TWI748108B - Polarizing film, polarizing plate, and manufacturing method of polarizing film - Google Patents

Abstract

The subject of the present invention is to provide a polarizing film with excellent optical properties. The solution is the polarizing film of the present invention, which is composed of a polyvinyl alcohol-based resin film containing iodine, has a thickness of 8 μm or less, and has an orthogonal absorbance of 1.00 or less per 1 μm thickness at a wavelength of 210 nm. The polarizing film can be produced, for example, by a production method comprising: forming a polyvinyl alcohol-based resin layer on one side of a long-shaped thermoplastic resin substrate to form a laminate, the polyvinyl alcohol-based resin layer including Halide and polyvinyl alcohol-based resin; and, sequentially perform aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment on the laminate, and the drying shrinkage treatment is to transport and heat the laminate in the longitudinal direction Make it shrink by more than 2% in the width direction.

Description

Polarizing film, polarizing plate, and manufacturing method of polarizing film

FIELD OF THE INVENTION The present invention relates to polarizing films, polarizing plates, and methods for manufacturing polarizing films.

BACKGROUND OF THE INVENTION In a representative image display device, that is, a liquid crystal display device, due to its image forming method, polarizing films are arranged on both sides of the liquid crystal cell. As a manufacturing method of a polarizing film, for example, a method has been proposed in which a laminate having a resin substrate and a polyvinyl alcohol (PVA)-based resin layer is stretched, and then dyed to obtain a polarizing film on the resin substrate ( For example, Patent Document 1). By this method, a thinner polarizing film can be obtained, so it can contribute to the thinning of image display devices in recent years and has attracted attention. However, as mentioned above, the optical properties of the conventional thin polarizing film are not sufficient, so the optical properties of the thin polarizing film are sought to be further improved. Prior Art Documents Patent Documents

Patent Document 1: Japanese Patent Laid-Open No. 2001-343521

SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION The present invention is an invention made to solve the above-mentioned conventional problems, and its main purpose is to provide a thin polarizing film with excellent optical characteristics, a polarizing plate, and a manufacturing method of the polarizing film. Means to solve the problem

The polarizing film of the present invention is composed of a polyvinyl alcohol-based resin film containing iodine, and has a thickness of 8 μm or less, and the orthogonal absorbance at a wavelength of 210 nm per 1 μm of thickness is 1.00 or less. In one embodiment, the ratio of the orthogonal absorbance A ₄₇₀ at a wavelength of 470 nm to the orthogonal absorbance A _{600 at a wavelength of 600 nm (A 470} /A ₆₀₀ ) of the polarizing film is 0.7 or more. In one embodiment, the orthogonal b value of the polarizing film is greater than -10. In one embodiment, the thickness of the polarizing film is 4 μm or less. In one embodiment, the orthogonal absorbance per 1 μm thickness at a wavelength of 210 nm is 0.60 or less. In one embodiment, the iodine concentration of the polarizing film is 3.0% by weight or more. In one embodiment, the single transmittance of the polarizing film is 42.5% or more. According to another aspect of the present invention, a polarizing plate can be provided. The polarizing plate has the above-mentioned polarizing film and a protective layer arranged on at least one side of the polarizing film. According to another aspect of the present invention, a manufacturing method of the above-mentioned polarizing film can be provided. The method includes: forming a polyvinyl alcohol-based resin layer on one side of a long-shaped thermoplastic resin substrate to form a laminate, the polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin; and, the laminate The body is sequentially subjected to aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment. The drying shrinkage treatment is to transport the laminated body in the longitudinal direction and heat to shrink it by more than 2% in the width direction. In one embodiment, the above-mentioned halide is potassium iodide. In one embodiment, relative to 100 parts by weight of the polyvinyl alcohol-based resin, the content of the halide in the polyvinyl alcohol-based resin layer is 5 parts by weight to 20 parts by weight. In one embodiment, the above-mentioned drying and shrinking treatment is performed using a heated roller. In one embodiment, the temperature of the heating roller is 60°C to 120°C. Invention effect

According to the present invention, a combination of: addition of halide (representatively potassium iodide) to polyvinyl alcohol (PVA)-based resin, two-stage extension including air-assisted extension and underwater extension, and drying and shrinking by heating rollers , It can realize a thin polarizing film with a very small cross-absorbance per 1μm thickness at a wavelength of 210nm.

Modes for Carrying Out the Invention Hereinafter, embodiments of the present invention will be described, but the present invention is not limited by these embodiments.

A. Polarizing film The polarizing film of the embodiment of the present invention is composed of a polyvinyl alcohol resin film containing iodine, with a thickness of 8 μm or less, and the orthogonal absorbance (hereinafter referred to as unit absorbance) at a wavelength of 210 nm per 1 μm thickness is 1.00 the following. Compared with a general thin polarizing film, the polarizing film of the embodiment of the present invention has a very small unit absorbance at a wavelength of 210 nm. This means that the content ratio of iodide ions that do not form a complex with PVA (absorption in the ultraviolet region near 210 nm) in the polarizing film is very small. In a polarizing film, iodine can be roughly divided into: iodine ions that absorb in the ultraviolet region and PVA-iodine complexes that absorb in visible light. Among them, the PVA-iodine complex compound contributes to the polarization properties of the polarizing film. The amount of iodine that can be contained in the polarizing film is limited, so reducing the iodine ion is beneficial to increase the PVA-iodine complex. That is, in a thin polarizing film with a thickness of 8 μm or less, the optical characteristics can be improved by reducing iodide ions. This trend is particularly noticeable in polarizing films that have a very thin thickness and a high iodine concentration in the film. The unit absorbance at a wavelength of 210nm should preferably be below 0.80, more preferably below 0.60. The lower limit of the unit absorbance at a wavelength of 210 nm can be, for example, 0.20. _{The unit absorbance is obtained by calculating the cross absorbance A 210} by the following formula based on the cross transmittance Tc of the polarizing plate measured when obtaining the polarization degree described later, and then dividing by the thickness. In addition, the unit absorbance of the polarizing plate can substantially correspond to the unit absorbance of the polarizing film. Orthogonal absorbance=log10(100/Tc) One of the achievements of the present invention is the realization of a thin polarizing film with the aforementioned characteristics. The polarizing film can be used in an image display device, and is particularly suitable for use in a back-side polarizing plate of a liquid crystal display device. In addition, the polarizing film of the embodiment of the present invention has the unit absorbance as described above, and the ratio _{of the orthogonal absorbance A 550} at a wavelength of 550 nm to the orthogonal absorbance A _{210 at a wavelength of 210 nm (A 550} /A ₂₁₀ ) is preferably 1.4 or more, more preferably 1.8 or more, more preferably 2.0 or more, especially 2.2 or more. The upper limit of the ratio (A ₅₅₀ /A ₂₁₀ ) may be 3.5, for example. This means that the polarizing film of the present embodiment of the invention, the reduction ratio of iodide ions were contained in the vicinity of 600nm and having absorption of PVA-I ₅ ^- complexes containing ratio increases.

