WO2020261778A1 - 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°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

A polarizing film, a polarizing plate, and a method for manufacturing the polarizing film.

The present invention relates to a polarizing film, a polarizing plate, and a method for producing the polarizing film.

A liquid crystal display device, which is a typical image display device, has polarizing films arranged on both sides of the liquid crystal cell due to the image forming method. As a method for producing a polarizing film, for example, a method in which a laminate having a resin base material and a polyvinyl alcohol (PVA) -based resin layer is stretched and then dyed to obtain a polarizing film on the resin base material is used. It has been proposed (for example, Patent Document 1). According to such a method, a thin polarizing film can be obtained, which is attracting attention as it can contribute to the thinning of image display devices in recent years. However, the thin polarizing film is required to have further improved durability in a high temperature and high humidity environment.

Japanese Unexamined Patent Publication No. 2001-343521

The present invention has been made to solve the above-mentioned conventional problems, and a main object thereof is to obtain a polarizing film, a polarizing plate, and a method for producing such a polarizing film, which are excellent in durability in a high temperature and high humidity environment. To provide.

The polarizing film of the present invention is composed of a polyvinyl alcohol-based resin film containing iodine, and the absorbance Abs _{240 at} a wavelength of 470 nm after a durability test at a temperature of 60 ° C. and a relative humidity of 95% for 240 hours is the absorbance Abs before the durability test. _A polarizing film that satisfies the following relationship with respect to ₀ :
Abs ₂₄₀ / Abs ₀ > 0.90
In one embodiment, the polarizing film has a simple substance transmittance of 43.0% or more.
In one embodiment, the polarizing film has a thickness of 8 μm or less.
According to another aspect of the present invention, a polarizing plate is provided. This 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, there is provided a method for producing the above-mentioned polarizing film. In this method, a polyvinyl alcohol-based resin layer is formed on one side of a long thermoplastic resin base material to form a laminate; the laminate is stretched and dyed, and the polyvinyl alcohol-based resin layer is made into a polarizing film. And contacting the polarizing film with a treatment liquid having a pH of 3.0 or less;
In one embodiment, the manufacturing method comprises applying the treatment liquid to the polarizing film. In another embodiment, the manufacturing method comprises immersing the polarizing film in the treatment solution.
In one embodiment, the production method forms a polyvinyl alcohol-based resin layer containing iodide or sodium chloride and a polyvinyl alcohol-based resin on one side of the thermoplastic resin base material.
In one embodiment, the manufacturing method shrinks the laminate by 2% or more in the width direction by heating the laminate while carrying it in the air auxiliary stretching treatment, the dyeing treatment, the underwater stretching treatment, and the longitudinal direction. The drying shrinkage treatment to be carried out is included in this order.
In one embodiment, the drying shrinkage treatment is performed using a heating roll. In this case, the temperature of the heating roll is, for example, 60 ° C to 120 ° C.
Another method for producing a polarizing film of the present invention is to stretch and dye a polyvinyl alcohol-based resin film to obtain the polyvinyl alcohol-based resin film as a polarizing film; and the polarizing film having a pH of 3.0 or less. In contact with the treatment liquid of;

According to the present invention, a polarizing film having excellent durability in a high temperature and high humidity environment can be obtained by bringing the polarizing film into contact with a treatment liquid having a pH of 3.0 or less. Specifically, in the polarizing film according to the embodiment of the present invention, the absorbance Abs _{240 at} a wavelength of 470 nm after a durability test at a temperature of 60 ° C. and a relative humidity of 95% for 240 hours has a absorbance of Abs ₀ before the durability test. Satisfy the following relationships:
Abs ₂₄₀ / Abs ₀ > 0.90
That is, in the polarizing film according to the embodiment of the present invention, the absorbance at a wavelength of 470 nm does not decrease so much even by the heating / humidifying durability test. This means that the polarizing film according to the embodiment of the present invention suppresses the deterioration of the polarizing performance in a high temperature and high humidity environment to a practically acceptable level. The polarization performance of a polarizing film (particularly a thin polarizing film) is usually significantly reduced in a high temperature and high humidity environment. However, according to the embodiment of the present invention, such a problem is solved and the high temperature and high humidity environment is solved. It is possible to provide a polarizing film having excellent durability underneath (particularly, a thin polarizing film).

It is the schematic sectional drawing of the polarizing plate by one Embodiment of this invention. It is the schematic which shows an example of the drying shrinkage treatment using a heating roll.

