KR20220025733A - Polarizing film, polarizing plate, and manufacturing method of the polarizing film - Google Patents

Abstract

A polarizing film having excellent durability in a high-temperature, high-humidity environment is provided. The polarizing film of the present invention is composed of a polyvinyl alcohol-based resin film containing iodine, and the absorbance at a wavelength of 600 nm after a durability test of 240 hours at a temperature of 60° C. and a relative humidity of 95% (Abs ₂₄₀ ) is the absorbance before the durability test For (Abs ₀ ), the following relation is satisfied.
Abs ₂₄₀ /Abs ₀ >1.00
In one embodiment, the single transmittance of the polarizing film is 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 method for manufacturing the polarizing film.

In a liquid crystal display device, which is a typical image display device, polarizing films are disposed on both sides of a liquid crystal cell due to its image forming method. As a method of manufacturing a polarizing film, for example, a method of obtaining a polarizing film on a resin substrate by stretching a laminate including a resin substrate and a polyvinyl alcohol (PVA)-based resin layer, and then performing a dyeing treatment has been proposed (for example, , Patent Document 1). According to such a method, since a thin polarizing film is obtained, it attracts attention as being able to contribute to thickness reduction of the image display apparatus in recent years. However, in a thin polarizing film, the further improvement of durability in a high-temperature, high-humidity environment is calculated|required.

Japanese Patent Laid-Open No. 2001-343521

The present invention has been made in order to solve the above conventional problems, and its main object is to provide a polarizing film having excellent durability in a high-temperature, high-humidity environment, a polarizing plate, and a method for manufacturing such a polarizing film.

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 600 nm after a durability test of 240 hours at a temperature of 60° C. and a relative humidity of 95% is, before the durability test For the absorbance (Abs ₀ ), the following relationship is satisfied:

Abs ₂₄₀ /Abs ₀ >1.00

In one embodiment, the polarizing film has a single 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 includes the above-described polarizing film and a protective layer disposed on at least one side of the polarizing film.

According to another aspect of the present invention, a method for manufacturing the polarizing film is provided. In this method, a polyvinyl alcohol-based resin layer is formed on one side of a long thermoplastic resin substrate to form a laminate; stretching and dyeing the laminate to use 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.

In one embodiment, the manufacturing method includes applying the treatment liquid to the polarizing film. In another embodiment, the manufacturing method includes immersing the polarizing film in the processing liquid.

In one embodiment, in the manufacturing method, a polyvinyl alcohol-based resin layer including iodide or sodium chloride and a polyvinyl alcohol-based resin is formed on one side of the thermoplastic resin substrate.

In one embodiment, in the above manufacturing method, the laminate is subjected to an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment for shrinking the laminate by 2% or more in the width direction by heating while conveying it in the longitudinal direction in this order. including carrying out

In one embodiment, the dry 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 includes stretching and dyeing a polyvinyl alcohol-based resin film to use 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.

ADVANTAGE OF THE INVENTION According to this invention, the polarizing film excellent in durability in a high-temperature, high-humidity environment can be obtained by making a polarizing film contact the processing liquid whose pH is 3.0 or less. Specifically, the polarizing film according to the embodiment of the present invention has an absorbance (Abs ₂₄₀ ) at a wavelength of 600 nm after a durability test of 240 hours at a temperature of 60° C. and a relative humidity of 95%, and the absorbance before the durability test (Abs ₀ ). The following relationship is satisfied:

Abs ₂₄₀ /Abs ₀ >1.00

That is, in the polarizing film according to the embodiment of the present invention, the absorbance at a wavelength of 600 nm increases by the heating and humidification endurance test. This means that, in the polarizing film according to the embodiment of the present invention, polarization performance can be improved in a high-temperature, high-humidity environment. The polarization performance of the polarizing film is generally expected to decrease in a high-temperature, high-humidity environment, and the improvement in durability of the polarizing film according to the embodiment of the present invention in a high-temperature, high-humidity environment is unexpectedly excellent.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing of the polarizing plate which concerns on one Embodiment of this invention.
2 is a schematic diagram showing an example of a drying shrinkage treatment using a heating roll.

EMBODIMENT OF THE INVENTION Hereinafter, although embodiment of this invention is described, this invention is not limited to these embodiment.

A. Polarizing film

The polarizing film according to an embodiment of the present invention is composed of a polyvinyl alcohol (PVA)-based resin film containing iodine, and absorbance (Abs ₂₄₀ ) at a wavelength of 600 nm after a durability test of 240 hours 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 durability test.

Abs ₂₄₀ /Abs ₀ >1.00

This is PVA-I ₅ ^- having absorption near 600 nm in the polarizing film according to the embodiment of the present invention It has been shown that the complex is not destroyed even in the heating and humidification endurance test, but rather can increase. PVA-I ₅ ^- The complex is destroyed in a high-temperature, high-humidity environment, and the polarization performance of the polarizing film is generally expected to deteriorate in a high-temperature, high-humidity environment. Such excellent durability of the polarizing film according to the embodiment of the present invention is unexpectedly excellent. Although not clear in theory, such excellent durability can be realized 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 1.05 or more, more preferably 1.10 or more, still more preferably 1.15 or more, particularly preferably 1.20 or more, and most preferably 1.25 or more. The upper limit of Abs ₂₄₀ /Abs ₀ may be, for example, 2.00. In addition, the absorbance is typically orthogonal absorbance. Orthogonal absorbance is calculated|required by the following formula based on the orthogonal transmittance|permeability (Tc) measured when calculating|requiring the polarization degree mentioned later.