_{The ratio of the orthogonal absorbance A 470} at a wavelength of 470 nm to the orthogonal absorbance A ₆₀₀ at a wavelength of 600 nm (A ₄₇₀ /A ₆₀₀ ) of the polarizing film of the embodiment of the present invention is preferably 0.7 or more, more preferably 0.75 or more, more preferably It is 0.80 or more, especially 0.85 or more. The upper limit of the ratio (A ₄₇₀ /A ₆₀₀ ) is, for example, 2.00, and preferably 1.33. Ratio (A ₄₇₀ / A ₆₀₀₎ when within the range, can be maintained in the vicinity of 480nm with absorption of PVA-I ₃ ^- containing complexes of ratio, so that it does not substantially reduced. As a result, good polarization performance can be achieved over the entire range of visible light. When the amount of iodine in the thin polarizing film is limited, it is difficult to make the above-mentioned unit absorbance and ratio (A ₄₇₀ /A ₆₀₀ ) fall within the expected range with the conventional technology. The embodiment of the present invention is Can make these two fall within the expected range.

In addition, in the embodiment of the present invention, the orthogonal b value of the polarizing film is greater than -10 as described above, and is preferably greater than -7, more preferably greater than -5. The upper limit of the orthogonal b value is preferably +10 or less, more preferably +5 or less. According to the invention of this application, the orthogonal b value of the range can be realized. The orthogonal b value indicates the hue when the polarizing film (polarizing plate) is arranged in an orthogonal state. The larger the absolute value of this value, the orthogonal hue (black display in the image display device) will directly see the hue. For example, when the orthogonal b value is lower than -10, the black display will look bluish, and the display performance will decrease. That is, according to the embodiment of the present invention, it is possible to produce a polarizing film capable of realizing an excellent hue during black display. In addition, the orthogonal b value can be measured with a spectrophotometer represented by V-7100.

The thickness of the polarizing film is preferably 1μm~8μm, more preferably 1μm~7μm, more preferably 2μm~5μm, particularly preferably 2μm~4μm, most preferably 2μm~3μm.

The iodine concentration of the polarizing film is preferably 3% by weight or more, more preferably 4% by weight or more, and more preferably 6% by weight or more. The upper limit of the iodine concentration may be 12% by weight, for example. If the iodine concentration is within the above range, the effect obtained by reducing the above-mentioned unit absorbance is significant. In other words, the above-mentioned effect is quite remarkable in a thin polarizing film whose iodine concentration becomes higher as described above.

The polarizing film should exhibit absorption dichroism at any wavelength from 380nm to 780nm. The monomer transmittance of the polarizing film is preferably 49.0% or less, more preferably 48.0% or less. On the other hand, the monomer transmittance is preferably 41.5% or more, more preferably 42.0% or more, and more preferably 42.5% or more. The degree of polarization of the polarizing film should be above 99.990%, more preferably below 99.998%. According to the embodiment of the present invention, both high monomer transmittance and high polarization can be achieved as described above. The above-mentioned monomer transmittance represents the Y value measured by an ultraviolet-visible light spectrophotometer and compensated for visual sensitivity. In addition, the single transmittance is the value obtained when the refractive index of one surface of the polarizing plate is converted to 1.50, and the refractive index of the other surface is converted to 1.53. The above-mentioned degree of polarization is representatively based on the parallel transmittance Tp and the orthogonal transmittance Tc measured with an ultraviolet-visible light spectrophotometer and compensated for visual sensitivity, and is obtained by the following formula. Polarization (%)={(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

In one embodiment, the transmittance of a thin polarizing film with a thickness of 8μm or less is represented by a laminated body of a polarizing film (surface refractive index: 1.53) and a protective film (refractive index: 1.50) as the measurement object, and the ultraviolet-visible light is used for spectroscopy. Measured with a photometer. The reflectance at the interface of each layer varies depending on the surface refractive index of the polarizing film and/or the surface refractive index of the protective film in contact with the air interface. As a result, the measured value of the transmittance may also be different. Therefore, for example, when a protective film with a refractive index other than 1.50 is used, the measured value of transmittance can also be compensated according to the refractive index of the surface of the protective film in contact with the air interface. Specifically, the compensation value C of the transmittance is expressed by the polarized light reflectance R1 (transmission axis reflectance) parallel to the transmission axis of the interface between the protective film and the air layer, and is expressed by the following formula. C=R ₁ -R ₀ R ₀ =(( ^{1.50-1) 2} /(1.50+1) ² )×(T ₁ /100) R ₁ =((n ₁ -1) ² /(n1+1) ² )×(T ₁ /100) Here, R ₀ is the reflectance of the transmission axis when a protective film with a refractive index of 1.50 is used, n ₁ is the refractive index of the protective film used, and T ₁ is the transmittance of the polarizing film. For example, when using a substrate with a surface refractive index of 1.53 (cycloolefin-based film, film with hard coat, etc.) as a protective film, the compensation amount C is about 0.2%. At this time, by adding 0.2% to the measured transmittance, a polarizing film with a surface refractive index of 1.53 can be converted to the transmittance when a protective film with a refractive index of 1.50 is used. In addition, according to the calculation performed by the above formula, _{the change in the compensation value C when the transmittance T 1 of the} polarizing film is fine-tuned by 2% is less than 0.03%, and the transmittance of the polarizing film has a limited influence on the value of the compensation value C. . In addition, when the protective film has absorption other than surface reflection, it can be appropriately compensated according to the amount of absorption.

As the polarizing film, an arbitrary and appropriate polarizing film can be used. The polarizing film is typically made by using a laminate of two or more layers.

Specific examples of the polarizing film obtained by using the laminate include a polarizing film obtained by using a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate by coating. A polarizing film obtained by using a resin substrate and a laminate of a PVA-based resin layer formed on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and making it Drying and forming a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; and extending and dyeing the laminate to form the PVA-based resin layer into a polarizing film. In the present embodiment, the extension means includes immersing the laminate in a boric acid aqueous solution to perform extension. Furthermore, if necessary, stretching may further include stretching the laminate in the air at a high temperature (for example, 95° C. or higher) before stretching in a boric acid aqueous solution. The obtained resin substrate/polarizing film laminate can be used directly (that is, the resin substrate can be used as the protective layer of the polarizing film), or the resin substrate can be peeled from the resin substrate/polarizing film laminate, and The peeling surface is used by stacking an arbitrary and appropriate protective layer according to the purpose. The details of the manufacturing method of the polarizing film are described in, for example, Japanese Patent Laid-Open No. 2012-73580. In this specification, the entire description of the gazette is used as a reference.

The manufacturing method of the polarizing film of the present invention includes: forming a polyvinyl alcohol-based resin layer on one side of a long-shaped thermoplastic resin substrate to form a laminate, the polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin ; And, the above-mentioned layered body is sequentially subjected to aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying and shrinking treatment, and the drying and shrinking treatment is to transport the layered body in the longitudinal direction and use heating rollers to heat it. Thereby, even if the thickness is very thin, it is possible to provide a polarizing film with excellent optical properties with a monomer transmittance of 43.0% or more and a unit absorbance of 0.85 or more. That is, by introducing auxiliary extension, even when PVA is coated on a thermoplastic resin, the crystallinity of PVA can be improved and high optical properties can be achieved. In addition, by simultaneously improving the orientation of PVA in advance, it is possible to prevent problems such as degradation or dissolution of the orientation of PVA when immersed in water in the subsequent dyeing step and stretching step, and to achieve high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, compared to the case where the PVA-based resin layer does not contain a halide, it is possible to suppress the disorder of the orientation of the polyvinyl alcohol molecule and the decrease in the orientation. Thereby, the optical properties of the polarizing film obtained by the process of immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment, can be improved. Furthermore, by shrinking the laminated body in the width direction by the drying shrinkage treatment, the optical characteristics can be improved.

