CN113661421A

CN113661421A - Polarizing plate

Info

Publication number: CN113661421A
Application number: CN202080027545.5A
Authority: CN
Inventors: 三轮和哉; 上条卓史; 滨本大介
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2019-04-09
Filing date: 2020-04-06
Publication date: 2021-11-16
Also published as: TW202041365A; KR20210148166A; WO2020209224A1; JP7513594B2; JPWO2020209224A1

Abstract

The invention provides a polarizing plate which has excellent durability even if the polarizing plate is very thin and has excellent adhesion between the polarizing plate and a protective layer. The polarizing plate of the present invention includes a polarizing plate and a protective layer disposed on one side of the polarizing plate via an easy-adhesion layer. The protective layer is composed of a cured product of a coating film of a thermoplastic acrylic resin in an organic solvent solution having a glass transition temperature of 95 ℃ or higher. The easy-adhesion layer contains at least 1 selected from polyester resin and polyurethane resin.

Description

Polarizing plate

Technical Field

The present invention relates to a polarizing plate.

Background

In image display devices (for example, liquid crystal display devices and organic EL display devices), a polarizing plate is often disposed on at least one side of a display cell due to the image forming system. In recent years, as the thinning and flexibility of image display devices have progressed, the thinning of polarizing plates has been strongly demanded. However, as the thickness of the polarizing plate is reduced, the problem of deterioration in durability of the polarizing plate under a heating and humidifying environment becomes more remarkable. As a polarizer protective film that can realize a thin polarizing plate having excellent durability, a polarizer protective film composed of a cured product of a coating film of a predetermined resin solution has been studied. Such techniques are in the initial stage of development, leaving room for various studies.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-210474

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above conventional problems, and a main object thereof is to provide a polarizing plate having excellent durability even when it is very thin and excellent adhesion between a polarizing plate and a protective layer.

Means for solving the problems

The polarizing plate of the present invention includes a polarizing plate and a protective layer disposed on one side of the polarizing plate via an easy-adhesion layer. The protective layer is composed of a cured product of a coating film of a thermoplastic acrylic resin in an organic solvent solution having a glass transition temperature of 95 ℃ or higher. The easy-adhesion layer contains at least 1 selected from polyester resin and polyurethane resin.

In one embodiment, the easy adhesion layer is composed of a cured product of a coating film containing an aqueous dispersion of at least 1 selected from a polyester resin and a polyurethane resin.

In one embodiment, the easy adhesion layer has a thickness of 1.0 μm or less.

In one embodiment, the polarizer and the protective layer are directly laminated on the easy adhesion layer.

In one embodiment, the thickness of the protective layer is 10 μm or less.

In one embodiment, the protective layer has an in-plane retardation Re (550) of 0nm to 10nm and a retardation Rth (550) in the thickness direction of-20 nm to +10 nm.

In one embodiment, the total thickness of the polarizing plate is 10 μm or less.

In one embodiment, the polarizer is disposed on the visible side of the image display device, and the protective layer is disposed on the visible side.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a polarizing plate having excellent durability even when it is very thin can be obtained by forming the protective layer from a cured product of a coating film of a thermoplastic acrylic resin in an organic solvent solution. Further, the protective layer is laminated with the polarizing plate by an easy-adhesion layer containing a polyester resin and/or a polyurethane resin, whereby excellent adhesion between the polarizing plate and the protective layer can be achieved.

Drawings

Fig. 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention.

Fig. 2 is a schematic view showing an example of drying shrinkage treatment using a heating roller in the method for manufacturing a polarizing plate according to the embodiment of the present invention.

Detailed Description

A. Outline of the polarizing plate

Fig. 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 illustrated in the figure includes a polarizer 10 and a protective layer 20 disposed on one side of the polarizer 10 via an easy-adhesion layer 30. If necessary, another protective layer (not shown) may be disposed on the side of the polarizing plate 10 opposite to the protective layer 20. When the polarizing plate 100 is applied to an image display device, it may be disposed on the viewing side of the display unit, or may be disposed on the side opposite to the viewing side (back side). In any case, the protective layer 20 may be disposed on the display cell side, or may be disposed on the side opposite (outside) the display cell. In one embodiment, the polarizer 100 is disposed on the viewing side of the display unit (and thus the image display device), and the protective layer 20 is disposed on the viewing side (opposite the display unit). The polarizing plate may be long or thin. When the polarizing plate is in a long form, it is preferably wound in a roll form.

Typically, the polarizing plate may have an adhesive layer as an outermost layer of one side (typically, the side of the polarizer 10 opposite to the protective layer 20) and be attached to the display unit. The surface protective film and/or the carrier film may be temporarily adhered to the polarizing plate in a peelable manner as necessary to reinforce and/or support the polarizing plate. When the polarizing plate includes an adhesive layer, the separator is temporarily bonded to the surface of the adhesive layer in a peelable manner, and the adhesive layer is protected until the polarizing plate is actually used, and the polarizing plate can be rolled.

In the embodiment of the present invention, the protective layer 20 is formed of a cured product of a coating film of a thermoplastic acrylic resin in an organic solvent solution having a glass transition temperature of 95 ℃. With such a configuration, the protective layer can be made very thin (for example, 10 μm or less). Further, in the present embodiment, the easy adhesion layer 30 containing a polyester resin and/or a polyurethane resin is provided between the polarizing plate 10 and the protective layer 20. By providing such an easy-adhesion layer, the adhesion between the polarizer and the protective layer can be significantly improved while maintaining the excellent effects of the protective layer (a polarizing plate having excellent durability even when it is very thin can be realized). The polarizing plate and/or the protective layer may be laminated on the easy-adhesion layer via an adhesive layer (e.g., an adhesive layer or an adhesive layer), or the polarizing plate and the protective layer may be directly laminated on the easy-adhesion layer. Preferably, the polarizing plate and the protective layer are directly laminated on the easy-adhesion layer. With such a configuration, the polarizing plate can be made thinner. In the present specification, "directly laminated" means laminated without an adhesive layer.

