TW202108384A - Polarizing film, polarizing plate, and method for producing said polarizing film - Google Patents

Abstract

The present invention provides a polarizing film that exhibits excellent durability in a high temperature, high humidity environment. A polarizing film according to the present invention is formed of a polyvinyl alcohol resin film containing iodine; and the absorbance Abs240 thereof at the wavelength of 470 nm after an endurance test for 240 hours at the temperature of 60 DEG C at the relative humidity of 95% satisfies the relational expression described below with respect to the absorbance Abs0 thereof before the endurance test. Abs240/Abs0 > 0.90 A polarizing film according to one embodiment of the present invention has a single transmittance of 43.0% or more.

Description

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

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

In the liquid crystal display device, which is a representative image display device, polarizing films are arranged on both sides of the liquid crystal cell according to the image forming method. 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) 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, thin polarizing films are required to have higher durability in high temperature and high humidity environments.

Prior art literature Patent literature Patent Document 1: Japanese Patent Application Publication No. 2001-343521

The problem to be solved by the invention The present invention was made in order to solve the aforementioned problems in the past, and its main purpose is to provide a polarizing film, a polarizing plate, and a method for manufacturing the polarizing film that are excellent in durability in a high-temperature and high-humidity environment.

Means to Solve the Problem The polarizing film of the present invention is composed of a polyvinyl alcohol resin film containing iodine; and after a durability test at a temperature of 60°C and a relative humidity of 95% for 240 hours, the absorbance at a wavelength of 470nm Abs ₂₄₀ satisfies the following relationship with respect to the absorbance Abs _{0 before the endurance test: Abs 240} /Abs ₀ >0.90 In one embodiment, the monomer transmittance of the polarizing film is 43.0% or more. In one embodiment, the thickness of the polarizing film is 8 μm or less. According to another aspect of the present invention, a polarizing plate is 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 yet another aspect of the present invention, a manufacturing method of the above-mentioned polarizing film is provided. The method includes the following steps: forming a polyvinyl alcohol-based resin layer on one side of a long-shaped thermoplastic resin substrate to form a laminated body; extending and dyeing the laminated body to make the polyvinyl alcohol-based resin layer into a polarized light Film; and, make the polarizing film contact a treatment solution with a pH below 3.0. In one embodiment, the above-mentioned manufacturing method includes applying the above-mentioned treatment liquid to the above-mentioned polarizing film. In another embodiment, the above-mentioned manufacturing method includes immersing the above-mentioned polarizing film in the above-mentioned treatment liquid. In one embodiment, the manufacturing method described above is to form a polyvinyl alcohol-based resin layer containing iodide or sodium chloride and a polyvinyl alcohol-based resin on one side of the thermoplastic resin substrate. In one embodiment, the above-mentioned manufacturing method includes the steps of sequentially performing aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment on the layered body. It is heated while conveying in the direction, thereby shrinking by more than 2% in the width direction. In one embodiment, the above-mentioned drying and shrinking treatment is performed using a heated roller. At this time, the temperature of the heating roller is, for example, 60°C to 120°C. Another method of manufacturing a polarizing film of the present invention includes the following steps: stretching and dyeing a polyvinyl alcohol-based resin film to make the polyvinyl alcohol-based resin film into a polarizing film; and making the polarizing film contact pH below 3.0的处理液。 The treatment fluid.

Effects of the Invention According to the present invention, by contacting the polarizing film with a treatment solution having a pH of 3.0 or less, a polarizing film having excellent durability under a high temperature and high humidity environment can be obtained. Specifically, after the polarizing film of the embodiment of the present invention is subjected to an endurance test at a temperature of 60°C and a relative humidity of 95% for 240 hours, the absorbance Abs ₂₄₀ at a wavelength of 470 nm relative to the absorbance Abs ₀ before the endurance test satisfies the following relationship : Abs ₂₄₀ /Abs ₀ ＞0.90 That is, the absorbance of the polarizing film of the embodiment of the present invention at a wavelength of 470 nm is unlikely to decrease even after the heating and humidification durability test. This means that the degradation of the polarization performance of the polarizing film of the embodiment of the present invention in a high-temperature and high-humidity environment has been suppressed to an allowable degree in practical use. The polarizing performance of polarizing films (especially thin polarizing films) is usually greatly reduced under high temperature and high humidity environments. However, according to the embodiment of the present invention, the problem can be solved, and a durability under high temperature and high humidity environments can be provided. Excellent polarizing film (especially thin polarizing film).

