WO2020184082A1

WO2020184082A1 - Polarizing film, polarizing plate, and polarizing film production method

Info

Publication number: WO2020184082A1
Application number: PCT/JP2020/006245
Authority: WO
Inventors: かおる ▲黒▼原; 後藤　周作; 善則南川; 真由美森崎
Original assignee: 日東電工株式会社
Priority date: 2019-03-08
Filing date: 2020-02-18
Publication date: 2020-09-17
Also published as: JP2023130424A; CN113508316A; JP7488252B2; CN113508316B; TW202039599A; KR20210136019A; JPWO2020184082A1

Abstract

Provided is a thin polarizing film that exhibits superior durability in a high-temperature, high-humidity environment. A polarizing film according to the present invention is formed from a polyvinyl-alcohol-based resin film containing iodine, has a thickness of 8 μm or less, and contains 5-350 ppm of an alcohol having a boiling point of less than 100°C. In one embodiment, the alcohol having a boiling point of less than 100°C is at least one alcohol selected from the group consisting of methanol, ethanol, n-propyl alcohol, and isopropyl alcohol. A polarizing plate according to the present invention has said polarizing film and a protective layer that is disposed at least on one side of the polarizing film.

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 its main purpose is a polarizing film, a polarizing plate, and such a polarizing film which are thin and have excellent durability in a high temperature and high humidity environment. The purpose is to provide a method for producing a membrane.

The polarizing film of the present invention is composed of a polyvinyl alcohol-based resin film containing iodine, has a thickness of 8 μm or less, and contains 5 ppm to 350 ppm of alcohol having a boiling point of less than 100 ° C.
In one embodiment, the alcohol having a boiling point below 100 ° C. is at least one selected from the group consisting of methanol, ethanol, n-propyl alcohol and isopropyl alcohol.
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 to introduce alcohol having a boiling point of less than 100 ° C. into the polarizing film.
In one embodiment, the production method comprises immersing the polarizing film in a treatment solution containing an alcohol having a boiling point of less than 100 ° C.
In one embodiment, the production method further comprises introducing the alcohol having a boiling point of less than 100 ° C. into the polarizing film and then heating the laminate.
In one embodiment, the stretching comprises stretching in water.

According to the present invention, by introducing an alcohol having a boiling point of less than 100 ° C. into the polarizing film, it is possible to obtain a polarizing film that is thin and has excellent durability in a high temperature and high humidity environment.

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 composed of a polyvinyl alcohol (PVA) resin film containing iodine, has a thickness of 8 μm or less, and has a boiling point of less than 100 ° C. (hereinafter referred to as low boiling point alcohol). There is) 5ppm to 350ppm. When the polarizing film contains such a low boiling point alcohol in a predetermined amount, it is possible to obtain a polarizing film that is thin and has excellent durability in a high temperature and high humidity environment. Such a low boiling point alcohol can be typically introduced into the polarizing film between the underwater stretching treatment and the drying shrinkage treatment, as will be described later in Section C regarding the production method. By introducing such a low boiling point alcohol, it is presumed that the durability in a high temperature and high humidity environment can be improved by the following mechanism: (i) Due to the low boiling point alcohol during the drying shrinkage treatment. As a result, the drying efficiency is increased and the orientation of PVA is increased; and (ii) the PVA-iodine complex is stabilized due to the low boiling point alcohol in the obtained polarizing film, so that the optical properties during humidification are deteriorated. It can be suppressed. Further, where the crystallization of PVA may not be sufficient in the production of the thin polarizing film, good crystallization of PVA can be realized by introducing a low boiling point alcohol. As a result, even with a thin polarizing film in which the iodine concentration is much higher and the iodine stability is insufficient with the same simple substance transmittance as compared with the conventional (thick) polarizer, the durability is excellent in a high temperature and high humidity environment. Sex can be realized. The content of the low boiling point alcohol in the polarizing film is, for example, 8 ppm to 320 ppm, preferably 20 ppm to 200 ppm, more preferably 40 ppm to 150 ppm, and further preferably 50 ppm to 120 ppm. If the content is too low, the effect of low boiling alcohol may not be obtained. If the content is too high, the amount introduced during manufacturing will be large, and the amount of volatilization into the work environment will be large, which may increase the safety risk.