Orthogonal absorbance=log10(100/Tc)

In addition, the absorbance (Abs ₀ ) before the durability test is the absorbance in a normal state of the polarizing film, and 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, for example, 2.0.

The thickness of the polarizing film is preferably 8 µm or less, more preferably 7 µm or less, still 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 2 μm in another embodiment. Such a thickness can be realized by, for example, producing a polarizing film using a laminate of a resin substrate and a PVA-based resin layer applied and formed on the resin substrate, as will be described later. When the polarizing film is made of a single resin film, the thickness of the polarizing film may 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 single transmittance of the polarizing film is preferably 42.0% or more, more preferably 42.5% or more, still more preferably 43.0% or more, particularly preferably 43.5% or more, and most preferably 44.0% or more. On the other hand, the single transmittance becomes like this. Preferably it is 47.0 % or less, More preferably, it is 46.0 % or less. The polarization degree 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. ADVANTAGE OF THE INVENTION According to embodiment of this invention, such high single transmittance and high polarization degree can be made compatible, and the outstanding durability in the high-temperature, high-humidity environment as mentioned above can be implement|achieved. The single transmittance is typically a Y value measured using an ultraviolet/visible spectrophotometer and corrected for visibility. In addition, single transmittance is a value when the refractive index of the one surface of a polarizing plate is converted into 1.50, and the refractive index of the other surface is converted into 1.53. The polarization degree is typically obtained by the following formula based on the parallel transmittance (Tp) and the orthogonal transmittance (Tc) measured using an ultraviolet/visible light spectrophotometer and corrected for visibility.

Polarization degree (%)={(Tp-Tc)/(Tp+Tc)} ^1/2 × 100

In one embodiment, the transmittance (single transmittance) of a thin polarizing film of 8 µm or less is typically a laminate of a polarizing film (surface refractive index: 1.53) and a protective layer (protective film) (refractive index: 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 in contact with the air interface of the protective layer, the reflectance at the interface of each layer changes, and as a result, the measured value of the transmittance may change. Therefore, for example, when a protective layer having a refractive index other than 1.50 is used, the measured value of transmittance may be corrected according to the refractive index of the surface of the protective layer in contact with the air interface. Specifically, the correction value C of the transmittance is expressed by the following formula using the reflectance R ₁ (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective layer and the air layer.

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 reflectance when the protective layer having a refractive index of 1.50 is used, n ₁ is the refractive index of the used protective layer, and T ₁ is the transmittance of the polarizing film. For example, when a substrate having a surface refractive index of 1.53 (a cycloolefin-based film, a 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, it is possible to convert the polarizing film having a surface refractive index of 1.53 to the transmittance when a protective layer having a refractive index of 1.50 is used. In addition, 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 value of the correction value (C) The impact it imparts is limited. In addition, when the protective layer has absorption other than surface reflection, appropriate correction can be performed according to the amount of absorption.

A polarizing film may be produced using a single resin film, and may be produced using a laminated body of two or more layers. As a specific example of the polarizing film obtained using a laminated body, the polarizing film obtained using the laminated body of the resin base material and the PVA system resin layer apply|coated to the said resin base material is mentioned. A polarizing film obtained by using a laminate of a resin substrate and a PVA-based resin layer applied and formed on the resin substrate is, for example, a PVA-based resin solution applied to a resin substrate, dried to form a PVA-based resin layer on the resin substrate, obtaining a laminate of a resin substrate and a PVA-based resin layer; stretching and dyeing the laminate, and using the PVA-based resin layer as a polarizing film; 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. Thereby, the excellent durability in the high-temperature, high-humidity environment as described above can be implement|achieved. Preferably, a polyvinyl alcohol-based resin layer including a halide and a polyvinyl alcohol-based resin is formed on one side of the resin substrate. Stretching typically includes stretching by immersing the laminate in an aqueous boric acid solution. In addition, the stretching may further include air stretching the laminate at a high temperature (eg, 95° C. or higher) before stretching in an aqueous boric acid solution, if necessary. Further, in this 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 manufacturing method of this embodiment includes performing an aerial auxiliary extending|stretching process, a dyeing|staining process, an underwater extending|stretching process, and drying shrinkage process to a laminated body in this order. By introducing auxiliary stretching, even when applying PVA on a thermoplastic resin, it becomes possible to increase the crystallinity of PVA, and it becomes possible to achieve high optical properties. In addition, by raising the orientation of PVA in advance at the same time, when it is immersed in water in a subsequent dyeing process or an extending process, problems, such as a fall and dissolution of the orientation of PVA, can be prevented, and it becomes possible to achieve high optical characteristic. . In addition, in the case where the PVA-based resin layer is immersed in a liquid, as compared to the case where the PVA-based resin layer does not contain a halide, disorder of the orientation of the polyvinyl alcohol molecules and a decrease in the orientation can be suppressed. Thereby, the optical characteristic of the polarizing film obtained through the treatment process performed by immersing a laminated body in a liquid, such as a dyeing process and an underwater extending|stretching process, can be improved. Moreover, an optical characteristic can be improved by shrinking|contracting a laminated body in the width direction by dry shrinkage process. The obtained laminate of the resin substrate / polarizing film may be used as it is (that is, the resin substrate may be used as a protective layer of the polarizing film), and the resin substrate is peeled from the laminate of the resin substrate / polarizing film, Any suitable protective layer may be laminated and used. The detail of the manufacturing method of a polarizing film is mentioned later in Section C.

