WO2022158234A1

WO2022158234A1 - Polarizing film, polarizing plate and image display device

Info

Publication number: WO2022158234A1
Application number: PCT/JP2021/047760
Authority: WO
Inventors: 直樹藤本; 理小島; 周作後藤
Original assignee: 日東電工株式会社
Priority date: 2021-01-22
Filing date: 2021-12-23
Publication date: 2022-07-28
Also published as: KR20230130017A; JP2022112800A; CN116940872A; TW202238185A

Abstract

The present invention provides a polarizing film which is capable of reducing the power consumption of an organic EL display device. A polarizing film according to one embodiment of the present invention is configured from a polyvinyl alcohol resin film that contains iodine; and the transmittance thereof at the wavelength of 470 nm is higher than the transmittance thereof at the wavelength of 600 nm. In addition, a polarizing plate according to the present invention comprises this polarizing film and a protective layer that is arranged on at least one side of this polarizing film.

Description

Polarizing film, polarizing plate and image display device

The present invention relates to a polarizing film, a polarizing plate and an image display device.

In recent years, image display devices represented by liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices) have rapidly spread. It is known that in an organic EL display device, problems such as external light reflection and background reflection can be prevented by placing a circularly polarizing plate including a λ/4 plate on the viewing side of the organic EL cell (for example, Patent Documents 1 and 2).

On the other hand, since organic EL display devices consume a large amount of power for light emission, there is a demand for energy saving.

JP-A-2002-311239 Japanese Patent Application Laid-Open No. 2002-372622

The present invention has been made to solve the conventional problems described above, and its main purpose is to provide a polarizing film capable of reducing the power consumption of an organic EL display device.

According to one aspect of the present invention, it is composed of a polyvinyl alcohol-based resin film containing iodine,
A polarizing film is provided that has a higher transmittance at a wavelength of 470 nm than at a wavelength of 600 nm.
In one embodiment, the polarizing film has a haze of 1% or less.
In one embodiment, the orthogonal absorbance A470 of the polarizing film at a wavelength of ₄₇₀ nm is 4.0 or less.
In one embodiment, the ratio (A ₄₇₀ /A ₆₀₀ ) of the orthogonal absorbance A ₄₇₀ at a wavelength of 470 nm to the orthogonal absorbance A ₆₀₀ at a wavelength of 600 nm of the polarizing film is 0.10 to 0.80.
In one embodiment, the polarizing film has a single transmittance of 42.0% to 65.0% and a degree of polarization of 40.0% to 99.998%.
In one embodiment, the polarizing film has a thickness of 12 μm or less.
According to another aspect of the present invention, there is provided a polarizing plate including the above polarizing film and a protective layer disposed on at least one side of the polarizing film.
In one embodiment, the polarizing plate further includes a retardation layer, the in-plane retardation of the retardation layer at a wavelength of 550 nm is 100 nm to 190 nm, and the slow axis of the retardation layer and the polarizing film The angle formed with the absorption axis is 40° to 50°.
According to another aspect of the present invention, an image display device comprising the polarizing plate is provided.
In one embodiment, the image display device is an organic electroluminescence display device.

Since the polarizing film according to the embodiment of the present invention has a higher transmittance at a wavelength of 470 nm than at a wavelength of 600 nm, it can transmit light on the short wavelength side more positively than light on the long wavelength side. By using such a polarizing film, even when the amount of blue light emission, which consumes a large amount of power, is reduced, it is possible to suppress the decrease in luminance in the short wavelength region, and as a result, the energy saving of the organic EL display device. It is possible to achieve both high brightness and high brightness.

FIG. 4 is a schematic diagram showing an example of drying shrinkage treatment using a heating roll. 1 is a schematic cross-sectional view of a polarizer according to one embodiment of the invention; FIG. 1 is a schematic cross-sectional view of a polarizer according to one embodiment of the invention; FIG. 1 is a schematic cross-sectional view of a polarizer according to one embodiment of the invention; FIG.

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

(Definition of terms and symbols)
Definitions of terms and symbols used herein are as follows.
(1) refractive index (nx, ny, nz)
"nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., slow axis direction), and "ny" is the in-plane direction orthogonal to the slow axis (i.e., fast axis direction) and "nz" is the refractive index in the thickness direction.
(2) In-plane retardation (Re)
“Re(λ)” is an in-plane retardation measured at 23° C. with light having a wavelength of λ nm. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23°C. Re(λ) is obtained by the formula: Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the layer (film).
(3) Thickness direction retardation (Rth)
“Rth(λ)” is the retardation in the thickness direction measured at 23° C. with light having a wavelength of λ nm. For example, “Rth(550)” is the retardation in the thickness direction measured at 23° C. with light having a wavelength of 550 nm. Rth(λ) is determined by the formula: Rth(λ)=(nx−nz)×d, where d (nm) is the thickness of the layer (film).
(4) Nz Coefficient The Nz coefficient is obtained by Nz=Rth/Re.
(5) Angle When referring to an angle in this specification, the angle includes both clockwise and counterclockwise directions with respect to a reference direction. Thus, for example, "45°" means ±45°.

A. Polarizing Film The polarizing film according to the embodiment of the present invention is composed of a polyvinyl alcohol resin film containing iodine, and has a transmittance (Ts ₄₇₀ ) at a wavelength of 470 nm that is greater than a transmittance (Ts ₆₀₀ ) at a wavelength of 600 nm. In other words, the polarizing film according to the embodiment of the present invention satisfies the relationship "1< _Ts470 / _Ts600 ", and preferably satisfies the relationship " _1.02≤Ts470 / _Ts600≤1.30 ". A polarizing film that satisfies such a relationship can more positively transmit light on the short wavelength side than light on the long wavelength side.

The transmittance (Ts ₄₇₀ ) at a wavelength of 470 nm is a value corresponding to the content of the PVA-I ₃ ^-complex having absorption near the wavelength of 470 nm, and generally decreases as the content of the PVA-I ₃ ^-complex increases. do. On the other hand, the transmittance (Ts ₆₀₀ ) at a wavelength of 600 nm is a value corresponding ^to the content of the PVA _- I ₅ ^-complex having absorption near the wavelength of 600 nm. descend. Therefore, the polarizing film that satisfies the relationship of “1<Ts ₄₇₀ /Ts ₆₀₀ ” is characterized in that the content ratio of the PVA-I ₃ ^-complex to the PVA-I ₅ ^-complex is lower than that of the polarizing film that does not satisfy the relationship. have

The Ts ₄₇₀ and Ts ₆₀₀ of the polarizing film can be any suitable value depending on the purpose. Ts ₄₇₀ can be, for example, 40.0% or more, preferably 42.0% or more, more preferably 44.0% or more, and can be, for example, 80.0% or less, preferably 60.0% or less . In addition, Ts ₆₀₀ can be, for example, 40.0% or more, preferably 41.0% or more, more preferably 42.0% or more, and, for example, 70.0% or less, preferably 60.0% or less, More preferably, it can be 50.0% or less.

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The transmittance of the polarizing film (single transmittance: Ts) is preferably 41.0% or more, more preferably 42.0% or more, and still more preferably 42.5% or more. On the other hand, the transmittance of the polarizing film is, for example, 65.0% or less, preferably 50.0% or less, more preferably 48.0% or less. Further, the polarization degree of the polarizing film is, for example, 40.0% or more, preferably 90.0% or more, more preferably 94.0% or more, still more preferably 96.0% or more, and still more It is preferably 99.0% or more, still more preferably 99.5% or more, and preferably 99.998% or less. The transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction. The degree of polarization is typically determined by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction.
Degree of polarization (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100

In one embodiment, the transmittance of a thin polarizing film of 12 μm or less is typically the polarizing film (surface refractive index: 1.53) and the protective layer (protective film) (refractive index: 1.50 ) is measured using an ultraviolet-visible spectrophotometer. Depending on the refractive index of the surface of the polarizing film and/or the refractive index of the protective layer contacting the air interface, the reflectance at each layer interface may change, resulting in a change in the measured transmittance. . Thus, for example, if a protective layer with a refractive index other than 1.50 is used, the transmittance measurements may be corrected according to the refractive index of the surface of the protective layer that is in contact with the air interface. Specifically, the transmittance correction value C is expressed by the following formula using the reflectance R ₁ (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective layer and the air layer.
C=R ₁ -R ₀
R ₀ = ((1.50−1) ² /(1.50+1) ² )×(T ₁ /100)
R ₁ = ((n ₁ −1) ² /(n ₁ +1) ² )×(T ₁ /100)
Here, R ₀ is the transmission axis reflectance when a protective layer having a refractive index of 1.50 is used, n ₁ is the refractive index of the protective layer used, and T ₁ is the transmittance of the polarizing film. is. For example, when a substrate having a surface refractive index of 1.53 (a cycloolefin film, a film with a hard coat layer, etc.) is used as the protective layer, the correction amount C is approximately 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, the transmittance of the polarizing film having a surface refractive index of 1.53 and the protective layer having a refractive index of 1.53 is used. It is possible to convert to a rate. According to the calculation based on the above formula, the amount of change in the correction value C when the transmittance T1 of the polarizing film is changed by ₂ % is 0.03% or less, and the transmittance of the polarizing film is equal to the correction value C has a limited effect on the value of Moreover, when the protective layer has absorption other than surface reflection, appropriate correction can be performed according to the amount of absorption.

