Polarizing film and polarizing plate

Abstract

To provide a polarizing film which offers superior durability in high-temperature high-humidity environments.SOLUTION: A polarizing film of the present invention consists of a polyvinyl alcohol-based resin film containing iodine, and light absorbance Abs240 thereof at 470 nm wavelength, as observed after going through a 240-hour durability test at temperature of 60°C and relative humidity of 95%, satisfies the following condition with respect to light absorbance Abs0 observed before the durability test: Abs240 / Abs0>0.90. In one embodiment, the polarizing film has a single transmittance of 43.0% or greater.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polarizing film and a polarizing plate.

Background Art

[0002] In a liquid crystal display device, which is a typical image display device, polarizing films are arranged on both sides of a liquid crystal cell due to its image forming method. As a method for manufacturing a polarizing film, for example, a method has been proposed in which a laminate having a resin substrate and a polyvinyl alcohol (PVA) - based resin layer is stretched and then subjected to a dyeing treatment to obtain a polarizing film on the resin substrate (for example, Patent Document 1). According to such a method, since a thin polarizing film can be obtained, it has been attracting attention as being able to contribute to the thinning of recent image display devices. However, in the case of a thin polarizing film, further improvement in durability under a high - temperature and high - humidity environment is required.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention has been made to solve the above - mentioned conventional problems, and its main object is to provide a polarizing film, a polarizing plate, and a method for manufacturing such a polarizing film, which are excellent in durability under a high - temperature and high - humidity environment.

Means for Solving the Problems

[0005] The polarizing film of the present invention is composed of a polyvinyl alcohol - based resin film containing iodine, and the absorbance Abs at a wavelength of 470 nm after a durability test at a temperature of 60 °C and a relative humidity of 95% for 240 hours 240 satisfies the following relationship with respect to the absorbance Abs0 before the durability test: a polarizing film: Abs240 / Abs0 > 0.90 In one embodiment, the polarization film has a single transmittance of 43.0% or more. In one embodiment, the polarization film has a thickness of 8 μm or less. According to another aspect of the present invention, a polarizing plate is provided. This polarizing plate has the above-described polarization film and a protective layer disposed on at least one side of the polarization film.

Advantages of the Invention

[0006] According to the present invention, by bringing the polarization film into contact with a treatment liquid having a pH of 3.0 or less, a polarization film excellent in durability under a high-temperature and high-humidity environment can be obtained. Specifically, the polarization film according to the embodiment of the present invention has an absorbance Abs at a wavelength of 470 nm after a durability test at a temperature of 60° C. and a relative humidity of 95% for 240 hours 240 which satisfies the following relationship with respect to the absorbance Abs0 before the durability test: Abs 240 / Abs0 > 0.90 That is, the polarization film according to the embodiment of the present invention has an absorbance at a wavelength of 470 nm that does not decrease so much even by a heat and humidity durability test. This means that the polarization film according to the embodiment of the present invention suppresses a decrease in polarization performance under a high-temperature and high-humidity environment to a practically acceptable level. Although the polarization performance of a polarization film (especially, a thin polarization film) often significantly decreases under a high-temperature and high-humidity environment, according to the embodiment of the present invention, such a problem can be solved, and a polarization film (especially, a thin polarization film) excellent in durability under a high-temperature and high-humidity environment can be provided.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0009] A. Polarizing film The polarizing film according to an embodiment of the present invention is composed of a polyvinyl alcohol (PVA)-based resin film containing iodine, and the absorbance Abs at a wavelength of 470 nm after a durability test at a temperature of 60°C and a relative humidity of 95% for 240 hours 240 satisfies the following relationship with respect to the absorbance Abs0 before the durability test. Abs 240 / Abs0 > 0.90 This indicates that in the polarizing film according to the embodiment of the present invention, the destruction of the PVA-I3 - complex having absorption near 470 nm due to the heat and humidity durability test is suppressed. Although not clear theoretically, such excellent durability can be realized by bringing the polarizing film into contact with a treatment liquid having a pH of 3.0 or less. Abs 240 / Abs0 is preferably 0.92 or more, more preferably 0.93 or more, and still more preferably 0.95 or more. Abs 240 The upper limit of / Abs0 can be, for example, 1.50. The absorbance is typically the orthogonal absorbance. The orthogonal absorbance is obtained by the following formula based on the orthogonal transmittance Tc measured when obtaining the polarization degree described later. Orthogonal absorbance = log10(100 / Tc) The absorbance Abs0 before the durability test is the absorbance of the polarizing film in its normal state, and the Abs0 of the polarizing film at a wavelength of 470 nm is, for example, less than 5.0, preferably 3.0 or less, and more preferably 2.2 or less. The lower limit of Abs0 can be, for example, 1.0.

