titanium dioxide, zirconium oxide, etc. can be used. As mineral particles, for example, mica, synthetic mica, vermiculite, montmorillonite, iron montmorillonite, bentonite, beidellite, saponite, hectorite, stevensite, nontronite, magadiite, illite, kanemite, layered titanic acid, smectite, synthetic smectite, etc. can be used. The mineral particles can be any one of natural and synthetic (including substitutions and derivatives), or a mixture of the two can be used. Among the mineral particles, layered organic clay is more preferred. Layered organoclay refers to a material obtained by introducing organic onium ions between the layers of swelling clay. There is no restriction on the organic onium ions as long as they can be organized by utilizing the cation exchangeability of the swelling clay. As the mineral particles, when using layered organoclay minerals, the above-mentioned synthetic smectite can be suitably used. Synthetic smectite has the function of increasing the viscosity of the anti-glare layer-forming composition, suppressing the sedimentation of resin particles and inorganic particles, and regulating the surface unevenness of the optical functional layer.

[0065] In order to cure the anti-glare layer forming composition by ultraviolet irradiation, a polymerization initiator may also be added. As a polymerization initiator, a polymerization initiator that generates free radicals by ultraviolet irradiation may be used. As a polymerization initiator, free radical polymerization initiators such as acetophenones, benzophenones, thioxanthones, benzoin, benzoin methyl ether, and acylphosphine oxides may be used. As a polymerization initiator, for example, diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, bis (2,4,6-trimethylbenzoyl) phenyl phosphine 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, 2-chlorothioxanthone, etc. may be used. Among these, one may be used alone or in combination of two or more.

[0066] In addition, in the anti-glare layer forming composition, as a component to improve antifouling properties, an antifouling agent, a leveling agent, an oleophobic agent, a hydrophobic agent, or an anti-fingerprint adhesion agent can be added. As these additives, fluorine-containing compounds or organosilicon compounds can be suitably used. In addition, various additives such as antistatic agents, defoaming agents, antioxidants, ultraviolet absorbers, infrared absorbers, colorants, light stabilizers, inhibitors, and photosensitizers can also be added as needed.

[0067] Furthermore, a solvent may be added to the anti-glare layer-forming composition as needed. Examples of the solvent include one or a mixture of two or more of the following: alcohols such as methanol, ethanol, 1-propanol, 2-propanol, butanol, isopropanol, and isobutanol; ketones such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone; ketoalcohols 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 and dimethylformamide.

[0068] The low-refractive-index layer 3 is a functional layer having a refractive index lower than that of the anti-glare layer 2 thereunder and suppressing reflection by optical interference.

[0069] The low-refractive index layer 3 can be formed by coating a composition containing an active energy ray-curable compound on the surface of the anti-glare layer 2 and curing the coating. The low-refractive index layer 3 may contain low-refractive index fine particles for adjusting the refractive index.

[0070] As low-refractive-index microparticles, for example, microparticles such as LiF, MgF, 3NaF·AlF or AlF (all with a refractive index of 1.4), or Na3AlF6 (cryolite, with a refractive index of 1.33) can be suitably used; or silica microparticles with voids inside. Silica microparticles with voids inside can make the void portion have the refractive index of air (approximately 1), which is beneficial for lowering the refractive index of the low-refractive-index layer 3. Specifically, porous silica particles and silica particles with a shell structure can be used. It should be noted that low-refractive-index microparticles are not necessarily required. When the refractive index of the active energy ray-curable compound after curing is lower than the refractive index of the anti-glare layer 2, the low-refractive-index microparticles can be omitted.

[0071] As the active energy ray-curable compound, the polymerizable compound described in the anti-glare layer can be used. In addition, the above-mentioned polymerization initiator or solvent can be appropriately added to the low refractive index layer-forming composition.

[0072] In the low refractive index layer forming composition, as a component to improve antifouling properties, an antifouling agent, a leveling agent, an oleophobic agent, a hydrophobic agent, or an anti-fingerprint adhesion agent can be added. As these additives, fluorine-containing compounds or organosilicon compounds can be suitably used. In addition, as needed, various additives such as antistatic agents, defoaming agents, antioxidants, ultraviolet absorbers, infrared absorbers, colorants, light stabilizers, inhibitors, and photosensitizers can also be added.

