TWI909588B - polarizing film and polarizing plate - Google Patents

Abstract

This invention provides a polarizing film with excellent durability under high temperature and high humidity conditions. The polarizing film of this invention is composed of an iodine-containing polyvinyl alcohol resin film; and after a durability test at a temperature of 60°C and a relative humidity of 95% for 240 hours, the absorbance Abs ₂₄₀ at a wavelength of 470 nm relative to the absorbance Abs ₀ before the durability test satisfies the following relationship: Abs ₂₄₀ / Abs ₀ > 0.90. In one embodiment, the unit transmittance of the polarizing film is 43.0% or more.

Description

polarizing film and polarizing plate

This invention relates to a polarizing film, a polarizing plate, and a method for manufacturing the polarizing film.

In liquid crystal displays (LCDs), a representative image display device, polarizing films are disposed on both sides of the liquid crystal cells according to the image formation method. One method for manufacturing polarizing films is to extend a laminate having a resin substrate and a polyvinyl alcohol (PVA)-based resin layer, followed by a dyeing treatment, to obtain a polarizing film on the resin substrate (e.g., Patent 1). This method can obtain thinner polarizing films, thus contributing significantly to the recent trend towards thinner image display devices. However, the durability of thin polarizing films in high-temperature and high-humidity environments is further required.

Prior Art Documents Patent Documents Patent Document 1: Japanese Patent Application Publication No. 2001-343521

Problem to be Solved by the Invention This invention addresses the aforementioned problems and aims to provide a polarizing film, a polarizing plate, and a method for manufacturing the polarizing film, all exhibiting excellent durability under high temperature and high humidity conditions.

The polarizing film of this invention, used to solve the problem, is composed of an iodine-containing polyvinyl alcohol resin film. Furthermore, after a 240-hour durability test at a temperature of 60°C and a relative humidity of 95%, the absorbance Abs ₂₄₀ at a wavelength of 470 nm satisfies the following relationship relative to the absorbance Abs ₀ before the durability test: Abs ₂₄₀ / Abs ₀ > 0.90. In one embodiment, the unit transmittance of the above-mentioned polarizing film is 43.0% or more. In one embodiment, the thickness of the above-mentioned polarizing film is 8 μm or less. According to another aspect of the invention, a polarizing plate is provided. The polarizing plate has the above-mentioned polarizing film and a protective layer disposed on at least one side of the polarizing film. According to yet another aspect of the invention, a method for manufacturing the above-mentioned polarizing film is provided. The method includes the following steps: forming a polyvinyl alcohol-based resin layer on one side of an elongated thermoplastic resin substrate to form a laminate; extending and dyeing the laminate to form a polarizing film from the polyvinyl alcohol-based resin layer; and contacting the polarizing film with a treatment solution with a pH below 3.0. In one embodiment, the above manufacturing method includes: coating the polarizing film with the treatment solution. In another embodiment, the above manufacturing method includes: immersing the polarizing film in the treatment solution. In one embodiment, the above manufacturing method involves forming a polyvinyl alcohol-based resin layer containing iodide or sodium chloride and polyvinyl alcohol-based resin on one side of the thermoplastic resin substrate. In one embodiment, the manufacturing method includes the following steps: sequentially performing an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying and shrinking treatment on the laminate, wherein the drying and shrinking treatment involves heating the laminate while conveying it along its long side, thereby causing it to shrink by more than 2% in the width direction. In one embodiment, the drying and shrinking treatment is performed using a heating roller. The temperature of the heating roller is, for example, 60°C to 120°C. Another method for manufacturing a polarizing film of the present invention includes the following steps: stretching and dyeing a polyvinyl alcohol-based resin film to form a polarizing film; and contacting the polarizing film with a treatment solution with a pH below 3.0.

According to this invention, by exposing the polarizing film to a treatment solution with a pH below 3.0, a polarizing film with excellent durability under high temperature and high humidity environments can be obtained. Specifically, after a 240-hour durability test at 60°C and 95% relative humidity, the absorbance Abs ₂₄₀ at a wavelength of 470 nm of the polarizing film of this invention satisfies the following relationship relative to the absorbance Abs ₀ before the durability test: Abs ₂₄₀ / Abs ₀ > 0.90. That is, the absorbance of the polarizing film of this invention at a wavelength of 470 nm does not decrease significantly even after a heating and humidification durability test. This means that the reduction in polarization performance of the polarizing film of the present invention under high temperature and high humidity environments has been suppressed to a level that is practically acceptable. The polarization performance of polarizing films (especially thin polarizing films) usually decreases significantly under high temperature and high humidity environments, but the present invention solves this problem and provides a polarizing film (especially a thin polarizing film) with excellent durability under high temperature and high humidity environments.

The following describes the embodiments of the present invention, but the present invention is not limited by such embodiments.

A. Polarizing Film The polarizing film of this invention is composed of an iodine-containing polyvinyl alcohol (PVA) resin film; and after a durability test at 60°C and 95% relative humidity for 240 hours, the absorbance Abs ₂₄₀ at a wavelength of 470 nm satisfies the following relationship relative to the absorbance Abs ₀ before the durability test: Abs ₂₄₀ / Abs ₀ > 0.90. This indicates that in the polarizing film of this invention, the destruction of the PVA-I _3- ^complex with absorption near 470 nm due to the heating and humidification durability test is suppressed. Although theoretically unclear, this excellent durability can be achieved by exposing the polarizing film to a treatment solution with a pH below 3.0. The Abs ₂₄₀ / Abs ₀ ratio should preferably be 0.92 or higher, more preferably 0.93 or higher, and even more preferably 0.95 or higher. The upper limit of the _{Abs 240} / Abs ₀ ratio can be, for example, 1.50. Furthermore, absorbance is represented by orthogonal absorbance. Orthogonal absorbance can be obtained based on the orthogonal transmittance Tc measured when calculating polarization, as described later, using the following formula: Orthogonal absorbance = log10(100/Tc). Additionally, the absorbance Abs ₀ before the durability test is the absorbance of the polarizing film under normal conditions. The Abs ₀ of the polarizing film at a wavelength of 470 nm should be, for example, less than 5.0, preferably less than 3.0, and even more preferably less than 2.2. The lower limit of Abs ₀ can be, for example, 1.0.

