Optical laminate

Abstract

An optical laminate characterized by comprising a support substrate made of polyethylene terephthalate and a protective layer laminated peelably on at least one side of the support substrate, wherein the film thickness of the protective layer is 1.0 μm or more and 5.0 μm or less, the Vickers hardness of the protective layer is 60 or more and 160 or less, and the pure contact angle on the peeling side of the protective layer is 50 degrees or more and 85 degrees or less. Additionally, the piercing force of the protective layer may be 0.25 N or more, the piercing elongation may be 1.0 mm or more, and the piercing modulus may be 0.15 N / mm or more.

Description

Technology Field

[0001] The present invention relates to an optical laminate having a peelable laminated cured film that can be used as a protective film for a polarizer. Background Technology

[0002] As a polarizing plate, a polarizer protection film is generally used by bonding it to both sides of a polarizer, which is composed of a polyvinyl alcohol (PVA)-based film and a dichromatic dye such as iodine, using a polyvinyl adhesive.

[0003] Recently, along with the thinning and weight reduction of display devices, there is a demand for thinning of polarizers and polarizer protection films used therein. Conventionally, laminated films in which a functional layer of a hard coat layer is laminated onto a transparent substrate, such as a triacetylcellulose (TAC) film, have been used as polarizer protection films, but in response to the demand for thinning of polarizer protection films, thinning of the transparent substrate is being pursued.

[0004] The transparent substrates used in polarizer protective films have a certain thickness, so there are limitations even if thinning is attempted. Furthermore, there is a problem in that thinning the transparent substrate makes it difficult to obtain various characteristics required for polarizer protective films, such as hardness, durability, and UV absorption.

[0005] Accordingly, as one method for thinning polarizers, a technique using a polarizer protection film that does not have a substrate such as a TAC film is being considered (see, for example, Patent Documents 1 to 3). In Patent Documents 1 to 3, a laminate is produced in which a protective layer is formed peelably on one side of a support substrate (release film), and the protective layer peeled from the support substrate is used as a polarizer protection film. In the case of such a substrate-free polarizer protection film, it is also possible to obtain a desired function by adding an additive to the protective layer formed on the support substrate. Prior art literature

[0006] International Publication No. 2019 / 054405, Japanese Patent Publication No. 2018-169513, Japanese Patent Publication No. 2017-65017 The problem to be solved

[0007] When a protective layer is laminated onto a supporting substrate in a peelable manner, the wettability of the protective layer (peeled surface) after peeling may deteriorate, and there is a possibility that problems such as poor adhesion may occur during the subsequent bonding process with other members.

[0008] In addition, as the demand for thinning and flexibility of display devices has recently increased, it is required that both hard coating properties and flexibility be achieved even when the polarizer protection film is thinned to, for example, 1 to 5 μm.

[0009] Accordingly, the present invention aims to provide an optical laminate that has excellent wettability of the peeled surface of the protective layer even after being peeled off from a supporting substrate, and good hard coat properties and flexibility even when the protective layer is thinned. means of solving the problem

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

[0011] According to the present invention, an optical laminate can be provided in which the wettability of the peeled surface of the protective layer is excellent even after being peeled off from a supporting substrate, and in which the protective layer is thinned, the hard coat properties and flexibility are good. Brief explanation of the drawing

[0012] FIG. 1 is a schematic cross-sectional view of an optical laminate according to an embodiment. Specific details for implementing the invention

[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 side of the support substrate (2). In the following description, among the two sides of the protective layer (3), the side that is the interface with air in the optical laminate (1) (the upper side in FIG. 1) is called the "air side," and the side that is in contact with the support substrate (2) in the optical laminate (1) (the lower side in FIG. 1) is called the "peeling side."

[0015] The support substrate (2) is a film that serves as a support when forming a protective layer (3) used as a protective film for a polarizer. As the support substrate (2), a polyethylene terephthalate (PET) film can be suitably used because it has excellent heat resistance and mechanical strength. It is preferable that the arithmetic mean roughness Ra of one side of the support substrate (2) (the side on which the protective layer (3) is laminated) is 20 nm or less, and the maximum height Rz is 100 nm or less. When the arithmetic mean roughness Ra and the maximum height Rz of one side of the support substrate (2) are within these ranges, the pure contact angle of the peeling surface of the protective layer (3) can be made within the preferred range described later, and the adhesion to the polarizer or other films can be improved. In addition, if the film has a side in which the arithmetic mean roughness Ra and the maximum height Rz are within the above-mentioned ranges, it is also possible to use a resin film other than PET as the support substrate (2). It is preferable that the thickness of the support substrate (2) be 75 μm or more. If the thickness of the support substrate (2) is less than 75 μm, the hardness in the press-fit direction of the protective layer (3) in the state before peeling the protective layer (3) from the support substrate (2) becomes insufficient, and there is a possibility that the preservation of the optical laminate (1) will be reduced, so this is not desirable. However, if the hardness is sufficiently secured by adjusting the composition of the protective layer (3), it may be less than 75 μm, and for example, it may be 50 μm or more. In addition, the upper limit of the thickness of the support substrate (2) is not particularly limited, but since an excessively thick thickness leads to an increase in material costs, it is preferable that it be 125 μm or less.