Further, by forming the protective layer from a cured product of a coating film of a thermoplastic acrylic resin in an organic solvent solution having a glass transition temperature of 95 ℃ or higher, a polarizing plate having excellent durability even when it is very thin can be realized. Specifically, a polarizing plate in which the reduction in optical characteristics is suppressed even in a heated and humidified environment can be realized. In the polarizing plate of the present invention, the change Δ Ts in the monomer transmittance Ts and the change Δ P in the polarization degree P after being left at 85 ℃ and 85% RH for 48 hours are each very small. The monomer transmittance Ts can be measured by using, for example, an ultraviolet-visible spectrophotometer (product name "V7100" manufactured by japan spectrophotometer). The polarization degree P can be calculated by the following formula from the monomer transmittance (Ts), the parallel transmittance (Tp), and the perpendicular transmittance (Tc) measured by an ultraviolet-visible spectrophotometer.

Polarization degree (P) (%) { (Tp-Tc)/(Tp + Tc) }^1/2×100

The Ts, Tp, and Tc are Y values obtained by measuring a 2-degree field of view (C light source) according to JIS Z8701 and correcting visibility. In addition, Ts and P are substantially the characteristics of the polarizing plate. Δ Ts and Δ P are each determined by the following equation.

ΔTs(％)＝Ts₄₈-Ts₀

ΔP(％)＝P₄₈-P₀

Here, Ts₀Transmittance of monomers before (initial) standing, Ts₄₈Transmittance of monomer after standing, P₀For degree of polarization before (initial) placement, P₄₈Is the polarization degree after the placement. Δ Ts is preferably 3.0% or less, more preferably 2.7% or less, and further preferably 2.4% or less. The Δ P is preferably-0.05% to 0%, more preferably-0.03% to 0%, and still more preferably-0.01% to 0%.

The total thickness of the polarizing plate is, for example, 40 μm or less, preferably 30 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less, and particularly preferably 7 μm or less. The lower limit of the total thickness of the polarizing plate may be, for example, 4 μm. According to the embodiment of the present invention, the polarizer, the protective layer, and the easy-adhesion layer are very thin, and the adhesive layer or the pressure-sensitive adhesive layer can be omitted, so that the total thickness of the polarizing plate can be extremely thin.

The polarizing plate of the present invention is extremely thin as described above, and therefore can be suitably used for a flexible image display device. More preferably, the image display device has a curved shape (substantially curved display screen), and/or is bendable or bendable. Specific examples of the image display device include: liquid crystal display devices, and Electroluminescence (EL) display devices (e.g., organic EL display devices, inorganic EL display devices). Needless to say, the foregoing description does not prevent the polarizing plate of the present invention from being applied to a general image display device.

The polarizing plate, the protective layer and the easy adhesion layer are explained in detail below.

B. Polarizing plate

The polarizing plate may be any suitable polarizing plate. The polarizing plate can be typically produced using a laminate of two or more layers. The polarizing plate manufacturing method is described in item E.

The thickness of the polarizing plate is preferably 1 μm to 8 μm, more preferably 1 μm to 7 μm, and still more preferably 2 μm to 5 μm.

The boric acid content of the polarizing plate is preferably 10 wt% or more, and more preferably 13 wt% to 25 wt%. When the boric acid content of the polarizing plate is within such a range, the appearance durability during heating can be improved while maintaining the ease of adjusting the curl during lamination and suppressing the curl during heating satisfactorily by a synergistic effect with the iodine content described later. The boric acid content can be calculated as the amount of boric acid contained in the polarizing plate per unit weight using the following formula by a neutralization method, for example.

The iodine content of the polarizing plate is preferably 2 wt% or more, and more preferably 2 wt% to 10 wt%. As long as the iodine content of the polarizing plate is in thisIn the above range, the appearance durability during heating can be improved while satisfactorily suppressing curl during heating while satisfactorily maintaining the easiness of curl adjustment during bonding by the synergistic effect with the boric acid content. The "iodine content" in the present specification means the amount of all iodine contained in the polarizing plate (PVA-based resin film). More specifically, iodine is doped with iodide ion (I) in the polarizing plate^-) Iodine molecule (I)₂) And polyiodide (I3-I5-), and the iodine content in the present specification means the amount of iodine including all of these forms. The iodine content can be calculated by a calibration curve method such as fluorescent X-ray analysis. The polyiodide exists in the polarizing plate in a state where a PVA-iodine complex is formed. By forming such a complex, absorption dichroism can be exhibited in a wavelength range of visible light. Specifically, a complex of PVA and triiodide ion (PVA. I)₃ ^-) Has an absorption peak around 470 nm; complex of PVA and pentaiodide ion (PVA. I)₅ ^-) Has an absorption peak around 600 nm. As a result, the polyiodide can absorb light in a wide range of visible light depending on its form. On the other hand, iodide ion (I)^-) Has an absorption peak near 230nm, and has no substantial correlation with the absorption of visible light. Therefore, the polyiodide existing in a complex state with PVA may be mainly related to the absorption performance of the polarizing plate.

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

C. Protective layer

The protective layer is formed of a cured product of a coating film of an organic solvent solution of a thermoplastic acrylic resin (hereinafter simply referred to as an acrylic resin) as described above. Hereinafter, the constituent components of the protective layer will be specifically described, and the characteristics of the protective layer will be described next.

C-1. acrylic resin

The glass transition temperature (Tg) of the acrylic resin is 95 ℃ or higher as described above. As a result, the Tg of the protective layer was 95 ℃ or higher. When the Tg of the acrylic resin is 95 ℃ or higher, a polarizing plate including a protective layer made of such a resin tends to have excellent durability. The Tg of the acrylic resin is typically 100 ℃ or higher, preferably 110 ℃ or higher, more preferably 115 ℃ or higher, still more preferably 120 ℃ or higher, and particularly preferably 125 ℃ or higher. On the other hand, the Tg of the acrylic resin is preferably 300 ℃ or lower, more preferably 250 ℃ or lower, still more preferably 200 ℃ or lower, and particularly preferably 160 ℃ or lower. When the Tg of the acrylic resin is within such a range, moldability is excellent.