[0073] Between the light-transmitting substrate 1 and the anti-glare 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, a color correction layer, etc. may also be stacked.

[0074] There is no particular limitation on the coating method of the anti-glare layer-forming composition and the low-refractive index layer-forming composition. For example, coating can be performed using a spin coater, a roll coater, a reverse roll coater, a gravure coater, a micro-gravure coater, an air knife coater, a rod coater, a wire rod coater, a die coater, a dip coater, a spray coater, an applicator, or the like.

[0075] Here, the details of the surface irregularities of the optical layered body according to the present embodiment will be described.

[0076] The optical layered body according to the present invention preferably has a total haze of 5% or greater. A total haze of 5% or greater allows sufficient diffusion of external light, suppressing iris unevenness from the light-transmitting substrate. A more preferred total haze is 22.0 to 71.6%. A total haze within this more preferred range is advantageous in suppressing iris unevenness.

[0077] The optical layered body according to the present invention preferably has a surface haze of 3% or greater. A surface haze of 3% or greater allows sufficient diffusion of external light, suppressing iris unevenness from the light-transmitting substrate. A surface haze of 12.0% to 68.6% is more preferred. A surface haze within this more preferred range is advantageous in suppressing iris unevenness.

[0078] The optical layered body according to the present invention preferably has an internal haze of 2% or greater. When the internal haze is 2% or greater, external light can be sufficiently diffused, thereby suppressing iris unevenness from the light-transmitting substrate. The internal haze is more preferably 3.1% to 55.6%. When the internal haze is within this more preferred range, it is advantageous to suppress iris unevenness.

[0079] In addition, the above-mentioned total haze, surface haze, and internal haze are values ​​measured in accordance with JIS K 7136.

[0080] In the optical layered body according to the present invention, the value of Δn×total haze is preferably 0.2 or greater (where Δn=nx-ny). A value of Δn×total haze of 0.2 or greater is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, within the above range, the value of Δn×total haze is more preferably 0.39 to 2.55, and the value of Δn×total haze is even more preferably 0.78 to 2.55.

[0081] In the optical layered body according to the present invention, the Re × total haze value is preferably 10,000 or greater. A Re × total haze value of 10,000 or greater is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, within the above range, the Re × total haze value is more preferably 19,725 to 301,028, and even more preferably 58,679 to 301,028.

[0082] In the optical layered body according to the present invention, the value of Δn×surface haze is preferably 0.12 or greater. A value of Δn×surface haze of 0.12 or greater is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, within the above range, the value of Δn×surface haze is more preferably 0.15 to 2.44, and the value of Δn×surface haze is even more preferably 0.37 to 2.44.

[0083] In the optical layered body according to the present invention, the Re × surface haze value is preferably 6,000 or greater. A Re × surface haze value of 6,000 or greater is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, 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.

[0084] In the optical layered body according to the present invention, the value of Δn × internal haze is preferably 0.08 or greater. A value of Δn × internal haze of 0.08 or greater is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, the value of Δn × internal haze is more preferably 0.11 to 1.98 within the above range.

[0085] In the optical layered body according to the present invention, the Re × internal haze value is preferably 4,000 or greater. A Re × internal haze value of 4,000 or greater is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, the Re × internal haze value is more preferably 8,268 to 207,991 within the above range.

[0086] In the optical laminate according to the present invention, the arithmetic mean roughness Ra of the optical functional layer surface is 0.04 μm or greater, and the average tilt angle θa of the concavities and convexities present on the optical functional layer surface is preferably 0.30° or greater. When the arithmetic mean roughness Ra and the average tilt angle θa are within the above ranges, external light can be sufficiently diffused, suppressing iris unevenness from the light-transmitting substrate. From the perspective of suppressing iris unevenness in the optical laminate, within the above ranges, the arithmetic mean roughness Ra is preferably 0.070 to 0.391 μm, and the average tilt angle θa is preferably 0.39 to 4.58°.

