JP7528062B2 - Polarizing plate using laminate for protecting polarizer - Google Patents

Description

The present invention relates to a laminate for protecting a polarizer and a polarizing plate using the laminate.

In image display devices (e.g., liquid crystal display devices, organic EL display devices), a polarizing plate is often arranged on at least one side of the display cell due to the image formation method. In recent years, image display devices have become thinner and more flexible, and as a result, there is a strong demand for thinner polarizing plates and their constituent films (e.g., polarizer protective films). However, the thinner the polarizer protective film, the more pronounced the durability problem becomes, in that the optical properties of the polarizing plate deteriorate in a heated and humidified environment. As a polarizer protective film that can realize a thin and durable polarizing plate, a polarizer protective film made of a solidified coating film of a specified resin solution is being considered. This technology is in the early stages of development, and there is still room for various considerations.

JP 2015-210474 A

The present invention has been made to solve the above-mentioned problems of the conventional art, and its main objective is to provide a laminate for protecting a polarizer that can realize a thin and highly durable polarizing plate and further suppresses cracks and/or breakage.

The polarizer protection laminate of the present invention has a first layer composed of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin having a glass transition temperature of 95° C. or more, and a second layer composed of a cured product of a curable resin, and the second layer has a thickness of 1.0 μm or more.
In one embodiment, the second layer has a modulus of elasticity of 50 MPa or more and an elongation of 2% or more. In one embodiment, the second layer has a pencil hardness of 2H or more.
In one embodiment, the first layer has a thickness of 10 μm or less.
In one embodiment, the first layer has an in-plane retardation Re(550) of 0 nm to 10 nm and a retardation in the thickness direction Rth(550) of −20 nm to +10 nm.
According to another aspect of the present invention, there is provided a polarizing plate comprising a polarizer and the above-described polarizer protection laminate disposed on one side of the polarizer, the polarizer protection laminate being disposed such that the first layer faces the polarizer.
In one embodiment, the polarizing plate is disposed on a viewer side of an image display device, and the second layer of the polarizer protection laminate is disposed on the viewer side.

According to the present invention, by forming a polarizer protective film as a laminate of a first layer composed of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin having a glass transition temperature of 95°C or higher, and a second layer composed of a cured product of a curable resin (typically, an active energy ray curable resin), it is possible to realize a thin polarizing plate having excellent durability, and further, a polarizer protective film (laminate for polarizer protection) in which cracks and/or cracks are suppressed can be realized.

1 is a schematic cross-sectional view of a polarizer protection laminate according to one embodiment of the present invention. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing an example of a drying shrinkage treatment using a heating roll in a method for producing a polarizing plate according to one embodiment of the present invention.

A. Polarizer Protective Laminate A-1. Overview of Polarizer Protective Laminate FIG. 1 is a schematic cross-sectional view of a polarizer protective laminate according to one embodiment of the present invention. The polarizer protective laminate 100 of the illustrated example has a first layer 10 and a second layer 20. The first layer 10 is composed of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin having a glass transition temperature of 95° C. or higher. The second layer 20 is composed of a cured product of a curable resin. In an embodiment of the present invention, the thickness of the second layer is 1.0 μm or more. The first layer and the second layer will be specifically described below.

A-2. First Layer The first layer can typically function as a protective layer for the polarizer. As described above, the first layer is composed of a solidified coating film of a solution of a thermoplastic acrylic resin (hereinafter simply referred to as an acrylic resin) in an organic solvent. Hereinafter, the components of the first layer will be specifically described, and then the characteristics of the first layer will be described.

A-2-1. Acrylic resin The glass transition temperature (Tg) of the acrylic resin is 95°C or higher as described above. As a result, the Tg of the first layer is 95°C or higher. If the Tg of the acrylic resin is 95°C or higher, the polarizing plate including the first layer obtained from such a resin tends to have excellent durability. The Tg of the acrylic resin is typically 100°C or higher, preferably 110°C or higher, more preferably 115°C or higher, even more preferably 120°C or higher, and particularly preferably 125°C or higher. On the other hand, the Tg of the acrylic resin is preferably 300°C or lower, more preferably 250°C or lower, even more preferably 200°C or lower, and particularly preferably 160°C or lower. If the Tg of the acrylic resin is in such a range, it may have excellent moldability.

As the acrylic resin, any suitable acrylic resin may be used as long as it has the above Tg. The acrylic resin typically contains alkyl (meth)acrylate as the main component as a monomer unit (repeating unit). In this specification, "(meth)acrylic" means acrylic and/or methacrylic. Examples of the alkyl (meth)acrylate constituting the main skeleton of the acrylic resin include linear or branched alkyl groups having 1 to 18 carbon atoms. These can be used alone or in combination. Furthermore, any suitable copolymerization monomer may be introduced into the acrylic resin by copolymerization. The repeating unit derived from the alkyl (meth)acrylate is typically represented by the following general formula (1):

In general formula (1), ^R4 represents a hydrogen atom or a methyl group, and ^R5 represents a hydrogen atom or an optionally substituted aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms. Examples of the substituent include halogen and a hydroxyl group. Specific examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, chloromethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate, 2,3,4,5-tetrahydroxypentyl (meth)acrylate, methyl 2-(hydroxymethyl)acrylate, ethyl 2-(hydroxymethyl)acrylate, and methyl 2-(hydroxyethyl)acrylate. In the general formula (1), ^R5 is preferably a hydrogen atom or a methyl group. Therefore, a particularly preferred alkyl (meth)acrylate is methyl acrylate or methyl methacrylate.

The acrylic resin may contain only a single alkyl(meth)acrylate unit, or may contain a plurality of alkyl(meth)acrylate units in which R ⁴ and R ⁵ in the above general formula (1) are different.

The content of alkyl (meth)acrylate units in the acrylic resin is preferably 50 mol% to 98 mol%, more preferably 55 mol% to 98 mol%, even more preferably 60 mol% to 98 mol%, particularly preferably 65 mol% to 98 mol%, and most preferably 70 mol% to 97 mol%. If the content is less than 50 mol%, the effects derived from the alkyl (meth)acrylate units (e.g., high heat resistance, high transparency) may not be fully exhibited. If the content is more than 98 mol%, the resin may be brittle and easily cracked, and high mechanical strength may not be fully exhibited, resulting in poor productivity.

