Optical laminate

Abstract

This optical laminate is characterized by comprising a support base material made of polyethylene terephthalate, and a protective layer detachably laminated on at least one surface of the support base material, and is characterized in that the film thickness of the protective layer is 1.0-5.0 µm, the Vickers hardness of the protective layer is 60-160, and the pure water contact angle of the protective layer on the detachment surface side is 50-85 degrees. The protective layer may exhibit a piercing force of 0.25 N or more, a piercing elongation of 1.0 mm or more, and a piercing elastic modulus of 0.15 N / mm or more.

Description

optical laminate

[0001] The present invention relates to an optical laminate in which a cured film that can be used as a protective film for a polarizing plate is peelably laminated.

[0002] A commonly used polarizing plate is one in which polarizer protective films are attached to both sides of a polarizer made of a polyvinyl alcohol (PVA) film and a dichroic dye such as iodine with a polyvinyl adhesive.

[0003]

[0003] Along with the recent trend toward thinner and lighter display devices, thinner polarizing plates and polarizer protective films used therein are also being demanded. Conventionally, as polarizer protective films, laminated films in which a functional layer of a hard coat layer is laminated on a transparent substrate such as a triacetyl cellulose (TAC) film have been used. However, in response to the demand for thinner polarizer protective films, efforts are being made to make the transparent substrate thinner.

[0004] The transparent substrate used in the polarizer protective film has a certain thickness, and there is a limit to how thin it can be made. Furthermore, as the transparent substrate is made thinner, it becomes difficult to obtain the various properties required for the polarizer protective film, such as hardness, durability, and ultraviolet absorbing function.

[0005] Therefore, as one method for thinning a polarizing plate, a technique of using a polarizer protective film that does not have a substrate such as a TAC film has been investigated (see, for example, Patent Documents 1 to 3). In Patent Documents 1 to 3, a laminate is produced in which a protective layer is releasably formed on one surface of a supporting substrate (release film), and the protective layer peeled from the supporting substrate is used as a polarizer protective film. In the case of such a substrate-less polarizer protective film, it is also possible to obtain desired functions by adding an additive to the protective layer formed on the supporting substrate.

[0006] International Publication No. 2019 / 054405 Japanese Patent Application Laid-Open No. 2018-169513 Japanese Patent Application Laid-Open No. 2017-65017

[0007] When a protective layer is peelably laminated on a supporting substrate, the wettability of the protective layer (peeling surface) after peeling may deteriorate, which may cause problems such as poor adhesion during the subsequent lamination process with other components.

[0008] Furthermore, in recent years, there has been an increasing demand for thinner and more flexible display devices, and even when the polarizer protective film is thinned to, for example, 1 to 5 μm, it is required that the film be able to have both hard coat properties and flexibility.

[0009] Therefore, an object of the present invention is to provide an optical laminate that has excellent wettability on the peeled surface of the protective layer even after peeling from the supporting substrate, and that has good hard coat properties and flexibility even when the protective layer is made thin.

[0010] The optical laminate of the present invention comprises a support substrate made of polyethylene terephthalate and a protective layer peelably laminated on at least one surface of the support substrate, and is characterized in that the protective layer has a film thickness of 1.0 μm or more and 5.0 μm or less, a Vickers hardness of 60 or more and 160 or less, and a pure water contact angle of the peelable surface side of the protective layer of 50 degrees or more and 85 degrees or less.

[0011] According to the present invention, an optical laminate can be provided which has excellent wettability on the peeled surface of the protective layer even after peeling from the supporting substrate, and has good hard coat properties and flexibility even when the protective layer is made thin.

[0012] Schematic cross-sectional view of an optical laminate according to an embodiment.

[0013] FIG. 1 is a schematic cross-sectional view of an optical laminate according to an embodiment.

[0014] The optical laminate 1 has a support substrate 2 and a protective layer 3 laminated on one surface of the support substrate 2. In the following description, of the two surfaces of the protective layer 3, the surface that forms an interface with air in the optical laminate 1 (the upper surface in FIG. 1 ) will be referred to as the "air surface," and the surface that contacts the support substrate 2 in the optical laminate 1 (the lower surface in FIG. 1 ) will be referred to as the "release surface."

