TW201915064A - Polarizing film, polarizing plate, and method for manufacturing polarizing film - Google Patents

Abstract

Provided is a polarizing film that has exceptional optical characteristics. This polarizing film is configured from a polyvinyl alcohol resin film containing iodine, the single-body transmissivity of the polarizing film being 43.0% or more, and the orthogonal absorbance per [mu]m of thickness at a wavelength of 550 nm being 0.85 or more. Such a polarizing film can be obtained using a manufacturing method that includes, for example: forming a polyvinyl alcohol resin layer that includes an iodide or sodium chloride, and also includes a polyvinyl alcohol resin, on one side of an elongated thermoplastic resin substrate to obtain a laminate body; and performing, on the laminate body in the stated order, an aerial auxiliary stretching process, a dyeing process, a stretching process in water, and a dry shrinkage process in which stretching of 2% or more in the width direction is induced by heating while conveying in the length direction.

Description

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

Field of the Invention The present invention relates to a polarizing film, a polarizing plate, and a method of manufacturing a polarizing film.

BACKGROUND OF THE INVENTION In a liquid crystal display device, which is a representative image display device, polarizing films are arranged on both sides of a liquid crystal cell due to its image forming method. As a method of manufacturing a polarizing film, for example, there has been proposed a method of extending a laminate having a resin substrate and a polyvinyl alcohol (PVA) resin layer, followed by dyeing treatment to obtain a polarizing film on the resin substrate ( For example, Patent Document 1). With this method, a thin polarizing film can be obtained, so it can contribute to the thinning of the image display device in recent years and attracts attention. However, as the above-mentioned conventional thin polarizing film has insufficient optical characteristics, the optical characteristics of the thin polarizing film are further improved. Prior art literature Patent literature

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

SUMMARY OF THE INVENTION The present invention is made to solve the above-mentioned conventional problems, and its main object is to provide a thin polarizing film, a polarizing plate, and a method for manufacturing the polarizing film having excellent optical characteristics. Means to solve the problem

The polarizing film of the present invention is composed of a polyvinyl alcohol-based resin film containing iodine, its monomer transmittance is 43.0% or more, and the orthogonal absorbance at a wavelength of 550 nm per 1 μm thickness is 0.85 or more. In one embodiment, the ratio (A ₄₇₀ / A ₆₀₀ ) of the orthogonal absorbance A ₄₇₀ at a wavelength of 470 nm of the polarizing film to the orthogonal absorbance A ₆₀₀ at a wavelength of 600 nm 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 8 μm or less. In one embodiment, the thickness of the polarizing film is 4 μm or less. In one embodiment, the orthogonal absorbance of the polarizing film at a wavelength of 550 nm per thickness of 1 μm is 2.0 or more. According to another aspect of the present invention, a polarizing plate can be provided. The polarizing plate has the polarizing film and a protective layer disposed on at least one side of the polarizing film. According to another aspect of the present invention, a method for manufacturing the above polarizing film can be provided. This method includes: forming a laminated body by forming a polyvinyl alcohol-based resin layer on one side of a long thermoplastic resin substrate, the polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin; and, the laminated layer The body is sequentially subjected to air-assisted extension treatment, dyeing treatment, underwater extension treatment, and drying shrinkage treatment. 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. In one embodiment, the halide is potassium iodide. In one embodiment, 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. In one embodiment, the drying shrinkage treatment is performed using a heating roller. In one embodiment, the temperature of the heating roller is 60 ° C to 120 ° C. Effect of invention

According to the present invention, a combination of: the addition of a halide (represented by potassium iodide) to a polyvinyl alcohol (PVA) resin, two-stage extension including air-assisted extension and underwater extension, and drying and shrinkage using a heating roller, It is possible to realize a thin polarizing film having very excellent optical characteristics (for example, both excellent single-body transmittance and excellent orthogonal absorbance).

Forms for Carrying Out the Invention Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

A. Polarizing film The polarizing film of the embodiment of the present invention is composed of an iodine-containing polyvinyl alcohol-based resin film, its monomer transmittance is 43.0% or more, and the orthogonal absorbance at a wavelength of 550 nm per 1 μm thickness (hereinafter referred to as The unit absorbance) is 0.85 or more. In general, the monomer transmittance and the orthogonal absorbance are mutually compensated. As the monomer transmittance is increased, the orthogonal absorbance may decrease; on the contrary, when the orthogonal absorbance is increased, the monomer transmittance may decrease. Therefore, it has conventionally been difficult to practically provide a thin polarizing film that can satisfy the optical characteristics of the monomer transmittance of 43.0% or more and the unit absorbance at a wavelength of 550 nm of 0.85 or more. As described above, the polarizing film according to an embodiment of the present invention has excellent optical characteristics with a monomer transmittance of 43.0% or more and a unit absorbance at a wavelength of 550 nm of 0.85 or more. One of the achievements of the present invention is to realize the thin polarizing film. The polarizing film can be used for an image display device, and is particularly suitable for a polarizing plate on the back side of a liquid crystal display device.

The thickness of the polarizing film is preferably 1 μm to 8 μm, preferably 1 μm to 7 μm, more preferably 2 μm to 5 μm, and particularly preferably 2 μm to 4 μm.