B. Polarizing plate Fig. 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 has a polarizing film 10, a first protective layer 20 arranged on one side of the polarizing film 10, and a second protective layer 30 arranged on the other side of the polarizing film 10. The polarizing film 10 is the polarizing film of the present invention described in item A above. One of the first protective layer 20 and the second protective layer 30 may also be omitted. And as described above, one of the first protective layer and the second protective layer may also be a resin substrate used for the production of the above-mentioned polarizing film.

The first and second protective layers are formed of arbitrary and appropriate thin films that can be used as protective layers of polarizing films. Specific examples of the material of the main component of the film include cellulose resins such as cellulose triacetate (TAC) or polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, etc. , Polyether series, polysulfide series, polystyrene series, polynorbornene series, polyolefin series, (meth)acrylic series, acetate series and other transparent resins. In addition, thermosetting resins such as (meth)acrylic type, urethane type, (meth)acrylate urethane type, epoxy type, and polysiloxane type, or ultraviolet curing type resin, etc. may also be cited. Other examples include glassy polymers such as silicone polymers. In addition, the polymer film described in Japanese Patent Laid-Open No. 2001-343529 (WO01/37007) can also be used. As the material of the film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted amide 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, and For example, a resin composition having an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be cited. The polymer film may be, for example, an extruded product of the above-mentioned resin composition.

When the polarizing plate 100 is applied to an image display device, the thickness of the protective layer (outer protective layer) arranged on the side opposite to the display panel is typically 300μm or less, preferably 100μm or less, more preferably 5μm~80μm, more preferably It is 10μm~60μm. In addition, when the surface treatment is performed, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.

When the polarizing plate 100 is applied to an image display device, the thickness of the protective layer (inner protective layer) disposed on the display panel side is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and more preferably 10 μm to 60 μm. In one embodiment, the inner protective layer is a retardation layer having an arbitrary and appropriate retardation value. At this time, the in-plane retardation Re (550) of the retardation layer is 110 nm to 150 nm, for example. "Re(550)" is the in-plane phase difference measured with light with a wavelength of 550nm at 23°C, and can be obtained by the formula: Re=(nx-ny)×d. Here, "nx" is the refractive index in the direction of the maximum refractive index in the plane (that is, the slow axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis (that is, the fast axis direction) in the plane, and "nz" Is the refractive index in the thickness direction, and "d" is the thickness (nm) of the layer (thin film).

C. Manufacturing method of polarizing film The manufacturing method of the polarizing film of one embodiment of the present invention includes: forming a polyvinyl alcohol resin layer (PVA resin layer) on one side of a long-shaped thermoplastic resin substrate to form a laminate , The polyvinyl alcohol-based resin layer includes a halide and a polyvinyl alcohol-based resin (PVA-based resin); and, sequentially performing aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment on the above-mentioned laminate. The drying shrinkage treatment is to transport and heat the laminate in the longitudinal direction to shrink it by 2% or more in the width direction. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. The drying and shrinking treatment should be done with a heating roller, and the temperature of the heating roller should be 60℃~120℃. The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment should be more than 2%. According to the manufacturing method, the polarizing film described in the above item A can be obtained. In particular, by producing a laminate containing a PVA-based resin layer containing a halide, and setting the extension of the laminate to a multi-stage extension including air-assisted extension and underwater extension, and then heating the extended laminate with a heating roller, A polarizing film with excellent optical properties (representatively, monomer transmittance and unit absorbance) can be obtained.

C-1. Production of laminated body Any and appropriate method can be adopted as a method of producing a laminated body of a thermoplastic resin base material and a PVA-based resin layer. It is desirable to form a PVA-based resin layer on the thermoplastic resin substrate by applying a coating solution containing a halide and a PVA-based resin and then drying it on the surface of the thermoplastic resin laminate. As mentioned above, the content of the halide in the PVA resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin.

Any suitable method can be adopted for the coating method of the coating liquid. Examples include: roller coating method, spin coating method, wire bar coating method, dip coating method, die coating method, curtain coating method, spraying method, knife coating method (cut corner wheel coating method, etc.), etc. . The coating and drying temperature of the above-mentioned coating liquid is preferably 50°C or higher.

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

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

C-1-1. Thermoplastic resin substrate The thickness of the thermoplastic resin substrate is preferably 20μm~300μm, more preferably 50μm~200μm. If it is less than 20 μm, it may be difficult to form a PVA-based resin layer. If it exceeds 300 μm, it may take a long time for the thermoplastic resin substrate to absorb water during the underwater stretching treatment described later, which may cause an excessive load on the stretching.

The water absorption rate of the thermoplastic resin substrate is preferably 0.2% or more, more preferably 0.3% or more. The thermoplastic resin substrate will absorb water, and the water can play the role of a plasticizer for plasticization. As a result, the elongation stress can be greatly reduced, and the elongation can be performed at a high magnification. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using the thermoplastic resin base material, it is possible to prevent the dimensional stability of the thermoplastic resin base material from being significantly reduced during manufacture, resulting in the deterioration of the appearance of the obtained polarizing film and other defects. In addition, it is possible to prevent breakage of the base material or peeling of the PVA-based resin layer from the thermoplastic resin base material during stretching in water. In addition, the water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material. Water absorption is the value obtained according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or less. By using the thermoplastic resin substrate, the crystallization of the PVA-based resin layer can be suppressed, and at the same time, the extensibility of the laminate can be sufficiently ensured. In addition, if considering the plasticization of the thermoplastic resin substrate with water and the smooth extension in water, the temperature is preferably below 100°C, and more preferably below 90°C. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60°C or higher. By using the thermoplastic resin substrate, it is possible to prevent defects such as deformation (for example, unevenness, sagging, wrinkles, etc.) of the thermoplastic resin substrate when coating and drying the coating solution containing the above-mentioned PVA-based resin, and The laminated body is produced well. In addition, the extension of the PVA-based resin layer can be performed well at an appropriate temperature (for example, about 60°C). In addition, the glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by heating the crystallization material into which the constituent material is introduced into the reforming base. The glass transition temperature (Tg) is a value obtained in accordance with JIS K 7121.

As the constituent material of the thermoplastic resin base material, any and appropriate thermoplastic resin can be used. Examples of thermoplastic resins include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, and polycarbonate resins. And these copolymer resins, etc. Among these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferred.

In one embodiment, it is preferable to use an amorphous (non-crystallized) polyethylene terephthalate resin. Among them, it is particularly suitable to use an amorphous (not easy to crystallize) polyethylene terephthalate resin. Specific examples of amorphous polyethylene terephthalate resins include: copolymers that further contain isophthalic acid and/or cyclohexane dicarboxylic acid as dicarboxylic acids, or further contain cyclohexane dimethanol or Diethylene glycol is used as a copolymer of glycol.