[0010] In one embodiment, the polarizing film has an absorbance Abs at a wavelength of 600 nm after a durability test at a temperature of 60°C and a relative humidity of 95% for 240 hours 240 satisfies the following relationship with respect to the absorbance Abs0 before the durability test. Abs 240 / Abs0 > 1.00 In the polarizing film according to an embodiment of the present invention, PVA-I5 having absorption near 600 nm - It is shown that the complex is not destroyed even in the heat and humidity endurance test, but rather can increase. PVA-I5 - The complex is destroyed in a high-temperature and high-humidity environment, and the polarization performance of the polarizing film is expected to decrease under normal high-temperature and high-humidity environments. However, such excellent durability of the polarizing film according to the embodiment of the present invention is unexpectedly excellent. Abs 240 / Abs0 is preferably 1.05 or more, more preferably 1.10 or more, still more preferably 1.15 or more, particularly preferably 1.20 or more, and especially preferably 1.25 or more. Abs 240 The upper limit of / Abs0 can be, for example, 2.00. Note that Abs0 of the polarizing film at a wavelength of 600 nm is less than, for example, 5.0, preferably 4.3 or less, and more preferably 4.0 or less. The lower limit of Abs0 can be, for example, 2.0.

[0011] The thickness of the polarizing film is preferably 8 μm or less, more preferably 7 μm or less, still more preferably 5 μm or less, and particularly preferably 3 μm or less. The lower limit of the thickness of the polarizing film can be 1 μm in one embodiment and 2 μm in another embodiment. Such a thickness can be realized, for example, by producing a polarizing film using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate, as will be described later. When the polarizing film is produced from a single resin film, the thickness of the polarizing film can be, for example, 12 μm to 35 μm.

[0012] The polarizing film preferably exhibits absorption dichroism at any wavelength in the range of 380 nm to 780 nm. The single transmittance of the polarizing film is preferably 42.0% or more, more preferably 42.5% or more, still more preferably 43.0% or more, particularly preferably 43.5% or more, and most preferably 44.0% or more. On the other hand, the single transmittance is preferably 47.0% or less, more preferably 46.0% or less. The degree of polarization of the polarizing film is preferably 99.95% or more, more preferably 99.99% or more. On the other hand, the degree of polarization is preferably 99.998% or less. According to the embodiment of the present invention, in this way, it is possible to achieve both a high single transmittance and a high degree of polarization, and it is possible to realize excellent durability in a high-temperature and high-humidity environment as described above. The above single transmittance is typically the Y value measured using an ultraviolet-visible spectrophotometer and subjected to visual sensitivity correction. Also, the single transmittance is the value when the refractive index of one surface of the polarizing plate is converted to 1.50 and the refractive index of the other surface is converted to 1.53. The above degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer and subjected to visual sensitivity correction. Degree of polarization (%) = {(Tp - Tc) / (Tp + Tc)} 1 / 2 ×100

[0013] In one embodiment, the transmittance (single transmittance) of a thin polarizing film with a thickness of 8 μm or less is typically measured using an ultraviolet-visible spectrophotometer with a laminate of a polarizing film (refractive index of the surface: 1.53) and a protective layer (protective film) (refractive index: 1.50) as the measurement target. Depending on the refractive index of the surface of the polarizing film and / or the refractive index of the surface of the protective layer in contact with the air interface, the reflectance at the interface of each layer changes, and as a result, the measured value of the transmittance may change. Therefore, for example, when using a protective layer with a refractive index other than 1.50, the measured value of the transmittance may be corrected according to the refractive index of the surface of the protective layer in contact with the air interface. Specifically, the correction value C of the transmittance is represented by the following formula using the reflectance R1 (transmittance axis reflectance) of the polarization parallel to the transmittance axis at the interface between the protective layer and the air layer. 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 a protective layer with a refractive index of 1.50 is used, n1 is the refractive index of the protective layer to be used, and T1 is the transmittance of the polarizing film. For example, when a substrate (such as a cycloolefin film or a film with a hard coat layer) with a surface refractive index of 1.53 is used as the protective layer, the correction amount C is about 0.2%. In this case, by adding 0.2% to the transmittance obtained by measurement, it is possible to convert the transmittance of the polarizing film with a surface refractive index of 1.53 to the transmittance when a protective layer with a refractive index of 1.50 is used. According to the calculation based on the above formula, the change amount of the correction value C when the transmittance T1 of the polarizing film is changed by 2% is 0.03% or less, and the influence of the transmittance of the polarizing film on the value of the correction value C is limited. Also, when the protective layer has absorption other than surface reflection, appropriate correction can be performed according to the absorption amount.