In one embodiment, after a 240-hour durability test at 60°C and 95% relative humidity, the absorbance Abs ₂₄₀ at 600 nm relative to the absorbance Abs ₀ before the durability test satisfies the following relationship: Abs ₂₄₀ / Abs ₀ > 1.00. This indicates that in the polarizing film of this embodiment, the PVA-I _5- ^complex with absorption around 600 nm is not destroyed even during the heated and humidified durability test, but rather increases. PVA- ^I ₅ complexes are destroyed in high-temperature and high-humidity environments, and the polarization performance of polarizing films is generally expected to decrease in such environments. However, the superior durability of the polarizing film of the present invention is unpredictable and excellent. Abs ₂₄₀ / Abs ₀ is preferably 1.05 or higher, more preferably 1.10 or higher, more preferably 1.15 or higher, especially preferably 1.20 or higher, and particularly preferably 1.25 or higher. The upper limit of _{Abs 240} / Abs ₀ can be, for example, 2.00. Furthermore, the Abs ₀ of the polarizing film at a wavelength of 600 nm is, for example, less than 5.0, preferably 4.3 or lower, more preferably 4.0 or lower. The lower limit of Abs ₀ can be, for example, 2.0.

The thickness of the polarizing film is preferably below 8µm, below 7µm is more preferred, below 5µm is even better, and below 3µm is especially preferred. The lower limit of the polarizing film thickness can be 1µm in one embodiment and 2µm in another. This thickness, as described later, can be achieved by fabricating the polarizing film using, for example, a resin substrate and a laminate coated with a PVA-based resin layer formed on the resin substrate. When the polarizing film is fabricated from a single resin film, the thickness of the polarizing film can be, for example, 12µm to 35µm.

The polarizing film preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The single-element transmittance of the polarizing film is preferably 42.0% or higher, more preferably 42.5% or higher, even more preferably 43.0% or higher, particularly preferably 43.5% or higher, and especially preferably 44.0% or higher. On the other hand, the single-element transmittance is preferably 47.0% or lower, more preferably 46.0% or lower. The polarization degree of the polarizing film is preferably 99.95% or higher, preferably 99.99% or higher. On the other hand, the polarization degree is preferably 99.998% or lower. According to the embodiment of the present invention, both high single-element transmittance and high polarization degree are achieved, and as mentioned above, excellent durability in high-temperature and high-humidity environments can be realized. The aforementioned unit transmittance represents the Y value obtained by measuring and correcting for visual sensitivity using an ultraviolet-visible spectrophotometer. Furthermore, unit transmittance is the value obtained by converting the refractive index of one surface of the polarizing plate to 1.50 and the refractive index of the other surface to 1.53. The aforementioned polarization value is based on the parallel transmittance Tp and orthogonal transmittance Tc obtained by measuring and correcting for visual sensitivity using an ultraviolet-visible spectrophotometer, and is calculated using the following formula: Polarization (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

In one embodiment, the transmittance (individual transmittance) of a thin polarizing film less than 8µm is measured using an ultraviolet-visible spectrophotometer on the composite of the polarizing film (surface refractive index: 1.53) and the protective layer (protective film) (refractive index: 1.50). Due to variations in the refractive index of the polarizing film surface and/or the refractive index of the protective layer's air-contact surface, the reflectance at each interface will differ, resulting in variations in the measured transmittance. Therefore, for example, when using a protective layer with a refractive index other than 1.50, the measured transmittance can be corrected based on the refractive index of the protective layer's air-contact surface. Specifically, the transmittance correction value C is the reflectance _R1 (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective layer and the air layer, and is expressed by the following formula: C = _R1 - _{R0 R0} = ((1.50-1) ^² /(1.50+1) ^² ) × ( _T1 /100) _R1 = (( _n1-1 ) ^² /( _n1 +1) ^² ) × ( _T1 /100) Here, _R0 is the transmission axis reflectance when using a protective layer with a refractive index of 1.50, _n1 is the refractive index of the protective layer used, and _T1 is the transmittance of the polarizing film. For example, when using a substrate with a surface refractive index of 1.53 (such as a cycloolefin film or a film with a hard coating) as a protective layer, the correction amount C is approximately 0.2%. In this case, adding 0.2% to the measured transmittance allows us to convert the transmittance of the polarizing film with a surface refractive index of 1.53 into that of a protective layer with a surface refractive index of 1.50. Furthermore, calculations based on the above formula show that the change in the correction value C after a 2% change in the transmittance _T1 of the polarizing film is less than 0.03%, therefore the influence of the polarizing film's transmittance on the value of the correction value C is limited. Moreover, when the protective layer has absorption other than surface reflection, appropriate corrections can be made according to the amount of absorption.