In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate resin having isophthalic acid units. The reason is that the extensibility of the thermoplastic resin substrate is extremely excellent, and crystallization during stretching can be suppressed. We believe that this is caused by the introduction of isophthalic acid units, which brings great flexure to the main chain. The polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of isophthalic acid unit is preferably 0.1 mol% or more, and more preferably 1.0 mol% or more with respect to the total of all repeating units. This is because a thermoplastic resin substrate with extremely excellent extensibility can be obtained. On the other hand, relative to the total of all repeating units, the content of isophthalic acid units is preferably 20 mol% or less, and more preferably 10 mol% or less. By setting the content ratio as described above, the degree of crystallinity can be increased well in the drying shrinkage treatment described later.

The thermoplastic resin substrate may be stretched in advance (before the formation of the PVA-based resin layer). In one embodiment, it extends in the lateral direction of the elongated thermoplastic resin substrate. The lateral direction is preferably a direction orthogonal to the extending direction of the laminate described later. In addition, the term "orthogonal" in this specification includes the case of being substantially orthogonal. Here, the so-called "substantially orthogonal" includes the case of 90°±5.0°, and it is preferably 90°±3.0°, and more preferably 90°±1.0°.

Relative to the glass transition temperature (Tg), the extension temperature of the thermoplastic resin substrate is preferably Tg-10°C~Tg+50°C. The stretch ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times.

An arbitrary and appropriate extension method can be adopted for the extension method of the thermoplastic resin substrate. Specifically, it can be a fixed end extension or a free end extension. The extension method can be dry or wet. The extension of the thermoplastic resin substrate can be carried out in one stage or in multiple stages. When it is carried out in multiple stages, the above-mentioned stretch magnification is the product of the stretch magnifications of each stage.

C-1-2. Coating liquid The coating liquid contains halide and PVA-based resin as described above. The above-mentioned coating liquid represents a solution in which the above-mentioned halide and the above-mentioned PVA-based resin are dissolved in a solvent. Solvents can include: water, dimethyl sulfide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, trimethylolpropane and other polyols, ethylene two Amines, diethylenetriamine and other amines. These can be used alone or in combination of two or more kinds. Among these, water is better. Relative to 100 parts by weight of the solvent, the concentration of the PVA-based resin in the solution is preferably 3 parts by weight to 20 parts by weight. As long as the resin concentration is the above, a uniform coating film that adheres to the thermoplastic resin substrate can be formed. The content of the halide in the coating liquid is 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

Additives can be blended into the coating solution. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyhydric alcohols such as ethylene glycol and glycerol. The surfactant can be, for example, a nonionic surfactant. These can be used for the purpose of further improving the uniformity, dyeability, and extensibility of the obtained PVA-based resin layer.

Any suitable resin can be used for the above-mentioned PVA-based resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of PVA resin is usually 85 mol%~100 mol%, preferably 95.0 mol%~99.95 mol%, and more preferably 99.0 mol%~99.93 mol%. The degree of saponification can be obtained according to JIS K 6726-1994. By using PVA-based resins with such a degree of saponification, a polarizing film with excellent durability can be obtained. When the saponification degree is too high, there is a risk of gelation.

The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000~10000, preferably 1200~4500, more preferably 1500~4300. In addition, the average degree of polymerization can be obtained in accordance with JIS K 6726-1994.

As the above-mentioned halide, any and appropriate halide can be used. Examples include iodide and sodium chloride. Examples of iodides include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is suitable.

The amount of halide in the coating solution is preferably 5 parts by weight to 20 parts by weight relative to 100 parts by weight of the PVA-based resin, and preferably 10 parts by weight to 15 parts by weight relative to 100 parts by weight of the PVA-based resin. If the amount of the halide relative to 100 parts by weight of the PVA-based resin exceeds 20 parts by weight, the halide will bleed out, resulting in the resulting polarized film becoming cloudy.

Generally speaking, by extending the PVA-based resin layer, the orientation of the polyvinyl alcohol molecules in the PVA-based resin will become higher. However, if the stretched PVA-based resin layer is immersed in a water-containing liquid, the polyvinyl alcohol molecules Orientation will be disordered, and the orientation may be reduced. In particular, when the laminate of thermoplastic resin and PVA-based resin layers is stretched in boric acid water, in order to stabilize the elongation of the thermoplastic resin and stretch the laminate in boric acid water at a relatively high temperature, the degree of orientation tends to decrease significantly. Significant. For example, compared to the general extension of PVA film monomer in boric acid water at 60°C, the extension of the laminate of A-PET (thermoplastic resin substrate) and PVA-based resin layer is at a higher temperature around 70°C. In this case, the orientation of the PVA at the beginning of the extension may be reduced at the stage before the rise by the extension in the water. On the other hand, before making a laminate of a halide-containing PVA-based resin layer and a thermoplastic resin substrate and stretching the laminate in boric acid water, high-temperature elongation in the air (assisted elongation) can promote the laminate after the assisted elongation The PVA resin in the PVA resin layer of the body crystallizes. As a result, when the PVA-based resin layer is immersed in a liquid, compared to the case where the PVA-based resin layer does not contain a halide, it is possible to suppress the disorder of the orientation of the polyvinyl alcohol molecule and the decrease in the orientation. Thereby, the optical properties of the polarizing film obtained by the process of immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment, can be improved.

C-2. Aerial auxiliary extension treatment In particular, in order to obtain high optical characteristics, a combination of dry extension (auxiliary extension) and two-stage extension method of boric acid water extension will be selected. For example, two-stage extension, by introducing auxiliary extension, the crystallization of the thermoplastic resin substrate can be suppressed and the extension can be carried out at the same time, which can solve the decrease in elongation caused by the excessive crystallization of the thermoplastic resin substrate in the subsequent boric acid water extension. Therefore, the laminate can be stretched at a higher magnification. Moreover, when coating PVA-based resin on a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, it is necessary to Lowering the coating temperature may result in a problem that the crystallization of the PVA-based resin is relatively low, and sufficient optical properties cannot be obtained. In contrast, by introducing auxiliary extension, when the PVA-based resin is coated on the thermoplastic resin, the crystallinity of the PVA-based resin can still be improved, and high optical properties can be achieved. In addition, by simultaneously improving the orientation of the PVA-based resin in advance, it is possible to prevent problems such as a decrease in the orientation and dissolution of the PVA-based resin when immersed in water in the subsequent dyeing step and the elongation step, and high optical properties can be achieved.

The extension method of aerial auxiliary extension can be fixed-end extension (for example, using a tenter stretcher for extension) or free-end extension (for example, uniaxial extension through a laminate between rolls with different peripheral speeds) Method), but in order to obtain a high degree of optical characteristics, the free end extension can be actively used. In one embodiment, the in-flight stretching process includes a heating roller stretching step in which the laminate is conveyed along the longitudinal direction thereof while being stretched by the peripheral speed difference between the heating rollers. The aerial stretching process typically includes a region stretching step and a heating roller stretching step. In addition, the sequence of the area extension step and the heating roller extension step is not limited, and the area extension step may be performed first, or the heating roller extension step may be performed first. The area extension step can also be omitted. In one embodiment, the area extension step and the heating roller extension step may be performed sequentially. Furthermore, in other embodiments, the tenter stretcher grips the end of the film and extends the distance between the tenters in the flow direction (the expansion of the distance between the tenters is the stretch magnification). At this time, the distance of the tenter in the width direction (vertical to the flow direction) is set to be arbitrarily close. Ideally, it can be set to the extension ratio relative to the flow direction to use the free end extension for closeness. In the case of free end extension, it is calculated as the shrinkage rate in the width direction=(1/stretching ratio) ^1/2.