B. Polarizer

1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 includes a polarizing film 10 , a first protective layer 20 disposed on one side of the polarizing film 10 , and a second protective layer disposed on the other side of the polarizing film 10 ( 30) is included. The polarizing film 10 is the polarizing film of the present invention described in section A above. One of the first protective layer 20 and the second protective layer 30 may be omitted. Moreover, as above-mentioned, the resin base material used for manufacture of said polarizing film may be sufficient as either one of a 1st protective layer and a 2nd protective layer.

The first and second protective layers are formed of any suitable film that can be used as a protective layer of a polarizing film. Specific examples of the material used as the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, polyethersulfone, and transparent resins such as polysulfone-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based and acetate-based resins. Moreover, thermosetting resins, such as (meth)acrylic type, a urethane type, a (meth)acrylic urethane type, an epoxy type, silicone type, or ultraviolet curing resin, etc. are mentioned. In addition, for example, glassy polymers, such as a siloxane type polymer, are also mentioned. Moreover, the polymer film of Unexamined-Japanese-Patent No. 2001-343529 (WO01/37007) can also be used. As a material for this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in a 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, isobutene and and a resin composition comprising an alternating copolymer composed of N-methylmaleimide and an acrylonitrile/styrene copolymer. The polymer film may be, for example, an extrusion molding of the resin composition.

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

When the polarizing plate 100 is applied to an image display device, the thickness of the protective layer (inner protective layer) disposed on the display panel side is preferably 5 µm to 200 µm, more preferably 10 µm to 100 µm, further preferably It is preferably 10 μm to 60 μm. In one embodiment, the inner protective layer is a retardation layer having 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 retardation 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 (ie, the slow axis direction), 'ny' is the refractive index in the direction orthogonal to the slow axis in the plane (ie, the fast axis direction), and '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

A method for manufacturing a polarizing film according to an embodiment of the present invention includes applying and drying a PVA-based resin solution on one side of a long thermoplastic resin substrate to form a PVA-based resin layer to form a laminate; stretching and dyeing the laminate and using the PVA-based resin layer as a polarizing film; and contacting the polarizing film with a treatment solution having a pH of 3.0 or less. A polarizing film excellent in durability in a high-temperature, high-humidity environment can be implement|achieved by making a polarizing film contact the processing liquid whose pH is 3.0 or less. Preferably, the PVA-based resin solution further comprises a halide. Preferably, in the above manufacturing method, the laminate is subjected to air-assisted stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment for shrinking the laminate by 2% or more in the width direction by heating while conveying in the longitudinal direction. This includes performing sequentially. The content of the halide in the PVA-based resin solution (as a result, the PVA-based resin layer) is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. It is preferable to process dry shrinkage using a heating roll, The temperature of a heating roll becomes like this. Preferably it is 60 degreeC - 120 degreeC. The shrinkage ratio in the width direction of the laminate by the drying shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizing film demonstrated in the said A section can be obtained. In particular, producing a laminate including a PVA-based resin layer containing a halide, stretching the laminate in multi-step stretching including air-assisted stretching and underwater stretching, and heating the laminate after stretching with a heating roll Accordingly, a polarizing film having excellent optical properties (typically, single transmittance and unit absorbance) can be obtained.

C-1. Fabrication of laminates

Any suitable method may be employed as a method for producing a laminate of the thermoplastic resin substrate and the PVA-based resin layer. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin substrate and dried to form a PVA-based resin layer on the thermoplastic resin substrate. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

Any suitable method can be employ|adopted as a coating method of a coating liquid. For example, the roll coat method, the spin coat method, the wire bar coat method, the dip coat method, the die coat method, the curtain coat method, the spray coat method, the knife coat method (comma coat method, etc.) etc. are mentioned. The application/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 substrate may be subjected to surface treatment (eg, corona treatment, etc.), or an easily adhesive layer may be formed on the thermoplastic resin substrate. By performing such a process, the adhesiveness of a thermoplastic resin base material and a PVA-type resin layer can be improved.

C-1-1. Thermoplastic resin substrate

As the thermoplastic resin substrate, any suitable thermoplastic resin film may be employed. About the detail of a thermoplastic resin base material, it describes in Unexamined-Japanese-Patent No. 2012-73580, for example. As for the said publication, the description in its entirety is incorporated herein by reference.

C-1-2. coating liquid

As described above, the coating liquid contains a halide and a PVA-based resin. 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, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. can be heard These can be used individually or in combination of 2 or more types. Among these, water is preferable. The concentration of the PVA-based resin in the solution is preferably 3 parts by weight to 20 parts by weight based on 100 parts by weight of the solvent. If it is such a resin concentration, the uniform coating film closely_contact|adhered to a 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.