The acrylic resin may have a repeating unit containing a ring structure. Examples of repeating units containing a ring structure include lactone ring units, glutaric anhydride units, glutarimide units, maleic anhydride units, and maleimide (N-substituted maleimide) units. The repeating units of the acrylic resin may contain only one type of repeating unit containing a ring structure, or may contain two or more types.

The lactone ring unit is preferably represented by the following general formula (2):

一般式（２）において、Ｒ^１、Ｒ^２およびＲ^３は、それぞれ独立して、水素原子または炭素数１～２０の有機残基を表す。なお、有機残基は酸素原子を含んでいてもよい。アクリル系樹脂には、単一のラクトン環単位のみが含まれていてもよく、上記一般式（２）におけるＲ^１、Ｒ^２およびＲ^３が異なる複数のラクトン環単位が含まれていてもよい。ラクトン環単位を有するアクリル系樹脂は、例えば特開２００８－１８１０７８号公報に記載されており、当該公報の記載は本明細書に参考として援用される。

In the general formula (2), R ¹ , R ² and R ³ each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom. The acrylic resin may contain only a single lactone ring unit, or may contain a plurality of lactone ring units in which R ¹ , R ² and R ³ in the general formula (2) are different. An acrylic resin having a lactone ring unit is described, for example, in JP 2008-181078 A, and the description of this publication is incorporated herein by reference.

The glutarimide unit is preferably represented by the following general formula (3):

In the general formula (3), R ¹¹ and R ¹² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ¹³ represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aryl group having 6 to 10 carbon atoms. In the general formula (3), preferably, R ¹¹ and R ¹² each independently represent hydrogen or a methyl group, and R ¹³ represents hydrogen, a methyl group, a butyl group, or a cyclohexyl group. More preferably, R ¹¹ represents a methyl group, R ¹² represents hydrogen, and R ¹³ represents a methyl group. The acrylic resin may contain only a single glutarimide unit, or may contain a plurality of glutarimide units in which R ¹¹ , R ¹² , and R ¹³ in the general formula (3) are different. Acrylic resins having glutarimide units are described, for example, in JP-A-2006-309033, JP-A-2006-317560, JP-A-2006-328334, JP-A-2006-337491, JP-A-2006-337492, JP-A-2006-337493, and JP-A-2006-337569, the disclosures of which are incorporated herein by reference. Note that, for the glutaric anhydride unit, the above description of the glutarimide unit applies, except that the nitrogen atom substituted with R ¹³ in the above general formula (3) becomes an oxygen atom.

As the structures of maleic anhydride units and maleimide (N-substituted maleimide) units are specified from their names, detailed explanations are omitted.

The content of repeating units containing a ring structure in the acrylic resin is preferably 1 mol% to 50 mol%, more preferably 10 mol% to 40 mol%, and even more preferably 20 mol% to 30 mol%. If the content is too low, the Tg may be less than 110°C, and the heat resistance, solvent resistance, and surface hardness of the resulting first layer may be insufficient. If the content is too high, the moldability and transparency may be insufficient.

The acrylic resin may contain repeating units other than the alkyl (meth)acrylate units and the repeating units containing a ring structure. Examples of such repeating units include repeating units derived from vinyl monomers that are copolymerizable with the monomers that constitute the above units (other vinyl monomer units). Examples of other vinyl monomers include acrylic acid, methacrylic acid, crotonic acid, 2-(hydroxymethyl)acrylic acid, 2-(hydroxyethyl)acrylic acid, acrylonitrile, methacrylonitrile, ethacrylonitrile, allyl glycidyl ether, maleic anhydride, itaconic anhydride, N-methylmaleimide, N-ethylmaleimide, N-cyclohexylmaleimide, aminoethyl acrylate, propylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylaminopropyl methacrylate, cyclohexylaminoethyl methacrylate, N-vinyldiethylamine, N-acetylvinylamine, allylamine, methallylamine, N-methylallylamine, 2-isopropenyl-oxazoline, 2-vinyl-oxazoline, 2-acroyl-oxazoline, N-phenylmaleimide, phenylaminoethyl methacrylate, styrene, α-methylstyrene, p-glycidylstyrene, p-aminostyrene, and 2-styryl-oxazoline. These may be used alone or in combination. The type, number, combination, content ratio, etc. of the other vinyl monomer units may be appropriately set depending on the purpose.

The weight average molecular weight of the acrylic resin is preferably 1,000 to 2,000,000, more preferably 5,000 to 1,000,000, even more preferably 10,000 to 500,000, particularly preferably 50,000 to 500,000, and most preferably 60,000 to 150,000. The weight average molecular weight can be determined, for example, using a gel permeation chromatograph (GPC system, manufactured by Tosoh Corporation) in terms of polystyrene. Tetrahydrofuran can be used as the solvent.

The acrylic resin may be polymerized by any suitable polymerization method using an appropriate combination of the above monomer units.

In an embodiment of the present invention, an acrylic resin may be used in combination with another resin. That is, a monomer component constituting an acrylic resin may be copolymerized with a monomer component constituting another resin, and the copolymer may be used to form the first layer described below; a blend of an acrylic resin and another resin may be used to form the first layer. Examples of other resins include thermoplastic resins such as styrene resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyether ether ketone, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, and polyetherimide. The type and amount of the resin used in combination may be appropriately set depending on the purpose and the desired properties of the resulting film. For example, a styrene resin (preferably an acrylonitrile-styrene copolymer) may be used in combination as a retardation control agent.

When acrylic resin is used in combination with other resins, the content of the acrylic resin in the blend of the acrylic resin with other resins is preferably 50% by weight to 100% by weight, more preferably 60% by weight to 100% by weight, even more preferably 70% by weight to 100% by weight, and particularly preferably 80% by weight to 100% by weight. If the content is less than 50% by weight, the high heat resistance and high transparency inherent to the acrylic resin may not be fully reflected.

A-2-2. Configuration and characteristics of the first layer As described above, the first layer is composed of a solidified coating film of an organic solvent solution of an acrylic resin having a glass transition temperature of 95°C or higher. Such a solidified coating film can be made significantly thinner than an extrusion-molded film. The thickness of the first layer is, for example, 10 μm or less, preferably 7 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. The lower limit of the thickness of the first layer can be, for example, 1 μm. Although not theoretically clear, such a solidified coating film has the advantages of being smaller in shrinkage during film formation than a cured product of a thermosetting resin or an active energy ray-curable resin (for example, an ultraviolet-curable resin), and of being free of residual monomers and the like, thereby suppressing deterioration of the film itself, and of being able to suppress adverse effects on a polarizing plate (polarizer) caused by residual monomers and the like. Furthermore, it has the advantage of being superior in humidification durability because it has smaller moisture absorption and moisture permeability than a solidified coating film of a water-based solution such as an aqueous solution or water dispersion. As a result, it is possible to realize a polarizing plate having excellent durability and capable of maintaining its optical properties even in a heated and humidified environment.