As long as the acrylic resin has Tg as described above, any suitable acrylic resin can be used. The acrylic resin typically contains an alkyl (meth) acrylate as a main component as a monomer unit (repeating unit). In the present specification, "(meth) acrylic acid" means acrylic acid and/or methacrylic acid. Examples of the alkyl (meth) acrylate constituting the main skeleton of the acrylic resin include those having 1 to 18 carbon atoms in a linear or branched alkyl group. These may be used alone or in combination. Further, any suitable comonomer 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 the general formula (1), R⁴Represents a hydrogen atom or a methyl group, R⁵Represents a hydrogen atom or a C1-6 aliphatic or alicyclic hydrocarbon group which may be substituted. Examples of the substituent include: halogen, hydroxyl. Specific examples of the alkyl (meth) acrylate 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) acrylateDicyclopentyl (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), R⁵Preferably a hydrogen atom or a methyl group. Thus, a particularly desirable 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 R in the general formula (1)⁴And R⁵Different alkyl (meth) acrylate units.

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

The acrylic resin may have a repeating unit including a ring structure. Examples of the repeating unit containing a ring structure include: lactone ring units, glutaric anhydride units, glutarimide units, maleic anhydride units, maleimide (N-substituted maleimide) units. The repeating unit including a ring structure may be included in only 1 kind of repeating unit of the acrylic resin, or may be included in 2 or more kinds.

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

general formula (VII)(2) In, R¹、R²And R³Each independently represents a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may also contain an oxygen atom. The acrylic resin may contain only a single lactone ring unit or may contain a plurality of R in the general formula (2)¹、R²And R³Different lactone ring units. Acrylic resins having a lactone ring unit are described in, for example, Japanese patent laid-open No. 2008-181078, the description of which is incorporated herein by reference.

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

in the general formula (3), R¹¹And R¹²Each independently represents hydrogen or C1-C8 alkyl, R¹³Represents 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, R¹¹And R¹²Each independently is hydrogen or methyl, R¹³Is hydrogen, methyl, butyl or cyclohexyl. More preferably, R¹¹Is methyl, R¹²Is hydrogen, R¹³Is methyl. The acrylic resin may contain only a single glutarimide unit or may contain a plurality of R in the general formula (3)¹¹、R¹²And R¹³Different glutarimide units. Acrylic resins having glutarimide units are described in, for example, Japanese patent laid-open Nos. 2006-309033, 2006-317560, 2006-328334, 2006-337491, 2006-337492, 2006-337493 and 2006-337569, the disclosures of which are incorporated herein by reference. It is to be noted that the glutaric anhydride unit is represented by R in the general formula (3) described above¹³In addition to the substitution of the nitrogen atom into an oxygen atom, the description of the glutarimide unit applies.

The maleic anhydride unit and the maleimide (N-substituted maleimide) unit may be structurally defined by names, and thus detailed description is omitted.

The content ratio of the repeating unit having a ring structure in the acrylic resin is preferably 1 to 50 mol%, more preferably 10 to 40 mol%, and still more preferably 20 to 30 mol%. When the content ratio is too small, Tg may be lower than 110 ℃ and the heat resistance, solvent resistance and surface hardness of the obtained protective layer may be insufficient. When the content ratio is too large, moldability and transparency may become insufficient.

The acrylic resin may contain a repeating unit other than the alkyl (meth) acrylate unit and the repeating unit containing the ring structure. Examples of such a repeating unit include: derived from repeating units of a vinyl monomer copolymerizable with the monomers constituting the above units (other vinyl monomer units). Examples of the other vinyl-based 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-methallylamine, 2-isopropenyl-oxazoline, 2-vinyl-oxazoline, 2-acryloyl-oxazoline, N-phenylmaleimide, 2-vinyl-oxazoline, 2-acryloyl-oxazoline, 2-arylmaleimide, allyl-2-allylmaleimide, allyl-2-allylmaleimide, allyl-aminoacrylate, and/2-allylglycidyl ether, Phenylaminoethyl methacrylate, styrene, alpha-methylstyrene, p-glycidylstyrene, p-aminostyrene, 2-styryl-oxazoline, and the like. These may be used alone or in combination. The kind, amount, combination, content ratio and the like of the other vinyl monomer units can be appropriately set according to the purpose.

The weight average molecular weight of the acrylic resin is preferably 1000 to 2000000, more preferably 5000 to 1000000, further preferably 10000 to 500000, particularly preferably 50000 to 500000, and most preferably 60000 to 150000. The weight average molecular weight can be determined by polystyrene conversion using, for example, gel permeation chromatography (GPC system, manufactured by tokyo corporation). Tetrahydrofuran may be used as a solvent.

The acrylic resin may be obtained by polymerizing the aforementioned monomer units in any suitable polymerization method, using a suitable combination of the aforementioned monomer units.

In the embodiment of the present invention, the acrylic resin and the other resin may be used in combination. That is, the monomer component constituting the acrylic resin and the monomer component constituting the other resin may be copolymerized, and the copolymer may be subjected to molding of a protective layer described later; a mixture of the acrylic resin and other resins may also be used for the molding of the protective layer. Examples of the 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 kind and amount of the resin to be used in combination may be appropriately determined depending on the purpose, the desired properties of the film to be obtained, and the like. For example, a styrene resin (preferably, an acrylonitrile-styrene copolymer) can be used in combination as a retardation controller.

When the acrylic resin and the other resin are used in combination, the content of the acrylic resin in the mixture of the acrylic resin and the other resin is preferably 50 to 100% by weight, more preferably 60 to 100% by weight, still more preferably 70 to 100% by weight, and particularly preferably 80 to 100% by weight. When the content is less than 50% by weight, the high heat resistance and high transparency inherent in the acrylic resin may not be sufficiently reflected.