You may mix|blend an additive with a coating liquid. As an additive, a plasticizer, surfactant, etc. are mentioned, for example. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. As surfactant, a nonionic surfactant is mentioned, for example. 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 may be employed as the PVA-based resin. For example, polyvinyl alcohol and an ethylene-vinyl alcohol copolymer are mentioned. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying the ethylene-vinyl acetate copolymer. The saponification degree of PVA-type resin is 85 mol% - 100 mol% normally, Preferably they are 95.0 mol% - 99.95 mol%, More preferably, they are 99.0 mol% - 99.93 mol%. The degree of saponification can be obtained according to JIS K 6726-1994. A polarizing film excellent in durability can be obtained by using the PVA-type resin of such a saponification degree. When the degree of saponification is excessively high, there is a possibility 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 to 10000, preferably 1200 to 4500, more preferably 1500 to 4300. In addition, an average degree of polymerization can be calculated|required according to JISK6726-1994.

As the halide, any suitable halide may be employed. Examples include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide and lithium iodide. Among these, potassium iodide is preferable.

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

In general, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin increases. This may become disturbed, and the orientation may fall. In particular, in the case of stretching a laminate of a thermoplastic resin and a PVA-based resin layer in boric acid water, when stretching the laminate in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin, the tendency of the orientation degree to decrease is remarkable Do. For example, compared to the general case that the PVA film alone is stretched in boric acid water at 60° C., the stretching of the laminate of A-PET (thermoplastic resin substrate) and the PVA-based resin layer is performed at a high temperature of around 70° C. It is carried out at a temperature, and in this case, the orientation of PVA at the initial stage of stretching may be lowered at a stage before it is raised by stretching in water. On the other hand, by producing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate, and stretching the laminate at a high temperature in air (auxiliary stretching) before stretching the laminate in boric acid water, the laminate after auxiliary stretching Crystallization of the PVA-based resin in the PVA-based resin layer can be promoted. As a result, in the case where the PVA-based resin layer is immersed in a liquid, as compared to the case in which the PVA-based resin layer does not contain a halide, disorder in the orientation of polyvinyl alcohol molecules and a decrease in orientation can be suppressed. Thereby, the optical characteristic of the polarizing film obtained through the processing process performed by immersing a laminated body in a liquid, such as a dyeing process and an underwater extending|stretching process, can be improved.

C-2. Aerial Auxiliary Stretch Treatment

In particular, in order to obtain high optical properties, a method of two-stage stretching in which dry stretching (auxiliary stretching) and stretching in boric acid water is combined is selected. As in the case of two-stage stretching, by introducing auxiliary stretching, stretching can be performed while suppressing crystallization of the thermoplastic resin substrate, and the problem that stretchability is reduced due to excessive crystallization of the thermoplastic resin substrate in subsequent stretching in boric acid water is solved. and the laminate can be stretched at a higher magnification. Furthermore, when applying the PVA-based resin on the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, it is necessary to lower the application temperature compared to the case of applying the PVA-based resin on a normal metal drum. As a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical properties cannot be obtained. On the other hand, even when apply|coating PVA-type resin on a thermoplastic resin by introduce|transducing auxiliary stretching, it becomes possible to improve the crystallinity of PVA-type resin, and it becomes possible to achieve high optical characteristic. In addition, by increasing the orientation of the PVA-based resin in advance at the same time, when it is immersed in water in a subsequent dyeing process or stretching process, problems such as a decrease in the orientation or dissolution of the PVA-based resin can be prevented, and high optical properties It becomes possible to achieve

The stretching method of the aerial assisted stretching may be fixed-end stretching (eg, stretching using a tenter stretching machine) or free-end stretching (eg, uniaxial stretching by passing a laminate between rolls having different circumferential speeds) However, in order to obtain high optical properties, free-end stretching may be actively employed. In one embodiment, the aerial stretching process includes a heating roll stretching step of stretching the laminate by a difference in circumferential speed between heating rolls while conveying the laminate in its longitudinal direction. The aerial stretching treatment typically includes a zone stretching process and a hot roll stretching process. In addition, the order of a zone extending|stretching process and a heated roll extending process is not limited, A zone extending|stretching process may be performed first, and a hot roll extending|stretching process may be performed first. The zone stretching step may be omitted. In one embodiment, the zone stretching process and the heated roll stretching process are performed in this order. In another embodiment, in a tenter stretching machine, it is extended|stretched by holding|gripping a film edge and extending the distance between tenters in a flow direction (extension of the distance between tenters becomes a draw ratio). At this time, the distance of the tenter in the width direction (direction perpendicular to the flow direction) is set so as to be arbitrarily close. Preferably, with respect to the draw ratio in the flow direction, it can be set to be close to the free end drawing. In the case of free-end stretching, it is calculated as the shrinkage ratio in the width direction = (1/stretch ratio) ^1/2 .

Aerial assisted stretching may be performed in one step, and may be performed in multiple steps. When carrying out in multiple steps, the draw ratio is the product of the draw ratios of each step. The stretching direction in the aerial assisted stretching is preferably approximately the same as the stretching direction in the underwater stretching.

The draw ratio in aerial auxiliary drawing becomes like this. Preferably it is 2.0 times - 3.5 times. The maximum draw ratio in the case of combining aerial assisted stretching and underwater stretching is preferably 5.0 times or more, more preferably 5.5 times or more, still more preferably 6.0 times or more with respect to the original length of the laminate. In the present specification, the term 'maximum draw ratio' refers to the draw ratio just before the laminate is broken, separately confirms the draw ratio at which the laminate is broken, and refers to a value 0.2 lower than that value.