[0016] It is preferable that the pure contact angle of one side of the support substrate (2) (the side on which the protective layer (3) is laminated) be 50 degrees or more and 95 degrees or less. In addition, it is preferable that the hexadecane contact angle be 1 degree or more and 30 degrees or less. It is preferable that the diiodomethane contact angle be 3 degrees or more and 63 degrees or less. When the contact angle of the solvent of the support substrate (2) is within these ranges, the wettability of the support substrate (2) is improved, the coating properties of the coating solution for forming the protective layer described later are improved, and the peelability of the protective layer (3) is improved.

[0017] It is preferable that the surface free energy of one side of the support substrate (2) (the side on which the protective layer (3) is laminated) be 30 mJ / m² or higher and 85 mJ / m² or lower. If the surface free energy of the support substrate (2) is 30 mJ / m² or higher, it is desirable because the wettability is improved and the coating properties of the coating liquid for forming the protective layer described later are improved, and it is more preferable that it be 32 mJ / m² or higher. In addition, if it is 85 mJ / m² or lower, it is desirable because it is difficult for zipping or tearing to occur when peeling off the protective layer (3). In addition, 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 laminated on one side of the support substrate (2) so as to be peelable, and is used as a protective film for a polarizer when peeled off from the support substrate (2). The film thickness of the protective layer (3) is preferably 1.0 μm or more and 5.0 μm or less, and examples of lower limits include 1.0 μm or more, 1.5 μm or more, 2.0 μm or more, etc., and examples of upper limits include 5.0 μm or less and 4.0 μm or less. If the film 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 coating properties required for the protective film become insufficient, and there is a possibility that zipping or tearing may occur during peeling due to insufficient strength. If the film thickness of the protective layer (3) exceeds 5.0 μm, it is not desirable because it is disadvantageous for thinning the polarizer and image display device and tends to reduce flexibility.

[0019] In the state where the protective layer (3) is peeled off from the supporting substrate (2), the pure contact angle of the peeled surface of the protective layer (3) is preferably 50 degrees or more and 85 degrees or less, and as a lower limit, examples include 50 degrees or more, 53 degrees or more, 59 degrees or more, etc., and as an upper limit, examples include 85 degrees or less, 83 degrees or less, 79 degrees or less, etc. In addition, the pure 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 contact angles of the peeled surface and the air surface of the protective layer (3) are within these ranges, the wettability of each surface is good, and in subsequent processes of bonding to other films, etc., the adhesion is good and adhesion defects can be reduced, so an improvement in quality and good product rate can be expected.

[0020] As mentioned above, the protective layer (3) is preferably 0.25 N or more and more preferably 0.30 N or more in terms of excellent hard coat properties even when thinned, so that the piercing force is excellent. The upper limit is not particularly limited, but examples include 1.00 N or less, 0.70 N or less, and 0.50 N or less in terms of excellent hardness in the direction perpendicular to the surface of the protective layer. In order to exhibit flexibility, the protective layer (3) 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 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 in terms of achieving both flexibility and strength. In addition, the protective layer (3) is preferably 0.15 N / mm or higher in terms of improving peelability by achieving both hard coat properties and flexibility, more preferably 0.16 N / mm or higher, even more preferably 0.18 N / mm or higher, and even more preferably 0.20 N / mm or higher. The upper limit is not specifically limited, but examples include 0.50 N / mm or lower, 0.40 N / mm or lower, 0.30 N / mm or lower. In addition, in this specification, the piercing force, piercing elongation, and piercing elasticity can be evaluated using a universal testing machine (STB-1225L, A&D) in accordance with JIS Z 1707.