C-2. formation and characteristics of protective layer

As described above, the protective layer is formed of a cured product of a coating film of an organic solvent solution of an acrylic resin having a glass transition temperature of 95 ℃. If the cured product of such a coating film is used, the thickness can be made significantly thinner than that of an extrusion-molded film. The thickness of the protective layer is 10 μm or less, preferably 7 μm or less, more preferably 5 μm or less, and still more preferably 3 μm or less as described above. The lower limit of the thickness of the protective layer may be, for example, 1 μm. Further, although not theoretically clear, the cured product of such a coating film has advantages that the shrinkage during film molding is smaller than that of a cured product of a thermosetting resin or an active energy ray-curable resin (for example, an ultraviolet-curable resin), and the residual monomer or the like is not contained, so that the deterioration of the film itself can be suppressed, and the adverse effect of the residual monomer or the like on the polarizing plate (polarizing plate) can be suppressed. Furthermore, since the moisture absorption and the moisture permeability are smaller than those of a cured product of an aqueous coating film such as an aqueous solution or an aqueous dispersion, there is an advantage of excellent humidification durability. As a result, a polarizing plate that can maintain optical characteristics even in a heated and humidified environment and has excellent durability can be realized.

The Tg of the protective layer is as described in the above item C-1 with respect to the acrylic resin.

The protective layer preferably has substantially optical isotropy. In the present specification, "substantially optically isotropic" means that the in-plane retardation Re (550) is 0nm to 10nm, and the retardation Rth (550) in the thickness direction is-20 nm to +10 nm. The in-plane retardation Re (550) is more preferably 0nm to 5nm, still more preferably 0nm to 3nm, and particularly preferably 0nm to 2 nm. The retardation Rth (550) in the thickness direction is more preferably from-5 nm to +5nm, still more preferably from-3 nm to +3nm, and particularly preferably from-2 nm to +2 nm. When Re (550) and Rth (550) of the protective layer are within such ranges, adverse effects on display characteristics can be prevented when the polarizing plate including the protective layer is applied to an image display device. Re (550) is an in-plane retardation of the film measured at 23 ℃ with light having a wavelength of 550 nm. Re (550) can be represented by the formula: re (550) ═ (nx-ny) × d. Rth (550) is a retardation in the thickness direction of the film measured at 23 ℃ with light having a wavelength of 550 nm. Rth (550) can be represented by the formula: rth (550) is determined as (nx-nz) × d. Here, nx is a refractive index in a direction in which an in-plane refractive index is maximum (i.e., a slow axis direction), ny is a refractive index in a direction orthogonal to the slow axis in the plane (i.e., a fast axis direction), nz is a refractive index in a thickness direction, and d is a thickness (nm) of the thin film.

The higher the light transmittance of the protective layer at 380nm at a thickness of 3 μm, the more preferable. Specifically, the light transmittance is preferably 85% or more, more preferably 88% or more, and further preferably 90% or more. If the light transmittance is within such a range, the desired transparency can be ensured. The light transmittance can be measured, for example, according to the method of ASTM-D-1003.

The lower the haze of the protective layer, the more preferable. Specifically, it is preferably 5% or less, more preferably 3% or less, still more preferably 1.5% or less, and particularly preferably 1% or less. When the haze is 5% or less, a good transparent feeling can be imparted to the film. Further, even in the case of a visible-side polarizing plate used for an image display device, display contents can be recognized well.

The YI of the protective layer at a thickness of 3 μm is preferably 1.27 or less, more preferably 1.25 or less, still more preferably 1.23 or less, and particularly preferably 1.20 or less. When the YI exceeds 1.3, the optical transparency may be insufficient. YI can be obtained by the following equation using a color tristimulus value (X, Y, Z) obtained by measurement using a high-speed integrating sphere spectral transmittance measuring instrument (trade name DOT-3C: manufactured by Chou color technology research Co., Ltd.).

YI＝[(1.28X-1.06Z)/Y]×100

The b value (hue scale based on Hunter chromaticity system) of the protective layer at a thickness of 3 μm is preferably less than 1.5, and more preferably 1.0 or less. When the b value is 1.5 or more, an undesirable color tone may appear. The b value can be obtained, for example, as follows: the protective layer was obtained by cutting a sample of the film constituting the protective layer into 3cm squares, measuring the hue using a high-speed integrating sphere spectral transmittance measuring instrument (trade name DOT-3C, manufactured by Colorado research Co., Ltd.), and evaluating the hue according to the Hunter color system.

The protective layer (cured product of the coating film) may contain any suitable additive depending on the purpose. Specific examples of the additives include: an ultraviolet absorber; leveling agent; antioxidants such as hindered phenol type, phosphorus type, and sulfur type; stabilizers such as light-resistant stabilizers, weather-resistant stabilizers and heat stabilizers; reinforcing materials such as glass fibers and carbon fibers; a near infrared ray absorber; 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; an organic filler or an inorganic filler; a resin modifier; organic fillers and inorganic fillers; a plasticizer; a lubricant; an antistatic agent; flame retardants, and the like. The additive may be added at the time of polymerization of the acrylic resin or may be added to the solution at the time of film formation. The kind, amount, combination, addition amount and the like of the additives can be appropriately set according to the purpose.

A hard coat layer may be formed on the side of the protective layer opposite to the easy-adhesion layer. The hard coat layer may be formed when the protective layer is used as a protective layer for the viewing side of the viewing-side polarizing plate.

D. Easy adhesive layer

The easy adhesion layer contains a polyester resin and/or a polyurethane resin as described above. By providing such an easy-adhesion layer, the adhesion between the polarizing plate and the protective layer can be improved. The easy-adhesion layer is preferably formed of a cured product of a coating film containing an aqueous dispersion of a polyester resin and/or a polyurethane resin. With such a configuration, the adhesion between the polarizing plate and the protective layer can be further improved.