A typical example of a low boiling point alcohol is a lower monoalcohol having 1 to 4 carbon atoms. Specific examples include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, and tert-butyl alcohol. The low boiling point alcohol may be used alone or in combination of two or more. Preferred are methanol, ethanol, n-propyl alcohol and isopropyl alcohol. Since these have a low boiling point, the drying efficiency in the drying step described later is improved, which is advantageous for improving the characteristics of the obtained polarizing film.

As described above, the thickness of the polarizing film is 8 μm or less, preferably 7 μm or less, more preferably 5 μm or less, and further 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.

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, and further preferably 43.0% 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 99.90% or more, more preferably 99.95% 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 with 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 calculated 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 the polarizing film, the amount of change ΔP in the degree of polarization after a durability test at a temperature of 60 ° C. and a relative humidity of 95% for 120 hours is preferably −0.70% or more, more preferably −0.55% or more. , More preferably −0.20% or more. The upper limit of ΔP may be, for example, 0.0% or more, and ΔP may be, for example, 0.10% or less. ΔP is represented by the following formula.
ΔP = P ₁₂₀ −P ₀
In the above formula, P ₁₂₀ is the degree of polarization after the durability test, and P ₀ is the degree of polarization before the durability test (the degree of polarization described above). That is, the polarizing film according to the embodiment of the present invention has a feature that the decrease in the degree of polarization is small and may increase in a high temperature and high humidity environment.

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, a low boiling point alcohol is introduced into the polarizing film. 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. Includes: stretching and dyeing the laminate to form a PVA-based resin layer as a polarizing film; and introducing low boiling alcohol into the polarizing film. By introducing a low boiling point alcohol, it is possible to realize a polarizing film having excellent durability in a high temperature and high humidity environment. 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. In this case, the introduction of the low boiling point alcohol can preferably be carried out between the underwater stretching treatment and the drying shrinkage treatment. 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 coating method of the coating liquid. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (comma coating method, etc.) 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, and further 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 higher 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, insolubilization treatment is performed after the aerial auxiliary stretching treatment and before the underwater stretching treatment and 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 laminated body 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. Introduction of low boiling point alcohol In the embodiment of the present invention, the low boiling point alcohol is introduced after the stretching treatment in water (and typically before the drying shrinkage treatment described later). The introduction of low boiling alcohols can be done in any suitable manner. For example, the laminate may be immersed in a treatment liquid containing a low boiling point alcohol, or the treatment liquid containing a low boiling point alcohol may be applied to the surface of the polarizing film of the laminate. Typically, the introduction of low boiling alcohol can be done by immersion. Immersion can be done in any suitable manner. For example, a low boiling point alcohol may be added to the washing bath for the washing treatment to serve as a bath for the treatment liquid, or a bath for the treatment liquid may be used instead of the washing bath. A bath for the treatment liquid may be provided separately from the washing bath. May be good. Typically, low boiling point alcohol can be added to the washing bath (washing liquid) of the washing treatment. The low boiling point alcohol concentration of the treatment liquid (cleaning liquid) is preferably 5% by weight to 35% by weight.

C-6. Dry shrinkage treatment The dry shrinkage treatment can preferably be carried out after the introduction of the low boiling point alcohol. By performing the drying shrinkage treatment after the introduction of the low boiling point alcohol, the drying efficiency can be increased, and as a result, the orientation of PVA can be increased.

The drying shrinkage treatment may be performed 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 using 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).

The 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. At such a temperature, the appearance of the obtained polarizing film can be kept good. Furthermore, the synergistic effect with the effect of the low boiling point alcohol can enhance the orientation of PVA while maintaining the appearance. In addition, 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 both drying with a heating roll and hot air drying together, a steep temperature change between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of hot air drying is preferably 30 ° C to 100 ° C. At such a temperature, the appearance of the obtained polarizing film can be kept good. Furthermore, the synergistic effect with the effect of the low boiling point alcohol can enhance the orientation of PVA while maintaining the appearance. 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-7. Others The laminate of the thermoplastic resin base material / polarizing film obtained as described above may be used as it is as a polarizing plate (the thermoplastic resin base material may be used as a protective layer); polarized light of the laminate. After the protective layer is attached to the surface of the film, the thermoplastic resin base material may be peeled off and used as a polarizing plate having a protective layer / polarizing film configuration; another protection is provided on the peeled surface of the thermoplastic resin base material. The layers may be bonded together and used as a polarizing plate having a protective layer / polarizing film / protective layer configuration.