The polarizing film should show absorption dichroism at any wavelength between 380nm and 780nm. The monomer transmittance of the polarizing film is preferably 44.0% or less, and more preferably 43.5% or less. The polarizing degree of the polarizing film should be 99.990% or more, more preferably 99.998% or less. The above-mentioned monomer transmittance represents the Y value measured with an ultraviolet-visible light spectrophotometer and compensated for visual sensitivity. The single transmittance is a 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 polarization degree is representatively obtained based on the parallel transmittance Tp and the orthogonal transmittance Tc measured with an ultraviolet-visible 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 8 μm or less means that the layered body of the polarizing film (surface refractive index: 1.53) and the protective film (refractive index: 1.50) is the measurement object, and ultraviolet-visible light spectroscopy is used Measured by photometer. The reflectance at the interface of each layer will be different depending on the surface refractive index of the polarizing film and / or the surface refractive index of the protective film that is in contact with the air interface, and as a result, the measured value of the transmittance may sometimes vary accordingly . Therefore, for example, when a protective film with a refractive index other than 1.50 is used, the measured value of the transmittance can also be compensated according to the surface refractive index of the protective film that is in contact with the air interface. Specifically, the compensation value C of the transmittance is a polarized light reflectance R1 (transmission axis reflectance) parallel to the transmission axis of the interface between the protective film and the air layer, which 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 / (n 1 +1) _{^{2) × (T 1/100}} ) here, R ₀ is a refractive index-based transmission axis reflectance of the protective film of 1.50, n ₁ is the refractive index of the protective film using, T ₁ is transmittance of the polarizing film. For example, when using a substrate with a surface refractive index of 1.53 (cycloolefin-based film, hard-coated film, etc.) as the protective film, the compensation amount C is about 0.2%. At this time, by adding 0.2% to the measured transmittance, the polarizing film with a surface refractive index of 1.53 can be converted into the transmittance when a protective film with a refractive index of 1.50 is used. In addition, according to the calculation made by the above formula, the amount of change of the compensation value C when the transmittance T _{1 of the} polarizing film is fine-tuned by 2% is 0.03% or less, 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, appropriate compensation can be made according to the absorption amount.

The unit absorbance of the polarizing film at a wavelength of 550 nm is 0.85 or more as described above, preferably 0.9 or more, more preferably 1.0 or more, and even more preferably 1.3 or more. The upper limit of unit absorbance may be 1.9, for example. The orthogonal absorbance A _λ at the wavelength λnm is obtained from the above orthogonal transmittance Tc using the following formula. Orthogonal absorbance = log10 (100 / Tc) The unit absorbance at a wavelength of 550 nm can be obtained by dividing the orthogonal absorbance A ₅₅₀ obtained above by the thickness. In addition, the unit absorbance of the polarizing plate can substantially correspond to the unit absorbance of the polarizing film. When the polarizing film is used in an organic electroluminescence (EL) display device and an inorganic EL display device (such as a quantum dot display device), the orthogonal absorbance A ₅₅₀ may be 2.0 or more (for example, the unit absorbance is 0.8 or more and the thickness is 2.5 μm the above). When the polarizing film is used in a liquid crystal display device, the orthogonal absorbance A ₅₅₀ may be 3.0 or more, for example.

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, and more preferably Above 0.80, especially above 0.85. The upper limit of the ratio (A ₄₇₀ / A ₆₀₀ ) is, for example, 2.00, and is preferably 1.33. If the ratio (A ₄₇₀ / A ₆₀₀ ) is in the above range, good polarization performance can be achieved in the entire range of visible light. In the case where the amount of iodine in the thin polarizing film is limited, it is difficult to make the above unit absorbance and ratio (A ₄₇₀ / A ₆₀₀ ) fall within the desired range by conventional techniques. The solution to the problem made 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 -7 or more, and more preferably -5 or more. The upper limit of the orthogonal b value is preferably +10 or less, and more preferably +5 or less. According to the invention of the present 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 greater the absolute value of this value, the more the orthogonal hue (black display on the image display device) will be seen from the hue. For example, when the orthogonal b value is below -10, the black display will look bluish, degrading the display performance. That is, according to the embodiment of the present invention, a polarizing film that can achieve an excellent hue during black display can be produced. In addition, the orthogonal b value can be measured with a spectrophotometer represented by V-7100.

As the polarizing film, any and appropriate polarizing film can be used. The polarizing film is typically made by using two or more layers of laminates.

Specific examples of the polarizing film obtained by using the laminate include a polarizing film obtained by using a resin substrate and a laminate of a PVA-based resin layer formed on the resin substrate. 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 applying 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 stretching and dyeing the laminate to form the PVA-based resin layer into a polarizing film. In the present embodiment, stretching typically includes immersing the laminate in a boric acid aqueous solution to perform stretching. Further, if necessary, the stretching may further include aerial stretching at a high temperature (for example, 95 ° C. or higher) before stretching in the boric acid aqueous solution. The resulting 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 The peeling surface is laminated with an arbitrary and appropriate protective layer depending on the purpose and used later. 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 this gazette is used as a reference.

The method of manufacturing a polarizing film of the present invention includes forming a laminate by forming a polyvinyl alcohol-based resin layer on one side of a long thermoplastic resin substrate, the polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin layer Resin; and, the above-mentioned laminate is sequentially subjected to aerial assisted stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment, and the drying shrinkage treatment is carried out by transporting the laminate in the longitudinal direction and heating using a heating roller. Thereby, even if the thickness is very thin, it is possible to provide a polarizing film having excellent optical characteristics with a single 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 the thermoplastic resin, the crystallinity of PVA can be improved and a high degree of optical characteristics can be achieved. In addition, by improving the orientation of PVA at the same time in advance, it is possible to prevent problems such as reduction of orientation of PVA or dissolution when immersed in water in the subsequent dyeing step and elongation step, and achieve high optical characteristics. Furthermore, when the PVA-based resin layer is immersed in liquid, compared with 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 molecules and the decrease in the orientation. Thereby, the optical characteristics of the polarizing film obtained by the treatment step of immersing the laminate in the liquid by dyeing treatment, water extension treatment, etc. can be improved. Furthermore, by shrinking the laminate in the width direction by dry 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 includes a polarizing film 10, a first protective layer 20 disposed on one side of the polarizing film 10, and a second protective layer 30 disposed on the other side of the polarizing film 10. The polarizing film 10 is the polarizing film of the present invention described in the above item A. One of the first protective layer 20 and the second protective layer 30 may be omitted. Furthermore, as described above, one of the first protective layer and the second protective layer may be a resin substrate used for the manufacture of the polarizing film.

