CN115398291A

CN115398291A - Polarizing film and polarizing film

Info

Publication number: CN115398291A
Application number: CN202180028180.2A
Authority: CN
Inventors: 泽田浩明; 山下智弘
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2020-04-14
Filing date: 2021-03-19
Publication date: 2022-11-25
Also published as: JP2021170044A; JP2024056037A; WO2021210342A1; KR20230002273A

Abstract

The present invention provides a polarizing film formed by adsorbing iodine to a polyvinyl alcohol film and orienting the film, wherein the content of iodine in the polarizing film exceeds 10% by weight, the monomer transmittance is 41% or less, and the peak temperature of the maximum strength of water detected by the polarizing film is 175 ℃ or more in the presence of an inert gas under the conditions that the temperature rising rate is 10 ℃/min and the temperature rising range is 40 ℃ to 350 ℃ in a generated gas analysis. The polarizing film has a high iodine content, an initial monomer transmittance of 41% or less, and an excellent effect of suppressing a decrease in the monomer transmittance due to coloring of the polarizing film in a high-temperature environment.

Description

Polarizing film and polarizing film

Technical Field

The present invention relates to a polarizing film and a polarizing film.

Background

Conventionally, as a polarizing film used for various image display devices such as a liquid crystal display device and an organic EL display device, a polyvinyl alcohol-based film (containing a dichroic material such as iodine or a dichroic dye) subjected to dyeing treatment has been used in view of having both high transmittance and high polarization degree. The polarizing film was produced as follows: the polyvinyl alcohol film is subjected to various treatments such as swelling, dyeing, crosslinking, stretching, and the like in a bath, and then subjected to a cleaning treatment, followed by drying. The polarizing film is generally used in the form of a polarizing film (polarizing plate) in which a protective film such as triacetylcellulose is bonded to one surface or both surfaces thereof with an adhesive.

On the other hand, a polarizing film having a large iodine content is required as the polarizing film is made thinner (patent document 1). Further, among such thin polarizing films, a polarizing film capable of suppressing the amount of change in the monomer transmittance in a high-temperature environment (105 ℃x30 hours) is also known (patent document 2).

Documents of the prior art

Patent document

Patent document 1: international publication No. 2018/186244

Patent document 2: international publication No. 2019/103002

Disclosure of Invention

Problems to be solved by the invention

However, the thin polarizing films specifically disclosed in patent documents 1 and 2 are not sufficient in suppressing the decrease in the monomer transmittance in a high-temperature environment, and there is room for improvement in the performance.

On the other hand, the present inventors have found that iodine contained in an iodine-based polarizing film promotes the polyalkyleneization in a high-temperature environment. Therefore, in order to suppress a decrease in the monomer transmittance caused by coloring of the polarizing film in a high-temperature environment, it is effective to reduce the content of iodine in the polarizing film. On the other hand, it is difficult to obtain a polarizing film having a high iodine content and a good degree of polarization.

As described in patent document 2, in a polarizing film containing a large amount of iodine, a polarizing film having a monomer transmittance of 41% or less is required from the viewpoint of improving the contrast by setting a low monomer transmittance.

In view of the above circumstances, an object of the present invention is to provide a polarizing film having a high iodine content, which has an initial monomer transmittance of 41% or less and is excellent in the effect of suppressing the decrease in the monomer transmittance due to the coloration of the polarizing film in a high-temperature environment.

Another object of the present invention is to provide a polarizing film using the above polarizing film.

Means for solving the problems

That is, the present invention relates to a polarizing film formed by adsorbing iodine to a polyvinyl alcohol-based film and orienting the same, the polarizing film having an iodine content of more than 10% by weight and a monomer transmittance of 41% or less, and the polarizing film having a peak temperature of maximum strength of water detected in the presence of an inert gas in a generated gas analysis of 175 ℃ or more under conditions of a temperature rise rate of 10 ℃/min and a temperature rise range of 40 to 350 ℃.

