KR20210136019A - Polarizing film, polarizing plate, and manufacturing method of the polarizing film - Google Patents

Abstract

The present invention provides a polarizing film that is thin and has excellent durability in a high-temperature, high-humidity environment. The polarizing film of this invention is comprised from the polyvinyl alcohol-type resin film containing an iodine, thickness is 8 micrometers or less, and contains 5 ppm - 350 ppm of alcohol whose boiling point is less than 100 degreeC. In one embodiment, the alcohol whose boiling point is less than 100 degreeC is at least 1 selected from the group which consists of methanol, ethanol, n-propyl alcohol, and isopropyl alcohol. The polarizing plate of the present invention includes the polarizing film and a protective layer disposed on at least one side of the polarizing film.

Description

Polarizing film, polarizing plate, and manufacturing method of the polarizing film

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

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

Japanese Laid-Open Patent Publication No. 2001-343521

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

The polarizing film of this invention is comprised from the polyvinyl alcohol-type resin film containing an iodine, thickness is 8 micrometers or less, and contains 5 ppm - 350 ppm of alcohol whose boiling point is less than 100 degreeC.

In one embodiment, the alcohol whose boiling point is less than 100 degreeC is at least 1 selected from the group which consists of methanol, ethanol, n-propyl alcohol, and isopropyl alcohol.

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

According to another aspect of the present invention, a method for manufacturing the polarizing film is provided. This method forms a polyvinyl alcohol-type resin layer on one side of a long thermoplastic resin base material, and sets it as a laminated body; stretching and dyeing the laminate to make the polyvinyl alcohol-based resin layer a polarizing film; and, introducing an alcohol having a boiling point of less than 100° C. into the polarizing film.

In one embodiment, the manufacturing method includes immersing the polarizing film in a treatment liquid containing an alcohol having a boiling point of less than 100°C.

In one embodiment, the manufacturing method further includes heating the laminate after introducing the alcohol having the boiling point of less than 100° C. into the polarizing film.

In one embodiment, said stretching comprises underwater stretching.

ADVANTAGE OF THE INVENTION According to this invention, the polarizing film which is thin and excellent in durability in a high-temperature, high-humidity environment can be obtained by introduce|transducing the alcohol whose boiling point is less than 100 degreeC into a polarizing film.

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

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

A. Polarizing film

The polarizing film according to an embodiment of the present invention is composed of a polyvinyl alcohol (PVA)-based resin film containing iodine, has a thickness of 8 µm or less, and has a boiling point of less than 100°C (hereinafter referred to as low-boiling alcohol in some cases) ) from 5 ppm to 350 ppm. When the polarizing film contains a predetermined amount of such a low-boiling alcohol, it is possible to obtain a polarizing film having a thin shape and excellent durability in a high-temperature, high-humidity environment. Such a low-boiling alcohol may be typically introduced into the polarizing film between an underwater stretching treatment and a drying shrinkage treatment, as will be described later in Section C regarding the manufacturing method. By introducing such a low-boiling alcohol, it is estimated that durability under a high-temperature, high-humidity environment can be improved by the following mechanism: (i) Drying efficiency is increased due to the low-boiling alcohol during drying shrinkage treatment, the orientation of PVA is increased, (ii) Since the PVA-iodine complex is stabilized due to the low-boiling alcohol in the obtained polarizing film, it is possible to suppress the deterioration of the optical properties during humidification. Moreover, in the manufacture of a thin polarizing film, although crystallization of PVA is not enough in some cases, good crystallization of PVA can be implement|achieved by introduce|transducing a low boiling point alcohol. As a result, at the same single transmittance, even in a thin polarizing film having a significantly higher iodine concentration and insufficient iodine stability compared to a conventional (thick) polarizer, excellent durability in a high-temperature, high-humidity environment can be realized. Content of the low boiling point alcohol in a polarizing film is 8 ppm - 320 ppm, for example, Preferably it is 20 ppm - 200 ppm, More preferably, it is 40 ppm - 150 ppm, More preferably, it is 50 ppm - 120 ppm. When there is too little content, the effect of a low boiling point alcohol may not be acquired. When there is too much content, since the introduction amount at the time of manufacture will increase, the volatilization amount to a work environment may increase, and a safety risk may become high.