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

A. Polarizing film The polarizing film according to the embodiment of the present invention is made of a polyvinyl alcohol (PVA) -based resin film containing iodine, and has an absorbance Abs _{240 at} a wavelength of 470 nm after a durability test at a temperature of 60 ° C. and a relative humidity of 95% for 240 hours. , The following relationship is satisfied with respect to the absorbance Abs ₀ before the durability test.
Abs ₂₄₀ / Abs ₀ > 0.90
This indicates that in the polarizing film according to the embodiment of the present invention, the destruction of the PVA-I ₃ ^- complex having absorption in the vicinity of 470 nm due to the heating / humidifying durability test is suppressed. Although not theoretically clear, such excellent durability can be achieved by bringing the polarizing film into contact with a treatment liquid having a pH of 3.0 or less. Abs ₂₄₀ / Abs ₀ is preferably 0.92 or more, more preferably 0.93 or more, and further preferably 0.95 or more. The upper limit of Abs ₂₄₀ / Abs ₀ can be, for example, 1.50. The absorbance is typically orthogonal absorbance. The orthogonal absorbance is calculated by the following formula based on the orthogonal transmittance Tc measured when determining the degree of polarization described later.
Orthogonal absorbance = log10 (100 / Tc)
Incidentally, the absorbance Abs ₀ before the durability test is the absorbance at the polarizing film normal conditions, Abs ₀ of the polarizing film at a wavelength of 470nm is less than for example 5.0, preferably 3.0 or less, more preferably Is less than or equal to 2.2. The lower limit of Abs ₀ can be, for example, 1.0.

In one embodiment, the polarizing film has the following relationship in that the absorbance Abs _{240 at} a wavelength of 600 nm after a durability test at a temperature of 60 ° C. and a relative humidity of 95% for 240 hours has the following relationship with respect to the absorbance Abs ₀ before the durability test. I am satisfied.
Abs ₂₄₀ / Abs ₀ > 1.00
This indicates that in the polarizing film according to the embodiment of the present invention, the PVA-I ₅ ^- complex having absorption near 600 nm is not destroyed even in the heating / humidifying durability test, but rather can be increased. The PVA-I ₅ ^- complex is destroyed in a high temperature and high humidity environment, and the polarization performance of the polarizing film is usually expected to decrease in a high temperature and high humidity environment. However, such an excellent polarizing film according to the embodiment of the present invention is used. Durability is unexpectedly excellent. Abs ₂₄₀ / Abs ₀ is preferably 1.05 or more, more preferably 1.10 or more, still more preferably 1.15 or more, particularly preferably 1.20 or more, and particularly preferably 1 It is .25 or more. The upper limit of Abs ₂₄₀ / Abs ₀ can be, for example, 2.00. 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 can be, for example, 2.0.

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

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The simple substance transmittance of the polarizing film is preferably 42.0% or more, more preferably 42.5% or more, further preferably 43.0% or more, and particularly preferably 43.5% or more. , Especially preferably 44.0% or more. On the other hand, the simple substance transmittance is preferably 47.0% or less, and more preferably 46.0% or less. The degree of polarization of the polarizing film is preferably 99.95% or more, and more preferably 99.99% or more. 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 a high single transmittance and a high degree of polarization as described above, and to realize excellent durability in a high temperature and high humidity environment as described above. it can. The simple substance transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and corrected for luminosity factor. The single transmittance is a value 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 degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured with an ultraviolet-visible spectrophotometer and corrected for luminosity factor.
Polarization degree (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 x 100

In one embodiment, the transmittance (single transmittance) of a thin polarizing film of 8 μm or less is typically a polarizing film (refractive index of the surface: 1.53) and a protective layer (protective film) (refraction). The laminate with the rate: 1.50) is measured using an ultraviolet-visible spectrophotometer. Depending on the refractive index of the surface of the polarizing film and / or the refractive index of the surface of the protective layer in contact with the air interface, the reflectance at the interface of each layer may change, and as a result, the measured value of transmittance may change. .. Therefore, for example, when a protective layer having a refractive index of not 1.50 is used, the measured value of the transmittance may be corrected according to the refractive index of the surface of the protective layer in contact with the air interface. Specifically, the correction value C of the transmittance with reflectance R _{1 (transmission} axis reflectance) of light polarized parallel to the transmission axis at the interface between the protective layer and the air layer is expressed by the following equation.
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 transmittance of the transmission axis when a protective layer having a refractive index of 1.50 is used, n ₁ is the refractive index of the protective layer to be used, and T ₁ is the transmittance of the polarizing film. Is. For example, when a base material having a surface refractive index of 1.53 (cycloolefin film, film with a hard coat layer, etc.) is used as the protective layer, the correction amount C is about 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, the transmittance when a polarizing film having a surface refractive index of 1.53 is used and a protective layer having a refractive index of 1.50 is used. It can be converted into a rate. According to the calculation based on the above formula, the amount of change in the correction value C when the transmittance T _{1 of the} polarizing film is changed by 2% is 0.03% or less, and the transmittance of the polarizing film is the correction value C. The effect on the value of is limited. Further, when the protective layer has absorption other than surface reflection, appropriate correction can be performed according to the amount of absorption.