The present invention also relates to a polarizing film having a transparent protective film or an optically functional film bonded to at least one surface of the polarizing film.

ADVANTAGEOUS EFFECTS OF INVENTION

The details of the mechanism of action of the effect of the polarizing film of the present invention are not clear, but are presumed as follows. However, the present invention may be explained without being limited to this mechanism of action.

The polarizing film of the present invention is formed by adsorbing iodine to a polyvinyl alcohol film and orienting the film, has an iodine content of more than 10% by weight and a monomer transmittance of 41% or less, and has a peak temperature of maximum strength of water detected by the polarizing film of 175 ℃ or higher in the presence of an inert gas under conditions of a temperature rise rate of 10 ℃/min and a temperature rise range of 40 ℃ to 350 ℃ in a generated gas analysis. As described above, although the iodine-based polarizing film undergoes polyalkylenation due to dehydration reaction of polyvinyl alcohol in a high-temperature environment, the polarizing film of the present invention can suppress a decrease in the monomer transmittance due to coloring of the polarizing film in a high-temperature environment by setting the temperature at which this dehydration reaction occurs to a high-temperature side, that is, by setting the peak temperature of the maximum intensity of water detected (observed) by a generated gas analysis method to 175 ℃. In addition, in the polarizing film of the present invention, by setting the iodine content in the polarizing film to be constant or more, the peak temperature of the maximum intensity of water detected (observed) by a generated gas analysis method can be controlled to be 175 ℃ or more, and the monomer transmittance is 41% or less, and the initial degree of polarization is good.

On the other hand, the present inventors have observed that radicals are generated from a polarizing film formed by adsorbing iodine to an iodine-containing polyvinyl alcohol film and orienting the film for a certain period of time when the polarizing film is exposed to a high-temperature environment. Since the time for coloring the polarizing film by the polyalkylenization is very similar to the time for generating the radical, a phenomenon that the radical is generated due to the progress of the polyene formation of the polarizing film is suggested. Therefore, in order to set the temperature of the polarizing film at which the above-described dehydration reaction occurs to a high temperature side, that is, to set the peak temperature of the maximum intensity of water detected (observed) by a generated gas analysis method to 175 ℃ or higher, it is preferable to contain a radical scavenger in the polarizing film.

Drawings

Fig. 1 is an example of a graph showing the peak of water detected in a generated gas analysis method using an iodine polarizing film as a sample.

Detailed Description

< polarizing film >

The polarizing film of the present invention is an iodine-based polarizing film formed by adsorbing iodine to a polyvinyl alcohol-based film and orienting the film, the polarizing film having an iodine content of more than 10% by weight and a monomer transmittance of 41% or less, and the polarizing film having a peak temperature of maximum strength of water detected in the presence of an inert gas under conditions of a temperature rise rate of 10 ℃/min and a temperature rise range of 40 ℃ to 350 ℃ in a generated gas analysis method of 175 ℃ or more.

The content of iodine in the polarizing film is more than 10% by weight from the viewpoint of improving the initial degree of polarization of the polarizing film. The content of iodine in the polarizing film is preferably 12 wt% or more, more preferably 15 wt% or more from the viewpoint of controlling the initial degree of polarization to 99.98 or more, and is preferably 30 wt% or less, more preferably 25 wt% or less from the viewpoint of controlling the peak temperature of the maximum intensity of water detected by a generated gas analysis method to 175 ℃ or more.

The thickness of the polarizing film is preferably 0.2 μm or more, more preferably 0.5 μm or more from the viewpoint of controlling the initial degree of polarization to 99.98 or more, and is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 5 μm or less from the viewpoint of thinning the polarizing film.