Representative examples of low-boiling alcohols include lower monoalcohols having 1 to 4 carbon atoms. Specific examples include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, and tert-butyl alcohol. A low boiling point alcohol may be used independently and may use 2 or more types together. Preferably, they are methanol, ethanol, n-propyl alcohol, and isopropyl alcohol. Since these have a low boiling point, the drying efficiency in the drying process mentioned later improves, and it is advantageous for the characteristic improvement of the polarizing film obtained.

As mentioned above, the thickness of a polarizing film is 8 micrometers or less, Preferably it is 7 micrometers or less, More preferably, it is 5 micrometers or less, More preferably, it is 3 micrometers or less. The lower limit of the thickness of the polarizing film may be 1 μm in one embodiment and 2 μm in another embodiment.

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of a polarizing film becomes like this. Preferably it is 42.0 % or more, More preferably, it is 42.5 % or more, More preferably, it is 43.0 % or more. On the other hand, the single transmittance becomes like this. Preferably it is 47.0 % or less, More preferably, it is 46.0 % or less. The polarization degree of the polarizing film is preferably 99.90% or more, and more preferably 99.95% or more. On the other hand, the polarization degree becomes like this. Preferably it is 99.998 % or less. ADVANTAGE OF THE INVENTION According to embodiment of this invention, high single transmittance and high polarization degree can be made compatible in this way, and the outstanding durability in the high-temperature, high-humidity environment as mentioned above can be implement|achieved. The single transmittance is typically a Y value measured using an ultraviolet/visible spectrophotometer and corrected for visibility. In addition, single transmittance is a value when the refractive index of one surface of a polarizing plate is converted into 1.50, and the refractive index of the other surface of a polarizing plate is converted into 1.53. The polarization degree can be obtained by the following formula based on the parallel transmittance (Tp) and the orthogonal transmittance (Tc), typically measured using an ultraviolet/visible light spectrophotometer and corrected for visibility.

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

The polarizing film has a polarization degree change (ΔP) after a endurance test of 120 hours at a temperature of 60°C and a relative humidity of 95%, preferably -0.70% or more, more preferably -0.55% or more, still more preferably - 0.20% or more. The upper limit of ΔP may be, for example, 0.0% or more, and ΔP may be, for example, 0.10% or less. ΔP is represented by the following formula.

ΔP=P ₁₂₀ -P ₀

In the above formula, P ₁₂₀ is the polarization degree after the endurance test, and P ₀ is the polarization degree before the endurance test (polarization degree described above). That is, the polarizing film according to the embodiment of the present invention has a characteristic that the decrease in the degree of polarization is small and sometimes increases in a high-temperature, high-humidity environment.

A polarizing film may be produced using a single resin film, and may be produced using a laminated body of two or more layers. As a specific example of the polarizing film obtained using a laminated body, the polarizing film obtained using the laminated body of the resin base material and the PVA-type resin layer apply|coated to the said resin base material is mentioned. A polarizing film obtained by using a laminate of a resin substrate and a PVA-based resin layer applied and formed on the resin substrate is, for example, a PVA-based resin solution applied to a resin substrate and dried to form a PVA-based resin layer on the resin substrate to form a resin obtaining a laminate of a base material and a PVA-based resin layer; stretching and dyeing the laminate to use the PVA-based resin layer as a polarizing film; In the embodiment of the present invention, a low-boiling alcohol is introduced into the polarizing film. Accordingly, excellent durability under the high temperature, high humidity environment as described above can be realized. Preferably, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of the resin substrate. Extending typically includes extending|stretching by immersing a laminated body in boric-acid aqueous solution. In addition, the stretching may further include aerial stretching of the laminate at a high temperature (eg, 95° C. or higher) before stretching in an aqueous boric acid solution, if necessary. Moreover, in this embodiment, Preferably, a laminated body is subjected to a drying shrinkage treatment in which it shrinks by 2% or more in the width direction by heating while conveying it in the longitudinal direction. Typically, the manufacturing method of this embodiment includes performing an aerial auxiliary extending|stretching process, a dyeing|staining process, an underwater extending|stretching process, and a drying shrinkage process to a laminated body in this order. By introducing auxiliary stretching, even when PVA is applied on a thermoplastic resin, it becomes possible to increase the crystallinity of PVA, and it becomes possible to achieve high optical properties. In addition, by increasing the orientation of PVA in advance at the same time, it is possible to prevent problems such as a decrease in orientation and dissolution of PVA when immersed in water in a subsequent dyeing process or stretching process, so that it is possible to achieve high optical properties do. In addition, in the case where the PVA-based resin layer is immersed in the liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. Thereby, the optical characteristic of the polarizing film obtained through the processing process performed by immersing a laminated body in a liquid, such as a dyeing process and an underwater extending|stretching process, can be improved. Moreover, an optical characteristic can be improved by shrinking|contracting a laminated body in the width direction by dry shrinkage process. The obtained laminate of the resin substrate / polarizing film may be used as it is (that is, the resin substrate may be used as a protective layer of the polarizing film), or the resin substrate is peeled from the laminate of the resin substrate / polarizing film, Any suitable protective layer may be laminated and used. Details of the method for manufacturing the polarizing film will be described later in Section C.