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

[0022] As a UV-curable compound, for example, a monofunctional, difunctional, or trifunctional (meth)acrylate monomer may be used. In addition, 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, isobornyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate. Benzyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, ethyl carbitol (meth)acrylate, phosphate (meth)acrylate, ethylene oxide modified phosphate (meth)acrylate, phenoxy (meth)acrylate, ethylene oxide modified phenoxy (meth)acrylate, propylene oxide 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-hydroxypropylphthalate, 2-Hydroxy-3-phenoxypropyl(meth)acrylate, 2-(meth)acryloyloxyethylhydrogenphthalate, 2-(meth)acryloyloxypropylhydrogenphthalate, 2-(meth)acryloyloxypropylhexahydrohydrogenphthalate, 2-(meth)acryloyloxypropyltetrahydrohydrogenphthalate, dimethylaminoethyl(meth)acrylate, trifluoroethyl(meth)acrylate, tetrafluoropropyl(meth)acrylate, hexafluoropropyl(meth)acrylate, octafluoropropyl(meth)acrylate, 2-adamantane,Examples include adamantan derivative mono(meth)acrylates, such as adamantyl acrylate having a mono(meth)acrylate derived from adamantanediol.

[0024] Examples of difunctional (meth)acrylates include 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, hydroxypivalate neopentyl glycol di(meth)acrylate, etc. Examples include di(meth)acrylates.

[0025] Examples of (meth)acrylates with three or more functions 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; or pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, and dipentaerythritol penta(meth)acrylate. Examples include polyfunctional (meth)acrylate compounds with three or more functions, such as ditrimethylolpropane penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ditrimethylolpropane hexa(meth)acrylate, or polyfunctional (meth)acrylate compounds in which some of these (meth)acrylates are substituted with alkyl groups or ε-caprolactone.

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

[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, dipentaerythritol pentaacrylate isophorone diisocyanate urethane prepolymer, etc.

[0028] As a UV-curable compound, a (meth)acrylate having a cyclocyclic structure may be used. As for the (meth)acrylate having a cyclocyclic structure, for example, a (meth)acrylate having one or more of the following structures may be used: a cyclopentane structure, a dicyclopentane structure, a cyclohexane structure, a cyclodecane structure, a tricyclodecane structure, an isobornyl structure, or an adamantane structure. By incorporating these compounds into a coating solution for forming a protective layer, hydrophobicity can be imparted to the protective layer (3), and the moisture permeability required for the protective film of the polarizer can be reduced.

[0029] Specific examples of (meth)acrylates comprising a dicyclic 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, dicyclofentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, 2-dicyclopentenoxyethyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, bornyl (meth)acrylate, isobornyl (meth)acrylate, and tricyclodecanyl (meth)acrylate. Monofunctional (meth)acrylates such as tricyclodecanedimethanol mono(meth)acrylate, adamanthyl(meth)acrylate, etc., or cyclohexanedimethanol di(meth)acrylate, dicyclofentanyl di(meth)acrylate, dicyclopentenyl di(meth)acrylate, dicyclopentadienyl di(meth)acrylate, dicyclopentadienyl di(meth)acrylate, bornyl di(meth)acrylate, isobornyl di(meth)acrylate, tricyclodecanyl di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, adamanthyl di(meth)acrylate, adamantanedimethanol di(meth)acrylate, adamantanediethanol di(meth)acrylate, dimethylol dicyclopentane di(meth)acrylate, Examples of polyfunctional (meth)acrylates include norbornandimethylol di(meth)acrylate, cyclohexanetrimethanoltri(meth)acrylate, adamanthyltri(meth)acrylate, adamantantrimethanoltri(meth)acrylate, norbornandimethyloltri(meth)acrylate, tricyclodecanetrimethanoltri(meth)acrylate, and perhydro-1,4,5,8-dimethanonaphthalene-2,3,7-(oxymethyl)tri(meth)acrylate. (Meth)acrylates containing these alicyclic structures may be used alone or in a mixture of two or more types.

[0030] The above-described UV-curable compound may be used as a single type or in combination of two or more types. In addition, the above-described UV-curable compound may be a monomer in the composition or an oligomer in which a portion is polymerized.

[0031] The double bond equivalent of the UV-curable compound is preferably 90 g / mol or more and 140 g / mol or less. The lower limit may be 90 g / mol or more, 99 g / mol or more, 109 g / mol or more, etc., and the upper limit may be 140 g / mol or less, 138 g / mol or less, etc. When the double bond equivalent of the UV-curable compound is within this range, the hardness and flexibility of the protective layer (3) after curing can be achieved, and the peelability from the supporting 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 supporting substrate (2) increases, and the peelability deteriorates, so it is not desirable. In addition, if the double bond equivalent of the UV-curable compound is less than 90 g / mol, the number of polymerizable double bonds increases relative to the mass of the UV-curable compound, so 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 UV-curable compound exceeds 140 g / mol, the curability of the protective layer (3) decreases, and there is a possibility that the surface hardness and scratch resistance will deteriorate.