[0015] The support substrate 2 is a film that serves as a support when forming the protective layer 3 used as a protective film for a polarizer. A polyethylene terephthalate (PET) film is preferably used as the support substrate 2 due to its excellent heat resistance and mechanical strength. It is preferable that one surface of the support substrate 2 (the surface on which the protective layer 3 is laminated) has an arithmetic mean roughness Ra of 20 nm or less and a maximum height Rz of 100 nm or less. When the arithmetic mean roughness Ra and maximum height Rz of one surface of the support substrate 2 are within these ranges, the pure water contact angle of the release surface of the protective layer 3 can be set within the preferred range described below, thereby improving adhesion to the polarizer and other films. It is also possible to use resin films other than PET as the support substrate 2, as long as the film has a surface with an arithmetic mean roughness Ra and maximum height Rz within the above ranges. The thickness of the support substrate 2 is preferably 75 μm or more. If the thickness of the support substrate 2 is less than 75 μm, the hardness of the protective layer 3 in the indentation direction before peeling it off from the support substrate 2 may be insufficient, which is undesirable as it may reduce the storage stability of the optical laminate 1. However, if sufficient hardness can be ensured by adjusting the composition of the protective layer 3, the thickness may be less than 75 μm, for example, 50 μm or more. There is no particular upper limit on the thickness of the support substrate 2, but an excessively thick thickness increases material costs, so it is preferably 125 μm or less.

[0016] The pure water contact angle of one surface of the supporting substrate 2 (the surface on which the protective layer 3 is laminated) is preferably 50 degrees or more and 95 degrees or less. The hexadecane contact angle is preferably 1 degree or more and 30 degrees or less. The diiodomethane contact angle is preferably 3 degrees or more and 63 degrees or less. When the contact angles of the above solvents of the supporting substrate 2 are within these ranges, the wettability of the supporting substrate 2 is improved, the coatability of the protective layer-forming coating liquid described below is improved, and the releasability of the protective layer 3 is improved.

[0017] The surface free energy of one surface of the support substrate 2 (the surface on which the protective layer 3 is laminated) is 30 mJ / m ２ 85mJ / m or more ２ The surface free energy of the supporting substrate 2 is preferably 30 mJ / m or less. ２If the amount is more than 32 mJ / m, the wettability will be good and the coatability of the coating liquid for forming the protective layer described below will be improved, which is preferable. ２ More preferably, it is 85 mJ / m or more. ２ If the thickness is less than this, zipping or tearing is less likely to occur when peeling off the protective layer 3, which is preferable. The surface free energy can be calculated for three types of solvents (water, hexadecane, and diiodomethane) using the known surface free energy and contact angle of each solvent.

[0018] The protective layer 3 is a thin film releasably laminated on one surface of the support substrate 2, and is used as a protective film for a polarizer after being peeled off from the support substrate 2. The thickness of the protective layer 3 is preferably 1.0 μm or more and 5.0 μm or less, with examples of lower limits being 1.0 μm or more, 1.5 μm or more, or 2.0 μm or more, and examples of upper limits being 5.0 μm or less and 4.0 μm or less. If the thickness of the protective layer 3 is less than 1.0 μm, when the protective layer 3 is used alone as a protective film for a polarizer, the hard coat properties required of the protective film may be insufficient, and zipping, tearing, and the like may occur upon peeling due to insufficient strength. If the thickness of the protective layer 3 exceeds 5.0 μm, this is undesirable because it is disadvantageous for making polarizing plates and image display devices thinner and tends to reduce bending resistance.

[0019] In a state in which the protective layer 3 is peeled from the support substrate 2, the pure water contact angle of the peeled surface of the protective layer 3 is preferably 50 degrees or more and 85 degrees or less, with examples of lower limits being 50 degrees or more, 53 degrees or more, or 59 degrees or more, and examples of upper limits being 85 degrees or less, 83 degrees or less, or 79 degrees or less. The pure water contact angle of the air surface of the protective layer 3 is preferably 50 degrees or more and 85 degrees or less, and may be 53 degrees or more and 83 degrees or less. When the pure water contact angles of the peeled surface and air surface of the protective layer 3 are within these ranges, the wettability of each surface is good, and the adhesiveness is good in a subsequent step of laminating the protective layer 3 to another film or the like, and adhesive defects can be reduced, so that improvements in quality and yield rate can be expected.

[0020] Since the protective layer 3 has excellent hard coat properties even when thinned as described above, the piercing force is preferably 0.25 N or more, and more preferably 0.30 N or more. The upper limit is not particularly limited, but from the viewpoint of excellent hardness in the direction perpendicular to the protective layer surface, examples include 1.00 N or less, 0.70 N or less, and 0.50 N or less. Since the protective layer 3 exhibits flexibility, the piercing elongation is preferably 1.0 mm or more, more preferably 1.4 mm or more, and even more preferably 1.5 mm or more. The upper limit is not particularly limited, but from the viewpoint of achieving both flexibility and strength, examples include 5.0 mm or less, 4.0 mm or less, 3.0 mm or less, 2.0 mm or less, and 1.7 mm or less. Furthermore, from the viewpoint of achieving both hard coat properties and flexibility and improving releasability, the protective layer 3 preferably has a puncture modulus of 0.15 N / mm or more, more preferably 0.16 N / mm or more, even more preferably 0.18 N / mm or more, and even more preferably 0.20 N / mm or more. There are no particular limitations on the upper limit, but examples include 0.50 N / mm or less, 0.40 N / mm or less, and 0.30 N / mm or less. In this specification, the puncture force, puncture elongation, and puncture modulus can be evaluated in accordance with JIS Z 1707 using a universal testing machine (STB-1225L, A&D).