[0014] The polarizing film may be produced using a single resin film or may be produced using a laminate of two or more layers. Specific examples of the polarizing film obtained using a laminate include a polarizing film obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate. The polarizing film obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and drying to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; stretching and dyeing the laminate to make the PVA-based resin layer into a polarizing film. In an embodiment of the present invention, the polarizing film is brought into contact with a treatment liquid having a pH of 3.0 or less. Thereby, excellent durability in a high-temperature and high-humidity environment as described above can be realized. Preferably, a PVA-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of the resin substrate. Stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching it. Further, stretching may further include, if necessary, air stretching the laminate at a high temperature (for example, 95° C. or higher) before stretching in the aqueous boric acid solution. In addition, in the present embodiment, preferably, the laminate is subjected to a drying shrinkage treatment in which it is heated while being conveyed in the longitudinal direction to shrink by 2% or more in the width direction. Typically, the manufacturing method of the present embodiment includes sequentially performing an air-assisted stretching treatment, a dyeing treatment, a water stretching treatment, and a drying shrinkage treatment on the laminate. By introducing the auxiliary stretching, even when PVA is applied on a thermoplastic resin, it becomes possible to enhance the crystallinity of PVA and achieve high optical characteristics. At the same time, by enhancing the orientation of PVA in advance, problems such as a decrease in the orientation of PVA and dissolution when immersed in water in subsequent dyeing and stretching steps can be prevented, and high optical characteristics can be achieved. Further, when the PVA-based resin layer is immersed in a liquid, the disturbance of the orientation and the decrease in the orientation of polyvinyl alcohol molecules can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. Thereby, the optical characteristics of the polarizing film obtained through treatment steps such as a dyeing treatment and a water stretching treatment in which the laminate is immersed in a liquid can be improved.Furthermore, by shrinking the laminate in the width direction through a drying shrinkage treatment, the optical properties can be improved. The obtained resin substrate / polarizing film laminate may be used as it is (i.e., the resin substrate may serve as the protective layer of the polarizing film), or the resin substrate may be peeled off from the resin substrate / polarizing film laminate, and any appropriate protective layer according to the purpose may be laminated on the peeled surface and used. Details of the method for manufacturing the polarizing film will be described later in Section C.

[0015] B. Polarizing Plate FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 has a polarizing film 10, a first protective layer 20 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. As described above, one of the first protective layer and the second protective layer may be the resin substrate used in the manufacture of the above polarizing film.

[0016] The first and second protective layers are formed of any suitable film that can be used as a protective layer for a polarizing film. Specific examples of the material that is the main component of the film include cellulose resins such as triacetyl cellulose (TAC), and transparent resins such as polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyether sulfone-based, polysulfone-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, acetate-based resins, etc. Also, thermosetting resins or ultraviolet curable resins such as (meth)acrylic-based, urethane-based, (meth)acrylic urethane-based, epoxy-based, silicone-based resins, etc. are also included. In addition, for example, glassy polymers such as siloxane-based polymers are also included. Also, the polymer film described in Japanese Patent Application Laid-Open No. 2001-343529 (WO01 / 37007) can also be used. As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used. For example, a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be mentioned. The polymer film can be, for example, an extruded product of the above resin composition.

[0017] 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 even more preferably 10 μm to 60 μm. When surface treatment is performed, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.

[0018] 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 even more preferably 10 μm to 60 μm. In one embodiment, the inner protective layer is a retardation layer having any appropriate retardation value. In this case, the in-plane retardation Re(550) of the retardation layer is, for example, 110 nm to 150 nm. "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23° C., and is obtained by the formula: Re = (nx - ny) × d. Here, "nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), "nz" is the refractive index in the thickness direction, and "d" is the thickness (nm) of the layer (film).

[0019] C. Method for manufacturing polarizing film According to one embodiment of the present invention, a method for manufacturing a polarizing film includes: applying and drying a PVA-based resin solution on one side of a long thermoplastic resin substrate to form a PVA-based resin layer and obtain a laminate; stretching and dyeing the laminate to make the PVA-based resin layer into a polarizing film; and contacting the polarizing film with a treatment liquid having a pH of 3.0 or less. By contacting the polarizing film with a treatment liquid having a pH of 3.0 or less, a polarizing film excellent in durability under a high-temperature and high-humidity environment can be realized. Preferably, the PVA-based resin solution further contains a halide. Preferably, the manufacturing method includes sequentially performing an air-assisted stretching treatment, a dyeing treatment, a water stretching treatment, and a drying shrinkage treatment on the laminate to shrink the laminate by 2% or more in the width direction by heating while conveying it in the longitudinal direction. The content of the halide in the PVA-based resin solution (and as a result, the PVA-based resin layer) is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. The shrinkage rate of the laminate in the width direction by the drying shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizing film described in item A above can be obtained. In particular, by producing a laminate including a PVA-based resin layer containing a halide, performing multi-stage stretching of the laminate including air-assisted stretching and water stretching, and heating the stretched laminate with a heating roll, a polarizing film having excellent optical properties (typically, single transmittance and unit absorbance) can be obtained.

[0020] C-1. Production of laminate As a method for producing a laminate of a thermoplastic resin substrate and a PVA-based resin layer, any suitable method can be adopted. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin substrate and dried to form a PVA-based resin layer on the thermoplastic resin substrate. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

[0021] As the method for applying the coating liquid, any appropriate method can be adopted. For example, roll coating method, spin coating method, wire bar coating method, dip coating method, die coating method, curtain coating method, spray coating method, knife coating method (comma coating method, etc.) and the like can be mentioned. The application and drying temperature of the above coating liquid is preferably 50°C or higher.

[0022] The thickness of the PVA-based resin layer is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm.

[0023] Before forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to surface treatment (for example, corona treatment, etc.), or an easy adhesion layer may be formed on the thermoplastic resin substrate. By performing such treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved.

[0024] C-1-1. Thermoplastic resin substrate As the thermoplastic resin substrate, any appropriate thermoplastic resin film can be adopted. Details of the thermoplastic resin substrate are described, for example, in Japanese Patent Application Laid-Open No. 2012-73580. The entire description of the said publication is incorporated herein by reference.