The first and second protective layers are formed of any suitable thin films that can be used as protective layers for polarizing films. Specific examples of the material of the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, and polyamide-based Transparent resins such as imine-based, polyether-based, poly-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth) acrylic, and acetate-based. In addition, thermosetting resins such as (meth) acrylic resins, urethane resins, (meth) acrylic acid urethane resins, epoxy resins, and polysiloxane-based resins, and ultraviolet-curable resins can also be mentioned. Other examples include glassy polymers such as siloxane-based polymers. Furthermore, 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 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, and For example, a resin composition having an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer is mentioned. The polymer film may be, for example, an extruded product of the above resin composition.

When the polarizing plate 100 is applied to an image display device, the thickness of the protective layer (outer protective layer) disposed on the side opposite to the display panel is typically 300 μm or less, preferably 100 μm or less, more preferably 5 μm to 80 μm, and It is 10μm ~ 60μm. In addition, when 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 (inside protective layer) disposed on the display panel side is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and even more preferably 10 μm to 60 μm. In one embodiment, the inner protective layer is a phase difference layer having an arbitrary and appropriate phase difference value. At this time, the in-plane retardation Re (550) of the retardation layer is, for example, 110 nm to 150 nm. "Re (550)" is the in-plane phase difference measured with light having a wavelength of 550 nm 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 in-plane refractive index (that is, the direction of the slow axis), "ny" is the refractive index in the direction orthogonal to the slow axis (that is, the direction of the fast axis), "nz" Is the refractive index in the thickness direction, and "d" is the thickness (nm) of the layer (thin film).

C. Method for manufacturing polarizing film A method for manufacturing a polarizing film according to an embodiment of the present invention includes forming a polymer including a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin substrate The vinyl alcohol-based resin layer (PVA-based resin layer) is used to form a laminate; and, the laminate is sequentially subjected to aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and transported in the longitudinal direction and heated to the width direction Dry shrinkage treatment with over 2% shrinkage. The content of the halide in the PVA-based resin layer is preferably 5-20 parts by weight relative to 100 parts by weight of the PVA-based resin. Drying shrinkage treatment should be processed by heating roller, and the temperature of heating roller should be 60 ℃ ~ 120 ℃. The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is preferably at least 2%. According to the manufacturing method, the polarizing film described in the above item A can be obtained. In particular, by preparing a laminate containing a halide-containing PVA-based resin layer, and setting the extension of the laminate as a multi-stage extension including air-assisted extension and underwater extension, and then heating the extension with a heating roller, It is possible to obtain a polarizing film having excellent optical characteristics (representatively, monomer transmittance and unit absorbance).

C-1. Production of laminates A method for producing a laminate of a thermoplastic resin base material and a PVA-based resin layer can adopt any appropriate method. It is desirable to form a PVA-based resin layer on a thermoplastic resin substrate by applying and drying a coating liquid containing a halide and a PVA-based resin on the surface of the thermoplastic resin laminate. As described above, 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 method for applying the coating liquid can be any appropriate method. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a blade coating method (angular wheel coating method, etc.), etc. . The coating and drying temperature of the coating liquid is preferably 50 ° C or higher.

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

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

C-1-1. Thermoplastic resin base material The thickness of the thermoplastic resin base material 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 a PVA-based resin layer. If it exceeds 300 μm, for example, the thermoplastic resin substrate may take a long time to absorb water during the water stretching process described later, which may cause an excessive load on the stretching.

The thermoplastic resin substrate preferably has a water absorption rate of 0.2% or more, and more preferably 0.3% or more. Thermoplastic resin substrates will absorb water, and water will act as a plasticizer for plasticization. As a result, the stretching stress can be greatly reduced, and the stretching can be performed at a high rate. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, and more preferably 1.0% or less. By using the thermoplastic resin substrate, it is possible to prevent defects such as deterioration in the appearance of the polarizing film obtained due to a significant decrease in the dimensional stability of the thermoplastic resin substrate during manufacturing. In addition, it is possible to prevent the base material from breaking or the PVA-based resin layer from being peeled from the thermoplastic resin base material when extending in water. In addition, the water absorption rate of the thermoplastic resin base material can be adjusted by, for example, introducing a modified group into the constituent material. The water absorption rate is a value determined according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120 ° C or lower. By using the thermoplastic resin base material, the crystallization of the PVA-based resin layer can be suppressed, and the extensibility of the laminate can be sufficiently ensured. In addition, considering the plasticization of the thermoplastic resin substrate by water and smooth extension in water, it is preferably 100 ° C or lower, and more preferably 90 ° C or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60 ° C or higher. By using the thermoplastic resin substrate, it is possible to prevent defects such as deformation of the thermoplastic resin substrate (for example, unevenness, sag, wrinkles, etc.) when applying and drying the coating solution containing the PVA-based resin, and Make a good laminate. In addition, the stretching of the PVA-based resin layer can be performed favorably at an appropriate temperature (for example, about 60 ° C). In addition, the glass transition temperature of the thermoplastic resin substrate can be adjusted by, for example, heating the crystallizing material that introduces the constituent material into the modified group. The glass transition temperature (Tg) is a value determined in accordance with JIS K 7121.

