Optical laminate

Abstract

To provide an optical laminate that maintains excellent wettability of the peeled surface of a protective layer even after separation from a support substrate, and that retains excellent hard-coating performance and flexibility even when the protective layer is thinned.SOLUTION: An optical laminate comprises a support substrate which comprises polyethylene terephthalate and a protective layer which is peelably laminated on at least one surface 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 a pure water contact angle on the peeling surface side of the protective layer is 50 degrees or more and 85 degrees or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[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 laminated in a peelable manner.

Background Art

[0002] As a polarizing plate, a polarizer composed of a polyvinyl alcohol (PVA) - based film and a dichroic dye such as iodine, with a polarizer protective film bonded to both sides thereof with a polyvinyl - based adhesive, is generally used.

[0003] With the recent trend of thinning and lightening display devices, there is also a demand for thinning of polarizing plates and the polarizer protective films used therein. Conventionally, as a polarizer protective film, a laminated film in which a functional layer of a hard - coat layer is laminated on a transparent base material such as a triacetyl cellulose (TAC) film has been used. However, in response to the demand for thinning of the polarizer protective film, thinning of the transparent base material has been attempted.

[0004] The transparent base material used for the polarizer protective film has a certain thickness, and there is a limit even if thinning is attempted. In addition, with the thinning of the transparent base material, there is a problem that it becomes difficult to obtain various properties required for the polarizer protective film, such as hardness, durability, and ultraviolet - absorption function.

[0005] Therefore, as one method for thinning a polarizing plate, a technique using a polarizer protective film without a base material such as a TAC film has been studied (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 in a peelable manner on one surface of a support base material (release film), and the protective layer peeled from the support base material is used as a polarizer protective film. In the case of such a substrate - less polarizer protective film, it is also possible to obtain a desired function by adding an additive to the protective layer formed on the support base material.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] International Publication No. 2019 / 054405 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-169513 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-65017 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] When a protective layer is laminated on a support substrate so as to be peelable, the wettability of the protective layer (peel surface) after peeling may deteriorate, and problems such as poor adhesion may occur in the subsequent bonding step with other members.

[0008] In recent years, there has been an increasing demand for thinning and flexibility of display devices. Even when a polarizer protection film is thinned to, for example, 1 to 5 μm, it is required to achieve both hard coat properties and flexibility.

[0009] Therefore, an object of the present invention is to provide an optical laminate that has excellent wettability of the peel surface of the protective layer even after peeling from the support substrate, and has good hard coat properties and flexibility even when the protective layer is thinned. [Means for Solving the Problems]

[0010] The optical laminate according to the present invention includes a support substrate made of polyethylene terephthalate and a protective layer laminated on at least one surface of the support substrate so as to be peelable, the 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 water contact angle on the peel surface 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, even after being peeled off from the support substrate, the wettability of the peeled surface of the protective layer is excellent, and even when the protective layer is made thinner, an optical laminate having good hard coat properties and flexibility can be provided.

Brief Description of Drawings

[0012]

Figure 1

Embodiments for Carrying Out the Invention

[0013] FIG. 1 is a schematic cross-sectional view of the optical laminate according to the 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 becomes the interface with air in the optical laminate 1 (the upper surface in FIG. 1) is referred to as the "air surface", and the surface that is in contact with the support substrate 2 in the optical laminate 1 (the lower surface in FIG. 1) is referred to as the "peeled 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. As the support substrate 2, a polyethylene terephthalate (PET) film can be preferably used because of its excellent heat resistance and mechanical strength. It is preferable that the arithmetic mean roughness Ra of one surface of the support substrate 2 (the surface 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 surface of the support substrate 2 are within these ranges, the pure water contact angle of the peeling surface of the protective layer 3 can be within a preferable range described later, and the adhesion with a polarizer or other films can be improved. In addition, as long as the film has a surface with the arithmetic mean roughness Ra and the maximum height Rz within the above ranges, a resin film other than PET can also be used as the support substrate 2. The thickness of the support substrate 2 is preferably 75 μm or more. When the thickness of the support substrate 2 is less than 75 μm, the hardness in the pushing direction of the protective layer 3 in the state before peeling the protective layer 3 from the support substrate 2 becomes insufficient, and the storage stability of the optical laminate 1 may decrease, which is not preferable. However, if sufficient hardness can be ensured by adjusting the composition of the protective layer 3, it may be less than 75 μm, for example, 50 μm or more is sufficient. Also, the upper limit of the thickness of the support substrate 2 is not particularly limited, but if it becomes too thick, it will cause an increase in material cost, so it is preferably 125 μm or less.