[0025] C-1-2. Coating liquid As described above, the coating liquid contains a halide and a PVA-based resin. Typically, the coating liquid is a solution in which the halide and the PVA-based resin are dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferably used. The PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film adhered to the thermoplastic resin substrate can be formed. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

[0026] Additives may be incorporated into the coating liquid. Examples of the additives include plasticizers, surfactants, etc. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability, and stretchability of the obtained PVA-based resin layer.

[0027] As the PVA-based resin, any suitable resin can be adopted. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer can be mentioned. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer is obtained by saponifying 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%, more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be determined according to JIS K 6726-1994. By using a PVA-based resin with such a saponification degree, a polarizing film with excellent durability can be obtained. If the saponification degree is too high, there is a risk of gelation.

[0028] The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually from 1000 to 10000, preferably from 1200 to 4500, and more preferably from 1500 to 4300. The average degree of polymerization can be determined according to JIS K 6726-1994.

[0029] As the above-mentioned halide, any appropriate halide can be adopted. For example, iodide and sodium chloride can be mentioned. Examples of iodides include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferably used.

[0030] The amount of the halide in the coating liquid is preferably from 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, and more preferably from 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA-based resin. When the amount of the halide with respect to 100 parts by weight of the PVA-based resin exceeds 20 parts by weight, the halide may bleed out and the finally obtained polarizing film may become cloudy.

[0031] Generally, when the PVA-based resin layer is stretched, the orientation of polyvinyl alcohol molecules in the PVA-based resin becomes higher. However, when the stretched PVA-based resin layer is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules may be disrupted and the orientation may decrease. In particular, when stretching a laminate of a thermoplastic resin and a PVA-based resin layer in boric acid water, when stretching the laminate in boric acid water at a relatively high temperature to stabilize the stretching of the thermoplastic resin, the tendency of the above-mentioned decrease in orientation degree is remarkable. For example, while the stretching of a single PVA film in boric acid water is generally carried out at 60 °C, the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is carried out at a high temperature of around 70 °C. In this case, the orientation of PVA at the initial stage of stretching may decrease before the orientation is increased by stretching in water. On the other hand, by producing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate, and performing high-temperature stretching (auxiliary stretching) in air before stretching the laminate in boric acid water, the 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, the disruption of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. Thereby, the optical properties of a polarizing film obtained through a treatment step such as a dyeing treatment and a stretching treatment in water, which are carried out by immersing the laminate in a liquid, can be improved.

[0032] C-2. Air auxiliary stretching treatment In particular, in order to obtain high optical properties, a two-step stretching method that combines dry stretching (auxiliary stretching) and stretching in boric acid water is selected. By introducing auxiliary stretching as in the two-step stretching, it is possible to stretch while suppressing the crystallization of the thermoplastic resin substrate, and solve the problem that the stretchability decreases due to excessive crystallization of the thermoplastic resin substrate in the subsequent stretching in boric acid water, and the laminate can be stretched at a higher magnification. Furthermore, when applying a PVA-based resin onto 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 compared to the case of applying the PVA-based resin onto a normal metal drum. As a result, the crystallization of the PVA-based resin becomes relatively low, and there may arise a problem that sufficient optical properties cannot be obtained. On the other hand, by introducing auxiliary stretching, even when applying a PVA-based resin onto a thermoplastic resin, it becomes possible to enhance the crystallinity of the PVA-based resin and achieve high optical properties. At the same time, by enhancing the orientation of the PVA-based resin in advance, problems such as a decrease in the orientation or dissolution of the PVA-based resin when immersed in water in the subsequent dyeing process or stretching process can be prevented, and high optical properties can be achieved.

[0033] The stretching method of air-assisted stretching may be fixed-end stretching (for example, the method of stretching using a tenter stretching machine) or free-end stretching (for example, the method of uniaxially stretching a laminate through rolls with different peripheral speeds). However, in order to obtain high optical properties, free-end stretching can be actively adopted. In one embodiment, the air stretching process includes a heating roll stretching step of stretching the laminate while conveying it in its longitudinal direction by the peripheral speed difference between the heating rolls. The air stretching process typically includes a zone stretching step and a heating roll stretching step. Note that the order of the zone stretching step and the heating roll stretching step is not limited, and the zone stretching step may be performed first, or the heating roll stretching step may be performed first. The zone stretching step may be omitted. In one embodiment, the zone stretching step and the heating roll stretching step are performed in this order. Also, in another embodiment, in a tenter stretching machine, the film ends are gripped and stretched by widening the distance between the tenters in the flow direction (the widening of the distance between the tenters becomes the stretching ratio). At this time, the distance between the tenters in the width direction (the direction perpendicular to the flow direction) is set to approach arbitrarily. Preferably, it can be set to be closer to the free-end stretching with respect to the stretching ratio in the flow direction. In the case of free-end stretching, the shrinkage rate in the width direction = (1 / stretching ratio) 1 / 2 is calculated by

[0034] The air-assisted stretching may be performed in one step or in multiple steps. When performed in multiple steps, the stretching ratio is the product of the stretching ratios of each step. The stretching direction in the air-assisted stretching is preferably substantially the same as the stretching direction in the underwater stretching.