The following describes embodiments of the present invention, 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 (PVA) resin film containing iodine; and after a durability test at a temperature of 60°C and a relative humidity of 95% for 240 hours, the wavelength is 470nm The absorbance Abs ₂₄₀ below satisfies the following relationship with respect to the absorbance Abs _{0 before the endurance test.} Abs ₂₄₀ / Abs _0> 0.90 which represents a polarizing film of the present embodiment of the invention, the absorption in the vicinity of 470nm with PVA-I ₃ ^- complexes case by being heated humidification durability test destruction suppressed. Although it is not clear in theory, the excellent durability can be achieved by contacting the polarizing film with a treatment solution with a pH of 3.0 or less. Abs ₂₄₀ /Abs _{0 is} preferably 0.92 or more, more preferably 0.93 or more, and more preferably 0.95 or more. The upper limit of Abs ₂₄₀ /Abs ₀ can be, for example, 1.50. In addition, the absorbance represents the orthogonal absorbance. The cross absorbance can be obtained by the following formula based on the cross transmittance Tc measured when obtaining the polarization degree described later. Orthogonal absorbance = log10 (100 / Tc) Also, the absorbance Abs _0-based polarizing film before the durability test in the general state of the absorbance, for example, the polarizing film at a wavelength of less than 5.0 under the 470nm Abs _0, is suitably 3.0 or less, more suitably from 2.2 or less. The lower limit of Abs ₀ may be 1.0, for example.

In one embodiment, after the polarizing film is subjected to an endurance test at a temperature of 60° C. and a relative humidity of 95% for 240 hours, the absorbance Abs _{240 at a wavelength of 600 nm and the absorbance Abs 0} before the endurance test satisfy the following relationship. Abs ₂₄₀ / Abs _0> 1.00 which represents a polarizing film of the embodiment of the present invention having absorption in the vicinity of 600nm PVA-I ₅ ^- complexes will not be damaged even in the heated humidification durability test, but also increase. PVA-I ₅ ^- complexes will be destroyed at high temperature and high-humidity environment, and the expected polarization of the polarized film typically decreases at high temperature and high-humidity environment, but the durability of the polarizing film is excellent in the above-described embodiment of the present invention It is unpredictable and excellent. Abs ₂₄₀ /Abs _{0 is} preferably 1.05 or more, more preferably 1.10 or more, more preferably 1.15 or more, particularly preferably 1.20 or more, particularly preferably 1.25 or more. The upper limit of Abs ₂₄₀ /Abs ₀ can be, for example, 2.00. _{In addition, the Abs 0} of the polarizing film at a wavelength of 600 nm is, for example, less than 5.0, preferably 4.3 or less, and more preferably 4.0 or less. The lower limit of Abs ₀ may be 2.0, for example.

The thickness of the polarizing film is preferably 8 µm or less, preferably 7 µm or less, more preferably 5 µm or less, and particularly preferably 3 µm or less. The lower limit of the thickness of the polarizing film may be 1 μm in one embodiment, and may be 2 μm in another embodiment. The thickness can be achieved by producing a polarizing film using, for example, a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate by coating, as described later. When the polarizing film is made from a single resin film, the thickness of the polarizing film can be, for example, 12µm~35µm.

The polarizing film should exhibit absorption dichroism at any wavelength from 380nm to 780nm. The monomer transmittance of the polarizing film is preferably 42.0% or more, more preferably 42.5% or more, more preferably 43.0% or more, particularly preferably 43.5% or more, particularly preferably 44.0% or more. On the other hand, the transmittance of the monomer is preferably 47.0% or less, and more preferably 46.0% or less. The degree of polarization of the polarizing film is preferably over 99.95%, more preferably over 99.99%. On the other hand, the degree of polarization is preferably 99.998% or less. According to the embodiment of the present invention, it is possible to achieve both high monomer transmittance and high polarization degree, and as described above, it is possible to achieve excellent durability in a high temperature and high humidity environment. The above monomer transmittance represents the Y value obtained by measuring and calibrating the visual sensitivity using an ultraviolet-visible spectrophotometer. In addition, 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 degree of polarization is representatively calculated based on the parallel transmittance Tp and the orthogonal transmittance Tc obtained by measuring with an ultraviolet-visible light spectrophotometer and performing visual sensitivity correction, using the following equations. Polarization (%)={(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

In one embodiment, the transmittance (single transmittance) of a thin polarizing film of 8 µm or less represents a combination of a polarizing film (surface refractive index: 1.53) and a protective layer (protective film) (refractive index: 1.50) The body is the object of measurement, and it is measured using an ultraviolet-visible spectrophotometer. Depending on the refractive index of the polarizing film surface and/or the refractive index of the surface of the protective layer in contact with the air interface, the reflectance at the interface of each layer will vary, and as a result, the measured value of the transmittance will change. Therefore, for example, when a protective layer with a refractive index other than 1.50 is used, the measured value of transmittance can also be corrected according to the refractive index of the surface of the protective layer in contact with the air interface. _{Specifically, the transmittance correction value C uses the reflectance R 1} (transmission axis reflectance) of polarized light parallel to the transmission axis on the interface between the protective layer 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 /(n ₁ +1) ² )×(T ₁ /100) Here, R ₀ is the reflectance of the transmission axis when a protective layer with a refractive index of 1.50 is used, n ₁ is the refractive index of the protective layer used, and T ₁ is the transmission of the polarizing film rate. For example, when a substrate with a surface refractive index of 1.53 (a cycloolefin-based film, a film with a hard coat layer, etc.) is used as a protective layer, the correction amount C is about 0.2%. At this time, 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 layer with a surface refractive index of 1.50 is used. In addition, after calculating according to the above formula, _{the change amount of the correction value C after changing the transmittance T 1 of the} polarizing film by 2% is 0.03% or less, so the influence of the transmittance of the polarizing film on the value of the correction value C is limited. In addition, when the protective layer has absorption other than surface reflection, it can be appropriately corrected according to the amount of absorption.