[0032] As a photopolymerization initiator, radical polymerization initiators such as acetophenone-based, benzophenone-based, thioxantone-based, benzoin, benzoin methyl ether, and acylphosphine oxide can be used. As a photopolymerization initiator, for example, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,2-diethoxyacetophenone, 1-hydroxycyclohexylphenyl ketone, 2,2-dimethoxy-phenylacetophenone, dibenzoyl, benzoin, benzoin methyl ether, benzoin ethyl ether, p-chlorobenzophenone, p-methoxybenzophenone, mihiller ketone, acetophenone, 2-chlorothioxantone, 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropan-1-one, 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone, etc. may be used. You may use one of these types alone, or combine two or more types.

[0033] It is preferable that the amount of photopolymerization initiator be 3.0 mass% or more and 6.0 mass% or less of the coating solution for forming a protective layer. The lower limit may be 3.0 mass% or more, 3.6 mass% or more, etc., and the upper limit may be 6.0 mass% or less, 5.2 mass% or less, etc. If the amount of photopolymerization initiator is less than 3.0 mass% of the coating solution for forming a protective layer, it is not desirable because the peel strength of the protective layer (3) from the supporting substrate (2) increases, and the peelability may deteriorate. If the amount of photopolymerization initiator exceeds 6.0 mass% of the coating solution for forming a protective layer, it is not desirable because the solubility of the photopolymerization initiator deteriorates. In addition, when based on the total solid content of the coating solution for forming a protective layer, it is preferable that the amount of photopolymerization initiator be 9.0 mass% or more and 13.0 mass% or less of the total solid content.

[0034] As solvents, 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 among N-methylpyrrolidone, dimethylformamide, etc. One type or a mixture of two or more types can be used.

[0035] In the coating solution for forming the protective layer, inorganic fine particles may be added to improve the mechanical strength or surface strength (pencil strength) of the protective layer (3). As inorganic fine particles, silica fine particles (SiO2) or metal oxide fine particles may be used. As metal oxide fine particles, one or more types of antimony-doped tin oxide (ATO), phosphorus-doped tin oxide (PTO), gallium-doped tin oxide (GTO), zirconia (ZrO2), and titania (TiO2) may be used in combination. The surface of the inorganic fine particles may be modified by attaching a silane coupling agent. As a silane coupling agent, one having one or more types of functional groups such as vinyl groups, acryloyl groups, and methacryloyl groups may be used.

[0036] In addition, various additives such as antistatic agents, defoaming agents, antioxidants, ultraviolet absorbers, infrared absorbers, colorants, light stabilizers, polymerization inhibitors, photosensitizers, antifouling agents, leveling agents, oil repellents, water repellents, and anti-fingerprint agents may be added to the coating solution for forming the protective layer as needed. By appropriately adding these additives, various functions can be imparted to the protective layer (3). Furthermore, to improve the hydrophobicity of the protective layer (3), hydrophobic materials such as cycloolefin polymers may be incorporated.

[0037] The coating method for forming a protective layer is not particularly limited, and can be applied using, for example, a spin coater, a roll coater, a reverse roll coater, a gravure coater, a micro-gravure coater, a knife coater, a bar coater, a wire bar coater, a die coater, a dip coater, a spray coater, an applicator, etc.

[0038] It is preferable that the total amount of ultraviolet light when curing the protective layer (3) be 60 mJ / cm² or more and 300 mJ / cm² or less. If the total amount of ultraviolet light is less than 60 mJ / cm², there is a possibility that the peel strength of the protective layer (3) will increase.

[0039] It is preferable that the peeling force when peeling the protective layer (3) from the support substrate (2) after the formation of the optical laminate (1) be 0.030 N / 25 mm or more and 0.150 N / 25 mm or less. In addition, from the perspective of excellent peelability, it may be 0.030 N / 25 mm or more and 0.100 N / 25 mm or less. In addition, the peeling force is a value measured by a 180° peel test in accordance with JIS K 6854-2. If the peeling force when peeling the protective layer (3) from the support substrate (2) is within this range, defects such as tearing or zipping during peeling or inability to peel can be reduced.