The polarizing film may be produced by using a single resin film, or may be produced by using a laminate of two or more layers. Specific examples of the polarizing film obtained by using the laminated body include a polarizing film obtained by using a laminated body of a resin base material and a PVA-based resin layer coated and formed on the resin base material. The polarizing film obtained by using the laminate of the resin base material and the PVA-based resin layer coated and formed on the resin base material is, for example, a resin base material obtained by applying a PVA-based resin solution to the resin base material and drying it. It is produced by forming a PVA-based resin layer on the PVA-based resin layer to obtain a laminate of a resin base material and a PVA-based resin layer; stretching and dyeing the laminate to form a PVA-based resin layer as a polarizing film. obtain. In the embodiment of the present invention, the polarizing film is brought into contact with a treatment liquid having a pH of 3.0 or less. As a result, excellent durability in a high temperature and high humidity environment as described above can be realized. Preferably, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of the resin base material. Stretching typically includes immersing the laminate in an aqueous boric acid solution for stretching. Further, stretching may further include, if necessary, stretching the laminate in the air at a high temperature (eg, 95 ° C. or higher) prior to stretching in boric acid aqueous solution. In addition, in the present embodiment, preferably, the laminate is subjected to a drying shrinkage treatment in which the laminate is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction. Typically, the production method of the present embodiment includes subjecting the laminate to an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order. By introducing the auxiliary stretching, even when PVA is coated on the thermoplastic resin, the crystallinity of PVA can be enhanced, and high optical characteristics can be achieved. At the same time, by increasing the orientation of PVA in advance, it is possible to prevent problems such as deterioration of PVA orientation and dissolution when immersed in water in a subsequent dyeing step or stretching step, resulting in high optical characteristics. Will be possible to achieve. Further, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This makes it possible to improve the optical characteristics of the polarizing film obtained through a treatment step of immersing the laminate in a liquid, such as a dyeing treatment and a stretching treatment in water. Further, the optical characteristics can be improved by shrinking the laminated body in the width direction by the drying shrinkage treatment. The obtained laminate of the resin base material / polarizing film may be used as it is (that is, the resin base material may be used as the protective layer of the polarizing film), or the resin base material is peeled off from the laminate of the resin base material / polarizing film. Then, an arbitrary appropriate protective layer according to the purpose may be laminated on the peeled surface. Details of the method for producing the polarizing film will be described later in Section C.

B. Polarizing Plate FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 has a polarizing film 10, a first protective layer 20 arranged on one side of the polarizing film 10, and a second protective layer 30 arranged on the other side of the polarizing film 10. The polarizing film 10 is the polarizing film of the present invention described in the above section A. One of the first protective layer 20 and the second protective layer 30 may be omitted. As described above, one of the first protective layer and the second protective layer may be a resin base material used for producing the above-mentioned polarizing film.

The first and second protective layers are formed of any suitable film that can be used as a protective layer for the polarizing film. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based. , Polystyrene-based, polycarbonate-based, polyolefin-based, (meth) acrylic-based, acetate-based transparent resins and the like. Further, thermosetting resins such as (meth) acrylic, urethane, (meth) acrylic urethane, epoxy, and silicone, or ultraviolet curable resins can also be mentioned. In addition to this, for example, glassy polymers such as siloxane-based polymers can also be mentioned. Further, the polymer film described in JP-A-2001-343529 (WO01 / 37007) can also be used. As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain. Can be used, and examples thereof include a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer. The polymer film can be, for example, an extruded product of the above resin composition.

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 100 μm or less. It is 5 μm to 80 μm, more preferably 10 μm to 60 μm. When the surface treatment is applied, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.

The thickness of the protective layer (inner protective layer) arranged on the display panel side when the polarizing plate 100 is applied to the image display device is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and further preferably 10 μm to 60 μm. is there. In one embodiment, the inner protective layer is a retardation layer with any suitable retardation value. In this case, the in-plane retardation Re (550) of the retardation layer is, for example, 110 nm to 150 nm. “Re (550)” is an in-plane phase difference measured with light having a wavelength of 550 nm at 23 ° C., and is 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 maximized (that is, the slow-phase axis direction), and "ny" is the in-plane direction orthogonal to the slow-phase axis (that is, phase-advance). It is the refractive index in the axial direction), “nz” is the refractive index in the thickness direction, and “d” is the thickness (nm) of the layer (film).

C. Method for producing a polarizing film In the method for producing a polarizing film according to one embodiment of the present invention, a PVA-based resin solution is applied and dried on one side of a long thermoplastic resin base material to form a PVA-based resin layer. It includes forming a laminate; stretching and dyeing the laminate to form a PVA-based resin layer as a polarizing film; and bringing the polarizing film into contact with a treatment liquid having a pH of 3.0 or less. By bringing the polarizing film into contact with a treatment liquid having a pH of 3.0 or less, a polarizing film having excellent durability in a high temperature and high humidity environment can be realized. Preferably, the PVA-based resin solution further comprises a halide. Preferably, the above-mentioned production method comprises an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in which the laminate is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction. Is included in this order. The content of the halide in the PVA-based resin solution (as a result, the PVA-based resin layer) 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 treatment is preferably carried out using a heating roll, and the temperature of the heating roll is preferably 60 ° C. to 120 ° C. The shrinkage ratio in the width direction of the laminated body by the drying shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizing film described in the above item A can be obtained. In particular, by preparing a laminate containing a PVA-based resin layer containing a halide, stretching the laminate to multi-step stretching including aerial auxiliary stretching and underwater stretching, and heating the stretched laminate with a heating roll. , A polarizing film having excellent optical properties (typically, single transmittance and unit absorbance) can be obtained.