The polarizing film can be made of a single resin film, or a laminate of two or more layers. Specific examples of the polarizing film obtained using the laminate include a polarizing film obtained 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 laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate by coating can be produced by, for example, applying a PVA-based resin solution to the resin substrate, and It is dried to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; and the laminate is stretched and dyed to form the PVA-based resin layer into a polarizing film. In the embodiment of the present invention, the polarizing film is brought into contact with a treatment solution whose pH is below 3.0. Thereby, the above-mentioned excellent durability under high temperature and high humidity environment can be realized. It is suitable to form a polyvinyl alcohol resin layer containing halide and polyvinyl alcohol resin on one side of the resin substrate. Stretching typically includes immersing the laminate in a boric acid aqueous solution and stretching. 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. In addition, in this embodiment, it is preferable that the laminated system is subjected to a drying shrinkage treatment in which it is heated while being transported in the longitudinal direction to shrink it by 2% or more in the width direction. Representatively, the manufacturing method of this embodiment includes sequentially performing aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment on the laminate. 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, at the same time, the orientation of PVA can be improved in advance to prevent problems such as degradation or dissolution of the orientation of PVA when immersed in water in the subsequent dyeing step or stretching step, and high optical properties can be achieved. In addition, 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 orientation disorder of the polyvinyl alcohol molecules and the decrease in orientation. Therefore, it is possible to improve the optical properties of the polarizing film obtained by the treatment step of immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment. In addition, by drying and shrinking the laminate in the width direction, the optical properties can be improved. The obtained resin substrate/polarizing film laminate can be used directly (that is, the resin substrate can also 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 then peeled off. Lay any appropriate protective layer according to the purpose and use it later. The detailed content of the manufacturing method of the polarizing film will be explained in item C.

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 based on the polarizing film of the present invention described in item A above. It is also possible to omit one of the first protective layer 20 and the second protective layer 30. In addition, as described above, one of the first protective layer and the second protective layer may be a resin substrate used for the production of the above-mentioned polarizing film.

The first and second protective films are formed of any suitable film that can be used as a protective layer of a polarizing film. Specific examples of the material that becomes the main component of the film include cellulose resins such as cellulose triacetate (TAC), polyesters, polyvinyl alcohols, polycarbonates, polyamides, and polyamides. Transparent resins such as imine-based, polyether-based, poly-based, polystyrene, polynorbornene, polyolefin, (meth)acrylic, and acetate-based transparent resins, etc. In addition, thermosetting resins such as (meth)acrylic, urethane, (meth)acrylate urethane, epoxy, and silicone resins, or ultraviolet curable resins, etc. may also be mentioned. Other examples include glassy polymers such as silicone polymers. In addition, the polymer film described in JP 2001-343529 A (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 iminium 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, for example, Examples include resin compositions having alternating copolymers composed of isobutylene and N-methylmaleimide and acrylonitrile-styrene copolymers. 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 300 μm or less, preferably 100 μm or less, more preferably 5 μm to 80 μm, and more It should be 10μm~60μm. In addition, when the surface treatment is applied, the thickness of the outer protective layer includes 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 any 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 in which the in-plane refractive index is the largest (that is, the slow axis direction), and "ny" is the refractive index in the direction orthogonal to the slow axis in the plane (that is, the fast axis direction) , "Nz" is the refractive index in the thickness direction, and "d" is the thickness (nm) of the layer (film).

C. Manufacturing method of polarizing film The manufacturing method of the polarizing film of one embodiment of the present invention includes the following steps: apply a PVA-based resin solution on one side of a long-shaped thermoplastic resin substrate and dry to form a PVA-based resin layer to form a laminate; Body extension and dyeing to make the PVA-based resin layer into a polarizing film; and, contacting the polarizing film with a treatment solution with a pH below 3.0. By contacting the polarizing film with a treatment solution with a pH below 3.0, a polarizing film with excellent durability under high temperature and high humidity environments can be realized. Preferably, the PVA-based resin solution further contains a halide. Preferably, the above-mentioned manufacturing method includes the following steps: sequentially performing aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment on the layered body, and the drying and shrinking treatment system heats the layered body while conveying the layered body in the longitudinal direction. , Thereby making it shrink by more than 2% in the width direction. The halide content in the PVA-based resin solution (the PVA-based resin layer as a result) is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage should be treated with a heating roller, and the temperature of the heating roller should be 60°C~120°C. The shrinkage in the width direction of the laminate after drying and shrinking is preferably 2% or more. According to the manufacturing method, the polarizing film described in the above item A can be obtained. In particular, a polarizing film with excellent optical properties (representatively, monomer transmittance and unit polarization) can be obtained by the following method: After making a laminate containing a PVA-based resin layer containing a halide, the laminate The stretching performs multi-stage stretching including aerial auxiliary stretching and underwater stretching, and then the stretched laminate is heated by heating rollers.