The thickness of the easy adhesion layer is preferably 1.0 μm or less, more preferably 800nm or less, still more preferably 600nm or less, and particularly preferably 300nm or less. The lower limit of the easy adhesion layer thickness is preferably 100 nm. When the thickness of the easy-adhesion layer is within such a range, the adhesion between the polarizer and the protective layer can be improved while maintaining excellent durability of the polarizing plate in a high-temperature and high-humidity environment. And the easy-adhesion layer can be inhibited from exhibiting a phase difference, and as a result, the optical characteristics of the polarizing plate can be inhibited from being adversely affected. If the thickness of the easy-adhesion layer is too large, the polarizing plate may have insufficient excellent durability in a high-temperature and high-humidity environment. If the thickness of the easy-adhesion layer is too small, the adhesion between the polarizing plate and the protective layer may be insufficient.

The easy-adhesion layer can be typically formed by applying an easy-adhesion composition (for example, the above-described aqueous dispersion) to one side of the polarizing plate and drying (curing) the composition. The easy-adhesion layer composition can be applied by any suitable method. Examples thereof include: bar coating, roll coating, gravure coating, bar coating, slot coating, curtain coating, fountain coating, and the like. The drying temperature is typically 50 ℃ or higher, preferably 70 ℃ or higher, and more preferably 90 ℃ or higher. By setting the drying temperature in such a range, a polarizing plate excellent in color resistance (particularly under high temperature and high humidity) can be provided. The drying temperature is preferably 120 ℃ or lower, and more preferably 100 ℃ or lower.

The easy-adhesion layer may be formed using a commercially available easy-adhesion agent composition (e.g., an aqueous dispersion). Specific examples of commercially available products include: "SUPERFLEX 210", "ELASTRON BN-11, BN-69, BN-77" manufactured by the first Industrial pharmaceutical Co., Ltd "," POLYESTER "manufactured by Nippon synthetic chemical Co., Ltd", "Vylonal (registered trademark) MD-1480, MD-1985, MD-2000" manufactured by Toyo Boseki Co., Ltd.

E. Method for manufacturing polarizing plate

E-1. method for producing polarizing plate

The method for producing a polarizing plate according to item B above, comprising: forming a polyvinyl alcohol resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol resin (PVA-based resin) on one side of a long thermoplastic resin base material to form a laminate; and sequentially applying an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment to the laminate, wherein the drying shrinkage treatment is performed by heating the laminate while conveying the laminate in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. The halide content in the PVA-based resin layer is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably carried out using a heated roller, and the temperature of the heated roller is preferably 60 to 120 ℃. The polarizing plate as described above can be obtained by such a manufacturing method. In particular, a polarizing plate having excellent optical characteristics (typically, monomer transmittance and polarization degree) and suppressed variations in optical characteristics can be obtained by producing a laminate including a halide-containing PVA-based resin layer, stretching the laminate in multiple stages including in-air auxiliary stretching and underwater stretching, and heating the stretched laminate with a heating roll. Specifically, by using a heating roller in the drying and shrinking treatment step, the entire laminate can be uniformly shrunk while the laminate is conveyed. Therefore, not only the optical characteristics of the obtained polarizing plate can be improved, but also a polarizing plate excellent in optical characteristics can be stably produced, and variations in optical characteristics (particularly, monomer transmittance) of the polarizing plate can be suppressed. The halide and the drying shrinkage treatment will be described below. Details of manufacturing methods other than these are described in, for example, japanese patent laid-open No. 2012-73580. The entire disclosure of this publication is incorporated herein by reference.

E-1-1. halides

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 to a thermoplastic resin substrate and drying the coating film. The coating liquid is typically a solution obtained by dissolving the halide and the PVA-based resin 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 may be used alone or in combination of two or more. Among these, water is also preferred. The concentration of the PVA based resin in the solution is preferably 3 to 20 parts by weight based on 100 parts by weight of the solvent. If the resin concentration is such as this, a uniform coating film can be formed in close contact with the thermoplastic resin substrate.

The halide may be any suitable halide. Examples thereof include: iodides and sodium chloride. Examples of the iodide include: potassium iodide, sodium iodide and lithium iodide. Of these, potassium iodide is also preferable.

The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight, and more preferably 10 to 15 parts by weight, based on 100 parts by weight of the PVA-based resin. When the amount of the halide is too large, the halide may bleed out, and the polarizing plate finally obtained may be clouded.

In general, the PVA-based resin layer is stretched to increase the orientation of polyvinyl alcohol molecules in the PVA-based resin layer, but when the stretched PVA-based resin layer is immersed in a liquid containing water, the orientation of polyvinyl alcohol molecules may be disturbed and the orientation may be reduced. In particular, when a laminate of a thermoplastic resin substrate and a PVA-based resin layer is subjected to boric acid underwater stretching, the degree of orientation tends to decrease significantly when the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin substrate. For example, while stretching of a PVA film alone in boric acid water is generally performed at 60 ℃, stretching of a laminate of a-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a high temperature, i.e., a temperature of about 70 ℃, in this case, the orientation of PVA at the beginning of stretching is reduced in a stage before it is increased by underwater stretching. In contrast, by preparing a laminate of a halide-containing PVA-based resin layer and a thermoplastic resin substrate and stretching the laminate at a high temperature in air (auxiliary stretching) before stretching in boric acid water, 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, disturbance of orientation of polyvinyl alcohol molecules and reduction of orientation can be more suppressed than in the case where the PVA-based resin layer does not contain a halide. Thus, the optical properties of the polarizing plate obtained through a treatment step of immersing the laminate in a liquid, such as dyeing treatment or underwater stretching treatment, can be improved.

E-1-2. drying shrinkage treatment

The drying shrinkage treatment may be performed by heating the entire region, or may be performed by heating a transport roller (so-called, using a hot roller) (hot roller drying method). Both are preferably used. By drying the laminate with a heating roller, the laminate can be effectively prevented from curling by heating, and a polarizing plate having excellent appearance can be produced. Specifically, by drying the laminate in a state where the laminate is along the heating roller, the crystallization of the thermoplastic resin substrate can be effectively promoted to increase the crystallinity, and the crystallinity of the thermoplastic resin substrate can be favorably increased even at a relatively low drying temperature. As a result, the rigidity of the thermoplastic resin substrate increases to a state in which the PVA-based resin layer can withstand shrinkage due to drying, and curling is suppressed. Further, since the laminate can be dried while maintaining a flat state by using the heating roller, not only the occurrence of curl but also the occurrence of wrinkles can be suppressed. In this case, the laminate can be shrunk in the width direction by a drying shrinkage treatment to improve the optical properties. This is because the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage in the width direction of the laminate by the drying shrinkage treatment is preferably 2% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roller, the laminate can be continuously shrunk in the width direction while being conveyed, and high productivity can be achieved.