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) Alcohol concentration of polarizing film The polarizing film obtained in Examples and Comparative Examples was cut into 10 cm ² and used as a measurement sample. After encapsulating this measurement sample in a 20 mL headspace vial, the ethanol-containing sample is heated at 175 ° C. and the isopropyl alcohol-containing sample at 215 ° C. for 30 minutes with a headspace sampler (HSS), and 1 mL of the gas phase portion after heating is gas chromatographed. The alcohol content was calculated from the peak area corresponding to each alcohol type by injecting into a tograph (manufactured by Agilent Technologies, product name "6890N") using the following calibration curve.
Ethanol calibration curve y = 4.743E ⁺⁰⁰ x + 3.105E- ⁰²
Isopropyl alcohol calibration curve y = 4.565E ⁺⁰⁰ x + 8.922E- ⁰³
(3) Single-unit transmittance and polarization degree The single-unit transmittance Ts measured using an ultraviolet-visible spectrophotometer (LPF-200 manufactured by Otsuka Electronics) for the polarizing plates (protective film / polarizing film) of Examples and Comparative Examples, 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. From the obtained Tp and Tc, the degree of polarization was determined using the following formula.
Polarization degree (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 x 100
Next, the polarizing plate was subjected to a durability test at a temperature of 85 ° C. and a relative humidity of 85% for 120 hours. The orthogonal transmittance polarization degree P ₁₂₀ after the durability test was determined in the same manner as described above. The durability test was carried out by putting a test sample in which the polarizing film side of the polarizing plate was attached to a glass plate via an adhesive layer into a humidifying oven.
(4) Humidification durability From the polarization degrees P ₀ and P ₁₂₀ before and after the durability test in (3) above, ΔP was calculated using the following formula.
ΔP = P ₁₂₀ −P ₀
Since ΔP is a parameter that changes depending on the simple substance transmittance, it is necessary to compare with a polarizing plate having substantially the same simple substance transmittance before the test. Therefore, the durability in a high temperature and high humidity environment was evaluated based on Comparative Example 1 as follows.
⊚: ΔP is remarkably large compared to Comparative Example 1 (absolute value in the negative direction is remarkably small).
◯: ΔP is larger than that of Comparative Example 1 (absolute value in the negative direction is smaller)
Δ: ΔP is equivalent to Comparative Example 1 ×: ΔP is smaller than Comparative Example 1 (absolute value in the negative direction is larger)

[Example 1]
As the thermoplastic resin base material, an amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a long shape and a Tg of about 75 ° C. was used. One side of the resin base material was corona-treated.
100 weight of PVA-based resin in which polyvinyl alcohol (polymerization degree 4200, saponification degree 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: 1. 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 13 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 cut out in the direction of the auxiliary stretching axis of 15 cm × 10 cm, and the short side of the cut laminate piece was fixed with a dedicated stretching jig, and the solution was placed in an insolubilizing bath at a liquid temperature of 30 ° C. It was immersed in a boric acid aqueous solution obtained by blending 3 parts by weight of boric acid for 30 seconds (insolubilization treatment).
Next, 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), the polarizing film finally obtained Immersion was carried out for 60 seconds while adjusting the concentration so that the simple substance transmittance (Ts) was 43.0% ± 0.2% (staining treatment).
Next, it was immersed in a cross-linked bath at a liquid temperature of 30 ° 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 5.0% by weight) at a liquid temperature of 70 ° C., the total draw ratio is 5 in the longitudinal direction (longitudinal direction). The uniaxial stretching was performed so as to be 5.5 times (underwater stretching treatment).
Then, the laminate is immersed in a treatment bath at a liquid temperature of 20 ° C. (an aqueous solution of 3% by weight of potassium iodide and 5% by weight of ethanol) for 3 seconds to wash the laminate and ethanol is added to the PVA-based resin layer (polarizing film). Introduced (cleaning treatment and introduction of ethanol).
Then, it was dried for 4 minutes in an oven kept at 60 ° C. (drying treatment).
In this way, a polarizing film having a thickness of 5.0 μm was formed on the resin substrate. A cycloolefin-based film (manufactured by ZEON, product name "G-Film") as a protective layer (protective film) is bonded to the surface of the polarizing film with a UV curable adhesive (thickness 1.0 μm), and then a resin base is used. The material was peeled off to obtain a polarizing plate having a protective layer / polarizing film structure. The ethanol concentration in the polarizing film of the obtained polarizing plate was 45 ppm.