[0040] The Vickers hardness of the protective layer (3) in the optical laminate (1) is preferably 60 or higher and 160 or lower. The lower limit may be 60 or higher, 61 or higher, etc., and the upper limit may be 160 or lower, 150 or lower, 140 or lower, 130 or lower, 120 or lower, 113 or lower, 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 the polarizer is obtained.

[0041] The protective layer (3) of the optical laminate (1) according to the present embodiment can be used as a protective film for a polarizer in a peeled state from the support substrate (2). The surface that becomes the interface with the polarizer may be either an air surface or a peeled surface, but it is preferable to make the air surface the interface with the polarizer. The polarizer and the protective layer (3) may be bonded together by using an adhesive. Alternatively, a polarizer bonded to the protective layer (3) may be formed by applying a coating solution of PVA resin containing a dichromatic pigment onto the protective layer (3). The other side of the protective layer (3) may be bonded to another member, such as a resin film or a phase difference plate, through an adhesive. The peeling of the protective layer (3) from the support substrate (2) may be performed before bonding with the polarizer or after bonding with the polarizer.

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

[0043] In addition, another optical laminate (1) according to the present embodiment comprises a support substrate (2) made of polyethylene terephthalate and a protective layer (3) laminated peelably on at least one side of the support substrate (2), wherein the film thickness of the protective layer (3) is 1.0 μm or more and 5.0 μm or less, the piercing force of the protective layer (3) is 0.25 N or more, the piercing elongation is 1.0 mm or more, the piercing elastic modulus is 0.15 N / mm or more, and the pure contact angle on the peeling surface side of the protective layer (3) is 50 degrees or more and 85 degrees or less. According to the present embodiment, even after being peeled from the support substrate (2), the wettability of the peeling surface of the protective layer (3) is excellent, and even when the protective layer (3) is thinned to 1.0 to 5.0 μm, an optical laminate (1) with good hard-coat properties and flexibility can be realized.

[0044] Examples

[0045] Hereinafter, specific embodiments of the present invention will be described.

[0046] (Example 1)

[0047] A coating solution for forming a protective layer having the composition listed in Table 1 was prepared, and applied to one side of a PET substrate (T60, Toray Co., Ltd.) with a thickness of 75 μm by the bar coating method to achieve a cured film thickness of 2.0 μm, and dried at 70°C for 30 seconds. After drying, the coating film was cured by irradiating ultraviolet light using a metal halide lamp so that the integrated light intensity was 122 mJ / cm², thereby obtaining an optical laminate with a protective layer laminated on a support substrate.

[0048] (Examples 2 to 5)

[0049] An optical laminate was obtained under the same conditions as Example 1, except that the composition of the coating solution for forming the protective layer was changed as described in Table 1.

[0050] (Example 6)

[0051] An optical laminate was obtained under the same conditions as in Example 1, except that the coating solution was applied such that the thickness of the cured protective layer was 4.0 μm.

[0052] (Example 7)

[0053] An optical laminate was obtained under the same conditions as in Example 1, except that the coating solution was applied such that the thickness of the cured protective layer was 1.5 μm.

[0054] (Example 8)

[0055] An optical laminate was obtained under the same conditions as Example 1, except that a PET substrate with a thickness of 50 μm (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 solution for forming the protective layer was changed as described in Table 2.

[0056] (Comparative Example 1)

[0057] An optical laminate was obtained under the same conditions as Example 1, except that a PET substrate (S100H, thickness 23 μm, Mitsubishi Chemical Co., Ltd.) having the surface roughness and surface free energy shown in Table 3 was used as the support substrate.

[0058] (Comparative Examples 2 to 5)

[0059] An optical laminate was obtained under the same conditions as Example 1, except that the composition of the coating solution for forming the protective layer was changed as described in Table 3.

[0060] (Comparative Example 6)

[0061] An optical laminate was obtained under the same conditions as in Example 1, except that the coating solution was applied such that the thickness of the cured protective layer was 7.0 μm.

[0062] (Comparative Example 7)

[0063] An optical laminate was obtained under the same conditions as in Example 1, except that the coating solution was applied such that the thickness of the cured film of the protective layer was 0.9 μm.

[0064] (Comparative Example 8)

[0065] An optical laminate was obtained under the same conditions as Example 1, except that a PET substrate with a thickness of 38 μm (Toray, 38-SY) having the surface roughness and surface free energy shown in Table 4 was used as the support substrate.

[0066] (Comparative Example 9)

[0067] An optical laminate was obtained under the same conditions as Example 1, except that a PET substrate with a thickness of 75 μm (Toyobo, TN200) having the surface roughness and surface free energy shown in Table 4 was used as the support substrate.