[0021] The protective layer 3 can be formed by applying a coating liquid containing an ultraviolet-curable compound, a photopolymerization initiator, and a solvent onto the supporting substrate 2, drying the coating, and then curing the coating film by ultraviolet irradiation. The protective layer 3 is a layer having hard coat properties necessary for a protective film, and can typically be formed as a hard coat layer.

[0022] As the ultraviolet-curable compound, for example, a monofunctional, difunctional, trifunctional or higher functional (meth)acrylate monomer can be used. In this specification, "(meth)acrylate" is a general term for both acrylate and methacrylate, and "(meth)acryloyl" is a general term for both acryloyl and methacryloyl.

[0023] Examples of monofunctional (meth)acrylate compounds include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 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 Side-modified phenoxy (meth)acrylate, b-phenol (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,adamantane derivative mono(meth)acrylates such as adamantyl acrylate having a monovalent mono(meth)acrylate derived from adamantanediol, etc.

[0024] Examples of bifunctional (meth)acrylates include di(meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene 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.

[0025] Examples of tri- or higher functional (meth)acrylates include tri(meth)acrylates such as trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, tris-2-hydroxyethyl isocyanurate tri(meth)acrylate, and glycerin tri(meth)acrylate; trifunctional (meth)acrylate compounds such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and ditrimethylolpropane tri(meth)acrylate;

[0033] Examples of the polyfunctional (meth)acrylate include tri- or higher functional (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.

[0026] Urethane (meth)acrylates can also be used as polyfunctional monomers. Examples of urethane (meth)acrylates include those obtained by reacting a polyester polyol with an isocyanate monomer or a prepolymer, and then reacting the resulting product with a (meth)acrylate monomer having a hydroxyl group.

[0027] Examples of urethane (meth)acrylates include pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer, and dipentaerythritol pentaacrylate isophorone diisocyanate urethane prepolymer.

[0028] The ultraviolet-curable compound may be a (meth)acrylate having an alicyclic structure. Examples of the (meth)acrylate having an alicyclic structure include (meth)acrylates having one or more of a cyclopentane structure, a dicyclopentane structure, a cyclohexane structure, a cyclodecane structure, a tricyclodecane structure, an isobornyl structure, and an adamantane structure. Adding these compounds to the coating liquid for forming the protective layer can impart hydrophobicity to the protective layer 3, thereby reducing the moisture permeability required for the protective film of a polarizer.

[0029] Specific examples of (meth)acrylates containing an alicyclic structure include cyclohexyl (meth)acrylate, cyclohexanedimethanol mono(meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexanol (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentadienyl (meth)acrylate. monofunctional (meth)acrylates such as cyclohexanedimethanol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, 2-dicyclopentenoxyethyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, bornyl (meth)acrylate, isobornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, tricyclodecane dimethanol mono(meth)acrylate, and adamantyl (meth)acrylate; Pentenyl di(meth)acrylate, dicyclopentadienyl di(meth)acrylate, bornyl di(meth)acrylate, isobornyl di(meth)acrylate, tricyclodecanyl di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, adamantyl di(meth)acrylate, adamantane dimethanol di(meth)acrylate, adamantane diethanol di(meth)acrylate, dimethylol dicyclopentane di(meth)acrylate, norbornyl dimethacrylate, and polyfunctional (meth)acrylates such as nandimethylol di(meth)acrylate, cyclohexanetrimethanol tri(meth)acrylate, adamantyl tri(meth)acrylate, adamantanetrimethanol tri(meth)acrylate, norbornanetrimethylol tri(meth)acrylate, tricyclodecanetrimethanol tri(meth)acrylate, perhydro-1,4,5,8-dimethanonaphthalene-2,3,7-(oxymethyl)tri(meth)acrylate, etc. These (meth)acrylates containing an alicyclic structure may be used alone or in combination of two or more.

[0030] The ultraviolet-curable compound may be used alone or in combination of two or more kinds. In addition, the ultraviolet-curable compound may be a monomer in the composition, or may be a partially polymerized oligomer.