The orthogonal absorbance A ₄₇₀ of the polarizing film at a wavelength of 470 nm is preferably 4.0 or less, more preferably 3.5 or less, even more preferably 3.0 or less, and even more preferably 2.5 or less. be. Also, the orthogonal absorbance A ₄₇₀ is, for example, 0.2 or more, preferably 1.0 or more, and more preferably 1.5 or more. The orthogonal absorbance Aλ at the wavelength _λnm is obtained by the following formula based on the orthogonal transmittance Tc.
Orthogonal absorbance = log10(100/Tc)

The ratio of the orthogonal absorbance A ₄₇₀ at a wavelength of 470 nm to the orthogonal absorbance A ₆₀₀ at a wavelength of 600 nm of the polarizing film (A ₄₇₀ /A ₆₀₀ ) is, for example, 0.80 or less, preferably 0.70 or less, and more preferably 0. .60 or less. The ratio ( _A470 / _A600 ) is, for example, 0.10 or more, preferably 0.30 or more, and more preferably 0.35 or more.

The orthogonal absorbance A ₄₇₀ is a value corresponding ^to the content of the PVA _{-I 3} _-complex ^aligned _in the direction of the absorption axis. It means that the content of the complex is large. On the other hand, the orthogonal absorbance A ₆₀₀ is a value corresponding to the content of the PVA-I ₅ ^-complex _aligned along the absorption axis. It means that the content of ₅ ^- complexes is high. Therefore, a low ratio (A ₄₇₀ /A ₆₀₀ ) indicates that the content of PVA-I ₃ ^-complexes aligned along the absorption axis is relatively small and that the content of PVA-I ₅ ^-complexes aligned along the absorption axis is relatively small. It means that the quantity is relatively large.

The haze of the polarizing film is preferably 1% or less, more preferably 0.8% or less, and even more preferably 0.6% or less. If the haze is within this range, an organic EL display device with a high contrast ratio can be obtained.

The iodine concentration in the polarizing film is preferably 3% by weight or more, more preferably 4% to 10% by weight, and more preferably 4% to 8% by weight. In this specification, "iodine concentration" means the total amount of iodine contained in the polarizing film. More specifically, iodine exists in the form of I ⁻ , I ₂ , I ₃ ⁻ , PVA-I ₃ ^-complex , PVA-I ₅ ^-complex , etc. in the polarizing film. , means the concentration of iodine including all these forms. The iodine concentration can be calculated, for example, from the fluorescent X-ray intensity and film (polarizing film) thickness obtained by fluorescent X-ray analysis.

The thickness of the polarizing film is typically 25 μm or less, preferably 12 μm or less, more preferably 1 μm to 12 μm, even more preferably 1 μm to 7 μm, still more preferably 2 μm to 5 μm.

B. Method for producing polarizing film The polarizing film described in Section A can be obtained, for example, by a production method including contacting a PVA-based resin film having a water content of 15% by weight or less and having iodine adsorbed and oriented with an aqueous solvent. . By bringing such a PVA-based resin film into contact with an aqueous solvent, the polyiodine ions forming the PVA-I ₃ ^-complex are released preferentially over the polyiodine ions forming the PVA-I ₅ ^-complex , resulting in decolorization. As a result, a polarizing film that satisfies the relationship "1< _Ts470 / _Ts600 " can be easily obtained. In one embodiment, the ratio of increase in transmittance after contact to the transmittance at wavelength λ nm of the PVA-based resin film before contact with the aqueous solvent (ΔTs _λ = Ts _λ (after contact)/Ts _λ (before contact)) is The relationship ΔTs ₄₁₅ >ΔTs ₄₇₀ >ΔTs ₆₀₀ is satisfied.

B-1. PVA-based resin film A PVA-based resin film having a moisture content of 15% by weight or less and having iodine adsorbed and oriented (also referred to herein as an “unbleached original film”) typically has a “1≧Ts ₄₇₀ / Ts ₆₀₀ ". In addition, the unbleached original film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm and is in a state capable of functioning as a polarizing film. Specifically, the unbleached original film is preferably a PVA-based resin film that has been subjected to various treatments such as stretching, dyeing with iodine, and drying.

In one embodiment, the transmittance of the unbleached original film (single transmittance: Ts) is preferably 41.0% or more, more preferably 42.0% or more, and still more preferably 42.5%. That's it. On the other hand, the transmittance of the unbleached original film is preferably 46.0% or less, more preferably 45.0% or less. The degree of polarization of the unbleached original film is preferably 98.0% or more, more preferably 99.0% or more, still more preferably 99.9% or more. On the other hand, the degree of polarization of the unbleached original film is preferably 99.998% or less. The above transmittance and degree of polarization are obtained in the same manner as the transmittance and degree of polarization of the polarizing film.

The moisture content of the unbleached original film is typically 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight or less, and even more preferably 1% to 5% by weight. If the moisture content of the unbleached original film is within this range, it is possible to prevent dissolution and wrinkling upon contact with an aqueous solvent.

The thickness of the unbleached original film is typically 25 μm or less, preferably 12 μm or less, more preferably 1 μm to 12 μm, even more preferably 1 μm to 7 μm, still more preferably 2 μm to 5 μm.

The unbleached original film may be produced using a single-layer PVA-based resin film, or may be produced using a laminate of two or more layers including a PVA-based resin layer (PVA-based resin film). The unbleached base film prepared using a laminate of two or more layers avoids the occurrence of wrinkles and the like even after contact with an aqueous solvent, and has excellent optical properties (typically, single transmittance and degree of polarization) can be preferably maintained.

B-1-1. Production of an unbleached original film using a laminate of two or more layers The production of an unbleached original film using a laminate of two or more layers is, for example, a PVA-based resin film containing a halide and a PVA-based resin, which is It can be carried out by a method including subjecting in the state of a laminate with a bar-shaped thermoplastic resin substrate to an auxiliary air stretching treatment, a dyeing treatment, an underwater stretching treatment and a drying shrinkage treatment in this order. A laminate of a thermoplastic resin substrate and a PVA-based resin film includes, for example, a PVA-based resin layer (PVA-based resin film) containing a halide and a PVA-based resin on one side of a long thermoplastic resin substrate. is obtained by forming a laminate. In the drying shrinkage treatment, for example, the laminate of the long thermoplastic resin substrate and the PVA-based resin film is heated while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction, and the PVA-based resin film. It includes drying until the moisture content of the system resin film becomes 15% by weight or less. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The underwater stretching treatment is preferably carried out in an aqueous boric acid solution. 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 production method, it is possible to obtain an unbleached raw film having a high degree of orientation of the PVA-based resin and excellent optical properties.

B-1-1-1. Production of Laminate Any appropriate method can be adopted as a method for producing a laminate of a thermoplastic resin substrate and a PVA-based resin layer. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin substrate and dried to form a PVA-based resin layer on the thermoplastic resin substrate. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

Any appropriate method can be adopted as the method of applying the coating liquid. Examples thereof include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (comma coating, etc.). The coating/drying temperature of the coating liquid is preferably 50° C. or higher.

The thickness of the PVA-based resin layer is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm.

Before forming the PVA-based resin layer, the thermoplastic resin substrate may be surface-treated (for example, corona treatment, etc.), or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By performing such treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved.

The thickness of the thermoplastic resin substrate is preferably 20 µm to 300 µm, more preferably 50 µm to 200 µm. If the thickness is less than 20 μm, it may be difficult to form the PVA-based resin layer. If it exceeds 300 μm, for example, in the later-described underwater stretching treatment, it may take a long time for the thermoplastic resin substrate to absorb water, and an excessive load may be required for stretching.

