Polarizing film, polarizing plate, and image display device

Abstract

To provide a polarizing film which may reduce power consumption of an organic EL display device.SOLUTION: A polarizing film is provided, consisting of a polyvinyl alcohol-based resin film containing iodine and having transmittance at 470 nm wavelength that is greater than that at 600 nm wavelength. A polarizing plate is also provided, comprising the polarizing film and a protective layer provided on at least one side of the polarizing film.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a polarizing film, a polarizing plate, and an image display device.

Background Art

[0002] In recent years, image display devices typified by liquid crystal display devices and electroluminescence (EL) display devices (for example, organic EL display devices and inorganic EL display devices) have been rapidly spreading. In an organic EL display device, it is known to prevent problems such as external light reflection and background reflection by disposing a circular polarizing plate including a λ / 4 plate on the viewing side of the organic EL cell (for example, Patent Documents 1 and 2).

[0003] On the other hand, since an organic EL display device has a large power consumption for light emission, energy saving is required.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made to solve the above-described conventional problems, and a main object thereof is to provide a polarizing film capable of reducing the power consumption of an organic EL display device.

Means for Solving the Problems

[0006] According to one aspect of the present invention, there is provided a polarizing film composed of a polyvinyl alcohol-based resin film containing iodine, wherein the transmittance at a wavelength of 470 nm is larger than the transmittance at a wavelength of 600 nm. In one embodiment, the haze of the polarizing film is 1% or less. In one embodiment, the orthogonal absorbance A of the polarizing film at a wavelength of 470 nm 470 is 4.0 or less. In one embodiment, the orthogonal absorbance A of the polarizing film at a wavelength of 600 nm 600 with respect to the orthogonal absorbance A at a wavelength of 470 nm 470 The ratio of (A 470 / A 600 ) is 0.10 to 0.80. In one embodiment, the single transmittance of the polarizing film is 42.0% to 65.0%, and the degree of polarization is 40.0% to 99.998%. In one embodiment, the thickness of the polarizing film is 12 μm or less. According to another aspect of the present invention, a polarizing plate including the polarizing film and a protective layer disposed on at least one side of the polarizing film is provided. 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 angle formed by the slow axis of the retardation layer and the absorption axis of the polarizing film is 40° to 50°. According to another aspect of the present invention, an image display device including the polarizing plate is provided. In one embodiment, the image display device is an organic electroluminescence display device.

Advantages of the Invention

[0007] In the polarizing film according to the embodiment of the present invention, since the transmittance at a wavelength of 470 nm is larger than the transmittance at a wavelength of 600 nm, light on the short wavelength side can be transmitted more actively than light on the long wavelength side. By using such a polarizing film, even when the amount of blue light emission with high power consumption is reduced, a decrease in luminance in the short wavelength region can be suppressed. As a result, it is possible to achieve both energy saving and high luminance of the organic EL display device.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0010] (Definition of Terms and Symbols) The definitions of terms and symbols in this specification are as follows. (1) Refractive Index (nx, ny, nz) “nx” is the refractive index in the direction where the in-plane refractive index is maximum (i.e., the slow axis direction), “ny” is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and “nz” is the refractive index in the thickness direction. (2) In-Plane Phase Difference (Re) “Re(λ)” is the in-plane phase difference measured with light of wavelength λ nm at 23°C. For example, “Re(550)” is the in-plane phase difference measured with light of wavelength 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) Phase Difference in the Thickness Direction (Rth) “Rth(λ)” is the phase difference in the thickness direction measured with light of wavelength λ nm at 23°C. For example, “Rth(550)” is the phase difference in the thickness direction measured with light of wavelength 550 nm at 23°C. Rth(λ) is obtained 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 the reference direction. Therefore, for example, "45°" means ±45°.

[0011] A. Polarizing film The polarizing film according to an embodiment of the present invention is composed of a polyvinyl alcohol-based resin film containing iodine, and the transmittance (Ts 470 ) at a wavelength of 470 nm is greater than the transmittance (Ts 600 ) at a wavelength of 600 nm. In other words, the polarizing film according to an embodiment of the present invention satisfies the relationship of "1 < Ts 470 / Ts 600 ", and preferably satisfies the relationship of "1.02 ≦ Ts 470 / Ts 600 ≦ 1.30". A polarizing film satisfying such a relationship can transmit light on the short-wavelength side more actively than light on the long-wavelength side.

[0012] The transmittance (Ts 470 ) at the wavelength of 470 nm is a value corresponding to the content of the PVA-I3 - complex having absorption near the wavelength of 470 nm, and usually decreases as the content of the PVA-I3 - complex increases. On the other hand, the transmittance (Ts 600 ) at the wavelength of 600 nm is a value corresponding to the content of the PVA-I5 - complex having absorption near the wavelength of 600 nm, and usually decreases as the content of the PVA-I5 - complex increases. Therefore, a polarizing film satisfying the relationship of "1 < Ts 470 / Ts 600 " has the characteristic that the content ratio of the PVA-I3 - complex to the PVA-I5 - complex is lower than that of a polarizing film not satisfying the relationship.

[0013] Ts 470 and Ts 600 of the polarizing film can be any appropriate values according to the purpose. Ts 470can 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. Also, Ts 600 can be, for example, 40.0% or more, preferably 41.0% or more, more preferably 42.0% or more, and can be, for example, 70.0% or less, preferably 60.0% or less, more preferably 50.0% or less.

[0014] The polarizing film preferably exhibits absorption dichroism at any wavelength in the wavelength range 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 even 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, and more preferably 48.0% or less. Also, the degree of polarization of the polarizing film is, for example, 40.0% or more, preferably 90.0% or more, more preferably 94.0% or more, even more preferably 96.0% or more, even more preferably 99.0% or more, even more preferably 99.5% or more, and preferably 99.998% or less. The above transmittance is typically the Y value measured using an ultraviolet-visible spectrophotometer and subjected to visual sensitivity correction. The above degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer and subjected to visual sensitivity correction. Degree of polarization (%) = {(Tp - Tc) / (Tp + Tc)} 1 / 2 × 100

[0015] In one embodiment, the transmittance of a thin polarizing film with a thickness of 12 μm or less is typically measured using an ultraviolet-visible spectrophotometer with a laminate of a polarizing film (refractive index of the surface: 1.53) and a protective layer (protective film) (refractive index: 1.50) as the measurement target. Depending on the refractive index of the surface of the polarizing film and / or the refractive index of the surface of the protective layer in contact with the air interface, the reflectance at the interface of each layer changes, and as a result, the measured value of the transmittance may change. Therefore, for example, when using a protective layer with a refractive index other than 1.50, the measured value of the transmittance may be corrected according to the refractive index of the surface of the protective layer in contact with the air interface. Specifically, the correction value C of the transmittance is expressed by the following formula using the reflectance R1 (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective layer and the air layer. C = R1 - R0 R0 = ((1.50 - 1) 2 / (1.50 + 1) 2 ) × (T1 / 100) R1 = ((n1 - 1) 2 / (n1 + 1) 2 ) × (T1 / 100) Here, R0 is the transmission axis reflectance when using a protective layer with a refractive index of 1.50, n1 is the refractive index of the protective layer to be used, and T1 is the transmittance of the polarizing film. For example, when using a substrate (cycloolefin-based film, film with a hard coat layer, etc.) with a surface refractive index of 1.53 as the protective layer, the correction amount C is about 0.2%. In this case, by adding 0.2% to the transmittance obtained by measurement, it is possible to convert the transmittance of the polarizing film with a surface refractive index of 1.53 to the transmittance when using a protective layer with a refractive index of 1.50 . According to the calculation based on the above formula, the change amount of the correction value C when the transmittance T1 of the polarizing film is changed by 2% is 0.03% or less, and the influence of the transmittance of the polarizing film on the value of the correction value C is limited. Also, when the protective layer has absorption other than surface reflection, appropriate correction can be performed according to the absorption amount.