[0031] The double bond equivalent of the UV-curable compound is preferably 90 g / mol or more and 140 g / mol or less, with lower limits such as 90 g / mol or more, 99 g / mol or more, and 109 g / mol or more, and upper limits such as 140 g / mol or less and 138 g / mol or less. When the double bond equivalent of the UV-curable compound is within this range, the hardness and flexibility of the cured protective layer 3 can be achieved, and the peelability from the support substrate 2 is also good. When the double bond equivalent of the UV-curable compound is outside the above range, the adhesion strength between the protective layer 3 and the support substrate 2 increases, which is undesirable because the peelability deteriorates. Furthermore, when the double bond equivalent of the UV-curable compound is less than 90 g / mol, the number of polymerizable double bonds relative to the mass of the UV-curable compound increases, and therefore the hardness of the protective layer 3 increases but the bending resistance deteriorates, making it unsuitable for use in a bendable display device. If the double bond equivalent of the ultraviolet curable compound exceeds 140 g / mol, the curability of the protective layer 3 may decrease, and the surface hardness and scratch resistance may deteriorate.

[0032] Examples of the photopolymerization initiator that can be used include radical polymerization initiators such as acetophenones, benzophenones, thioxanthones, benzoin, benzoin methyl ether, and acylphosphine oxides. Examples of the photopolymerization initiator that can be used include 2,4,6-trimethylbenzoyl-diphenylphosphine 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, 2-chlorothioxanthone, 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropan-1-one, and 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone. One of these may be used alone, or two or more may be used in combination.

[0033] The amount of the photopolymerization initiator is preferably 3.0% by mass or more and 6.0% by mass or less of the protective layer-forming coating liquid, with the lower limit being 3.0% by mass or more and 3.6% by mass or more, and the upper limit being 6.0% by mass or less and 5.2% by mass or less. If the amount of the photopolymerization initiator is less than 3.0% by mass of the protective layer-forming coating liquid, the peel strength of the protective layer 3 from the support substrate 2 may increase, resulting in poor peelability, which is not preferred. If the amount of the photopolymerization initiator is more than 6.0% by mass of the protective layer-forming coating liquid, the solubility of the photopolymerization initiator may deteriorate, which is not preferred. Based on the total solids content of the protective layer-forming coating liquid, the amount of the photopolymerization initiator is preferably 9.0% by mass or more and 13.0% by mass or less of the total solids content.

[0034] Examples of the solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, butanol, isopropyl alcohol, and isobutanol; ketones such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone; ketone alcohols such as diacetone alcohol; aromatic hydrocarbons such as benzene, toluene, and xylene; glycols such as ethylene glycol, propylene glycol, and hexylene glycol; glycol ethers such as ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, diethyl cellosolve, diethyl carbitol, and propylene glycol monomethyl ether; esters such as dimethyl carbonate, methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, butyl acetate, and amyl acetate; ethers such as dimethyl ether and diethyl ether; and N-methylpyrrolidone and dimethylformamide. These may be used alone or in combination.

[0035] Inorganic fine particles may be added to the coating solution for forming the protective layer in order to improve the mechanical strength and surface strength (pencil strength) of the protective layer 3. Examples of inorganic fine particles include silica fine particles (SiO ２ ) and metal oxide fine particles can be used. Examples of metal oxide fine particles include antimony-doped tin oxide (ATO), phosphorus-doped tin oxide (PTO), gallium-doped tin oxide (GTO), zirconia (ZrO ２ ) and titania (TiO ２ ) can be used alone or in combination of two or more. The inorganic fine particles may be surface-modified by bonding with a silane coupling agent. As the silane coupling agent, those having one or more of a vinyl group, an acryloyl group, and a methacryloyl group as a functional group can be used.

[0036] In addition, various additives such as antistatic agents, antifoaming agents, antioxidants, ultraviolet absorbers, infrared absorbers, colorants, light stabilizers, polymerization inhibitors, photosensitizers, antifouling agents, leveling agents, oil repellents, water repellents, and fingerprint inhibitors may be added to the coating liquid for forming the protective layer as needed. By adding these additives appropriately, various functions can be imparted to the protective layer 3. Furthermore, in order to improve the hydrophobicity of the protective layer 3, a hydrophobic material such as a cycloolefin polymer may be blended therein.

[0037] The method for applying the coating liquid for forming the protective layer is not particularly limited, and the coating can be performed using, for example, 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.

[0038] The cumulative amount of ultraviolet light when curing the protective layer 3 is 60 mJ / cm ２ More than 300mJ / cm ２ It is preferable that the integrated amount of ultraviolet light is 60 mJ / cm or less. ２ If it is less than this, the peel strength of the protective layer 3 may become high.

[0039] The peel force when peeling the protective layer 3 from the supporting substrate 2 after the formation of the optical laminate 1 is preferably 0.030 N / 25 mm or more and 0.150 N / 25 mm or less. From the viewpoint of excellent releasability, it may be 0.030 N / 25 mm or more and 0.100 N / 25 mm or less. The peel force is a value measured by a 180° peel test in accordance with JIS K 6854-2. When the peel force when peeling the protective layer 3 from the supporting substrate 2 is within this range, it is possible to reduce defects such as tearing or zipping during peeling, or inability to peel.