[0087] Furthermore, in the optical laminate according to the present invention, the maximum height Rz of the concavities and convexities present on the surface of the optically functional layer is preferably 0.2 μm or greater. When the maximum height Rz is 0.2 μm or greater, external light can be sufficiently diffused, thereby suppressing iris unevenness from the light-transmitting substrate. From the perspective of suppressing iris unevenness in the optical laminate, the maximum height Rz is more preferably 0.280 to 2.982 μm within the above range.

[0088] Furthermore, in the optical layered body according to the present invention, the value of Ra × Rsm is preferably 1.6 or greater. Here, Rsm is the average length of the profile curve elements. A value of Ra × Rsm of 1.6 or greater is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, the value of Ra × Rsm is more preferably 1.77 to 23.09 within the above range.

[0089] In the optical layered body according to the present invention, the value of Ra×θa is preferably 0.018 or greater. A value of Ra×θa of 0.018 or greater is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, the value of Ra×θa is more preferably 0.027 to 2.457 within the above range.

[0090] In the optical layered body according to the present invention, the value of Ra × Rsm × θa is preferably 1.6 or greater. A value of Ra × Rsm × θa of 1.6 or greater is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, the value of Ra × Rsm × θa is more preferably 1.79 to 105.78 within the above range.

[0091] In the optical layered body according to the present invention, the value of Δn×Ra is preferably 0.002 to 0.02. A value of Δn×Ra of 0.002 to 0.02 is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, within the above range, the value of Δn×Ra is more preferably 0.0025 to 0.0191.

[0092] In the optical layered body according to the present invention, the Re×Ra value is preferably 140 to 1,500. A Re×Ra value of 140 to 1,500 is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, within the above range, the Re×Ra value is more preferably 159 to 1,431.

[0093] In the optical layered body according to the present invention, the value of Δn×θa is preferably 0.01 to 0.17. A value of Δn×θa of 0.01 to 0.17 is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, within the above range, the value of Δn×θa is more preferably 0.014 to 0.163.

[0094] In the optical layered body according to the present invention, the Re×θa value is preferably 800 to 12,500. A Re×θa value of 800 to 12,500 is advantageous in suppressing iris unevenness in the optical layered body. From the perspective of suppressing iris unevenness in the optical layered body, within the above range, the Re×θa value is more preferably 886 to 12,218.

[0095] The optical laminate involved in this embodiment can be used to be attached to the outermost surface of an image display panel such as a liquid crystal panel or an organic EL panel to form an image display device. A touch panel can also be provided between the optical laminate and the image display panel. Since the optical laminate involved in this embodiment uses a biaxially stretched PET film as a light-transmitting substrate, it has excellent moisture permeability resistance and bending resistance. However, due to the light diffusion caused by the anti-glare layer, the iris unevenness from the biaxially stretched PET film is suppressed, making it suitable as an optical film provided on the outermost surface of the image display device. Since the optical laminate has bending resistance, it can also be used as an optical film used in a foldable image display device.

[0096] As described above, the optical laminate according to this embodiment comprises a biaxially stretched PET film having an in-plane retardation Re of 2,000 to 7,500 nm as a translucent substrate. While the use of biaxially stretched PET film can lead to noticeable iris unevenness, by controlling the overall optical properties (anti-glare or anti-reflection properties) of the optical laminate using an optical functional layer, the occurrence of iris unevenness can be suppressed. When using a biaxially stretched PET film having an in-plane retardation Re of less than 2,000, the surface hardness tends to decrease as the thickness of the translucent substrate is reduced. However, in this embodiment, by using a biaxially stretched PET film having an in-plane retardation Re of 2,000 to 7,500 nm, the required surface hardness of the optical laminate can be ensured. Furthermore, when using a PET film known as an ultra-high Re PET film as the translucent substrate, adjusting the angle of the slow axis of the translucent substrate can eliminate blackouts when using polarized sunglasses. However, since the ultra-high Re PET film is a uniaxially stretched film, it has the problem of poor folding resistance. In this embodiment, since the light-transmitting substrate is a biaxially stretched PET film, it has excellent bending resistance. This offers the advantage of eliminating blackouts regardless of the angle of the light-transmitting substrate's slow axis, even when viewing through a polarizing plate, such as polarized sunglasses. Specifically, the optical layered body of this embodiment eliminates both the problems associated with using a PET film with a low in-plane retardation Re (less than 2,000 nm) and the problems associated with using a PET film with a high in-plane retardation Re (exceeding 7,500 nm), making it suitable for use in image display devices that are viewed through a polarizing plate, such as polarized sunglasses.