The polarizing film has a monomer transmittance of 41% or less. The monomer transmittance of the polarizing film is preferably 30% or more, more preferably 35% or more from the viewpoint of the luminance of the display panel, and is preferably 41% or less, more preferably 40% or less from the viewpoint of controlling the initial degree of polarization to 99.98 or more. The monomer transmittance is a Y value obtained by measuring and correcting visibility with a spectrophotometer with an integrating sphere (for example, product name: V7100, manufactured by japan spectro corporation) in a 2-degree field of view (C light source) according to JIS Z8701.

In the generated gas analysis method, the peak temperature of the maximum strength of water detected by the polarizing film is 175 ℃ or higher in the presence of an inert gas under the conditions that the temperature rise rate is 10 ℃/min and the temperature rise range is 40 ℃ to 350 ℃. In the above polarizing film, the temperature at which the dehydration reaction of polyvinyl alcohol occurs is set to a high temperature side, that is, the peak temperature of the maximum intensity of water detected by a generated gas analysis method is set to 175 ℃ or higher, whereby the decrease in the monomer transmittance due to the coloring of the polarizing film in a high temperature environment can be suppressed. On the other hand, when the peak temperature of the maximum intensity of water is lower than 175 ℃ or higher, it is difficult to control the change amount of the monomer transmittance of the polarizing film before and after the heating durability test (105 ℃ c. × 96 hours) which is regarded as an index of the heat resistance of the display to 0% or more and 5% or less.

Fig. 1 is an example of a graph showing the peak of water detected by the generated gas analysis method, and the peak temperature of the maximum intensity of the detected water is 175 ℃.

The generated gas analysis method is an analysis method in which a gas chromatograph apparatus and a mass spectrometer apparatus are directly connected by an inert metal capillary or the like, and a gas generated when a sample is heated by raising the temperature is monitored in real time, and is generally called an EGA/MS method, an EGA/TOFMS method, or the like.

The polarizing film preferably contains a radical scavenger. It is estimated that the trapping agent can trap radicals generated by heating polyvinyl alcohol of the polarizing film, and the temperature of dehydration reaction at which the polyalkylene reaction occurs is set to a high temperature side. Examples of the radical scavenger include: hindered phenol, hindered amine, phosphorus, sulfur, benzotriazole, benzophenone, hydroxylamine, salicylate, triazine compounds and other radical trapping agents. The radical scavenger is preferably a compound having a nitroxyl radical or nitroxyl group, for example, from the viewpoint of easily setting the temperature at which the dehydration reaction of the polyalkylene compound occurs to a high temperature side.

Examples of the compound having a nitroxyl radical or nitroxyl group include N-oxyl compounds (having C-N (-C) -O) from the viewpoint of having a relatively stable radical at room temperature in air ^· Compound (O) as a functional group ^· Oxygen radical)), a known compound can be used. Examples of the N-oxyl compound include compounds having an organic group having the following structure.

[ chemical formula 1]

(in the general formula (1), R ¹ Represents an oxygen radical, R ² ～R ⁵ Independently represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and n represents 0 or 1), and the left side of the dotted line portion in the general formula (1) represents an arbitrary organic group.

Examples of the compound having an organic group include compounds represented by the following general formulae (2) to (5).

[ chemical formula 2]

(in the general formula (2), R ¹ ～R ⁵ And n is as defined above, R ⁶ Represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an acyl group or an aryl group, and n represents 0 or 1. )

[ chemical formula 3]

(in the general formula (3), R ¹ ～R ⁵ And n is as defined above, R ⁷ And R ⁸ Independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an acyl group, or an aryl group. )

[ chemical formula 4]

(in the general formula (4), R ¹ ～R ⁵ And n is as defined above, R ⁹ ～R ¹¹ Independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an acyl group, an amino group, an alkoxy group, a hydroxyl group, or an aryl group. )

[ chemical formula 5]

(in the general formula (5), R ¹ ～R ⁵ And n is as defined above, R ¹² Represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an amino group, an alkoxy group, a hydroxyl group, or an aryl group. )

