CN113508316B

CN113508316B - Polarizing film, polarizing plate, and method for producing polarizing film

Info

Publication number: CN113508316B
Application number: CN202080017274.5A
Authority: CN
Inventors: 黑原薫; 后藤周作; 南川善则; 森崎真由美
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2019-03-08
Filing date: 2020-02-18
Publication date: 2024-09-17
Anticipated expiration: 2040-02-18
Also published as: JP2023130424A; TW202039599A; JPWO2020184082A1; KR20210136019A; WO2020184082A1; CN113508316A; JP7488252B2

Abstract

Provided is a polarizing film which is thin and has excellent durability in a high-temperature and high-humidity environment. The polarizing film of the present invention is composed of a polyvinyl alcohol resin film containing iodine, the thickness of the polarizing film is 8 [ mu ] m or less, and the polarizing film contains 5ppm to 350ppm of alcohol having a boiling point lower than 100 ℃. In 1 embodiment, the alcohol having a boiling point below 100 ℃ is at least 1 selected from the group consisting of methanol, ethanol, n-propanol and isopropanol. The polarizing plate of the present invention comprises: the polarizing film, and a protective layer disposed on at least one side of the polarizing film.

Description

Polarizing film, polarizing plate, and method for producing polarizing film

Technical Field

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

Background

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 an image forming method. As a method for producing a polarizing film, for example, the following method has been proposed: a laminate including a resin substrate and a polyvinyl alcohol (PVA) -based resin layer is stretched and then dyed to obtain a polarizing film on the resin substrate (for example, patent document 1). With such a method, a polarizing film having a small thickness can be obtained, and thus, attention has been paid as a method for contributing to the reduction in thickness of image display devices in recent years. However, a thin polarizing film is required to have further improved durability under high-temperature and high-humidity environments.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2001-343521

Disclosure of Invention

Problems to be solved by the invention

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

Solution for solving the problem

The polarizing film of the present invention is composed of a polyvinyl alcohol resin film containing iodine, the thickness of the polarizing film is 8 [ mu ] m or less, and the polarizing film contains 5ppm to 350ppm of alcohol having a boiling point lower than 100 ℃.

In 1 embodiment, the alcohol having a boiling point lower than 100 ℃ is at least 1 selected from the group consisting of methanol, ethanol, n-propanol and isopropanol.

According to another aspect of the present invention, there is provided a polarizing plate. The polarizing plate comprises: the polarizing film, and a protective layer disposed on at least one side of the polarizing film.

According to still another aspect of the present invention, there is provided a method for producing the polarizing film. The method comprises the following steps: forming a polyvinyl alcohol resin layer on one side of a long thermoplastic resin substrate to form a laminate; stretching and dyeing the laminate, and preparing a polarizing film from the polyvinyl alcohol resin layer; and introducing an alcohol having a boiling point lower than 100 ℃ into the polarizing film.

In one embodiment, the method for producing the polarizing film includes immersing the polarizing film in a treatment liquid containing the alcohol having a boiling point lower than 100 ℃.

In one embodiment, the method further comprises introducing the alcohol having a boiling point lower than 100 ℃ into the polarizing film and heating the laminate.

In 1 embodiment, the stretching comprises stretching in water.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, by introducing an alcohol having a boiling point lower than 100 ℃ into the polarizing film, a polarizing film which is thin and has excellent durability in a high-temperature and high-humidity environment can be obtained.

Drawings

Fig. 1 is a schematic cross-sectional view of a polarizing plate according to 1 embodiment of the present invention.

Fig. 2 is a schematic diagram showing an example of a drying shrinkage process using a heating roller.

Detailed Description

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) -based resin film containing iodine, the thickness of the polarizing film being 8 μm or less, and containing 5ppm to 350ppm of an alcohol having a boiling point lower than 100 ℃ (hereinafter, sometimes referred to as a low boiling point alcohol). By containing a predetermined amount of such a low boiling point alcohol in the polarizing film, a polarizing film which is thin and has excellent durability in a high-temperature and high-humidity environment can be obtained. As for such a low boiling point alcohol, as described later in item C regarding the production method, it is typical that a polarizing film may be introduced between the stretching treatment in water and the drying shrinkage treatment. It is presumed that by introducing such a low boiling point alcohol, durability in a high temperature and high humidity environment can be improved by the following mechanism: (i) The drying efficiency is improved due to the low boiling point alcohol during the drying shrinkage treatment, and the orientation of PVA is improved; and (ii) the polarizing film obtained is stabilized with a PVA-iodine complex by a low boiling point alcohol, whereby deterioration of optical characteristics during humidification can be suppressed. Further, although crystallization of PVA is sometimes insufficient in the production of a thin polarizing film, good crystallization of PVA can be achieved by introducing a low boiling point alcohol. As a result, even a thin polarizing film having the same single transmittance, a particularly high iodine concentration as compared with conventional (thick) polarizing materials, and insufficient iodine stability can be realized, and excellent durability in a high-temperature and high-humidity environment can be realized. The content of the low boiling point alcohol in the polarizing film is, for example, 8ppm to 320ppm, preferably 20ppm to 200ppm, more preferably 40ppm to 150ppm, and still more preferably 50ppm to 120ppm. If the content is too small, the effect of the low boiling point alcohol may not be obtained. If the content is too large, the amount of the volatile matter to be introduced into the operating environment increases, and the safety risk may be increased.