[0016] The orthogonal absorbance A of the polarizing film at a wavelength of 470 nm 470is preferably 4.0 or less, more preferably 3.5 or less, still more preferably 3.0 or less, and even more preferably 2.5 or less. 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 A λ at the wavelength λ nm is determined by the following formula based on the above orthogonal transmittance Tc. Orthogonal absorbance = log10(100 / Tc)

[0017] The ratio of the orthogonal absorbance A 600 at a wavelength of 600 nm of the polarizing film to the orthogonal absorbance A 470 at a wavelength of 470 nm (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 (A 470 / A 600 ) is, for example, 0.10 or more, preferably 0.30 or more, and more preferably 0.35 or more.

[0018] The orthogonal absorbance A 470 is a value corresponding to the content of the PVA-I3 - complex arranged in the absorption axis direction. Usually, a high orthogonal absorbance A 470 means a large content of the PVA-I3 - complex arranged in the absorption axis direction. On the other hand, the orthogonal absorbance A 600 is a value corresponding to the content of the PVA-I5 - complex arranged in the absorption axis direction. Usually, a high orthogonal absorbance A 600 means a large content of the PVA-I5 - complex arranged in the absorption axis direction. Therefore, a low ratio (A 470 / A 600 ) means that the content of the PVA-I3 - complex arranged in the absorption axis direction is relatively small, and the content of the PVA-I5 - complex arranged in the absorption axis direction is relatively large.

[0019] The haze of the polarizing film is preferably 1% or less, more preferably 0.8% or less, and still more preferably 0.6% or less. If the haze is within this range, an organic EL display device having a high contrast ratio can be obtained.

[0020] The iodine concentration in the polarizing film is preferably 3% by weight or more, more preferably 4% to 10% by weight, and still more preferably 4% to 8% by weight. In the present specification, the "iodine concentration" means the amount of all iodine contained in the polarizing film. More specifically, in the polarizing film, iodine is present in the form of I - , I2, I3 - , PVA-I3 - complex, PVA-I5 - complex, etc. The iodine concentration in the present specification means the concentration of iodine including all these forms. The iodine concentration can be calculated, for example, from the fluorescence X-ray intensity by fluorescence X-ray analysis and the film (polarizing film) thickness.

[0021] The thickness of the polarizing film is typically 25 μm or less, preferably 12 μm or less, more preferably 1 μm to 12 μm, still more preferably 1 μm to 7 μm, and even more preferably 2 μm to 5 μm.

[0022] B. Method for manufacturing a polarizing film The polarizing film described in item A can be obtained, for example, by a manufacturing method including bringing a PVA-based resin film in which iodine is adsorbed and oriented into contact with an aqueous solvent. By bringing such a PVA-based resin film into contact with an aqueous solvent, polyiodide ions forming a PVA-I3 - complex escape preferentially over polyiodide ions forming a PVA-I5 - complex, resulting in decolorization. As a result, a polarizing film satisfying the relationship of "1 < Ts 470 / Ts 600 " can be easily obtained. In one embodiment, the increase ratio (ΔTs λ = Ts λ(After contact) / Ts λ (Before contact)) is ΔTs 415 > ΔTs 470 > ΔTs 600 satisfies the relationship of.

[0023] B-1. PVA-based resin film The PVA-based resin film with a moisture content of 15% by weight or less and iodine adsorbed and oriented (also referred to as the "original undecolorized film" in this specification) typically satisfies the relationship of "1 ≧ Ts 470 / Ts 600 ". Further, the original undecolorized film preferably exhibits absorption dichroism at any wavelength in the wavelength range of 380 nm to 780 nm and is in a state where it can function as a polarizing film. Specifically, the original undecolorized film is preferably a PVA-based resin film that has been subjected to various treatments such as stretching treatment, dyeing treatment with iodine, and drying treatment.

[0024] In one embodiment, the transmittance (single transmittance: Ts) of the original undecolorized film is preferably 41.0% or more, more preferably 42.0% or more, and even more preferably 42.5% or more. On the other hand, the transmittance of the original undecolorized film is preferably 46.0% or less, more preferably 45.0% or less. The degree of polarization of the original undecolorized film is preferably 98.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more. On the other hand, the degree of polarization of the original undecolorized film is preferably 99.998% or less. The above transmittance and degree of polarization are determined in the same manner as the transmittance and degree of polarization of the polarizing film.

[0025] The moisture content of the original undecolorized 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 original undecolorized film is within this range, dissolution and wrinkle generation can be prevented when in contact with an aqueous solvent.

[0026] The thickness of the original undecolorized 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, and even more preferably 2 μm to 5 μm.

[0027] The undecolorized 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 undecolorized original film produced using a laminate of two or more layers can suitably maintain excellent optical properties (typically, single transmittance and degree of polarization) while avoiding the occurrence of wrinkles and the like even after contact with an aqueous solvent.

[0028] B-1-1. Production of Undecolorized Original Film Using Laminate of Two or More Layers The production of the undecolorized original film using a laminate of two or more layers can be carried out, for example, by subjecting a PVA-based resin film containing a halide and a PVA-based resin to air-assisted stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment in this order in the state of a laminate with a long thermoplastic resin base material. The laminate of the thermoplastic resin base material and the PVA-based resin film can be obtained, for example, by forming a PVA-based resin layer (PVA-based resin film) containing a halide and a PVA-based resin on one side of the long thermoplastic resin base material to form a laminate. The drying shrinkage treatment includes, for example, heating the laminate of the long thermoplastic resin base material and the PVA-based resin film while conveying it in the longitudinal direction to shrink it by 2% or more in the width direction and drying it until the moisture content of the PVA-based 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 carried out using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. According to such a production method, an undecolorized original film having a high degree of orientation of the PVA-based resin and excellent optical properties can be obtained.

[0029] B-1-1-1. Production of Laminate As a method for producing a laminate of a thermoplastic resin substrate and a PVA-based resin layer, any suitable method can be adopted. Preferably, a coating solution 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.

[0030] As a method for applying the coating solution, any suitable method can be adopted. For example, roll coating method, spin coating method, wire bar coating method, dip coating method, die coating method, curtain coating method, spray coating method, knife coating method (comma coating method, etc.) and the like can be mentioned. The application and drying temperature of the above coating solution is preferably 50°C or higher.

[0031] The thickness of the PVA-based resin layer is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm.

[0032] Before forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to surface treatment (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.

[0033] The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If it 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 underwater stretching treatment described later, the thermoplastic resin substrate may take a long time to absorb water and may require an excessive load for stretching.

[0034] The thermoplastic resin base material preferably has a water absorption rate of 0.2% or more, more preferably 0.3% or more. The thermoplastic resin base material can absorb water, and the water can act as a plasticizer to cause plasticization. As a result, the stretching stress can be significantly reduced, and stretching at a high magnification can be achieved. On the other hand, the water absorption rate of the thermoplastic resin base material is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin base material, it is possible to prevent problems such as a significant decrease in the dimensional stability of the thermoplastic resin base material during production and deterioration of the appearance of the obtained undecolorized original film. In addition, it is possible to prevent the base material from breaking during stretching in water or the PVA-based resin layer from peeling off from the thermoplastic resin base material. The water absorption rate of the thermoplastic resin base material can be adjusted, for example, by introducing a modified group into the constituent material. The water absorption rate is a value determined according to JIS K 7209.

[0035] The glass transition temperature (Tg) of the thermoplastic resin base material is preferably 120°C or lower. By using such a thermoplastic resin base material, it is possible to sufficiently ensure the stretchability of the laminate while suppressing the crystallization of the PVA-based resin layer. Furthermore, considering the plasticization of the thermoplastic resin base material by water and the good performance of stretching in water, it is more preferably 100°C or lower, further preferably 90°C or lower. On the other hand, the glass transition temperature of the thermoplastic resin base material is preferably 60°C or higher. By using such a thermoplastic resin base material, when applying and drying the coating liquid containing the above PVA-based resin, it is possible to prevent problems such as deformation of the thermoplastic resin base material (for example, the occurrence of unevenness, sagging, wrinkles, etc.) and to produce a laminate well. In addition, the stretching of the PVA-based resin layer can be performed well at a suitable temperature (for example, about 60°C). The glass transition temperature of the thermoplastic resin base material can be adjusted, for example, by introducing a modified group into the constituent material or heating using a crystallization material. The glass transition temperature (Tg) is a value determined according to JIS K 7121.

[0036] As a constituent material of the thermoplastic resin substrate, any suitable thermoplastic resin can be employed. Examples of the thermoplastic resin 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. Among these, norbornene resins and amorphous polyethylene terephthalate resins are preferably used.