The Tg of the first layer is as described above in section A-2-1 for acrylic resins.

The first layer is preferably substantially optically isotropic. In this specification, "substantially optically isotropic" means that the in-plane retardation Re(550) is 0 nm to 10 nm, and the thickness direction retardation Rth(550) is -20 nm to +10 nm. The in-plane retardation Re(550) is more preferably 0 nm to 5 nm, even more preferably 0 nm to 3 nm, and particularly preferably 0 nm to 2 nm. The thickness direction retardation Rth(550) is more preferably -5 nm to +5 nm, even more preferably -3 nm to +3 nm, and particularly preferably -2 nm to +2 nm. If the Re(550) and Rth(550) of the first layer are in such a range, it is possible to prevent adverse effects on the display characteristics when a polarizing plate including the first layer is applied to an image display device. Note that Re(550) is the in-plane retardation of the film measured with light having a wavelength of 550 nm at 23 ° C. Re(550) is calculated by the formula: Re(550)=(nx-ny)×d. Rth(550) is the retardation in the thickness direction of the film measured with light having a wavelength of 550 nm at 23° C. Rth(550) is calculated by the formula: Rth(550)=(nx-nz)×d. Here, nx is the refractive index in the direction in which the in-plane refractive index is maximized (i.e., the slow axis direction), ny is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), nz is the refractive index in the thickness direction, and d is the thickness of the film (nm).

The higher the light transmittance at 380 nm for a first layer thickness of 3 μm, the better. Specifically, the light transmittance is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. If the light transmittance is within this range, the desired transparency can be ensured. The light transmittance can be measured, for example, by a method conforming to ASTM-D-1003.

The lower the haze of the first layer, the better. Specifically, the haze is preferably 5% or less, more preferably 3% or less, even more preferably 1.5% or less, and particularly preferably 1% or less. A haze of 5% or less can give the film a good sense of clarity. Furthermore, even when used as the viewing side polarizing plate of an image display device, the displayed content can be clearly seen.

The YI at a thickness of 3 μm of the first layer is preferably 1.27 or less, more preferably 1.25 or less, even more preferably 1.23 or less, and particularly preferably 1.20 or less. If the YI exceeds 1.3, the optical transparency may be insufficient. The YI can be calculated from the tristimulus values (X, Y, Z) of the color obtained by measurement using, for example, a high-speed integrating sphere type spectral transmittance measuring device (product name DOT-3C: manufactured by Murakami Color Research Laboratory) according to the following formula:
YI=[(1.28X-1.06Z)/Y]×100

The b value (a measure of hue according to the Hunter color system) of the first layer at a thickness of 3 μm is preferably less than 1.5, and more preferably 1.0 or less. If the b value is 1.5 or more, an undesired color tone may result. The b value can be obtained, for example, by cutting a sample of the film constituting the first layer into a 3 cm square, measuring the hue using a high-speed integrating sphere spectroscopic transmittance measuring instrument (product name DOT-3C: manufactured by Murakami Color Research Laboratory), and evaluating the hue according to the Hunter color system.

The first layer (solidified coating film) may contain any suitable additive depending on the purpose. Specific examples of additives include ultraviolet absorbers; leveling agents; antioxidants such as hindered phenols, phosphorus, and sulfur; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fibers and carbon fibers; near-infrared absorbers; flame retardants such as tris(dibromopropyl)phosphate, triallyl phosphate, and antimony oxide; antistatic agents such as anionic, cationic, and nonionic surfactants; colorants such as inorganic pigments, organic pigments, and dyes; organic or inorganic fillers; resin modifiers; organic and inorganic fillers; plasticizers; lubricants; antistatic agents; flame retardants; and the like. The additives may be added during polymerization of the acrylic resin, or may be added to the solution during film formation. The type, number, combination, and amount of additives may be appropriately set depending on the purpose.

An easy-adhesion layer may be formed on the side of the first layer opposite the second layer (typically, the polarizer side when used in a polarizing plate). The easy-adhesion layer contains, for example, a water-based polyurethane and an oxazoline-based crosslinking agent. By forming such an easy-adhesion layer, the adhesion between the first layer and the polarizer can be increased.

A-3. Second layer The second layer can typically function as a hard coat layer. By providing the second layer, cracks and/or breaks in the first layer can be suppressed while maintaining the excellent characteristics of the first layer (a polarizing plate with excellent durability can be realized despite being very thin). As described above, the second layer is composed of a cured product of a curable resin. Although not theoretically clear, it is presumed that the three-dimensional crosslinked structure of the cured product suppresses cracks and/or breaks. The curable resin may be an active energy ray curable resin or a thermosetting resin. It is preferably an active energy ray curable resin. An active energy ray curable resin has the advantage that the reaction can be easily controlled and it is excellent in operability.

In an embodiment of the present invention, the thickness of the second layer is 1.0 μm or more, preferably 2.0 μm or more, and more preferably 2.5 μm or more, as described above. By making the thickness of the second layer a predetermined value or more, the desired rigidity can be obtained and cracks can be suppressed. The upper limit of the thickness of the second layer can be, for example, 5.0 μm. If the thickness of the second layer is too small, the curing reaction may be insufficient, making it difficult to form a layer, and the rigidity of the formed layer may be insufficient. If the thickness of the second layer is too large, the flexibility may be insufficient and cracks may be easily generated.

Preferably, the modulus of elasticity of the second layer is 50 MPa or more, and the elongation rate is 2% or more. By providing such a second layer, cracks and/or cracks in the first layer (as a result, the laminate for protecting a polarizer) can be significantly suppressed. The modulus of elasticity of the second layer is more preferably 500 MPa or more, even more preferably 1000 MPa or more, particularly preferably 2800 MPa or more, and especially preferably 2900 MPa or more. The upper limit of the modulus of elasticity of the second layer may be, for example, 7000 MPa. If the modulus of elasticity of the second layer is too high, it may become brittle and may not function as a protective layer. The elongation rate of the second layer is more preferably 5% or more, even more preferably 10% or more, particularly preferably 20% or more, and especially preferably 40% or more. The upper limit of the second layer may be, for example, 300%. If the modulus of elasticity of the second layer is large, the elongation rate may be small, and if the modulus of elasticity of the second layer is small, the elongation rate may be large. The modulus of elasticity and the elongation rate may be measured, for example, in accordance with JIS K 7161.