As a representative example of the low boiling point alcohol, there may be mentioned a lower monohydric alcohol having 1 to 4 carbon atoms. Specific examples thereof include methanol, ethanol, n-propanol, isopropanol, and t-butanol. The low boiling point alcohol may be used alone or in combination of 2 or more. Methanol, ethanol, n-propanol, isopropanol are preferred. Since these have low boiling points, the drying efficiency in the drying step described later is improved, and this is advantageous in improving the characteristics of the obtained polarizing film.

The thickness of the polarizing film is 8 μm or less, preferably 7 μm or less, more preferably 5 μm or less, and still more preferably 3 μm or less as described above. The lower limit of the thickness of the polarizing film may be 1 μm in 1 embodiment, and may be 2 μm in another embodiment.

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380nm to 780 nm. The monomer transmittance of the polarizing film is preferably 42.0% or more, more preferably 42.5% or more, and still more preferably 43.0% or more. On the other hand, the monomer transmittance is preferably 47.0% or less, more preferably 46.0% or less. The polarization degree 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 embodiments of the present invention, it is possible to achieve both high monomer transmittance and high polarization degree as described above, and to achieve excellent durability in a high-temperature and high-humidity environment as described above. The above-mentioned monomer transmittance is typically a Y value obtained by measurement using an ultraviolet-visible spectrophotometer and by performing sensitivity correction. The single transmittance is a value obtained when the refractive index of one surface of the polarizing plate is converted to 1.50 and the refractive index of the other surface is converted to 1.53. The polarization degree is typically obtained by the following equation based on the parallel transmittance Tp and the orthogonal transmittance Tc obtained by measuring with an ultraviolet-visible spectrophotometer and correcting for visibility.

The polarization degree (%) = { (Tp-Tc)/(tp+tc) } ^1/2 ×100

The change amount Δp of the polarization degree of the polarization film after a 120-hour endurance test at a temperature of 60 ℃ and a relative humidity of 95% is preferably-0.70% or more, more preferably-0.55% or more, and still more preferably-0.20% or more. The upper limit of Δp is, for example, 0.0% or more, and Δp may be, for example, 0.10% or less. Δp is represented by the following formula.

ΔP＝P₁₂₀-P₀

In the above formula, P ₁₂₀ is the degree of polarization after the endurance test, and P ₀ is the degree of polarization before the endurance test (the degree of polarization described above). That is, the polarizing film of the embodiment of the present invention has the following features: there are cases where the decrease in the degree of polarization is small and there is also an increase in the degree of polarization under a high-temperature and high-humidity environment.

The polarizing film may be formed using a single resin film, or may be formed using a laminate of two or more layers. Specific examples of the polarizing film obtained by using the laminate include a polarizing film obtained by using a laminate of a resin base material and a PVA-based resin layer formed on the resin base material. A polarizing film obtained by using a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate can be produced, for example, as follows: a step of applying a PVA-based resin solution to a resin substrate and drying the same to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; the laminate was stretched and dyed to prepare a polarizing film from the PVA-based resin layer. In an embodiment of the present invention, a low boiling point alcohol is introduced into the polarizing film. This can realize excellent durability in the high-temperature and high-humidity environment as described above. It is preferable to form a polyvinyl alcohol resin layer containing a halide and a polyvinyl alcohol resin on one side of the resin base material. Stretching typically involves immersing the laminate in an aqueous boric acid solution and stretching. Further, the stretching may further include, if necessary, subjecting the laminate to air stretching at a high temperature (for example, 95 ℃ or higher) before stretching in the aqueous boric acid solution. In the present embodiment, the laminate is preferably subjected to a drying shrinkage treatment in which the laminate is heated while being conveyed in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. Typically, the manufacturing method of the present embodiment includes: the laminate was subjected to an air-assisted stretching treatment, a dyeing treatment, an in-water stretching treatment, and a drying shrinkage treatment in this order. By introducing the auxiliary stretching, even when PVA is coated on the thermoplastic resin, crystallinity of PVA can be improved, and high optical characteristics can be achieved. Further, by simultaneously improving the orientation of PVA in advance, problems such as degradation and dissolution of the orientation of PVA can be prevented when immersed in water in a subsequent dyeing step and stretching step, and high optical characteristics can be achieved. Further, when the PVA-based resin layer is immersed in a liquid, disorder of orientation of polyvinyl alcohol molecules and decrease of orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This improves the optical properties of the polarizing film obtained by the treatment step of immersing the laminate in a liquid, such as dyeing treatment and stretching in water. Further, by shrinking the laminate in the width direction by the drying shrinkage treatment, the optical characteristics can be improved. The obtained laminate of the resin substrate and the polarizing film may be used as it is (that is, the resin substrate may be used as a protective layer for the polarizing film), or may be used by peeling the resin substrate from the laminate of the resin substrate and the polarizing film and laminating any appropriate protective layer suitable for the purpose on the peeled surface. Details of the method for producing the polarizing film are described in item C below.