[0037] In one embodiment, an amorphous (non-crystallized) polyethylene terephthalate resin is preferably used. Among them, an amorphous (difficult-to-crystallize) polyethylene terephthalate resin is particularly preferably used. Specific examples of the amorphous polyethylene terephthalate resin include copolymers further containing isophthalic acid and / or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further containing cyclohexanedimethanol or diethylene glycol as glycols.

[0038] In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate resin having isophthalic acid units. This is because such a thermoplastic resin substrate is extremely excellent in stretchability and crystallization during stretching can be suppressed. This is presumably due to the introduction of isophthalic acid units, which gives a large bend to the main chain. The polyethylene terephthalate resin has terephthalic acid units and ethylene glycol units. The content ratio of the isophthalic acid units is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, based on the total of all repeating units. This is because a thermoplastic resin substrate with extremely excellent stretchability can be obtained. On the other hand, the content ratio of the isophthalic acid units is preferably 20 mol% or less, more preferably 10 mol% or less, based on the total of all repeating units. By setting such a content ratio, the crystallinity can be favorably increased in the drying shrinkage treatment described later.

[0039] The thermoplastic resin substrate may be pre-stretched (before forming the PVA-based resin layer). In one embodiment, it is stretched in the lateral direction of the long thermoplastic resin substrate. The lateral direction is preferably a direction perpendicular to the stretching direction of the laminate described later. In this specification, "perpendicular" includes cases where it is substantially perpendicular. Here, "substantially perpendicular" includes cases where it is 90° ± 5.0°, preferably 90° ± 3.0°, and more preferably 90° ± 1.0°.

[0040] 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 stretching ratio of the thermoplastic resin substrate is preferably 1.5 times to 3.0 times.

[0041] As the stretching method of the thermoplastic resin substrate, any suitable method can be adopted. Specifically, it may be fixed-end stretching or free-end stretching. The stretching method may be dry or wet. The stretching of the thermoplastic resin substrate may be performed in one step or in multiple steps. When performed in multiple steps, the above-mentioned stretching ratio is the product of the stretching ratios of each step.

[0042] 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 the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferably used. The PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film adhering to the thermoplastic resin substrate can be formed. The content 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-based resin.

[0043] Additives may be blended into the coating liquid. Examples of the additives include plasticizers, surfactants, etc. Examples of the plasticizers include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactants include nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability, and stretchability of the resulting PVA-based resin layer.

[0044] As the above PVA-based resin, any suitable resin can be adopted. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer can be mentioned. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer is obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be determined according to JIS K 6726-1994. By using such a PVA-based resin with a saponification degree, an undecolorized original film with excellent durability can be obtained. If the saponification degree is too high, there is a risk of gelation.

[0045] The average polymerization degree of the PVA-based resin can be appropriately selected according to the purpose. The average polymerization degree is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average polymerization degree can be determined according to JIS K 6726-1994.

[0046] As the above halide, any suitable halide can be adopted. For example, iodide and sodium chloride can be mentioned. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

[0047] The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, based on 100 parts by weight of the PVA-based resin. When the amount of the halide based on 100 parts by weight of the PVA-based resin exceeds 20 parts by weight, the halide may bleed out, and the finally obtained undyed original film may become cloudy.

[0048] Generally, when the PVA-based resin layer is stretched, the orientation of polyvinyl alcohol molecules in the PVA-based resin layer becomes higher. However, when the stretched PVA-based resin layer is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules may be disturbed and the orientation may decrease. In particular, when stretching a laminate of a thermoplastic resin substrate and a PVA-based resin layer in boric acid water, when stretching the laminate in boric acid water at a relatively high temperature to stabilize the stretching of the thermoplastic resin substrate, the tendency of the above-mentioned decrease in the degree of orientation is remarkable. For example, while stretching of a single PVA film in boric acid water is generally carried out at 60 °C, stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is carried out at a high temperature of around 70 °C. In this case, the orientation of PVA at the initial stage of stretching can decrease before increasing due to 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 performing high-temperature stretching (auxiliary stretching) in air before stretching the laminate in boric acid water, crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, disturbance of the orientation of the polyvinyl alcohol molecules and decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. Thereby, the optical properties of the undyed original film obtained through a treatment step such as a dyeing treatment and a stretching treatment in water, which are carried out by immersing the laminate in a liquid, can be improved.

[0049] B-1-1-2. Air Auxiliary Stretching Treatment In particular, in order to obtain high optical properties, a two-stage stretching method that combines dry stretching (auxiliary stretching) and stretching in boric acid water is selected. By introducing auxiliary stretching as in the two-stage stretching, it is possible to stretch while suppressing the crystallization of the thermoplastic resin substrate, and solve the problem that the stretchability decreases due to excessive crystallization of the thermoplastic resin substrate in the subsequent stretching in boric acid water, and the laminate can be stretched at a higher magnification. Furthermore, when applying a PVA-based resin on the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, it is necessary to lower the coating temperature 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, and there may arise a problem that sufficient optical properties cannot be obtained. On the other hand, by introducing auxiliary stretching, even when applying a PVA-based resin on the thermoplastic resin substrate, it becomes possible to enhance the crystallinity of the PVA-based resin and achieve high optical properties. At the same time, by enhancing the orientation of the PVA-based resin in advance, problems such as a decrease in the orientation or dissolution of the PVA-based resin when immersed in water during subsequent dyeing or stretching treatments can be prevented, and high optical properties can be achieved.

[0050] The stretching method of air-assisted stretching may be fixed-end stretching (for example, the method of stretching using a tenter stretching machine) or free-end stretching (for example, the method of uniaxially stretching a laminate through rolls with different peripheral speeds). However, in order to obtain high optical properties, free-end stretching can be actively adopted. In one embodiment, the air stretching process includes a heating roll stretching step of stretching the laminate while conveying it in its longitudinal direction by the peripheral speed difference between heating rolls. The air stretching process typically includes a zone stretching step and a heating roll stretching step. Note that the order of the zone stretching step and the heating roll stretching step is not limited, and the zone stretching step may be performed first, or the heating roll stretching step may be performed first. The zone stretching step may be omitted. In one embodiment, the zone stretching step and the heating roll stretching step are performed in this order. In another embodiment, in a tenter stretching machine, the laminate end is gripped and stretched by widening the distance between the tenters in the flow direction (the widening of the distance between the tenters becomes the stretching ratio). At this time, the distance between the tenters in the width direction (the direction perpendicular to the flow direction) is set to approach arbitrarily. Preferably, it can be set to be closer to the free-end stretching with respect to the stretching ratio in the flow direction. In the case of free-end stretching, the shrinkage rate in the width direction = (1 / stretching ratio) 1 / 2 is calculated by

[0051] The air-assisted stretching may be performed in one step or multiple steps. When performed in multiple steps, the stretching ratio is the product of the stretching ratios of each step. The stretching direction in the air-assisted stretching is preferably substantially the same as the stretching direction in the underwater stretching.

[0052] The stretching ratio in the air-assisted stretching is preferably 2.0 times to 3.5 times. When combining air-assisted stretching and underwater stretching, the maximum stretching ratio is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times or more with respect to the original length of the laminate. In this specification, the "maximum stretching ratio" refers to the stretching ratio immediately before the laminate breaks, and separately, the stretching ratio at which the laminate breaks is confirmed, and a value 0.2 lower than that value is referred to.

[0053] The stretching temperature of the air-assisted stretching can be set to any appropriate value according to the forming material of the thermoplastic resin substrate, the stretching method, etc. The stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C, 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, the crystallization of the PVA-based resin can be suppressed from proceeding rapidly, and the defects caused by such crystallization (for example, preventing the orientation of the PVA-based resin layer by stretching) can be suppressed. The crystallization index of the PVA-based resin after the air-assisted stretching 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, the measurement is carried out using polarized light as the measurement light, and the crystallization index is calculated according to the following formula using the intensities at 1141 cm -1 and 1440 cm -1 . Crystallization index = (I C / I R ) However, I C : The intensity at 1141 cm -1 when the measurement light is incident and measured I R : The intensity at 1440 cm -1 when the measurement light is incident and measured .