The pencil hardness of the second layer is preferably 2H or more, more preferably 3H or more, and even more preferably 4H or more. The upper limit of the pencil hardness of the second layer may be, for example, 6H. If the pencil hardness of the second layer is in such a range, cracks and/or cracks in the first layer can be further suppressed. The pencil hardness may be measured, for example, in accordance with JIS K 5400.

The second layer may typically be composed of any suitable active energy ray curable resin that can satisfy the above-mentioned characteristics. Examples of active energy ray curable resins include ultraviolet ray curable resins and electron beam curable resins. UV curable resins are preferred because they can efficiently form the second layer with simple processing operations. Examples of UV curable resins include various resins such as polyester, acrylic, urethane, amide, silicone, and epoxy. In one embodiment, the UV curable resin is a urethane acrylate resin. Details of the UV curable resin are described, for example, in Japanese Patent No. 6199605 as an organic component of the hard coat layer. The description in this publication is incorporated herein by reference.

B. Polarizing Plate The polarizer protection laminate described in the above section A can be applied to a polarizing plate as a polarizer protection film. Therefore, the embodiment of the present invention also includes such a polarizing plate. FIG. 2 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 200 of the illustrated example has a polarizer 120 and a polarizer protection laminate 100 arranged on one side of the polarizer 120. The polarizer protection laminate 100 is a polarizer protection laminate according to the embodiment of the present invention described in the above section A. The polarizer protection laminate 100 is arranged so that the first layer 10 is on the polarizer 120 side, and when the polarizing plate 200 is applied to an image display device, it is typically arranged on the viewing side of a display cell. In this case, typically, the second layer 20 of the polarizer protection laminate 100 is arranged on the viewing side.

If necessary, another protective layer (not shown) may be provided on the side of the polarizer 120 opposite the polarizer protection laminate 100. Typically, the polarizing plate has an adhesive layer as the outermost layer on one side (typically, the side opposite the polarizer protection laminate 100 of the polarizer 120), and can be attached to a display cell. If necessary, a surface protection film and/or a carrier film may be temporarily attached in a peelable manner to the polarizing plate to reinforce and/or support the polarizing plate. When the polarizing plate includes an adhesive layer, a separator is temporarily attached in a peelable manner to the surface of the adhesive layer to protect the adhesive layer until actual use and to enable the polarizing plate to be rolled.

The polarizing plate may be in a long shape or in a sheet shape. If the polarizing plate is in a long shape, the polarizing plate can preferably be wound into a roll.

In an embodiment of the present invention, by adopting the polarizer protection laminate described in section A above, the thickness of the polarizer protection film can be made very thin. Furthermore, such a polarizer protection laminate can be formed directly on the polarizer (i.e., without an adhesive layer or pressure-sensitive adhesive layer). As a result, the total thickness of the polarizing plate can be made extremely thin. The total thickness of the polarizing plate is, for example, 40 μm or less, preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 15 μm or less. The lower limit of the total thickness of the polarizing plate can be, for example, 10 μm.

Furthermore, by adopting the laminate for protecting a polarizer described in the above item A, a polarizing plate having excellent durability despite being very thin can be realized. Specifically, a polarizing plate in which the deterioration of optical properties is suppressed even in a heated and humidified environment can be realized. The polarizing plate of the present invention has a very small change ΔTs in the single-piece transmittance Ts and a very small change ΔP in the degree of polarization P after being left for 48 hours in an environment of 85° C. and 85% RH. The single-piece transmittance Ts can be measured, for example, using a UV-Vis spectrophotometer (manufactured by JASCO Corporation, product name "V7100"). The degree of polarization P is calculated from the single-piece transmittance (Ts), parallel transmittance (Tp), and cross transmittance (Tc) measured using the UV-Vis spectrophotometer according to the following formula.
Degree of polarization (P) (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 ×100
The above Ts, Tp and Tc are Y values measured using a 2-degree visual field (C light source) according to JIS Z 8701 and corrected for visibility. Ts and P are essentially characteristics of a polarizer. ΔTs and ΔP can be calculated by the following formulas.
ΔTs (%) = Ts ₄₈ - Ts ₀
ΔP (%) = P ₄₈ - P ₀
Here, Ts ₀ is the single transmittance before being left standing (initial), Ts ₄₈ is the single transmittance after being left standing, P ₀ is the polarization degree before being left standing (initial), and P ₄₈ is the polarization degree after being left standing. ΔTs is preferably 3.0% or less, more preferably 2.7% or less, and even more preferably 2.4% or less. ΔP is preferably -0.05% to 0%, more preferably -0.03% to 0%, and even more preferably -0.01% to 0%.

As described above, the polarizing plate of the present invention is extremely thin and can therefore be suitably applied to flexible image display devices. More preferably, the image display device has a curved shape (essentially a curved display screen) and/or can be bent or folded. Specific examples of image display devices include liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices, inorganic EL display devices). Needless to say, the above description does not prevent the polarizing plate of the present invention from being applied to ordinary image display devices.

B-1. Polarizer Any appropriate polarizer may be used as the polarizer. The polarizer may typically be produced using a laminate of two or more layers. A method for producing a polarizer will be described later in section B-2 as a method for producing a polarizing plate.

The thickness of the polarizer is preferably 1 μm to 8 μm, more preferably 1 μm to 7 μm, and even more preferably 2 μm to 5 μm.

The boric acid content of the polarizer is preferably 10% by weight or more, and more preferably 13% by weight to 25% by weight. When the boric acid content of the polarizer is in this range, due to a synergistic effect with the iodine content described below, it is possible to maintain ease of curl control during lamination and to improve appearance durability during heating while effectively suppressing curl during heating. The boric acid content can be calculated as the amount of boric acid contained in the polarizer per unit weight, for example, using the following formula from the neutralization method.