Aerial auxiliary extension can be carried out in one stage or in multiple stages. When it is carried out in multiple stages, the stretching ratio is the product of the stretching ratios of each stage. The extension direction of the aerial auxiliary extension is preferably slightly the same as the extension direction of the underwater extension.

The extension ratio in aerial auxiliary extension should be 2.0 to 3.5 times. The maximum extension ratio when combined aerial auxiliary extension and underwater extension is preferably 5.0 times or more, more preferably 5.5 times or more, and more preferably 6.0 times or more relative to the original length of the layered body. In this specification, the "maximum extension ratio" means the extension ratio before the laminate is about to be broken, and it is a value that is 0.2 lower than the value after confirming that the extension ratio at which the laminate is broken.

The stretching temperature of the air-assisted stretching can be set to an arbitrary and appropriate value according to the forming material and stretching method of the thermoplastic resin substrate. The elongation temperature is preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate +10°C, and particularly preferably above Tg+15°C. On the other hand, the upper limit of the extension temperature is preferably 170°C. Stretching at the temperature can suppress the rapid progress of the crystallization of the PVA-based resin, and further suppress the defects caused by the crystallization (for example, hindering the orientation of the PVA-based resin layer due to the stretching).

C-3. Insolubilization treatment If necessary, perform insolubilization treatment after the aerial auxiliary extension treatment and before the underwater extension treatment or dyeing treatment. The above-mentioned insolubilization treatment can typically be performed by immersing the PVA-based resin layer in a boric acid aqueous solution. The insolubilization treatment can impart water resistance to the PVA-based resin layer and prevent the orientation of the PVA from being reduced when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 4 parts by weight relative to 100 parts by weight of water. The temperature of the insoluble bath (aqueous solution of boric acid) should be 20℃~50℃.

C-4. Dyeing treatment The above-mentioned dyeing treatment is typically performed by dyeing the PVA-based resin layer with iodine. Specifically, it is performed by adsorbing iodine to the PVA-based resin layer. The adsorption method may include, for example, a method of immersing the PVA-based resin layer (layered body) in a dyeing solution containing iodine, a method of applying the dyeing solution on the PVA-based resin layer, and spraying the PVA-based resin layer. Methods of dyeing liquid, etc. Ideally, the layered body is immersed in a dyeing solution (dyeing bath). Because it can adsorb iodine well.

The above-mentioned dyeing solution is preferably an aqueous solution of iodine. The blending amount of iodine is preferably 0.05 to 0.5 parts by weight relative to 100 parts by weight of water. In order to improve the solubility of iodine in water, it is advisable to mix iodide in the iodine aqueous solution. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is suitable. Relative to 100 parts by weight of water, the blending amount of 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. In order to prevent the PVA resin from dissolving, the temperature of the dyeing solution during dyeing should be 20°C to 50°C. When the PVA-based resin layer is immersed in the dyeing solution, in order to ensure the transmittance of the PVA-based resin layer, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds.

The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the monomer transmittance of the finally obtained polarizing film becomes 43.0% or more, and the polarization degree becomes 99.980% or more. The dyeing conditions should preferably use an aqueous iodine solution as the dyeing solution, and set the ratio of the content of iodine and potassium iodide in the iodine aqueous solution to 1:5 to 1:20. The ratio of the content of iodine and potassium iodide in the iodine aqueous solution should be 1:5~1:10. Thereby, a polarizing film having the above-mentioned optical characteristics can be obtained.

When the layered body is immersed in a treatment bath containing boric acid (insolubilization treatment above) followed by dyeing treatment, the boric acid contained in the treatment bath mixed into the dyeing bath will cause the concentration of boric acid in the dyeing bath to evolve over time If the change occurs, the dyeability may become unstable as a result. In order to suppress the destabilization of the dyeability as described above, the upper limit of the concentration of boric acid in the dyeing bath is preferably adjusted to 4 parts by weight, more preferably 2 parts by weight relative to 100 parts by weight of water. On the other hand, relative to 100 parts by weight of water, the lower limit of the concentration of boric acid in the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and more preferably 0.5 parts by weight. In one embodiment, the dyeing process is performed using a dyeing bath preliminarily blended with boric acid. Thereby, it is possible to reduce the rate of change in the concentration of boric acid when the boric acid of the above-mentioned treatment bath is mixed into the dyeing bath. Relative to 100 parts by weight of water, the blending amount of boric acid pre-blended in the dyeing bath (that is, the content of boric acid not derived from the above-mentioned treatment bath) is preferably 0.1 parts by weight to 2 parts by weight, more preferably 0.5 parts by weight~ 1.5 parts by weight.

C-5. Cross-linking treatment If necessary, a cross-linking treatment is performed after the dyeing treatment and before the water extension treatment. The above-mentioned cross-linking treatment can typically be performed by immersing the PVA-based resin layer in a boric acid aqueous solution. The cross-linking treatment can impart water resistance to the PVA-based resin layer and prevent the orientation of PVA from being reduced when the PVA is immersed in high-temperature water during the subsequent extension in water. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 5 parts by weight relative to 100 parts by weight of water. In addition, when the cross-linking treatment is performed after the above-mentioned dyeing treatment, it is preferable to further blend an iodide. By blending iodide, it is possible to suppress the elution of iodine that has been adsorbed on the PVA-based resin layer. The blending amount of iodide is preferably 1 part by weight to 5 parts by weight relative to 100 parts by weight of water. The specific examples of the iodide are the same as described above. The temperature of the cross-linking bath (aqueous solution of boric acid) should be 20℃~50℃.

C-6. Underwater stretching treatment The underwater stretching treatment is performed by immersing the laminate in a stretching bath. The stretching treatment in water can stretch at a temperature lower than the glass transition temperature of the above-mentioned thermoplastic resin substrate or PVA resin layer (typically around 80°C), which can inhibit the crystallization of the PVA resin layer while simultaneously reducing The high magnification extension. As a result, a polarizing film having excellent optical characteristics can be manufactured.

Any and appropriate method can be adopted for the extension method of the laminate. Specifically, it may be a fixed-end extension or a free-end extension (for example, a method of uniaxially extending the laminate through rollers with different peripheral speeds). It is more ideal to choose free end extension. The extension of the laminated body can be carried out in one stage or in multiple stages. When it is performed in multiple stages, the stretching magnification (maximum stretching magnification) of the laminate described later is the product of the stretching magnifications of each stage.

The stretching in water is preferably carried out by immersing the layered body in an aqueous boric acid solution (extending in boric acid in water). By using an aqueous solution of boric acid as a stretching bath, the PVA-based resin layer can be imparted with rigidity that can withstand the tension during stretching and water resistance that is insoluble in water. Specifically, boric acid can generate tetrahydroxyborate anions in an aqueous solution, which can be cross-linked with PVA-based resins through hydrogen bonds. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, and it can be stretched well, and a polarizing film having excellent optical properties can be produced.