The thermoplastic resin substrate preferably has a water absorption of 0.2% or more, more preferably 0.3% or more. Thermoplastic resin substrates can absorb water and be plasticized with the water acting like a plasticizer. As a result, the stretching stress can be greatly reduced, and the film can be stretched at a high draw ratio. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin substrate, it is possible to prevent problems such as deterioration of the appearance of the obtained unbleached base film due to a marked decrease in the dimensional stability of the thermoplastic resin substrate during production. . Moreover, it is possible to prevent breakage of the base material and separation of the PVA-based resin layer from the thermoplastic resin base material during stretching in water. The water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption is a value determined according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or less. By using such a thermoplastic resin substrate, it is possible to sufficiently secure the stretchability of the laminate while suppressing the crystallization of the PVA-based resin layer. Furthermore, considering the plasticization of the thermoplastic resin substrate with water and the satisfactory stretching in water, the temperature is preferably 100° C. or lower, more preferably 90° C. or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60°C or higher. By using such a thermoplastic resin substrate, deformation of the thermoplastic resin substrate (for example, generation of unevenness, sagging, wrinkles, etc.) occurs when the coating liquid containing the PVA-based resin is applied and dried. It is possible to prevent the problem of and produce a good laminate. Moreover, the PVA-based resin layer can be satisfactorily stretched at a suitable temperature (for example, about 60°C). The glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by heating using a crystallization material that introduces a modifying group into the constituent material. The glass transition temperature (Tg) is a value determined according to JIS K 7121.

Any appropriate thermoplastic resin can be adopted as a constituent material of the thermoplastic resin base material. Examples of thermoplastic resins include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. is mentioned. Among these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferred.

In one embodiment, an amorphous (not crystallized) polyethylene terephthalate resin is preferably used. Among them, amorphous (difficult to crystallize) polyethylene terephthalate resin is particularly preferably used. Specific examples of amorphous polyethylene terephthalate resins include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further containing cyclohexanedimethanol or diethylene glycol as glycols.

In a preferred embodiment, the thermoplastic resin base material is composed of a polyethylene terephthalate resin having an isophthalic acid unit. This is because such a thermoplastic resin substrate is extremely excellent in stretchability and can suppress crystallization during stretching. This is probably because the introduction of the isophthalic acid unit gives the main chain a large bend. A polyethylene terephthalate-based resin has a terephthalic acid unit and an ethylene glycol unit. The isophthalic acid unit content is preferably 0.1 mol % or more, more preferably 1.0 mol % or more, relative to the total of all repeating units. This is because a thermoplastic resin base material having extremely excellent stretchability can be obtained. On the other hand, the isophthalic acid unit content is preferably 20 mol % or less, more preferably 10 mol % or less, relative to the total of all repeating units. By setting such a content ratio, the degree of crystallinity can be favorably increased in the drying shrinkage treatment described later.

The thermoplastic resin substrate may be stretched in advance (before forming the PVA-based resin layer). In one embodiment, it is stretched in the transverse direction of the elongated thermoplastic resin substrate. The lateral direction is preferably a direction perpendicular to the stretching direction of the laminate described below. In addition, in this specification, "perpendicular" also includes the case of being substantially perpendicular. Here, "substantially orthogonal" includes 90°±5.0°, preferably 90°±3.0°, more preferably 90°±1.0°.

The stretching temperature of the thermoplastic resin substrate is preferably Tg-10°C to Tg+50°C with respect to the glass transition temperature (Tg). The draw ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times.

Any appropriate method can be adopted as a method for stretching the thermoplastic resin base material. Specifically, the drawing may be fixed end drawing or free end drawing. The stretching method may be a dry method or a wet method. The stretching of the thermoplastic resin substrate may be performed in one step or in multiple steps. When performing in multiple stages, the above-mentioned draw ratio is the product of the draw ratios in each step.

The coating liquid contains a halide and a PVA-based resin, as described above. The coating liquid is typically a solution in which the halide and the PVA-based resin are dissolved in a solvent. Examples of solvents include water, dimethylsulfoxide, 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. Among these, water is preferred. The concentration of the PVA-based resin in 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, it is possible to form a uniform coating film in close contact with the thermoplastic resin substrate. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

Additives may be added to the coating liquid. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyhydric alcohols such as ethylene glycol and glycerin. Surfactants include, for example, nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the obtained PVA-based resin layer.

Any appropriate resin can be adopted as the PVA-based resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. . The degree of saponification can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a degree of saponification, an unbleached original film having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.

The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1,000 to 10,000, preferably 1,200 to 4,500, more preferably 1,500 to 4,300. The average degree of polymerization can be determined according to JIS K 6726-1994.

Any appropriate halide can be adopted as the halide. Examples include iodide and sodium chloride. Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

The amount of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA resin, and more preferably 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA resin. Department. If the amount of the halide exceeds 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may bleed out and the finally obtained unbleached original film may become cloudy.

In general, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin layer increases. orientation may be disturbed and the orientation may be lowered. In particular, when a laminate of a thermoplastic resin substrate and a PVA-based resin layer is stretched in boric acid water, the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin substrate. When the film is stretched, the tendency of the degree of orientation to decrease is remarkable. For example, the stretching of a single PVA film in boric acid water is generally carried out at 60° C., whereas the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is It is carried out at a high temperature of about 70° C., and in this case, the orientation of PVA at the initial stage of stretching may be lowered before it is increased by stretching in water. On the other hand, by preparing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate and stretching the laminate at a 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 disturbance of the orientation of the polyvinyl alcohol molecules and the deterioration of the orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. This makes it possible to improve the optical properties of the unbleached base film obtained through a treatment step in which the laminate is immersed in a liquid, such as dyeing treatment and stretching treatment in water.

B-1-1-2. Aerial Auxiliary Stretching In order to obtain particularly high optical properties, a two-stage stretching method combining dry stretching (auxiliary stretching) and stretching in boric acid solution is selected. By introducing auxiliary stretching, such as two-step stretching, it is possible to stretch while suppressing crystallization of the thermoplastic resin substrate, and excessive crystallization of the thermoplastic resin substrate in the subsequent stretching in boric acid water. It is possible to solve the problem that stretchability is reduced by stretching, and stretch the laminate at a higher magnification. Furthermore, when applying the PVA-based resin on the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, compared to the case of applying the PVA-based resin on a normal metal drum As a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical properties cannot be obtained. On the other hand, by introducing auxiliary stretching, it is possible to increase the crystallinity of the PVA-based resin even when the PVA-based resin is applied onto a thermoplastic resin substrate, thereby achieving high optical properties. It becomes possible. At the same time, by increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as deterioration of the orientation and dissolution of the PVA-based resin when it is immersed in water in the subsequent dyeing treatment or stretching treatment. , making it possible to achieve high optical properties.

The stretching method of the in-air auxiliary stretching may be fixed edge stretching (e.g., a method of stretching using a tenter stretching machine) or free edge stretching (e.g., a method of uniaxially stretching the laminate through rolls having different peripheral speeds). Although good, free-end drawing may be positively employed in order to obtain high optical properties. In one embodiment, the in-air stretching process includes a heating roll stretching step in which the laminate is stretched by a peripheral speed difference between heating rolls while being conveyed in the longitudinal direction. The air drawing process typically includes a zone drawing process and a hot roll drawing process. The order of the zone stretching process and the heating roll stretching process is not limited, and the zone stretching process may be carried out first, or the heating roll stretching process may be carried out first. The zone drawing step may be omitted. In one embodiment, the zone drawing step and the heated roll drawing step are performed in this order. In another embodiment, the laminate is stretched by gripping the ends of the laminate and widening the distance between the tenters in the machine direction in a tenter stretching machine (the widening of the distance between the tenters is the stretching ratio). At this time, the distance between the tenters in the width direction (perpendicular to the machine direction) is set to be arbitrarily close. Preferably, the draw ratio in the machine direction can be set to be closer to the free end draw. In the case of free end stretching, the shrinkage ratio in the width direction is calculated by (1/stretching ratio) ^1/2 .

Aerial auxiliary stretching may be performed in one step or in multiple steps. When it is carried out in multiple stages, the draw ratio is the product of the draw ratios in each step. The stretching direction in the in-air auxiliary stretching is preferably substantially the same as the stretching direction in the underwater stretching.

The draw ratio in the in-air auxiliary drawing is preferably 2.0 to 3.5 times. The maximum draw ratio when the auxiliary drawing in the air and the drawing in water are combined is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 6.0 times the original length of the laminate. That's it. As used herein, the term "maximum draw ratio" refers to the draw ratio immediately before the laminate breaks, and is 0.2 lower than the draw ratio at which the laminate breaks.

The stretching temperature for the in-air auxiliary stretching can be set to any appropriate value depending on the material for forming the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably the glass transition temperature (Tg) of the thermoplastic resin substrate or higher, more preferably the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C or higher, and particularly preferably Tg + 15°C or higher. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, it is possible to suppress rapid crystallization of the PVA-based resin and suppress problems caused by the crystallization (for example, hindrance of orientation of the PVA-based resin layer due to stretching). can. The crystallization index of the PVA-based resin after auxiliary stretching in air is preferably 1.3 to 1.8, more preferably 1.4 to 1.7. The crystallization index of the PVA-based resin can be measured by the ATR method using a Fourier transform infrared spectrophotometer. Specifically, measurement is performed using polarized light as measurement light, and the crystallization index is calculated according to the following formula using the intensities at 1141 cm ⁻¹ and 1440 cm ⁻¹ of the obtained spectrum.
_{Crystallization} index = (IC/ _IR )
however,
I _C : Intensity at 1141 cm ⁻¹ when measurement light is incident and measured I _R : Intensity at 1440 cm ⁻¹ when measurement light is incident and measured.