B. Polarizing plate

Fig. 1 is a schematic cross-sectional view of a polarizing plate according to 1 embodiment of the present invention. The polarizing plate 100 includes: a polarizing film 10, a 1 st protective layer 20 disposed on one side of the polarizing film 10, and a2 nd protective layer 30 disposed on the other side of the polarizing film 10. The polarizing film 10 is the polarizing film of the present invention described in item a above. One of the 1 st protective layer 20 and the 2 nd protective layer 30 may be omitted. As described above, one of the 1 st protective layer and the 2 nd protective layer may be a resin base material used for the production of the polarizing film.

The 1 st and 2 nd protective layers are formed of any appropriate thin film that can be used as a protective layer for a polarizing film. Specific examples of the material as the main component of the film include cellulose resins such as Triacetylcellulose (TAC), transparent resins such as polyester resins, polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether sulfone resins, polysulfone resins, polystyrene resins, polynorbornene resins, polyolefin resins, (meth) acrylic resins, and acetate resins. Further, a thermosetting resin such as a (meth) acrylic resin, a urethane resin, a (meth) acrylic urethane resin, an epoxy resin, or a silicone resin, an ultraviolet curable resin, or the like can be mentioned. Further, for example, a vitreous polymer such as a siloxane polymer can be used. In addition, a polymer film described in Japanese patent application laid-open No. 2001-343529 (WO 01/37007) can also be used. As a material of the 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 a side chain, and for example, a resin composition having an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be used. The polymer film may be, for example, an extrusion molded product of the above resin composition.

When the polarizing plate 100 is applied to an image display device, the thickness of the protective layer (outer protective layer) disposed on the side opposite to the display panel is typically 300 μm or less, preferably 100 μm or less, more preferably 5 μm to 80 μm, and still more preferably 10 μm to 60 μm. In the case of performing the surface treatment, the thickness of the outer protective layer is a 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, and still more preferably 10 μm to 60 μm. In 1 embodiment, the inner protective layer is a phase difference layer having any suitable phase difference value. In this case, the in-plane retardation Re (550) of the retardation layer is, for example, 110nm to 150nm. "Re (550)" is the in-plane retardation measured at 23℃with light having a wavelength of 550nm by the formula: re= (nx-ny) x d. Here, "nx" is a refractive index in a direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is a refractive index in a direction orthogonal to the slow axis (i.e., the fast axis direction) in the plane, "nz" is a refractive index in the thickness direction, and "d" is a thickness (nm) of the layer (thin film).

C. method for producing polarizing film

The method for producing a polarizing film according to embodiment 1 of the present invention comprises: a laminate is produced by applying a PVA-based resin solution to one side of a long thermoplastic resin substrate and drying the solution to form a PVA-based resin layer; stretching and dyeing the laminate, and preparing a polarizing film from the PVA resin layer; and introducing a low boiling point alcohol into the polarizing film. By introducing the low boiling point alcohol, a polarizing film excellent in durability in a high-temperature and high-humidity environment can be realized. Preferably, the PVA-based resin solution further comprises a halide. Preferably, the above-mentioned production method includes sequentially subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an in-water stretching treatment, and a drying shrinkage treatment for shrinking the laminate by 2% or more in the width direction by heating while conveying the laminate in the longitudinal direction. In this case, the introduction of the low boiling point alcohol may be preferably performed between the stretching treatment in water and the drying shrinkage treatment. The content of the halide in the PVA-based resin solution (resulting in the PVA-based resin layer) is preferably 5 parts by weight to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heated roller, and the temperature of the heated roller is preferably 60 to 120 ℃. The shrinkage in the width direction of the laminate due to the drying shrinkage treatment is preferably 2% or more. According to the above manufacturing method, the polarizing film described in item a above can be obtained. In particular, by producing a laminate having a PVA-based resin layer containing a halide, stretching the laminate into a multi-stage stretching including air-assisted stretching and in-water stretching, and heating the stretched laminate with a heating roller, a polarizing film having excellent optical characteristics (typically, monomer transmittance and unit absorbance) can be obtained.

C-1. Production of laminate

As a method for producing the laminate of the thermoplastic resin base material and the PVA-based resin layer, any suitable method can be used. The PVA-based resin layer is preferably formed on the thermoplastic resin substrate by coating a coating liquid containing a halide and a PVA-based resin on the surface of the thermoplastic resin substrate and drying. 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.

As a coating method of the coating liquid, any suitable method can be employed. For example, a roll coating method, a spin coating method, a 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 cited. The coating and drying temperature of the coating liquid is preferably 50 ℃ or higher.

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

Before forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to a surface treatment (for example, corona treatment or the like), or an easy-to-adhere layer may be formed on the thermoplastic resin substrate. 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 substrate

As the thermoplastic resin base material, any suitable thermoplastic resin film can be used. Details of the thermoplastic resin base material are described in, for example, japanese patent application laid-open No. 2012-73580. The entire disclosure of this publication is incorporated by reference into this specification.