[0016] The pure water contact angle of one surface of the support substrate 2 (the surface on which the protective layer 3 is laminated) is preferably 50 degrees or more and 95 degrees or less. Also, 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 support substrate 2 are within these ranges, the wettability of the support substrate 2 becomes good, the coatability of the coating liquid for forming the protective layer described later is improved, and the peelability of the protective layer 3 becomes good.

[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 or more and 85 mJ / m 2 or less. When the surface free energy of the support substrate 2 is 30 mJ / m2 If it is above this value, it is preferable because the wettability becomes good and the coatability of the coating liquid for forming the protective layer described later is improved. 32 mJ / m 2 or more is more preferable. Also, if it is 85 mJ / m 2 or less, it is preferable because dipping, tearing, etc. are less likely to occur when the protective layer 3 is peeled off. The surface free energy can be calculated using the known surface free energy and contact angle of each of the three solvents (water, hexadecane, diiodomethane).

[0018] The protective layer 3 is a thin film laminated on one surface of the support substrate 2 so as to be peelable, and is used as a protective film for a polarizer in a state 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. Examples of the lower limit include 1.0 μm or more, 1.5 μm or more, 2.0 μm or more, etc., and examples of the upper limit include 5.0 μm or less, 4.0 μm or less, etc. When 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 coat property required for the protective film becomes insufficient, and there is a possibility of dipping, tearing, etc. during peeling due to insufficient strength. When the film thickness of the protective layer 3 exceeds 5.0 μm, it is disadvantageous for thinning the polarizing plate and the image display device, and the flex resistance tends to decrease, which is not preferable.

[0019] In a state where the protective layer 3 is peeled off from the support substrate 2, the pure water contact angle of the peeling surface of the protective layer 3 is preferably 50 degrees or more and 85 degrees or less. Examples of the lower limit include 50 degrees or more, 53 degrees or more, 59 degrees or more, etc., and examples of the upper limit include 85 degrees or less, 83 degrees or less, 79 degrees or less, etc. Also, 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 peeling surface and the air surface of the protective layer 3 are within these ranges, the wettability of each surface is good, the adhesiveness is good in the subsequent process after bonding to other films, etc., and adhesion failure can be reduced, so an improvement in quality and yield 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, more preferably 0.30 N or more. The upper limit is not particularly limited, but examples include 1.00 N or less, 0.70 N or less, 0.50 N or less, etc. from the viewpoint of also having excellent hardness in the direction perpendicular to the surface of the protective layer. In order for the protective layer 3 to exhibit flexibility, the piercing elongation is preferably 1.0 mm or more, more preferably 1.4 mm or more, still 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, 1.7 mm or less, etc. from the viewpoint of achieving both flexibility and strength. Further, from the viewpoint of achieving both hard coat properties and flexibility and improving peelability, the piercing elastic modulus of the protective layer 3 is preferably 0.15 N / mm or more, more preferably 0.16 N / mm or more, still more preferably 0.18 N / mm or more, and even more preferably 0.20 N / mm or more. The upper limit is not particularly limited, but examples include 0.50 N / mm or less, 0.40 N / mm or less, 0.30 N / mm or less, etc. Note that in this specification, the piercing force, piercing elongation, and piercing elastic modulus 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 liquid containing an ultraviolet curable compound, a photoinitiator, and a solvent onto the support substrate 2, drying it, and then curing the coating film by ultraviolet irradiation. The protective layer 3 is a layer having the hard coat properties required for the protective film, and can typically be formed as a hard coat layer.