C-1. Making multilayer body Any appropriate method can be adopted as a method of producing a laminate of a thermoplastic resin base material and a PVA-based resin layer. Preferably, a coating solution containing halide and PVA-based resin is applied to the surface of the thermoplastic resin substrate and dried, thereby forming a PVA-based resin layer on the thermoplastic resin substrate. As mentioned above, the halide content in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

Any appropriate method can be adopted for the coating method of the coating liquid. 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 knife coating method (comma coating method, etc.) etc. are mentioned. The coating and drying temperature of the above-mentioned coating liquid is preferably 50°C or higher.

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

Before forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to surface treatment (for example, corona treatment, etc.), or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By performing 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 As the thermoplastic resin substrate, any appropriate thermoplastic resin film can be used. The details of the thermoplastic resin film substrate are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. In this manual, the entirety of the bulletin is cited as a reference.

C-1-2. Coating liquid The coating liquid system contains a halide and a PVA-based resin as described above. The above-mentioned coating liquid represents a solution obtained by dissolving the above-mentioned halide and the above-mentioned PVA-based resin in a solvent. As the solvent, for example, water, dimethyl sulfide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, trimethylolpropane and other polyols, ethylene oxide Amines such as diamine and diethylenetriamine. 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 it is the resin concentration, a uniform coating film that adheres to the thermoplastic resin substrate can be formed. The halide content in the coating liquid is preferably 5 parts by weight to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

Additives can also 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 glycerol. Examples of the surfactant include nonionic surfactants. These can be used in order to further improve the uniformity, dyeability, and extensibility of the obtained PVA-based resin layer.

Any appropriate resin can be adopted 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 determined in accordance with JIS K 6726-1994. By using the PVA-based resin with the 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.

Any appropriate halide can be used as the above-mentioned halide. Examples include iodide and sodium chloride. Examples of iodides 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 parts by weight to 20 parts by weight relative to 100 parts by weight of the PVA-based resin, and more 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 halide is greater than 20 parts by weight relative to 100 parts by weight of the PVA-based resin, the halide may overflow and the resulting polarizing film may become cloudy.

Generally speaking, the extension of the PVA-based resin layer will increase the orientation of the polyvinyl alcohol molecules in the PVA resin layer. However, if the extended PVA-based resin layer is immersed in a water-containing liquid, there will be polyethylene A situation where the orientation of the alcohol molecules is disordered and the orientation is reduced. Especially when the laminate of thermoplastic resin and PVA-based resin layer is stretched in boric acid water, in order to stabilize the elongation of the thermoplastic resin, when the laminate is stretched in boric acid water at a relatively high temperature, the degree of orientation tends to decrease It's remarkable. For example, the extension of the PVA film monomer in boric acid water is generally performed at 60°C. In contrast, the extension of the laminate of A-PET (thermoplastic resin substrate) and PVA-based resin layer is performed at 70°C. The temperature before and after is performed at a higher temperature. At this time, the orientation of the PVA at the beginning of the extension will decrease in the stage before it rises due to the extension in the water. In this regard, by making a laminate of a halide-containing PVA-based resin layer and a thermoplastic resin substrate, and stretching the laminate in the air at a high temperature before stretching in boric acid water (assisted extension), the post-assisted extension can be promoted. Crystallization of the PVA resin in the PVA resin layer of the laminate. 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 orientation disorder of the polyvinyl alcohol molecules and the decrease in orientation. Thereby, it is possible to improve the optical properties of the polarizing film obtained by the treatment step of immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment.

C-2. Air auxiliary extension processing Especially in order to obtain high optical properties, a two-stage extension method combining dry extension (auxiliary extension) and extension in boric acid water is selected. Like the two-stage extension method, by introducing the auxiliary extension, the extension can be performed while suppressing the crystallization of the thermoplastic resin substrate, which solves the problem of the extension of the thermoplastic resin substrate due to the excessive crystallization of the thermoplastic resin substrate in the subsequent boric acid extension. , So that the laminate can be stretched at a higher magnification. In addition, when applying PVA-based resin to a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, the coating temperature must be higher than that when PVA-based resin is applied to a general metal roller. Lower, as a result, the crystallization of the PVA-based resin is relatively low and the problem that sufficient optical properties cannot be obtained. In this regard, by introducing auxiliary extension, the crystallinity of the PVA-based resin can be improved even when the PVA-based resin is coated on the thermoplastic resin, and high optical properties can be achieved. In addition, at the same time, the orientation of the PVA-based resin is improved in advance to prevent problems such as the decrease in orientation or dissolution of the PVA-based resin when immersed in water in the subsequent dyeing step or the stretching 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, a method of uniaxial extension by passing the laminated body between rollers with different peripheral speeds) ), but in order to obtain high optical characteristics, 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 in the longitudinal direction and stretched using the difference in peripheral speed between the heating rollers. The air extension process means that the above system includes a zone extension step and a heating roller extension 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 are sequentially performed. In another embodiment, the end of the film is gripped in a tenter stretcher, and the distance between the tenters is expanded in the direction of travel to stretch (the increase in the distance between the tenters is the stretch magnification). At this time, the distance of the tenter in the width direction (vertical to the direction of travel) is set to be arbitrarily close. Preferably, it can be set to a stretch magnification relative to the direction of travel so that the free end stretch is used for approaching. When the free end is extended, it is calculated as the shrinkage rate in the width direction=(1/stretching ratio) ^1/2.