[0040] The Vickers hardness of the protective layer 3 in the optical laminate 1 is preferably 60 or more and 160 or less, with the lower limit being 60 or more, 61 or more, and the upper limit being 160 or less, 150 or less, 140 or less, 130 or less, 120 or less, 113 or less, etc. The Vickers hardness is a value measured in accordance with ISO 14577. When the Vickers hardness is within this range, the surface hardness required for the protective film of a polarizer can be obtained.

[0041] The protective layer 3 of the optical laminate 1 according to this embodiment can be used as a protective film for a polarizer in a state where it is peeled from the support substrate 2. The surface that forms the interface with the polarizer may be either the air surface or the peel surface, but it is preferable that the air surface be the interface with the polarizer. The polarizer and the protective layer 3 may be bonded together using an adhesive. Alternatively, a polarizer that is in close contact with the protective layer 3 may be formed by applying a coating liquid of a PVA resin containing a dichroic dye onto the protective layer 3. The other surface of the protective layer 3 may be bonded to another member such as a resin film or a retardation plate via an adhesive or the like. The protective layer 3 may be peeled from the support substrate 2 before or after bonding to the polarizer.

[0042] As described above, the optical laminate 1 according to this embodiment comprises a supporting substrate 2 made of polyethylene terephthalate and a protective layer 3 releasably laminated on at least one surface of the supporting substrate 2, the protective layer 3 having a film thickness of 1.0 μm or more and 5.0 μm or less, a Vickers hardness of 60 or more and 160 or less, and a pure water contact angle of 50 degrees or more and 85 degrees or less on the release surface side of the protective layer 3. According to this embodiment, the release surface of the protective layer 3 has excellent wettability even after being peeled from the supporting substrate 2, and an optical laminate 1 having good hard coat properties and flexibility can be realized even when the protective layer 3 is thinned to a thickness of 1.0 to 5.0 μm.

[0043] Another optical laminate 1 according to this embodiment includes a supporting substrate 2 made of polyethylene terephthalate and a protective layer 3 releasably laminated on at least one surface of the supporting substrate 2, the protective layer 3 having a film thickness of 1.0 μm or more and 5.0 μm or less, a piercing force of 0.25 N or more, a piercing elongation of 1.0 mm or more, a piercing elastic modulus of 0.15 N / mm or more, and a pure water contact angle of 50 degrees or more and 85 degrees or less on the peeled surface side of the protective layer 3. According to this embodiment, the peeled surface of the protective layer 3 has excellent wettability even after being peeled from the supporting substrate 2, and an optical laminate 1 having good hard coat properties and flexibility can be realized even when the protective layer 3 is thinned to a thickness of 1.0 to 5.0 μm.

[0044] Examples of specific implementations of the present invention will be described below.

[0045] Example 1 A coating solution for forming a protective layer having the composition shown in Table 1 was prepared and applied to one side of a 75 μm-thick PET substrate (T60, Toray Industries, Inc.) by a bar coating method so that the cured film thickness was 2.0 μm, and then dried at 70° C. for 30 seconds. After drying, a metal halide lamp was used to apply the coating to the cured film, with an integrated light intensity of 122 mJ / cm. ２ The coating film was cured by irradiating it with ultraviolet light so that the protective layer was formed on the supporting substrate, thereby obtaining an optical laminate having the protective layer laminated on the supporting substrate.

[0046] Examples 2 to 5 Optical laminates were obtained under the same conditions as in Example 1, except that the composition of the coating liquid for forming a protective layer was changed as shown in Table 1.

[0047] Example 6 An optical layered body was obtained under the same conditions as in Example 1, except that the coating liquid was applied so that the cured thickness of the protective layer became 4.0 μm.

[0048] Example 7 An optical layered body was obtained under the same conditions as in Example 1, except that the coating liquid was applied so that the cured thickness of the protective layer became 1.5 μm.

[0049] (Example 8) An optical laminate was obtained under the same conditions as in Example 1, except that a 50 μm thick PET substrate (O324H50[H39E], Mitsubishi Chemical Corporation) having the surface roughness and surface free energy shown in Table 2 was used and the composition of the coating liquid for forming a protective layer was changed as shown in Table 2.

[0050] (Comparative Example 1) An optical laminate was obtained under the same conditions as in Example 1, except that a PET substrate (S100H, thickness 23 μm, Mitsubishi Chemical Corporation) having the surface roughness and surface free energy shown in Table 3 was used as the supporting substrate.

[0051] Comparative Examples 2 to 5 Optical laminates were obtained under the same conditions as in Example 1, except that the composition of the coating liquid for forming a protective layer was changed as shown in Table 3.

[0052] Comparative Example 6 An optical layered body was obtained under the same conditions as in Example 1, except that the coating liquid was applied so that the cured thickness of the protective layer became 7.0 μm.