Table 1 shows the single transmittance and ΔP of the obtained polarizing plate (substantially, a polarizing film). Furthermore, the evaluation results of (4) above are also shown in Table 1.

[Example 2]
A polarizing plate was produced in the same manner as in Example 1 except that the ethanol concentration in the treatment bath was 20% by weight. The obtained polarizing plate (or polarizing film) was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 3]
A polarizing plate was produced in the same manner as in Example 1 except that the ethanol concentration in the treatment bath was 25% by weight. The obtained polarizing plate (or polarizing film) was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 4]
A polarizing plate was produced in the same manner as in Example 1 except that the ethanol concentration in the treatment bath was 2% by weight. The obtained polarizing plate (or polarizing film) was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 5]
A polarizing plate was produced in the same manner as in Example 4. The obtained polarizing plate was subjected to a durability test at a temperature of 60 ° C. and a relative humidity of 95% for 120 hours to obtain ΔP. The procedure of the durability test was as described in (3) above. The durability of the obtained ΔP was evaluated based on Comparative Example 3 (described later) as follows. The results are shown in Table 1.
⊚: ΔP is remarkably large compared to Comparative Example 3 (absolute value in the negative direction is remarkably small).
◯: ΔP is larger than that of Comparative Example 3 (absolute value in the negative direction is smaller)
Δ: ΔP is equivalent to Comparative Example 3 ×: ΔP is smaller than Comparative Example 3 (absolute value in the negative direction is larger)

[Example 6]
A polarizing plate was produced in the same manner as in Example 1. The obtained polarizing plate was subjected to the same evaluation as in Example 5. The results are shown in Table 1.

[Example 7]
A polarizing plate was produced in the same manner as in Example 2. The obtained polarizing plate was subjected to the same evaluation as in Example 5. The results are shown in Table 1.

[Example 8]
A polarizing plate was produced in the same manner as in Example 3. The obtained polarizing plate was subjected to the same evaluation as in Example 5. The results are shown in Table 1.

[Example 9]
A polarizing plate was produced in the same manner as in Example 3 except that the immersion time in the treatment bath was 10 seconds. The obtained polarizing plate was subjected to the same evaluation as in Example 5. The results are shown in Table 1.

[Example 10]
The concentration of the dyeing bath was adjusted so that the single transmittance of the polarizing film was 42.0% ± 0.2%, and the alcohol type of the washing treatment bath was isopropyl alcohol, and the concentration was 5% by weight. A polarizing plate was produced in the same manner as in Example 5 except for the above. The obtained polarizing plate was subjected to the same durability test as in Example 5 and evaluated according to the following criteria. The results are shown in Table 1.
⊚: ΔP is remarkably large compared to Comparative Example 4 (absolute value in the negative direction is remarkably small).
◯: ΔP is larger than that of Comparative Example 4 (absolute value in the negative direction is smaller)
Δ: ΔP is equivalent to Comparative Example 4 ×: ΔP is smaller than Comparative Example 4 (absolute value in the negative direction is larger)

[Example 11]
A polarizing plate was prepared in the same manner as in Example 10 except that the isopropyl alcohol concentration in the treatment bath was 20% by weight. The obtained polarizing plate was subjected to the same evaluation as in Example 10. The results are shown in Table 1.

[Example 12]
A polarizing plate was prepared in the same manner as in Example 10 except that the isopropyl alcohol concentration in the treatment bath was 25% by weight. The obtained polarizing plate was subjected to the same evaluation as in Example 10. The results are shown in Table 1.

[Comparative Example 1]
A polarizing plate was prepared in the same manner as in Example 1 except that low boiling point alcohol was not added to the washing bath (washing liquid). The obtained polarizing plate (or polarizing film) was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
The polarizing plate was used in the same manner as in Example 1 except that low boiling point alcohol was not added to the washing bath (washing liquid) and the temperature of the drying oven after the uneven washing bath was set to 130 ° C. in order to improve the drying efficiency. Made. However, it was not possible to obtain an evaluable measurement sample due to wrinkles and / or dents in the film due to heat shrinkage.