[0068] (Comparative Example 10)

[0069] An optical laminate was obtained under the same conditions as Example 1, except that the composition of the coating solution for forming the protective layer was changed as described in Table 4.

[0070] Details of the compounds shown in Tables 1 to 4 are shown below.

[0071] 1. UV-curable compound (monomer)

[0072] (1) NK Ester A-TMM-3L (trade name), Shin-Nakamura Kagaku Kogyo Co., Ltd., pentaerythritol triacrylate and pentaerythritol tetraacrylate

[0073] (2) Light Acrylate (registered trademark) 3EG-A (product name), Kyoesha Kagaku Kabushiki Kaisha, triethylene glycol diacrylate

[0074] (3) Light Acrylate 9EG-A (product name), Kyoesha Kagaku Kabushiki Kaisha, PEG400 diacrylate

[0075] (4) Light Acrylate DPE-6A (product name), Kyoesha Kagaku Kabushiki Kaisha, Dipentaerythritol Hexacrylate

[0076] 2. Photopolymerization initiator

[0077] (1) Omnirad (registered trademark) 184 (trade name), IGM Resins BV, 1-hydroxycyclohexyl-phenylketone

[0078] (2) Omnirad TPO (trade name), IGM Resins BV, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide

[0079] (3) Omnirad 127 (trade name), IGM Resins BV, 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropan-1-one

[0080] (4) Omnirad 369 (trade name), IGM Resins BV, 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone

[0081] 3. Additives

[0082] (1) GRANDIC PC4300, DIC, leveling agent

[0083] (2) BYK-3566, BYK Priest, Leveling Agent

[0084] 4. Solvent

[0085] (1) Dimethyl carbonate

[0086] (2) MIBK (methylisobutyl ketone)

[0087] The optical laminates for each example and each comparative example were evaluated by the following method.

[0088] [Arithmetic mean illuminance Ra, maximum height Rz]

[0089] Using a white interference microscope (ECLIPSE LV150N, Nikon Co., Ltd.), the surface shape of the evaluation surface (the surface on which the protective layer is laminated) was observed, and Ra and Rz were calculated by averaging the surface shape data from six locations.

[0090] [Peel-off force]

[0091] A 180° peel test was performed in accordance with JIS K 6854-2 to measure the peel strength. Specifically, a measurement sample was prepared by attaching a protective layer of an optical laminate to a glass plate using an adhesive tape (TD06A, Tomoegawa Paper Co., Ltd.). Using a Tensilon single-column type material testing machine (STB-1225L, A&D Co., Ltd.), the load was measured while peeling the support substrate from the protective layer by stretching it in a 180° direction under conditions of load cell: 50 N and peel speed: 500 mm / min. The peel strength was calculated from the peel curve (weighted-displacement) obtained from the measurement.

[0092] [Pure contact angle of the protective layer]

[0093] Using a contact angle meter (Drop Master 300, Kyowa Kaimen Kagaku Co., Ltd.), the measurement value taken 5 seconds after pure water was deposited on the measurement surface was used. 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 after bonding the protective layer of the optical laminate to a glass plate with an adhesive tape (TD06A, Tomoegawa Paper Co., Ltd.), peeling the support substrate from the protective layer, and with the protective layer bonded to the glass plate through the adhesive tape.

[0094] [Pencil Hardness]

[0095] Pencil hardness was evaluated in accordance with JIS K 5400-1900. The pencil hardness of the protective layer surface was measured using a pencil (uni, Mitsubishi Enbitsu Co., Ltd.) and a Clemens-type scratch tester (HA-301, Tester Sangyo Co., Ltd.). Repeated tests were performed while varying the pencil hardness, and changes in appearance due to scratches were observed visually; the maximum hardness at which no scratches were observed was set as the evaluation value. A pencil hardness of F or higher was considered acceptable. In addition, "in Tables 1 to 4<B」는, 연필 경도가 B보다 낮은 것을 나타내고, 「> "H" indicates that the pencil hardness is higher than H.

[0096] [Abrasion resistance]

[0097] The top and bottom of a sample of an optical laminate cut to a size of 50 mm × 170 mm were fixed to a support using cellophane tape. A 20 mm × 20 mm steel wool (Bornstar #0000) was brought into contact with the air surface of the protective layer, and after applying a test load of 1,000 g / 4 cm² and reciprocating 10 times with an abrasion length of 80 mm or more, scratches occurring in the center 30 mm along the abrasion length direction were visually counted. A number of 10 or fewer scratches was considered a pass.