B. Polarizer

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing of the polarizing plate which concerns on one Embodiment of this invention. The polarizing plate 100 includes a polarizing film 10 , a first protective layer 20 disposed on one side of the polarizing film 10 , and a second protective layer disposed on the other side of the polarizing film 10 ( 30). The polarizing film 10 is the polarizing film of the present invention described in section A above. One of the first protective layer 20 and the second protective layer 30 may be omitted. Moreover, as mentioned above, the resin base material used for manufacture of the said polarizing film may be sufficient as one of a 1st protective layer and a 2nd protective layer.

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

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

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

C. Manufacturing method of polarizing film

A method for manufacturing a polarizing film according to an embodiment of the present invention includes applying and drying a PVA-based resin solution on one side of a long thermoplastic resin substrate to form a PVA-based resin layer to form a laminate; stretching and dyeing the laminate to form a PVA-based resin layer as a polarizing film; and, introducing a low-boiling alcohol into the polarizing film. By introducing a low-boiling alcohol, a polarizing film having excellent durability in a high-temperature, high-humidity environment can be realized. Preferably, the PVA-based resin solution further comprises a halide. Preferably, in the above manufacturing method, the laminate is subjected to air-assisted stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment for shrinking the laminate by 2% or more in the width direction by heating while conveying in the longitudinal direction in this order includes doing In this case, the introduction of the low-boiling alcohol can be preferably performed between the stretching treatment in water and the drying shrinkage treatment. The content of the halide in the PVA-based resin solution (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 ratio in the width direction of the laminate by the drying shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizing film demonstrated in the said A section can be obtained. In particular, by producing a laminate including a PVA-based resin layer containing a halide, stretching the laminate in multi-step stretching including aerial-assisted stretching and underwater stretching, and heating the laminate after stretching with a heating roll, A polarizing film having excellent optical properties (typically, single transmittance and unit absorbance) can be obtained.

C-1. Fabrication of laminates

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

Any suitable method can be employ|adopted as a coating method of a coating liquid. For example, the roll coat method, the spin coat method, the wire bar coat method, the dip coat method, the die coat method, the curtain coat method, the spray coat method, the knife coat method (comma coat method, etc.) etc. are mentioned. The application and drying temperature of the coating liquid is preferably 50°C or higher.

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

Before forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to surface treatment (eg, corona treatment, etc.), or an easily adhesive layer may be formed on the thermoplastic resin substrate. By performing such a process, the adhesiveness of a thermoplastic resin base material and a PVA-type resin layer can be improved.

C-1-1. Thermoplastic base material

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

C-1-2. coating liquid

The coating liquid contains a halide and PVA-type resin as mentioned above. The coating liquid is typically a solution in which the halide and the PVA-based resin are dissolved in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. can be heard These can be used individually or in combination of 2 or more types. Among these, water is preferable. The concentration of the PVA-based resin in the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. If it is such a resin concentration, a uniform coating film closely_contact|adhered to a thermoplastic resin base material can be formed. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

You may mix|blend an additive with a coating liquid. As an additive, a plasticizer, surfactant, etc. are mentioned, for example. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. As surfactant, a nonionic surfactant is mentioned, for example. These can be used for the purpose of further improving the uniformity, dyeability, and stretchability of the obtained PVA-based resin layer.

Any suitable resin may be employed as the PVA-based resin. For example, polyvinyl alcohol and an ethylene-vinyl alcohol copolymer are mentioned. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying the ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. The degree of saponification can be obtained according to JIS K 6726-1994. By using the PVA-based resin having such a degree of saponification, a polarizing film having excellent durability can be obtained. When the degree of saponification is too high, there is a risk of gelation.