The extending|stretching temperature of air-assisted extending|stretching can be set to arbitrary appropriate values according to the forming material of a thermoplastic resin base material, an extending|stretching method, etc. The stretching temperature is preferably at least the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably at least the glass transition temperature (Tg) of the thermoplastic resin substrate +10°C, particularly preferably at least Tg+15°C. On the other hand, the upper limit of extending|stretching temperature becomes like this. Preferably it is 170 degreeC. By stretching at such a temperature, it is possible to suppress the rapid progress of crystallization of the PVA-based resin, thereby suppressing problems due to the crystallization (eg, hindering the orientation of the PVA-based resin layer by stretching).

C-3. Insolubilization treatment, dyeing treatment and crosslinking treatment

If necessary, an insolubilization treatment is performed after the aerial auxiliary stretching treatment and before the underwater stretching treatment or dyeing treatment. The said insolubilization process is typically performed by immersing a PVA-type resin layer in boric-acid aqueous solution. The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). If necessary, a crosslinking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. About the detail of an insolubilization process, a dyeing process, and a crosslinking process, it describes in Unexamined-Japanese-Patent No. 2012-73580 (above), for example.

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, stretching can be performed at a temperature lower than the glass transition temperature (typically, about 80° C.) of the thermoplastic resin substrate or the PVA-based resin layer, and the PVA-based resin layer can be formed at a high magnification while suppressing its crystallization. can be stretched As a result, a polarizing film having excellent optical properties can be manufactured.

Any suitable method can be employ|adopted for the extending|stretching method of a laminated body. Specifically, fixed-end stretching may be used, or free-end stretching (eg, a method of uniaxial stretching by passing a laminated body between rolls having different circumferential speeds) may be employed. Preferably, free-end stretching is selected. Extending|stretching of a laminated body may be performed in one step, and may be performed in multiple steps. When carrying out in multiple steps, the draw ratio (maximum draw ratio) of the laminated body mentioned later is the product of the draw ratios of each step.

Stretching in water is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using an aqueous boric acid solution as a stretching bath, rigidity to withstand the tension applied at the time of stretching and water resistance insoluble in water can be imparted to the PVA-based resin layer. Specifically, boric acid can generate a tetrahydroxyborate 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 stretched favorably by imparting rigidity and water resistance, and a polarizing film having excellent optical properties can be manufactured.

The aqueous boric acid solution is preferably obtained by dissolving boric acid and/or a borate salt in water as a solvent. The boric acid concentration is preferably 1 part by weight to 10 parts by weight, more preferably 2.5 parts by weight to 6 parts by weight, and particularly preferably 3 parts by weight to 5 parts by weight with respect to 100 parts by weight of water. By making boric acid density|concentration into 1 weight part or more, melt|dissolution of a PVA-type resin layer can be suppressed effectively and a polarizing film of a higher characteristic can be manufactured. 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 mix|blended with the said stretching bath (boric acid aqueous solution). By mix|blending an iodide, the elution of the iodine made to adsorb|suck to the PVA-type resin layer can be suppressed. Specific examples of the iodide are as described above. The concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight, more preferably 0.5 parts by weight to 8 parts by weight 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. If it is such a temperature, it can extend|stretch at a high magnification, suppressing melt|dissolution of a PVA-type resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or higher in relation to the formation of the PVA-based resin layer. In this case, when extending|stretching temperature is less than 40 degreeC, even if it considers plasticization of the thermoplastic resin base material by water, there exists a possibility that extending|stretching may not be satisfactory. On the other hand, as the temperature of the stretching bath increases, the solubility of the PVA-based resin layer increases, and there is a fear that excellent optical properties may not be obtained. The immersion time for the stretching bath of the laminate is preferably 15 seconds to 5 minutes.

The draw ratio by extending|stretching in water becomes like this. Preferably it is 1.5 times or more, More preferably, it is 3.0 times or more. The total draw ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more with respect to the original length of the laminate. By achieving such a high draw ratio, the polarizing film which was extremely excellent in an optical characteristic can be manufactured. Such a high draw ratio can be achieved by employ|adopting the underwater extending|stretching system (boric acid underwater extending|stretching).

C-5. dry shrinkage treatment

The said drying shrinkage process may be performed by zone heating performed by heating the whole zone, and may be performed by heating a conveyance roll (using what is called a heating roll) (heating roll drying method). Preferably, both are used. By drying using a heating roll, the heating curl of a laminated body can be suppressed efficiently, and the polarizing film excellent in an external appearance can be manufactured. Specifically, by drying in a state in which the laminate is poured on a heating roll, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the crystallinity, and even at a relatively low drying temperature, the crystallinity of the thermoplastic resin substrate can be increased favorably. can As a result, the rigidity of a thermoplastic resin base material increases, it becomes a state which can withstand the shrinkage of the PVA-type resin layer by drying, and curl is suppressed. Moreover, by using a heating roll, since it can dry, maintaining a laminated body in a flat state, not only curl but generation|occurrence|production of wrinkles can also be suppressed. At this time, the optical characteristic can be improved by shrinking|contracting a laminated body in the width direction by drying shrinkage process. It is because the orientation of PVA and PVA/iodine complex can be improved effectively. 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%.

2 is a schematic diagram showing an example of a drying shrinkage treatment. In a dry shrinkage process, it is made to dry, conveying the laminated body 200 with conveyance rolls R1-R6 heated to predetermined temperature, and guide rolls G1-G4. In the illustrated example, the conveying rolls R1 to R6 are disposed so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate. For example, one surface of the laminate 200 (eg, the surface of the thermoplastic resin substrate) You may arrange|position conveyance rolls R1-R6 so that a bay may be continuously heated.