[0098] [Flexibility (Mandrel Test)]

[0099] Flexural strength 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 so that the protective layer was on the outside, and the minimum cylinder diameter at which no crack occurred in the protective layer was set as the evaluation value. A minimum cylinder diameter of 2 mm or less was considered acceptable.

[0100] [Vickers Hardness]

[0101] Vickers hardness was measured by a micro-indentation test in accordance with ISO 14577 (nano-indentation method) using a micro-hardness tester (Fischer Scope HM2000, Fischer Instruments Co., Ltd.). A Vickers indenter HM2000 023 was used as the measuring indenter, and the indenter was brought into contact with the air surface of the protective layer supported on the supporting substrate. Measurements were performed under conditions of a maximum load of 1 mN (reaching 1 mN in 5 seconds) and a holding time of 1 second.

[0102] [Bending Test]

[0103] With a planar body no-load U-shaped extension test jig (DMX-FS) installed on a desktop durability tester (Yuasah System Kiki Co., Ltd.), samples of optical laminates for each example and each comparative example were attached in a flat manner. When folded with the protective layer facing outward, the samples were continuously folded so that the distance between opposing protective layers was 4 mm. The folding operation was performed once per second, and the number of folds until a crack occurred in the protective layer was evaluated as the evaluation value. A folding count of 200,000 or more was considered a pass.

[0104] [Contact angle of supporting material]

[0105] Using a contact angle meter (Drop Master 300, Kyowa Kaimen Kagaku Co., Ltd.), the measurement value taken 5 seconds after each solvent (pure water, hexadecane, diiodomethane) was deposited on the measurement surface was used.

[0106] [Surface free energy of the supporting material]

[0107] Equation (3) was derived from Equation (1) and Equation (2) below, and the contact angle of the solvent (pure water, hexadecane, diiodomethane) obtained above was introduced into Equation (3) to calculate the surface free energy using a system of three linear equations.

[0108]

[0109] [Piercing Strength (Piercing Test)]

[0110] In accordance with JIS Z 1707, the evaluation was performed using a universal testing machine (STB-1225L, A&D). A protective layer was transferred onto a base plate with a 10 mm diameter hole, and the piercing force (N) and piercing elongation (mm) were determined when the portion overlapping the hole was pierced vertically at a speed of 50 mm / min using a needle (a semicircular needle with a diameter of 1.0 mm and a tip radius of 0.5 mm). The piercing elasticity modulus (N / mm) was calculated by dividing the piercing force by the piercing elongation, and the average value obtained from 5 measurements was used as the evaluation value. A test was deemed acceptable if the piercing force was 0.25 N or higher, the piercing elongation was 1.0 mm or higher, and the piercing elasticity modulus was 0.15 N / mm or higher.

[0111] Tables 1 to 4 show the composition (coating solution composition) and evaluation results of the optical laminate for each example and each comparative example.

[0112]

[0113]

[0114]

[0115]

[0116] As shown in Table 1, all optical laminates according to Examples 1 to 6 exhibited excellent wettability (pure contact angle), and as indicated by the evaluation results of pencil hardness, scratch resistance, Vickers hardness, flexural resistance, and bending tests, the protective layer of the optical laminates according to Examples 1 to 6 had excellent surface hardness and good flexural resistance. In addition, the optical laminates according to Examples 1 to 6 exhibited good peelability 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 terms of wettability, hard coat properties, and flexibility of the peel surface of the protective layer, and also exhibited excellent peelability from the supporting substrate.

[0117] Example 7 was a protective layer with the same composition as Example 1 but thinned to 1.5 μm, and compared to Example 1, the Vickers hardness did not change, and while the piercing strength was slightly lower, the strength was maintained, the peelability was good, and the surface hardness, flexural resistance, and flexural durability were excellent. Example 8 used a support substrate with a small surface roughness structure and low surface free energy compared to other examples, but the coating properties of the protective layer were not an issue, and even when thinned to 2.0 μm, the peelability was good, the surface hardness was excellent, and the flexural resistance was also good.

[0118] In contrast, the optical laminate according to Comparative Example 1 was formed using a thinner support substrate compared to Example 1. Since the pencil hardness and scratch resistance tests were performed by applying a horizontal force to the protective layer, the influence of the substrate thickness was small, and both evaluations were good. However, since the measurement of Vickers hardness was performed by pressing a measuring indenter perpendicularly to the protective layer, the influence of the substrate thickness was large, and the Vickers hardness was lower compared to Example 1. In addition, in Comparative Example 1, a PET substrate having a rough surface was used as the support substrate compared to Examples 1 to 6, so the pure contact angle of the peel surface of the protective layer deteriorated. Consequently, compared to Examples 1 to 6, the wettability of the peel surface of the protective layer was poor, and there is a possibility that the adhesion during bonding with other members may be reduced.