As the constituent material of the thermoplastic resin substrate, any suitable 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. Copolymer resins, etc. Among these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are more desirable.

In one embodiment, an amorphous (uncrystallized) polyethylene terephthalate resin is preferably used. Among them, non-crystalline (difficult to crystallize) polyethylene terephthalate resins are particularly suitable. Specific examples of the amorphous polyethylene terephthalate-based resin include copolymers further containing isophthalic acid and / or cyclohexane dicarboxylic acid as the dicarboxylic acid, and further containing cyclohexane dicarboxylic acid. Methanol or diethylene glycol is a copolymer of glycol.

In a preferred embodiment, the thermoplastic resin substrate is made of polyethylene terephthalate resin having isophthalic acid units. The reason is that the thermoplastic resin base material is extremely excellent in elongation, and crystallization during elongation can be suppressed. We believe that this is due to the introduction of isophthalic acid units, which causes a large bend in the main chain. The polyethylene terephthalate-based resin has terephthalic acid units and ethylene glycol units. The content ratio of isophthalic acid units is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, relative to the total of all repeating units. This is because a thermoplastic resin substrate with extremely excellent extensibility can be obtained. On the other hand, the content ratio of isophthalic acid units is preferably 20 mol% or less and more preferably 10 mol% or less with respect to the total of all repeating units. By setting it as the said content ratio, the crystallinity can be increased favorably in the drying shrinkage process mentioned later.

The thermoplastic resin substrate may be stretched in advance (before the PVA-based resin layer is formed). In one embodiment, it extends laterally of the long thermoplastic resin substrate. The lateral direction is preferably a direction orthogonal to the extending direction of the laminate to be described later. In addition, "orthogonal" in this specification includes the case where it is substantially orthogonal. Here, the term "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 extension ratio of the thermoplastic resin substrate is preferably 1.5 times to 3.0 times.

The stretching method of the thermoplastic resin substrate can be any suitable stretching method. Specifically, it may 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 performed in one stage or in multiple stages. When carried out in multiple stages, the above-mentioned stretching magnification is the product of the stretching magnifications in each stage.

C-1-2. Coating liquid The coating liquid contains halide and PVA resin as described above. The coating liquid represents a solution in which the halide and the PVA-based resin have been dissolved in a solvent. Examples of the solvent include polyhydric alcohols such as water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, and trimethylolpropane. Ethylenediamine, diethylenetriamine and other amines. These can be used alone or in combination of two or more. Among these, water is better. The concentration of the PVA-based resin in the solution is preferably 3-20 parts by weight relative to 100 parts by weight of the solvent. As long as it is the resin concentration, a uniform coating film adhered 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 in the coating liquid. Examples of additives include plasticizers and surfactants. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. The surfactant may, for example, be a nonionic surfactant. These can be used for the purpose of further improving the uniformity, dyeability, and extensibility of the resulting PVA-based resin layer.

Any appropriate resin can be used for the PVA-based resin. Examples thereof include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying the ethylene-vinyl acetate copolymer. The saponification degree of the PVA 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 degree of saponification is determined in accordance with JIS K 6726-1994. By using the saponification degree PVA-based resin, a polarizing film excellent in durability can be obtained. When the degree of saponification 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 polymerization degree is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. In addition, the average degree of polymerization can be obtained in accordance with JIS K 6726-1994.

As the halide, any suitable halide can be used. Examples include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

The amount of halide in the coating liquid is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, and more preferably 10 to 15 parts by weight with respect to 100 parts by weight of the PVA-based resin. If the amount of the halide exceeds 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may bleed out, resulting in a white turbidity of the polarizing film finally obtained.

Generally speaking, by extending the PVA-based resin layer, the orientation of the polyvinyl alcohol molecules in the PVA-based resin becomes higher, but if the extended PVA-based resin layer is immersed in a liquid containing water, the polyvinyl alcohol molecules Orientation will be disordered, and there may be a decrease in orientation. Especially when the laminate of the thermoplastic resin and the PVA-based resin layer is stretched in boric acid water, in order to stabilize the stretching of the thermoplastic resin, when the laminate is stretched in boric acid water at a relatively high temperature, the above-mentioned tendency to decrease the degree of orientation will Notable. For example, the extension of the laminate of A-PET (thermoplastic resin base material) and PVA-based resin layer is generally higher than the temperature around 70 ° C, as compared to the extension of PVA film monomer in boric acid water at 60 ° C. It is carried out at a temperature, and in this case, the orientation of the PVA at the initial stage of stretching may decrease before it rises by extension in water. In contrast to this, a laminate containing a halide-containing PVA-based resin layer and a thermoplastic resin base material is produced, and high-temperature elongation (auxiliary extension) is performed in the air before the laminate is extended in boric acid water, thereby promoting the accumulation after auxiliary extension Crystallization of the PVA resin in the PVA resin layer of the body. As a result, when the PVA-based resin layer is immersed in liquid, it is possible to suppress the disorder of the orientation of the polyvinyl alcohol molecule and the decrease in the orientation compared to the case where the PVA-based resin layer does not contain a halide. Thereby, the optical characteristics of the polarizing film obtained by the treatment step of immersing the laminate in the liquid by dyeing treatment, water extension treatment, etc. can be improved.