The above-mentioned boric acid aqueous solution is preferably obtained by dissolving boric acid and/or borate in water of a solvent. Relative to 100 parts by weight of water, the concentration of boric acid 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. Setting the boric acid concentration to 1 part by weight or more can effectively inhibit the dissolution of the PVA-based resin layer, and furthermore, a polarizing film with higher characteristics can be produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, etc. in a solvent can also be used.

It is suitable to blend iodide in the above-mentioned extension bath (aqueous boric acid solution). By blending iodide, it is possible to suppress the elution of iodine that has been adsorbed on the PVA-based resin layer. The specific examples of the iodide are the same as described above. Relative to 100 parts by weight of water, the concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight, more preferably 0.5 parts by weight to 8 parts by weight.

The extension temperature (bath temperature of the extension bath) is preferably 40℃~85℃, more preferably 60℃~75℃. As long as the temperature is above, the dissolution of the PVA-based resin layer can be suppressed, and at the same time, high-rate elongation can be achieved. 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. At this time, if the stretching temperature is lower than 40°C, even if it is considered to plasticize the thermoplastic resin base material with water, it may not be able to stretch well. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and it may not be possible to obtain excellent optical properties. The immersion time of the laminate in the extension bath is preferably 15 seconds to 5 minutes.

The extension ratio for underwater extension is preferably 1.5 times or more, more preferably 3.0 times or more. Relative to the original length of the laminate, the total extension ratio of the laminate is preferably 5.0 times or more, and more preferably 5.5 times or more. By achieving the above-mentioned high stretching magnification, a polarizing film with extremely excellent optical properties can be manufactured. This kind of high extension ratio can be achieved by using the underwater extension method (boric acid extension in water).

C-7. Drying and shrinking treatment The above-mentioned drying and shrinking treatment can be carried out by zone heating, that is, heating the entire zone, or zone heating, that is, heating the entire zone by heating the conveying roller (using a so-called heating roller). (Heating roller drying method). It is more desirable to use both. By using a heating roller to dry it, heating and bending of the laminate can be effectively suppressed, and a polarizing film with excellent appearance can be produced. Specifically, drying the laminated body in the state where it is placed next to the heating roller can effectively promote the crystallization of the thermoplastic resin substrate and increase the degree of crystallinity. Even at a relatively low drying temperature, it is still good Increase the crystallinity of the thermoplastic substrate. As a result, the rigidity of the thermoplastic resin substrate can be increased, the PVA-based resin layer can withstand the shrinkage due to drying, and bending can be suppressed. In addition, since the heating roller is used, the layered body can be maintained in a flat state and dried. Therefore, it is possible not only to suppress bending, but also to suppress the generation of wrinkles. At this time, the layered body shrinks in the width direction by the drying shrinkage treatment, so that the optical characteristics can be improved. This is because it can effectively improve the orientation of PVA and PVA/iodine complexes. The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment should be 1%~10%, more preferably 2%~8%, especially 4%~6%.

Fig. 2 is a schematic diagram showing an example of drying shrinkage treatment. In the drying shrinkage process, the layered body 200 is transported and dried by the transport rollers R1 to R6 and the guide rollers G1 to G4 heated to a predetermined temperature. In the example shown in the figure, the conveyor rollers R1 to R6 are arranged so that the surface of the PVA resin layer and the surface of the thermoplastic resin laminate can be alternately and continuously heated. However, for example, only one surface of the laminate 200 (for example, thermoplastic resin The conveyor rollers R1 to R6 are arranged in the manner of the substrate surface).

The drying conditions can be controlled by adjusting the heating temperature of the conveying roller (temperature of the heating roller), the number of heating rollers and the contact time of the heating roller, etc. The temperature of the heating roller is preferably 60℃~120℃, more preferably 65℃~100℃, especially 70℃~80℃. A good increase in the degree of crystallinity of the thermoplastic resin can well suppress bending and can produce an optical laminate with extremely excellent durability. In addition, the temperature of the heating roller can be measured with a contact thermometer. Although 6 conveying rollers are provided in the example shown in the figure, there is no particular limitation as long as there are a plurality of conveying rollers. The number of conveyor rollers is usually 2~40, and 4~30 should be set. The contact time (total contact time) between the laminate and the heating roller is preferably 1 second to 300 seconds, preferably 1 to 20 seconds, and more preferably 1 to 10 seconds.

The heating roller can be installed in a heating furnace (such as an oven), or can be installed in a general manufacturing line (at room temperature). It is ideal to be installed in a heating furnace equipped with an air blowing mechanism. By combining the drying by the heating roller and the hot air drying, the rapid temperature change between the heating rollers can be suppressed, so that the shrinkage in the width direction can be easily suppressed. The temperature of hot air drying should be 30℃~100℃. In addition, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air should be about 10m/s~30m/s. In addition, the wind speed is the wind speed in the heating furnace, which can be measured with a small impeller type digital anemometer.

C-8. Other treatments It is desirable to perform a washing treatment after the water extension treatment and before the drying shrinkage treatment. The above-mentioned washing treatment can typically be performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution. Example

Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited by these examples. The measuring methods of each characteristic are as follows. In addition, unless otherwise specified, the "parts" and "%" in the examples and comparative examples are based on weight. (1) The thickness was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"). (2) Monomer transmittance, unit absorbance, and orthogonal absorbance were measured for the polarizing plates (protective film/polarizing film) of the examples and comparative examples using an ultraviolet-visible spectrophotometer (V-7100, manufactured by JASCO Corporation), and The obtained monomer transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc are set as Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp, and Tc are Y values measured in accordance with JIS Z8701's 2 degree field of view (C light source) and compensated for visual sensitivity. In addition, the refractive index of the protective film is 1.50, and the refractive index of the surface of the polarizing film on the opposite side of the protective film is 1.53. Using UV-3150 manufactured by Shimadzu Corporation, from the orthogonal transmittance Tc ₂₁₀ measured at a measurement wavelength of 210 nm, the orthogonal absorbance A _{210 was} obtained by the following formula, and then divided by the thickness as the unit absorbance. Also, using V-7100 manufactured by JASCO Corporation, the orthogonal absorbance A _{470 was obtained from the orthogonal transmittance Tc 470 at} the measurement wavelength of 470 nm, and the orthogonal absorbance A _{600 was obtained from the orthogonal transmittance Tc 600 at} the measurement wavelength of 600 nm. Orthogonal absorbance=log10(100/Tc) In addition, for A ₄₇₀ and A ₆₀₀ , the same measurement can be performed on LPF-200 manufactured by Otsuka Electronics Co., Ltd., etc. (3) Iodine concentration For the polarizing films obtained in the examples and comparative examples, the fluorescent X-ray intensity ( kcps). From the obtained fluorescent X-ray intensity and thickness, the iodine concentration (% by weight) was calculated by the following formula. (Iodine concentration)=20.5×(Fluorescence X-ray intensity)/(Film thickness) In addition, the coefficient when calculating the concentration varies depending on the measuring device, but the coefficient can be obtained with an appropriate calibration curve. In this embodiment, a plurality of samples in which KI (I:K=1:1 (molar ratio)) is added to the PVA at an arbitrary value are prepared, and these are measured to obtain a calibration curve. (4) Cross-b value The polarizing plates of the Examples and Comparative Examples were measured using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"), and the hue in a state of cross-polarized light was determined. A polarizer with a lower orthogonal b value (negative value and large absolute value) indicates that the hue is not neutral but blue.