[0035] The stretching ratio in the air-assisted stretching is preferably 2.0 to 3.5 times. When combining the air-assisted stretching and the underwater stretching, the maximum stretching ratio is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times or more with respect to the original length of the laminate. In this specification, the "maximum stretching ratio" refers to the stretching ratio immediately before the laminate breaks, and separately, the stretching ratio at which the laminate breaks is confirmed, and a value 0.2 lower than that value is referred to.

[0036] The stretching temperature for air-assisted stretching can be set to any appropriate value according to the forming material of the thermoplastic resin substrate, the stretching method, etc. The stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably Tg + 10°C or higher, and particularly preferably Tg + 15°C or higher. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, the crystallization of the PVA-based resin can be suppressed from proceeding rapidly, and defects due to such crystallization (for example, hindering the orientation of the PVA-based resin layer by stretching) can be suppressed.

[0037] C-3. Insolubilization treatment, dyeing treatment, and crosslinking treatment If necessary, after the air-assisted stretching treatment and before the underwater stretching treatment and dyeing treatment, an insolubilization treatment is performed. The above insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The above dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically, iodine). If necessary, after the dyeing treatment and before the underwater stretching treatment, a crosslinking treatment is performed. The above 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, for example, in Japanese Patent Application Laid-Open No. 2012-73580 (above).

[0038] C-4. Underwater stretching treatment The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, stretching can be performed at a temperature lower than the glass transition temperature (typically about 80°C) of the thermoplastic resin substrate and the PVA-based resin layer, and the PVA-based resin layer can be stretched at a high magnification while suppressing its crystallization. As a result, a polarizing film having excellent optical properties can be manufactured.

[0039] Any suitable method can be adopted for the stretching method of the laminate. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching the laminate through rolls with different peripheral speeds). Preferably, free-end stretching is selected. The stretching of the laminate may be performed in one step or in multiple steps. When performed in multiple steps, the stretching ratio (maximum stretching ratio) of the laminate described below is the product of the stretching ratios of each step.

[0040] Stretching in water is preferably carried out by immersing the laminate in an aqueous boric acid solution (stretching in aqueous boric acid). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be imparted with rigidity to withstand the tension during stretching and water resistance that does not dissolve in water. Specifically, boric acid can generate tetrahydroxyborate anions in an aqueous solution and crosslink with the PVA-based resin through hydrogen bonds. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, enabling good stretching and manufacturing a polarizing film with excellent optical properties.

[0041] The above aqueous boric acid solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent. The boric acid concentration is preferably 1 part by weight to 10 parts by weight, more preferably 2.5 parts by weight to 6 parts by weight, and particularly preferably 3 parts by weight to 5 parts by weight based on 100 parts by weight of water. 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, and a polarizing film with higher characteristics can be manufactured. 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.

[0042] Preferably, an iodide is added to the above stretching bath (aqueous boric acid solution). By adding an iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Specific examples of the iodide are as described above. The concentration of the iodide is preferably 0.05 part by weight to 15 parts by weight, more preferably 0.5 part by weight to 8 parts by weight based on 100 parts by weight of water.

[0043] The stretching temperature (the temperature of the stretching bath solution) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such temperatures, high magnification stretching can be achieved while suppressing the dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is below 40°C, there is a risk that good stretching cannot be achieved even considering the plasticization of the thermoplastic resin substrate by water. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a risk that excellent optical properties cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

[0044] The stretching magnification by stretching in water is preferably 1.5 times or more, more preferably 3.0 times or more. The total stretching magnification 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 magnification, a polarizing film with extremely excellent optical properties can be manufactured. Such a high stretching magnification can be achieved by adopting a stretching method in water (stretching in boric acid water).

[0045] C-5. Drying and shrinkage treatment The above drying and shrinkage treatment may be performed by zone heating in which the entire zone is heated, or may be performed by heating the conveying rolls (using so-called heating rolls) (heating roll drying method). Preferably, both are used. By drying using heating rolls, the heating curl of the laminate can be efficiently suppressed, and a polarizing film with excellent appearance can be manufactured. Specifically, by drying the laminate in a state where it is in contact with the heating roll, the crystallization of the thermoplastic resin base material can be efficiently promoted and the degree of crystallization can be increased. Even at a relatively low drying temperature, the degree of crystallization of the thermoplastic resin base material can be favorably increased. As a result, the rigidity of the thermoplastic resin base material increases, and it becomes a state where it can withstand the shrinkage of the PVA-based resin layer due to drying, and curl is suppressed. In addition, by using heating rolls, drying can be performed while maintaining the laminate in a flat state, so that not only curl but also the occurrence of wrinkles can be suppressed. At this time, the optical properties of the laminate can be improved by shrinking it in the width direction by the drying and shrinkage treatment. This is because the orientation of PVA and the PVA / iodine complex can be effectively enhanced. The shrinkage rate of the laminate in the width direction by the drying and shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%.

[0046] Figure 2 is a schematic diagram showing an example of the drying and shrinkage treatment. In the drying and shrinkage treatment, the laminate 200 is dried while being conveyed by the conveying rolls R1 to R6 heated to a predetermined temperature and the guide rolls G1 to G4. In the illustrated example, the conveying rolls R1 to R6 are arranged so as to alternately and continuously heat the surfaces of the PVA resin layer and the thermoplastic resin base material. However, for example, the conveying rolls R1 to R6 may be arranged so as to continuously heat only one surface of the laminate 200 (for example, the thermoplastic resin base material surface).