The iodine content of the polarizer is preferably 2% by weight or more, more preferably 2% by weight to 10% by weight. When the iodine content of the polarizer is in such a range, the synergistic effect with the boric acid content can maintain the ease of curl control during lamination, and can improve the appearance durability during heating while suppressing curl during heating. In this specification, the "iodine content" means the amount of all iodine contained in the polarizer (PVA-based resin film). More specifically, iodine exists in the polarizer in the form of iodine ion (I ^- ), iodine molecule (I ₂ ), polyiodine ion (I ₃ ^- , I ₅ ^- ), etc., and the iodine content in this specification means the amount of iodine including all of these forms. The iodine content can be calculated, for example, by a calibration curve method of fluorescent X-ray analysis. The polyiodine ion exists in the polarizer in the form of a PVA-iodine complex. The formation of such a complex can result in absorption dichroism in the wavelength range of visible light. Specifically, the complex of PVA and triiodide ion (PVA·I ₃ ⁻ ) has an absorption peak near 470 nm, and the complex of PVA and pentaiodide ion (PVA·I ₅ ⁻ ) has an absorption peak near 600 nm. As a result, polyiodine ions can absorb light in a wide range of visible light depending on their form. On the other hand, iodine ions (I ⁻ ) have an absorption peak near 230 nm and are not substantially involved in the absorption of visible light. Therefore, polyiodine ions present in a complex state with PVA can mainly contribute to the absorption performance of the polarizer.

The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single transmittance Ts of the polarizer is preferably between 40% and 48%, and more preferably between 41% and 46%. The degree of polarization P of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

B-2. Manufacturing method of polarizing plate B-2-1. Manufacturing method of polarizer The manufacturing method of the polarizer described in the above B-1 includes forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin substrate to form a laminate, and subjecting the laminate to an auxiliary air stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order, in which the laminate is heated while being conveyed in the longitudinal direction to shrink the laminate by 2% or more in the width direction. The content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60° C. to 120° C. According to such a manufacturing method, the above-mentioned polarizer can be obtained. In particular, a laminate including a PVA-based resin layer containing a halide is prepared, the laminate is stretched in multiple stages including auxiliary air stretching and underwater stretching, and the stretched laminate is heated with a heating roll, whereby a polarizer having excellent optical properties (typically, single transmittance and polarization degree) and suppressed variation in optical properties can be obtained. Specifically, by using a heating roll in the drying shrinkage treatment step, the laminate can be uniformly shrunk throughout the laminate while being transported. This not only improves the optical properties of the obtained polarizer, but also allows a polarizer having excellent optical properties to be stably produced, and suppresses variation in the optical properties (particularly, single transmittance) of the polarizer. Hereinafter, the halide and the drying shrinkage treatment will be described. Details of the manufacturing method other than these are described in, for example, JP 2012-73580 A. The entire description of this publication is incorporated herein by reference.

B-2-1-1. Halide The PVA-based resin layer containing a halide and a PVA-based resin can be formed by applying a coating liquid containing a halide and a PVA-based resin onto a thermoplastic resin substrate and drying the coating film. The coating liquid is typically a solution in which the above-mentioned halide and the above-mentioned PVA-based resin are dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Of these, water is preferred. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film that is in close contact with the thermoplastic resin substrate can be formed.

As the halide, any suitable halide may be employed. Examples include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred.

The amount of halide in the coating solution is preferably 5 to 20 parts by weight, and more preferably 10 to 15 parts by weight, per 100 parts by weight of the PVA-based resin. If the amount of halide is too high, the halide may bleed out, causing the final polarizer to become cloudy.

Generally, the orientation of the polyvinyl alcohol molecules in the PVA-based resin increases when the PVA-based resin layer is stretched, but when the stretched PVA-based resin layer is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules may become disordered, and the orientation may decrease. In particular, when a laminate of a thermoplastic resin substrate and a PVA-based resin layer is stretched in boric acid water, the tendency for the degree of orientation to decrease is remarkable when the laminate is stretched in boric acid water at a relatively high temperature to stabilize the stretching of the thermoplastic resin substrate. For example, while a PVA film alone is generally stretched in boric acid water at 60°C, a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is stretched at a high temperature of around 70°C, in this case, the orientation of the PVA at the beginning of the stretching may decrease before it increases due to the stretching in water. In contrast, by preparing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate, and stretching the laminate at high temperature (auxiliary stretching) in air before stretching in boric acid water, the crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the orientation disorder and the decrease in the orientation of the polyvinyl alcohol molecules can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of the polarizer obtained by immersing the laminate in a liquid through a treatment process such as a dyeing treatment and an underwater stretching treatment.

B-2-1-2. Drying shrinkage treatment Drying shrinkage treatment may be performed by zone heating in which the entire zone is heated, or by heating the transport roll (using a so-called heating roll) (heat roll drying method). Preferably, both are used. By drying using a heating roll, it is possible to efficiently suppress the heat curl of the laminate and produce a polarizer with excellent appearance. Specifically, by drying the laminate in a state where it is aligned with the heating roll, it is possible to efficiently promote the crystallization of the thermoplastic resin substrate and increase the crystallinity, and even at a relatively low drying temperature, it is possible to satisfactorily increase the crystallinity of the thermoplastic resin substrate. As a result, the rigidity of the thermoplastic resin substrate increases and it becomes in a state where it can withstand the shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. In addition, by using a heating roll, it is possible to dry the laminate while maintaining it in a flat state, so that it is possible to suppress not only curling but also wrinkles. At this time, the laminate can be shrunk in the width direction by the drying shrinkage treatment, thereby improving the optical properties. This is because the orientation of the PVA and the PVA/iodine complex can be effectively increased. The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is preferably 2% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using a heating roll, the laminate can be continuously shrunk in the width direction while being transported, and high productivity can be achieved.

Figure 3 is a schematic diagram showing an example of a drying shrinkage process. In the drying shrinkage process, the laminate 200 is dried while being transported by transport rolls R1 to R6 heated to a predetermined temperature and guide rolls G1 to G4. In the illustrated example, the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but, for example, the transport rolls R1 to R6 may be arranged so as to continuously heat only one surface of the laminate 200 (for example, the thermoplastic resin substrate surface).