[0054] B-1-1-3. Insolubilization treatment If necessary, after the air-assisted stretching treatment and before the underwater stretching treatment and the dyeing treatment, an insolubilization treatment is performed. The above insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing the insolubilization treatment, water resistance can be imparted to the PVA-based resin layer, and the orientation degradation of PVA when immersed in water can be prevented. The concentration of the aqueous boric acid solution is preferably 1 part by weight to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilization bath (aqueous boric acid solution) is preferably 20°C to 50°C.

[0055] B-1-1-4. Dyeing Treatment The above dyeing treatment is typically carried out by dyeing the PVA-based resin layer with iodine. Specifically, it is carried out by adsorbing iodine onto the PVA-based resin layer. Examples of the adsorption method include immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, applying the dyeing solution to the PVA-based resin layer, spraying the dyeing solution onto the PVA-based resin layer, etc. Preferably, it is the method of immersing the laminate in the dyeing solution (dyeing bath). This is because iodine can be adsorbed well.

[0056] The above dyeing solution is preferably an aqueous iodine solution. The compounding amount of iodine is preferably 0.05 parts by weight to 0.5 parts by weight with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to compound iodide in the aqueous iodine solution. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. Among these, preferably, it is potassium iodide. The compounding amount of the iodide is preferably 0.1 parts by weight to 10 parts by weight, more preferably 0.3 parts by weight to 5 parts by weight with respect to 100 parts by weight of water. The liquid temperature during dyeing of the dyeing solution is preferably 20°C to 50°C in order to suppress the dissolution of the PVA-based resin. When immersing the PVA-based resin layer in the dyeing 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.

[0057] The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the single transmittance of the finally obtained undecolorized original film becomes a desired value. Such dyeing conditions preferably use an aqueous iodine solution as the dyeing solution, and the ratio of the contents of iodine and potassium iodide in the aqueous iodine solution is 1:5 to 1:20. The ratio of the contents of iodine and potassium iodide in the aqueous iodine solution is preferably 1:5 to 1:10. Thereby, an undecolorized original film having optical properties as described later can be obtained.

[0058] When a dyeing treatment is continuously carried out after a treatment (typically, an insolubilization treatment) of immersing a laminate in a treatment bath containing boric acid, the boric acid contained in the treatment bath may mix into the dyeing bath, causing the boric acid concentration in the dyeing bath to change over time. As a result, the dyeability may become unstable. In order to suppress the destabilization of the dyeability as described above, the upper limit of the boric acid concentration in the dyeing bath is preferably adjusted to 4 parts by weight, more preferably 2 parts by weight, per 100 parts by weight of water. On the other hand, the lower limit of the boric acid concentration in the dyeing bath is preferably 0.1 part by weight, more preferably 0.2 part by weight, and even more preferably 0.5 part by weight, per 100 parts by weight of water. In one embodiment, a dyeing treatment is carried out using a dyeing bath in which boric acid has been previously blended. Thereby, the rate of change in the boric acid concentration when the boric acid in the treatment bath mixes into the dyeing bath can be reduced. The blending amount of boric acid previously blended in the dyeing bath (that is, the content of boric acid not derived from the treatment bath) is preferably 0.1 part by weight to 2 parts by weight, more preferably 0.5 part by weight to 1.5 part by weight, per 100 parts by weight of water.

[0059] B-1-1-5. Crosslinking treatment If necessary, a crosslinking treatment is carried out after the dyeing treatment and before the stretching treatment in water. The above crosslinking treatment is typically carried out by immersing the PVA-based resin layer in an aqueous boric acid solution. By carrying out the crosslinking treatment, water resistance can be imparted to the PVA-based resin layer, and it is possible to prevent a decrease in the orientation of PVA when immersed in high-temperature water during subsequent stretching in water. The concentration of the aqueous boric acid solution is preferably 1 part by weight to 5 parts by weight per 100 parts by weight of water. Further, when the crosslinking treatment is carried out after the dyeing treatment, it is preferable to further blend an iodide. By blending an iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The blending amount of the iodide is preferably 1 part by weight to 5 parts by weight per 100 parts by weight of water. Specific examples of the iodide are as described above. The liquid temperature of the crosslinking bath (aqueous boric acid solution) is preferably 20°C to 50°C.

[0060] B-1-1-6. Stretching treatment in water The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, stretching can be performed at a temperature lower than the glass transition temperature of the thermoplastic resin base material or the PVA-based resin layer (typically about 80 °C), and the PVA-based resin layer can be stretched at a high magnification while suppressing its crystallization. As a result, an undecolorized original film having excellent optical properties can be produced.

[0061] Any suitable method can be adopted as the stretching method of the laminate. Specifically, fixed-end stretching may be used, or free-end stretching (for example, a method of uniaxially stretching the laminate through rolls with different peripheral speeds) may be used. Preferably, free-end stretching is selected. The stretching of the laminate may be performed in one step or in multiple steps. When performed in multiple steps, the stretching ratio (maximum stretching ratio) of the laminate described below is the product of the stretching ratios of each step.

[0062] The underwater stretching is preferably performed by immersing the laminate in an aqueous boric acid solution (underwater stretching in boric acid water). By using an aqueous boric acid solution as the stretching bath, rigidity to withstand the tension applied during stretching and water resistance that does not dissolve in water can be imparted to the PVA-based resin layer. Specifically, boric acid can generate tetrahydroxyborate anions in an aqueous solution and crosslink with the PVA-based resin by hydrogen bonds. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, enabling good stretching and producing an undecolorized original film having excellent optical properties.

[0063] The above-mentioned aqueous boric acid solution is preferably obtained by dissolving boric acid and / or borate 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. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and an undecolorized original film with higher properties can be produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, etc. in a solvent can also be used.

[0064] Preferably, an iodide is added to the above-mentioned stretching bath (aqueous boric acid solution). By adding an iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Specific examples of the iodide are as described above. The concentration of the iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, based on 100 parts by weight of water.

[0065] 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, high magnification stretching can be performed 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, there is a risk that good stretching cannot be achieved even considering plasticization of the thermoplastic resin substrate by water. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a risk that excellent optical properties cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

[0066] The stretching ratio by stretching in water is preferably 1.5 times or more, more preferably 3.0 times or more. The total stretching ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, based on the original length of the laminate. By achieving such a high stretching ratio, an undecolorized original film with extremely excellent optical properties can be manufactured. Such a high stretching ratio can be achieved by adopting a stretching method in water (stretching in aqueous boric acid).

[0067] B-1-1-7. Drying and Shrinking Treatment The above-mentioned drying and shrinking treatment includes, for example, heating the laminate of the long thermoplastic resin substrate and the PVA-based resin film while transporting it in the longitudinal direction to shrink it by 2% or more in the width direction and drying it until the moisture 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 it until the moisture content becomes 12% by weight or less, more preferably 10% by weight or less, and even more preferably 1% to 5% by weight.

[0068] The drying and shrinking treatment may be carried out by zone heating in which the entire zone is heated, or may be carried out by heating the conveying rolls (using so-called heating rolls) (heating roll drying method). Preferably, both are used. By drying using heating rolls, the heating curl of the laminate can be efficiently suppressed, and an undecolorized original film with excellent appearance can be produced. Specifically, by drying with the laminate along the heating roll, the crystallization of the thermoplastic resin base material can be efficiently promoted and the degree of crystallization can be increased. Even at a relatively low drying temperature, the degree of crystallization of the thermoplastic resin base material can be favorably increased. As a result, the thermoplastic resin base material increases in rigidity and becomes capable of withstanding the shrinkage of the PVA-based resin layer due to drying, and curl is suppressed. Further, by using heating rolls, drying can be performed while maintaining the laminate in a flat state, so that not only curl but also the occurrence of wrinkles can be suppressed. At this time, the optical properties of the laminate can be improved by shrinking it in the width direction by the drying and shrinking treatment. This is because the orientation of PVA and the PVA / iodine complex can be effectively enhanced. The shrinkage rate in the width direction of the laminate by the drying and shrinking treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using heating rolls, the laminate can be continuously shrunk in the width direction while being conveyed, and high productivity can be achieved.