C-1. Preparation of Laminate As a method for preparing a laminate of a thermoplastic resin base material and a PVA-based resin layer, any appropriate method can be adopted. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin base material and dried to form a PVA-based resin layer on the thermoplastic resin base material. As described above, the content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

Any appropriate method can be adopted as the application 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.) and the like can be mentioned. The coating / drying temperature of the coating liquid is preferably 50 ° C. or higher.

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

Before forming the PVA-based resin layer, the thermoplastic resin base material may be surface-treated (for example, corona treatment or the like), or the easy-adhesion layer may be formed on the thermoplastic resin base material. By performing such a 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 As the thermoplastic resin base material, any suitable thermoplastic resin film can be adopted. Details of the thermoplastic resin base material are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. The entire description of the publication is incorporated herein by reference.

C-1-2. Coating liquid The coating liquid contains a halide and a PVA-based resin as described above. The coating liquid is typically a solution in which the halide and the PVA-based resin are dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Of these, water is preferred. The PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film that adheres to the thermoplastic resin base material can be formed. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

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

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

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

As the above-mentioned halide, any suitable halide can be adopted. For example, iodide and sodium chloride. Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred.

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

Generally, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin is increased. However, when the stretched PVA-based resin layer is immersed in a liquid containing water, the polyvinyl alcohol molecules become more oriented. The orientation may be disturbed and the orientation may decrease. In particular, when the laminate of the thermoplastic resin and the PVA-based resin layer is stretched in boric acid water, when the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin, The tendency of the degree of orientation to decrease is remarkable. For example, while stretching a PVA film alone in boric acid water is generally performed at 60 ° C., stretching of a laminate of A-PET (thermoplastic resin base material) and a PVA-based resin layer is performed. It is carried out at a high temperature of about 70 ° C., and in this case, the orientation of PVA at the initial stage of stretching may decrease before it is increased by stretching in water. On the other hand, a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin base material is prepared, and the laminate is stretched at a high temperature (auxiliary stretching) in air before being stretched in boric acid water. , Crystallization of the PVA-based resin in the PVA-based resin layer of the laminated body after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This makes it possible to improve the optical characteristics of the polarizing film obtained through a treatment step of immersing the laminate in a liquid, such as a dyeing treatment and a stretching treatment in water.

C-2. Aerial Auxiliary Stretching Treatment In particular, in order to obtain high optical properties, a two-stage stretching method that combines dry stretching (auxiliary stretching) and boric acid water stretching is selected. By introducing the auxiliary stretching as in the two-stage stretching, the thermoplastic resin base material can be stretched while suppressing the crystallization of the thermoplastic resin base material, and the thermoplastic resin base material is excessively crystallized in the subsequent drawing in boric acid in water. This solves the problem that the stretchability is lowered, and the laminated body can be stretched at a higher magnification. Furthermore, when the PVA-based resin is applied on the thermoplastic resin base material, it is compared with the case where the PVA-based resin is applied on a normal metal drum in order to suppress the influence of the glass transition temperature of the thermoplastic resin base material. Therefore, it is necessary to lower the coating temperature, and as a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical characteristics cannot be obtained. On the other hand, by introducing the auxiliary stretching, even when the PVA-based resin is coated on the thermoplastic resin, the crystallinity of the PVA-based resin can be enhanced, and high optical characteristics can be achieved. Become. At the same time, by increasing the orientation of the PVA resin in advance, it is possible to prevent problems such as deterioration and dissolution of the orientation of the PVA resin when immersed in water in a subsequent dyeing step or stretching step. , It becomes possible to achieve high optical characteristics.

The stretching method of the aerial auxiliary stretching may be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Good, but in order to obtain high optical properties, free end stretching can be positively adopted. In one embodiment, the aerial stretching treatment includes a heating roll stretching step of stretching the laminated body in the longitudinal direction due to a difference in peripheral speed between the heating rolls. The aerial stretching treatment typically includes a zone stretching step and a heating roll stretching step. The order of the zone stretching step and the heating roll stretching step is not limited, and the zone stretching step may be performed first, or the heating roll stretching step may be performed first. The zone stretching step may be omitted. In one embodiment, the zone stretching step and the heating roll stretching step are performed in this order. Further, in another embodiment, in the tenter stretching machine, the film is stretched by grasping the end portion of the film and widening the distance between the tenters in the flow direction (the widening of the distance between the tenters is the stretching ratio). At this time, the distance of the tenter in the width direction (perpendicular to the flow direction) is set to approach arbitrarily. Preferably, it can be set to be closer to the free end stretch with respect to the stretch ratio in the flow direction. In the case of free-end stretching, the contraction rate in the width direction = (1 / stretching ratio) ^1/2 .