C-2. Air-assisted extension processing In particular, in order to obtain a high degree of optical characteristics, the two-stage extension method combining dry extension (auxiliary extension) and boric acid underwater extension will be selected. Such as two-stage extension, by introducing auxiliary extension, the crystallization of the thermoplastic resin substrate can be suppressed and the extension is performed at the same time, and the reduction of the extensibility caused by the excessive crystallization of the thermoplastic resin substrate in the subsequent boric acid water extension can be solved Problem, the laminate can be extended at a higher rate. In addition, when PVA-based resin is coated on a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, it must be reduced compared to the case where PVA-based resin is applied to a normal metal cylinder. As a result of the coating temperature, the crystallization of the PVA-based resin may be relatively low, and sufficient optical characteristics may not be obtained. On the other hand, 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 characteristics can be achieved. In addition, by simultaneously improving the orientation of the PVA-based resin beforehand, it is possible to prevent problems such as reduction in the orientation of the PVA-based resin and dissolution when immersed in water in the subsequent dyeing step and extension step, thereby achieving high optical characteristics.

The extension method of air-assisted extension can be fixed-end extension (for example, a method using a tenter extension machine 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 aerial stretching process includes a heating roller stretching step. This step is to transport the above-mentioned layered body along its longitudinal direction, and at the same time, it is extended by a difference in peripheral speed between the heating rollers. The air stretching process typically includes an area stretching step and a heating roller stretching step. In addition, the order of the region stretching step and the heating roller stretching step is not limited, and the region stretching step may be performed first, or the heating roller stretching step may be performed first. The step of extending the area can also be omitted. In one embodiment, the area extending step and the heating roller extending step may be performed in sequence. Furthermore, in other embodiments, the tenter stretching machine grips the film end and extends the distance between the tenter machines in the direction of flow to extend (the expansion of the distance between the tenter machines is the stretching ratio). At this time, the distance of the tenter in the width direction (the direction perpendicular to the flow direction) is set to be arbitrarily accessible. Ideally, it can be set to an extension ratio with respect to the flow direction to use the free-end extension for approach. For the extension at the free end, it is calculated as the shrinkage in the width direction = (1 / extension ratio) ^1/2 .

The air-assisted extension can be performed in one stage or in multiple stages. When carried out in multiple stages, the stretching magnification is the product of the stretching magnifications in each stage. The extension direction in the air-assisted extension is preferably slightly the same as the extension direction in the underwater extension.

The extension magnification in the air-assisted extension is preferably 2.0 times to 3.5 times. The maximum extension magnification when combining air-assisted extension and underwater extension is preferably 5.0 times or more, more preferably 5.5 times or more, and 6.0 times or more relative to the original length of the laminate. The "maximum elongation ratio" in this specification means the elongation ratio before the laminate is broken, and it is a value lower than its value by 0.2 after confirming the elongation ratio of the laminate breakage.

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

C-3. Insolubilization treatment If necessary, perform insolubilization treatment after the air-assisted extension treatment and before the water extension treatment or dyeing treatment. The above-mentioned insolubilization treatment can be performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. By performing the insolubilization treatment, the PVA-based resin layer can be provided with water resistance, and the orientation can be prevented from decreasing when PVA is 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 liquid temperature of the insoluble bath (boric acid aqueous solution) is preferably 20 ° C to 50 ° C.

C-4. Dyeing treatment The above dyeing treatment is performed by dyeing the PVA-based resin layer with iodine on the upper system. Specifically, it is performed by adsorbing iodine to the PVA-based resin layer. Examples of the adsorption method include a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of applying the dyeing solution to the PVA-based resin layer, and spraying the PVA-based resin layer The method of staining solution. Ideally, it is a method of immersing the laminate in a dyeing liquid (dyeing bath). This is because it can adsorb iodine well.

The dyeing solution is preferably an aqueous iodine solution. The blending amount of iodine relative to 100 parts by weight of water is preferably 0.05 parts by weight to 0.5 parts by weight. In order to improve the solubility of iodine in water, it is appropriate to mix iodide in the iodine aqueous 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, and titanium iodide. Among these, potassium iodide is preferred. The blending amount of iodide is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight relative to 100 parts by weight of water. In order to suppress the dissolution of the PVA-based resin, the temperature of the dyeing liquid during dyeing is preferably 20 ° C to 50 ° C. When immersing the PVA-based resin layer 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 polarizing film finally obtained becomes 43.0% or more, and the degree of polarization becomes 99.980% or more. For the dyeing conditions, an iodine aqueous solution is preferably used as the dyeing solution, and the ratio of the content of iodine and potassium iodide in the iodine aqueous solution is set to 1: 5 to 1:20. The ratio of the content of iodine and potassium iodide in the iodine aqueous solution is preferably 1: 5 ~ 1: 10. With this, a polarizing film having optical characteristics as described above can be obtained.

When the layered body is immersed in a treatment bath containing boric acid (typically insoluble treatment) and then dyeing is carried out, 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 occur over time As a result, the dyeability may become unstable. In order to suppress the destabilization of the dyeing property as described above, the upper limit of the boric acid concentration of 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, with respect to 100 parts by weight of water, the lower limit of the boric acid concentration of the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and even more preferably 0.5 parts by weight. In one embodiment, a dyeing bath in which boric acid is mixed in advance is used for dyeing treatment. This can reduce the rate of change in boric acid concentration when boric acid in the treatment bath is mixed in the dyeing bath. The amount of boric acid admixed in the dyeing bath in advance (ie, the content of boric acid not from the above treatment bath) is preferably 0.1 to 2 parts by weight, preferably 0.5 to 1.5 parts by weight, relative to 100 parts by weight of water Copies.