[0097] Example

[0098] Hereinafter, embodiments for implementing the present invention will be described.

[0099] First, a method for producing a light-transmitting substrate will be described.

[0100] <Unstretched Film>

[0101] The material obtained by dissolving the polyethylene terephthalate raw material at 285°C was filtered with a stainless steel sintered filter material (nominal filtration accuracy: 95% retention of 10μm particles), stacked with two types of three-layer confluence blocks, extruded from the bayonet in sheet form, and then wound on a casting drum with a surface temperature of 30°C using an electrostatic casting method. It was cooled and solidified to obtain an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the three layers was 10:80:10. Then, the reverse roller method was used to make the coating amount after drying to be 0.08g / m 2 The adhesiveness-modifying coating liquid was applied to both sides of the unstretched PET film in a manner of 100° C. and then dried at 80° C. for 20 seconds.

[0102] Uniaxially stretched film

[0103] The unstretched film with the coating layer formed thereon was introduced into a tenter stretching machine. While gripping the film ends with clips, the film was introduced into a hot air zone at 125°C and stretched 4.0 times in the width direction. Subsequently, while maintaining the stretched width in the width direction, the film was treated at 225°C for 30 seconds, and further subjected to a 3% relaxation treatment in the width direction, resulting in a uniaxially stretched PET film with a thickness of 80 μm.

[0104] Biaxially stretched film

[0105] The unstretched film, with the coating layer formed thereon, was heated to 105°C using a heated roller set and an infrared heater. It was then stretched 2.6 times in the forward direction and 4.0 times in the width direction using a roller set with a peripheral speed difference, resulting in biaxially stretched PET films with thicknesses of 38, 50, 75, 125, and 188 μm. Separately, a biaxially stretched PET film with a thickness of 23 μm was obtained by stretching it 1.4 times in the forward direction and 4.0 times in the width direction.

[0106] Tables 1 to 4 below show the compositions of the anti-glare layer-forming coating solutions and the low-refractive-index layer-forming coating solutions used in the examples and comparative examples. It should be noted that each coating solution was diluted to a concentration suitable for coating using the solvents listed in Tables 1 to 4. In addition, the addition ratio of each component shown in Tables 1 to 4 is the ratio (mass %) of the total solid content of the coating solution. Here, the total solid content of the optically functional layer-forming coating solution refers to the components excluding the solvent. Therefore, the proportion (mass %) of the resin particles and inorganic microparticles in the total solid content of the optically functional layer-forming coating solution is equal to the proportion (mass %) of the resin particles and inorganic microparticles in the optically functional layer of the cured film of the optically functional layer-forming coating solution. "-" in Table 1 indicates that the corresponding material is not mixed.

[0107] [Table 1]

[0108]

[0109] [Table 2]

[0110]

[0111] [Table 3]

[0112]

[0113] [Table 4]

[0114]

[0115] The materials used in Tables 1 to 4 are as follows.

[0116] <Anti-glare layer (hard coat layer) forming coating liquid>

[0117] UV / EB curable resin

[0118] Lightweight acrylate PE-3A (pentaerythritol triacrylate), manufactured by Kyoeisha Chemical Co., Ltd.

[0119] Photopolymerization initiator

[0120] Omnirad (registered trademark) 184 (1-hydroxycyclohexyl-phenyl ketone), IGM Resins BV

[0121] Resin particles (organic spherical fillers)

[0122] (1) Acrylic acid / styrene copolymer, average particle size 3.5 μm, n = 1.515

[0123] (2) Acrylic acid / styrene copolymer, average particle size 3.5 μm, n = 1.565

[0124] (3) Acrylic acid / styrene copolymer, average particle size 3.5 μm, n = 1.555

[0125] (4) Polystyrene, average particle size 3.5 μm, n = 1.595

[0126] (5) Acrylic acid / styrene copolymer, average particle size 2.0 μm, n = 1.595

[0127] Amorphous silica particles

[0128] Average particle size 2.7 μm, n=1.45, Fuji silica Corporation

[0129] Leveling agent

[0130] F565, DIC Co., Ltd.