The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually from 1000 to 10000, preferably from 1200 to 4500, more preferably from 1500 to 4300. In addition, an average degree of polymerization can be calculated|required according to JISK6726-1994.

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

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

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

C-2. Aerial Auxiliary Stretch Treatment

In particular, in order to obtain high optical properties, a two-stage stretching method combining dry stretching (auxiliary stretching) and stretching in boric acid water is selected. By introducing auxiliary stretching as in two-stage stretching, it is possible to stretch while suppressing crystallization of the thermoplastic resin substrate, and to solve the problem that stretchability is reduced due to excessive crystallization of the thermoplastic resin substrate in subsequent stretching in boric acid water, thereby solving the problem of a laminate can be drawn at a higher magnification. Furthermore, when applying the PVA-based resin on the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, it is necessary to lower the application temperature compared to the case of applying the PVA-based resin on a conventional metal drum. As a result, the crystallization of the PVA-based resin is relatively low, which may cause a problem that sufficient optical properties are not obtained. On the other hand, by introducing auxiliary stretching, even when the PVA-based resin is applied on the thermoplastic resin, it becomes possible to increase the crystallinity of the PVA-based resin, and it becomes possible to achieve high optical properties. At the same time, by increasing the orientation of the PVA-based resin in advance, problems such as a decrease in the orientation and dissolution of the PVA-based resin when immersed in water in a subsequent dyeing process or stretching process can be prevented, and high optical properties are achieved it becomes possible to do

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

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

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

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

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

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

C-4. Underwater stretching treatment

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

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

Stretching in water is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using a boric acid aqueous solution as a stretching bath, the rigidity which withstands the tension|tensile_strength applied at the time of extending|stretching, and the water resistance which does not melt|dissolve in water can be provided to a PVA-type resin layer. Specifically, silver boric acid can be crosslinked by hydrogen bonding with a PVA-based resin by generating a tetrahydroxy boric acid anion in an aqueous solution. As a result, rigidity and water resistance are provided to the PVA-based resin layer, so that it can be stretched favorably, and a polarizing film having excellent optical properties can be manufactured.

The aqueous boric acid solution can be preferably obtained by dissolving boric acid and/or a borate salt in water as a solvent. The concentration of boric acid is preferably 1 part by weight to 10 parts by weight, more preferably 2.5 parts by weight to 6 parts by weight, and particularly preferably 3 parts by weight to 5 parts by weight with respect to 100 parts by weight of water. When the concentration of boric acid is 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film having higher properties can be manufactured. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde or the like in a solvent can also be used.

Preferably, an iodide is blended in the stretching bath (aqueous boric acid solution). By mix|blending an iodide, the elution of the iodine made to adsorb|suck to the PVA-type resin layer can be suppressed. Specific examples of the iodide are as described above. The concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight, more preferably 0.5 parts by weight to 8 parts by weight with respect to 100 parts by weight of water.

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. If it is such a temperature, it can extend|stretch at a high magnification, suppressing melt|dissolution of a PVA-type resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or higher in relation to the formation of the PVA-based resin layer. In this case, when extending|stretching temperature is less than 40 degreeC, even if it considers plasticization of the thermoplastic resin base material by water, there exists a possibility that extending|stretching may not be satisfactory. On the other hand, as the temperature of the stretching bath increases, the solubility of the PVA-based resin layer increases, and there is a fear that excellent optical properties may not be obtained. The immersion time of the layered product in the stretching bath is preferably 15 seconds to 5 minutes.

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

C-5. introduction of low-boiling alcohol

In the embodiment of the present invention, the low-boiling alcohol is introduced after the underwater stretching treatment (and typically before the drying shrinkage treatment described later). The introduction of the low-boiling alcohol may be done in any suitable manner. For example, the laminate may be immersed in a treatment liquid containing a low-boiling alcohol, or a treatment liquid containing a low-boiling alcohol may be applied to the surface of the polarizing film of the laminate. Typically, the introduction of the low-boiling alcohol can be done by immersion. Immersion may be done by any suitable mode. For example, a low boiling point alcohol may be added to the washing bath of the washing treatment to form a bath of the treatment liquid, or a bath of the treatment liquid may be used instead of the cleaning bath, and a bath of the treatment liquid is provided separately from the cleaning bath You can do it. Typically, low-boiling alcohol may be added to the washing bath (washing liquid) of the washing treatment. The low boiling point alcohol concentration of the treatment liquid (washing liquid) is preferably 5 wt% to 35 wt%.