Polarizing films can be made from a single resin film or from a laminate of two or more layers. A specific example of a polarizing film obtained using a laminate is a polarizing film obtained by using a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizing film obtained by using a resin substrate and a laminate of a PVA-based resin layer coated on the resin substrate can be manufactured, for example, by: applying a PVA-based resin solution to the resin substrate and allowing it to dry 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; and extending and dyeing the laminate to form a polarizing film from the PVA-based resin layer. In an embodiment of the present invention, the polarizing film is exposed to a treatment solution with a pH below 3.0. This achieves the aforementioned excellent durability under high temperature and high humidity conditions. It is suitable to form a polyvinyl alcohol (PVA) resin layer comprising halides and polyvinyl alcohol resin on one side of a resin substrate. Stretching typically includes immersing the laminate in an aqueous boric acid solution and then stretching it. Furthermore, if necessary, stretching may further include air stretching of the laminate at a high temperature (e.g., above 95°C) before stretching in the aqueous boric acid solution. In this embodiment, it is preferable to subject the laminate system to a drying and shrinkage treatment by heating while conveying it along its longitudinal direction, thereby causing it to shrink by more than 2% in the width direction. Typically, the manufacturing method of this embodiment includes sequentially performing an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying and shrinkage treatment on the laminate. By introducing an auxiliary stretching agent, the crystallinity of PVA can be improved even when it is coated onto thermoplastic resins, thus achieving high optical properties. Furthermore, simultaneously enhancing the orientation of PVA beforehand prevents problems such as decreased orientation or dissolution during subsequent dyeing or stretching steps when immersed in water, further achieving high optical properties. Moreover, immersing the PVA-based resin layer in liquid further suppresses the orientation disorder and reduction of polyvinyl alcohol molecules compared to when the PVA-based resin layer does not contain halides. Therefore, the optical properties of polarizing films obtained through dyeing and underwater stretching processes involving immersion of the laminate in liquid can be improved. Furthermore, by drying and shrinking the laminate in the width direction, the optical properties can be improved. The resulting resin-based/polarizing film laminate can be used directly (i.e., the resin-based material can also be used as a protective layer for the polarizing film), or the resin-based material can be peeled off from the resin-based/polarizing film laminate and any suitable protective layer can be laminated on the peeled surface before use. Detailed information regarding the manufacturing method of the polarizing film will be explained in section C.

B. Polarizing Plate Figure 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 includes: a polarizing film 10, a first protective layer 20 disposed on one side of the polarizing film 10, and a second protective layer 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 section A above. One of the first protective layer 20 and the second protective layer 30 may be omitted. Furthermore, as described above, one of the first protective layer and the second protective layer may be a resin substrate used in the manufacture of the polarizing film.

The first and second protective films are formed from any suitable film that can be used as a protective layer for a polarizing film. Specific examples of materials that are the main components of the film include cellulose resins such as triacetin (TAC), polyester resins, polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether resins, polyether resins, polystyrene resins, polynorcamphene resins, polyolefin resins, (meth)acrylic acid resins, and acetate resins, etc., as well as transparent resins. Furthermore, thermosetting or UV-curing resins such as (meth)acrylic acid resins, carbamate resins, (meth)acrylate carbamate resins, epoxy resins, and polysiloxane resins can also be mentioned. Other examples include glassy polymers such as silicate polymers. Furthermore, the polymer film described in Japanese Patent Application Publication No. 2001-343529 (WO01/37007) may also be used. As a material for this film, for example, resin compositions containing thermoplastic resins with substituted or unsubstituted amide groups on the side chains and thermoplastic resins with substituted or unsubstituted phenyl and nitrile groups on the side chains can be used. Examples include resin compositions having an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film may, for example, be an extruded product of the aforementioned resin composition.

When the polarizing plate 100 is used in 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 even more preferably 10 μm to 60 μm. Furthermore, when a surface treatment is applied, the thickness of the outer protective layer includes the thickness of the surface treatment layer.

When the polarizer 100 is applied to an image display device, the thickness of the protective layer (inner protective layer) disposed on the side of the display panel is preferably 5μm to 200μm, more preferably 10μm to 100μm, and even more preferably 10μm to 60μm. In one embodiment, the inner protective layer is a phase difference layer with any appropriate phase difference value. In this case, the in-plane phase difference Re(550) of the phase difference layer is, for example, 110nm to 150nm. "Re(550)" is the in-plane phase difference measured at 23°C with light of wavelength 550nm, which can be obtained by the formula: Re=(nx-ny)×d. Here, "nx" is the refractive index in the direction where the in-plane refractive index is maximized (i.e., the slow axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis (i.e., the fast axis direction), "nz" is the refractive index in the thickness direction, and "d" is the thickness (nm) of the layer (thin film).

C. Manufacturing Method of Polarizing Film A manufacturing method of a polarizing film according to an embodiment of the present invention includes the following steps: applying a PVA-based resin solution to one side of a strip-shaped thermoplastic resin substrate and drying it to form a PVA-based resin layer, thereby forming a laminate; extending and dyeing the laminate to form a polarizing film from the PVA-based resin layer; and contacting the polarizing film with a treatment solution with a pH below 3.0. By contacting the polarizing film with a treatment solution with a pH below 3.0, a polarizing film with excellent durability under high temperature and high humidity environments can be achieved. Preferably, the PVA-based resin solution further contains halides. Preferably, the above manufacturing method includes the following steps: sequentially performing an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying and shrinkage treatment on the laminate. The drying and shrinkage treatment involves heating the laminate while conveying it along its long side, thereby causing it to shrink by more than 2% in the width direction. The halogen content in the PVA-based resin solution (resulting in a PVA-based resin layer) is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. The drying and shrinkage treatment is preferably performed using a heating roller, and the heating roller temperature is preferably 60°C to 120°C. The width shrinkage rate of the laminate obtained after the drying and shrinkage treatment is preferably more than 2%. The polarizing film described in section A above can be obtained according to the manufacturing method described above. In particular, a polarizing film with excellent optical properties (represented by unit transmittance and unit polarization) can be obtained by the following method: after fabricating a laminate containing a PVA-based resin layer containing halides, the laminate is stretched in multiple stages, including air-assisted stretching and underwater stretching, and then the stretched laminate is heated using a heating roller.