B-1-1-3. Insolubilization Treatment If necessary, an insolubilization treatment is performed after the auxiliary stretching treatment in the air and before the stretching treatment in water or the dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The insolubilization treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably 20°C to 50°C.

B-1-1-4. Dyeing Treatment The dyeing treatment is typically performed by dyeing the PVA-based resin layer with iodine. Specifically, it is carried out by allowing the PVA-based resin layer to adsorb iodine. Examples of the adsorption method include a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of coating the PVA-based resin layer with the dyeing solution, and a method of applying the dyeing solution to the PVA-based resin layer. A spraying method and the like can be mentioned. A preferred method is to immerse the laminate in a dyeing solution (dyeing bath). This is because iodine can be well adsorbed.

The staining solution is preferably an iodine aqueous solution. The amount of iodine compounded is preferably 0.05 to 0.5 parts by weight per 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add an iodide to the iodine aqueous solution. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. etc. Among these, potassium iodide is preferred. The amount of iodide compounded is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, per 100 parts by weight of water. The liquid temperature of the dyeing liquid during dyeing is preferably 20° C. to 50° C. in order to suppress the dissolution of the PVA-based resin. When the PVA-based resin layer is immersed in the staining solution, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds, in order to ensure the transmittance of the PVA-based resin layer.

The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the single transmittance of the finally obtained unbleached raw film has a desired value. As for such dyeing conditions, it is preferable to use an iodine aqueous solution as a dyeing solution and to set the content ratio of iodine and potassium iodide in the iodine aqueous solution to 1:5 to 1:20. The content ratio of iodine and potassium iodide in the aqueous iodine solution is preferably 1:5 to 1:10. As a result, an unbleached original film having optical properties as described below can be obtained.

When dyeing treatment is performed continuously after the treatment of immersing the laminate in a treatment bath containing boric acid (typically, insolubilization treatment), the boric acid contained in the treatment bath is mixed into the dyeing bath. The boric acid concentration in the dyeing bath may change over time, resulting in unstable dyeability. In order to suppress the destabilization of dyeability as described above, the upper limit of the boric acid concentration in the dyeing bath is preferably 4 parts by weight, more preferably 2 parts by weight with respect to 100 parts by weight of water. adjusted. On the other hand, the lower limit of the boric acid concentration in the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and still more preferably 0.5 parts by weight with respect to 100 parts by weight of water. is. In one embodiment, the dyeing process is performed using a dyeing bath pre-blended with boric acid. This can reduce the rate of change in boric acid concentration when the boric acid in the treatment bath is mixed into the dyeing bath. The amount of boric acid blended in advance in the dyeing bath (that is, the content of boric acid not derived from the treatment bath) is preferably 0.1 to 2 parts by weight with respect to 100 parts by weight of water. , more preferably 0.5 to 1.5 parts by weight.

B-1-1-5. Crosslinking Treatment If necessary, a crosslinking treatment is applied after the dyeing treatment and before the underwater stretching treatment. The cross-linking treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. The cross-linking treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA when immersed in high-temperature water in the subsequent underwater stretching. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight with respect to 100 parts by weight of water. Moreover, when cross-linking treatment is carried out after the dyeing treatment, it is preferable to further add an iodide. By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The amount of iodide compounded is preferably 1 to 5 parts by weight per 100 parts by weight of water. Specific examples of iodides are as described above. The liquid temperature of the cross-linking bath (boric acid aqueous solution) is preferably 20°C to 50°C.

B-1-1-6. Underwater Stretching Treatment Underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin substrate and the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80° C.), and the PVA-based resin layer undergoes its crystallization. can be stretched at a high magnification while suppressing the As a result, an unbleached original film having excellent optical properties can be produced.

Any appropriate method can be adopted as the method for stretching the laminate. Specifically, fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching a laminate by passing it between rolls having different peripheral speeds) may be used. Free-end drawing is preferably chosen. The laminate may be stretched in one step or in multiple steps. When the stretching is performed in multiple stages, the draw ratio (maximum draw ratio) of the laminate described below is the product of the draw ratios in each step.

The stretching in water is preferably carried out by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be imparted with rigidity to withstand tension applied during stretching and water resistance that does not dissolve in water. Specifically, boric acid can form a tetrahydroxyborate anion in an aqueous solution and crosslink with a PVA-based resin through hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, which can be satisfactorily stretched, and an unbleached base film having excellent optical properties can be produced.

The boric acid aqueous solution is preferably obtained by dissolving boric acid and/or a borate salt in water as a solvent. The boric acid concentration is preferably 1 part by weight to 10 parts by weight, more preferably 2.5 parts by weight to 6 parts by weight, and particularly preferably 3 parts by weight to 5 parts by weight with respect to 100 parts by weight of water. is. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and an unbleached original film with higher properties can be produced. In addition to boric acid or borate salts, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.

Preferably, an iodide is added to the stretching bath (boric acid aqueous solution). By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Specific examples of iodides are as described above. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, per 100 parts by weight of water.

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, the film can be stretched at a high magnification while suppressing dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40° C., it may not be possible to stretch well even if the plasticization of the thermoplastic resin base material by water is considered. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, which may make it impossible to obtain excellent optical properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The draw ratio by underwater drawing is preferably 1.5 times or more, more preferably 3.0 times or more. The total draw ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, relative to the original length of the laminate. By achieving such a high draw ratio, it is possible to produce an unbleached base film with extremely excellent optical properties. Such a high draw ratio can be achieved by adopting an underwater drawing method (boric acid solution drawing).

B-1-1-7. Dry shrinkage treatment In the dry shrinkage treatment, for example, the laminate of the long thermoplastic resin substrate and the PVA-based resin film is heated while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. and drying until the water content of the PVA-based resin film becomes 15% by weight or less. From the viewpoint of obtaining a stable appearance, it is preferable to dry to a moisture content of 12% by weight or less, more preferably 10% by weight or less, and even more preferably 1% to 5% by weight.

The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or by heating the transport roll (using a so-called heating roll) (heating roll drying method). Preferably both are used. By drying using a heating roll, it is possible to efficiently suppress heat curling of the laminate and produce an unbleached original film with excellent appearance. Specifically, by drying the laminated body along the heating roll, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the degree of crystallinity, which is relatively low. Even at the drying temperature, the degree of crystallinity of the thermoplastic resin substrate can be favorably increased. As a result, the thermoplastic resin base material has increased rigidity and is in a state capable of withstanding shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. Moreover, by using a heating roll, the layered product can be dried while being maintained in a flat state, so that not only curling but also wrinkling can be suppressed. At this time, the laminate can be shrunk in the width direction by drying shrinkage treatment, thereby improving the optical properties. This is because the orientation of PVA and PVA/iodine complex can be effectively enhanced. The shrinkage ratio of the laminate in the width direction due to drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roll, the laminate can be continuously shrunk in the width direction while being transported, and high productivity can be achieved.

FIG. 1 is a schematic diagram showing an example of drying shrinkage treatment. 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-based resin layer and the surface of the thermoplastic resin substrate. The transport rolls R1 to R6 may be arranged so as to continuously heat only the plastic resin substrate surface).

The drying conditions can be controlled by adjusting the heating temperature of the transport rolls (the temperature of the heating rolls), the number of heating rolls, the contact time with the heating rolls, and so on. 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 degree of crystallinity of the thermoplastic resin can be favorably increased, curling can be favorably suppressed, and an optical laminate having extremely excellent durability can be produced. The temperature of the heating roll can be measured with a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular limitation as long as the number of transport rolls is plural. Conveying rolls are usually 2 to 40, preferably 4 to 30 in number. 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, still more preferably 1 to 10 seconds.

The heating roll may be provided in a heating furnace (for example, an oven), or may be provided in a normal production line (under room temperature environment). Preferably, it is provided in a heating furnace equipped with air blowing means. By using both heating roll drying and hot air drying, abrupt temperature changes between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature for hot air drying is preferably 20°C to 100°C. Moreover, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10m/s to 30m/s. The wind speed is the wind speed in the heating furnace and can be measured with a mini-vane digital anemometer.

B-1-1-8. Other Treatments Preferably, a washing treatment is performed after the underwater stretching treatment and before the drying shrinkage treatment. The cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide.