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 obtained by dissolving the halide and the PVA-based resin in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various diols, polyols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These may be used singly or in combination of two or more. Among these, water is preferable. The PVA-based resin concentration of the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. When the resin concentration is such, a uniform coating film can be formed to adhere to the thermoplastic resin substrate. The halide content in the coating liquid is preferably 5 parts by weight to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

The coating liquid may be mixed with an additive. Examples of the additive include a plasticizer and a surfactant. Examples of the plasticizer include polyols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. They can be used for the purpose of further improving the uniformity, dyeing property, and stretchability of the resulting PVA-based resin layer.

As the PVA-based resin, any suitable resin may be used. For example, polyvinyl alcohol and an ethylene-vinyl alcohol copolymer can be cited. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree 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 saponification degree can be determined according to JIS K6726-1994. By using the PVA-based resin having such a saponification degree, a polarizing film excellent in durability can be obtained. If the saponification degree is too high, gelation may occur.

The average polymerization degree of the PVA-based resin may be appropriately selected according to purpose. The average polymerization degree is usually 1000 to 10000, preferably 1200 to 4500, more preferably 1500 to 4300. The average polymerization degree can be determined according to JIS K6726-1994.

As the above-mentioned halide, any suitable halide may be used. For example, iodide and sodium chloride may be mentioned. 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 relative to 100 parts by weight of the PVA-based resin, and more preferably 10 to 15 parts by weight relative to 100 parts by weight of the PVA-based resin. If the amount of the halide exceeds 20 parts by weight relative to 100 parts by weight of the PVA-based resin, the halide may ooze out and the finally obtained polarizing film may be clouded.

In general, the orientation of the polyvinyl alcohol molecules in the PVA-based resin is increased by stretching the PVA-based resin layer, but when the PVA-based resin layer after stretching is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules may be disordered and the orientation may be decreased. In particular, when a laminate of a thermoplastic resin and a PVA-based resin layer is stretched in boric acid water, the degree of orientation tends to be significantly reduced when the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin. For example, stretching of a PVA film itself in boric acid water is usually performed at 60 ℃, whereas stretching of a laminate of a-PET (thermoplastic resin base) and a PVA-based resin layer is performed at a temperature as high as about 70 ℃, and in this case, the orientation of PVA at the initial stage of stretching is reduced at a stage before the stretching in water is increased. In contrast, 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, crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, disorder of orientation and decrease of orientation of polyvinyl alcohol molecules can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This improves the optical properties of the polarizing film obtained by the treatment step of immersing the laminate in a liquid, such as dyeing treatment and stretching in water.

C-2, air assisted stretching treatment

In particular, in order to obtain high optical characteristics, a method of 2-stage stretching in which dry stretching (auxiliary stretching) and stretching in boric acid water are combined is selected. By introducing the auxiliary stretching as in the 2-stage stretching, the stretching can be performed while suppressing crystallization of the thermoplastic resin base material, and the problem of the decrease in stretchability due to excessive crystallization of the thermoplastic resin base material in the subsequent stretching in boric acid water can be solved, whereby the laminate can be stretched at a high magnification. Further, in the case of coating a PVA-based resin on a 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 coating temperature as compared with the case of coating a PVA-based resin on a metal cylinder in general, and as a result, there is a problem that crystallization of the PVA-based resin is relatively low and sufficient optical characteristics are not obtained. In contrast, by introducing the auxiliary stretching, even when the PVA-based resin is coated on the thermoplastic resin, crystallinity of the PVA-based resin can be improved, and high optical characteristics can be achieved. In addition, by simultaneously improving the orientation of the PVA-based resin in advance, it is possible to prevent problems such as a decrease in orientation and dissolution of the PVA-based resin when immersed in water in the subsequent dyeing step and stretching step, and to achieve high optical characteristics.

The stretching method of the air-assisted stretching may be fixed-end stretching (for example, stretching using a tenter), or free-end stretching (for example, stretching the laminate unidirectionally by passing it between rolls having different circumferential speeds), and free-end stretching may be positively employed in order to obtain high optical characteristics. In one embodiment, the air stretching process includes a heated roll stretching step of stretching the laminate by using a peripheral speed difference between heated rolls while conveying the laminate in the longitudinal direction thereof. The air stretching treatment typically includes a zone stretching process and a heated roll stretching process. The order of the region stretching step and the heat roller stretching step is not limited, and the region stretching step may be performed first, or the heat roller stretching step may be performed first. The region stretching step may be omitted. In 1 embodiment, the zone stretching step and the heat roller stretching step are sequentially performed. In another embodiment, the stretching is performed by grasping the film end portion and expanding the distance between the tenters in the flow direction in the tenter stretching machine (the expansion of the distance between the tenters is the stretching ratio). At this time, the distance of the tenter in the width direction (the direction perpendicular to the flow direction) is set to be arbitrarily close. The stretching ratio in the flow direction can be preferably set so as to be closer to the free end stretching. In the case of the free end stretching, it is calculated by a shrinkage ratio= (1/stretch ratio) ^1/2 in the width direction.