C-1. Fabrication of the Laminate Any suitable method may be used to fabricate the laminate of a thermoplastic resin substrate and a PVA-based resin layer. A preferred method is to apply a coating solution containing halogens and PVA-based resin to the surface of the thermoplastic resin substrate and dry it, thereby forming the PVA-based resin layer on the thermoplastic resin substrate. As mentioned above, the halogen content in the PVA-based resin layer should preferably be 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

The coating liquid can be applied using any suitable method. Examples include roller coating, swirl coating, wire rod coating, dip coating, mold coating, curtain coating, spray coating, and scraper coating (comma coating, etc.). The application and drying temperature for the above coating liquids should preferably be above 50°C.

The thickness of the PVA-based resin layer should preferably be 3μm~40μm, and more preferably 3μm~20μm.

Before forming the PVA-based resin layer, the thermoplastic resin substrate can be surface-treated (e.g., corona treatment), or an easy-adhesion layer can be formed on the thermoplastic resin substrate. By performing the aforementioned treatments, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved.

C-1-1. Thermoplastic Resin Substrate The thermoplastic resin substrate may be any suitable thermoplastic resin film. Detailed information regarding thermoplastic resin film substrates can be found, for example, in Japanese Patent Application Publication No. 2012-73580. This specification incorporates the entire contents of that publication.

C-1-2. Coating Solution The coating solution comprises, as described above, a halogenated compound and a PVA-based resin. The coating solution described above represents a solution formed by dissolving the aforementioned halogenated compound and PVA-based resin in a solvent. Examples of solvents include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination. Water is preferred. The concentration of PVA-based resin in the solution should be 3 to 20 parts by weight relative to 100 parts by weight of solvent. At the specified resin concentration, a uniform coating film adhering closely to the thermoplastic resin substrate can be formed. The halogen content in the coating solution is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

Additives may also be mixed into the coating solution. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyols such as ethylene glycol or glycerol. Examples of surfactants include nonionic surfactants. These can be used to further improve the uniformity, stainability, or elongation of the resulting PVA-based resin layer.

The aforementioned PVA-based resins can be any suitable resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymers can be obtained by saponifying ethylene-vinyl acetate copolymers. The degree of saponification of PVA-based resins is typically 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 PVA-based resins with the aforementioned degree of saponification, polarizing films with excellent durability can be obtained. If the degree of saponification is too high, there is a risk of gelation.

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

The aforementioned halides can be any suitable halides. Examples include iodides and sodium chloride. Examples of iodides include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

The amount of halogenated compounds in the coating solution should preferably be 5 to 20 parts by weight relative to 100 parts by weight of PVA-based resin, more preferably 10 to 15 parts by weight relative to 100 parts by weight of PVA-based resin. If the amount of halogenated compounds relative to 100 parts by weight of PVA-based resin is greater than 20 parts by weight, halogenated compounds will overflow, causing the final polarizing film to become white and cloudy.

Generally, stretching a PVA-based resin layer increases the orientation of polyvinyl alcohol molecules within the layer. However, when the stretched PVA-based resin layer is immersed in an aqueous liquid, the orientation of the polyvinyl alcohol molecules becomes disordered, resulting in a decrease in orientation. This tendency to decrease orientation is particularly pronounced when stretching a laminate of thermoplastic resin and PVA-based resin layers in boric acid water at a relatively high temperature to stabilize the stretching of the thermoplastic resin. For example, the stretching of PVA film monomers in boric acid water is generally carried out at 60°C. In contrast, the stretching of the laminate of A-PET (thermoplastic resin substrate) and PVA-based resin layer is carried out at a higher temperature, around 70°C. At this temperature, the orientation of the PVA at the beginning of stretching decreases before it rises due to stretching in water. To address this, by preparing a laminate of PVA-based resin layer containing halides and thermoplastic resin substrate, and then subjecting the laminate to high-temperature stretching in air before stretching in boric acid water (assisted stretching), the crystallization of PVA-based resin in the PVA-based resin layer of the laminate after assisted stretching can be promoted. As a result, when the PVA-based resin layer is immersed in liquid, the orientation disorder and reduction of polyvinyl alcohol molecules are suppressed more effectively compared to the case where the PVA-based resin layer does not contain halides. This improves the optical properties of polarizing films obtained through treatment steps such as dyeing and underwater stretching by immersing the laminate in liquid.

C-2. Aerial Assisted Stretching Treatment Especially to obtain high-gloss properties, a two-stage stretching method combining dry stretching (assisted stretching) and boric acid water stretching is selected. In the two-stage stretching method, by introducing assisted stretching, the crystallization of the thermoplastic resin substrate can be suppressed while stretching is being performed. This solves the problem of reduced elongation caused by excessive crystallization of the thermoplastic resin substrate during subsequent boric acid water stretching, thereby allowing for higher magnification stretching of the laminate. Furthermore, when PVA-based resins are applied to thermoplastic resin substrates, the application temperature must be lower than when applying PVA-based resins to ordinary metal rollers in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate. This results in relatively lower crystallinity of the PVA-based resins, failing to achieve sufficient optical properties. To address this, by introducing an auxiliary extension, the crystallinity of PVA-based resins can be improved even when applied to thermoplastic resins, thus achieving high optical properties. Furthermore, simultaneously enhancing the orientation of PVA-based resins beforehand prevents issues such as decreased orientation or dissolution during subsequent staining or extension steps when immersed in water, thus achieving superior optical properties.