B-1-2. Preparation of unbleached original film using single-layer PVA-based resin film ) A long PVA-based resin film is dyed and stretched (typically, uniaxially stretched using a roll stretcher in an aqueous boric acid solution), and then the moisture content is 15% by weight or less, preferably 12% by weight. % or less, more preferably 10 wt % or less, more preferably 1 wt % to 5 wt %. The dyeing is performed by, for example, immersing the PVA-based resin film in an iodine aqueous solution. The draw ratio of the uniaxial drawing is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment, or may be performed while dyeing. Moreover, you may dye after extending|stretching. If necessary, the PVA-based resin film is subjected to swelling treatment, cross-linking treatment, washing treatment, and the like. For example, by immersing the PVA-based resin film in water and washing it with water before dyeing, it is possible not only to wash away stains and anti-blocking agents on the surface of the PVA-based resin film, but also to swell the PVA-based resin film for dyeing. Unevenness and the like can be prevented.

B-2. Aqueous Solvent As the aqueous solvent, any appropriate solvent can be used as long as iodine can be eluted from the unbleached original film. The aqueous solvent can be, for example, water or a mixture of water and a water-soluble organic solvent. Preferred examples of the water-soluble organic solvent include lower monoalcohols having 1 to 4 carbon atoms such as methanol, ethanol, n-propyl alcohol and isopropyl alcohol, and polyhydric alcohols such as glycerin and ethylene glycol.

B-3. Contact method The method of contact with the aqueous solvent is not particularly limited, and any appropriate method such as immersion, spraying, or coating can be used. Immersion is preferred from the viewpoint of bringing the entire surface of the unbleached original film into contact with the aqueous solvent uniformly.

The contact time with the aqueous solvent and the temperature of the aqueous solvent during contact can be appropriately set according to desired Ts ₄₇₀ , Ts ₆₀₀ , A ₄₇₀ , A ₆₀₀ and the like. Increasing the contact time or increasing the temperature of the aqueous solvent tends to increase the transmittance (especially Ts ₄₇₀ ) and decrease the orthogonal absorbance (especially A ₄₇₀ ). The contact time can be, for example, 10 minutes or less, preferably 60 seconds to 9 minutes, more preferably 60 seconds to 4 minutes. The temperature of the aqueous solvent can be preferably 20°C to 70°C, more preferably 30°C to 65°C, even more preferably 40°C to 60°C.

The contact between the unbleached original film and the aqueous solvent may be carried out by bringing only one surface of the unbleached original film into contact with the aqueous solvent, or by bringing both surfaces into contact with the aqueous solvent. Therefore, a laminate of [unbleached original film/resin substrate] or a laminate of [unbleached original film/protective layer] produced using a laminate of [PVA-based resin layer/resin substrate] is dissolved in an aqueous solvent. can be used for contact with Alternatively, an unbleached original film prepared using a single-layer PVA-based resin film can be used as it is or in the form of a laminate with a protective layer provided on one side for contact with an aqueous solvent.

B-4. Other Treatments If necessary, the polarizing film obtained by contact with an aqueous solvent may be subjected to a drying treatment. The drying temperature can be, for example, 20°C to 100°C, preferably 30°C to 80°C. The moisture content of the dried polarizing film is typically 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight or less, and still more preferably 1% to 5% by weight. is.

C. Polarizing Plate A polarizing plate according to an embodiment of the present invention includes a polarizing film and a protective layer disposed on at least one side of the polarizing film, and may further include a retardation layer if necessary. In this specification, a polarizing plate including a retardation layer may be referred to as a polarizing plate with a retardation layer.

The b ^* value of the polarizing plate is, for example, −3 or less, preferably −4 or less, more preferably −20 to −5. A polarizing plate having a b ^* value within this range has a high transmittance for light in the short wavelength region, and therefore exhibits a bluish hue.

C-1. Overall Configuration of 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 100 includes a polarizing film 10, a first protective layer 12 disposed on one side of the polarizing film 10, and a second protective layer 14 disposed on the other side of the polarizing film 10. .

FIG. 3 is a schematic cross-sectional view of a polarizing plate including a retardation layer according to another embodiment of the invention. The polarizing plate with a retardation layer 200a includes a polarizing film 10, a first protective layer 12 arranged on one side of the polarizing film 10, and a second protective layer arranged on the other side of the polarizing film 10. 14 and a first retardation layer 20 disposed on the opposite side of the second protective layer 14 to the side on which the polarizing film 10 is disposed. Depending on the purpose, one of the first protective layer 12 and the second protective layer 14 may be omitted. For example, if the retardation layer 20 can also function as a protective layer for the polarizing film 10, the second protective layer 14 may be omitted.

FIG. 4 is a schematic cross-sectional view of a polarizing plate including a retardation layer according to still another embodiment of the invention. The polarizing plate with a retardation layer 200b includes a polarizing film 10, a first protective layer 12 arranged on one side of the polarizing film 10, and a second protective layer arranged on the other side of the polarizing film 10. 14, and a first retardation layer 20, a second retardation layer 30 and a conductive layer or an isotropic substrate with a conductive layer on the side opposite to the side on which the polarizing film 10 of the second protective layer 14 is arranged 40 are provided in this order. The second retardation layer 30 typically exhibits a refractive index characteristic of nz>nx=ny. The second retardation layer 30 and the conductive layer or the isotropic substrate with a conductive layer 40 are typically optional layers provided as needed, and either or both of them may be omitted. In addition, when a conductive layer or an isotropic substrate with a conductive layer is provided, the polarizing plate with a retardation layer is a so-called inner It can be applied to a touch panel type input display device.

Re(550) of the first retardation layer 20 is, for example, 100 nm to 190 nm. The angle between the slow axis of the first retardation layer 20 and the absorption axis of the polarizing film 10 is, for example, 40° to 50°.

The above embodiments may be combined as appropriate, and the constituent elements in the above embodiments may be modified in a way that is obvious in the art. For example, the configuration in which the isotropic substrate 40 with a conductive layer is provided outside the second retardation layer 30 is replaced with an optically equivalent configuration (for example, a laminate of the second retardation layer and the conductive layer). good too.

The polarizing plate or the polarizing plate with a retardation layer according to the embodiment of the present invention may further contain other retardation layers. Other optical properties of the retardation layer (for example, refractive index properties, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, arrangement position, etc. can be appropriately set according to the purpose.

The polarizing plate of the present invention may be sheet-shaped or elongated. As used herein, the term "long shape" means an elongated shape whose length is sufficiently long relative to its width, for example, an elongated shape whose length is 10 times or more, preferably 20 times or more, its width. include. A long polarizing plate can be wound into a roll. When the retardation layer-attached polarizing plate is elongated, the polarizing plate and the retardation layer are also elongated. In this case, the polarizing film preferably has an absorption axis in the longitudinal direction. The first retardation layer is preferably an obliquely stretched film having a slow axis in a direction forming an angle of 40° to 50° with respect to the longitudinal direction. If the polarizing film and the first retardation layer have such structures, the retardation layer-attached polarizing plate can be produced by roll-to-roll.

Practically, an adhesive layer (not shown) is provided on the side of the retardation layer opposite to the polarizing plate, and the polarizing plate with the retardation layer can be attached to the image display cell. Furthermore, it is preferable that a release film is temporarily attached to the surface of the pressure-sensitive adhesive layer until the polarizing plate with the retardation layer is used. Temporarily attaching the release film protects the pressure-sensitive adhesive layer and enables roll formation.

The total thickness of the polarizing plate is preferably 150 µm or less, more preferably 120 µm or less, even more preferably 100 µm or less, even more preferably 90 µm or less, and even more preferably 85 µm or less. A lower limit for the total thickness can be, for example, 30 μm.

C-2. Polarizing Film As the polarizing film, the polarizing film described in Section A is used.

C-3. Protective Layers The first protective layer and the second protective layer are each formed of any suitable film that can be used as a protective layer for a polarizing film. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based resins. , polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, and acetate-based transparent resins. Thermosetting resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, and silicone, or ultraviolet curable resins may also be used. In addition, for example, a glassy polymer such as a siloxane-based polymer can also be used. Further, polymer films described in JP-A-2001-343529 (WO01/37007) can also be used. Materials for this film include, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in a side chain. can be used, for example, a resin composition comprising an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extrudate of the resin composition.

The thickness of the protective layer is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, still more preferably 10 μm to 60 μm.

C-4. First Retardation Layer The first retardation layer may have any appropriate optical properties and/or mechanical properties depending on the purpose. The first retardation layer typically has a slow axis. In one embodiment, the angle θ between the slow axis of the first retardation layer and the absorption axis of the polarizing film is 40° to 50° as described above, preferably 42° to 48°. , more preferably about 45°. If the angle θ is in such a range, by using a λ / 4 plate as the first retardation layer as described later, very good circular polarization properties (as a result, very good antireflection properties) can be obtained.

The first retardation layer preferably exhibits a refractive index characteristic of nx>ny≧nz. The first retardation layer is typically provided to impart antireflection properties to the polarizing plate, and in one embodiment can function as a λ/4 plate. In this case, the in-plane retardation Re(550) of the first retardation layer is preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, still more preferably 130 nm to 160 nm. Here, "ny=nz" includes not only the case where ny and nz are completely equal but also the case where they are substantially equal. Therefore, it is possible that ny<nz to the extent that the effects of the present invention are not impaired.