[0131] Nanoparticles (organic silica sol)

[0132] MEK-ST-40, Nissan Chemical Co., Ltd.

[0133] <Coating Liquid for Forming Low Refractive Index Layer>

[0134] Binder resin

[0135] Lightweight acrylate PE-3A (pentaerythritol triacrylate), Kyoeisha Chemical Co., Ltd.

[0136] Photopolymerization initiator

[0137] Omnirad (registered trademark) 184 (1-hydroxycyclohexyl-phenyl ketone), IGM Resins BV

[0138] Hollow silica (porous silica microparticle dispersion)

[0139] (1) Average particle size 60nm

[0140] (2) Average particle size 75nm

[0141] Leveling agent

[0142] RS-75, DIC Co., Ltd.

[0143] (Examples 1, 2, 7, 8, 11, Comparative Example 3)

[0144] An anti-glare layer-forming coating solution having the composition listed in Tables 1 to 4 was prepared and applied to the biaxially stretched PET film listed in Table 5. The coating film was dried and then polymerized and cured by irradiation with ultraviolet light to form an anti-glare layer. Next, a low-refractive-index layer-forming coating solution having the composition listed in Tables 1 to 4 was prepared and applied to the anti-glare layer. The coating film was dried and then polymerized and cured by irradiation with ultraviolet light to form a low-refractive-index layer. Through the above steps, an optical laminate (AGLR film) was obtained.

[0145] (Examples 3 to 6, 9, 10, 12 to 16, Comparative Examples 4 and 5)

[0146] An optical laminate (AG film) was obtained in the same manner as in Example 1, etc., except that the low-refractive-index layer was not formed on the anti-glare layer.

[0147] (Comparative Example 1)

[0148] A coating liquid for forming a hard coat layer having the composition shown in Table 4 was prepared and applied to the uniaxially stretched PET film shown in Table 5 so that the film thickness after curing was 5 μm. The coating film was dried and then polymerized and cured by irradiation with ultraviolet light to form a hard coat layer. An optical laminate (HC film) was obtained through the above steps.

[0149] (Comparative Example 2)

[0150] An optical layered body (HC film) was obtained in the same manner as in Comparative Example 1 except that the biaxially stretched PET film described in Table 5 was used as the light-transmitting substrate.

[0151] (Haze)

[0152] According to JIS K 7136, the haze value was measured using a haze meter (NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.). Here, the haze value of the optical laminate was set as the total haze. In addition, the internal haze of the optical laminate was obtained by subtracting the haze value of the transparent sheet with an adhesive from the haze value measured by attaching a transparent sheet with an adhesive to the surface of the optical functional layer of the optical laminate. It should be noted that, as the transparent sheet with an adhesive, a transparent sheet obtained by coating an acrylic adhesive (thickness 10 μm) on a polyethylene terephthalate film (thickness 38 μm) was used. In addition, the surface haze was calculated by the following formula.

[0153] Surface haze (%) = total haze (%) - internal haze (%)

[0154] (Delay)

[0155] The in-plane retardation and thickness direction retardation of the produced uniaxially or biaxially stretched PET film were measured using a retardation film / optical material inspection device (RETS-100, manufactured by Otsuka Electronics Co., Ltd.) The measurement conditions were as follows.

[0156] [Measurement conditions]

[0157] Delay measurement method: Polarimetry

[0158] Measuring point diameter: φ5mm

[0159] Tilt angle range: 0°

[0160] Measurement wavelength range: above 400nm and below 800nm

[0161] The value calculated from the average refractive index N of the light-transmitting substrate: nx, ny, and nz, using the formula N = (nx + ny + nz) / 3. In the case of a PET film, N = 1.660.

[0162] In addition, the in-plane retardation Re and the thickness direction retardation Rth' are values ​​at a wavelength of 589 nm.