The air-assisted stretching may be performed in one stage or may be performed in multiple stages. When the stretching is performed in multiple stages, the stretching ratio is the product of the stretching ratios in the respective stages. The stretching direction in the air-assisted stretching is preferably substantially the same as the stretching direction in the underwater stretching.

The stretching ratio of the air-assisted stretching is preferably 2.0 to 3.5 times. The maximum stretching ratio in the combination of the air-assist stretching and the underwater stretching is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 6.0 times or more, relative to the original length of the laminate. In the present specification, the "maximum stretch ratio" refers to the stretch ratio immediately before the laminate breaks, and refers to a value that is 0.2 lower than the value at which the laminate breaks is separately confirmed.

The stretching temperature of the air-assisted stretching may be set to any appropriate value depending on the material forming the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably not less than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably not less than the glass transition temperature (Tg) +10 ℃ of the thermoplastic resin substrate, particularly preferably not less than tg+15 ℃. On the other hand, the upper limit of the stretching temperature is preferably 170 ℃. By stretching at such a temperature, crystallization of the PVA-based resin can be suppressed from proceeding rapidly, and defects caused by the crystallization (e.g., impeding orientation of the PVA-based resin layer caused by stretching) can be suppressed.

C-3 insolubilization treatment, dyeing treatment and crosslinking treatment

If necessary, the insolubilization treatment is performed after the air-assisted stretching treatment and before the underwater stretching treatment and dyeing treatment. The insolubilization treatment is typically performed by immersing the 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, the crosslinking treatment is performed after the dyeing treatment and before the stretching treatment in water. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. Details of the insolubilization treatment, dyeing treatment, and crosslinking treatment are described in, for example, japanese patent application laid-open No. 2012-73580 (mentioned above).

C-4 in-water stretching treatment

The stretching treatment in water is performed by immersing the laminate in a stretching bath. By the in-water stretching treatment, the stretching can be performed at a temperature lower than the glass transition temperature (typically about 80 ℃) of the thermoplastic resin base material and the PVA-based resin layer, and the crystallization of the PVA-based resin layer can be suppressed and the PVA-based resin layer can be stretched at a high magnification. As a result, a polarizing film having excellent optical characteristics can be produced.

Any suitable method may be used for stretching the laminate. Specifically, the stretching may be performed at a fixed end or at a free end (for example, a method of stretching a laminate unidirectionally by passing the laminate between rolls having different peripheral speeds). The free end stretch is preferably selected. Stretching of the laminate may be performed in one stage or may be performed in multiple stages. When the stretching is performed in multiple stages, the stretching ratio (maximum stretching ratio) of the laminate to be described later is the product of the stretching ratios in the respective stages.

The 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 the stretching bath, rigidity against tensile force applied at the time of stretching and water resistance against dissolution in water can be imparted to the PVA-based resin layer. Specifically, boric acid generates a tetrahydroxyboric acid anion in an aqueous solution and crosslinks with the PVA-based resin through hydrogen bonds. As a result, the PVA-based resin layer can be stretched well by imparting rigidity and water resistance, and a polarizing film having excellent optical characteristics can be produced.

The aqueous boric acid solution is preferably obtained by dissolving boric acid and/or a borate in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, particularly preferably 3 to 5 parts by weight, relative to 100 parts by weight of water. 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 obtained. 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 may be used.

Preferably, the iodide is mixed in the stretching bath (boric acid aqueous solution). By adding iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. Specific examples of iodides are described above. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, relative to 100 parts by weight of water.

The stretching temperature (liquid temperature of the stretching bath) is preferably 40 to 85 ℃, more preferably 60 to 75 ℃. At such a temperature, the PVA-based resin layer can be stretched at a high rate while suppressing dissolution. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ℃ or higher from the viewpoint of the relationship with the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40 ℃, there is a concern that the stretching cannot be performed satisfactorily even if plasticization of the thermoplastic resin substrate by water is considered. On the other hand, the higher the temperature of the stretching bath is, the higher the solubility of the PVA-based resin layer becomes, and there is a concern 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 based on stretching in water is preferably 1.5 times or more, more preferably 3.0 times or more. The total stretch ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, relative to the original length of the laminate. By achieving such a high stretching ratio, a polarizing film having very excellent optical characteristics can be produced. Such a high stretching ratio can be achieved by adopting an underwater stretching method (boric acid underwater stretching).

C-5 introduction of low-boiling alcohols

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 the low-boiling alcohol may be carried out by any suitable means. 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 the low boiling point alcohol may be performed by impregnation. The impregnation may be carried out in any suitable manner. For example, a bath of the treatment liquid may be prepared by adding a low boiling point alcohol to a cleaning bath of the cleaning treatment, and a bath of the treatment liquid may be used instead of the cleaning bath, or a bath of the treatment liquid may be provided separately from the cleaning bath. Typically, a low boiling point alcohol may be added to the cleaning bath (cleaning liquid) of the cleaning process. The concentration of the low boiling point alcohol in the treatment liquid (cleaning liquid) is preferably 5 to 35% by weight.

C-6 drying shrinkage treatment

The drying shrinkage treatment may be preferably performed after the introduction of the low boiling point alcohol. Drying efficiency can be improved by performing drying shrinkage treatment after introduction of the low boiling point alcohol, and as a result, orientation of PVA can be improved.