The aerial extension method can be fixed-end extension (e.g., using a tenter frame) or free-end extension (e.g., uniaxial extension of the laminate between rollers with different circumferential speeds). However, to obtain high-gloss properties, free-end extension is actively preferred. In one embodiment, the aerial extension process includes a heated roller extension step, in which the laminate is conveyed along its long side while being extended using the difference in circumferential speed between the heated rollers. The aerial extension process typically includes a zone extension step and a heated roller extension step. Furthermore, the order of the zone stretching step and the heated roller stretching step is not limited; the zone stretching step can be performed first, or the heated roller stretching step can be performed first. The zone stretching step can also be omitted. In one embodiment, the zone stretching step and the heated roller stretching step are performed sequentially. In another embodiment, the film end is held in a tenter frame, and the distance between the tenter frames is increased in the traveling direction to stretch the film (the increase in the distance between the tenter frames is the stretching ratio). In this case, the distance between the tenter frames in the width direction (perpendicular to the traveling direction) is set to be arbitrarily close. Preferably, it can be set to the stretching ratio relative to the traveling direction to utilize free-end stretching for close approach. When extending the free end, the shrinkage rate in the width direction is calculated as (1/extension ratio) ^1/2 .

Aerial assisted extension can be conducted in one phase or in multiple phases. When conducted in multiple phases, the extension ratio is the product of the extension ratios of each phase. The extension direction in aerial assisted extension should be approximately the same as the extension direction in water.

The extension ratio for aerial-assisted extension should be 2.0 to 3.5 times. When combining aerial-assisted extension and underwater extension, the maximum extension ratio relative to the original length of the laminar mass should preferably be 5.0 times or more, preferably 5.5 times or more, and even better if it is 6.0 times or more. In this manual, "maximum extension ratio" refers to the extension ratio before the laminar mass fractures, which is 0.2 times lower than the confirmed extension ratio for fracture.

The stretching temperature for air-assisted stretching can be set to any suitable value depending on the forming material of the thermoplastic resin substrate and the stretching method. The stretching temperature should preferably be above the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably above Tg + 10°C, and particularly suitable above Tg + 15°C. On the other hand, the upper limit of the stretching temperature should preferably be 170°C. Stretching at this temperature can suppress the rapid crystallization of the PVA resin, thereby suppressing the adverse effects caused by crystallization (e.g., hindering the orientation of the PVA resin layer due to stretching).

C-3. Insoluble Treatment, Staining Treatment, and Crosslinking Treatment An insoluble treatment may be performed, if necessary, after air-assisted stretching treatment and before water-based stretching treatment or staining treatment. The aforementioned insoluble treatment typically involves immersing the PVA-based resin layer in an aqueous boric acid solution. The aforementioned staining treatment typically involves staining the PVA-based resin layer with a dichroic substance (represented by iodine). A crosslinking treatment may be performed, if necessary, after staining treatment and before water-based stretching treatment. The aforementioned crosslinking treatment may be performed by immersing the PVA-based resin layer in an aqueous boric acid solution. Detailed information regarding the insoluble treatment, staining treatment, and crosslinking treatment is available, for example, in Japanese Patent Application Publication No. 2012-73580 (as described above).

C-4. Underwater Spinning Treatment Underwater spinning treatment involves immersing the laminate in a spinning bath. This method allows for spinning at temperatures lower than the glass transition temperatures (approximately 80°C) of the aforementioned thermoplastic resin substrates or PVA-based resin layers, enabling high-ratio spinning while suppressing crystallization of the PVA-based resin layer. The result is a polarizing film with excellent optical properties.

The extension of the laminate can be achieved using any suitable method. Specifically, it can be an extension at a fixed end or an extension at a free end (e.g., a method of uniaxial extension of the laminate between rollers with different circumferential speeds). Extension at a free end is preferred. The extension of the laminate can be performed in one stage or in multiple stages. When performed in multiple stages, the extension ratio (maximum extension ratio) of the laminate, as described later, is the product of the extension ratios of each stage.

Water stretching is best performed by immersing the laminate in an aqueous boric acid solution (boric acid water stretching). By using an aqueous boric acid solution as the stretching bath, the PVA resin layer can be endowed with the rigidity to withstand the tension during stretching and water resistance to be insoluble in water. Specifically, boric acid in aqueous solution generates tetrahydroxyboric acid anions, which can crosslink with PVA resins via hydrogen bonds. As a result, the PVA resin layer is endowed with rigidity and water resistance, allowing for good stretching and thus producing a polarizing film with excellent optical properties.

The aforementioned boric acid aqueous solution is preferably obtained by dissolving boric acid and/or borate in water, which is a solvent. The boric acid concentration relative to 100 parts by weight of water is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, and especially preferably 3 to 5 parts by weight. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, resulting in a polarizing film with higher properties. In addition to boric acid or borate, aqueous solutions obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, etc., in a solvent can also be used.

Iodides should be added to the above-mentioned extended bath (boric acid aqueous solution). Adding iodides can inhibit the dissolution of iodine adsorbed on the PVA-based resin layer. Specific examples of iodides are as described above. The concentration of iodide relative to 100 parts by weight of water is preferably 0.05 parts by weight to 15 parts by weight, more preferably 0.5 parts by weight to 8 parts by weight.

The stretching temperature (liquid temperature of the stretching bath) should preferably be 40°C to 85°C, more preferably 60°C to 75°C. At these temperatures, the dissolution of the PVA-based resin layer can be suppressed, while allowing for high-ratio stretching. Specifically, as mentioned above, in relation to the formation of the PVA-based resin layer, the glass transition temperature (Tg) of the thermoplastic resin substrate should preferably be above 60°C. If the stretching temperature is below 40°C, even considering plasticizing the thermoplastic resin substrate with water, good stretching may not be possible. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and excellent optical properties may not be obtained. The immersion time of the laminate in the stretching bath should preferably be 15 seconds to 5 minutes.

The elongation ratio during underwater stretching should preferably be 1.5 times or more, preferably 3.0 times or more. The total elongation ratio of the laminate relative to its original length should preferably be 5.0 times or more, more preferably 5.5 times or more. By achieving the aforementioned high elongation ratio, polarizing films with excellent optical properties can be manufactured. The high elongation ratio can be achieved by using an underwater stretching method (boric acid water stretching).