C-5. Cross-linking treatment If necessary, perform cross-linking treatment after dyeing treatment and before extension treatment in water. The above-mentioned cross-linking treatment can be performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing cross-linking treatment, water resistance can be imparted to the PVA-based resin layer to prevent the orientation from decreasing when PVA is immersed in high-temperature water during subsequent water extension. 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 iodide. By blending iodide, the elution of iodine that has adsorbed to the PVA-based resin layer can be suppressed. The blending amount of iodide relative to 100 parts by weight of water is preferably 1 part by weight to 5 parts by weight. Specific examples of iodide are as described above. The liquid temperature of the cross-linking bath (boric acid aqueous solution) is preferably 20 ° C to 50 ° C.

C-6. Stretching treatment in water Stretching treatment in water is performed by immersing the laminate in a stretch bath. Through water stretching, it can be stretched at a temperature lower than the glass transition temperature of the thermoplastic resin substrate or the PVA-based resin layer (typically around 80 ° C), while suppressing the crystallization of the PVA-based resin layer. The high magnification can be extended. As a result, a polarizing film having excellent optical characteristics can be manufactured.

The method for extending the laminate can be any appropriate method. Specifically, it may be a fixed-end extension or a free-end extension (for example, a method of uniaxially extending a laminate between rollers having different peripheral speeds). Ideally, choose the free end extension. The extension of the laminate can be performed in one stage or in multiple stages. When performing in multiple stages, the stretching magnification (maximum stretching magnification) of the laminate to be described later is the product of the stretching magnification in each stage.

The extension in water is preferably carried out by immersing the laminate in an aqueous solution of boric acid (boric acid extension in water). By using a boric acid aqueous solution as an extension bath, the PVA-based resin layer can be given rigidity that can withstand the tension applied during extension and water resistance that is insoluble in water. Specifically, boric acid generates tetrahydroxyboric acid anions in the aqueous solution and can be cross-linked with the PVA-based resin by hydrogen bonding. As a result, the PVA-based resin layer can be imparted with rigidity and water resistance, can be stretched well, and can produce a polarizing film having excellent optical characteristics.

The aforementioned aqueous solution of boric acid is preferably obtained by dissolving boric acid and / or borate in water of a solvent. The concentration of boric acid is preferably 1 part by weight to 10 parts by weight relative to 100 parts by weight of water, more preferably 2.5 parts by weight to 6 parts by weight, and particularly preferably 3 parts by weight to 5 parts by weight. By setting the concentration of boric acid to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film with higher characteristics can be manufactured. 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.

Ideally, iodide is blended into the above-mentioned extension bath (boric acid aqueous solution). By blending iodide, the elution of iodine that has adsorbed to the PVA-based resin layer can be suppressed. Specific examples of iodide are as described above. Relative to 100 parts by weight of water, the concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight.

The extension temperature (bath temperature of the extension bath) is preferably 40 ° C to 85 ° C, more preferably 60 ° C to 75 ° C. As long as it is the above temperature, it is possible to suppress the dissolution of the PVA-based resin layer and at the same time it can be stretched at a high rate. Specifically, as described above, in terms of forming the PVA-based resin layer, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ° C. or higher. At this time, if the stretching temperature is lower than 40 ° C, even if the thermoplastic resin base material is considered to be plasticized with water, it may not be able to be stretched 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 be impossible to obtain excellent optical characteristics. The immersion time of the laminate in the extension bath is preferably 15 seconds to 5 minutes.

The stretching magnification in water stretching is preferably 1.5 times or more, and 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 extension magnification, a polarizing film with extremely excellent optical characteristics can be manufactured. The high extension ratio can be achieved by using an underwater extension method (boric acid underwater extension).

C-7. Drying shrinkage treatment The above-mentioned drying shrinkage treatment can be carried out by heating the area, that is, heating the entire area, or by heating and conveying rollers (using so-called heating rollers) (heating roller drying method). It is desirable to use both. By using a heating roller to dry, it is possible to efficiently suppress the heating and bending of the laminate, and to manufacture a polarizing film having an excellent appearance. Specifically, drying the laminate with the heating roller can effectively promote the crystallization of the thermoplastic resin base material and increase the degree of crystallization, even at a lower drying temperature, it is still good To increase the crystallinity of the thermoplastic substrate. As a result, the rigidity of the thermoplastic resin substrate can be increased, and the PVA-based resin layer can withstand shrinkage due to drying, and bending can be suppressed. In addition, since the heating roller is used, the laminate can be dried while being kept in a flat state. Therefore, not only the bending but also the generation of wrinkles can be suppressed. At this time, the laminate shrinks in the width direction by the drying shrinkage treatment, and the optical characteristics can be improved. This is because it can effectively improve the orientation of PVA and PVA / iodine complex. The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%.

Fig. 2 is a schematic diagram showing an example of drying shrinkage treatment. In the drying shrinkage process, the laminated body 200 is conveyed and dried by the conveying rollers R1 to R6 and guide rollers G1 to G4 that have been heated to a predetermined temperature. In the example shown in the figure, the conveying rollers R1 to R6 are arranged in such a manner that the surface of the PVA resin layer and the surface of the thermoplastic resin layer can be continuously heated alternately. However, for example, only one side of the layered body 200 may be continuously heated The conveying rollers R1 to R6 are arranged in the manner of the material surface.