[0163] [Surface shape analysis]

[0164] The surface roughness of the optically functional layer of each of the optical layered bodies in each Example and Comparative Example was measured using an optical interferometry method using a non-contact surface / layer cross-sectional shape measurement system (measurement device: Bart Scan R3300FL-Lite-AC, analysis software: VS-Viewer6, manufactured by MYOKA SYSTEMS Co., Ltd.). The measurement data were analyzed using the device's particle analysis software to measure the arithmetic mean roughness Ra, maximum height Rz, average length Rsm of the curve elements, and average tilt angle θa of the low refractive index layer surface.

[0165] The average concavity and convexity are generated under the cross-sectional profile (multi-line) analysis conditions in VS-Viewer. The arithmetic mean roughness Ra, maximum height Rz, average length Rsm of the curve elements, and average inclination angle θa, calculated from the cross-sectional profile averaged using the six measurement cursors, are defined as the arithmetic mean roughness Ra, maximum height Rz, average length Rsm of the curve elements, and average inclination angle θa of the concavity and convexity according to the present invention.

[0166] The measurement software of the device was used to perform the measurement under the following conditions, and an image file as the measurement result of the surface unevenness was obtained.

[0167] Optical conditions

[0168] Camera: Sony HR-50 1 / 3-inch

[0169] Objective lens: 10XDI (10 times)

[0170] Imaging lens (barrel): 0.5 times

[0171] Zoom lens: 1x

[0172] Light source / wavelength filter: 520nm

[0173] ND filter: Not used

[0174] A-Stop (aperture opening): Not used (fully open)

[0175] F-Stop (field of view aperture): Not used (fully open)

[0176] Measurement conditions

[0177] Measuring device: Piezoelectric

[0178] Measurement mode: Phase

[0179] Scanning speed: 4μm / s

[0180] Scanning range: -10~10μm

[0181] Effective pixels: 50%

[0182] Measurement area: 704.192 μm × 938.923 μm

[0183] The obtained image files were analyzed using the analysis software of the device under the following conditions.

[0184] Analysis conditions (VS-Viewer6)

[0185] Surface correction: 4 times

[0186] S filter: Automatic

[0187] L filter: Not used

[0188] Particle analysis conditions (VS-Viewer6)

[0189] Analysis type: convex analysis

[0190] Image correction: No

[0191] Height threshold: 0.1μm

[0192] Particle shaping: No

[0193] (Calculation method of Ra, Rz, Rsm and θa)

[0194] In an image obtained after applying surface correction (four times) and an S filter, the measurement cursors were set at 200μm, 500μm, and 800μm in the vertical (X) direction, and 200μm, 400μm, and 600μm in the horizontal (Y) direction. The Ra, Rz, Rsm, and θa values ​​at each cursor position (six locations, three sections parallel to the X direction and three sections parallel to the Y direction) were automatically calculated using the VS-Viewer cross-sectional profiler. The average (arithmetic mean) of these values ​​was used as the measurement result.

[0195] (Evaluation of iris unevenness)

[0196] The observation of iris unevenness was performed as follows, assuming the use of polarized sunglasses. 2 A sample for observation is prepared by sequentially arranging a first polarizer, an optical laminate of an embodiment or a comparative example, and a second polarizer (assuming polarized sunglasses) on a display (left and right). At this time, the absorption axis of the first polarizer is orthogonal to the up-down direction of the display, and the absorption axis of the second polarizer is orthogonal to the absorption axis of the first polarizer. In addition, the up-down direction of the display and the direction parallel to the lag axis of the light-transmitting substrate of the optical laminate are used as the reference rotation position (0°), the optical laminate is rotated 45° clockwise, and then rotated another 45° (rotation position 90° from the reference rotation position), and the iris unevenness at each orientation is visually observed. It should be noted that the observer observes from a front position 50 to 60 cm away from the display and from an inclined position 50 to 60 cm away from the display and inclined 45° to the left and right direction relative to the normal direction when observed from the front. Based on the observation results, the iris unevenness is evaluated according to the following criteria.

[0197] -: Black vision, cannot determine iris unevenness (not practical application)

[0198] ×: Iris unevenness occurs, so it cannot be used in practice.

[0199] △: Although iris unevenness occurs, it is not a problem in practical use.

[0200] ○: Although there is slight iris unevenness, it is not a problem in practical use.