The drying shrinkage treatment may be performed by zone heating in which the entire zone is heated, or may be performed by heating a conveying roller (using a so-called heating roller) (heating roller drying method). Both are preferably used. By drying with the heating roller, the laminate can be effectively prevented from curling by heating, and a polarizing film excellent in appearance can be produced. Specifically, by drying the laminate while the laminate is in a state of being brought along the heated roller, crystallization of the thermoplastic resin base material can be effectively promoted to increase the crystallinity, and even at a low 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 increases, and the PVA-based resin layer is allowed to shrink due to drying, so that curling can be suppressed. Further, by using the heating roller, the laminate can be dried while maintaining a flat state, and therefore, not only curling but also the generation of wrinkles can be suppressed. At this time, the laminate is shrunk in the width direction by the drying shrinkage treatment, whereby the optical characteristics can be improved. This is because the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage in the width direction of the laminate due to the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%.

Fig. 2 is a schematic diagram showing an example of the drying shrinkage treatment. In the drying shrinkage process, the laminate 200 is dried while being conveyed by the conveying rollers R1 to R6 and the guide rollers G1 to G4 heated to a predetermined temperature. In the example shown in the figure, the conveying rollers R1 to R6 are arranged so as to heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate alternately and continuously, but for example, the conveying rollers R1 to R6 may be arranged so as to heat only one surface (for example, the surface of the thermoplastic resin substrate) of the laminate 200 continuously.

The drying condition can be controlled by adjusting the heating temperature of the conveying roller (temperature of the heating roller), the number of heating rollers, the contact time with the heating roller, and the like. The temperature of the heating roller is preferably 60 to 120 ℃, more preferably 65 to 100 ℃, particularly preferably 70 to 80 ℃. At such a temperature, the appearance of the obtained polarizing film can be maintained well. Further, the synergistic effect with the effect of the low-boiling alcohol can maintain the appearance and improve the orientation of PVA. Further, an optical laminate which can satisfactorily increase the crystallinity of the thermoplastic resin, can satisfactorily suppress curling, and is extremely excellent in durability can be produced. The temperature of the heating roller may be measured by a contact thermometer. In the example of the figure, 6 conveying rollers are provided, but there is no particular limitation as long as the conveying rollers are plural. The number of the conveying rollers is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) of the laminate with the heating roller is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and still more preferably 1 to 10 seconds.

The heating roller may be provided in a heating furnace (for example, an oven) or may be provided in a usual production line (in a room temperature environment). Preferably, the air supply device is arranged in a heating furnace provided with an air supply means. By using the drying by the heating roller and the hot air drying in combination, abrupt temperature changes between the heating rollers can be suppressed, and the shrinkage in the width direction can be easily controlled. The temperature of the hot air drying is preferably 30 to 100 ℃. At such a temperature, the appearance of the obtained polarizing film can be maintained satisfactorily. Further, the synergistic effect with the effect of the low-boiling alcohol can maintain the appearance and improve the orientation of PVA. The hot air drying time is preferably 1 to 300 seconds. The wind speed of the hot air is preferably about 10m/s to 30 m/s. The wind speed is the wind speed in the heating furnace, and can be measured by a mini-blade type digital anemometer.

C-7. Other

The laminate of the thermoplastic resin substrate/polarizing film obtained as described above can be used as a polarizing plate as it is (the thermoplastic resin substrate can be used as a protective layer); the laminate may be used as a polarizing plate having a configuration of a protective layer/polarizing film by bonding a protective layer to the surface of the polarizing film and then peeling off the thermoplastic resin substrate; the other protective layer may be bonded to the release surface of the thermoplastic resin substrate, and may be used as a polarizing plate having a configuration of a protective layer, a polarizing film, and a protective layer.

Examples

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 weight basis.

(1) Thickness of (L)

The measurement was performed using an interference film thickness meter (product name "MCPD-3000" manufactured by tsukamu electronics corporation).

(2) Alcohol concentration of polarizing film

The polarizing films obtained in examples and comparative examples were cut into 10cm ² to obtain measurement samples. After the measurement sample was sealed in a 20mL headspace bottle, the ethanol-containing sample was heated at 175℃and the isopropanol-containing sample at 215℃for 30 minutes by a headspace sampler (HSS), and 1mL of the heated gas phase was injected into a gas chromatograph (manufactured by Agilent TechNologies Co., ltd., product name "6890N"), and the alcohol content was calculated from the peak area corresponding to each alcohol type by the following standard curve.

Ethanol standard curve

y＝4.743E⁺⁰⁰x+3.105E^-02

Standard curve of isopropanol

y＝4.565E⁺⁰⁰x+8.922E^-03

(3) Monomer transmittance and polarization degree

For the polarizing plates (protective film/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 spectrophotometer (LPF-200 of tsukamu electronics) were used as the polarizing films Ts, tp, and Tc, respectively. These Ts, tp, and Tc are Y values obtained by measuring a 2-degree field of view (C light source) of JISZ8701 and performing sensitivity correction. The protective film had a refractive index of 1.50, and the surface of the polarizing film opposite to the protective film had a refractive index of 1.53. The polarization degree was determined from the obtained Tp and Tc by the following formula.