[0053] Comparative Example 7 An optical layered body was obtained under the same conditions as in Example 1, except that the coating liquid was applied so that the cured thickness of the protective layer was 0.9 μm.

[0054] (Comparative Example 8) An optical laminate was obtained under the same conditions as in Example 1, except that a 38 μm thick PET substrate (manufactured by Toray, 38-SY) having the surface roughness and surface free energy shown in Table 4 was used as the supporting substrate.

[0055] (Comparative Example 9) An optical laminate was obtained under the same conditions as in Example 1, except that a 75 μm thick PET substrate (Toyobo, TN200) having the surface roughness and surface free energy shown in Table 4 was used as the supporting substrate.

[0056] Comparative Example 10 An optical layered body was obtained under the same conditions as in Example 1, except that the composition of the coating liquid for forming a protective layer was changed as shown in Table 4.

[0057] Details of the compounds shown in Tables 1 to 4 are shown below. 1. UV-curable compounds (monomers) (1) NK Ester A-TMM-3L (trade name), Shin-Nakamura Chemical Co., Ltd., pentaerythritol triacrylate and pentaerythritol tetraacrylate (2) Light Acrylate (registered trademark) 3EG-A (trade name), Kyoeisha Chemical Co., Ltd., triethylene glycol diacrylate (3) Light Acrylate 9EG-A (trade name), Kyoeisha Chemical Co., Ltd., PEG400 diacrylate (4) Light Acrylate DPE-6A (trade name), Kyoeisha Chemical Co., Ltd., dipentaerythritol hexaacrylate

[0058] 2. Photopolymerization initiators (1) Omnirad® 184 (trade name), IGM Resins B.V., 1-hydroxycyclohexyl-phenyl ketone (2) Omnirad TPO (trade name), IGM Resins B.V., 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (3) Omnirad 127 (trade name), IGM Resins B.V., 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropan-1-one (4) Omnirad 369 (trade name), IGM Resins B.V., 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone

[0059] 3. Additives (1) GRANDIC PC4300, manufactured by DIC Corporation, leveling agent (2) BYK-3566, manufactured by BYK Corporation, leveling agent

[0060] 4. Solvents (1) Dimethyl carbonate (2) MIBK (methyl isobutyl ketone)

[0061] The optical laminates according to the examples and comparative examples were evaluated by the following methods.

[0062] [Arithmetic Average Roughness Ra, Maximum Height Rz] The surface shape of the evaluation surface (the surface on which the protective layer is laminated) was observed using a white light interference microscope (ECLIPSE LV150N, Nikon Corporation), and average Ra and Rz were calculated from the surface shape data at six points.

[0063] [Peel Force] A 180° peel test was performed in accordance with JIS K 6854-2 to measure the peel force. Specifically, a measurement sample was prepared by attaching a protective layer of an optical laminate to a glass plate using adhesive tape (TD06A, Tomoegawa Paper Co., Ltd.), and the load was measured using a Tensilon single-column material testing machine (STB-1225L, A&D Co., Ltd.) under conditions of a load cell of 50 N and a peel rate of 500 mm / min, while pulling the support substrate in a 180° direction to peel it from the protective layer. The peel force was calculated from the peel curve (load-displacement) obtained by the measurement.

[0064] [Pure Water Contact Angle of Protective Layer] A contact angle meter (Drop Master 300, Kyowa Interface Science Co., Ltd.) was used, and the measurement value was taken 5 seconds after pure water was dropped onto the measurement surface. The pure water contact angle of the air surface of the protective layer was measured without peeling the protective layer from the support substrate. The peeled surface was measured in a state where the protective layer of the optical laminate was attached to a glass plate with adhesive tape (TD06A, Tomoegawa Paper Co., Ltd.), and then the support substrate was peeled from the protective layer, and the protective layer was attached to the glass plate via the adhesive tape.

[0065] [Pencil Hardness] Pencil hardness was evaluated in accordance with JIS K5400-1900. The pencil hardness of the protective layer surface was measured using a pencil (uni, Mitsubishi Pencil Co., Ltd.) and a Clemens scratch tester (HA-301, Tester Sangyo Co., Ltd.). The test was repeated while changing the pencil hardness, and changes in appearance due to scratches were visually observed. The maximum hardness at which no scratches were observed was taken as the evaluation value. A pencil hardness of F or higher was considered to be acceptable. In Tables 1 to 4, "<B" indicates that the pencil hardness is lower than B, and ">H" indicates that the pencil hardness is higher than H.