[Example 1-1] 1. A polarizing film was made as a thermoplastic resin substrate, using a long strip of amorphous isophthalic acid copolymerized polyethylene terephthalate with a water absorption rate of 0.75% and a Tg of about 75°C Thin film (thickness: 100 μm). And perform corona treatment on one side of the resin substrate (treatment conditions: 55Wmin/m ² ). PVA-based resin mixed with polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetyl acetyl modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") at a ratio of 9:1 To 100 parts by weight, 13 parts by weight of potassium iodide was added to prepare a PVA aqueous solution (coating liquid). The above-mentioned 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 to produce a laminate. The obtained laminate was subjected to uniaxial extension of the free end 2.4 times in the longitudinal direction (long side direction) between rollers with different peripheral speeds in an oven at 130° C. (in-air auxiliary extension treatment). Next, the layered body was immersed in an insoluble bath (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water with a liquid temperature of 40°C) for 30 seconds (insolubilization treatment). Then, in a dyeing bath with a liquid temperature of 30°C (aqueous iodine solution obtained by blending iodine and potassium iodide in a weight ratio of 1:7 relative to 100 parts by weight of water), the concentration is adjusted so that the final polarizing film is single The volume transmittance (Ts) became the value shown in Table 1, and was immersed for 60 seconds (dyeing treatment). Then, it was immersed in a cross-linking bath (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid to 100 parts by weight of water in a cross-linking bath at a liquid temperature of 40°C) for 30 seconds (cross-linking treatment). Then, while immersing the layered body in a boric acid aqueous solution (boric acid concentration 4.0% by weight) at a liquid temperature of 70°C, uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to increase the total stretch magnification Up to 5.5 times (extension treatment in water). Then, the layered body was immersed in a washing bath (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water in a washing bath having a liquid temperature of 20°C) (washing treatment). After that, it was dried in an oven kept at 90°C while keeping the contact surface temperature at 75°C with a SUS-made heating roller for about 2 seconds (drying shrinkage treatment). The laminate has a shrinkage rate of 2% in the width direction due to the drying shrinkage treatment. A polarizing film with a thickness of 3.4 μm was formed on the resin substrate according to the above procedure.

2. Preparation of polarizing plate On the surface of each polarizing film obtained above (the surface opposite to the resin substrate), an acrylic film (surface refractive index: 1.50, 40 μm) was bonded as a protective film through an ultraviolet curable adhesive. Specifically, after coating the curable adhesive with a total thickness of 1.0 μm, it is laminated using a roll press. Then, UV light is irradiated from the protective film side to harden the adhesive. Next, the resin substrate is peeled off to obtain a polarizing plate having a protective film/polarizing film configuration.

For the obtained polarizing film and polarizing plate, the monomer transmittance, the unit absorbance at a wavelength of 210 nm (hereinafter referred to as unit absorbance 210), A ₄₇₀ /A _600, and the orthogonal b value are listed in Table 1. In addition, the iodine concentration of the obtained polarizing film (monomer transmittance: about 43.5%) was 7.5% by weight.

[Example 1-2] A polarizing film and a polarizing plate were produced in the same manner as in Example 1-1 except that the concentration of the dyeing bath was adjusted so that the monomer transmittance (Ts) of the polarizing film became the value shown in Table 1. . For the obtained polarizing film and polarizing plate, the monomer transmittance and unit absorbance 210 are listed in Table 1. The relationship between monomer transmittance and unit absorbance 210 is compared with the results of Examples 2 to 3 and Comparative Example 1, and is shown in FIG. 3.

[Examples 2-1 to 2-4] In addition to changing the thickness of the polarizing film obtained by changing the PVA aqueous solution (coating solution) to 4.6 μm, and adjusting the concentration of the dye bath so that the monomer transmittance of the polarizing film (Ts Except for the values shown in Table 1, a polarizing film and a polarizing plate were produced in the same manner as in Example 1-1. The monomer transmittance and unit absorbance 210 are listed in Table 1 for the obtained polarizing film and polarizing plate. For Example 2-3 (single transmittance of 43.5%), A ₄₇₀ /A ₆₀₀ and the orthogonal b value are also listed in Table 1. The relationship between monomer transmittance and unit absorbance 210 is shown in FIG. 3. In addition, the iodine concentration of the polarizing film (Example 2-3) having a monomer transmittance of around 43.5% in the obtained polarizing film was 6.0% by weight.

[Examples 3-1 to 3-5] Except that the thickness of the polarizing film obtained by changing the PVA aqueous solution (coating solution) was set to 5.0 μm, and the concentration of the dyeing bath was adjusted to make the monomer transmittance (Ts) of the polarizing film A polarizing film and a polarizing plate were produced in the same manner as in Example 1-1 except that the conditions of the drying shrinkage treatment were changed to the values shown in Table 1 and the shrinkage in the width direction was set to 5%. The monomer transmittance and unit absorbance 210 are listed in Table 1 for the obtained polarizing film and polarizing plate. The relationship between monomer transmittance and unit absorbance 210 is shown in FIG. 3. In addition, the iodine concentration of the polarizing film (Example 3-3) having a monomer transmittance of around 43.5% in the obtained polarizing film was 6.0% by weight.

[Comparative Examples 1-1 to 1-3] Except that potassium iodide was not added to the PVA aqueous solution (coating liquid), the thickness of the polarizing film obtained by changing the PVA aqueous solution (coating liquid) was set to 3.3 μm, and it was subjected to drying shrinkage treatment No heating roller is used and the shrinkage in the width direction is set to 0.1% or less, and the concentration of the dyeing bath is adjusted so that the monomer transmittance (Ts) of the polarizing film becomes outside of the value shown in Table 1, according to Example 1. -1 Make the polarizing film and polarizing plate in the same way. For the obtained polarizing film and polarizing plate, the monomer transmittance and unit absorbance 210 are listed in Table 1. For Comparative Example 1-1 (single transmittance of 43.4%), A ₄₇₀ /A ₆₀₀ and the orthogonal b value are also listed in Table 1. The relationship between monomer transmittance and unit absorbance 210 is shown in FIG. 3. In addition, the iodine concentration of the polarizing film (Comparative Example 1-2) having a monomer transmittance of around 43.5% in the obtained polarizing film was 10.0% by weight.

[Comparative Examples 1-4 to 1-5] A polarizing film and a polarizing plate were produced in the same manner as in Comparative Example 1-1 except that the KI concentration of the washing bath was changed as shown in Table 1. For the obtained polarizing film and polarizing plate, the monomer transmittance, A ₄₇₀ /A ₆₀₀ and the orthogonal b value are listed in Table 1. In addition, regarding the polarizing plates obtained in these comparative examples, the measurement of the unit absorbance 210 was not performed because the display characteristics were significantly reduced.