[0201] ◎: No iris unevenness (very good)

[0202] (Bending resistance)

[0203] A planar unloaded U-shaped stretch test fixture (DMX-FS) was installed in a tabletop durability tester (manufactured by Yuasa System Instruments Co., Ltd.) and each sample was attached flatly. The samples were bent continuously with the optically functional layer facing outward and the distance between the opposing surfaces being 2 mm. After 50,000 and 200,000 consecutive bends, the presence of cracks in the bent sections was visually inspected and evaluated according to the following criteria.

[0204] ○: No breakage occurred at the bent portion in any of the continuous folding tests.

[0205] ×: The bent portion was broken in any of the continuous folding tests.

[0206] (Pencil hardness)

[0207] Pencil hardness was evaluated according to JIS K 5400-1900. The pencil hardness of the protective layer surface was measured using a pencil (uni, Mitsubishi Pencil Co., Ltd.) and a Clement scratch tester (HA-301, Tester Sangyo Co., Ltd.). The test was repeated while varying the pencil hardness. Changes in appearance due to scratches were visually observed, and the maximum hardness at which no scratches were observed was used as the evaluation value. A pencil hardness of H or higher was considered acceptable.

[0208] Table 5 shows the type, thickness, and optical properties such as retardation of the light-transmitting substrate in each of the Examples and Comparative Examples, together with the layer configuration of the optical layered body.

[0209] [Table 5]

[0210]

[0211] Table 6 shows measured values ​​and the like related to the surface roughness of the optical layered bodies according to each Example and each Comparative Example.

[0212] [Table 6]

[0213]

[0214] Table 7 shows measured values ​​and the like related to the haze of the optical layered bodies according to each Example and each Comparative Example.

[0215] [Table 7]

[0216]

[0217] Table 8 shows the evaluation results of iris unevenness, bending resistance, and pencil hardness of the optical layered bodies according to each Example and each Comparative Example.

[0218] [Table 8]

[0219]

[0220] The optical layered bodies of 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 used in polarized sunglasses, blackout vision is prevented regardless of the slow axis orientation of the light-transmitting substrate, and iris unevenness is suppressed by the optically functional layer. Furthermore, the use of biaxially stretched PET film in the optical layered bodies of Examples 1 to 16 resulted in excellent surface hardness and flex resistance.

[0221] In contrast, the optical layered body according to Comparative Example 1 uses a uniaxially stretched PET film having high in-plane retardation Re as a translucent substrate. Therefore, black vision occurs depending on the slow axis direction of the translucent substrate, making it unsuitable for applications such as polarized sunglasses.

[0222] Furthermore, the optical laminates according to Comparative Examples 2 and 3 were unable to suppress iris unevenness and were not suitable for applications where polarized sunglasses were envisioned.

[0223] The optical layered body according to Comparative Example 4 used a biaxially stretched PET film having an in-plane retardation Re of less than 2,000 nm. Therefore, although iris unevenness was suppressed, the pencil hardness was insufficient.

[0224] INDUSTRIAL APPLICABILITY The present invention can be used as an optical laminated body provided on the front side of an image display panel.

Claims

1. An optical laminate for an image display device, comprising: A light-transmitting substrate composed of a biaxially stretched polyethylene terephthalate film and having in-plane birefringence; and An optical functional layer is provided on one surface of the light-transmitting substrate, The total haze of the optical layered body is 5% or more, 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) here, nx: refractive index in the direction of the slow axis, ny: refractive index in the direction of the leading axis, d: thickness of the light-transmitting substrate.

2. The optical laminate according to claim 1, wherein The surface haze is 3% or more.

3. The optical laminate according to claim 1, wherein The internal haze is 2% or more.

4. The optical layered body according to claim 1, which satisfies the following condition (2): (nx-ny)<0.06 (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) here, nz: refractive index in the thickness direction. The optical layered body 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).

7. The optical layered body according to claim 1, wherein When a folding test in which the optical function layer was placed on the outside and the distance between the opposing surfaces was 2 mm was repeated 200,000 times, no breakage occurred.

8. An image display device comprising: Image display panel, and The optical laminate according to any one of claims 1 to 7 provided on the front surface of the image display panel.

Images