[0022] As the ultraviolet curable compound, for example, monofunctional, bifunctional, or trifunctional or higher (meth)acrylate monomers can be used. Note that in this specification, “(meth)acrylate” is a general term for both acrylate and methacrylate, and “(meth)acryloyl” is a general term for both acryloyl and methacryloyl.

[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, phosphoric acid (meth)acrylate, ethylene oxide-modified phosphoric acid (meth)acrylate, phenoxy (meth)acrylate, ethylene oxide-modified phenoxy (meth)acrylate, propylene oxide-modified phenoxy (meth)acrylate, 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 hydrogen phthalate, 2-(meth)acryloyloxypropyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hexahydrohydrogen phthalate, 2-(meth)acryloyloxypropyl tetrahydrohydrogen phthalate, dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, 2-adamantane,Examples of adamantyl acrylate derivatives mono(meth)acrylates such as adamantyl acrylate having a monovalent mono(meth)acrylate derived from adamantane diol can be mentioned.

[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, neopentyl glycol hydroxypivalate di(meth)acrylate, etc.

[0025] Examples of (meth)acrylates having three or more functional groups 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; polyfunctional (meth)acrylate compounds having three or more functional groups 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; and polyfunctional (meth)acrylate compounds in which a part of these (meth)acrylates is substituted with an alkyl group or ε-caprolactone.

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

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

[0028] As the ultraviolet curable compound, (meth)acrylate containing an alicyclic structure may be used. As the (meth)acrylate containing an alicyclic structure, for example, (meth)acrylate 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 can be used. By blending these compounds in the coating liquid for forming the 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 containing an alicyclic structure include monofunctional (meth)acrylates such as 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, dicyclopentadienyl (meth)acrylate, 2-dicyclopentenoxyethyl (meth)acrylate, dicyclopentenyl oxyethyl (meth)acrylate, bornyl (meth)acrylate, isobornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, tricyclodecanedimethanol mono(meth)acrylate, adamantyl (meth)acrylate, etc., and polyfunctional (meth)acrylates such as cyclohexanedimethanol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, dicyclopentenyl di(meth)acrylate, dicyclopentadienyl di(meth)acrylate, bornyl di(meth)acrylate, isobornyl di(meth)acrylate, tricyclodecanyl di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, adamantyl di(meth)acrylate, adamantane dimethanol di(meth)acrylate, adamantane diethanol di(meth)acrylate, dimethylol dicyclopentane di(meth)acrylate, norbornane dimethylol di(meth)acrylate, cyclohexane trimethanol tri(meth)acrylate, adamantyl tri(meth)acrylate, adamantane trimethanol tri(meth)acrylate, norbornane trimethylol tri(meth)acrylate, tricyclodecane trimethanol tri(meth)acrylate, perhydro-1,4,5,8-dimethanonaphthalene-2,3,7-(oxymethyl)tri(meth)acrylate. These (meth)acrylates containing an alicyclic structure may be used alone or in combination of two or more.

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

[0031] The double bond equivalent of the ultraviolet-curable compound is preferably 90 g / mol or more and 140 g / mol or less. Examples of the lower limit include 90 g / mol or more, 99 g / mol or more, 109 g / mol or more, etc., and examples of the upper limit include 140 g / mol or less, 138 g / mol or less, etc. When the double bond equivalent of the ultraviolet-curable compound is within this range, both 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 ultraviolet-curable compound is outside the above range, the adhesion strength between the protective layer 3 and the support substrate 2 becomes high, and the peelability deteriorates, which is not preferable. Further, when the double bond equivalent of the ultraviolet-curable compound is less than 90 g / mol, the number of polymerizable double bonds increases with respect to the mass of the ultraviolet-curable compound. Therefore, although the hardness of the protective layer 3 increases, the flexural resistance deteriorates, and it becomes unsuitable for use in a foldable display device. When the double bond equivalent of the ultraviolet-curable compound exceeds 140 g / mol, the curability of the protective layer 3 decreases, and the surface hardness and scratch resistance may deteriorate.