C-6. dry shrinkage treatment

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

The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or may be performed by heating a conveyance roll (a so-called heating roll is used) (a heating roll drying method). Preferably, both are used. By drying using a heating roll, the heating curl of a laminated body can be suppressed efficiently, and the polarizing film excellent in an external appearance can be manufactured. Specifically, by drying in a state in which the laminate is poured on a heating roll, crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the crystallinity, and even at a relatively low drying temperature, the crystallinity of the thermoplastic resin substrate can be increased favorably. have. As a result, the rigidity of a thermoplastic resin base material increases, it becomes a state which can withstand the shrinkage of the PVA-type resin layer by drying, and curl is suppressed. Moreover, since a laminated body can be dried, maintaining a flat state by using a heating roll, not only curl but generation|occurrence|production of wrinkles can also be suppressed. At this time, the optical characteristic can be improved by shrinking|contracting a laminated body in the width direction by drying shrinkage process. It is because the orientation of PVA and a PVA/iodine complex can be improved effectively. The shrinkage ratio in the width direction of the laminate by the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%.

2 is a schematic diagram showing an example of a drying shrinkage treatment. In the dry shrinkage treatment, the laminate 200 is dried while being conveyed by the conveying rolls R1 to R6 and the guide rolls G1 to G4 heated to a predetermined temperature. In the illustrated example, the conveying rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate. For example, only one surface of the laminate 200 (eg, the surface of the thermoplastic resin substrate) You may arrange|position conveyance rolls R1-R6 so that it may heat continuously.

Drying conditions are controllable by adjusting the heating temperature (temperature of a heating roll) of a conveyance roll, the number of heating rolls, contact time with a heating roll, etc. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. If it is such a temperature, the external appearance of the polarizing film obtained can be maintained favorably. Moreover, the orientation of PVA can be improved while maintaining an external appearance by the synergistic effect with the effect by low boiling point alcohol. Moreover, while the crystallinity degree of a thermoplastic resin can be increased favorably and curl can be suppressed favorably, the optical laminated body extremely excellent in durability can be manufactured. In addition, the temperature of a heating roll can be measured with a contact thermometer. Although six conveyance rolls are provided in the example of illustration, if there are several conveyance rolls, there will be no restriction|limiting in particular. The number of conveyance rolls is 2-40 normally, Preferably 4-30 pieces are provided. 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 still more preferably 1 to 10 seconds.

A heating roll may be provided in a heating furnace (for example, oven), and may be provided in a normal production line (under a room temperature environment). Preferably, it is provided in the heating furnace provided with the blowing means. By using together drying by a heating roll and hot air drying, the rapid temperature change between heating rolls can be suppressed, and the shrinkage|contraction of the width direction can be controlled easily. The temperature of hot air drying becomes like this. Preferably it is 30 degreeC - 100 degreeC. If it is such a temperature, the external appearance of the polarizing film obtained can be maintained favorably. Moreover, the orientation of PVA can be improved while maintaining an external appearance by the synergistic effect with the effect by low boiling point alcohol. In addition, the hot air drying time becomes like this. Preferably it is 1 second - 300 second. The wind speed of the hot air is preferably about 10 m/s to 30 m/s. In addition, the said wind speed is a wind speed in a heating furnace, and can be measured with a mini vane type digital anemometer.

C-7. etc

The laminate of the thermoplastic resin substrate/polarizing film obtained as described above may be used as it is as a polarizing plate (a thermoplastic resin substrate may be used as a protective layer); After bonding a protective layer to the polarizing film surface of a laminated body, a thermoplastic resin base material may be peeled and it may use as a polarizing plate which has the structure of a protective layer/polarizing film; Another protective layer may be bonded together on the peeling surface of a thermoplastic resin base material, and it may use as a polarizing plate which has the structure of a protective layer / polarizing film / protective layer.

[Example]

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

(1) thickness

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

(2) Alcohol concentration of polarizing film

The polarizing film obtained by the Example and the comparative example was cut out to 10 cm<2>, and it was set as the measurement sample. After the measurement sample was sealed in a 20 mL headspace vial, the ethanol-containing sample was heated at 175° C. and the isopropyl alcohol-containing sample at 215° C. for 30 minutes with a headspace sampler (HSS), and 1 mL of the gaseous phase portion after heating was subjected to a gas chromatograph (Agilent Technologies Co., Ltd., product name '6890N') was injected and the amount of alcohol contained was calculated using the following calibration curve from the peak area corresponding to each alcohol species.