The aerial auxiliary extension may be performed in one step or in multiple steps. When performed in multiple stages, the draw ratio is the product of the draw ratios of each stage. The stretching direction in the aerial auxiliary stretching is preferably substantially the same as the stretching direction in the underwater stretching.

The draw ratio in the aerial auxiliary stretching is preferably 2.0 to 3.5 times. The maximum draw ratio when the aerial auxiliary stretching and the underwater stretching are combined is preferably 5.0 times or more, more preferably 5.5 times or more, still more preferably 6.0 times, the original length of the laminated body. That is all. In the present specification, the "maximum draw ratio" means the draw ratio immediately before the laminate breaks, and separately confirms the draw ratio at which the laminate breaks, and means a value 0.2 lower than that value.

The stretching temperature of the aerial auxiliary stretching can be set to an arbitrary appropriate value depending on the forming material of the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably the glass transition temperature (Tg) or more of the thermoplastic resin base material, more preferably the glass transition temperature (Tg) of the thermoplastic resin base material (Tg) + 10 ° C. or higher, and particularly preferably Tg + 15 ° C. or higher. On the other hand, the upper limit of the stretching temperature is preferably 170 ° C. By stretching at such a temperature, it is possible to suppress the rapid progress of crystallization of the PVA-based resin and suppress defects due to the crystallization (for example, hindering the orientation of the PVA-based resin layer due to stretching). it can.

C-3. Insolubilization treatment, dyeing treatment and cross-linking treatment If necessary, an insolubilization treatment is performed after the aerial auxiliary stretching treatment and before the underwater stretching treatment or the dyeing treatment. The insolubilization treatment is typically performed by immersing a PVA-based resin layer in an aqueous boric acid solution. The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). If necessary, a cross-linking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The cross-linking treatment is typically performed by immersing a PVA-based resin layer in an aqueous boric acid solution. 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 (above).

C-4. Underwater stretching treatment The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin base material or the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically about 80 ° C.), and the PVA-based resin layer is crystallized. Can be stretched at a high magnification while suppressing the above. As a result, a polarizing film having excellent optical characteristics can be produced.

Any appropriate method can be adopted as the stretching method of the laminated body. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Preferably, free end stretching is selected. The stretching of the laminate may be carried out in one step or in multiple steps. When performed in multiple stages, the draw ratio (maximum draw ratio) of the laminate described later is the product of the draw ratios of each stage.

The underwater stretching is preferably carried out by immersing the laminate in a boric acid aqueous solution (boric acid water stretching). By using an aqueous boric acid solution as the stretching bath, it is possible to impart rigidity to withstand the tension applied during stretching and water resistance that does not dissolve in water to the PVA-based resin layer. Specifically, boric acid can generate a tetrahydroxyboric acid anion in an aqueous solution and crosslink with a 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 satisfactorily, and a polarizing film having excellent optical characteristics can be produced.

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

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

The stretching temperature (liquid temperature of the stretching bath) is preferably 40 ° C. to 85 ° C., more preferably 60 ° C. to 75 ° C. At such a temperature, the PVA-based resin layer can be stretched at a high magnification while suppressing dissolution. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin base material is preferably 60 ° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40 ° C., it may not be stretched well even when the plasticization of the thermoplastic resin base material by water is taken into consideration. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a possibility that excellent optical characteristics cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio by stretching in water is preferably 1.5 times or more, more preferably 3.0 times or more. The total draw ratio of the laminated body is preferably 5.0 times or more, more preferably 5.5 times or more, with respect to the original length of the laminated body. By achieving such a high draw ratio, it is possible to manufacture a polarizing film having extremely excellent optical characteristics. Such a high draw ratio can be achieved by adopting an underwater stretching method (boric acid underwater stretching).

C-5. Drying shrinkage treatment The drying shrinkage treatment may be carried out by heating the entire zone by zone heating, or by heating the transport roll (using a so-called heating roll) (heating roll drying method). Preferably, both are used. By drying with a heating roll, it is possible to efficiently suppress the heating curl of the laminate and produce a polarizing film having an excellent appearance. Specifically, by drying the laminate along the heating roll, the crystallization of the thermoplastic resin base material can be efficiently promoted and the crystallinity can be increased, which is relatively low. Even at the drying temperature, the crystallinity of the thermoplastic resin base material can be satisfactorily increased. As a result, the rigidity of the thermoplastic resin base material is increased so that it can withstand the shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. Further, by using the heating roll, the laminated body can be dried while being maintained in a flat state, so that not only curling but also wrinkles can be suppressed. At this time, the laminated body can be improved in optical characteristics by shrinking in the width direction by a drying shrinkage treatment. This is because the orientation of PVA and the PVA / iodine complex can be effectively enhanced. The shrinkage ratio in the width direction of the laminate by 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 view showing an example of the drying shrinkage treatment. In the drying shrinkage treatment, the laminate 200 is dried while being transported by the transport rolls R1 to R6 heated to a predetermined temperature and the guide rolls G1 to G4. In the illustrated example, the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin base material. For example, one surface of the laminate 200 (for example, thermoplastic) is arranged. The transport rolls R1 to R6 may be arranged so as to continuously heat only the resin base material surface).