The drying conditions can be controlled by adjusting the heating temperature of the conveyor roller (temperature of the heating roller), the number of heating rollers, and the time of contact with the heating roller. The temperature of the heating roller is preferably 60 ° C to 120 ° C, more preferably 65 ° C to 100 ° C, and particularly preferably 70 ° C to 80 ° C. 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 using a contact thermometer. In the example shown in the figure, although six conveying rollers are provided, there is no particular limitation as long as there are plural conveying rollers. The conveying roller is usually 2 ~ 40, and it should be set 4 ~ 30. The contact time (total contact time) between the laminate and the heating roller is preferably 1 second to 300 seconds, more 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 normal manufacturing line (room temperature environment). Preferably, it is installed in a heating furnace equipped with a blowing mechanism. By combining the drying with the heating roller and the hot air drying, the rapid temperature change between the heating rollers can be suppressed, and 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 hot air should be about 10m / s ~ 30m / s. In addition, the wind speed is the wind speed in the heating furnace and can be measured by a small impeller-type digital anemometer.

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

Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited by these examples. The measuring method of each characteristic is as follows. In addition, "parts" and "%" in the examples and comparative examples are based on weight, unless otherwise noted. (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 The polarizing plates (protective film / polarizing film) of Examples and Comparative Examples were measured using an ultraviolet-visible light spectrophotometer (V-7100 manufactured by Japan Spectroscopy), and Let the obtained monomer transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc be Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp and Tc are Y values obtained by measuring and compensating for visual acuity according to the 2 degree field of view (C light source) of JIS Z8701. 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 side opposite to the protective film is 1.53. Based on the orthogonal transmittance Tc550 measured at a measurement wavelength of 550 nm, the orthogonal absorbance A _{550 was} obtained by the following formula, and then divided by the thickness as the unit absorbance. Further, a measurement wavelength of 470nm obtained cross transmittance Tc ₄₇₀ orthogonal absorbance A _470, by measurement wavelength of 600nm obtained cross transmittance Tc ₆₀₀ orthogonal absorbance A _600. Orthogonal absorbance = log10 (100 / Tc) In addition, the spectrophotometer can also be equivalently measured by LPF-200 manufactured by Otsuka Electronics Co., Ltd. (3) Orthogonal b value Using an ultraviolet-visible spectrophotometer (manufactured by Japan Spectroscopy Co., Ltd., product name "V7100"), the polarizing plates of Examples and Comparative Examples were measured, and the hue in the state of orthogonal polarization was determined. A polarizer with a lower orthogonal b value (negative and large absolute value) indicates that the hue is not neutral but blue.

[Example 1-1] 1. A polarized film thermoplastic resin substrate was prepared by using a long-length amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness) with a water absorption of 0.75% and a Tg of about 75 ° C. : 100 μm). Corona treatment (treatment conditions: 55W · min / m ² ) is applied to one side of the resin substrate. PVA-based resin 100 mixed with polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetate modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gohsefimer Z410") at 9: 1 13 parts by weight of potassium iodide was added to parts by weight to prepare a PVA aqueous solution (coating solution). 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 13 μm thick A PVA-based resin layer was used to produce a laminate. The obtained laminate was uniaxially stretched in the longitudinal direction (longitudinal direction) by 2.4 times in the longitudinal direction (longitudinal direction) in a 130 ° C oven between rolls with different peripheral speeds (air assisted stretching treatment) Next, the laminate is immersed in an insoluble bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40 ° C for 30 seconds (insoluble treatment). In a dyeing bath at a temperature of 30 ° C (aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water), the concentration is adjusted so that the monomer transmittance of the polarizing film finally obtained Ts) becomes the value shown in Table 1 and is immersed for 60 seconds (dyeing treatment). Next, It was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40 ° C (crosslinking treatment). Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 4.0% by weight) at a liquid temperature of 70 ° C, uniaxial stretching was performed in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to increase the total stretching ratio Up to 5.5 times (extended treatment in water). Thereafter, the laminate was immersed in a washing bath (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 20 ° C (washing treatment). Next, it was dried in an oven maintained at 90 ° C. while maintaining its contact surface temperature at 75 ° C. with a SUS heating roller for approximately 2 seconds (drying shrinkage treatment). The width direction of the laminate due to the drying shrinkage treatment The shrinkage ratio is 5.2%. A polarizing film with a thickness of 5 μm is formed on the resin substrate as described above.

2. Production of polarizing plates On the surfaces (surfaces opposite to the resin substrate) of the polarizing films obtained above, an acrylic film (surface refractive index 1.50, 40 μm) is bonded as a protective film through an ultraviolet curing adhesive. Specifically, after applying the total thickness of the hardening type adhesive to 1.0 μm, the lamination is performed using a roller 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, Table 1 shows the unit transmittance, polarization degree and unit absorbance at a wavelength of 550 nm (hereinafter referred to as unit absorbance 550).

[Examples 1-2 to 1-18] Polarized light was 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. Film and polarizing plate. For the obtained polarizing film and polarizing plate, Table 1 shows the single transmittance and unit absorbance of 550. For Examples 1-12 (single transmittance near 43.5%), A ₄₇₀ / A ₆₀₀ and orthogonal b values are also listed in Table 1. The relationship between the monomer transmittance and the unit absorbance is compared with the results of Example 2, Comparative Example 1, and Comparative Example 2 and is shown in FIG. 3. In addition, the relationship between the wavelength and the unit absorbance is shown in FIG. 4 together with Example 2 and Comparative Example 2. In addition, the comparison data of FIG. 4 is for the single transmittance of 43.6%.