Drying conditions can be controlled by adjusting the heating temperature of the transport roll (temperature of the heating roll), the number of heating rolls, the contact time with the heating roll, etc. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. The crystallization degree of the thermoplastic resin can be increased well, curling can be suppressed well, and an optical laminate with extremely excellent durability can be produced. The temperature of the heating roll can be measured by a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular restriction as long as there are multiple transport rolls. The number of transport rolls is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roll is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

The heating roll may be installed in a heating furnace (e.g., an oven) or in a normal production line (at room temperature). It is preferably installed in a heating furnace equipped with a blowing means. By using both drying with a heating roll and hot air drying, it is possible to suppress abrupt temperature changes between the heating rolls, and it is possible to easily control shrinkage in the width direction. The hot air drying temperature is preferably 30°C to 100°C. The hot air drying time is preferably 1 second to 300 seconds. The hot air speed is preferably about 10 m/s to 30 m/s. The wind speed is the wind speed in the heating furnace and can be measured by a mini-vane type digital anemometer.

Preferably, after the underwater stretching process and before the drying shrinkage process, a cleaning process is performed. The cleaning process is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

In this manner, a thermoplastic resin substrate/polarizer laminate can be obtained.

B-2-2. Manufacturing Method of Polarizing Plate A solution of an acrylic resin in an organic solvent is applied to the surface of the laminate obtained in the above B-2-1 to form a coating film, and the coating film is solidified to form the first layer of the polarizer protective laminate.

Acrylic resins are as explained in section A-2-1 above.

As the organic solvent, any suitable organic solvent capable of dissolving or uniformly dispersing the acrylic resin can be used. Specific examples of organic solvents include ethyl acetate, toluene, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, and cyclohexanone.

The acrylic resin concentration in the solution is preferably 3 to 20 parts by weight per 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film that adheres closely to the polarizer can be formed.

The solution may be applied to any suitable substrate or to a polarizer. When the solution is applied to a substrate, the solidified coating film formed on the substrate is transferred to the polarizer. When the solution is applied to a polarizer, the coating film is dried (solidified) to form the first layer directly on the polarizer. Preferably, the solution is applied to a polarizer, and the first layer is formed directly on the polarizer. With such a configuration, the adhesive layer or pressure-sensitive adhesive layer required for transfer can be omitted, so that the polarizing plate can be made even thinner. Any suitable method can be adopted as a method for applying the solution. Specific examples include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (comma coating, etc.).

The first layer can be formed by drying (solidifying) the coating film of the solution. The drying temperature is preferably 100°C or less, and more preferably 50°C to 70°C. If the drying temperature is in this range, adverse effects on the polarizer can be prevented. The drying time can vary depending on the drying temperature. The drying time can be, for example, 1 minute to 10 minutes.

Next, the second layer is formed by applying and curing an active energy ray curable resin on the surface of the first layer. The method of applying the active energy ray curable resin is as described above for the first layer. The active energy ray curable resin (resin composition) may contain a leveling agent. Examples of the leveling agent include a fluorine-based leveling agent and a silicone-based leveling agent. Furthermore, the active energy ray curable resin (resin composition) may contain an additive. Examples of the additive include fine particles, a filler, a dispersant, a plasticizer, an ultraviolet absorber, a surfactant, an antioxidant, and a thixotropic agent. The curing conditions may be appropriately set depending on the type of active energy ray curable resin.

In this manner, a polarizer protection laminate is formed. Although the above describes an embodiment in which a polarizer protection laminate is formed directly on a polarizer, a preformed polarizer protection laminate may be transferred to a polarizer. For example, a laminate having a substrate/polarizer protection laminate (second layer/first layer) configuration may be produced by forming the second layer and the first layer in this order on any suitable substrate, and the polarizer protection laminate may be transferred from this laminate to the polarizer.

As a result of the above, a laminate having a configuration of thermoplastic resin substrate/polarizer/polarizer protective laminate can be obtained. By peeling off the thermoplastic resin substrate from this laminate, a polarizing plate 200 having a polarizer 120 and a polarizer protective laminate 100 as shown in FIG. 2 can be obtained. Alternatively, a resin film constituting another protective layer may be attached to the polarizer surface of the thermoplastic resin substrate/polarizer laminate, and then the thermoplastic resin substrate may be peeled off to form a polarizer protective laminate on the peeled surface. In this case, a polarizing plate further having another protective layer can be obtained.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows. Unless otherwise specified, "parts" and "%" in the examples are by weight.

(1) Glass transition temperature Tg
The film constituting the first layer of the polarizer protection laminate used in the examples and comparative examples was measured using a heating TMA analyzer (manufactured by Hitachi High-Tech Science Corporation, product name "TMA-7100C") under the following measurement conditions: load 2 g; nitrogen atmosphere (200 ml/min); heating from 25°C to 150°C, holding at 150°C for 5 minutes, then cooling to 25°C, heating again to 150°C, and holding at 150°C for 5 minutes; heating rate 2°C/min.
(2) Elastic Modulus and Elongation Percentage The elastic modulus and elongation percentage of the film constituting the second layer of the polarizer protective laminate used in the examples and comparative examples were measured in accordance with JIS K 7161 and JIS K 7113.
(3) Cracks Test pieces (50 mm x 50 mm) were cut out from the polarizing plates obtained in the Examples and Comparative Examples, with two sides perpendicular to the absorption axis direction of the polarizer and facing the absorption axis direction, respectively. The test pieces were attached to a glass plate with an adhesive so that the polarizer protective laminate or protective layer was on the outside to prepare test samples, which were then left in an oven at 85°C and 85% RH for 48 hours to be heated and humidified, and the state of the polarizer protective laminate or protective layer in the humidified polarizing plate was visually or microscopically examined and evaluated according to the following criteria.
◯: No cracks were observed. △: Cracks were observed in some areas. ×: Significant cracks and cracks were also observed. (4) Single Transmittance and Degree of Polarization For the polarizing plates obtained in the Examples and Comparative Examples, the single transmittance (Ts), parallel transmittance (Tp) and crossed transmittance (Tc) were measured using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"), and the degree of polarization (P) was calculated using the following formula.
Degree of polarization (P) (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 ×100
The above Ts, Tp and Tc are Y values measured with a 2-degree visual field (C light source) according to JIS Z 8701 and corrected for visibility. Ts and P are substantially the characteristics of a polarizer.
Next, the polarizing plate was left in an oven at 85° C. and 85% RH for 48 hours to be heated and humidified (heating test), and the amount of change in single unit transmittance ΔTs was calculated from the single unit transmittance Ts ₀ before the heating test and the single unit transmittance Ts ₄₈ after the heating test using the following formula.
ΔTs (%) = Ts ₄₈ - Ts ₀
Similarly, the change in the degree of polarization ΔP was calculated from the degree of polarization P ₀ before the heating test and the degree of polarization P ₄₈ after the heating test using the following formula.
ΔP (%) = P ₄₈ - P ₀
The heating test was carried out by preparing test samples in the same manner as in the case of cracks described above.