The Nz coefficient of the first retardation layer is preferably 0.9 to 3, more preferably 0.9 to 2.5, even more preferably 0.9 to 1.5, particularly preferably 0.9 to 1.5. 3. By satisfying such a relationship, when the obtained polarizing plate with a retardation layer is used in an image display device, a very excellent reflection hue can be achieved.

The first retardation layer may exhibit a reverse wavelength dispersion characteristic in which the retardation value increases according to the wavelength of the measurement light, or has a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light. It may also show a flat wavelength dispersion characteristic in which the phase difference value hardly changes even with the wavelength of the measurement light. In one embodiment, the first retardation layer exhibits reverse dispersion wavelength characteristics. In this case, Re(450)/Re(550) of the retardation layer is preferably 0.8 or more and less than 1, more preferably 0.8 or more and 0.95 or less. With such a configuration, very excellent antireflection properties can be achieved.

The absolute value of the photoelastic coefficient of the first retardation layer is preferably 2×10 ⁻¹¹ m ² /N or less, more preferably 2.0×10 ⁻¹³ m ² /N to 1.5×10 ⁻¹¹ m ² /N, more preferably 1.0×10 ⁻¹² m ² /N to 1.2×10 ⁻¹¹ m ² /N of resin. If the absolute value of the photoelastic coefficient is within such a range, the phase difference is less likely to change when shrinkage stress occurs during heating. As a result, heat unevenness in the obtained image display device can be satisfactorily prevented.

The first retardation layer may be a stretched resin film or a liquid crystal alignment fixed layer. The thickness of the first retardation layer composed of a stretched resin film is preferably 70 μm or less, more preferably 45 μm to 60 μm. If the thickness of the first retardation layer is within such a range, it is possible to satisfactorily control curling during bonding while satisfactorily suppressing curling during heating. Further, as described later, in an embodiment in which the first retardation layer is composed of a polycarbonate-based resin film, the thickness of the first retardation layer is preferably 40 μm or less, more preferably 10 μm to 40 μm. and more preferably 20 μm to 30 μm. By forming the first retardation layer from a polycarbonate-based resin film having such a thickness, it is possible to contribute to improvement in bending durability and reflection hue while suppressing the occurrence of curling.

Representative examples of resins capable of forming the first retardation layer include polycarbonate-based resins, polyester carbonate-based resins, polyester-based resins, polyvinyl acetal-based resins, polyarylate-based resins, cyclic olefin-based resins, cellulose-based resins, polyvinyl Examples include alcohol-based resins, polyamide-based resins, polyimide-based resins, polyether-based resins, polystyrene-based resins, and acrylic-based resins. These resins may be used alone or in combination (for example, blended, copolymerized). When the first retardation layer is composed of a resin film exhibiting reverse wavelength dispersion characteristics, a polycarbonate-based resin or a polyester carbonate-based resin (hereinafter sometimes simply referred to as a polycarbonate-based resin) can be suitably used.

Any appropriate polycarbonate-based resin can be used as the polycarbonate-based resin as long as the effects of the present invention can be obtained. For example, a polycarbonate-based resin includes a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, an alicyclic diol, an alicyclic dimethanol, di-, tri- or polyethylene glycol, and an alkylene and a structural unit derived from at least one dihydroxy compound selected from the group consisting of glycols or spiroglycols. Preferably, the polycarbonate-based resin contains a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, a structural unit derived from an alicyclic dimethanol, and/or di-, tri- or polyethylene glycol. more preferably a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from di-, tri- or polyethylene glycol. . The polycarbonate-based resin may contain structural units derived from other dihydroxy compounds as necessary. The details of the polycarbonate resin that can be preferably used in the present invention are, for example, JP-A-2014-10291, JP-A-2014-26266, JP-A-2015-212816, JP-A-2015-212817. , JP-A-2015-212818, which is incorporated herein by reference.

The glass transition temperature of the polycarbonate-based resin is preferably 110°C or higher and 150°C or lower, more preferably 120°C or higher and 140°C or lower. If the glass transition temperature is excessively low, the heat resistance tends to be poor, which may cause dimensional changes after film formation, and may lower the image quality of the resulting organic EL panel. If the glass transition temperature is excessively high, the molding stability during film molding may deteriorate, and the transparency of the film may be impaired. The glass transition temperature is obtained according to JIS K 7121 (1987).

The molecular weight of the polycarbonate-based resin can be represented by the reduced viscosity. The reduced viscosity is measured using an Ubbelohde viscometer at a temperature of 20.0°C ± 0.1°C, using methylene chloride as a solvent, precisely adjusting the polycarbonate concentration to 0.6 g/dL. The lower limit of the reduced viscosity is usually preferably 0.30 dL/g, more preferably 0.35 dL/g or more. The upper limit of the reduced viscosity is usually preferably 1.20 dL/g, more preferably 1.00 dL/g, still more preferably 0.80 dL/g. If the reduced viscosity is less than the above lower limit, there may be a problem that the mechanical strength of the molded product is reduced. On the other hand, if the reduced viscosity is higher than the upper limit, there may be a problem that the fluidity during molding is lowered, and the productivity and moldability are lowered.

A commercially available film may be used as the polycarbonate resin film. Specific examples of commercially available products include "Pure Ace WR-S", "Pure Ace WR-W" and "Pure Ace WR-M" manufactured by Teijin, and "NRF" manufactured by Nitto Denko. be done.

The first retardation layer is obtained, for example, by stretching a film formed from the above polycarbonate-based resin. Any appropriate molding method can be adopted as a method for forming a film from a polycarbonate-based resin. Specific examples include compression molding method, transfer molding method, injection molding method, extrusion molding method, blow molding method, powder molding method, FRP molding method, cast coating method (e.g., casting method), calendar molding method, and heat press. law, etc. Extrusion or cast coating methods are preferred. This is because the smoothness of the resulting film can be enhanced and good optical uniformity can be obtained. Molding conditions can be appropriately set according to the composition and type of the resin used, properties desired for the retardation layer, and the like. As described above, many film products of polycarbonate-based resins are commercially available, and the commercially available films may be subjected to the stretching treatment as they are.

The thickness of the resin film (unstretched film) can be set to any appropriate value depending on the desired thickness of the first retardation layer, desired optical properties, stretching conditions described later, and the like. It is preferably 50 μm to 300 μm.

Any suitable drawing method and drawing conditions (eg, drawing temperature, draw ratio, drawing direction) may be employed for the above-mentioned drawing. Specifically, various drawing methods such as free-end drawing, fixed-end drawing, free-end contraction, and fixed-end contraction can be used singly or simultaneously or sequentially. As for the stretching direction, the stretching can be performed in various directions and dimensions such as the length direction, the width direction, the thickness direction, the oblique direction, and the like. The stretching temperature is preferably Tg-30°C to Tg+60°C, more preferably Tg-10°C to Tg+50°C, relative to the glass transition temperature (Tg) of the resin film.

By appropriately selecting the stretching method and stretching conditions, a retardation film having the desired optical properties (for example, refractive index properties, in-plane retardation, Nz coefficient) can be obtained.

In one embodiment, the retardation film is produced by uniaxially stretching or fixed-end uniaxially stretching a resin film. As a specific example of fixed-end uniaxial stretching, there is a method in which the resin film is stretched in the width direction (horizontal direction) while running in the longitudinal direction. The draw ratio is preferably 1.1 times to 3.5 times.

In another embodiment, the retardation film can be produced by continuously obliquely stretching a long resin film in the direction of the above angle θ with respect to the longitudinal direction. By adopting oblique stretching, a long stretched film having an orientation angle of θ with respect to the longitudinal direction of the film (slow axis in the direction of angle θ) can be obtained. Roll-to-roll is possible, and the manufacturing process can be simplified. The angle θ may be an angle formed by the absorption axis of the polarizing film and the slow axis of the retardation layer in the retardation layer-attached polarizing plate. The angle θ is preferably 40° to 50°, more preferably 42° to 48°, and even more preferably about 45°, as described above.

A stretching machine used for diagonal stretching includes, for example, a tenter-type stretching machine capable of applying a feeding force, a pulling force, or a taking-up force at different speeds in the horizontal and/or vertical direction. The tenter-type stretching machine includes a horizontal uniaxial stretching machine, a simultaneous biaxial stretching machine, and the like, but any suitable stretching machine can be used as long as it can continuously obliquely stretch a long resin film.

By appropriately controlling the left and right speeds in the stretching machine, the retardation layer (substantially, a long retardation film) can be obtained.