[Examples 2-1 to 2-12] The thickness of the polarizing film obtained by changing the PVA aqueous solution (coating liquid) was set to 2.4 μm, and the concentration of the dyeing bath was adjusted so that the polarizing film had a single transmittance (Ts) A polarizing film and a polarizing plate were produced in the same manner as in Example 1-1 with the values shown in Table 1 and changing the conditions of the drying shrinkage treatment and setting the shrinkage ratio in the width direction to 2.5%. For the obtained polarizing film and polarizing plate, Table 1 shows the single transmittance, polarization degree, and unit absorbance of 550. For Example 2-6 (single transmittance near 43.5%), A ₄₇₀ / A ₆₀₀ and orthogonal b value are also listed in Table 1. The relationship between the unit transmittance and unit absorbance is shown in Figure 3. In addition, the relationship between the wavelength and the unit absorbance is shown in FIG. 4.

[Comparative Examples 1-1 to 1-4] Except that potassium iodide was not added to the PVA aqueous solution (coating solution), 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 the dyeing bath was adjusted The concentration is such that the polarizing film and the polarizing plate are produced in the same manner as in Example 1-1, except that the monomer transmittance (Ts) of the polarizing film is other than the value shown in Table 1. For the obtained polarizing film and polarizing plate, Table 1 shows the single transmittance, polarization degree, and unit absorbance of 550. For Comparative Examples 1-4 (in the series of this Comparative Example, the monomer transmittance is closest to 43.5%), A ₄₇₀ / A ₆₀₀ and orthogonal b value are also listed in Table 1. The relationship between the unit transmittance and unit absorbance is shown in Figure 3.

[Comparative Examples 1-5 to 1-6] A polarizing film and a polarizing plate were produced in the same manner as Comparative Example 1-4 except that the KI concentration of the washing bath was changed as shown in Table 1. For the obtained polarizing film and polarizing plate, Table 1 lists the monomer transmittance, polarization degree, unit absorbance 550, A ₄₇₀ / A ₆₀₀ and orthogonal b value.

[Comparative Examples 2-1 to 2-7] Except that 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 the concentration of the dyeing bath was adjusted so that the monomer transmittance of the polarizing film was ( 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. For the obtained polarizing film and polarizing plate, Table 1 lists the monomer transmittance, polarization degree, and unit absorbance. The relationship between the unit transmittance and unit absorbance is shown in Figure 3. In addition, the relationship between the wavelength and the unit absorbance is shown in FIG. 4.

[Table 1]

As is clear from Table 1, Figure 3 and Figure 4, the polarizing film of the embodiment of the present invention has a significantly higher unit absorbance at the same monomer transmittance than the polarizing film of the comparative example. The monomer transmittance of 43.0% or more and the unit absorbance of 0.85 or more at a wavelength of 550nm. In addition, as is clear from FIG. 4, the excellent characteristics (unit absorbance) of the polarizing film of the embodiment of the present invention can be realized in the entire range of visible light. In addition, it was also found that the excellent characteristics can be promoted by reducing the thickness of the polarizing film. Furthermore, the polarizing films of the embodiments of the present invention have an orthogonal b value that is exceptionally close to zero (zero) compared to the polarizing films of Comparative Examples 1-5 and 1-6. Therefore, a polarizing film with a neutral display hue in an 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 liquid crystal display devices.

10‧‧‧ Polarizing film

20‧‧‧The first protective layer

30‧‧‧Second protective layer

100‧‧‧ Polarizer

200‧‧‧Layered body

G1 ~ G4‧‧‧Guide roller

R1 ~ R6‧‧‧Conveying 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 view showing an example of drying shrinkage treatment using a heating roller. 3 is a graph showing the relationship between the unit transmittance and unit absorbance of the polarizing films obtained in Comparative Examples and Comparative Examples. 4 is a graph showing the relationship between the wavelength of the polarizing film obtained in Comparative Example 1, Example 2 and Comparative Example 2 and the unit absorbance.

Claims (12)

A polarizing film is composed of a polyvinyl alcohol resin film containing iodine, its monomer transmittance is 43.0% or more, and the orthogonal absorbance at a wavelength of 550 nm per 1 μm thickness is 0.85 or more. For the polarizing film of claim 1, the ratio (A ₄₇₀ / A ₆₀₀ ) of the orthogonal absorbance A ₄₇₀ at a wavelength of ₄₇₀ nm to the orthogonal absorbance A ₆₀₀ at a wavelength of 600 nm is 0.7 or more. If the polarizing film of claim 1 or 2, the orthogonal b value is greater than -10. The polarizing film according to any one of claims 1 to 3 has a thickness of 8 μm or less. The polarizing film of claim 4 has a thickness of 4 μm or less. The polarizing film according to any one of claims 1 to 5, wherein the aforementioned orthogonal absorbance at a wavelength of 550 nm per 1 μm thickness is 2.0 or more. A polarizing plate having the polarizing film according to any one of claims 1 to 6 and a protective layer disposed on at least one side of the polarizing film. A manufacturing method for manufacturing a polarizing film according to any one of claims 1 to 6, the manufacturing method comprising: forming a polyvinyl alcohol-based resin layer on one side of a long thermoplastic resin substrate to form a laminate , The polyvinyl alcohol-based resin layer contains a halide and a polyvinyl alcohol-based resin; and the layered body is sequentially subjected to aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment, the drying shrinkage treatment is to the laminate The body is transported along the long side and heated to shrink it by more than 2% in the width direction. The manufacturing method according to claim 8, wherein the aforementioned halide is potassium iodide. The manufacturing method according to claim 9, 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 8 to 10, wherein the aforementioned drying shrinkage treatment is performed using a heating roller. The manufacturing method according to claim 11, wherein the temperature of the aforementioned heating roller is 60 ° C to 120 ° C.