Air assist 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 should be approximately the same as the extension direction of the underwater extension.

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

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

C-3. Insoluble treatment, dyeing treatment and cross-linking treatment If necessary, after the aerial auxiliary extension treatment and before the underwater extension treatment or dyeing treatment, an insolubilization treatment is performed. The above-mentioned insolubilization treatment means that the PVA-based resin layer is immersed in an aqueous boric acid solution. The dyeing process described above is performed by dyeing the PVA-based resin layer with a dichroic substance (iodine in representative). If necessary, a cross-linking treatment is performed after the dyeing treatment and before the water extension treatment. The above-mentioned crosslinking treatment can typically be performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The details of the insolubilization treatment, the dyeing treatment, and the cross-linking treatment are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580 (mentioned above).

C-4. Water extension 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 thermoplastic resin substrate or PVA resin layer (typically around 80°C), and can suppress the crystallization of the PVA resin layer at the same time Perform high-magnification extension. As a result, a polarizing film with excellent optical properties can be produced.

Any 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). Preferably, the free end extension is selected. The extension of the laminated body can be carried out in one stage or in multiple stages. When it is carried out 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 tension during stretching and water resistance that is insoluble in water. Specifically, boric acid generates tetrahydroxyborate anions in an aqueous solution and 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 the PVA-based resin layer can be stretched well, thereby producing a polarizing film with excellent optical properties.

The above-mentioned boric acid aqueous solution is preferably obtained by dissolving boric acid and/or borate in water which is 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 produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, etc. in a solvent can also be used.

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

The extension temperature (liquid 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, it can be stretched at a high rate. Specifically, as described above, in relation to the formation of 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 it is considered that the thermoplastic resin base material is plasticized with water, it may not 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 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 stretching magnification performed in water stretching is preferably 1.5 times or more, preferably 3.0 times or more. The total extension ratio of the laminate is preferably 5.0 times or more, and more preferably 5.5 times or more relative to the original length of the laminate. By achieving the high stretching magnification, a polarizing film with extremely excellent optical properties can be manufactured. The high stretch magnification can be achieved by using an underwater stretch method (boric acid stretch in water).

C-5. Drying shrinkage treatment The above-mentioned drying and shrinking treatment may be performed by heating the area by heating the entire area, or may be performed by heating the conveying roller (so-called heating roller) (heat roller drying method). It is preferable to use both. By using a heating roller to dry it, heating and curling of the laminate can be effectively suppressed, and a polarizing film with excellent appearance can be produced. Specifically, by drying the laminate in a state where the laminate is moved along the heating roller, the crystallization of the thermoplastic resin substrate can be efficiently promoted and the degree of crystallinity can be increased, even at a relatively low drying temperature. It can still increase the crystallinity of the thermoplastic resin substrate. As a result, the rigidity of the thermoplastic resin base material is increased and the PVA-based resin layer can withstand the shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. In addition, by using a heating roller, the layered body can be dried while maintaining a flat state. Therefore, not only can the generation of curls be suppressed, but also the generation of wrinkles can be suppressed. At this time, the laminated body can be shrunk in the width direction through a drying shrinkage treatment to improve optical properties. It is because it can effectively improve the orientation of PVA and PVA/iodine complexes. The shrinkage rate of the laminate in the width direction obtained by drying and shrinking is preferably 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 and shrinking treatment, the layered body 200 is dried while being conveyed by the conveying rollers R1 to R6 and the guide rollers G1 to G4 heated to a predetermined temperature. In the example of the figure, the conveying rollers R1 to R6 are arranged to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but for example, the conveying rollers R1 to R6 may be arranged to only continuously heat the laminate 200 One side (such as the thermoplastic resin substrate side).

By adjusting the heating temperature of the conveying roller (temperature of the heating roller), the number of heating rollers and the contact time with the heating roller, etc., the drying conditions can be controlled. The temperature of the heating roller is preferably 60℃~120℃, more preferably 65℃~100℃, especially 70℃~80℃. The degree of crystallinity of the thermoplastic resin can be increased well and curling can be well suppressed, and an optical laminate with extremely excellent durability can be produced. In addition, the temperature of the heating roller can be measured with a contact thermometer. In the example of the drawing, there are 6 conveying rollers, but there is no particular limitation as long as there are a plurality of conveying rollers. The number of conveying rollers is usually 2-40, preferably 4-30. 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 suitable to be installed in a heating furnace with an air supply mechanism. By combining drying with heating rollers and hot air drying, sudden temperature changes between the heating rollers can be suppressed, and the shrinkage in the width direction can be easily controlled. The temperature of hot air drying should be 30℃~100℃. Moreover, 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 by a mini fan blade type digital anemometer.