[Comparative Example 2-1] Except that the thickness of the polarizing film obtained by changing the PVA aqueous solution (coating liquid) was set to 5.0 μm, the heating roller was not used in the drying shrinkage treatment, and the shrinkage rate in the width direction was set to 0.1% or less , And adjusting the concentration of the dye bath so that the monomer transmittance (Ts) of the polarizing film becomes the value shown in Table 1, a polarizing film and a polarizing plate were produced in the same manner as in Example 1-1. For the obtained polarizing film and polarizing plate, the monomer transmittance and unit absorbance 210 are listed in Table 1. In addition, the monomer transmittance of the polarizing film obtained was around 43.5%, and the iodine concentration was 5.0% by weight.

[Comparative Example 3-1] A PVA-based resin film (manufactured by Kuraray, trade name "PS-7500", thickness: 75 μm, average degree of polymerization: 2,400, degree of saponification: 99.9 mol%) was immersed in a 30°C water bath 1 After stretching 1.2 times in the conveying direction for minutes, it is 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, and the film is stretched twice based on the unstretched film (original length). Then, the stretched film was immersed in a 30°C aqueous solution with a boric acid concentration of 4% by weight and a potassium iodide concentration of 5% by weight, and was further stretched to three times the original length based on the original length, and then immersed in a boric acid concentration of 4% by weight and potassium iodide concentration of 5%. It is further extended to 6 times the original length and immersed in a washing bath (potassium iodide 4% by weight aqueous solution) at 30°C, and dried at 70°C for 2 minutes to obtain a thickness of 27μm. Polarized parts. The monomer transmittance of the obtained polarizer is 43.0%. Although I wanted to measure the orthogonal absorbance at a wavelength of 210 nm, the unit absorbance of 210 could not be obtained because it was too large to exceed the measurement limit. The results are shown in Table 1. In addition, the monomer transmittance of the polarizer obtained was around 43.5%, and the iodine concentration was 2.2% by weight.

[Table 1]

As clearly shown in Table 1 and Figure 3, compared with the polarizing film of the comparative example, the unit absorbance 210 of the polarizing film of the embodiment of the present invention is significantly smaller, so the polarizing film does not form a complex with PVA iodide ions The content ratio is very small, so it can be seen that the content ratio of the PVA-iodine complex that absorbs visible light is very large. On the other hand, since the A ₄₇₀ / A ₆₀₀ is maintained without greatly reduced, thus PVA- iodine complexes vicinity of 600 nm (having absorbed the PVA-I ₅ ^- complexes in the vicinity of 470nm and with the absorption of the PVA-I ₃ ^-The complex compound) can maintain a good balance, and it can be seen that it has a high degree of polarization performance in the full range of visible light. In addition, assuming that the balance is greatly changed, when A ₄₇₀ /A _{600 is} lower than 0.5 or higher than 2.0, it means that the partial polarization performance of the visible light region is reduced, and the hue deviates greatly from neutral, which may cause problems such as discoloration. Regarding A ₄₇₀ /A ₆₀₀ , the polarizing film of Comparative Example 1-1 is larger than the polarizing film of Example, but the unit absorbance of 210 is exceptionally large. _{In addition, the A 470} /A ₆₀₀ of the polarizing film of Comparative Examples 1-4 and 1-5 is too small, so that the polarization performance in the short wavelength region is greatly reduced. It can be found that the result is that the short-wavelength orthogonal transmittance is selectively increased, the orthogonal b value becomes smaller, and the display hue of the orthogonal state (black display) deviates greatly from neutral and becomes blue. That is, the polarizing film of the embodiment of the present invention can increase the ratio of PVA-iodine complexes that absorb light in the visible region. As a result, it can achieve both high polarization performance and thinning of the polarizing film. Furthermore, compared with the polarizing films of Comparative Examples 1-4 and 1-5, the polarizing film of the embodiment of the present invention has a cross-b value that is extremely close to 0 (zero). Therefore, a polarizing film with a neutral display hue in the orthogonal state (black display) can be produced. Industrial availability

The polarizing plate having the polarizing film of the present invention is suitable for use in a liquid crystal display device.

10‧‧‧Polarizing film 20‧‧‧First protective layer 30‧‧‧Second protective layer 100‧‧‧Polarizing plate 200‧‧‧Laminated body R1~R6‧‧‧Conveying roller G1~G4‧‧‧Guide roller

Fig. 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. Fig. 2 is a schematic diagram showing an example of drying shrinkage treatment using a heating roller. 3 is a graph showing the relationship between the monomer transmittance of the polarizing film obtained in the comparative example and the comparative example and the unit absorbance at a wavelength of 210 nm.

10‧‧‧Polarizing film

20‧‧‧The first protective layer

30‧‧‧Second protective layer

100‧‧‧Polarizer

Claims (11)

A polarizing film composed of a polyvinyl alcohol resin film containing iodine with a thickness of 8μm or less; its monomer transmittance is 41.5% or more and 43.5 or less, and its polarization degree is 99.990% or more and 99.998% or less; its thickness per 1μm The orthogonal absorbance at a wavelength of 210 nm is below 1.00, the ratio _{of the orthogonal absorbance A 470} at a wavelength of 470 nm to the orthogonal absorbance A _{600 at a wavelength of 600 nm (A 470} /A ₆₀₀ ) is 0.7 to 2.00; and the orthogonal b value Greater than -10 and less than +10. For example, the polarizing film of claim 1 has a thickness of 4 μm or less. The polarizing film of claim 1 or 2, wherein the aforementioned orthogonal absorbance per 1 μm thickness at a wavelength of 210 nm is 0.60 or less. For example, the polarizing film of claim 1 or 2 has an iodine concentration of 3.0% by weight or more. For example, the polarizing film of claim 1 or 2 has a single transmittance of 42.5% or more. A polarizing plate has the polarizing film as claimed in any one of claims 1 to 5, and a protective layer arranged on at least one side of the polarizing film. A method for manufacturing a polarizing film, the polarizing film is composed of a polyvinyl alcohol resin film containing iodine, with a thickness of 8μm or less; its thickness per 1μm at a wavelength of 210nm has an orthogonal absorbance of 1.00 or less, and a wavelength of 470nm. The ratio of the absorbance A ₄₇₀ to the orthogonal absorbance A _{600 at the wavelength of 600nm (A 470} /A ₆₀₀ ) is 0.7~2.00; and the orthogonal b value is greater than -10 and below +10; the manufacturing method includes: in a long strip A polyvinyl alcohol-based resin layer is formed on one side of the thermoplastic resin substrate to form a laminate, the polyvinyl alcohol-based resin layer containing iodide or sodium chloride, and a polyvinyl alcohol-based resin; and, the laminate is sequentially Air-assisted stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment are performed. The dry shrinkage treatment is to transport the laminate in the longitudinal direction and heat to shrink it by 2% or more in the width direction. The manufacturing method of claim 7, wherein the aforementioned iodide is potassium iodide. The manufacturing method of claim 8, wherein the content of the potassium iodide in the polyvinyl alcohol-based resin layer is 5 to 20 parts by weight relative to 100 parts by weight of the polyvinyl alcohol-based resin. The manufacturing method according to any one of claims 7 to 9, wherein the aforementioned drying and shrinking treatment is performed using a heated roller. The manufacturing method of claim 10, wherein the temperature of the heating roller is 60°C to 120°C.

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