[0032] As the photopolymerization initiator, radical polymerization initiators such as acetophenone-based, benzophenone-based, thioxanthone-based, benzoin, benzoin methyl ether, acylphosphine oxide, etc. can be used. As the photopolymerization initiator, for example, 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, 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone, etc. can be used. Among these, one type can be used alone, or two or more types can be used in combination.

[0033] The blending amount of the photopolymerization initiator is preferably 3.0 mass% or more and 6.0 mass% or less of the coating liquid for forming the protective layer. Examples of the lower limit include 3.0 mass% or more and 3.6 mass% or more, and examples of the upper limit include 6.0 mass% or less and 5.2 mass% or less. When the blending amount of the photopolymerization initiator is less than 3.0 mass% of the coating liquid for forming the protective layer, the peel strength of the protective layer 3 from the support substrate 2 may increase, and the peelability may deteriorate, which is not preferable. When the blending amount of the photopolymerization initiator exceeds 6.0 mass% of the coating liquid for forming the protective layer, the solubility of the photopolymerization initiator deteriorates, which is not preferable. In addition, when based on the total solid content of the coating liquid for forming the protective layer, the blending amount of the photopolymerization initiator is preferably 9.0 mass% or more and 13.0 mass% or less of the total solid content.

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

[0035] In the coating solution for forming the protective layer, inorganic fine particles may be added to improve the mechanical strength and surface strength (pencil hardness) of the protective layer 3. As the inorganic fine particles, silica fine particles (SiO2) or metal oxide fine particles can be used. As the metal oxide fine particles, one or more of antimony-doped tin oxide (ATO), phosphorus-doped tin oxide (PTO), gallium-doped tin oxide (GTO), zirconia (ZrO2), and titania (TiO2) can be used in combination. The inorganic fine particles may be surface-modified by bonding 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 functional groups can 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, fingerprint adhesion preventives, etc. may be added to the coating liquid for forming the protective layer as needed. By appropriately adding these additives, various functions can be imparted to the protective layer 3. Further, in order to improve the hydrophobicity of the protective layer 3, a hydrophobic material such as a cycloolefin polymer may be blended.

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

[0038] The integrated light amount of ultraviolet rays when curing the protective layer 3 is preferably 60 mJ / cm 2 or more and 300 mJ / cm 2 or less. When the integrated light amount of ultraviolet rays is less than 60 mJ / cm 2 the peel strength of the protective layer 3 may increase.

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

[0040] The Vickers hardness of the protective layer 3 in the optical laminate 1 is preferably 60 or more and 160 or less. Examples of the lower limit include 60 or more and 61 or more, and examples of the upper limit include 160 or less, 150 or less, 140 or less, 130 or less, 120 or less, and 113 or less. The Vickers hardness is a value measured in accordance with ISO14577. When the Vickers hardness is within this range, the surface hardness required for the protective film of the polarizer can be 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 state of being peeled off from the support substrate 2. The surface that becomes the interface with the polarizer may be either the air surface or the peeling surface, but it is preferable to use the air surface as the interface with the polarizer. The polarizer and the protective layer 3 may be adhered by using an adhesive. Alternatively, a polarizer adhered to the protective layer 3 may be formed by applying a coating solution of a PVA resin containing a dichroic dye onto the protective layer 3. The other surface of the protective layer 3 may be adhered to other members such as a resin film or a retardation plate via an adhesive or the like. The peeling of the protective layer 3 from the support substrate 2 may be performed before or after the adhesion to the polarizer.

[0042] As described above, the optical laminate 1 according to the present embodiment includes a support substrate 2 made of polyethylene terephthalate and a protective layer 3 laminated on at least one surface of the support substrate 2 in a peelable manner. 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 water 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 off from the support substrate 2, the wettability of the peeling surface of the protective layer 3 is excellent, and an optical laminate 1 having good hard coat properties and flexibility can be realized even when the protective layer 3 is thinned to 1.0 to 5.0 μm.