C-6. Contact with treatment liquid In the above manner, a laminate of a thermoplastic resin substrate and a polarizing film can be obtained. In the embodiment of the present invention, the polarizing film is brought into contact with a treatment solution whose pH is below 3.0. In one embodiment, by directly contacting the layered body with the processing liquid, the polarizing film can be brought into contact with the processing liquid. At this time, it means that the thermoplastic resin substrate can be directly used as the protective layer of the polarizing film. Alternatively, a resin film (to become a protective layer) can be bonded to the surface of the polarizing film of the laminate that is in contact with the treatment liquid to produce a laminate of protective layer/polarizing film/thermoplastic resin substrate, and the thermoplastic resin may be peeled from the laminate Base material to produce a polarizing plate with a protective layer/polarizing film composition. In another embodiment, a resin film (which becomes a protective layer) is attached to the surface of the polarizing film of the laminate to produce a laminate of protective layer/polarizing film/thermoplastic resin substrate, and the thermoplastic resin substrate is peeled from the laminate , And produced a protective layer/polarizing film laminate (polarizing plate). By bringing the obtained polarizing plate into contact with the processing liquid, the polarizing film can be brought into contact with the processing liquid.

The contact between the polarizing film and the treatment liquid can be performed by any appropriate method. Representative examples include applying a treatment liquid to a polarizing film, and immersing a polarizing film (substantially a laminate or a polarizing plate) in the treatment liquid. Any appropriate method can be adopted as the coating method. Specific examples include the method described in the section C-1 as the coating method of the coating liquid. The impregnation can also be performed in any appropriate manner. For example, the treatment liquid may be added to the washing bath of the washing treatment, a bath of the treatment liquid may be used instead of the washing bath, or a bath of the treatment liquid may be provided separately from the washing bath. In addition, the washing treatment is typically carried out after the underwater stretching treatment and before the drying shrinkage treatment. In addition, when the treatment liquid bath is set, the treatment liquid bath can be set between the washing bath and the drying shrinkage treatment equipment (that is, the contact with the treatment liquid can also be carried out between the washing treatment and the drying shrinkage treatment). It can be installed downstream of the mechanism for peeling the thermoplastic resin substrate (that is, contact with the treatment liquid may be performed after peeling the thermoplastic resin substrate).

Any appropriate acidic liquid can be used as long as the pH of the treatment liquid is below 3.0. Specific examples of the treatment liquid include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and citric acid. The treatment liquid is preferably a strong acid aqueous solution. Specific examples of strong acids include hydrochloric acid, sulfuric acid, and nitric acid. The lower the pH of the treatment solution (the stronger the acidity), the better. Specifically, the pH is preferably 2.7 or less, more preferably 2.5 or less, more preferably 2.0 or less, and particularly preferably 1.5 or less.

The acid concentration of the treatment liquid is preferably 0.02% by weight to 3.0% by weight, more preferably 0.04% by weight to 2.0% by weight, and more preferably 0.1% by weight to 1.0% by weight.

The treatment liquid may also contain water-soluble resin (for example, PVA-based resin). Water-soluble resin can function as a binder. The concentration of the water-soluble resin in the treatment solution is preferably 3% by weight to 5% by weight. In this case, the treatment layer can be formed by coating and drying the treatment liquid. By forming the treatment layer, a polarizing film having the aforementioned desired durability can also be obtained. The thickness of the treatment layer should be less than 1.7µm, more preferably 0.2µm~1.4µm.

After contacting with the treatment liquid, it can be dried as required. The drying temperature is preferably 40°C to 90°C, more preferably 50°C to 70°C.

C-7. Modifications Sections C-1 to C-6 describe the manufacturing method of a laminate using a resin substrate and a PVA-based resin layer formed on the resin substrate. However, the present invention can also be applied to the use of a single PVA-based resin The manufacturing method of the film. The manufacturing method typically includes the following steps: using a roll stretcher to uniaxially stretch a long PVA-based resin film in the longitudinal direction, simultaneously perform swelling, dyeing, crosslinking, and washing treatments, and finally perform a drying treatment. The contact with the treatment liquid can typically be performed by immersing in a washing bath to which the treatment liquid is added, immersing in a treatment bath after the washing treatment, or applying the treatment liquid after the washing treatment. 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, as long as there is no special note, the "parts" and "%" in the examples and comparative examples are the basis of 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 and orthogonal absorbance For the polarizing plates (protective layer/polarizing film) of the examples and comparative examples, the ultraviolet-visible light spectrophotometer (LPF-200 manufactured by Otsuka Electronics) was used to measure, and the measured single The volume transmittance Ts, the parallel transmittance Tp, and the orthogonal transmittance Tc are respectively used as the Ts, Tp, and Tc of the polarizing film. These Ts, Tp, and Tc are Y values obtained by measuring and calibrating the visual sensitivity 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 opposite side of the protective film is 1.53. In addition, using the Tc measured at each wavelength, the orthogonal absorbance was obtained by the following formula. Orthogonal absorbance = log10 (100/Tc) Using "LPF-200" manufactured by Otsuka Electronics Co., Ltd., the orthogonal absorbance Abs _{0 was} determined from the orthogonal transmittance Tc at a measurement wavelength of 470 nm. In addition, for Abs ₀ , the same measurement can be performed using JASCO Corporation "V-7100" or the like. Next, the polarizing plate was subjected to an endurance test at a temperature of 60° C. and a relative humidity of 95% for 240 hours. _{Obtain the orthogonal absorbance Abs 240} after the endurance test in the same manner as above.