[0047] The drying conditions can be controlled by adjusting the heating temperature of the conveying roll (temperature of the heating roll), the number of heating rolls, the contact time with the heating roll, etc. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. The crystallinity of the thermoplastic resin can be increased well, curl can be suppressed well, and an optical laminate with extremely excellent durability can be manufactured. The temperature of the heating roll can be measured by a contact thermometer. In the illustrated example, six conveying rolls are provided, but there is no particular limitation as long as there are a plurality of conveying rolls. Usually, 2 to 40 conveying rolls are provided, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roll is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

[0048] The heating roll may be provided in a heating furnace (for example, an oven), or may be provided on a normal production line (under room temperature environment). Preferably, it is provided in a heating furnace equipped with a blowing means. By using drying by the heating roll and hot air drying in combination, a sharp temperature change between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of the hot air drying is preferably 30°C to 100°C. Also, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10 m / s to 30 m / s. The wind speed is the wind speed in the heating furnace and can be measured by a mini-vane type digital anemometer.

[0049] C-6. Contact with the treatment liquid As described above, 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 brought into contact with a treatment liquid having a pH of 3.0 or less. In one embodiment, the polarizing film can be brought into contact with the treatment liquid by bringing the laminate into contact with the treatment liquid as it is. In this case, typically, the thermoplastic resin substrate can be used as it is as a protective layer of the polarizing film. Alternatively, a resin film (which becomes a protective layer) may be bonded to the surface of the polarizing film of the laminate brought into contact with the treatment liquid to produce a laminate of a protective layer / polarizing film / thermoplastic resin substrate, and the thermoplastic resin substrate may be peeled off from the laminate to produce a polarizing plate having a structure of a protective layer / polarizing film. In another embodiment, a resin film (which becomes a protective layer) is bonded to the surface of the polarizing film of the laminate to produce a laminate of a protective layer / polarizing film / thermoplastic resin substrate, and the thermoplastic resin substrate is peeled off from the laminate to produce a laminate (polarizing plate) of a protective layer / polarizing film. By bringing the obtained polarizing plate into contact with the treatment liquid, the polarizing film can be brought into contact with the treatment liquid.

[0050] The contact between the polarizing film and the treatment liquid can be carried out by any suitable method. Representative examples include application of the treatment liquid to the polarizing film and immersion of the polarizing film (substantially, the laminate or the polarizing plate) in the treatment liquid. As the application method, any suitable method can be adopted. Specific examples include the method described in item C-1 as the application method of the coating liquid. The immersion can also be carried out in any suitable manner. For example, the treatment liquid may be added to the cleaning bath for the cleaning treatment, 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. Note that the cleaning treatment is typically carried out after the stretching treatment in water and before the drying and shrinking treatment. When the bath of the treatment liquid is provided separately, the bath of the treatment liquid may be provided between the cleaning bath and the drying and shrinking treatment equipment (that is, the contact with the treatment liquid may be carried out between the cleaning treatment and the drying and shrinking treatment), or may be provided downstream of the means for peeling the thermoplastic resin substrate (that is, the contact with the treatment liquid may be carried out after peeling the thermoplastic resin substrate).

[0051] As the treatment liquid, any appropriate acidic liquid can be used as long as the pH is 3.0 or less. Specific examples of the treatment liquid include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and citric acid. The treatment liquid is preferably a strong acid aqueous solution. Specific examples of the strong acid include hydrochloric acid, sulfuric acid, and nitric acid. The lower the pH of the treatment liquid (the stronger the acidity), the more preferable. Specifically, the pH is preferably 2.7 or less, more preferably 2.5 or less, still more preferably 2.0 or less, and particularly preferably 1.5 or less.

[0052] The acid concentration of the treatment liquid is preferably 0.02% by weight to 3.0% by weight, more preferably 0.04% by weight to 2.0% by weight, and still more preferably 0.1% by weight to 1.0% by weight.

[0053] The treatment liquid may contain a water-soluble resin (for example, a PVA-based resin). The water-soluble resin can function as a binder. The concentration of the water-soluble resin in the treatment liquid is preferably 3% by weight to 5% by weight. In this case, a treatment layer can be formed by applying and drying the treatment liquid. By forming such a treatment layer, a polarizing film having the above-described desired durability can also be obtained. The thickness of the treatment layer is preferably 1.7 μm or less, more preferably 0.2 μm to 1.4 μm.

[0054] After contact with the treatment liquid, drying can be performed as necessary. The drying temperature is preferably 40°C to 90°C, more preferably 50°C to 70°C.

[0055] C-7. Modification In C-1 to C-6, a manufacturing method using a laminate of a resin base material and a PVA-based resin layer formed by coating on the resin base material was described. However, the present invention can also be applied to a manufacturing method using a single PVA-based resin film. Such a manufacturing method typically includes uniaxially stretching a long PVA-based resin film in the longitudinal direction by a roll stretching machine, while performing swelling, dyeing, crosslinking, and washing treatments, and finally performing a drying treatment. The contact with the treatment liquid can typically be performed by dipping into a washing bath added with the treatment liquid, dipping into a treatment bath after the washing treatment, or applying the treatment liquid after the washing treatment.