[0119] The optical laminates according to Comparative Examples 2 and 3 both used a monomer with a double bond equivalent weight exceeding 140 g / mol as a UV-curable compound for forming a protective layer. In the optical laminates according to Comparative Examples 2 and 3, because the number of polymerizable double bonds relative to the mass of the monomer was low, the curing of the protective layer was insufficient, 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 strength of the protective layer was excessively high, and the peelability also deteriorated.

[0120] The optical laminates according to Comparative Examples 4 and 5 both used a monomer with a double bond equivalent of less than 90 g / mol as a UV-curable compound for forming a protective layer. In the optical laminates according to Comparative Examples 4 and 5, the hard coat properties were excellent because the number of polymerizable double bonds relative to the mass of the monomer was large; however, the Vickers hardness of the protective layer became excessively high, resulting in poor flexural resistance and bending test results, and insufficient flexibility. Furthermore, in Comparative Examples 4 and 5, the peel strength of the protective layer became excessively high, and peelability deteriorated.

[0121] The optical laminate according to Comparative Example 6 had a cured film thickness of 7.0 μm for the protective layer, but because the film thickness was thick, the results of the bending test were poor and the flexibility was insufficient.

[0122] Comparative Example 7 was a thin film with a protective layer thickness of 0.9 μm, and although it had excellent flexural resistance, it lacked practicality because the surface hardness and the strength of the film itself were poor. In Comparative Example 8, compared to Examples 1 to 6, the support substrate had low affinity for any of the solvents among pure water, hexadecane, and diiodomethane, so the coating properties of the coating solution for forming the protective layer deteriorated, and the resulting protective layer had a lower pencil hardness, which is an indicator of surface hardness in the horizontal direction, and also had a lower pure contact angle of the peel surface, so there was a possibility that the adhesion during bonding with other components would be reduced. In Comparative Example 9, the surface free energy of the support substrate was excessively high, making it difficult to peel off the protective layer and thus difficult to form a peelable film. Comparative Example 10 used the same support substrate as Examples 1 to 6, and although the peelability was good, the curing of the formed protective layer was insufficient, and the surface hardness and the strength of the film itself were poor. Industrial applicability

[0123] The present invention can be used as an optical laminate that supports a protective layer, which can be used as a protective film for a polarizer, in a peelable manner. Explanation of the symbols

[0124] 1: Optical laminate 2: Supporting material 3: Protective layer

Claims

Claim 1 An optical laminate characterized by having a support substrate made of polyethylene terephthalate and a protective layer peelably laminated on at least one side of the support substrate, wherein the film thickness of the protective layer is 1.0 μm or more and 5.0 μm or less, the Vickers hardness of the protective layer is 60 or more and 160 or less, and the pure contact angle on the peeling side of the protective layer is 50 degrees or more and 85 degrees or less. Claim 2 An optical laminate comprising a support substrate made of polyethylene terephthalate and a protective layer peelably laminated on at least one side of the support substrate, wherein the film thickness of the protective layer is 1.0 μm or more and 5.0 μm or less, the piercing force of the protective layer is 0.25 N or more, the piercing elongation is 1.0 mm or more, and the piercing modulus is 0.15 N / mm or more, and the pure contact angle on the peeling surface side of the protective layer is 50 degrees or more and 85 degrees or less. Claim 3 An optical laminate according to claim 1 or 2, wherein the peel 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. Claim 4 An optical laminate according to claim 1 or 2, wherein the surface free energy of the surface on which the protective layer of the support substrate is laminated is 30 mJ / m² or more and 85 mJ / m² or less. Claim 5 An optical laminate according to claim 1 or 2, characterized in that the arithmetic mean roughness Ra of the surface on which the protective layer of the support substrate is laminated is 20 nm or less, and the maximum height Rz is 100 nm or less. Claim 6 An optical laminate according to claim 1 or 2, wherein the protective layer is composed of a cured film of a coating solution comprising a UV-curable compound, a photopolymerization initiator, and a solvent, the photopolymerization initiator is 3.0 mass% or more and 6.0 mass% or less of the coating solution, and the double bond equivalent of the UV-curable compound is 90 g / mol or more and 140 g / mol or less.

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