Drying conditions are controllable by adjusting the heating temperature (temperature of a heating roll) of a conveyance roll, the number of heating rolls, contact time with a heating roll, etc. 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. While the crystallinity degree of a thermoplastic resin can be increased favorably and curl can be suppressed favorably, the optical laminated body extremely excellent in durability can be manufactured. In addition, the temperature of a heating roll can be measured with a contact thermometer. Although six conveyance rolls are provided in the example of illustration, if it is a plurality of conveyance rolls, it will not restrict|limit in particular. 2-40 pieces of conveyance rolls are normally provided, Preferably 4-30 pieces are provided. The contact time between the laminate and the heating roll (total contact time) is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and still more preferably 1 to 10 seconds.

A heating roll may be provided in a heating furnace (for example, oven), and may be provided in a normal production line (under a room temperature environment). Preferably, it is provided in the heating furnace provided with the blowing means. By using together drying by a heating roll and hot air drying, the rapid temperature change between heating rolls can be suppressed, and the contraction|shrinkage of the width direction can be controlled easily. The temperature of hot air drying becomes like this. Preferably it is 30 degreeC - 100 degreeC. In addition, the hot air drying time becomes like this. Preferably it is 1 second - 300 second. The wind speed of the hot wind is preferably about 10 m/s to 30 m/s. In addition, the said wind speed is a wind speed in a heating furnace, and can measure with a mini vane type digital anemometer.

C-6. contact with the treatment liquid

In this way, a laminate of the thermoplastic resin substrate 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, a polarizing film can be made to contact with a process liquid by making the said laminated body contact a process liquid as it is. In this case, typically, a thermoplastic resin substrate may be used as a protective layer of the polarizing film as it is. Alternatively, a resin film (which becomes a protective layer) is bonded to the surface of the polarizing film of the laminate in contact with the treatment liquid to produce a laminate of protective layer/polarizing film/thermoplastic resin substrate, and the thermoplastic resin substrate is peeled from the laminate Thus, a polarizing plate having a configuration of a protective layer/polarizing film may be produced. In another embodiment, a resin film (which becomes a protective layer) is bonded to the polarizing film surface of the laminate to prepare a laminate of a protective layer/polarizing film/thermoplastic resin substrate, and the thermoplastic resin substrate is peeled from the laminate to protect A laminate (polarizing plate) of a layer/polarizing film is produced. 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 of the polarizing film with the treatment liquid may be performed by any suitable method. Representative examples include application of a treatment liquid to a polarizing film and immersion in a treatment liquid of a polarizing film (substantially a laminate or a polarizing plate). Any suitable method can be employ|adopted as an application|coating method. As a specific example, the method demonstrated in C-1 as a coating method of a coating liquid is mentioned. Immersion may also be done by any suitable modality. For example, the treatment liquid may be added to the cleaning bath of the cleaning treatment, a bath of the treatment liquid may be used instead of the cleaning bath, or the bath of the treatment liquid may be provided separately from the cleaning bath. In addition, a washing process is typically performed after an underwater extending|stretching process, and before a dry shrinkage process. When the treatment liquid bath is provided separately, 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 performed between the cleaning treatment and the drying shrinkage treatment) may be performed) or may be provided downstream of the means for peeling the thermoplastic resin substrate (that is, contact with the processing liquid may be performed after peeling the thermoplastic resin substrate).

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 the strong acid include hydrochloric acid, sulfuric acid and nitric acid. The smaller the pH of the treatment liquid (the stronger the acidity), the more preferable. Specifically, pH becomes like this. Preferably it is 2.7 or less, More preferably, it is 2.5 or less, More preferably, it is 2.0 or less, Especially preferably, it is 1.5 or less.

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

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

After contact with the treatment liquid, drying may be performed if necessary. Drying temperature becomes like this. Preferably it is 40 degreeC - 90 degreeC, More preferably, it is 50 degreeC - 70 degreeC.

C-7. variation

Paragraphs C-1 to C-6 describe a manufacturing method using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate, but the present invention can also be applied to a manufacturing method using a single PVA-based resin film. there is. Such a manufacturing method typically involves performing swelling, dyeing, crosslinking and washing treatment while uniaxially stretching a long PVA-based resin film in the elongate direction by a roll stretching machine, and finally drying treatment. . The contact with the treatment liquid can be typically performed by immersion in a cleaning 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.

Example

Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples. The measuring method of each characteristic is as follows. In addition, unless otherwise specified, 'part' and '%' in Examples and Comparative Examples are based on weight.

(1) thickness

It was measured using the interference film thickness meter (manufactured by Otsuka Denshi, product name 'MCPD-3000').

(2) single transmittance and orthogonal absorbance

For the polarizing plates (protective layer/polarizing film) of Examples and Comparative Examples, the single transmittance Ts, the parallel transmittance (Tp), and the orthogonal transmittance Tc measured using an ultraviolet/visible light spectrophotometer (LPF-200 manufactured by Otsuka Denshi Corporation) It was set as Ts, Tp, and Tc of a polarizing film, respectively. These Ts, Tp, and Tc are Y values which measured by the 2 degree field of view (C light source) of JIS Z8701, and performed the visibility correction|amendment. Moreover, the refractive index of the protective film was 1.50, and the refractive index of the surface on the opposite side to the protective film of a polarizing film was 1.53.