Example

[0056] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. The measurement methods for each property are as follows. Unless otherwise specified, "parts" and "%" in the examples and comparative examples are based on weight. (1) Thickness It was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"). (2) Single transmittance and orthogonal absorbance For the polarizing plates (protective layer / polarizing film) in the examples and comparative examples, the single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer (LPF-200 manufactured by Otsuka Electronics) were taken as the Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp, and Tc are Y values measured by the 2-degree field of view (C light source) of JIS Z8701 and subjected to visual sensitivity correction. The refractive index of the protective film was 1.50, and the refractive index of the surface of the polarizing film opposite to the protective film was 1.53. Also, using the measured Tc at each wavelength, the orthogonal absorbance was determined by the following formula. Orthogonal absorbance = log10(100 / Tc) The orthogonal absorbance Abs0 was determined from the orthogonal transmittance Tc at a measurement wavelength of 470 nm using "LPF-200" manufactured by Otsuka Electronics Co., Ltd. Note that for Abs0, equivalent measurements can also be made using, for example, "V-7100" manufactured by JASCO. Next, the polarizing plate was subjected to a durability test at a temperature of 60°C and a relative humidity of 95% for 240 hours. The orthogonal absorbance Abs 240 after the durability test was determined in the same manner as above.

[0057] [Example 1] As the thermoplastic resin substrate, an amorphous isophthalic copolyethylene terephthalate film (thickness: 100 μm) in a long strip shape with a water absorption rate of 0.75% and a Tg of about 75°C was used. Corona treatment (treatment conditions: 55 W·min / m 2 ) was performed on one side of the resin substrate. 13 parts by weight of potassium iodide was added to 100 parts by weight of a PVA-based resin obtained by mixing polyvinyl alcohol (degree of polymerization 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer Z410") in a ratio of 9:1 to prepare a PVA aqueous solution (coating solution). The PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60°C to form a PVA-based resin layer with a thickness of 20 μm, thereby producing a laminate. The obtained laminate was uniaxially stretched freely by 2.4 times in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds in an oven at 130°C (air-assisted stretching treatment). Next, the laminate was immersed in an insolubilizing bath at a liquid temperature of 40°C (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds (insolubilizing treatment). Next, the laminate was immersed in a dyeing bath at a liquid temperature of 30°C (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with respect to 100 parts by weight of water) for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizing plate was 44.0% (dyeing treatment). Next, the laminate was immersed in a crosslinking bath at a liquid temperature of 40°C (an aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds (crosslinking treatment). Thereafter, while immersing the laminate in an aqueous boric acid solution (boric acid concentration: 4.0 wt%, potassium iodide: 5 wt%) at a liquid temperature of 70°C, uniaxial stretching was performed in the longitudinal direction (length direction) between rolls with different peripheral speeds so that the total draw ratio was 5.5 times (stretching treatment in water). Thereafter, the laminate was immersed in a cleaning bath at a liquid temperature of 20°C (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water, pH = 6) (cleaning treatment). Thereafter, while drying in an oven maintained at 90°C, it was brought into contact with a SUS heating roll having a surface temperature maintained at 75°C for about 2 seconds (dry shrinkage treatment). The shrinkage rate in the width direction of the laminate by the dry shrinkage treatment was 2%. In this way, a polarizing film with a thickness of 5.0 μm was formed on the resin substrate, and a cycloolefin-based film (manufactured by ZEON, product name "G-Film") as a protective layer (protective film) was laminated on the surface of the polarizing film with a UV curable adhesive (thickness: 1.0 μm). Thereafter, the resin substrate was peeled off to obtain a laminate having a structure of protective layer / polarizing film. The single transmittance (Ts) of the obtained laminate was 44.0%, which is a value obtained by correcting the actual measured value by +0.2% and converting it to a state of 1.53 / 1.50 because the surface refractive indices of the polarizing film / protective layer constituting the laminate are 1.53 / 1.53. Next, a treatment liquid (pH = 1.3) obtained by dissolving 0.3 wt% hydrochloric acid and 3.5 wt% PVA (JC-25) in water was coated on the surface of the polarizing film of the laminate to a thickness of 0.6 μm and dried at 60°C for 4 minutes to form a treatment layer. In this way, the polarizing plate of this example was obtained.

[0058] Regarding the obtained polarizing plate (substantially a polarizing film), the single transmittance and Abs 240 / Abs0 are shown in Table 1.

[0059] [Examples 2 to 10] The polarizing plate was produced by adjusting the single transmittance of the polarizing film, the contact method with the treatment liquid, the pH of the treatment liquid, the type of acid contained in the treatment liquid, and the thickness of the treatment layer as shown in Table 1. Regarding the obtained polarizing plate (substantially a polarizing film), the single transmittance and Abs 240 / Abs0 is shown in Table 1.

[0060] [Example 11] A polarizing plate was produced in the same manner as in Example 1, except that the treatment liquid did not contain a PVA-based resin (i.e., the treatment layer was not formed), and the pH of the treatment liquid was set to 0.9. For the obtained polarizing plate (substantially, a polarizing film), the single transmittance and Abs 240 / Abs0 is shown in Table 1.