The polarization degree (%) = { (Tp-Tc)/(tp+tc) } ^1/2 ×100

Next, the polarizing plate was subjected to a durability test at a temperature of 85 ℃ and a relative humidity of 85% for 120 hours. The orthogonal transmittance polarization degree P ₁₂₀ after the durability test was obtained in the same manner as described above. The durability test was performed by putting a test sample in which the polarizing film side of the polarizing plate was bonded to the glass plate via the adhesive layer into a humidifying oven.

(4) Humidification durability

From the polarization values P ₀ and P ₁₂₀ before and after the endurance test of (3), Δp was determined by the following formula.

ΔP＝P₁₂₀-P₀

Since Δp is a parameter that varies depending on the transmittance of the monomer, it is necessary to compare the transmittance of the monomer before the test with a polarizing plate having substantially the same transmittance of the monomer. Therefore, durability in a high-temperature and high-humidity environment was evaluated with reference to comparative example 1 as follows.

And (3) the following materials: Δp is significantly large (absolute value in negative direction is significantly small) compared to comparative example 1

O: compared with comparative example 1, ΔP is large (absolute value in negative direction is smaller)

Delta: Δp is equivalent to that of comparative example 1

X: Δp is small (absolute value in negative direction is larger) relative to comparative example 1

Example 1

As the thermoplastic resin base material, an amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm) having a long-length shape and a Tg of about 75℃was used. Corona treatment is performed on one side of the resin base material.

In the case of polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (trade name "GOHSEFIMER Z410" manufactured by Japanese chemical Co., ltd.) were used in the following manner: 1 to 100 parts by weight of the PVA-based resin mixed in the above-mentioned manner, 13 parts by weight of potassium iodide was added to prepare a PVA aqueous solution (coating liquid).

The PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60 ℃ to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.

The obtained laminate was subjected to free-end unidirectional stretching to 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130 ℃.

Next, the laminate was cut into 15cm×10cm pieces in the auxiliary stretching axis direction, and the short sides of the cut laminate pieces were fixed with a dedicated stretching jig and immersed in an insolubilization bath (an aqueous boric acid solution obtained by mixing 3 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 30 ℃ for 30 seconds (insolubilization treatment).

Next, the polarizing film was immersed 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 ℃ for 60 seconds while adjusting the concentration so that the monomer transmittance (Ts) of the finally obtained polarizing film became 43.0% ± 0.2% (dyeing treatment).

Then, the resultant was immersed in a crosslinking bath (aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide with 5 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 30℃for 30 seconds (crosslinking treatment).

Thereafter, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4.0 wt% and potassium iodide: 5.0 wt%) at a liquid temperature of 70 ℃ and uniaxially stretched (in-water stretching treatment) so that the total stretching ratio became 5.5 times in the longitudinal direction.

Thereafter, the laminate was immersed in a treatment bath (potassium iodide 3 wt% aqueous solution and ethanol 5 wt% aqueous solution) at a liquid temperature of 20 ℃ for 3 seconds, and the laminate was washed, and ethanol was introduced into the PVA-based resin layer (polarizing film) (washing treatment and ethanol introduction).

Thereafter, drying (drying treatment) was performed in an oven maintained at 60℃for 4 minutes.

In this way, a polarizing film having a thickness of 5.0 μm was formed on the resin substrate. A cycloolefin Film (product name "G-Film" manufactured by ZEON Co., ltd.) as a protective layer (protective Film) was bonded to the surface of the polarizing Film by a UV curable adhesive (thickness: 1.0 μm), and then the resin base material was peeled off to obtain a polarizing plate having a constitution of a protective layer/polarizing Film. The ethanol concentration in the polarizing film of the obtained polarizing plate was 45ppm.

The transmittance of the resulting polarizing plate (substantially polarizing film) and Δp are shown in table 1. The evaluation results of (4) 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 set to 20 wt%. 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 set to 25 wt%. 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 set to 2 wt%. 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 resulting polarizing plate was subjected to a durability test at a temperature of 60℃and a relative humidity of 95% for 120 hours to obtain ΔP. The procedure of the endurance test is 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.

And (3) the following materials: Δp is significantly large (absolute value in negative direction is significantly small) relative to comparative example 3

O: compared with comparative example 3, ΔP is large (absolute value in negative direction is smaller)

Delta: Δp is equivalent to that of comparative example 3

X: Δp is small (absolute value in negative direction is larger) relative to comparative example 3

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 set to 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

A polarizing plate was produced in the same manner as in example 5, except that the concentration of the dyeing bath was adjusted so that the monomer transmittance of the polarizing film became 42.0% ± 0.2%, and the alcohol type of the cleaning treatment bath was isopropyl alcohol and the concentration thereof was 5% by weight. 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.