Fig. 2 is a schematic view showing an example of the drying shrinkage treatment. In the drying shrinkage process, the laminate 200 is dried while being conveyed by the conveying rollers R1 to R6 and the guide rollers G1 to G4 heated to a predetermined temperature. In the illustrated example, the conveying rollers R1 to R6 are disposed 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 conveying rollers R1 to R6 may be disposed so as to continuously heat only one surface (for example, the surface of the thermoplastic resin substrate) of the laminate 200.

The drying condition can be controlled by adjusting the heating temperature of the conveying roller (temperature of the heating roller), the number of heating rollers, the contact time with the heating roller, and the like. The temperature of the heating roller is preferably 60 to 120 ℃, more preferably 65 to 100 ℃, and particularly preferably 70 to 80 ℃. An optical laminate having excellent durability is produced while the crystallinity of a thermoplastic resin is favorably increased and curling is favorably suppressed. The temperature of the heating roller may be measured by a contact thermometer. In the illustrated example, 6 conveying rollers are provided, but there is no particular limitation as long as there are a plurality of conveying rollers. The number of the conveying rollers is usually 2 to 40, and preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roller is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and still more preferably 1 to 10 seconds.

The heating roller may be installed in a heating furnace (for example, an oven) or may be installed in a general production line (room temperature environment). Preferably, the air blowing mechanism is provided in a heating furnace having an air blowing mechanism. By using drying by the heating roller and hot air drying in combination, rapid temperature change between the heating rollers is suppressed, and the shrinkage in the width direction can be easily controlled. The temperature of the hot air drying is preferably 30 to 100 ℃. The hot air drying time is preferably 1 to 300 seconds. The wind speed of the hot wind is preferably about 10m/s to 30 m/s. The wind speed is a wind speed in the heating furnace, and can be measured by a miniature vane-type digital anemometer.

It is preferable to perform the washing treatment after the stretching treatment in water and before the drying shrinkage treatment. The cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

This can provide a thermoplastic resin substrate/polarizing plate laminate.

E-2. method for manufacturing polarizing plate

The easy-adhesive composition is applied to the surface of the polarizing plate of the laminate obtained in item E-1 to form a coating film, and the coating film is cured to form an easy-adhesive layer. The easy adhesion layer is formed as described in item D above.

Further, an organic solvent solution of an acrylic resin is applied to the surface of the easy-adhesion layer to form a coating film, and the coating film is cured to directly form a protective layer on the surface of the easy-adhesion layer.

The acrylic resin is as described in the above item C-1.

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

The acrylic resin concentration of the solution is preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film can be formed that adheres to the polarizing plate.

As the solution coating method, any suitable method can be adopted. Specific examples thereof include: roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and doctor blade coating (comma coating, etc.).

The protective layer can be formed by drying (curing) the coating film of the solution. The drying temperature is preferably 100 ℃ or lower, and more preferably 50 to 70 ℃. If the drying temperature is within such a range, it is possible to prevent adverse effects on the polarizing plate. The drying time may vary depending on the drying temperature. The drying time may be, for example, 1 minute to 10 minutes.

This enables the formation of the easy-adhesion layer and the protective layer, and as a result, a laminate of the thermoplastic resin substrate, the polarizing plate, the easy-adhesion layer, and the protective layer can be obtained. By peeling the thermoplastic resin substrate from the laminate, a polarizing plate having the polarizing plate 10, the easy-adhesion layer 30, and the protective layer 20 shown in fig. 1 can be obtained. Alternatively, a resin film constituting another protective layer may be bonded to the polarizing plate surface of the laminate of the thermoplastic resin substrate/polarizing plate, and the thermoplastic resin substrate may be peeled off to form the easy-adhesion layer and the protective layer on the peeled surface. At this time, a polarizing plate further having another protective layer can be obtained.

In the above, the easy-adhesion layer and the protective layer are directly formed on the surface of the polarizing plate in this order, but the easy-adhesion layer and/or the protective layer may be formed on any suitable substrate and then transferred through any suitable adhesive layer.

Examples

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement method of each property is as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

(1) Glass transition temperature Tg

The films constituting the protective layers used in examples and comparative examples were measured using a heated TMA analyzer (manufactured by Hitachi High-Tech Science Corporation, product name "TMA-7100C"). The measurement conditions were as follows: the load is 2 g; nitrogen atmosphere (200 ml/min); heating from 25 ℃ to 150 ℃, keeping at 150 ℃ for 5 minutes, cooling to 25 ℃, heating to 150 ℃ again, and keeping at 150 ℃ for 5 minutes; the temperature rise rate was 2 ℃/min.

(2) Transmittance and degree of polarization of monomer

The polarizing plates obtained in examples and comparative examples were measured for the monomer transmittance (Ts), the parallel transmittance (Tp), and the orthogonal transmittance (Tc) using an ultraviolet-visible spectrophotometer (product name "V7100" manufactured by japan spectrophotometers), and the degree of polarization (P) was determined by the following equation.

Polarization degree (P) (%) { (Tp-Tc)/(Tp + Tc) }^1/2×100

The Ts, Tp, and Tc are Y values obtained by measuring a 2-degree field of view (C light source) according to JIS Z8701 and correcting visibility. In addition, Ts and P are substantially the characteristics of the polarizing plate.

Then, the polarizing plate was placed in an oven at 85 ℃ and 85% RH for 48 hours to heat and humidify (heat test), and the monomer transmittance Ts before the heat test was measured₀And a monomer transmittance Ts after a heat test₄₈The change in the monomer transmittance Δ Ts was obtained by the following equation.