Drying conditions can be controlled by adjusting the heating temperature of the transport roll (temperature of the heating roll), the number of heating rolls, the contact time with the heating roll, and the like. The temperature of the heating roll is preferably 60 ° C. to 120 ° C., more preferably 65 ° C. to 100 ° C., and particularly preferably 70 ° C. to 80 ° C. The crystallinity of the thermoplastic resin can be satisfactorily increased, curling can be satisfactorily suppressed, and an optical laminate having extremely excellent durability can be produced. The temperature of the heating roll can be measured with a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular limitation as long as there are a plurality of transport rolls. The number of transport rolls is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roll is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and further preferably 1 to 10 seconds.

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

C-6. Contact with the treatment liquid As described above, a laminate of the thermoplastic resin base material and the polarizing film can be obtained. In the embodiment of the present invention, the polarizing film is brought into contact with a treatment liquid having a pH of 3.0 or less. In one embodiment, the polarizing film can be brought into contact with the treatment liquid by bringing the laminate into contact with the treatment liquid as it is. In this case, typically, the thermoplastic resin base material can be used as it is as the protective layer of the polarizing film. Alternatively, a resin film (which serves as a protective layer) is attached to the surface of the polarizing film of the laminated body in contact with the treatment liquid to prepare a laminated body of a protective layer / polarizing film / thermoplastic resin base material, and heat is generated from the laminated body. A polarizing plate having a protective layer / polarizing film configuration may be produced by peeling off a plastic resin base material. In another embodiment, a resin film (which serves as a protective layer) is attached to the surface of the polarizing film of the laminate to prepare a laminate of a protective layer / polarizing film / thermoplastic resin base material, and the laminate is thermoplastic. The resin base material is peeled off to prepare a laminated body (polarizing plate) of a protective layer / polarizing film. By contacting the obtained polarizing plate with the treatment liquid, the polarizing film can be brought into contact with the treatment liquid.

The contact between the polarizing film and the treatment liquid can be performed by any suitable method. Typical examples include application of a treatment liquid to a polarizing film and immersion of a polarizing film (substantially a laminate or a polarizing plate) in a treatment liquid. As the coating method, any appropriate method can be adopted. As a specific example, the method described in Section C-1 can be mentioned as a method for applying the coating liquid. Soaking can also be done in any suitable manner. For example, the treatment liquid may be added to the washing bath for the washing treatment, the treatment liquid bath may be used instead of the washing bath, and the treatment liquid bath may be provided separately from the washing bath. The washing treatment is typically performed after the underwater stretching treatment and before the drying shrinkage treatment. When the treatment liquid bath is separately provided, the treatment liquid bath may be provided between the washing bath and the drying shrinkage treatment facility (that is, the contact with the treatment liquid is between the washing treatment and the drying shrinkage treatment). It may be provided downstream of the means for peeling the thermoplastic resin base material (that is, contact with the treatment liquid may be performed after the thermoplastic resin base material is peeled off).

As the treatment liquid, any suitable acidic liquid can be used as long as the pH is 3.0 or less. 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 smaller the pH of the treatment liquid (the stronger the acidity), the more preferable. Specifically, the pH is preferably 2.7 or less, more preferably 2.5 or less, still 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 further preferably 0.1% by weight to 1% by weight. It is 0.0% by weight.

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

After contact with the treatment liquid, drying can be performed if necessary. The drying temperature is preferably 40 ° C. to 90 ° C., more preferably 50 ° C. to 70 ° C.

C-7. Modification Examples C-1 to C-6 have described a manufacturing method using a laminate of a resin base material and a PVA-based resin layer coated and formed on the resin base material, but the present invention describes a single PVA. It can also be applied to a manufacturing method using a based resin film. In such a manufacturing method, typically, a long PVA-based resin film is uniaxially stretched in the long direction by a roll stretching machine, swelled, dyed, crosslinked, and washed, and finally dried. Including applying. The contact with the treatment liquid can be typically carried out by immersion in a washing bath to which the treatment liquid is added, immersion in the treatment bath after the cleaning treatment, or application of the treatment liquid after the cleaning treatment.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. Unless otherwise specified, "parts" and "%" in Examples and Comparative Examples are based on weight.
(1) Thickness Measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000").
(2) Single-unit transmittance and orthogonal absorbance For the polarizing plates (protective layer / polarizing film) of the examples and comparative examples, the single-unit transmittance Ts measured using an ultraviolet-visible spectrophotometer (LPF-200 manufactured by Otsuka Electronics), parallel. The transmittance Tp and the orthogonal transmittance Tc were defined as Ts, Tp and Tc of the polarizing film, respectively. These Ts, Tp, and Tc are Y values measured by the JIS Z8701 two-degree visual field (C light source) and corrected for luminosity factor. The refractive index of the protective film was 1.50, and the refractive index of the surface of the polarizing film opposite to the protective film was 1.53.
Moreover, the orthogonal absorbance was determined by the following formula using the Tc measured at each wavelength.
Orthogonal absorbance = log10 (100 / Tc)
The orthogonal absorbance Abs ₀ was determined from the orthogonal transmittance Tc having a measurement wavelength of 470 nm using "LPF-200" manufactured by Otsuka Electronics Co., Ltd. For Abs ₀ , the same measurement can be performed with "V-7100" manufactured by JASCO Corporation.
Next, the polarizing plate was subjected to a durability test at a temperature of 60 ° C. and a relative humidity of 95% for 240 hours. The orthogonal absorbance Abs ₂₄₀ after the durability test was determined in the same manner as described above.