C-5. Drying and Shrinkage Treatment The above-mentioned drying and shrinkage treatment can be carried out by regional heating, which involves heating the entire area, or by heating the conveyor rollers (so-called using heated rollers) (heated roller drying method). Both methods are preferred. By using heated rollers for drying, the heat curling of the laminate can be effectively suppressed, resulting in a polarizing film with excellent appearance. Specifically, by drying the laminate along the heated rollers, the crystallization of the thermoplastic resin substrate can be effectively promoted, increasing the degree of crystallinity. Even at relatively low drying temperatures, the degree of crystallinity of the thermoplastic resin substrate can still be significantly increased. As a result, the increased rigidity of the thermoplastic resin substrate allows it to withstand the shrinkage of the PVA-based resin layer during drying, thus suppressing curling. Furthermore, by using heated rollers, drying can be performed while maintaining the laminate's flatness, thereby suppressing not only curling but also wrinkling. At this point, the laminate can be dried and shrunk in the width direction through drying shrinkage treatment, thereby improving its optical properties. This is because it effectively enhances the orientation of PVA and PVA/iodine complexes. The width shrinkage rate obtained after drying shrinkage treatment of the laminate is preferably 1%~10%, more preferably 2%~8%, and especially preferably 4%~6%.

Figure 2 is a schematic diagram showing one example of a drying shrinkage process. In the drying shrinkage process, the laminate 200 is conveyed and dried using conveyor rollers R1-R6 and guide rollers G1-G4, which have been heated to a predetermined temperature. In the example diagram, the conveyor rollers R1-R6 are configured to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate. However, the conveyor rollers R1-R6 may also be configured to continuously heat only one side of the laminate 200 (e.g., the thermoplastic resin substrate side).

Drying conditions can be controlled by adjusting the heating temperature of the conveyor rollers, the number of heating rollers, and the contact time with the heating rollers. The heating roller temperature is preferably 60℃~120℃, more preferably 65℃~100℃, and especially preferably 70℃~80℃. This can effectively increase the crystallinity of the thermoplastic resin and suppress curling, while producing optically laminates with excellent durability. The heating roller temperature can be measured using a contact thermometer. The example diagram shows 6 conveyor rollers, but there are no particular restrictions on the number of conveyor rollers. The number of conveyor rollers is typically 2 to 40, with 4 to 30 being preferred. The contact time (total contact time) between the laminate and the heating roller should be between 1 second and 300 seconds, preferably between 1 and 20 seconds, and even better between 1 and 10 seconds.

The heating rollers can be installed inside a heating furnace (such as an oven) or in a general manufacturing production line (at room temperature). It is preferable to install them in a heating furnace equipped with a blower mechanism. By combining drying with hot air drying, rapid temperature changes between the heating rollers can be suppressed, and width contraction can be easily controlled. The temperature for hot air drying should be between 30°C and 100°C. The hot air drying time should be between 1 second and 300 seconds. The air velocity should be approximately 10 m/s to 30 m/s. This air velocity is within the heating furnace and can be measured using a miniature fan-blade digital anemometer.

C-6. Contact with the treatment solution According to the above method, a laminate of a thermoplastic resin substrate and a polarizing film can be obtained. In an embodiment of the present invention, the polarizing film is in contact with a treatment solution with a pH below 3.0. In another embodiment, the polarizing film can be in contact with the treatment solution by directly contacting the laminate with the treatment solution. In this case, it means that the thermoplastic resin substrate can be directly used as a protective layer for the polarizing film. Alternatively, a resin film (as a protective layer) can be laminated onto the surface of the polarizing film of the laminate that comes into contact with the treatment liquid to create a laminate of protective layer/polarizing film/thermoplastic resin substrate. The thermoplastic resin substrate can then be peeled off from the laminate to create a polarizing plate having a protective layer/polarizing film. In another embodiment, a laminate of protective layer/polarizing film/thermoplastic resin substrate is created by laminating a resin film (as a protective layer) onto the surface of the polarizing film of the laminate. The thermoplastic resin substrate can then be peeled off from the laminate to create a laminate of protective layer/polarizing film (polarizing plate). By bringing the obtained polarizing plate into contact with the treatment solution, the polarizing film can also come into contact with the treatment solution.

Contact between the polarizing film and the treatment solution can be achieved using any suitable method. Examples include applying the treatment solution to the polarizing film or immersing the polarizing film (essentially a laminate or polarizing plate) in the treatment solution. The application method can be any suitable method. Specific examples include the method described in section C-1 as the application method for the coating solution. Immersion can also be performed in any suitable manner. For example, the treatment solution can be added to the washing bath of the washing treatment, a bath of treatment solution can be used instead of the washing bath, or a separate bath of treatment solution can be provided, distinct from the washing bath. Furthermore, washing treatment is typically performed after underwater extension treatment and before drying and shrinkage treatment. Alternatively, when setting up a treatment liquid bath, the treatment liquid bath can be set between the washing bath and the drying and shrinkage treatment equipment (that is, contact with the treatment liquid can also be carried out between the washing treatment and the drying and shrinkage treatment), or it can be set downstream of the mechanism for peeling off the thermoplastic resin substrate (that is, contact with the treatment liquid can also be carried out after peeling off the thermoplastic resin substrate).

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

The acid concentration of the treatment solution should be 0.02% to 3.0% by weight, preferably 0.04% to 2.0% by weight, and even more preferably 0.1% to 1.0% by weight.

The treatment solution may also contain water-soluble resins (such as PVA-based resins). The water-soluble resins function as binders. The concentration of water-soluble resins in the treatment solution is preferably 3% to 5% by weight. A treatment layer can then be formed by applying and drying the treatment solution. By forming the treatment layer, a polarizing film with the desired durability can be obtained. The thickness of the treatment layer is preferably less than 1.7 µm, and more preferably 0.2 µm to 1.4 µm.