ΔTs(％)＝Ts₄₈-Ts₀

Similarly, the polarization degree P before the heat test₀And polarization degree P after heating test₄₈The polarization degree change amount Δ P was obtained by the following equation.

ΔP(％)＝P₄₈-P₀

In the heat test, a test sample in which a polarizing plate was bonded to a glass plate with an adhesive was prepared.

(3) Adhesion Property

The adhesiveness between the polarizing plates and the protective layer in the polarizing plates obtained in examples and comparative examples was measured in accordance with the cross-cut adhesion peel test (number of cross-cut adhesion: 100) of JIS K5400, and evaluated in accordance with the following criteria.

O: the number of peeled crosscuts (number of peeled pieces) was less than 5.

And (delta): the number of peeling is 5 to 80.

X: the number of peels exceeded 80.

< example 1>

1. Production of polarizing plate/resin substrate laminate

As the resin base material, an amorphous copolymerized polyethylene terephthalate isophthalate film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of about 75 ℃ in a long form was used. And one side of the resin base material is subjected to corona treatment.

In the following, with 9: 1 an aqueous PVA solution (coating solution) was prepared by mixing 100 parts by weight of a PVA resin comprising polyvinyl alcohol (polymerization degree: 4200, saponification degree: 99.2 mol%) and acetoacetyl-modified PVA (trade name: GOHSEFIMER Z410, manufactured by Nippon Synthesis chemical industries, Ltd.) and adding 13 parts by weight of potassium iodide.

The aqueous PVA solution was applied to the corona-treated surface of the resin substrate and dried at 60 ℃ to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.

The obtained laminate was subjected to free-end uniaxial stretching 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130 ℃ (in-air auxiliary stretching treatment).

Next, the laminate was immersed in an insolubilization bath (an aqueous boric acid solution prepared by adding 4 parts by weight of boric acid to 100 parts by weight of water) at a liquid temperature of 40 ℃ for 30 seconds (insolubilization treatment).

Next, the polarizing plate finally obtained was immersed in a dyeing bath (aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ℃ for 60 seconds while adjusting the concentration of the bath to 41.5% ± 0.1% monomer transmittance (Ts) (dyeing treatment).

Subsequently, the resultant was immersed in a crosslinking bath (an aqueous boric acid solution prepared by adding 3 parts by weight of potassium iodide and 5 parts by weight of boric acid to 100 parts by weight of water) at a liquid temperature of 40 ℃ for 30 seconds (crosslinking treatment).

Then, while immersing the laminate in an aqueous boric acid solution (boric acid concentration 4.0 wt%, potassium iodide 5.0 wt%) having a liquid temperature of 62 ℃, uniaxial stretching was performed between rolls having different peripheral speeds in the longitudinal direction (longitudinal direction) so that the total stretching ratio became 5.5 times (underwater stretching treatment).

Then, the laminate was immersed in a cleaning bath (aqueous solution containing 4 parts by weight of potassium iodide per 100 parts by weight of water) at a liquid temperature of 20 ℃.

Then, the sheet was dried in an oven maintained at 90 ℃ while keeping the contact surface temperature of the sheet at 75 ℃ for about 2 seconds with a SUS-made heating roll (drying shrinkage treatment). The shrinkage in the width direction of the laminate by the drying shrinkage treatment was 5.2%.

Thus, a polarizing plate having a thickness of 5 μm was formed on the resin substrate to prepare a polarizing plate/resin substrate laminate.

2. Manufacture of polarizing plate

On the surface of the polarizing plate obtained above, a cycloolefin film (ZT-12, thickness 23 μm, manufactured by Zeon Corporation) was bonded as a film constituting another protective layer by an ultraviolet curing adhesive. Specifically, the curable adhesive was applied so that the total thickness thereof became 1.0 μm, and was bonded using a roll mill. After that, UV light is irradiated from the film side to cure the adhesive. Then, the resin substrate was peeled off to obtain a polarizing plate having a constitution of another protective layer (ZT-12)/polarizing plate.

An aqueous dispersion of a POLYESTER resin (product name "POLYESTER WR 905" manufactured by japan synthetic chemical corporation) was applied to the surface of the polarizing plate of the obtained polarizing plate using a wire bar, and the coating film was dried at 60 ℃ for 3 minutes to form an easy-adhesion layer composed of a cured product of the coating film. The thickness of the easy adhesion layer was 0.2 μm. On the other hand, 50 parts of an acrylic resin having a methyl methacrylate unit (product name "B728" manufactured by nanba ltd.) was dissolved in 50 parts of cyclopentanone to obtain an acrylic resin solution (50%). The acrylic resin solution was applied to the surface of the easy-adhesion layer with a wire bar, and the coating film was dried at 60 ℃ for 5 minutes to form a protective layer in the form of a cured product of the coating film. The thickness of the protective layer was 3 μm and Tg was 111 ℃. Thus, a polarizing plate having a structure of a protective layer (cured product of a coating film)/an easy-adhesion layer (cured product of a coating film)/a polarizing plate/another protective layer (ZT-12) was obtained. The obtained polarizing plate was subjected to the evaluations (2) and (3). The results are shown in Table 1.

< example 2>

A polarizing plate was produced in the same manner as in example 1 except that an easy-adhesion layer (thickness 0.2 μm) was formed using an aqueous dispersion of a POLYESTER resin ("POLYESTER WR 961" manufactured by japan synthetic chemical company) instead of the POLYESTER WR 905. The obtained polarizing plate was subjected to the same evaluation as in example 1. The results are shown in Table 1.

< example 3>

A polarizing plate was produced in the same manner as in example 1 except that an easy-adhesion layer (thickness: 0.2 μm) was formed using an aqueous dispersion of a POLYESTER resin ("Vylonal (registered trademark) MD-1480", manufactured by toyobo corporation) instead of the POLYESTER WR 905. The obtained polarizing plate was subjected to the same evaluation as in example 1. The results are shown in Table 1.