[Example 1] As the thermoplastic resin substrate, an amorphous isophthalic acid copolymer polyethylene terephthalate film (thickness: 100 μm) with a water absorption rate of 0.75% and a Tg of about 75° C. was used. And apply corona treatment to one side of the resin substrate (treatment condition: 55W·min/m ² ). In a 9:1 mixture of 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"). To 100 parts by weight of resin, 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., thereby forming a PVA-based resin layer with a thickness of 20 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 of different peripheral speeds in an oven at 130°C (air-assisted 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 respect to 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insoluble treatment). Next, adjust the concentration of the dyeing bath (an iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30°C, so that the monomers of the polarizing plate obtained finally are transmitted The rate (Ts) became 44.0%, and it was immersed in it for 60 seconds (dyeing treatment). Next, it was immersed in a cross-linking 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 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, potassium iodide 5% by weight) at a liquid temperature of 70°C, uniaxially stretched in the longitudinal direction (longitudinal direction) between rollers with different peripheral speeds In order to make the total extension ratio up to 5.5 times (extension treatment in water). After that, the layered body was immersed in a washing bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water, pH=6) at a liquid temperature of 20°C (washing treatment). After that, while drying in an oven maintained at 90°C, the contact surface temperature was maintained at 75°C with a heating roller made of SUS for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction obtained by the drying shrinkage treatment is 2%. According to the above method, a polarizing film with a thickness of 5.0 µm is formed on the resin substrate, and a cycloolefin-based film (Zeon Co., Ltd.) is laminated as a protective layer (protective film) through a UV curable adhesive (thickness 1.0 µm) on the surface of the polarizing film. Manufacture, product name "G-Film"), and then peel off the resin substrate to obtain a laminate with a protective layer/polarizing film composition. The monomer transmittance (Ts) of the resulting laminate is 44.0%, which is because the surface refractive index of the polarizing film/protective layer constituting the laminate is 1.53/1.53, so the actual measurement value +0.2% is corrected and converted into The value of the state of 1.53/1.50. Next, 0.3% by weight of hydrochloric acid and 3.5% by weight of PVA (JC-25) are dissolved in water to obtain a treatment solution (pH=1.3) and applied to the surface of the polarizing film of the laminate so that the thickness becomes 0.6um , Dried at 60°C for 4 minutes to form a treated layer. In the above manner, the polarizing plate of this embodiment is obtained.

For the obtained polarizing plate (essentially a polarizing film), Table 1 shows the monomer transmittance and Abs ₂₄₀ /Abs ₀ .

[Examples 2~10] The monomer transmittance of the polarizing film, the method of contact with the treatment liquid, the pH of the treatment liquid, the type of acid contained in the treatment liquid, and the thickness of the treatment layer were adjusted to the values shown in Table 1 to produce polarized light. board. For the obtained polarizing plate (essentially a polarizing film), Table 1 shows the monomer transmittance and Abs ₂₄₀ /Abs ₀ .

[Example 11] A polarizing plate was produced in the same manner as in Example 1, except that the treatment liquid was not made to contain the PVA-based resin (that is, the treatment layer was not formed) and the pH of the treatment liquid was set to 0.9. For the obtained polarizing plate (essentially a polarizing film), Table 1 shows the monomer transmittance and Abs ₂₄₀ /Abs ₀ .

[Example 12] In the same manner as in Example 1, the laminate of the thermoplastic resin substrate/PVA-based resin layer was subjected to aerial auxiliary stretching treatment, insolubilization treatment, dyeing treatment, cross-linking treatment, and underwater stretching treatment. The layered body after the water extension treatment is immersed in a treatment bath (pH=1.6) with a liquid temperature of 20°C (in contact with the treatment liquid). In addition, the treatment liquid was prepared by adding hydrochloric acid to a general washing bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water). After that, while drying in an oven maintained at 90°C, the contact surface temperature was maintained at 75°C with a heating roller made of SUS for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction obtained by the drying shrinkage treatment is 2%. Next, a protective layer (protective film) of cycloolefin-based film (manufactured by ZEON, product name "G-Film") is pasted on the surface of the polarizing film through a UV curable adhesive (thickness 1.0μm), and then the resin substrate is peeled off A polarizing plate with a protective layer/polarizing film composition is obtained. For the obtained polarizing plate (essentially a polarizing film), Table 1 shows the monomer transmittance and Abs ₂₄₀ /Abs ₀ .

[Comparative Example 1] A polarizing plate was produced in the same manner as in Example 1, except that the contact with the treatment liquid was not performed. For the obtained polarizing plate (essentially a polarizing film), Table 1 shows the monomer transmittance and Abs ₂₄₀ /Abs ₀ .