[0066] [Abrasion Resistance] A sample of 50 mm × 170 mm cut from the optical laminate was fixed to a base with cellophane tape on the top and bottom. A 20 mm × 20 mm piece of steel wool (Bonstar #0000) was placed in contact with the air surface of the protective layer, and scratches of 80 mm or more were made with a test load of 1,000 g / 4 cm. ２ After the sample was rubbed with a pressure of 10 times, the number of scratches occurring within the central 30 mm of the scratch length direction was visually counted. A sample with 10 or fewer scratches was rated as passing.

[0067] [Flexibility (Mandrel Test)] Flexibility was evaluated by a mandrel test in accordance with JIS K 5600-1. A sample of the optical laminate was wrapped around a metal cylinder with a diameter of 1 mm to 3 mm with the protective layer facing outward, and the diameter of the smallest cylinder at which no cracks occurred in the protective layer was used as the evaluation value. A minimum cylinder diameter of 2 mm or less was considered to be acceptable.

[0068] [Vickers Hardness] Vickers hardness was measured using a microhardness tester (Fisherscope HM2000, Fisher Instruments) by a microindentation test in accordance with ISO 14577 (nanoindentation method). A Vickers indenter HM2000 023 was used as the measuring indenter, and the measuring indenter was brought into contact with the air surface of the protective layer supported on the supporting substrate, and the measurement was performed under the conditions of a maximum load of 1 mN (reaching 1 mN in 5 seconds) and a holding time of 1 second.

[0069] [Bending Test] A sheet-shaped no-load U-shaped expansion and contraction test jig (DMX-FS) was attached to a tabletop durability tester (Yuasa System Co., Ltd.), and samples of the optical laminates according to each Example and Comparative Example were attached flat. When folded with the protective layer facing outward, the samples were folded continuously so that the distance between the opposing protective layers was 4 mm. The folding operation was performed once per second, and the number of times until cracks appeared in the protective layer was used as the evaluation value. A folding number of 200,000 or more was considered to be pass.

[0070] [Contact Angle of Support Substrate] A contact angle meter (Drop Master 300, Kyowa Interface Science Co., Ltd.) was used, and the measured value was taken 5 seconds after each solvent (pure water, hexadecane, diiodomethane) was dropped onto the measurement surface.

[0071] [Surface Free Energy of Support Substrate] Equation (3) was derived from the following equations (1) and (2), and the contact angles of the solvents (pure water, hexadecane, diiodomethane) determined above were introduced into equation (3) to calculate the surface free energy using simultaneous linear equations with three unknowns.

[0072]

[0073] [Puncture Strength (Puncture Test)] Evaluation was performed using a universal testing machine (STB-1225L, A&D) in accordance with JIS Z 1707. The protective layer was transferred to a mount with a hole of 10 mm diameter, and the portion overlapping the hole was pierced vertically with a needle (a semicircular needle with a diameter of 1.0 mm and a tip radius of 0.5 mm) at a speed of 50 mm / min to determine the piercing force (N) and piercing elongation (mm). The piercing elastic modulus (N / mm) was calculated by dividing the piercing force by the piercing elongation, and the average value calculated from five measurements was used as the evaluation value. A piercing force of 0.25 N or more, a piercing elongation of 1.0 mm or more, and a piercing elastic modulus of 0.15 N / mm or more was considered to be acceptable.

[0074] Tables 1 to 4 show the configurations (coating liquid compositions) of the optical laminates according to the examples and comparative examples, together with the evaluation results.

[0075]

[0076]

[0077]

[0078]

[0079] As shown in Table 1, all of the optical laminates according to Examples 1 to 6 had excellent wettability (pure water contact angle), and as shown by the evaluation results of pencil hardness, scratch resistance, Vickers hardness, flex resistance, and bending test, the protective layers of the optical laminates according to Examples 1 to 6 had excellent surface hardness and good flex resistance. Furthermore, the optical laminates according to Examples 1 to 6 had good releasability even when the protective layer was thinned to 2.0 to 4.0 μm. That is, the optical laminates according to Examples 1 to 6 had good performance in all of the wettability, hard coat properties, and flexibility of the release surface of the protective layer, and also had excellent releasability from the supporting substrate.

[0080] In Example 7, the protective layer had the same composition as in Example 1, but was thinner at 1.5 μm. However, compared to Example 1, the Vickers hardness remained unchanged, and the puncture strength was slightly lower but still maintained its strength. The releasability was also good, and the surface hardness, flex resistance, and flex durability were also excellent. In Example 8, a supporting substrate with a smaller surface unevenness structure and lower surface free energy than the other Examples was used, but the coatability of the protective layer was also good, and even when the protective layer was thinner at 2.0 μm, the releasability was good, the surface hardness was excellent, and the flex resistance was also good.