And (3) the following materials: Δp is significantly large (absolute value in negative direction is significantly small) compared to comparative example 4

O: compared with comparative example 4, ΔP is large (absolute value in negative direction is smaller)

Delta: Δp is equivalent to that of comparative example 4

X: Δp is small (absolute value in negative direction is larger) relative to comparative example 4

Example 11

A polarizing plate was produced in the same manner as in example 10, except that the isopropyl alcohol concentration in the treatment bath was set to 20 wt%. 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 produced in the same manner as in example 10, except that the isopropyl alcohol concentration in the treatment bath was set to 25 wt%. 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 produced in the same manner as in example 1, except that no low boiling point alcohol was added to the cleaning bath (cleaning 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

A polarizing plate was produced in the same manner as in example 1, except that the low boiling point alcohol was not added to the cleaning bath (cleaning liquid), and the temperature of the drying oven after the cleaning bath was 130 ℃ in order to improve the drying efficiency. However, since the film is wrinkled and/or dented due to shrinkage by heating, a measurement sample that can be evaluated cannot be obtained.

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 dye bath was adjusted so that the monomer transmittance of the polarizing film became 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.

TABLE 1

* Boiling point of ethanol: 78.29 DEG C

* Boiling point of isopropanol: 82.5 DEG C

Reference example 1

A polarizing film having a thickness of 17 μm was produced by uniaxially stretching a PVA film (KURARAY CO., LTD, product name "PS 4500") in the longitudinal direction by a roll stretcher so that the total stretching ratio became 6.0 times, simultaneously swelling, dyeing, crosslinking and washing, and finally drying. Namely, a thick polarizing film was produced without introducing low boiling point alcohol. A cycloolefin film (product name "ZT12" manufactured by ZEON corporation) and an acrylic resin film as protective layers (protective films) were bonded to both surfaces of the polarizing film with a UV curable adhesive (thickness 1.0 μm), and an adhesive layer was provided on the surface of the cycloolefin film, to obtain a polarizing plate having a configuration of protective layers/polarizing films/protective layers/adhesive layers. Next, the same evaluation as in example 1 was performed except that the conditions for the endurance test were set to 65 ℃ and 90% relative humidity and 500 hours for the test time, 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 the present reference example.

ΔP＝P₅₀₀-P₀

Reference example 2

The laminate of the PVA-based resin/resin substrate used in example 1 was uniaxially stretched in the longitudinal direction by a roll stretcher for longitudinal stretching so that the total stretching ratio became 2.4 times, simultaneously subjected to swelling, dyeing, crosslinking and washing treatment, and finally subjected to drying treatment, thereby producing a polarizing film having a thickness of 5 μm. Namely, a thin polarizing film was produced without introducing low boiling point alcohol. An adhesive layer was provided on the surface of the polarizing film in the same manner as in reference example 1 to obtain a polarizing plate having a configuration of a protective layer/polarizing film/protective layer/adhesive layer. Except that this polarizing plate was used, the same evaluation as in reference example 1 was performed, and the evaluation was performed according to the following criteria. The results are shown in Table 2.

And (3) the following materials: Δp is significantly large (absolute value in negative direction is significantly small) relative to reference example 1

O: Δp is large (absolute value in negative direction is smaller) relative to reference example 1

Delta: Δp is equivalent to that of reference example 1

X: Δp is small (absolute value in negative direction is larger) relative to reference example 1

TABLE 2

As is clear from table 1, the polarizing plate (polarizing film) according to the example of the present invention contains a predetermined amount of low boiling point alcohol, and thus has excellent durability in a high temperature and high humidity environment. Further, as is clear from table 2, durability in a high-temperature and high-humidity environment is a problem unique to a thin polarizing film.

Industrial applicability

The polarizing film and the polarizing plate of the present invention are suitable for use in a liquid crystal display device.

Description of the reference numerals

10. Polarizing film

20. 1 St protective layer

30. 2 Nd protective layer

100. Polarizing plate

Claims

1. A polarizing film comprising a polyvinyl alcohol resin film containing iodine, wherein the thickness of the polarizing film is 8 [ mu ] m or less, and the polarizing film contains 5ppm to 350ppm of an alcohol having a boiling point of less than 100 ℃, and the alcohol having a boiling point of less than 100 ℃ is a lower monohydric alcohol having 1 to 4 carbon atoms.

2. The polarizing film according to claim 1, wherein the lower monohydric alcohol having 1 to 4 carbon atoms is at least 1 selected from the group consisting of methanol, ethanol, n-propanol and isopropanol.

3. A polarizing plate is provided with: the polarizing film according to claim 1 or 2, and a protective layer disposed on at least one side of the polarizing film.

4. The method for producing a polarizing film according to claim 1 or 2, comprising:

Forming a polyvinyl alcohol resin layer on one side of a long thermoplastic resin substrate to form a laminate;

stretching and dyeing the laminate, and preparing a polarizing film from the polyvinyl alcohol resin layer;

Immersing the polarizing film in a treatment liquid containing the alcohol having a boiling point lower than 100 ℃ to introduce the alcohol having a boiling point lower than 100 ℃ into the polarizing film; and

The laminate is heated after the alcohol having a boiling point lower than 100 ℃ is introduced into the polarizing film.

5. The method of manufacturing according to claim 4, wherein the stretching comprises stretching in water.