Ethanol calibration curve

y = 4.743E ⁺⁰⁰ x + 3.105E ^-02

Isopropyl alcohol calibration curve

y = 4.565E ⁺⁰⁰ x + 8.922E ^-03

(3) Single transmittance and polarization degree

Single transmittance (Ts), parallel transmittance (Tp), orthogonal transmittance measured using an ultraviolet/visible light spectrophotometer (LPF-200 manufactured by Otsuka Electronics Co., Ltd.) for the polarizing plates (protective film/polarizing film) of Examples and Comparative Examples (Tc) was set as Ts, Tp, and Tc of a polarizing film, respectively. These Ts, Tp, and Tc are Y values which measured with the 2 degree field of view (C light source) of JIS Z8701, and performed visibility correction|amendment. In addition, the refractive index of the protective film was 1.50, and the refractive index of the surface on the opposite side to the protective film of a polarizing film was 1.53. From the obtained Tp and Tc, the polarization degree was calculated|required using the following formula.

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

Next, the polarizing plate was subjected to a 120-hour endurance test at a temperature of 85°C and a relative humidity of 85%. The orthogonal transmittance polarization degree (P ₁₂₀ ) after the endurance test was obtained in the same manner as above. In addition, the durability test was performed by injecting|throwing-in the test sample which bonded the polarizing film side of the polarizing plate to the glass plate through an adhesive layer into a humidification oven.

(4) Humidification durability

_{From the polarization degrees P 0} and P ₁₂₀ before and after the endurance test in (3) above, ΔP was calculated using the following formula.

ΔP=P ₁₂₀ -P ₀

Since ΔP is a parameter that changes depending on the single transmittance, when comparing, it is necessary to compare with a polarizing plate having substantially the same single transmittance before the test. Therefore, durability under a high-temperature, high-humidity environment was evaluated on the basis of Comparative Example 1 as follows.

(double-circle): ΔP is remarkably large with respect to Comparative Example 1 (the absolute value in the negative direction is remarkably small)

○: ΔP is larger than in Comparative Example 1 (the absolute value in the negative direction is smaller)

Δ: ΔP is equivalent to Comparative Example 1

x: ΔP is smaller than in Comparative Example 1 (the absolute value in the negative direction is larger)

[Example 1]

As the thermoplastic resin substrate, an amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 µm) having a long, Tg of about 75°C was used. Corona treatment was performed on one side of the resin substrate.

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

On the corona-treated surface of the resin substrate, the PVA aqueous solution was applied and dried at 60°C to form a PVA-based resin layer having a thickness of 13 µm to prepare a laminate.

The obtained laminate was uniaxially stretched at the free end by 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different circumferential speeds in an oven at 130°C (air-assisted stretching treatment).

Next, the laminate was cut out at 15 cm x 10 cm in the direction of the auxiliary stretching axis, and the short side of the cut out laminate piece was fixed with a dedicated stretching jig in an insolubilization bath with a liquid temperature of 30° C. (3 parts by weight of boric acid is blended with respect to 100 parts by weight of water. The obtained boric acid aqueous solution) was immersed for 30 seconds (insolubilization treatment).

Next, in a dyeing bath having a liquid temperature of 30°C (an aqueous solution of iodine obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with respect to 100 parts by weight of water), the single transmittance (Ts) of the finally obtained polarizing film was 43.0%± It was immersed for 60 seconds while adjusting the density|concentration so that it might become 0.2% (dyeing process).

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

Then, uniaxial stretching was performed so that the total draw ratio in the longitudinal direction (longitudinal direction) became 5.5 times while the laminate was immersed in an aqueous boric acid solution (boric acid concentration of 4.0% by weight, potassium iodide 5.0% by weight) having a liquid temperature of 70°C. (underwater stretching treatment).

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

Then, it dried in the oven maintained at 60 degreeC for 4 minutes (drying process).

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

About the obtained polarizing plate (substantially, a polarizing film), the single transmittance and (DELTA)P are shown in Table 1. In addition, the evaluation result of said (4) is shown in Table 1 together.