[0061] [Example 12] In the same manner as in Example 1, a laminate of a thermoplastic resin substrate / PVA-based resin layer was subjected to air-assisted stretching treatment, insolubilization treatment, dyeing treatment, crosslinking treatment, and underwater stretching treatment. The underwater-stretched laminate was immersed in a treatment bath (pH = 1.6) at a liquid temperature of 20°C (contact with the treatment liquid). The treatment bath was prepared by adding hydrochloric acid to a normal cleaning bath (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water). Thereafter, while drying in an oven maintained at 90°C, it was brought into contact with a SUS heating roll maintained at a surface temperature of 75°C for about 2 seconds (dry shrinkage treatment). The shrinkage rate in the width direction of the laminate due to the dry shrinkage treatment was 2%. Next, a cycloolefin-based film (manufactured by ZEON Corporation, product name "G-Film") as a protective layer (protective film) was bonded to the surface of the polarizing film with a UV-curable adhesive (thickness 1.0 μm), and then the resin substrate was peeled off to obtain a polarizing plate having a structure of protective layer / polarizing film. For the obtained polarizing plate (substantially, a polarizing film), the single transmittance and Abs 240 / Abs0 is shown in Table 1.

[0062] [Comparative Example 1] A polarizing plate was produced in the same manner as in Example 1, except that contact with the treatment liquid was not performed. For the obtained polarizing plate (substantially, a polarizing film), the single transmittance and Abs 240 / Abs0 is shown in Table 1.

[0063] [Comparative Example 2] A polarizing plate was produced in the same manner as in Comparative Example 1, except that the single transmittance of the polarizing film was set to 45.0%. For the obtained polarizing plate (substantially, the polarizing film), the single transmittance and Abs 240 / Abs0 are shown in Table 1.

[0064] [Comparative Examples 3 to 8] A polarizing plate was produced by adjusting the single 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 (when formed) as shown in Table 1. For the obtained polarizing plate (substantially, the polarizing film), the single transmittance and Abs 240 / Abs0 are shown in Table 1.

[0065] [Example 13] A long roll of a PVA-based resin film (manufactured by Nippon Gosei Co., Ltd., product name "PS7500") with a thickness of 55 μm was uniaxially stretched in the longitudinal direction by a roll stretching machine so that the total stretching ratio was 6.0 times, and at the same time, swelling, dyeing, crosslinking, and washing treatments were performed, and finally a drying treatment was performed to produce a polarizing film with a thickness of 23 μm. Before and after the washing treatment and before the drying treatment, a treatment liquid similar to that in Example 1 was applied to one surface of the PVA-based resin film (polarizing film) in the same manner as in Example 1. For the obtained polarizing film, the single transmittance and Abs 240 / Abs0 are shown in Table 1.

[0066] [Example 14] A polarizing film with a thickness of 23 μm was produced in the same manner as in Example 13, except that the PVA-based resin film (polarizing film) was passed through a treatment bath similar to that in Example 12 instead of the washing bath of the washing treatment (therefore, the treatment liquid was not applied after the washing treatment). For the obtained polarizing film, the single transmittance and Abs 240 / Abs0 are shown in Table 1.

[0067]

Table 1

[0068] As is clear from Table 1, the polarizing film of the example of the present invention has Abs after the durability test 240 / Abs0 exceeds 0.90, and the decrease in polarization performance in a high-temperature and high-humidity environment is suppressed. That is, the polarizing film of the embodiment of the present invention has excellent durability in a high-temperature and high-humidity environment. In particular, the polarizing film of Example 10 has Abs 240 / Abs0 exceeding 1.0, and the polarization performance is improved in a high-temperature and high-humidity environment. This is an unexpected excellent effect contrary to common technical knowledge. The polarizing films of Comparative Examples 1 and 2 that did not come into contact with the treatment liquid and the polarizing films of Comparative Examples 3 to 8 that were brought into contact with a treatment liquid having a pH exceeding 3.0 all had Abs 240 / Abs0 of 0.88 or less. In addition, in Comparative Example 6 where boric acid was used as the treatment liquid, the treatment liquid gelled and the contact itself was impossible.

Industrial Applicability

[0069] The polarizing film and polarizing plate of the present invention are suitably used in liquid crystal display devices.

Explanation of Reference Numerals

[0070] 10 Polarizing film 20 First protective layer 30 Second protective layer 100 Polarizing plate

Claims

1. It is made of a polyvinyl alcohol resin film containing iodine, Absorbance (Abs) at a wavelength of 470 nm after a 240-hour durability test at a temperature of 60°C and a relative humidity of 95% ２４０ is the absorbance Abs before the durability test ０ A polarizing film that satisfies the following relationship with respect to Abs ２４０ / Abs ０ >0.90

2. A polarizing film as described in claim 1, wherein a treatment layer is formed on the surface of the polyvinyl alcohol-based resin film.

3. The polarizing film according to claim 2, wherein the treatment layer has a function of suppressing destruction of the PVA-I 5 − complex in the polarizing film in a high-temperature, high-humidity environment.

4. A polarizing film as described in claim 2, wherein the treatment layer is a solidified layer of a treatment liquid containing a binder.

5. A polarizing film as described in claim 4, wherein the treatment liquid is an acidic liquid.

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