[0069] FIG. 1 is a schematic view showing an example of the drying and shrinking treatment. In the drying and shrinking treatment, the laminate 200 is dried while being conveyed by the conveying rolls R1 to R6 heated to a predetermined temperature and the guide rolls G1 to G4. In the illustrated example, the conveying 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 base material. For example, the conveying rolls R1 to R6 may be arranged so as to continuously heat only one surface of the laminate 200 (for example, the thermoplastic resin base material surface).

[0070] By adjusting the heating temperature of the conveying roll (temperature of the heating roll), the number of heating rolls, the contact time with the heating roll, etc., the drying conditions can be controlled. 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. It is possible to favorably increase the crystallinity of the thermoplastic resin, favorably suppress curling, and manufacture an optical laminate with extremely excellent durability. Note that the temperature of the heating roll can be measured by a contact thermometer. In the illustrated example, six conveying rolls are provided, but there is no particular limitation as long as there are a plurality of conveying rolls. Usually, 2 to 40 conveying rolls are provided, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roll is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

[0071] The heating roll may be provided in a heating furnace (for example, an oven), or may be provided on a normal production line (at room temperature environment). Preferably, it is provided in a heating furnace equipped with a blowing means. By using drying by the heating roll and hot air drying in combination, a steep temperature change between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of the hot air drying is preferably 20°C to 100°C. Also, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10 m / s to 30 m / s. Note that the wind speed is the wind speed in the heating furnace and can be measured by a mini vane type digital anemometer.

[0072] B-1-1-8. Other Treatments Preferably, after the underwater stretching treatment and before the dry shrinkage treatment, a washing treatment is performed. The above washing treatment is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

[0073] B-1-2. Preparation of Unbleached Original Film Using Single-Layer PVA-Based Resin Film The production of the undecolorized original film using a single-layer PVA-based resin film can be carried out by dyeing and stretching a long PVA-based resin film having self-supportability (i.e., not requiring support by a substrate), typically by uniaxial stretching using a roll stretching machine in an aqueous boric acid solution, and then drying until the moisture content becomes 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. The above dyeing can be carried out, for example, by immersing the PVA-based resin film in an aqueous iodine solution. The stretching ratio of the above uniaxial stretching is preferably 3 to 7 times. The stretching may be carried out after the dyeing treatment, or may be carried out while dyeing. Also, it may be dyed after stretching. If necessary, the PVA-based resin film is subjected to a swelling treatment, a cross-linking treatment, a washing treatment, etc. For example, by immersing the PVA-based resin film in water and washing it before dyeing, not only can the dirt on the surface of the PVA-based resin film and the blocking inhibitor be washed, but also the PVA-based resin film can be swollen to prevent uneven dyeing, etc.

[0074] B-2. Aqueous Solvent As the aqueous solvent, any suitable solvent can be used as long as iodine can be eluted from the undecolorized original film. The aqueous solvent can be, for example, water or a mixture of water and a water-soluble organic solvent. Examples of the water-soluble organic solvent preferably 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.

[0075] B-3. Contact Method The contact method with the aqueous solvent is not particularly limited, and any suitable method such as immersion, spraying, and coating can be used. From the viewpoint of uniformly contacting the entire surface of the undecolorized original film with the aqueous solvent, immersion is preferred.

[0076] The contact time with the aqueous solvent and the temperature of the aqueous solvent during contact are the desired Ts 470 、Ts 600 、A 470 、A 600It can be appropriately set according to etc. By increasing the contact time or increasing the temperature of the aqueous solvent, the transmittance (especially Ts 470 ) is large, and the orthogonal absorbance (especially A 470 ) tends to be small. 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, and even more preferably 40°C to 60°C.

[0077] The contact between the undecolorized original film and the aqueous solvent may be carried out by contacting only one side of the undecolorized original film with the aqueous solvent, or may be carried out by contacting both sides with the aqueous solvent. Therefore, a laminate of [undecolorized original film / resin substrate] or [undecolorized original film / protective layer] produced using a laminate of [PVA-based resin layer / resin substrate] can be used for contact with the aqueous solvent. Alternatively, the undecolorized original film produced using a single-layer PVA-based resin film as it is, or in the state of a laminate provided with a protective layer on one side, can be used for contact with the aqueous solvent.

[0078] B-4. Other treatments If necessary, the polarizing film obtained by contact with the 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 even more preferably 1% to 5% by weight.

[0079] C. Polarizing plate The polarizing plate according to the 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 as necessary. In this specification, a polarizing plate including a retardation layer may be referred to as a retardation layer-containing polarizing plate.

[0080] The b * value is, for example, -3 or less, preferably -4 or less, more preferably -20 to -5. b *A polarizing plate with a value within the range has a high transmittance of light in the short wavelength region, and thus exhibits a bluish hue.

[0081] C-1. Overall Structure of the 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.

[0082] FIG. 3 is a schematic cross-sectional view of a polarizing plate including a retardation layer according to another embodiment of the present invention. The polarizing plate 200a with a retardation layer includes a polarizing film 10, a first protective layer 12 disposed on one side of the polarizing film 10, a second protective layer 14 disposed on the other side of the polarizing film 10, and a first retardation layer 20 disposed on the side opposite to the side where the polarizing film 10 of the second protective layer 14 is disposed. Depending on the purpose, one of the first protective layer 12 and the second protective layer 14 may be omitted. For example, when the retardation layer 20 can also function as a protective layer of the polarizing film 10, the second protective layer 14 may be omitted.

[0083] FIG. 4 is a schematic cross-sectional view of a polarizing plate including a retardation layer according to still another embodiment of the present invention. The polarizing plate 200b with a retardation layer 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. On the side opposite to the side where the polarizing film 10 of the second protective layer 14 is disposed, a first retardation layer 20, a second retardation layer 30, and a conductive layer or an isotropic substrate with a conductive layer 40 are provided in this order. The second retardation layer 30 typically shows a refractive index characteristic relationship 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 one or both of them may be omitted. When a conductive layer or an isotropic substrate with a conductive layer is provided, the polarizing plate with a retardation layer can be applied to a so-called inner touch panel type input display device in which a touch sensor is incorporated between an image display cell (e.g., an organic EL cell) and the polarizing plate.

[0084] The Re(550) of the first retardation layer 20 is, for example, 100 nm to 190 nm. Also, the angle formed 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°.

[0085] The above embodiments may be combined as appropriate, and modifications obvious to those skilled in the art may be made to the components in the above embodiments. For example, the configuration in which the conductive layer-equipped isotropic substrate 40 is provided outside the second retardation layer 30 may be replaced with an optically equivalent configuration (for example, a laminate of the second retardation layer and the conductive layer).

[0086] The polarizing plate or the polarizing plate with a retardation layer according to the embodiments of the present invention may further include other retardation layers. The optical properties (for example, refractive index properties, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, arrangement position, etc. of the other retardation layers can be appropriately set according to the purpose.

[0087] The polarizing plate of the present invention may be in a sheet form or a long strip form. In this specification, "long strip form" means an elongated shape in which the length is sufficiently long compared to the width, and includes, for example, an elongated shape in which the length is 10 times or more, preferably 20 times or more, the width. The long strip-shaped polarizing plate can be wound into a roll. When the polarizing plate with a retardation layer is in a long strip form, the polarizing plate and the retardation layer are also in a long strip form. In this case, the polarizing film preferably has an absorption axis in the long axis 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 long axis direction. If the polarizing film and the first retardation layer have such a configuration, the polarizing plate with a retardation layer can be manufactured by roll-to-roll.

[0088] 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 a retardation layer can be attached to an image display cell. Further, it is preferable that a release film is temporarily attached to the surface of the adhesive layer until the polarizing plate with a retardation layer is put into use. By temporarily attaching the release film, the adhesive layer is protected and roll formation becomes possible.

[0089] The total thickness of the polarizing plate is preferably 150 μm or less, more preferably 120 μm or less, still more preferably 100 μm or less, even more preferably 90 μm or less, and even more preferably 85 μm or less. The lower limit of the total thickness can be, for example, 30 μm.

[0090] C-2. Polarizing film As the polarizing film, the polarizing film described in Item A is used.