In addition, using the measured Tc at each wavelength, the orthogonal absorbance was obtained by the following formula.

Orthogonal absorbance=log10(100/Tc)

The orthogonal absorbance (Abs ₀ ) was obtained from the orthogonal transmittance (Tc) at a measurement wavelength of 600 nm using 'LPF-200' manufactured by Otsuka Denshi Corporation. In addition, about Abs ₀ , it is possible to perform an equivalent measurement with "V-7100" manufactured by Nippon Bunko, etc.

Next, the polarizing plate was subjected to an endurance test of 240 hours at a temperature of 60° C. and a relative humidity of 95%. The orthogonal absorbance (Abs ₂₄₀ ) after the durability test was obtained in the same manner as above.

[Example 1]

As the thermoplastic resin substrate, an amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 µm) having a long water absorption rate of 0.75% and a Tg of about 75°C was used. Corona treatment (treatment conditions: 55 W·min/m ² ) was performed on one side of the resin substrate.

Polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name 'Kosepaimer Z410') in a 9:1 ratio of 100 parts by weight of a PVA-based resin mixed with potassium iodide 13 parts by weight was added to prepare an aqueous PVA solution (coating solution).

On the corona-treated surface of the resin substrate, the PVA aqueous solution was applied 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 at a length of 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different circumferential speeds in an oven at 130°C (air-assisted stretching treatment).

Next, the laminate was immersed in an insolubilization 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 (insolubilization treatment).

Then, in a dyeing bath (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) at a liquid temperature of 30° C. so that the single transmittance (Ts) of the finally obtained polarizing plate is 45.0% It was immersed for 60 seconds while adjusting the density|concentration (dyeing process).

Then, it was immersed in a crosslinking bath (a boric acid aqueous 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) with a liquid temperature of 40°C for 30 seconds (crosslinking treatment).

Thereafter, while the laminate was immersed in an aqueous boric acid solution (boric acid concentration of 4.0% by weight, potassium iodide 5% by weight) having a liquid temperature of 70°C, the total draw ratio was 5.5 in the longitudinal direction (longitudinal direction) between rolls having different circumferential speeds. Uniaxial stretching was performed so that it might become double (underwater stretching process).

Thereafter, the laminate was immersed in a washing bath having a liquid temperature of 20°C (aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water, pH=6) (washing treatment).

Thereafter, while drying in an oven maintained at 90°C, it was brought into contact with a heating roll made of SUS whose surface temperature was maintained at 75°C for about 2 seconds (dry shrinkage treatment). The shrinkage ratio 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 was formed on the resin substrate, and a cycloolefin-based film (manufactured by ZEON, product name ‘G-Film’) as a protective layer (protective film) was applied to the surface of the polarizing film with a UV curable adhesive (thickness). 1.0 micrometer), the resin base material was peeled after that, and the laminated body which has the structure of a protective layer/polarizing film was obtained. The single transmittance (Ts) of the obtained laminate is 45.0%, which is because the surface refractive index of the polarizing film/protective layer constituting the laminate is 1.53/1.53, so the actual measured value is corrected by +0.2%, and 1.53/1.50 It is a value converted to the state of

Next, on the surface of the polarizing film of the laminate, a treatment solution (pH = 1.3) obtained by dissolving 0.3 wt% of hydrochloric acid and 3.5 wt% of PVA (JC-25) in water is coated to a thickness of 0.6 μm, and 60 ° C. and dried for 4 minutes to form a treated layer.

In this way, the polarizing plate of the present Example was obtained.

About the obtained polarizing plate (substantially a polarizing film), the single transmittance and _Abs240 / _Abs0 are shown in Table 1.

[Example 2]

A polarizing plate was produced in the same manner as in Example 1, except that the concentration of the dyeing bath was adjusted and the single transmittance (Ts) of the polarizing film was set to 44.0%. About the obtained polarizing plate (substantially a polarizing film), the single transmittance and _Abs240 / _Abs0 are shown in Table 1.

[Examples 3-19]

The single transmittance of the polarizing plate, the contact method with the treatment liquid, the pH of the treatment liquid, the kind of acid contained in the treatment liquid, and the thickness of the treatment layer were adjusted as shown in Table 1 to prepare a polarizing plate. About the obtained polarizing plate (substantially a polarizing film), the single transmittance and _Abs240 / _Abs0 are shown in Table 1.

[Example 20]

A polarizing plate was produced in the same manner as in Example 2, 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. About the obtained polarizing plate (substantially a polarizing film), the single transmittance and _Abs240 / _Abs0 are shown in Table 1.

[Example 21]

In the same manner as in Example 2, the laminate of the thermoplastic resin substrate/PVA-based resin layer was subjected to air-assisted stretching treatment, insolubilization treatment, dyeing treatment, crosslinking treatment, and underwater stretching treatment. The layered product subjected to the underwater stretching treatment was immersed in a treatment bath (pH=1.6) having a liquid temperature of 20°C (contact with the treatment liquid). In addition, the treatment bath was prepared by adding hydrochloric acid to a normal washing bath (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water).

Thereafter, while drying in an oven maintained at 90°C, it was brought into contact with a heating roll made of SUS whose surface temperature was maintained at 75°C for about 2 seconds (dry shrinkage treatment). The shrinkage ratio in the width direction of the laminate by the drying shrinkage treatment was 2%.