[Example 1]
As the thermoplastic resin base material, an amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a long shape, a water absorption rate of 0.75%, and a Tg of about 75 ° C. was used. One side of the resin base material was subjected to corona treatment (treatment conditions: 55 W · min / m ² ).
100 weight of PVA-based resin in which polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer Z410") are mixed at a ratio of 9: 13 parts by weight of potassium iodide was added to the part to prepare a PVA aqueous solution (coating liquid).
The PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60 ° C. to form a PVA-based resin layer having a thickness of 20 μm to prepare a laminate.
The obtained laminate was uniaxially stretched at the free end 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130 ° C. (aerial auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath at a liquid temperature of 40 ° C. (an aqueous boric acid solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Next, the polarizing plate finally obtained is placed in a dyeing bath having a liquid temperature of 30 ° C. (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water). Immersion was carried out for 60 seconds while adjusting the concentration so that the simple substance transmittance (Ts) was 44.0% (dyeing treatment).
Next, it was immersed in a cross-linked bath at a liquid temperature of 40 ° C. (an aqueous boric acid solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds. (Crossing treatment).
Then, while immersing the laminate 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., in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds. Uniaxial stretching was performed so that the total stretching ratio was 5.5 times (underwater stretching treatment).
Then, the laminate was immersed in a washing bath at a liquid temperature of 20 ° C. (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water, pH = 6) (cleaning treatment).
Then, while drying in an oven kept at 90 ° C., it was brought into contact with a heating roll made of SUS whose surface temperature was kept at 75 ° C. for about 2 seconds (dry shrinkage treatment). The shrinkage rate in the width direction of the laminate by the drying shrinkage treatment was 2%.
In this way, a polarizing film having a thickness of 5.0 μm is formed on the resin base material, and a cycloolefin-based film (manufactured by ZEON, product name “G-Film”) as a protective layer (protective film) is formed on the surface of the polarizing film. ) Was bonded with a UV curable adhesive (thickness 1.0 μm), and then the resin base material was peeled off to obtain a laminate having a protective layer / polarizing film structure. The simple substance transmittance (Ts) of the obtained laminated body is 44.0%, because the surface refractive index of the polarizing film / protective layer constituting the laminated body is 1.53 / 1.53. , The value is corrected by + 0.2% to the actual measured value and converted into the state of 1.53 / 1.50.
Next, a treatment liquid (pH = 1.3) obtained by dissolving 0.3% by weight of hydrochloric acid and 3.5% by weight of PVA (JC-25) in water was applied to the surface of the polarizing film of the laminate to a thickness. It was coated to 0.6 um and dried at 60 ° C. for 4 minutes to form a treated layer.
In this way, the polarizing plate of this example was obtained.

Table 1 shows the single transmittance and Abs ₂₄₀ / Abs ₀ for the obtained polarizing plate (substantially, a polarizing film).

[Examples 2 to 10]
A polarizing plate was prepared by adjusting the single transmittance of the polarizing film, the contact method 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 as shown in Table 1. Table 1 shows the single transmittance and Abs ₂₄₀ / Abs ₀ for the obtained polarizing plate (substantially, a polarizing film).

[Example 11]
A polarizing plate was prepared in the same manner as in Example 1 except that the PVA-based resin was not included in the treatment liquid (that is, the treatment layer was not formed) and the pH of the treatment liquid was set to 0.9. did. Table 1 shows the single transmittance and Abs ₂₄₀ / Abs ₀ for the obtained polarizing plate (substantially, a polarizing film).

[Example 12]
In the same manner as in Example 1, the laminate of the thermoplastic resin base material / PVA-based resin layer was subjected to aerial auxiliary stretching treatment, insolubilization treatment, dyeing treatment, cross-linking treatment, and underwater stretching treatment. The laminated body stretched in water was immersed in a treatment bath (pH = 1.6) at a liquid temperature of 20 ° C. (contact with the treatment liquid). The treatment bath was prepared by adding hydrochloric acid to a normal washing bath (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water).
Then, while drying in an oven kept at 90 ° C., it was brought into contact with a heating roll made of SUS whose surface temperature was kept at 75 ° C. for about 2 seconds (dry shrinkage treatment). The shrinkage rate in the width direction of the laminate by the drying shrinkage treatment was 2%.
Next, a cycloolefin-based film (manufactured by ZEON, product name "G-Film") as a protective layer (protective film) is attached to the surface of the polarizing film with a UV curable adhesive (thickness 1.0 μm), and then The resin base material was peeled off to obtain a polarizing plate having a protective layer / polarizing film structure. Table 1 shows the single transmittance and Abs ₂₄₀ / Abs ₀ for the obtained polarizing plate (substantially, a polarizing film).