Example 1
1. Preparation of a laminate of a polarizer and a resin substrate As a resin substrate, a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a water absorption rate of 0.75% and a Tg of about 75° C. was used. One surface of the resin substrate was subjected to a corona treatment.
A PVA aqueous solution (coating solution) was prepared by adding 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (polymerization degree 4,200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name "GOHSEFFIMER Z410") in a ratio of 9:1.
The above PVA aqueous solution was applied to the corona-treated surface of a resin substrate and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.
The obtained laminate was uniaxially stretched at its free end to 2.4 times its original size in the machine direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130° C. (auxiliary air stretching treatment).
Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment).
Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) having a liquid temperature of 30° C. for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer would be 41.5%±0.1% (dyeing treatment).
Next, the plate was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment).
Thereafter, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4.0% by weight, potassium iodide concentration: 5.0% by weight) at a liquid temperature of 62°C, and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds to a total stretch ratio of 5.5 times (underwater stretching treatment).
Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (cleaning treatment).
Thereafter, while drying in an oven maintained at 90° C., the laminate was brought into contact with a SUS heated roll having a surface temperature maintained at 75° C. for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment was 5.2%.
In this manner, a polarizer having a thickness of 5 μm was formed on the resin substrate, and a laminate of polarizer/resin substrate was produced.

2. Preparation of Polarizing Plate A cycloolefin film (ZT-12, 23 μm thick, manufactured by Zeon Corporation) was attached to the surface of the polarizer obtained above as a film constituting another protective layer via an ultraviolet-curing adhesive. Specifically, the curing adhesive was applied so that the total thickness of the adhesive became 1.0 μm, and the films were laminated using a rolling machine. Thereafter, the adhesive was cured by irradiating it from the film side with UV light. Next, the resin substrate was peeled off to obtain a polarizing plate having a configuration of another protective layer (ZT-12)/polarizer.

20 parts of an acrylic resin having a methyl methacrylate unit (manufactured by Kusumoto Chemical Industries, product name "B728") was dissolved in 80 parts of methyl ethyl ketone to obtain an acrylic resin solution (20%). This acrylic resin solution was applied to the polarizer surface of the polarizing plate obtained above using a wire bar, and the applied film was dried at 60°C for 5 minutes to form a first layer of a polarizer protection laminate constituted as a solidified coating film. The thickness of the first layer was 2 μm, and the Tg was 116°C. Furthermore, a composition for forming a second layer was applied to the surface of the first layer. The composition for forming the second layer contained 100 parts of a UV-curable urethane acrylate resin for hard coat layer (manufactured by DIC Corporation, product name "UNIDIC 17-806"), 0.01 parts of a leveling agent (manufactured by DIC Corporation, product name "GRANDIC PC4100"), and 3 parts of a photopolymerization initiator (manufactured by IGM Resins B.V., product name "Omnirad 907") The coating film was dried at 90°C for 1 minute, and then irradiated with UV light with an integrated light amount of 200 mW/ ^cm2 from a high-pressure mercury lamp to form a second layer of a polarizer protective laminate constituted as a cured product of the coating film. The thickness of the second layer was 3 μm, the elastic modulus was 5000 MPa, and the elongation rate was greater than 3%. In this way, a polarizing plate having a configuration of a polarizer protective laminate (second layer/first layer)/polarizer/another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the above-mentioned evaluations (3) and (4), and the results are shown in Table 1.

Example 2
A polarizing plate having a structure of polarizer protective laminate (second layer/first layer)/polarizer/another protective layer (ZT-12) was obtained in the same manner as in Example 1, except that the second layer was formed using "UNIDIC ELS-888" (manufactured by DIC Corporation) instead of "UNIDIC 17-806" as the ultraviolet-curable urethane acrylate resin for the hard coat layer. The second layer had a thickness of 3 μm, an elastic modulus of 3000 MPa, and an elongation of 40%.
The obtained polarizing plate was subjected to the above-mentioned evaluations (3) and (4), and the results are shown in Table 1.

Example 3
A polarizing plate having a structure of polarizer protective laminate (second layer/first layer)/polarizer/another protective layer (ZT-12) was obtained in the same manner as in Example 1, except that the second layer was formed using "UNIDIC V-4221" (manufactured by DIC Corporation) instead of "UNIDIC 17-806" as the ultraviolet-curable urethane acrylate resin for the hard coat layer. The second layer had a thickness of 3 μm, an elastic modulus of 60 MPa, and an elongation of 200%.

Example 4
A polarizing plate having a structure of polarizer protective laminate (second layer/first layer)/polarizer/another protective layer (ZT-12) was obtained in the same manner as in Example 1, except that the first layer was formed using a copolymer of methyl acrylate/butyl acrylate (molar ratio 80/20) instead of "B728" as the acrylic resin. The first layer had a thickness of 2 μm and a Tg of 95° C.
The obtained polarizing plate was subjected to the above-mentioned evaluations (3) and (4), and the results are shown in Table 1.

Example 5
A polarizing plate having a structure of polarizer protective laminate (second layer/first layer)/polarizer/another protective layer (ZT-12) was obtained in the same manner as in Example 4, except that the second layer was formed using "UNIDIC ELS-888" (manufactured by DIC Corporation) instead of "UNIDIC 17-806" as the ultraviolet-curable urethane acrylate resin for the hard coat layer. The second layer had a thickness of 3 μm, an elastic modulus of 3000 MPa, and an elongation of 40%.
The obtained polarizing plate was subjected to the above-mentioned evaluations (3) and (4), and the results are shown in Table 1.

Example 6
A polarizing plate having a structure of polarizer protective laminate (second layer/first layer)/polarizer/another protective layer (ZT-12) was obtained in the same manner as in Example 4, except that the second layer was formed using "UNIDIC V-4221" (manufactured by DIC Corporation) instead of "UNIDIC 17-806" as the ultraviolet-curable urethane acrylate resin for the hard coat layer. The second layer had a thickness of 3 μm, an elastic modulus of 60 MPa, and an elongation of 200%.
The obtained polarizing plate was subjected to the above-mentioned evaluations (3) and (4), and the results are shown in Table 1.