[0091] C-3. Protective layer 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 the polarizing film. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, polysulfone-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, and acetate-based resins. Also included are thermosetting resins or ultraviolet curable resins such as (meth)acrylic-based, urethane-based, (meth)acrylic urethane-based, epoxy-based, and silicone-based resins. In addition, for example, glassy polymers such as siloxane-based polymers are also included. Also, the polymer film described in JP-A-2001-343529 (WO01 / 37007) can be used. As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used. Examples include a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extruded product of the above resin composition.

[0092] The thickness of the protective layer is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and still more preferably 10 μm to 60 μm.

[0093] C-4. First retardation layer The first retardation layer may have any suitable optical and / or mechanical properties depending on the purpose. The first retardation layer typically has a slow axis. In one embodiment, the angle θ formed between the slow axis of the first retardation layer and the absorption axis of the polarizing film is 40° to 50°, preferably 42° to 48°, and more preferably about 45° as described above. If the angle θ is within such a range, a polarizing plate with a retardation layer having very excellent circular polarization characteristics (and as a result, very excellent antireflection characteristics) can be obtained by using the first retardation layer as a λ / 4 plate as described later.

[0094] The first retardation layer preferably exhibits a refractive index characteristic of nx > ny ≧ nz. The first retardation layer is typically provided to impart antireflection characteristics to the polarizing plate and can function as a λ / 4 plate in one embodiment. 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, and even more preferably 130 nm to 160 nm. Here, "ny = nz" includes not only the case where ny and nz are exactly equal but also the case where they are substantially equal. Therefore, within a range that does not impair the effects of the present invention, ny < nz may occur.

[0095] 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, and particularly preferably 0.9 to 1.3. By satisfying such a relationship, when the obtained polarizing plate with a retardation layer is used in an image display device, a very excellent reflected hue can be achieved.

[0096] The first retardation layer may exhibit an inverse dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light, a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light, or a flat wavelength dispersion characteristic in which the retardation value hardly changes depending on the wavelength of the measurement light. In one embodiment, the first retardation layer exhibits an inverse dispersion wavelength characteristic. 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 characteristics can be realized.

[0097] The first retardation layer preferably has an absolute value of photoelastic coefficient of 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, still more preferably 1.0×10 -12 m 2 / N to 1.2×10 -11 m 2 / N and contains a resin. If the absolute value of the photoelastic coefficient is in such a range, a change in retardation is less likely to occur when shrinkage stress is generated during heating. As a result, thermal unevenness of the obtained image display device can be preferably prevented.

[0098] The first retardation layer can be a stretched film of a resin film or a liquid crystal alignment cured layer. The thickness of the first retardation layer composed of the stretched film of the 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, curling during heating can be favorably suppressed, and curling during bonding can be favorably adjusted. Further, in an embodiment in which the first retardation layer is composed of a polycarbonate-based resin film as described later, the thickness of the first retardation layer is preferably 40 μm or less, more preferably 10 μm to 40 μm, and still more preferably 20 μm to 30 μm. By the first retardation layer being composed of a polycarbonate-based resin film having such a thickness, generation of curling can be suppressed, and it can also contribute to improvement in bending durability and reflection hue.

[0099] Typical examples of resins that can form 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 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 dispersion wavelength characteristics, a polycarbonate-based resin or a polyester carbonate-based resin (hereinafter sometimes simply referred to as a polycarbonate-based resin) can be preferably used.

[0100] As the polycarbonate resin, any appropriate polycarbonate resin can be used as long as the effects of the present invention can be obtained. For example, the polycarbonate resin includes 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 at least one dihydroxy compound selected from the group consisting of alicyclic diols, alicyclic dimethanols, di-, tri- or polyethylene glycols, and alkylene glycols or spiroglycols. Preferably, the polycarbonate resin includes 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 an alicyclic dimethanol and / or a structural unit derived from di-, tri- or polyethylene glycol; more preferably, it includes 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 resin may optionally contain structural units derived from other dihydroxy compounds. The details of the polycarbonate resin that can be preferably used in the present invention are described in, for example, JP-A-2014-10291, JP-A-2014-26266, JP-A-2015-212816, JP-A-2015-212817, and JP-A-2015-212818, and the description is incorporated herein by reference.

[0101] The glass transition temperature of the polycarbonate 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 deteriorate, dimensional changes may occur after film forming, and the image quality of the obtained organic EL panel may be degraded. If the glass transition temperature is excessively high, the forming stability during film forming may deteriorate, and the transparency of the film may be impaired. The glass transition temperature is determined in accordance with JIS K 7121 (1987).

[0102] The molecular weight of the polycarbonate resin can be represented by the reduced viscosity. The reduced viscosity is measured using methylene chloride as the solvent, precisely adjusting the polycarbonate concentration to 0.6 g / dL, and using an Ubbelohde viscometer at a temperature of 20.0 °C ± 0.1 °C. 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, and even more preferably 0.80 dL / g. If the reduced viscosity is less than the lower limit value, there may be a problem that the mechanical strength of the molded product becomes small. On the other hand, if the reduced viscosity is greater than the upper limit value, there may be a problem that the fluidity during molding decreases, resulting in a decrease in productivity and moldability.

[0103] Commercially available films may be used as the polycarbonate resin film. Specific examples of commercially available products include "Pure Ace WR-S", "Pure Ace WR-W", "Pure Ace WR-M" manufactured by Teijin Limited, and "NRF" manufactured by Nitto Denko Corporation.

[0104] The first retardation layer can be obtained, for example, by stretching a film formed from the above polycarbonate resin. As a method for forming a film from a polycarbonate resin, any suitable molding process can be adopted. Specific examples include compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, cast coating (e.g., casting method), calender molding, hot press method, etc. Extrusion molding or cast coating is preferred. This is because the smoothness of the obtained film can be enhanced and good optical uniformity can be obtained. The molding conditions can be appropriately set according to the composition and type of the resin used, the properties desired for the retardation layer, etc. As described above, since many film products of polycarbonate resins are commercially available, the commercially available film may be directly subjected to the stretching treatment.

[0105] The thickness of the resin film (un-stretched film) can be set to any appropriate value according to the desired thickness of the first retardation layer, desired optical properties, stretching conditions described below, etc. Preferably, it is 50 μm to 300 μm.

[0106] For the above stretching, any appropriate stretching method and stretching conditions (e.g., stretching temperature, stretching ratio, stretching direction) can be adopted. Specifically, various stretching methods such as free-end stretching, fixed-end stretching, free-end shrinkage, and fixed-end shrinkage can be used alone, or used simultaneously or sequentially. Regarding the stretching direction, it can be performed in various directions and dimensions such as the length direction, width direction, thickness direction, and diagonal direction. The stretching temperature is preferably Tg - 30°C to Tg + 60°C with respect to the glass transition temperature (Tg) of the resin film, and more preferably Tg - 10°C to Tg + 50°C.

[0107] By appropriately selecting the above stretching method and stretching conditions, a retardation film having the above desired optical properties (e.g., refractive index property, in-plane retardation, Nz coefficient) can be obtained.

[0108] In one embodiment, the retardation film is produced by uniaxially stretching or fixed-end uniaxially stretching the resin film. As a specific example of fixed-end uniaxially stretching, a method of stretching the resin film in the width direction (lateral direction) while running it in the longitudinal direction can be mentioned. The stretching ratio is preferably 1.1 times to 3.5 times.

[0109] 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 angle θ (slow axis in the direction of angle θ) with respect to the longitudinal direction of the film can be obtained. For example, roll-to-roll becomes possible during lamination with a polarizing film, and the manufacturing process can be simplified. Note that the angle θ can be the angle formed by the absorption axis of the polarizing film and the slow axis of the retardation layer in the retardation layer-containing polarizing plate. As described above, the angle θ is preferably 40° to 50°, more preferably 42° to 48°, and even more preferably about 45°.

[0110] As the stretching machine used for diagonal stretching, for example, there is a tenter stretching machine that can apply feeding forces, tensile forces, or pulling forces with different speeds on the left and right in the horizontal and / or vertical directions. Examples of the tenter stretching machine include a single-axis horizontal stretching machine and a simultaneous biaxial stretching machine. Any appropriate stretching machine can be used as long as it can continuously stretch a long resin film diagonally.

[0111] By appropriately controlling the left and right speeds in the stretching machine, a retardation layer (substantially a long retardation film) having the desired in-plane retardation and having a slow axis in the desired direction can be obtained.