< example 4>

A polarizing plate was produced in the same manner as in example 1 except that an easy-adhesion layer (thickness: 0.2 μm) was formed using an aqueous dispersion of a POLYESTER resin ("Vylonal (registered trademark) MD-1985" manufactured by toyobo corporation) instead of the POLYESTER WR 905. The obtained polarizing plate was subjected to the same evaluation as in example 1. The results are shown in Table 1.

< example 5>

A polarizing plate was produced in the same manner as in example 1 except that an easy-adhesion layer (thickness: 0.2 μm) was formed using an aqueous dispersion of a POLYESTER resin ("Vylonal (registered trademark) MD-2000", manufactured by toyobo corporation) instead of the POLYESTER WR 905. The obtained polarizing plate was subjected to the same evaluation as in example 1. The results are shown in Table 1.

< example 6>

A polarizing plate was produced in the same manner as in example 1 except that an easy-adhesion layer (thickness: 0.2 μm) was formed using an aqueous dispersion of a polyurethane resin ("ELASTRON BN-11" manufactured by first Industrial pharmaceutical Co., Ltd.) in place of the POLYESTER WR 905. The obtained polarizing plate was subjected to the same evaluation as in example 1. The results are shown in Table 1.

< example 7>

A polarizing plate was produced in the same manner as in example 1 except that an easy-adhesion layer (thickness: 0.2 μm) was formed using an aqueous dispersion of a polyurethane resin ("ELASTRON BN-69", first Industrial pharmaceutical Co., Ltd.) in place of the POLYESTER WR 905. The obtained polarizing plate was subjected to the same evaluation as in example 1. The results are shown in Table 1.

< example 8>

A polarizing plate was produced in the same manner as in example 1 except that an easy-adhesion layer (thickness: 0.2 μm) was formed using an aqueous dispersion of a polyurethane resin ("ELASTRON BN-77" manufactured by first Industrial pharmaceutical Co., Ltd.) in place of POLYESTER WR 905. The obtained polarizing plate was subjected to the same evaluation as in example 1. The results are shown in Table 1.

< example 9>

A polarizing plate was produced in the same manner as in example 1 except that an easy adhesion layer (thickness 0.2 μm) was formed using an aqueous dispersion of a polyurethane resin ("SUPERFLEX 210", manufactured by first industrial pharmaceutical company) instead of using POLYESTER WR 905. The obtained polarizing plate was subjected to the same evaluation as in example 1. The results are shown in Table 1.

Further, polarizing plates were produced by changing the thickness of the easy-adhesion layer to 0.2 μm and 0.5 μm, respectively, and the relationship between the thickness and Δ Ts and Δ P was examined. The results are shown in Table 2.

< comparative example 1>

A polarizing plate was produced in the same manner as in example 1 except that an easy adhesion layer (thickness: 0.2 μm) was formed using a modified polyolefin resin emulsion ("Arrow Base (registered trademark) DA-1010" manufactured by Unitika) instead of the polymer WR 905. The obtained polarizing plate was subjected to the same evaluation as in example 1. The results are shown in Table 1.

< comparative example 2>

A polarizing plate was produced in the same manner as in example 1, except that the easy adhesive layer was not formed. The obtained polarizing plate was subjected to the same evaluation as in example 1. The results are shown in Table 1.

[ Table 1]

"PE" means polyester, "PU" means polyurethane, "PO" means polyolefin

[ Table 2]

Thickness of easy adhesion layer (mum)	ΔTs(％)	ΔP(％)
			0.2	1.70	-0.39
0.5	1.90	-0.81
			1.0	2.30	-3.20

< evaluation >

As is clear from table 1, the polarizing plate according to the example of the present invention maintained excellent durability of the protective layer formed of the cured product of the coating film of the organic solvent solution of the thermoplastic acrylic resin, and significantly improved adhesion between the polarizing plate and the protective layer. As is apparent from table 2, the durability can be significantly improved by reducing the thickness of the easy-adhesion layer.

Industrial applicability

The polarizing plate of the present invention can be suitably used for an image display device. Examples of the image display device include: portable devices such as mobile information terminals (PDAs), smart phones, mobile phones, clocks, digital cameras, and portable game machines; OA equipment such as computer monitors, notebook computers, and copiers; household electrical appliances such as video cameras, televisions, microwave ovens, and the like; vehicle-mounted devices such as a rear monitor, a monitor for a car navigation system, and a car audio; display devices such as digital signage and information monitors for commercial stores; security devices such as monitors; nursing and medical equipment such as nursing monitors and medical monitors.

Description of the reference numerals

10: polarizing plate

20: protective layer

30: easy adhesive layer

100: polarizing plate

Claims

1. A polarizing plate, comprising: a polarizing plate, and a protective layer disposed on one side of the polarizing plate via an easy-adhesion layer,

the protective layer is composed of a cured product of a coating film of a thermoplastic acrylic resin in an organic solvent solution having a glass transition temperature of 95 ℃ or higher,

the easy adhesion layer contains at least 1 selected from polyester resin and polyurethane resin.

2. The polarizing plate according to claim 1, wherein the easy-adhesion layer is composed of a cured product of a coating film containing an aqueous dispersion of at least 1 selected from a polyester resin and a polyurethane resin.

3. The polarizing plate according to claim 1 or 2, wherein the easy adhesion layer has a thickness of 1.0 μm or less.

4. The polarizing plate according to any one of claims 1 to 3, wherein the polarizer and the protective layer are directly laminated on the easy-adhesion layer.

5. The polarizing plate according to any one of claims 1 to 4, wherein the protective layer has a thickness of 10 μm or less.

6. The polarizing plate according to any one of claims 1 to 5, wherein the protective layer has an in-plane retardation Re (550) of 0nm to 10nm and a thickness-direction retardation Rth (550) of-20 nm to +10 nm.

7. The polarizing plate according to any one of claims 1 to 6, having a total thickness of 10 μm or less.

8. The polarizing plate according to any one of claims 1 to 7, which is disposed on a viewing side of an image display device, and the protective layer is disposed on the viewing side.