[0081] In contrast, the optical laminate according to Comparative Example 1 was formed using a thinner support substrate than that of Example 1. The pencil hardness and abrasion resistance tests were performed by applying a horizontal force to the protective layer, so the influence of the substrate thickness was small, and both evaluations were favorable. However, the Vickers hardness measurement was performed by pressing a measuring indenter vertically into the protective layer, so the influence of the substrate thickness was significant, resulting in a lower Vickers hardness than that of Example 1. Furthermore, in Comparative Example 1, a PET substrate having a rougher surface than that of Examples 1 to 6 was used as the support substrate, and the pure water contact angle of the release surface of the protective layer deteriorated. Therefore, the wettability of the release surface of the protective layer was poorer than that of Examples 1 to 6, which may reduce adhesion when attached to other members.

[0082] In both the optical laminates according to Comparative Examples 2 and 3, a monomer having a double bond equivalent of more than 140 g / mol was used as the ultraviolet-curable compound for forming the protective layer. In the optical laminates according to Comparative Examples 2 and 3, the number of polymerizable double bonds was small relative to the mass of the monomer, so the protective layer was not sufficiently cured, and the pencil hardness, scratch resistance, and Vickers hardness were poor, resulting in insufficient hard coat properties. Furthermore, in Comparative Examples 2 and 3, the peel force of the protective layer was too high, and the peelability was also deteriorated.

[0083] The optical laminates according to Comparative Examples 4 and 5 both used a monomer having a double bond equivalent of less than 90 g / mol as the ultraviolet-curable compound for forming the protective layer. The optical laminates according to Comparative Examples 4 and 5 had a large number of polymerizable double bonds relative to the mass of the monomer, which resulted in excellent hard coat properties. However, the Vickers hardness of the protective layer was too high, resulting in poor results in the flex resistance and bending tests and insufficient flexibility. Furthermore, in Comparative Examples 4 and 5, the peel force of the protective layer was too high, resulting in poor peelability.

[0084] The optical laminate of Comparative Example 6 had a protective layer with a cured thickness of 7.0 μm, but the thickness was too thick, resulting in poor results in the bending test and insufficient flexibility.

[0085] In Comparative Example 7, the protective layer was thinned to a thickness of 0.9 μm and had excellent flex resistance, but the surface hardness and strength of the film itself were poor, making it unsuitable for practical use. In Comparative Example 8, the support substrate had a lower affinity to all solvents, pure water, hexadecane, and diiodomethane, compared to Examples 1 to 6, resulting in poor applicability of the protective layer-forming coating liquid. The resulting protective layer had poor pencil hardness, an indicator of surface hardness in the horizontal direction, and a poor pure water contact angle on the release surface, potentially resulting in poor adhesion when attached to other components. In Comparative Example 9, the surface free energy of the support substrate was too high, making peeling of the protective layer difficult and making it difficult to form a peelable film. In Comparative Example 10, the same support substrate as Examples 1 to 6 was used, and although peelability was good, the formed protective layer did not harden sufficiently, resulting in poor surface hardness and film strength.

[0086] The present invention can be used as an optical laminate that peelably supports a protective layer that can be used as a protective film for a polarizing plate.

[0087] 1 Optical laminate 2 Support substrate 3 Protective layer

Claims

1. An optical laminate comprising a support substrate made of polyethylene terephthalate and a protective layer peelably laminated on at least one surface of the support substrate, wherein the protective layer has a film thickness of 1.0 μm or more and 5.0 μm or less, a Vickers hardness of 60 or more and 160 or less, and a pure water contact angle on the peel surface side of 50 degrees or more and 85 degrees or less.

2. An optical laminate comprising a support substrate made of polyethylene terephthalate and a protective layer peelably laminated on at least one surface of the support substrate, wherein the protective layer has a film thickness of 1.0 μm or more and 5.0 μm or less, a piercing force of 0.25 N or more, a piercing elongation of 1.0 mm or more, and a piercing elastic modulus of 0.15 N / mm or more, and a pure water contact angle on the peel surface side of 50 degrees or more and 85 degrees or less.

3. The optical laminate according to claim 1 or 2, wherein the peeling force when peeling the protective layer from the support substrate is 0.030 N / 25 mm or more and 0.150 N / 25 mm or less.

4. The surface free energy of the surface of the support substrate on which the protective layer is laminated is 30 mJ / m ２ or more and 85 mJ / m ２ or less. The optical laminate according to claim 1 or 2.

5. The optical laminate according to claim 1 or 2, wherein the arithmetic mean roughness Ra of the surface of the support substrate on which the protective layer is laminated is 20 nm or less, and the maximum height Rz is 100 nm or less.

6. The optical laminate according to claim 1 or 2, wherein the protective layer is formed of a cured film of a coating liquid containing an ultraviolet curable compound, a photoinitiator, and a solvent, the photoinitiator is 3.0% by mass or more and 6.0% by mass or less in the coating liquid, and the double bond equivalent of the ultraviolet curable compound is 90 g / mol or more and 140 g / mol or less.

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