[Example 2]

A polarizing plate was produced in the same manner as in Example 1, except that the ethanol concentration in the treatment bath was set to 20% by weight. The obtained polarizing plate (or polarizing film) was used for evaluation similar to Example 1. A result is shown in Table 1.

[Example 3]

A polarizing plate was produced in the same manner as in Example 1 except that the ethanol concentration in the treatment bath was 25% by weight. The obtained polarizing plate (or polarizing film) was used for evaluation similar to Example 1. A result is shown in Table 1.

[Example 4]

A polarizing plate was produced in the same manner as in Example 1, except that the ethanol concentration in the treatment bath was 2% by weight. The obtained polarizing plate (or polarizing film) was used for evaluation similar to Example 1. A result is shown in Table 1.

[Example 5]

It carried out similarly to Example 4, and produced the polarizing plate. The obtained polarizing plate was subjected to a 120-hour endurance test at a temperature of 60°C and a relative humidity of 95% to obtain ΔP. The sequence of the endurance test was as described in (3) above. About the obtained ΔP, durability was evaluated based on Comparative Example 3 (described later) as follows. A result is shown in Table 1.

(double-circle): ΔP is remarkably large with respect to Comparative Example 3 (the absolute value in the negative direction is remarkably small)

(circle): ΔP is larger than in Comparative Example 3 (the absolute value in the negative direction is smaller)

Δ: ΔP is equivalent to Comparative Example 3

x: ΔP is smaller than in Comparative Example 3 (the absolute value in the negative direction is larger)

[Example 6]

It carried out similarly to Example 1, and produced the polarizing plate. The obtained polarizing plate was used for evaluation similar to Example 5. A result is shown in Table 1.

[Example 7]

It carried out similarly to Example 2, and produced the polarizing plate. The obtained polarizing plate was used for evaluation similar to Example 5. A result is shown in Table 1.

[Example 8]

It carried out similarly to Example 3, and produced the polarizing plate. The obtained polarizing plate was used for evaluation similar to Example 5. A result is shown in Table 1.

[Example 9]

A polarizing plate was produced in the same manner as in Example 3 except that the immersion time of the treatment bath was set to 10 seconds. The obtained polarizing plate was used for evaluation similar to Example 5. A result is shown in Table 1.

[Example 10]

Example 5, except that the concentration of the dyeing bath was adjusted so that the single transmittance of the polarizing film was 42.0%±0.2%, and the alcohol species of the washing treatment bath was isopropyl alcohol and the concentration was 5% by weight. Similarly, a polarizing plate was produced. The obtained polarizing plate was used for the durability test similar to Example 5, and the following references|standards evaluated it. A result is shown in Table 1.

(double-circle): ΔP is remarkably large with respect to Comparative Example 4 (the absolute value in the negative direction is remarkably small)

(circle): ΔP is larger than in Comparative Example 4 (the absolute value in the negative direction is smaller)

Δ: ΔP is equivalent to Comparative Example 4

x: ΔP is smaller than in Comparative Example 4 (the absolute value in the negative direction is larger)

[Example 11]

A polarizing plate was produced in the same manner as in Example 10, except that the isopropyl alcohol concentration of the treatment bath was set to 20% by weight. The obtained polarizing plate was used for evaluation similar to Example 10. A result is shown in Table 1.

[Example 12]

A polarizing plate was produced in the same manner as in Example 10, except that the isopropyl alcohol concentration of the treatment bath was 25% by weight. The obtained polarizing plate was used for evaluation similar to Example 10. A result is shown in Table 1.

[Comparative Example 1]

A polarizing plate was produced in the same manner as in Example 1 except that low-boiling alcohol was not added to the washing bath (washing liquid). The obtained polarizing plate (or polarizing film) was used for evaluation similar to Example 1. A result is shown in Table 1.

[Comparative Example 2]

A polarizing plate was produced in the same manner as in Example 1 except that no low-boiling alcohol was added to the washing bath (washing liquid), and the temperature of the drying oven after the piece washing bath was 130° C. in order to improve drying efficiency. However, it was not possible to obtain a measurement sample that can be evaluated due to wrinkles and/or flaking of the film due to heat shrinkage.

[Comparative Example 3]

It carried out similarly to the comparative example 1, and produced the polarizing plate. The obtained polarizing plate was used for evaluation similar to Example 5. A result is shown in Table 1.