[0043] In addition, another optical laminate 1 according to this embodiment includes a support substrate 2 made of polyethylene terephthalate and a protective layer 3 laminated on at least one surface of the support substrate 2 in a peelable manner. 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, and the piercing elastic modulus is 0.15 N / mm or more. The pure water contact angle on the peeling surface side of the protective layer 3 is 50 degrees or more and 85 degrees or less. According to this embodiment, even after peeling from the support substrate 2, the wettability of the peeling surface of the protective layer 3 is excellent, and an optical laminate 1 with good hard coat properties and flexibility can be realized even when the protective layer 3 is thinned to 1.0 to 5.0 μm.

Example

[0044] Hereinafter, examples of specifically implementing the present invention will be described.

[0045] (Example 1) A coating solution for forming a protective layer having the composition shown in Table 1 was prepared, and it was applied to one side of a PET substrate (T60, Toray Industries, Inc.) with a thickness of 75 μm by a bar coating method so that the cured film thickness was 2.0 μm, and dried at 70°C for 30 seconds. After drying, using a metal halide lamp, ultraviolet rays were irradiated so that the integrated light quantity was 122 mJ / cm 2 to cure the coating film, and an optical laminate with a protective layer laminated on the support substrate was obtained.

[0046] (Examples 2 to 5) An optical laminate was obtained under the same conditions as in Example 1, except that the composition of the coating solution for forming the protective layer was changed as shown in Table 1.

[0047] (Example 6) An optical laminate was obtained under the same conditions as in Example 1, except that the coating solution was applied so that the cured film thickness of the protective layer was 4.0 μm.

[0048] (Example 7) An optical laminate was obtained under the same conditions as in Example 1, except that the coating solution was applied so that the cured film thickness of the protective layer was 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 solution for forming the protective layer was changed as described 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 support substrate.

[0051] (Comparative Examples 2 to 5) An optical laminate was obtained under the same conditions as in Example 1, except that the composition of the coating solution for forming the protective layer was changed as described in Table 3.

[0052] (Comparative Example 6) An optical laminate was obtained under the same conditions as in Example 1, except that the coating solution was applied so that the cured film thickness of the protective layer was 7.0 μm.

[0053] (Comparative Example 7) An optical laminate was obtained under the same conditions as in Example 1, except that the coating solution was applied so that the cured film 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 Industries, 38-SY) having the surface roughness and surface free energy shown in Table 4 was used as the support 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 support substrate.

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

[0057] The details of the compounds shown in Tables 1 to 4 are shown below. 1. UV curable compound (monomer) (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. Photoinitiator (1) Omnirad (registered trademark) 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. Additive (1) GRANDIC PC4300, manufactured by DIC, leveling agent (2) BYK-3566, manufactured by BYK, leveling agent

[0060] 4. Solvent (1) Dimethyl carbonate (2) MIBK (Methyl isobutyl ketone)

[0061] The optical laminates according to each example and each comparative example were evaluated by the following method.

[0062] [Arithmetic mean roughness Ra, maximum height Rz] Using a white light interference microscope (ECLIPSE LV150N, Nikon Corporation), the surface shape of the evaluation surface (the surface on which the protective layer is laminated) was observed, and Ra and Rz averaged from the surface shape data at 6 locations were calculated.

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

[0064] [Pure water contact angle of the protective layer] A contact angle meter (Drop Master 300, Kyowa Interface Science Co., Ltd.) was used, and the measured value 5 seconds after pure water was dropped onto the measurement surface was used. The pure water contact angle of the air side of the protective layer was measured with the protective layer not peeled from the support substrate. The peeled surface was measured in a state where the protective layer of the optical laminate was bonded to a glass plate using an adhesive tape (TD06A, Kakinokawa Seishi Co., Ltd.), then the support substrate was peeled from the protective layer, and the protective layer was bonded via the adhesive tape on the glass plate.