The stretching temperature of the film may vary depending on the desired in-plane retardation value and thickness of the retardation layer, the type of resin used, the thickness of the film used, the stretching ratio, and the like. Specifically, the stretching temperature is preferably Tg-30°C to Tg+30°C, more preferably Tg-15°C to Tg+15°C, most preferably Tg-10°C to Tg+10°C. By stretching at such a temperature, the first retardation layer having suitable properties in the present invention can be obtained. Note that Tg is the glass transition temperature of the constituent material of the film.

C-5. Second Retardation Layer As described above, the second retardation layer can be a so-called positive C plate whose refractive index characteristics exhibit a relationship of nz>nx=ny. By using a positive C plate as the second retardation layer, it is possible to satisfactorily prevent reflection in oblique directions and widen the viewing angle of the antireflection function. In this case, the thickness direction retardation Rth (550) of the second retardation layer is preferably −50 nm to −300 nm, more preferably −70 nm to −250 nm, still more preferably −90 nm to −200 nm, particularly preferably -100 nm to -180 nm. Here, "nx=ny" includes not only the case where nx and ny are strictly equal but also the case where nx and ny are substantially equal. That is, the in-plane retardation Re(550) of the second retardation layer can be less than 10 nm.

The second retardation layer having a refractive index characteristic of nz>nx=ny can be made of any suitable material. The second retardation layer preferably consists of a film containing a liquid crystal material fixed in homeotropic alignment. A liquid crystal material (liquid crystal compound) that can be homeotropically aligned may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the retardation layer include the liquid crystal compound and the method for forming the retardation layer described in [0020] to [0028] of JP-A-2002-333642. In this case, the thickness of the second retardation layer is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, still more preferably 0.5 μm to 5 μm.

C-6. Conductive layer or isotropic substrate with conductive layer It may be formed by depositing a metal oxide film thereon. Examples of metal oxides include indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Among them, indium-tin composite oxide (ITO) is preferred.

When the conductive layer contains a metal oxide, the thickness of the conductive layer is preferably 50 nm or less, more preferably 35 nm or less. The lower limit of the thickness of the conductive layer is preferably 10 nm.

The conductive layer may be transferred from the base material to the first retardation layer (or the second retardation layer if present), and the conductive layer alone may be used as a constituent layer of the polarizing plate with the retardation layer. It may be laminated on the first retardation layer (or, if present, on the second retardation layer) as a laminate with a substrate (a substrate with a conductive layer). Preferably, the substrate is optically isotropic, and therefore the conductive layer can be used as an isotropic substrate with a conductive layer in a polarizing plate with a retardation layer.

Any appropriate isotropic base material can be adopted as the optically isotropic base material (isotropic base material). Materials constituting the isotropic base material include, for example, norbornene-based resins, olefin-based resins, and other resins that do not have a conjugated system as the main skeleton, and acrylic resins that have cyclic structures such as lactone rings and glutarimide rings. Examples include materials that are present in the main chain. By using such a material, it is possible to suppress the development of retardation due to the orientation of molecular chains when forming an isotropic base material. The thickness of the isotropic substrate is preferably 50 μm or less, more preferably 35 μm or less. The lower limit of the thickness of the isotropic base material is, for example, 20 μm.

The conductive layer and/or the conductive layer of the isotropic substrate with a conductive layer may be patterned as necessary. The patterning may form conductive portions and insulating portions. As a result, electrodes can be formed. The electrodes may function as touch sensor electrodes that sense contact with the touch panel. Any appropriate method can be adopted as a patterning method. Specific examples of the patterning method include wet etching and screen printing.

D. Image Display Device The polarizing plate described in the above item C can be applied to an image display device. Therefore, the present invention includes an image display device including the polarizing plate. Typical examples of image display devices include liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices). Among them, an organic EL display device is preferable because it can save energy by reducing the amount of blue light emitted.

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 characteristic is as follows. "Parts" and "%" in Examples and Comparative Examples are by weight unless otherwise specified.
(1) Thickness Measured using the product name “Linear Gauge MODEL D-10HS” (manufactured by Ozaki Seisakusho).
(2) Single Transmittance, Degree of Polarization, and Orthogonal Absorbance For laminates of PVA-based resin films (polarizing films or unbleached original films) and protective layers obtained in Examples and Comparative Examples, from the PVA-based resin film side, Single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer ("LPF-200" manufactured by Otsuka Electronics Co., Ltd.) were defined as Ts, Tp, and Tc of the PVA-based resin film, respectively. . Regarding the retardation layer-attached polarizing plate, the single transmittance Ts was similarly measured from the retardation layer side. These Ts, Tp and Tc are Y values measured with a 2-degree field of view (C light source) according to JIS Z8701 and subjected to visibility correction. The refractive index of the protective layer was 1.53, and the refractive index of the surface of the polarizing film opposite to the protective layer was 1.53.
From the obtained Tp and Tc, the degree of polarization P was determined by the following formula.
Degree of polarization P (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100
Also, using the measured Tc at each wavelength, the orthogonal absorbance at each wavelength was determined by the following formula.
Orthogonal absorbance = log10(100/Tc)
Also, the measured Ts at wavelengths of 470 nm and 600 nm were defined as Ts ₄₇₀ and Ts ₆₀₀ , respectively.
Equivalent measurement can be performed with a spectrophotometer such as "V-7100" manufactured by JASCO Corporation, and equivalent measurement results can be obtained using any spectrophotometer. has been confirmed.
(3) Moisture content The unbleached raw film immediately after drying (when the laminate is stretched, the stretched substrate is peeled off) is cut into a size of 100 mm × 100 mm or more, and the weight before processing is measured with an electronic balance. . After that, it was placed in a heating oven maintained at 120° C. for 2 hours, the weight after removal (weight after treatment) was measured, and the moisture content was determined by the following formula.
Moisture content [%] = (weight before treatment - weight after treatment) / weight before treatment x 100
(4) Haze Measured according to JISK7136 using a product name "Haze Meter (NDH-5000)" manufactured by Nippon Denshoku Industries Co., Ltd.
(5) Front reflection hue The polarizing plates with retardation layers obtained in Examples and Comparative Examples were coated with an acrylic pressure-sensitive adhesive having no ultraviolet absorption function to form a reflector (manufactured by Toray Film Co., Ltd., trade name “DMS-X42”). ; reflectance 86%, reflection hue a ^* =−0.22, b ^* =0.32 without polarizing plate) to prepare a measurement sample. At this time, the retardation layer side of the retardation layer-attached polarizing plate was attached so as to face the reflector. The a ^* value and b ^* value of the measurement sample were measured by the SCE method using a spectrophotometer (CM-2600d manufactured by Konica Minolta).

[Example 1-1]
1. Preparation of polarizing film and polarizing plate A long roll of PVA-based resin film (manufactured by Kuraray, product name "PE3000") having a thickness of 30 µm was stretched 2.2 times in the transport direction while being immersed in a water bath at 30°C. While immersed in an aqueous solution of 0.04% by weight of iodine and 0.3% by weight of potassium at 30° C. for dyeing, the film was stretched 3 times with respect to the unstretched film (original length). Next, while immersing this stretched film in an aqueous solution of 3% by weight of boric acid and 3% by weight of potassium iodide at 30° C., the stretched film is further stretched to 3.3 times its original length. While immersed in a 60°C aqueous solution with a concentration of 4% by weight and a concentration of potassium iodide of 5% by weight, it is further stretched to 6 times its original length, and finally dried in an oven maintained at 60°C for 5 minutes. Thus, a polarizing film (unbleached original film a1) having a thickness of 12 μm was produced. The obtained unbleached original film a1 had a moisture content of 10.0% by weight and a single transmittance of 42.5%.

A PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “GOSEFIMER (registered trademark) Z-200”, resin concentration: 3% by weight) was applied to one side of the obtained unbleached raw film a1, and cyclo An olefin film (Zeonor, manufactured by Nippon Zeon Co., Ltd., thickness: 25 μm) was laminated to obtain an optical laminate having a structure of [unbleached original film a1/protective layer]. As the protective layer, a protective layer provided with a hard coat layer may be used. As such a protective layer, for example, a cycloolefin film with a hard coat layer (manufactured by ZEON, product name "G-Film , total thickness of 27 μm (film thickness of 25 μm+hard coat layer thickness of 2 μm), and the like.

The above optical layered body was cut into a size of 50 mm × 45 mm, and attached to a glass plate so that the unbleached original film side surface was exposed through an acrylic pressure-sensitive adhesive layer (thickness: 15 µm). for 9 minutes. Then, by drying at 50° C. for 5 minutes, a polarizing plate having a structure of [polarizing film A1/protective layer] was obtained.