[Comparative Example 3]
A polarizing plate was produced in the same manner as in Comparative Example 1. The obtained polarizing plate was subjected to the same evaluation as in Example 5. The results are shown in Table 1.

[Comparative Example 4]
A polarizing plate was produced in the same manner as in Comparative Example 1 except that the concentration of the dyeing bath was adjusted so that the single transmittance of the polarizing film was 42.0% ± 0.2%. The obtained polarizing plate was subjected to the same evaluation as in Example 10. The results are shown in Table 1.

[Reference Example 1]
A long roll of a PVA-based resin film (manufactured by Kuraray, product name "PS4500") with a thickness of 45 μm is uniaxially stretched in the long direction with a roll stretching machine so that the total stretching ratio is 6.0 times, and at the same time. A polarizing film having a thickness of 17 μm was prepared by swelling, dyeing, cross-linking, and washing, and finally drying. That is, a thick polarizing film without introducing low boiling point alcohol was produced. A cycloolefin film (manufactured by ZEON, product name "ZT12") as a protective layer (protective film) and an acrylic resin film are bonded to both sides of the polarizing film with a UV curable adhesive (thickness 1.0 μm). Further, a pressure-sensitive adhesive layer was provided on the surface of the cycloolefin-based film to obtain a polarizing plate having a structure of a protective layer / polarizing film / protective layer / pressure-sensitive adhesive layer. Next, the durability test was subjected to the same evaluation as in Example 1 except that the temperature was 65 ° C., the relative humidity was 90%, and the test time was 500 hours, and ΔP was obtained by the following formula. The results are shown in Table 2. The durability of Reference Example 2 described later was evaluated based on ΔP of this Reference Example.
ΔP = P ₅₀₀ −P ₀

[Reference example 2]
The long roll of the PVA-based resin / resin base material laminate used in Example 1 is uniaxially stretched in the long direction so that the total stretching ratio becomes 2.4 times by a roll stretching machine, and at the same time swells. , Dyeing, cross-linking and washing treatment, and finally drying treatment to prepare a polarizing film having a thickness of 5 μm. That is, a thin polarizing film without introducing low boiling point alcohol was produced. An adhesive layer was provided on the surface of the polarizing film as a protective layer in the same manner as in Reference Example 1, to obtain a polarizing plate having a structure of a protective layer / polarizing film / protective layer / adhesive layer. The evaluation was performed in the same manner as in Reference Example 1 except that this polarizing plate was used, and the evaluation was made according to the following criteria. The results are shown in Table 2.
⊚: ΔP is remarkably large compared to Reference Example 1 (absolute value in the negative direction is remarkably small).
◯: ΔP is larger than Reference Example 1 (absolute value in the negative direction is smaller)
Δ: ΔP is equivalent to Reference Example 1 ×: ΔP is smaller than Reference Example 1 (absolute value in the negative direction is larger)

As is clear from Table 1, the polarizing plate (polarizing film) of the embodiment of the present invention is excellent in durability in a high temperature and high humidity environment by containing a predetermined amount of low boiling point alcohol. Further, as is clear from Table 2, durability in a high temperature and high humidity environment is a problem peculiar to the thin polarizing film.

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

A polarizing film composed of a polyvinyl alcohol-based resin film containing iodine, having a thickness of 8 μm or less and containing 5 ppm to 350 ppm of alcohol having a boiling point of less than 100 ° C.
The polarizing film according to claim 1, wherein the alcohol having a boiling point of less than 100 ° C. is at least one selected from the group consisting of methanol, ethanol, n-propyl alcohol and isopropyl alcohol.
A polarizing plate having the polarizing film according to claim 1 or 2 and a protective layer arranged on at least one side of the polarizing film.
The method for producing a polarizing film according to claim 1 or 2.
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 introducing alcohol having a boiling point of less than 100 ° C. into the polarizing film.
Manufacturing method, including.
The production method according to claim 4, wherein the polarizing film is immersed in a treatment liquid containing an alcohol having a boiling point of less than 100 ° C.
The production method according to claim 4 or 5, further comprising heating the laminate after introducing alcohol having a boiling point of less than 100 ° C. into the polarizing film.
The production method according to any one of claims 4 to 6, wherein the stretching includes stretching in water.