After contact with the treatment fluid, drying can be performed as needed. The drying temperature should be 40℃~90℃, and preferably 50℃~70℃.

C-7. Variations Methods for manufacturing a laminate using a resin substrate and coating a PVA-based resin layer formed on the resin substrate are described in C-1 to C-6. However, this invention can also be applied to a method for manufacturing a single PVA-based resin film. The manufacturing method typically includes the following steps: uniaxially extending a strip of PVA-based resin film along its length using a roller stretcher, simultaneously performing swelling, dyeing, crosslinking, and washing treatments, and finally drying. Contact with the treatment solution can typically be achieved by immersion in a washing bath containing the treatment solution, immersion in a treatment bath after washing, or coating with the treatment solution after washing. Example

The present invention will be specifically described below with reference to embodiments, but the present invention is not limited to these embodiments. The methods for measuring each characteristic are as described below. In addition, unless otherwise noted, "parts" and "%" in the embodiments and comparative examples are weight bases. (1) Thickness was measured using an interferometric film thickness gauge (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"). (2) Individual transmittance and orthogonal absorbance were measured using an ultraviolet-visible spectrophotometer (manufactured by Otsuka Electronics Co., Ltd. LPF-200) for the polarizing plates (protective layer/polarizing film) of the embodiments and comparative examples, and the measured individual transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc were respectively used as Ts, Tp and Tc of the polarizing film. The Ts, Tp, and Tc values were Y values obtained by measuring and correcting for visual sensitivity according to JIS Z8701's 2-degree field of view (C light source). The refractive index of the protective film was 1.50, and the refractive index of the polarizing film's surface opposite to the protective film was 1.53. Furthermore, using Tc measured at various wavelengths, the cross-absorbance was calculated using the following formula: Cross-absorbance = log10(100/Tc). The cross-absorbance Abs_₀ was calculated from the cross-transmittance Tc at a measured wavelength of 470 nm using an Otsuka Denko "LPF-200". Alternatively, Abs _₀ could also be measured using a Japanese spectrometer such as the "V-7100". Next, the polarizing plate was subjected to a durability test for 240 hours at a temperature of 60°C and a relative humidity of 95%. The orthogonal absorbance Abs ₂₄₀ after the durability test was calculated in the same manner as above.

[Example 1] The thermoplastic resin substrate is a long strip of amorphous polyethylene terephthalate copolymer (thickness: 100 μm) with a water absorption rate of 0.75% and a Tg of approximately 75°C. One side of the resin substrate is subjected to corona treatment (treatment conditions: 55 W·min/ ^m² ). 13 parts by weight of potassium iodide are added to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoethyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") in a 9:1 ratio to prepare a PVA aqueous solution (coating solution). The aforementioned PVA aqueous solution was applied to the corona-treated surface of a resin substrate and dried at 60°C to form a 20μm thick PVA-based resin layer, thus creating a laminate. The obtained laminate was subjected to free-end uniaxial elongation (air-assisted elongation treatment) of 2.4 times between rollers at different circumferential speeds in an oven at 130°C. Next, the laminate was immersed in an insoluble bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insoluble treatment). Next, while adjusting the concentration of the staining bath (an iodine aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 relative to 100 parts by weight of water) at a temperature of 30°C, the polarizing plate was immersed in it for 60 seconds to achieve a final unit transmittance (Ts) of 44.0% (staining treatment). Then, it was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid relative to 100 parts by weight of water) at a temperature of 40°C for 30 seconds (crosslinking treatment). Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 4.0 wt%, potassium iodide 5 wt%) at a liquid temperature of 70°C, it is uniaxially stretched between rollers with different circumferential speeds along the longitudinal direction (long side direction) to achieve a total elongation ratio of 5.5 times (water stretching treatment). Afterward, the laminate is immersed in a washing bath at a liquid temperature of 20°C (an aqueous solution of 4 parts by weight of potassium iodide mixed with 100 parts by weight of water, pH=6) (washing treatment). Then, while drying in an oven maintained at 90°C, its contact surface temperature is maintained at 75°C on a SUS heating roller for approximately 2 seconds (drying shrinkage treatment). The width shrinkage rate of the laminate obtained by drying and shrinking treatment is 2%. In the above manner, a polarizing film with a thickness of 5.0µm is formed on a resin substrate, and a cycloolefin film (manufactured by ZEON Corporation, product name "G-Film") as a protective layer (protective film) is laminated on the surface of the polarizing film through a UV-curing adhesive (1.0µm thick). Then, the resin substrate is peeled off to obtain a laminate with a protective layer/polarizing film. The resulting laminate has a unit transmittance (Ts) of 44.0%, which is due to the surface refractive index of the polarizing film/protective layer constituting the laminate being 1.53/1.53. Therefore, a correction of +0.2% was made to convert it to a value of 1.53/1.50. Next, 0.3 wt% hydrochloric acid and 3.5 wt% PVA (JC-25) were dissolved in water to obtain a treatment solution (pH=1.3). This solution was then applied to the surface of the polarizing film of the laminate with a thickness of 0.6 μm and dried at 60°C for 4 minutes to form a treatment layer. The polarizing plate of this embodiment was obtained in the above manner.

For the obtained polarizing plate (actually a polarizing film), the unit transmittance and Abs ₂₄₀ / Abs ₀ are shown in Table 1.

[Examples 2-10] A polarizing plate was fabricated by adjusting the monomer transmittance of the polarizing film, the method of contact with the treatment liquid, the pH of the treatment liquid, the type of acid contained in the treatment liquid, and the thickness of the treatment layer as shown in Table 1. The monomer transmittance and Abs ₂₄₀ / Abs ₀ are shown in Table 1 for the obtained polarizing plate (which is essentially a polarizing film).