[0112] The stretching temperature of the film can 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, etc. Specifically, the stretching temperature is preferably Tg - 30°C to Tg + 30°C, more preferably Tg - 15°C to Tg + 15°C, and most preferably Tg - 10°C to Tg + 10°C. By stretching at such a temperature, a first retardation layer having appropriate characteristics in the present invention can be obtained. Note that Tg is the glass transition temperature of the constituent material of the film.

[0113] C-5. Second Retardation Layer As described above, the second retardation layer can be a so-called positive C-plate showing a refractive index characteristic of nz > nx = ny. By using a positive C-plate as the second retardation layer, reflection in the diagonal direction can be well prevented, and a wide viewing angle of the antireflection function can be achieved. In this case, the retardation Rth(550) in the thickness direction of the second retardation layer is preferably -50 nm to -300 nm, more preferably -70 nm to -250 nm, further preferably -90 nm to -200 nm, and particularly preferably -100 nm to -180 nm. Here, "nx = ny" includes not only the case where nx and ny are exactly 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.

[0114] The second retardation layer having a refractive index characteristic of nz > nx = ny can be formed of any suitable material. The second retardation layer preferably comprises a film containing a liquid crystal material fixed in a homeotropic alignment. The 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 compounds 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, and still more preferably 0.5 μm to 5 μm.

[0115] C-6. Conductive layer or isotropic substrate with conductive layer The conductive layer can be formed by forming a metal oxide film on any suitable substrate by any suitable film formation method (for example, vacuum evaporation method, sputtering method, CVD method, ion plating method, spray method, etc.). Examples of the metal oxide 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 preferably used.

[0116] 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.

[0117] The conductive layer may be transferred from the above substrate to the first retardation layer (or the second retardation layer if present) to be a constituent layer of the polarizing plate with retardation layer alone, or may be laminated on the first retardation layer (or the second retardation layer if present) as a laminate with the substrate (substrate with conductive layer). Preferably, the above substrate is optically isotropic, and therefore, the conductive layer can be used as an isotropic substrate with conductive layer for the polarizing plate with retardation layer.

[0118] As the optically isotropic substrate (isotropic substrate), any suitable isotropic substrate can be adopted. Examples of the material constituting the isotropic substrate include materials having a non-conjugated system resin such as a norbornene-based resin or an olefin-based resin as the main skeleton, and materials having a cyclic structure such as a lactone ring or a glutarimide ring in the main chain of an acrylic resin. When such materials are used, when the isotropic substrate is formed, the expression of the retardation associated with the orientation of the molecular chains can be suppressed to a small extent. 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 substrate is, for example, 20 μm.

[0119] The above conductive layer and / or the conductive layer of the isotropic substrate with the conductive layer can be patterned as necessary. By patterning, a conductive portion and an insulating portion can be formed. As a result, an electrode can be formed. The electrode can function as a touch sensor electrode for sensing contact with the touch panel. As the patterning method, any suitable method can be adopted. Specific examples of the patterning method include a wet etching method and a screen printing method.

[0120] 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. Representative examples of the image display device include a liquid crystal display device and an electroluminescence (EL) display device (for example, an organic EL display device and an inorganic EL display device). Among them, an organic EL display device is preferable in terms of achieving energy saving by reducing the blue light emission amount.

Examples

[0121] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. The measurement methods for each property are as follows. Unless otherwise specified, "parts" and "%" in the examples and comparative examples are based on weight. (1) Thickness Measurement was carried out using the product name "Linear Gauge MODEL D-10HS" (manufactured by Ozaki Seisakusho). (2) Monomer transmittance, degree of polarization, and orthogonal absorbance For the laminate of the PVA-based resin film (polarizing film or undecolorized original film) and the protective layer obtained in the examples and comparative examples, the monomer transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc measured from the PVA-based resin film side 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. For the polarizing plate with a retardation layer, the monomer transmittance Ts was measured in the same manner from the retardation layer side. These Ts, Tp, and Tc are Y values measured according to the 2-degree field of view (C light source) of JIS Z8701 and corrected for visual sensitivity. The refractive index of the protective layer was 1.53, and the refractive index of the surface on the side opposite to the protective layer of the polarizing film 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 Ts measured at wavelengths 470 nm and 600 nm were defined as Ts 470 and Ts 600 respectively. Note that the spectrophotometer can also perform equivalent measurements using, for example, "V-7100" manufactured by JASCO Corporation, and it has been confirmed that equivalent measurement results can be obtained regardless of which spectrophotometer is used. (3) Moisture content The undecolorized original film immediately after the drying treatment (when stretched in a laminate, the stretching substrate is peeled off) is cut into a size of 100 mm × 100 mm or more, and the weight before treatment is measured using an electronic balance. Then, it is placed in a heating oven maintained at 120 °C for 2 hours, and the weight after removal (weight after treatment) is measured, and the moisture content is determined by the following formula. Moisture content [%] = (weight before treatment - weight after treatment) / weight before treatment × 100 (4) Haze Measured in accordance with JIS K7136 using a haze meter (NDH-5000) manufactured by Nippon Denshoku Industries Co., Ltd. (5) Front reflection hue The retardation film-attached polarizing plates obtained in the examples and comparative examples were bonded onto a reflector (manufactured by Toray Film Co., Ltd., trade name "DMS-X42"; reflectance 86%, reflection hue a without a polarizing plate * = -0.22, b * = 0.32) to prepare measurement samples. At this time, they were bonded so that the retardation film side of the retardation film-attached polarizing plate faced the reflector. For the said measurement samples, the a * value and b * value were measured using a spectrophotometer (CM-2600d manufactured by Konica Minolta) in the SCE mode.

[0122] [Example 1-1] 1. Production of polarizing film and polarizing plate A long roll of a PVA-based resin film (manufactured by Kuraray Co., Ltd., product name "PE3000") with a thickness of 30 μm was immersed in a 30°C water bath and stretched 2.2 times in the conveying direction. Then, it was immersed in a 30°C aqueous solution with an iodine concentration of 0.04% by weight and a potassium concentration of 0.3% by weight for dyeing while being stretched 3 times based on the film (original length) that had not been stretched at all. Next, while immersing this stretched film in a 30°C aqueous solution with a boric acid concentration of 3% by weight and a potassium iodide concentration of 3% by weight, it was further stretched up to 3.3 times based on the original length. Subsequently, while immersing it in a 60°C aqueous solution with a boric acid concentration of 4% by weight and a potassium iodide concentration of 5% by weight, it was further stretched up to 6 times based on the original length. Finally, a drying treatment was performed in an oven maintained at 60°C for 5 minutes to produce a polarizing film (undecolorized original film a1) with a thickness of 12 μm. The moisture content of the obtained undecolorized original film a1 was 10.0% by weight, and the single transmittance was 42.5%.

[0123] An aqueous PVA-based resin 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 undecolorized original film a1, and a cycloolefin-based film (manufactured by Zeon Corporation, Zeonor, thickness: 25 μm) was laminated thereto to obtain an optical laminate having a structure of [undecolorized original film a1 / protective layer]. Note that, as the protective layer, a protective layer provided with a hard coat layer may be used, and examples of such a protective layer include a cycloolefin-based film with a hard coat layer (manufactured by ZEON Corporation, product name "G-Film", total thickness 27 μm (film thickness 25 μm + hard coat layer thickness 2 μm)).

[0124] The above optical laminate was cut into a size of 50 mm × 45 mm and immersed in water at 55°C for 9 minutes in a state where it was bonded to a glass plate through an acrylic adhesive layer (thickness 15 μm) so that the surface on the side of the undecolorized original film became the exposed surface. Subsequently, it was dried at 50°C for 5 minutes to obtain a polarizing plate having a structure of [polarizing film A1 / protective layer].