[0065] [Pencil hardness] The pencil hardness was evaluated in accordance with JIS K5400-1900. Using a pencil (uni, Mitsubishi Pencil Co., Ltd.) and a Clemens type scratch tester (HA-301, Tester Sangyo Co., Ltd.), the pencil hardness of the surface of the protective layer was measured. Repeated tests were conducted while changing the hardness of the pencil, and the change in appearance due to scratches was visually observed. The maximum hardness at which no scratches were observed was taken as the evaluation value. A pencil hardness of F or higher was considered a pass. 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] [Scratch resistance] The top and bottom of a sample obtained by cutting out the optical laminate to a size of 50 mm × 170 mm were fixed to a pedestal with cellophane tape. A 20 mm × 20 mm steel wool (BONSTAR #0000) was brought into contact with the air side of the protective layer, and a scratch length of 80 mm or more was applied with a test load of 1,000 g / 4 cm 2 and reciprocated 10 times. Then, the scratches generated between the central 30 mm in the scratch length direction were visually counted. A pass was defined as 10 or fewer scratches.

[0067] [Flexural resistance (mandrel test)] The flexural resistance was evaluated by a mandrel test in accordance with JIS K 5600-1. A sample of the optical laminate was wound around a metal cylinder with a diameter ranging from 1 mm to 3 mm such that the protective layer was on the outside, and the minimum diameter of the cylinder at which no cracks occurred in the protective layer was taken as the evaluation value. A pass was defined as a minimum cylinder diameter of 2 mm or less.

[0068] [Vickers hardness] The Vickers hardness was measured by a micro-indentation test in accordance with ISO14577 (nano-indentation method) using a micro-hardness tester (Fischer Scope HM2000, Fischer Instruments Co., Ltd.). Using a Vickers indenter HM2000 023 as the measurement indenter, the indenter was brought into contact with the air side of the protective layer supported on a support substrate, and the measurement was carried out 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] With a flat surface body no-load U-shaped expansion and contraction test jig (DMX-FS) attached to a desktop durability tester (Yuasa System Devices Co., Ltd.), samples of the optical laminate according to each example and each comparative example were attached flat. When bent so that the protective layer was on the outside, it was continuously bent so that the distance between the opposing protective layers was 4 mm. The bending operation was performed once per second, and the number of times until cracks occurred in the protective layer was used as the evaluation value. A folding count of 200,000 or more was considered a pass.

[0070] [Contact angle of the support substrate] Using a contact angle meter (Drop Master 300, Kyowa Interface Science Co., Ltd.), the measured value 5 seconds after each solvent (pure water, hexadecane, diiodomethane) was dropped onto the measurement surface was used.

[0071] [Surface free energy of the support substrate] Equation (3) was derived from the following equations (1) and (2), and the contact angles of the solvents (pure water, hexadecane, diiodomethane) obtained above were introduced into Equation (3) to calculate the surface free energy by a system of three linear equations with three unknowns.

[0072] [Number]

[0073] [Puncture strength (puncture test)] Evaluated by a universal testing machine (STB-1225L, A&D) in accordance with JIS Z 1707. The protective layer was transferred to a cardboard with a 10 mm diameter hole, and the puncture force (N) and puncture elongation (mm) when vertically puncturing the overlapping part of the hole with a needle (semicircular needle with a diameter of 1.0 mm and a tip shape radius of 0.5 mm) at a speed of 50 mm / min were determined. The puncture elastic modulus (N / mm) was obtained by dividing the puncture force by the puncture elongation, and the average value calculated by measuring 5 times was used as the evaluation value. A pass was considered when the puncture force was 0.25 N or more, the puncture elongation was 1.0 mm or more, and the puncture elastic modulus was 0.15 N / mm or more.

[0074] Table 1 to 4 shows the composition (coating liquid composition) of the optical laminate according to each example and each comparative example and the evaluation results together.

[0075]

Table 1

[0076]

Table 2

[0077]

Table 3

[0078]

Table 4

[0079] As shown in Table 1, all of the optical laminates according to Examples 1 to 6 were excellent in wettability (pure water contact angle), and as shown in 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 were excellent in surface hardness and also had good flex resistance. In addition, the optical laminates according to Examples 1 to 6 had 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 all of the wettability, hard coatability, and flexibility of the peel surface of the protective layer, and also had excellent peelability from the support substrate.