[Comparative Example 2] A polarizing plate was produced in the same manner as in Comparative Example 1 except that the single transmittance of the polarizing film was 45.0%. For the obtained polarizing plate (essentially a polarizing film), Table 1 shows the monomer transmittance and Abs ₂₄₀ /Abs ₀ .

<Comparative Examples 3-8> The monomer transmittance of the polarizing film, the method of contact with the treatment liquid, the pH of the treatment liquid, the type of acid contained in the treatment liquid, and the thickness of the treatment layer (when formed) are adjusted to Table 1 The polarizing plate is made as shown. For the obtained polarizing plate (essentially a polarizing film), Table 1 shows the monomer transmittance and Abs ₂₄₀ /Abs ₀ .

[Example 13] A long roll of PVA-based resin film (manufactured by Nippon Gosei Co., Ltd., product name "PS7500") with a thickness of 55 μm was uniaxially stretched in the longitudinal direction using a roll stretcher to achieve a total stretch ratio of 6.0 times , Simultaneously apply swelling, dyeing, cross-linking and washing treatments, and finally apply drying treatment to produce a polarizing film with a thickness of 23μm. After the washing treatment and before the drying treatment, the same treatment solution as in Example 1 was applied to one side of the PVA-based resin film (polarizing film) in the same manner as in Example 1. For the obtained polarizing film, the monomer transmittance and Abs ₂₄₀ /Abs _{0 are} shown in Table 1.

[Example 14] In place of the washing bath of the washing treatment, the PVA-based resin film (polarizing film) was passed through the same treatment bath as in Example 12 (therefore, the treatment liquid was not applied after the washing treatment), except that In the same manner as in Example 13, a polarizing film with a thickness of 23 µm was fabricated. For the obtained polarizing film, the monomer transmittance and Abs ₂₄₀ /Abs _{0 are} shown in Table 1.

[Table 1]

_{It is obvious from Table 1 that the Abs 240} /Abs ₀ of the polarizing film of the embodiment of the present invention after the endurance test is greater than 0.90, and the degradation of the polarization performance in the high temperature and high humidity environment is suppressed. That is, the polarizing film of the embodiment of the present invention has excellent durability in a high temperature and high humidity environment. _{In particular, the Abs 240} /Abs ₀ of the polarizing film of Example 10 is greater than 1.0, and the polarization property is improved in a high temperature and high humidity environment. This is an excellent effect that is different from technical common sense and cannot be expected. _{The Abs 240} /Abs ₀ of the polarizing films of Comparative Examples 1 and 2 that were not in contact with the treatment liquid, and the polarizing films of Comparative Examples 3 to 8 that were in contact with the treatment liquid with a pH greater than 3.0 were all less than 0.88. In addition, in Comparative Example 6 using boric acid as the treatment solution, the treatment solution gelled and could not be contacted.

Industrial availability The polarizing film and polarizing plate of the present invention can be suitably used in a liquid crystal display device.

10: Polarizing film 20: The first protective layer 30: The second protective layer 100: Polarizing plate 200: layered 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.

10: Polarizing film

20: The first protective layer

30: The second protective layer

100: Polarizing plate

Claims (12)

A polarizing film composed of a polyvinyl alcohol resin film containing iodine; and after a 240-hour endurance test at a temperature of 60°C and a relative humidity of 95%, the absorbance Abs ₂₄₀ at a wavelength of 470nm is relative to the endurance test The former absorbance Abs ₀ satisfies the following relationship: Abs ₂₄₀ /Abs ₀ > 0.90. For example, the polarizing film of claim 1 has a single transmittance of 43.0% or more. For example, the polarizing film of claim 1 or 2 has a thickness of 8 μm or less. A polarizing plate having the polarizing film as claimed in any one of claims 1 to 3 and a protective layer arranged on at least one side of the polarizing film. A method for manufacturing a polarizing film is a method for manufacturing a polarizing film as claimed in any one of Claims 1 to 3. The manufacturing method includes the following steps: Form a polyvinyl alcohol-based resin layer on one side of the elongated thermoplastic resin substrate to form a laminate; Extending and dyeing the laminated body to make the polyvinyl alcohol-based resin layer into a polarizing film; and The polarizing film is brought into contact with a treatment solution with a pH below 3.0. The manufacturing method of claim 5, which comprises: coating the treatment liquid on the polarizing film. The manufacturing method of claim 5, which comprises: immersing the polarizing film in the treatment liquid. The manufacturing method according to any one of claims 5 to 7, wherein a polyvinyl alcohol-based resin layer containing iodide or sodium chloride and a polyvinyl alcohol-based resin is formed on one side of the thermoplastic resin substrate. For example, the manufacturing method of claim 8, which includes the steps of sequentially performing aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment on the laminate body, and the drying shrinkage treatment is to extend the laminate body along the long sides. It is heated while conveying in the direction to shrink the width by more than 2%. The manufacturing method of claim 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. A method of manufacturing a polarizing film is a method of manufacturing the polarizing film of claim 1 or 2, and the manufacturing method includes the following steps: Stretching and dyeing the polyvinyl alcohol-based resin film to make the polyvinyl alcohol-based resin film into a polarizing film; and The polarizing film is brought into contact with a treatment solution with a pH below 3.0.

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