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

[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%. Table 1 shows the single transmittance and Abs ₂₄₀ / Abs ₀ for the obtained polarizing plate (substantially, a polarizing film).

[Comparative Examples 3 to 8]
A polarizing plate is adjusted by adjusting the single transmittance of the polarizing film, the contact method 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) as shown in Table 1. Was produced. Table 1 shows the single transmittance and Abs ₂₄₀ / Abs ₀ for the obtained polarizing plate (substantially, a polarizing film).

[Example 13]
A long roll of a PVA-based resin film (manufactured by Nippon Synthetic Chem Industry Co., Ltd., product name "PS7500") having a thickness of 55 μm is uniaxially stretched in the long direction so that the total stretching ratio is 6.0 times by a roll stretching machine. At the same time, swelling, dyeing, cross-linking and washing treatments were carried out, and finally a drying treatment was carried out to prepare a polarizing film having a thickness of 23 μm. After the washing treatment and before the drying treatment, the same treatment liquid as in Example 1 was applied to one surface of the PVA-based resin film (polarizing film) in the same manner as in Example 1. Table 1 shows the single transmittance and Abs ₂₄₀ / Abs ₀ for the obtained polarizing film.

[Example 14]
Example 13 except that the PVA-based resin film (polarizing film) was passed through the same treatment bath as in Example 12 instead of the washing bath for the cleaning treatment (thus, the treatment liquid was not applied after the cleaning treatment). In the same manner as above, a polarizing film having a thickness of 23 μm was produced. Table 1 shows the single transmittance and Abs ₂₄₀ / Abs ₀ for the obtained polarizing film.

As is clear from Table 1, in the polarizing film of the embodiment of the present invention, Abs ₂₄₀ / Abs ₀ after the durability test exceeds 0.90, and the deterioration of the polarizing performance in a 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 polarizing film of Example 10 has Abs ₂₄₀ / Abs ₀ exceeding 1.0, and the polarizing performance is improved in a high temperature and high humidity environment. This is an unexpectedly excellent effect contrary to the common sense of technology. Abs ₂₄₀ / Abs ₀ is 0 in both the polarizing films of Comparative Examples 1 and 2 that did not come into contact with the treatment liquid and the polarizing films of Comparative Examples 3 to 8 that came into contact with the treatment liquid having a pH exceeding 3.0. It was less than .88. In Comparative Example 6 in which boric acid was used as the treatment liquid, the treatment liquid gelled and contact itself was impossible.

The polarizing film and the polarizing plate of the present invention are suitably used for a liquid crystal display device.

10 Polarizing film 20 First protective layer 30 Second protective layer 100 Polarizing plate

Claims (12)

1. Consists of a polyvinyl alcohol-based resin film containing iodine,
   Absorbance Abs _{240 at} a wavelength of 470 nm after a 240-hour endurance test at a temperature of 60 ° C. and a relative humidity of 95% satisfies the following relationship with respect to the absorbance Abs ₀ before the endurance test.
   Abs ₂₄₀ / Abs ₀ > 0.90
2. The polarizing film according to claim 1, wherein the simple substance transmittance is 43.0% or more.
3. The polarizing film according to claim 1 or 2, wherein the thickness is 8 μm or less.
4. A polarizing plate having the polarizing film according to any one of claims 1 to 3 and a protective layer arranged on at least one side of the polarizing film.
5. The method for producing a polarizing film according to any one of claims 1 to 3.
   Forming a polyvinyl alcohol-based resin layer on one side of a long thermoplastic resin base material to form a laminate,
   Stretching and dyeing the laminate to form the polyvinyl alcohol-based resin layer as a polarizing film, and bringing the polarizing film into contact with a treatment liquid having a pH of 3.0 or less.
   Manufacturing method, including.
6. The production method according to claim 5, which comprises applying the treatment liquid to the polarizing film.
7. The production method according to claim 5, which comprises immersing the polarizing film in the treatment liquid.
8. The production 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 base material.
9. The laminate is subjected to an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment of shrinking by 2% or more in the width direction by heating while transporting in the longitudinal direction, in this order. The production method according to claim 8, which includes.
10. The manufacturing method according to claim 9, wherein the drying shrinkage treatment is performed using a heating roll.
11. The manufacturing method according to claim 10, wherein the temperature of the heating roll is 60 ° C to 120 ° C.
12. The method for producing a polarizing film according to claim 1 or 2.
    Stretching and dyeing a polyvinyl alcohol-based resin film to obtain the polyvinyl alcohol-based resin film as a polarizing film, and bringing the polarizing film into contact with a treatment liquid having a pH of 3.0 or less.
    Manufacturing method, including.

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