[0080] Example 7 had a protective layer with the same composition as that of Example 1 but with a thinner film thickness of 1.5 μm. Compared with Example 1, the Vickers hardness remained unchanged, the puncture strength decreased slightly but still maintained its strength, the peelability was good, and it was also excellent in surface hardness, flex resistance, and flex durability. Example 8 used a support substrate with a smaller surface unevenness structure and lower surface free energy compared to other examples. However, the coatability of the protective layer was also problem-free, and even when thinned to 2.0 μm, the peelability 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 compared to Example 1. The pencil hardness and abrasion resistance tests are performed by applying a horizontal force to the protective layer, so the influence of the substrate thickness is small, and both evaluations were good. However, the Vickers hardness measurement is performed by pressing the measuring indenter vertically against the protective layer, so the influence of the substrate thickness is large, and the Vickers hardness was lower compared to Example 1. Also, in Comparative Example 1, since a PET substrate with a rougher surface was used as the support substrate compared to Examples 1 to 6, the pure water contact angle of the peeling surface of the protective layer deteriorated. Therefore, compared to Examples 1 to 6, the wettability of the peeling surface of the protective layer is poor, and there is a possibility that the adhesion during bonding with other members may decrease.

[0082] Both of the optical laminates according to Comparative Examples 2 and 3 used a monomer with a double bond equivalent exceeding 140 g / mol as the ultraviolet curable compound for forming the protective layer. In the optical laminates according to Comparative Examples 2 and 3, since the number of polymerizable double bonds is small relative to the mass of the monomer, the curing of the protective layer is insufficient, the pencil hardness, abrasion resistance, and Vickers hardness are poor, and the hard coatability is insufficient. Also, in Comparative Examples 2 and 3, the peeling force of the protective layer became too high and the peelability also deteriorated.

[0083] 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 the ultraviolet curable compound for forming the protective layer. In the optical laminates according to Comparative Examples 4 and 5, since the number of polymerizable double bonds was large relative to the mass of the monomer, they had excellent hard coat properties. However, the Vickers hardness of the protective layer became too high, resulting in poor flex resistance and bending test results, and insufficient flexibility. Also, in Comparative Examples 4 and 5, the peel strength of the protective layer became too high, deteriorating the peelability.

[0084] The optical laminate according to Comparative Example 6 had a cured film thickness of the protective layer of 7.0 μm. However, due to the thick film thickness, the bending test results were poor and the flexibility was insufficient.

[0085] In Comparative Example 7, the thickness of the protective layer was reduced to 0.9 μm, which was excellent in flex resistance. However, it was inferior in surface hardness and the strength of the film itself, lacking practicality. In Comparative Example 8, since the support substrate had low affinity for any of the solvents of pure water, hexadecane, and diiodomethane compared to Examples 1 to 6, the coatability of the coating liquid for forming the protective layer deteriorated. The obtained protective layer was inferior in pencil hardness, which is an index of surface hardness in the horizontal direction, and also had an inferior pure water contact angle on the peeled surface, so there was a possibility that the adhesion when bonded to other members would decrease. In Comparative Example 9, since the surface free energy of the support substrate was too large, it was difficult to peel the protective layer, and it was difficult to form a peelable film. In Comparative Example 10, the same support substrate as in Examples 1 to 6 was used, and the peelability was good. However, the curing of the formed protective layer was not sufficient, and it was inferior in surface hardness and the strength of the film itself.

Industrial Applicability

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

Explanation of Symbols

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

Claims

1. A support substrate made of polyethylene terephthalate, and a protective layer peelably laminated on at least one surface 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 water contact angle on the peeling surface side of the protective layer is 50 degrees or more and 85 degrees or less. An optical laminate characterized by this.

2. A support substrate made of polyethylene terephthalate, and a protective layer peelably laminated on at least one surface 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 elastic modulus is 0.15 N / mm or more, and the pure water contact angle on the peeling surface side of the protective layer is 50 degrees or more and 85 degrees or less. An optical laminate characterized by this.

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 on which the protective layer of the support substrate 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 protective layer is composed of a cured film of a coating liquid containing an ultraviolet curable compound, a photopolymerization initiator, and a solvent, the photopolymerization initiator 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. The optical laminate according to claim 1 or 2, characterized by this.

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