[0125] 2. Production of a retardation film constituting a retardation layer 2-1. Polymerization of a polyester carbonate-based resin Polymerization was carried out using a batch polymerization apparatus consisting of two vertical reactors equipped with stirring blades and a reflux condenser controlled at 100°C. 29.60 parts by mass (0.046 mol) of bis[9-(2-phenoxycarbonylethyl)fluorene-9-yl]methane, 29.21 parts by mass (0.200 mol) of isosorbide (ISB), 42.28 parts by mass (0.139 mol) of spiroglycol (SPG), 63.77 parts by mass (0.298 mol) of diphenyl carbonate (DPC), and 1.19×10 -2 parts by mass (6.78×10 -5(xx mol) was charged. After replacing the inside of the reactor with nitrogen under reduced pressure, heating was carried out with a heat medium, and stirring was started when the internal temperature reached 100°C. After 40 minutes from the start of heating up, the internal temperature reached 220°C, and while controlling to maintain this temperature, reduced pressure was started and it was made 13.3 kPa in 90 minutes after reaching 220°C. The phenol vapor by-produced along with the polymerization reaction was led to a reflux condenser at 100°C, the monomer components contained in a small amount in the phenol vapor were returned to the reactor, and the phenol vapor that did not condense was led to a condenser at 45°C and recovered. Nitrogen was introduced into the first reactor to repressurize to atmospheric pressure once, and then the oligomerized reaction solution in the first reactor was transferred to the second reactor. Next, heating up and reduced pressure in the second reactor were started, and the internal temperature was made 240°C and the pressure was made 0.2 kPa in 50 minutes. Thereafter, polymerization was allowed to proceed until a predetermined stirring power was reached. When the predetermined power was reached, nitrogen was introduced into the reactor to repressurize, and the produced polyester carbonate-based resin was extruded into water, and the strands were cut to obtain pellets.

[0126] 2-2. Preparation of the retardation film The obtained polyester carbonate-based resin (pellets) was vacuum dried at 80°C for 5 hours, and then a film forming apparatus equipped with a single screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder set temperature: 250°C), a T-die (width 200 mm, set temperature: 250°C), a chill roll (set temperature: 120 - 130°C) and a winder was used to produce a long resin film with a thickness of 130 μm. The obtained long resin film was stretched while adjusting so as to obtain a predetermined retardation, and a retardation film with a thickness of 48 μm was obtained. The stretching conditions were a stretching temperature of 143°C and a stretching ratio of 2.8 times in the width direction. Re(550) of the obtained retardation film was 141 nm, Re(450) / Re(550) was 0.86, and the Nz coefficient was 1.12.

[0127] 3. Preparation of the polarizing plate with a retardation layer The retardation film obtained in the above item 2. was laminated on the surface of the polarizing film of the polarizing plate obtained in the above item 1. through an acrylic adhesive (thickness: 15 μm). At this time, the lamination was performed such that the absorption axis of the polarizing film and the slow axis of the retardation film formed an angle of 45°. In this way, a polarizing plate with a retardation layer having a structure of [retardation layer / polarizing film A1 / protective layer] was obtained.

[0128] [Example 1-2] Instead of immersing in water at 55°C for 9 minutes, 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 it was immersed in water at 65°C for 3 minutes. Further, a polarizing plate with a retardation layer was obtained in the same manner as in Example 1-1 except that the obtained polarizing plate was used.

[0129] [Example 1-3] Instead of immersing in water at 55°C for 9 minutes, 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 it was immersed in water at 23°C for 31 hours. Further, a polarizing plate with a retardation layer was obtained in the same manner as in Example 1-1 except that the obtained polarizing plate was used.

[0130] [Comparative Example 1] An optical laminate having a structure of [undecolorized 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 obtained polarizing plate was used.

[0131] [Example 2-1] As a thermoplastic resin substrate, an amorphous isophthalic copolyethylene terephthalate film (thickness: 100 μm) in a long strip shape with a Tg of about 75°C was used, and one side of the resin substrate was subjected to corona treatment. 13 parts by weight of potassium iodide was added to 100 parts by weight of a PVA-based resin obtained by mixing polyvinyl alcohol (degree of polymerization 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer") in a ratio of 9:1, and the mixture was dissolved in water to prepare a PVA aqueous solution (coating solution). The above PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60°C to form a PVA-based resin layer with a thickness of 13 μm, thereby producing a laminate. The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (length direction) in an oven at 130°C (air-assisted stretching treatment). Subsequently, the laminate was immersed in an insolubilization bath at a liquid temperature of 40°C (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment). Subsequently, the laminate was immersed in a dyeing bath at a liquid temperature of 30°C (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizing plate was 42.3% (dyeing treatment). Subsequently, the laminate was immersed in a crosslinking bath at a liquid temperature of 40°C (an aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (crosslinking treatment). Thereafter, while immersing the laminate in an aqueous boric acid solution at a liquid temperature of 70°C (boric acid concentration 4 wt%, potassium iodide concentration 5 wt%), uniaxial stretching was performed in the longitudinal direction (length direction) between rolls with different peripheral speeds so that the total stretching ratio was 5.5 times (stretching treatment in water). Thereafter, the laminate was immersed in a cleaning bath at a liquid temperature of 20°C (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment). Thereafter, while drying in an oven maintained at about 90°C, it was brought into contact with a SUS heating roll 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 dry shrinkage treatment was 2%. In this way, an undecolorized original film with a moisture content of 4.5% and a thickness of 5.4 μm was formed on the resin substrate, and a cycloolefin-based film (manufactured by Nippon Zeon Co., Ltd., Zeonor, thickness: 25 μm) was laminated on the surface of the undecolorized original film with a UV-curable adhesive (thickness 1.0 μm). Thereafter, the resin substrate was peeled off to obtain an optical laminate having a structure of [undecolorized original film b1 / protective layer].

[0132] The above optical laminate was cut into a size of 50 mm × 45 mm and immersed in water at 50°C for 9 minutes in a state where it was bonded to a glass plate through an acrylic adhesive layer (thickness: 15 μm) such that the surface on the side of the undecolorized original film was the exposed surface. Then, it was dried at 50°C for 5 minutes to obtain a polarizing plate having a structure of [polarizing film B1 / protective layer]. Further, a retardation layer - attached polarizing plate 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 above polarizing plate was used.

[0133] [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 it was immersed in water at 60°C for 3 minutes instead of being immersed in water at 50°C for 9 minutes. Further, a retardation layer - attached polarizing plate was obtained in the same manner as in Example 1 - 1 except that the above polarizing plate was used.

[0134] [Comparative Example 2] An optical laminate having a structure of [undecolorized original film b1 / protective layer] prepared in the same manner as in Example 2 - 1 was used as a polarizing plate. Further, a retardation layer - attached polarizing plate was obtained in the same manner as in Example 1 - 1 except that the above polarizing plate was used.

[0135] Various properties of the undecolorized original film, polarizing film, and retardation layer - attached polarizing plate obtained in the above examples and comparative examples were evaluated. The results are shown in Table 1.

Table 1

[0136] As is clear from Table 1, the polarizing films of the examples satisfy the relationship of "1 < Ts 470 / Ts 600 " and can transmit light on the short - wavelength side more actively than light on the long - wavelength side.

Industrial Applicability

[0137] 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 in organic EL display devices.

Explanation of Signs

[0138] 10 Polarizing film 20 Protective layer 30 Retardation layer 40 Adhesive layer 100 Polarizer

Claims

1. It is composed of a polyvinyl alcohol-based resin film containing iodine, the transmittance at a wavelength of 470 nm is greater than the transmittance at a wavelength of 600 nm, Orthogonal absorbance A at a wavelength of 600 nm ６００ to the orthogonal absorbance A at a wavelength of 470 nm ４７０ The ratio of (A ４７０ / A ６００ ) is 0.10 to 0.60, and the orthogonal absorbance A470 at a wavelength of 470 nm is 0.2 to 1.

96. A polarizing film.

2. The polarizing film according to Claim 1, having a haze of 1% or less.

3. The polarizing film according to Claim 1 or 2, having a single transmittance of 42.0% to 65.0% and a polarization degree of 40.0% to 99.998%.

4. The polarizing film according to any one of Claims 1 to 3, having a thickness of 12 μm or less.

5. A polarizing plate including the polarizing film according to any one of Claims 1 to 4 and a protective layer disposed on at least one side of the polarizing film.

6. Further including 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 angle formed by the slow axis of the retardation layer and the absorption axis of the polarizing film is 40° to 50°. The polarizing plate according to Claim 5.

7. An image display device including the polarizing plate according to Claim 5 or 6.

8. The image display device according to Claim 7, which is an organic electroluminescence display device.

Images