2. Preparation of Retardation Film Constituting Retardation Layer 2-1. Polymerization of polyester carbonate-based resin Polymerization was carried out using a batch polymerization apparatus consisting of two vertical reactors equipped with a stirring blade and a reflux condenser controlled at 100°C. Bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane 29.60 parts by weight (0.046 mol), isosorbide (ISB) 29.21 parts by weight (0.200 mol), spiroglycol (SPG) 42 .28 parts by mass (0.139 mol), 63.77 parts by mass (0.298 mol) of diphenyl carbonate (DPC) and 1.19 × 10 ^-2 parts by weight of calcium acetate monohydrate as a catalyst (6.78 × 10 ^{- 5} mol) was charged. After the interior of the reactor was replaced with nitrogen under reduced pressure, heating was performed with a heating medium, and stirring was started when the internal temperature reached 100°C. After 40 minutes from the start of heating, the internal temperature was allowed to reach 220°C, and the pressure was reduced at the same time as controlling to maintain this temperature. Phenol vapor produced as a by-product of the polymerization reaction was led to a reflux condenser at 100°C, a small amount of monomer components contained in the phenol vapor was returned to the reactor, and uncondensed phenol vapor was led to a condenser at 45°C and recovered. After nitrogen was introduced into the first reactor and the pressure was once restored to atmospheric pressure, the oligomerized reaction liquid in the first reactor was transferred to the second reactor. Next, the temperature rise and pressure reduction in the second reactor were started, and the internal temperature was brought to 240° C. and the pressure to 0.2 kPa in 50 minutes. After that, polymerization was allowed to proceed until a predetermined stirring power was obtained. When a predetermined power was reached, nitrogen was introduced into the reactor to restore the pressure, the polyester carbonate-based resin produced was extruded into water, and strands were cut to obtain pellets.

2-2. Preparation of retardation film After vacuum drying the obtained polyester carbonate resin (pellet) at 80 ° C. for 5 hours, a single screw extruder (Toshiba Machine Co., Ltd., cylinder setting temperature: 250 ° C.), T die (width 200 mm , set temperature: 250° C.), a chill roll (set temperature: 120 to 130° C.), and a winder were used to prepare a long resin film having a thickness of 130 μm. The obtained long resin film was stretched while being adjusted so as to obtain a predetermined retardation to obtain a retardation film having a thickness of 48 μm. The stretching conditions were a stretching temperature of 143° C. and a stretching ratio of 2.8 in the width direction. Re(550) of the obtained retardation film was 141 nm, Re(450)/Re(550) was 0.86, and Nz coefficient was 1.12.

3. Production of polarizing plate with retardation layer 1 above. 2. on the surface of the polarizing film of the polarizing plate obtained in 2. above. The retardation film obtained in 1. was pasted together via an acrylic pressure-sensitive adhesive (thickness: 15 μm). At this time, the absorption axis of the polarizing film and the slow axis of the retardation film were attached so as to form an angle of 45°. Thus, a polarizing plate with a retardation layer having a structure of [retardation layer/polarizing film A1/protective layer] was obtained.

[Example 1-2]
A polarizing plate having a structure of [polarizing film A2/protective layer] was obtained in the same manner as in Example 1-1, except that instead of immersing in water at 55°C for 9 minutes, it was immersed in water at 65°C for 3 minutes. rice field. Further, a polarizing plate with a retardation layer was obtained in the same manner as in Example 1-1 except that the polarizing plate was used.

[Example 1-3]
A polarizing plate having a structure of [polarizing film A3/protective layer] was obtained in the same manner as in Example 1-1, except that instead of immersing in water at 55°C for 9 minutes, it was immersed in water at 23°C for 31 hours. rice field. Further, a polarizing plate with a retardation layer was obtained in the same manner as in Example 1-1 except that the polarizing plate was used.

[Comparative Example 1]
An optical laminate having a structure of [unbleached original film a1/protective layer] prepared in the same manner as in Example 1-1 was used as a polarizing plate. Further, a polarizing plate with a retardation layer was obtained in the same manner as in Example 1-1 except that the polarizing plate was used.

[Example 2-1]
A long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used as the thermoplastic resin substrate, and one side of the resin substrate was subjected to corona treatment.
Polyvinyl alcohol (degree of polymerization: 4,200, degree of saponification: 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOSEFIMER") were mixed at a ratio of 9:1, and 100 parts by weight of PVA-based resin. was added with 13 parts by weight of potassium iodide and dissolved in water to prepare an aqueous PVA solution (coating solution).
The above PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.
The resulting laminate was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in an oven at 130° C. (in-air auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath (an aqueous boric acid 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, in a dyeing bath (iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ° C., the finally obtained unbleached original It was immersed for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the membrane was 42.3% (dyeing treatment).
Next, it was immersed for 30 seconds in a cross-linking bath at a liquid temperature of 40°C (an aqueous solution of boric acid obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water). (crosslinking treatment).
After that, while immersing the laminate in an aqueous solution of boric acid (boric acid concentration: 4% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70° C., the laminate was moved vertically (longitudinally) between rolls with different peripheral speeds. Uniaxial stretching was performed so that the stretching ratio was 5.5 times (underwater stretching treatment).
After that, the laminate was immersed in a washing bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (washing treatment).
Thereafter, while drying in an oven maintained at about 90° C., it was brought into contact with a heating roll made of SUS whose surface temperature was maintained at about 75° C. (dry shrinkage treatment). The shrinkage rate in the width direction of the laminate due to the drying shrinkage treatment was 2%.
In this way, an unbleached original film having a moisture content of 4.5% and a thickness of 5.4 μm was formed on the resin substrate, and a cycloolefin film (manufactured by Nippon Zeon Co., Ltd., Zeonor, thickness: 25 μm) are bonded together with a UV curable adhesive (thickness: 1.0 μm), and then the resin substrate is peeled off to obtain an optical laminate having a configuration of [unbleached original film b1/protective layer]. rice field.

The above optical layered body was cut into a size of 50 mm × 45 mm, and attached to a glass plate so that the unbleached original film side surface became an exposed surface through an acrylic pressure-sensitive adhesive layer (thickness 15 µm). for 9 minutes. Then, by drying at 50° C. for 5 minutes, a polarizing plate having a structure of [polarizing film B1/protective layer] was obtained. Further, a polarizing plate with a retardation layer having a structure of [retardation layer/polarizing film B1/protective layer] was obtained in the same manner as in Example 1-1 except that the polarizing plate was used.

[Example 2-2]
A polarizing plate having a structure of [polarizing film B2/protective layer] was obtained in the same manner as in Example 2-1, except that instead of immersing in water at 50°C for 9 minutes, it was immersed in water at 60°C for 3 minutes. rice field. Further, a polarizing plate with a retardation layer was obtained in the same manner as in Example 1-1 except that the polarizing plate was used.

[Comparative Example 2]
An optical laminate having a structure of [unbleached original film b1/protective layer] prepared in the same manner as in Example 2-1 was used as a polarizing plate. Further, a polarizing plate with a retardation layer was obtained in the same manner as in Example 1-1 except that the polarizing plate was used.

Various properties of the unbleached original film, the polarizing film, and the polarizing plate with a retardation layer obtained in the above Examples and Comparative Examples were evaluated. Table 1 shows the results.

As is clear from Table 1, the polarizing films of the examples satisfy the relationship "1< _Ts470 / _Ts600 ", and can positively transmit light on the short wavelength side more than light on the long wavelength side. .

The polarizing film of the present invention can be suitably used in image display devices such as liquid crystal display devices and EL display devices, particularly organic EL display devices.

REFERENCE SIGNS LIST 10 polarizing film 20 protective layer 30 retardation layer 40 adhesive layer 100 polarizing plate

Claims

Consists of a polyvinyl alcohol resin film containing iodine,
A polarizing film having a higher transmittance at a wavelength of 470 nm than at a wavelength of 600 nm.
The polarizing film according to claim 1, which has a haze of 1% or less.
3. The polarizing film according to claim 1, wherein the orthogonal absorbance A470 at a wavelength of 470 nm is 4.0 or less.
4. The polarizing film according to claim 1, wherein the ratio of orthogonal absorbance A 470 at wavelength 470 nm to orthogonal absorbance A 600 at wavelength 600 nm (A 470 /A 600 ) is 0.10 to 0.80.
The polarizing film according to any one of claims 1 to 4, which has a single transmittance of 42.0% to 65.0% and a degree of polarization of 40.0% to 99.998%.
The polarizing film according to any one of claims 1 to 5, having a thickness of 12 µm or less.
A polarizing plate comprising the polarizing film according to any one of claims 1 to 6 and a protective layer arranged on at least one side of the polarizing film.
further comprising a retardation layer,
The in-plane retardation of the retardation layer at a wavelength of 550 nm is 100 nm to 190 nm,
8. The polarizing plate according to claim 7, wherein the angle formed by the slow axis of the retardation layer and the absorption axis of the polarizing film is 40° to 50°.
An image display device comprising the polarizing plate according to claim 7 or 8.
10. The image display device according to claim 9, which is an organic electroluminescence display device.