Next, on the surface of the polarizing film, a cycloolefin-based film (manufactured by ZEON, product name 'G-Film') as a protective layer (protective film) was bonded with a UV curable adhesive (thickness of 1.0 µm), and then the resin substrate was It peeled and obtained the polarizing plate which has the structure of a protective layer/polarizing film. About the obtained polarizing plate (substantially a polarizing film), the single transmittance and _Abs240 / _Abs0 are shown in Table 1.

[Comparative Examples 1-2]

A polarizing plate was produced in the same manner as in Examples 1 and 2, respectively, except that the treatment liquid was not contacted. About the obtained polarizing plate (substantially a polarizing film), the single transmittance and _Abs240 / _Abs0 are shown in Table 1.

[Comparative Example 3]

A polarizing plate was produced in the same manner as in Comparative Example 1 except that the single transmittance of the polarizing film was 43.0%. About the obtained polarizing plate (substantially a polarizing film), the single transmittance and _Abs240 / _Abs0 are shown in Table 1.

[Comparative Examples 4 to 9]

The single transmittance of the polarizing plate, 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) were adjusted as shown in Table 1 to prepare a polarizing plate. About the obtained polarizing plate (substantially a polarizing film), the single transmittance and _Abs240 / _Abs0 are shown in Table 1.

[Example 22]

A long roll of a 55 μm thick PVA-based resin film (manufactured by Nippon Synthetic Company, product name 'PS7500') is uniaxially stretched in the long direction with a total draw ratio of 6.0 times by a roll stretching machine, while simultaneously swelling, dyeing, crosslinking and A polarizing film with a thickness of 23 µm was produced by washing and finally drying. After the washing treatment and before the drying treatment, the same treatment liquid as in Example 2 was applied to one side of the PVA-based resin film (polarizing film) in the same manner as in Example 2. About the obtained polarizing film, the single transmittance and _Abs240 / _Abs0 are shown in Table 1.

[Example 23]

In the same manner as in Example 22, except that the PVA-based resin film (polarizing film) was passed through the same treatment bath as in Example 21 instead of the washing bath of the washing treatment (therefore, the treatment liquid was not applied after the washing treatment) , a polarizing film having a thickness of 23 μm was produced. About the obtained polarizing film, the single transmittance and _Abs240 / _Abs0 are shown in Table 1.

As is apparent from Table 1, the polarizing film of Examples of the present invention has Abs ₂₄₀ /Abs ₀ after the durability test greater than 1.00, and is excellent in durability in a high-temperature, high-humidity environment. Abs ₂₄₀ /Abs ₀ was less than 1.00 in any of the polarizing films of Comparative Examples 1 to 3, which were not in contact with the treatment liquid, and the polarizing films of Comparative Examples 4-9, which were brought into contact with the treatment liquid having a pH exceeding 3.0. Moreover, in Comparative Example 7 using boric acid as a treatment liquid, the treatment liquid gelled, and contact itself was impossible.

Industrial Applicability

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

10 Polarizing film
20 first protective layer
30 second protective layer
100 polarizer

Claims (12)

Consists of a polyvinyl alcohol-based resin film containing iodine,
The absorbance (Abs ₂₄₀ ) at a wavelength of 600 nm after a durability test of 240 hours at a temperature of 60 ° C. and a relative humidity of 95% satisfies the following relation with respect to the absorbance (Abs ₀ ) before the durability test, a polarizing film:
Abs ₂₄₀ /Abs ₀ >1.00. According to claim 1,
A polarizing film having a single transmittance of 43.0% or more. 3. The method of claim 1 or 2,
A polarizing film having a thickness of 8 μm or less. A polarizing plate comprising the polarizing film according to any one of claims 1 to 3, and a protective layer disposed on at least one side of the polarizing film. A method for producing the polarizing film according to any one of claims 1 to 3, comprising:
forming a polyvinyl alcohol-based resin layer on one side of a long thermoplastic resin substrate to obtain a laminate;
stretching and dyeing the laminate to use the polyvinyl alcohol-based resin layer as a polarizing film, and
contacting the polarizing film with a treatment liquid having a pH of 3.0 or less;
A manufacturing method comprising a. 6. The method of claim 5,
A manufacturing method comprising applying the treatment liquid to the polarizing film. 6. The method of claim 5,
A manufacturing method comprising immersing the polarizing film in the treatment solution. 8. The method according to any one of claims 5 to 7,
A method of forming a polyvinyl alcohol-based resin layer comprising iodide or sodium chloride and a polyvinyl alcohol-based resin on one side of the thermoplastic resin substrate. 9. The method of claim 8,
The laminate is subjected to air-assisted stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment for shrinking 2% or more in the width direction by heating while conveying in the longitudinal direction in this order. which is a manufacturing method. 10. The method of claim 9,
The manufacturing method in which the said dry shrinkage process is performed using a heating roll. 11. The method of claim 10,
The temperature of the heating roll is 60 ℃ ~ 120 ℃, the manufacturing method. A method for producing the polarizing film according to claim 1 or 2, comprising:
stretching and dyeing a polyvinyl alcohol-based resin film to use the polyvinyl alcohol-based resin film as a polarizing film, and
contacting the polarizing film with a treatment liquid having a pH of 3.0 or less;
A manufacturing method comprising a.

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