[Example 11] A polarizing plate was fabricated in the same manner as in Example 1, except that the treatment solution did not contain PVA-based resin (i.e., no treatment layer was formed) and the pH of the treatment solution was set to 0.9. The monomer transmittance and Abs ₂₄₀ / Abs ₀ are shown in Table 1 for the resulting polarizing plate (which is essentially a polarizing film).

[Example 12] Following the same procedure as in Example 1, the thermoplastic resin substrate/PVA-based resin layer laminate was subjected to air-assisted stretching treatment, insolubility treatment, dyeing treatment, crosslinking treatment, and underwater stretching treatment. The laminate after underwater stretching treatment was immersed in a treatment bath (pH=1.6) at a liquid temperature of 20°C (in contact with the treatment solution). The treatment solution was prepared by adding hydrochloric acid to a general washing bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water). Subsequently, while drying in an oven maintained at 90°C, the contact surface temperature was maintained at 75°C on a SUS heating roller for approximately 2 seconds (drying shrinkage treatment). The width shrinkage rate obtained by drying and shrinking the laminate was 2%. Next, a cycloolefin film (manufactured by ZEON Corporation, product name "G-Film") was laminated onto the surface of the polarizing film as a protective layer (protective film) using a UV-curable adhesive (1.0 μm thick). The resin substrate was then peeled off to obtain a polarizing plate with a protective layer/polarizing film. Table 1 shows the monomer transmittance and Abs ₂₄₀ /Abs ₀ for the obtained polarizing plate (essentially a polarizing film).

[Comparative Example 1] A polarizing plate was manufactured in the same manner as in Example 1, except that it was not exposed to the treatment liquid. The unit transmittance and Abs ₂₄₀ / Abs ₀ of the resulting polarizing plate (which is essentially a polarizing film) are shown in Table 1.

[Comparative Example 2] The unit transmittance of the polarizing film was set to 45.0%, and the polarizing plate was manufactured in the same manner as in Comparative Example 1. The unit transmittance and Abs ₂₄₀ / Abs ₀ of the resulting polarizing plate (which is essentially a polarizing film) are shown in Table 1.

<Comparative Examples 3-8> Polarizing plates were fabricated by adjusting the monomer transmittance of the polarizing film, the method of contact with the treatment solution, the pH of the treatment solution, the type of acid contained in the treatment solution, and the thickness of the treatment layer (if formed) as shown in Table 1. The monomer transmittance and Abs ₂₄₀ / Abs ₀ are shown in Table 1 for the resulting polarizing plates (essentially polarizing films).

[Example 13] A long roll of PVA-based resin film (manufactured by Nippon Gosei Co., Ltd., product name "PS7500") with a thickness of 55 μm was uniaxially stretched along the strip direction using a roller stretcher to achieve a total elongation ratio of 6.0 times. Simultaneously, swelling, dyeing, crosslinking, and washing processes were applied, followed by drying to produce a polarizing film with a thickness of 23 μm. After washing and before drying, the same processing solution as in Example 1 was applied to one side of the PVA-based resin film (polarizing film) in the same manner as in Example 1. Table 1 shows the monomer transmittance and Abs ₂₄₀ /Abs ₀ for the obtained polarizing film.

[Example 14] Instead of a washing bath, a PVA-based resin film (polarizing film) was passed through the same treatment bath as in Example 12 (therefore, no coating solution was applied after washing). Otherwise, a polarizing film with a thickness of 23 µm was produced in the same manner as in Example 13. The monomer transmittance and Abs ₂₄₀ /Abs ₀ are shown in Table 1 for the obtained polarizing film.

[Table 1]

As clearly shown in Table 1, the polarizing film of the present invention exhibits an Abs ₂₄₀ /Abs ₀ ratio greater than 0.90 after the durability test, indicating that the reduction in polarization performance under high temperature and high humidity conditions is suppressed. In other words, the polarizing film of the present invention demonstrates excellent durability under high temperature and high humidity conditions. In particular, the polarizing film of Example 10 exhibits an Abs ₂₄₀ /Abs ₀ ratio greater than 1.0, demonstrating improved polarization performance under high temperature and high humidity conditions. This is a superior effect that is unpredictable and contrary to common technical knowledge. The polarizing films of Comparative Examples 1 and 2, which did not come into contact with the treatment solution, and the polarizing films of Comparative Examples 3-8, which came into contact with the treatment solution with a pH greater than 3.0, all had an Abs ₂₄₀ /Abs ₀ ratio of 0.88 or less. Furthermore, in Comparative Example 6, which used boric acid as the treatment solution, the treatment solution gelled and could not come into contact with the polarizing film.

Industrial Applicability The polarizing film and polarizing plate of this invention are suitable for use in liquid crystal display devices.

10: Polarizing film 20: First protective layer 30: Second protective layer 100: Polarizing plate 200: Laminator R1~R6: Conveyor rollers G1~G4: Guide rollers

Figure 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. Figure 2 is a schematic view showing an example of a drying shrinkage treatment using a heating roller.

10:Polarizing film

20: First protective layer

30: Second protective layer

100:Polarizing plate

Claims (4)

A polarizing film is composed of an iodine-containing polyvinyl alcohol resin film; a treatment layer is formed on the surface of the polarizing film; the treatment layer is formed with a treatment solution containing polyvinyl alcohol resin and having a pH below 3.0; and after a durability test of 240 hours at a temperature of 60°C and a relative humidity of 95%, the absorbance Abs ₂₄₀ at a wavelength of 470 nm relative to the absorbance Abs ₀ before the durability test satisfies the following relationship: Abs ₂₄₀ / Abs ₀ > 0.90. For example, the polarizing film in Request 1 has a single-unit transmittance of 43.0% or higher. For example, the polarizing film in request item 1 or 2 has a thickness of less than 8 μm. A polarizing plate having a polarizing film as described in any one of claims 1 to 3 and a protective layer disposed on at least one side of the polarizing film.