[Comparative Example 4]

A polarizing plate was produced in the same manner as in Comparative Example 1 except that the concentration of the dyeing bath was adjusted so that the single transmittance of the polarizing film was 42.0%±0.2%. The obtained polarizing plate was used for evaluation similar to Example 10. A result is shown in Table 1.

[Table 1]

[Reference Example 1]

A long roll of 45 μm thick PVA-based resin film (manufactured by Kuraray, product name 'PS4500') is uniaxially stretched in the long direction with a roll stretching machine so that the total draw ratio is 6.0 times, while simultaneously swelling, dyeing, crosslinking and A polarizing film with a thickness of 17 µm was produced by washing and finally drying. That is, a thick polarizing film into which low boiling point alcohol is not introduced was produced. On both sides of the polarizing film, a cycloolefin-based film (manufactured by ZEON, product name 'ZT12') as a protective layer (protective film) and an acrylic resin-based film are bonded together with a UV curable adhesive (thickness of 1.0 µm), and cyclo An adhesive layer was provided on the olefinic film surface, and the polarizing plate which has the structure of a protective layer / polarizing film / protective layer / adhesive layer was obtained. Next, it used for evaluation similar to Example 1 except having made the conditions of the endurance test into temperature 65 degreeC, 90% of relative humidity, and test time 500 hours, and obtained (DELTA)P with the following formula|equation. The results are shown in Table 2. Durability of Reference Example 2 to be described later was evaluated on the basis of ΔP of this Reference Example.

ΔP=P ₅₀₀ -P ₀

[Reference Example 2]

The long roll of the PVA-based resin/resin substrate laminate used in Example 1 was uniaxially stretched in the long direction with a roll stretching machine so that the total draw ratio was 2.4 times, and swelling, dyeing, crosslinking and washing treatment were performed at the same time. And finally, the polarizing film with a thickness of 5 micrometers was produced by performing a drying process. That is, a thin polarizing film into which low boiling point alcohol is not introduced was produced. On the surface of the polarizing film, an adhesive layer was provided on the protective layer in the same manner as in Reference Example 1 to obtain a polarizing plate having a configuration of protective layer/polarizing film/protective layer/adhesive layer. Except having used this polarizing plate, it used for evaluation similar to the reference example 1, and the following reference|standard evaluated. The results are shown in Table 2.

(double-circle): ΔP is remarkably large with respect to Reference Example 1 (the absolute value in the negative direction is remarkably small)

○: ΔP is larger than in Reference Example 1 (the absolute value in the negative direction is smaller)

Δ: ΔP is equivalent to Reference Example 1

x: ΔP is smaller than in Reference Example 1 (the absolute value in the negative direction is larger)

[Table 2]

As is clear from Table 1, the polarizing plate (polarizing film) of the Example of the present invention contains a predetermined amount of low-boiling alcohol, so that it is excellent in durability in a high-temperature, high-humidity environment. Moreover, as is clear from Table 2, it turns out that durability in a high-temperature, high-humidity environment is a subject peculiar to a thin-shaped polarizing film.

[Industrial Applicability]

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

10: polarizing film
20: first protective layer
30: second protective layer
100: polarizer

Claims (7)

A polarizing film comprising a polyvinyl alcohol-based resin film containing iodine, having a thickness of 8 µm or less, and containing 5 ppm to 350 ppm of alcohol having a boiling point of less than 100°C. According to claim 1,
The polarizing film, wherein the alcohol having a boiling point of less than 100° C. is at least one selected from the group consisting of methanol, ethanol, n-propyl alcohol and isopropyl alcohol. A polarizing plate comprising the polarizing film according to claim 1 or 2, and a protective layer disposed on at least one side of the polarizing film. A method for producing the polarizing film according to claim 1 or 2, comprising:
forming a polyvinyl alcohol-based resin layer on one side of a long thermoplastic resin substrate to form a laminate;
stretching and dyeing the laminate to use the polyvinyl alcohol-based resin layer as a polarizing film, and
introducing an alcohol having a boiling point of less than 100° C. into the polarizing film;
comprising, a manufacturing method. 5. The method of claim 4,
A manufacturing method comprising immersing the polarizing film in a treatment solution containing an alcohol having a boiling point of less than 100°C. 6. The method according to claim 4 or 5,
After introducing the alcohol having a boiling point of less than 100° C. into the polarizing film, further comprising heating the laminate. 7. The method according to any one of claims 4 to 6,
wherein said stretching comprises underwater stretching.

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