<Comparative Example 1>
A polarizing plate having a structure of polarizer protective laminate (second layer/first layer)/polarizer/another protective layer (ZT-12) was obtained in the same manner as in Example 1, except that the first layer was formed using "B734" (manufactured by Kusumoto Chemicals Co., Ltd.) instead of "B728" as the acrylic resin. The first layer had a thickness of 2 μm and a Tg of 71° C.
The obtained polarizing plate was subjected to the above-mentioned evaluations (3) and (4), and the results are shown in Table 1.

<Comparative Example 2>
A polarizing plate having a structure of polarizer protective laminate (second layer/first layer)/polarizer/another protective layer (ZT-12) was obtained in the same manner as in Comparative Example 1, except that the second layer was formed using "UNIDIC ELS-888" (manufactured by DIC Corporation) instead of "UNIDIC 17-806" as the ultraviolet-curable urethane acrylate resin for the hard coat layer. The second layer had a thickness of 3 μm, an elastic modulus of 3000 MPa, and an elongation of 40%.
The obtained polarizing plate was subjected to the above-mentioned evaluations (3) and (4), and the results are shown in Table 1.

<Comparative Example 3>
A polarizing plate having a structure of polarizer protective laminate (second layer/first layer)/polarizer/another protective layer (ZT-12) was obtained in the same manner as in Comparative Example 1, except that the second layer was formed using "UNIDIC V-4221" (manufactured by DIC Corporation) instead of "UNIDIC 17-806" as the ultraviolet-curable urethane acrylate resin for the hard coat layer. The second layer had a thickness of 3 μm, an elastic modulus of 60 MPa, and an elongation of 200%.
The obtained polarizing plate was subjected to the above-mentioned evaluations (3) and (4), and the results are shown in Table 1.

<Comparative Example 4>
A polarizing plate having a structure of polarizer protective laminate (second layer/first layer)/polarizer/another protective layer (ZT-12) was obtained in the same manner as in Example 1, except that the first layer was formed using "B722" (manufactured by Kusumoto Chemicals Co., Ltd.) instead of "B728" as the acrylic resin. The first layer had a thickness of 2 μm and a Tg of 39° C.
The obtained polarizing plate was subjected to the above-mentioned evaluations (3) and (4), and the results are shown in Table 1.

<Comparative Example 5>
A polarizing plate having a structure of polarizer protective laminate (second layer/first layer)/polarizer/another protective layer (ZT-12) was obtained in the same manner as in Comparative Example 4, except that the second layer was formed using "UNIDIC ELS-888" (manufactured by DIC Corporation) instead of "UNIDIC 17-806" as the ultraviolet-curable urethane acrylate resin for the hard coat layer. The second layer had a thickness of 3 μm, an elastic modulus of 3000 MPa, and an elongation of 40%.
The obtained polarizing plate was subjected to the above-mentioned evaluations (3) and (4), and the results are shown in Table 1.

<Comparative Example 6>
A polarizing plate having a structure of polarizer protective laminate (second layer/first layer)/polarizer/another protective layer (ZT-12) was obtained in the same manner as in Comparative Example 4, except that the second layer was formed using "UNIDIC V-4221" (manufactured by DIC Corporation) instead of "UNIDIC 17-806" as the ultraviolet-curable urethane acrylate resin for the hard coat layer. The second layer had a thickness of 3 μm, an elastic modulus of 60 MPa, and an elongation of 200%.
The obtained polarizing plate was subjected to the above-mentioned evaluations (3) and (4), and the results are shown in Table 1.

<Comparative Example 7>
A polarizing plate was produced in the same manner as in Example 1, except that the second layer was not formed (i.e., the protective layer was composed of only the first layer). The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Comparative Example 8>
A polarizing plate was produced in the same manner as in Example 4, except that the second layer was not formed (i.e., the protective layer was composed of only the first layer). The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Comparative Example 9>
A polarizing plate was produced in the same manner as in Comparative Example 1, except that the second layer was not formed (i.e., the protective layer was composed of only the first layer). The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Comparative Example 10>
A polarizing plate was produced in the same manner as in Comparative Example 4, except that the second layer was not formed (i.e., the protective layer was composed of only the first layer). The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Evaluation>
As is clear from Table 1, the polarizer protective laminate of the examples of the present invention is suppressed from cracking even in a heated and humidified environment. By using such a polarizer protective laminate, a polarizing plate having excellent durability and suppressing deterioration in optical properties even in a heated and humidified environment can be realized, despite its very thinness.

The polarizing plate of the present invention is suitable for use in image display devices. Examples of image display devices include portable devices such as personal digital assistants (PDAs), smartphones, mobile phones, watches, digital cameras, and portable game consoles; office automation devices such as personal computer monitors, notebook computers, and copy machines; household electrical appliances such as video cameras, televisions, and microwave ovens; in-vehicle devices such as rear monitors, monitors for car navigation systems, and car audio; exhibition devices such as digital signage and information monitors for commercial stores; security devices such as surveillance monitors; and nursing and medical devices such as nursing monitors and medical monitors.

10 First layer 20 Second layer 100 Polarizer protection laminate 120 Polarizer 200 Polarizing plate

Claims (4)

A polarizer and a polarizer protection laminate disposed on one side of the polarizer,
The polarizer protective laminate is
A first layer made of a thermoplastic acrylic resin that is soluble in an organic solvent and has a glass transition temperature of 95° C. or higher;
A second layer formed of a cured product of a curable resin,
The second layer has a thickness of 1.0 μm or more,
The first layer has a thickness of 7 μm or less,
the second layer is formed on a surface of the first layer;
the polarizer protection laminate is disposed so that the first layer faces the polarizer, and is formed directly on the polarizer;
The weight average molecular weight of the thermoplastic acrylic resin is 10,000 or more,
The second layer has an elastic modulus of 50 MPa or more and an elongation rate of 2% or more.
Polarizer. The polarizing plate according to claim 1 , wherein the second layer has a pencil hardness of 2H or more. 3. The polarizing plate according to claim 1, wherein the first layer has an in-plane retardation Re(550) of 0 nm to 10 nm and a retardation in a thickness direction Rth(550) of −20 nm to +10 nm. The polarizing plate according to claim 1 , which is disposed on a viewer side of an image display device, and the second layer of the polarizer protection laminate is disposed on the viewer side.

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