In the above general formulae (1) to (5), R is R from the viewpoint of easy availability ² ～R ⁵ Preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms. In the general formula (2), R is R from the viewpoint of easy acquisition ⁶ Preferably a hydrogen atomOr an alkyl group having 1 to 10 carbon atoms, and a hydrogen atom is more preferable. In the general formula (3), R is R from the viewpoint of easy acquisition ⁷ And R ⁸ Preferably independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably a hydrogen atom. In the general formula (4), R is R from the viewpoint of easy acquisition ⁹ ～R ¹¹ Preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. In the general formula (5), R is R from the viewpoint of easy acquisition ¹² Preferably hydroxyl, amino or alkoxy. In the general formulae (1) to (5), n is preferably 1 from the viewpoint of easy acquisition.

Examples of the N-oxyl compound include: n-oxyl compounds described in, for example, japanese patent application laid-open Nos. 2003-64022, 11-222462, 2002-284737 and 2016/047655.

The molecular weight of the radical scavenger is preferably 1000 or less, more preferably 500 or less, and still more preferably 300 or less, from the viewpoint of efficiently trapping radicals generated in the polyene formation reaction.

The radical scavenger is preferably soluble in 100 parts by weight of 25 ℃ water at 25 ℃ in 1 part by weight or more, more preferably soluble in 100 parts by weight of 25 ℃ water in 2 parts by weight or more, and further preferably soluble in 100 parts by weight of 25 ℃ water in 5 parts by weight or more, from the viewpoint of efficiently permeating the polarizing film together with water at the time of producing the polarizing film, from the viewpoint of being impregnated in a high concentration in the polarizing film, and from the viewpoint of being impregnated in a short time even when a polyvinyl alcohol film having a large thickness is used, thereby improving productivity of the polarizing film.

Examples of the compound having a nitroxyl radical or a nitroxyl group include the following compounds.

[ chemical formula 6]

(in the general formula (6), R represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an acyl group or an aryl group.)

[ chemical formula 7]

[ chemical formula 8]

In the case where the polarizing film contains the radical scavenger, the content of the radical scavenger in the polarizing film is preferably 0.1 wt% or more, more preferably 0.2 wt% or more, and even more preferably 0.5 wt% or more, and is preferably 30 wt% or less, more preferably 20 wt% or less, and even more preferably 10 wt% or less, from the viewpoint of suppressing a decrease in the monomer transmittance due to coloring of the polarizing film in a high-temperature environment.

In addition, in the case where the polarizing film contains the radical scavenger, the weight ratio of the content of the radical scavenger to the content of iodine in the polarizing film (weight ratio of the content of the radical scavenger/the content of iodine) is preferably 0.01 or more, more preferably 0.05 or more, and is preferably 1.0 or less, more preferably 0.5 or less, from the viewpoint of suppressing the decrease in the monomer transmittance due to the coloration of the polarizing film in a high-temperature environment.

< method for producing polarizing film >

The method for producing a polarizing film includes: the polarizing film is obtained by subjecting a polyvinyl alcohol film (PVA-based film) to at least a dyeing step, a crosslinking step, and a stretching step, optionally followed by a swelling step, a washing step, and a drying step. The content of the iodine contained in the polarizing film can be controlled by the concentration of the iodine, the iodide such as potassium iodide, or the like contained in any one of the treatment baths in the swelling step, the dyeing step, the crosslinking step, the stretching step, and the washing step, the treatment temperature and the treatment time in each of the treatment baths. The respective steps may be performed in any suitable order, and 1 step may be performed a plurality of times as needed.

The polyvinyl alcohol-based film may be, but is not particularly limited to, a polyvinyl alcohol (PVA) -based film that has light transmittance in the visible light region and is obtained by dispersing and adsorbing a dichroic substance such as iodine or a dichroic dye. Examples of the material of the polyvinyl alcohol film include polyvinyl alcohol and derivatives thereof. Examples of the derivative of the polyvinyl alcohol include: polyvinyl formal, polyvinyl acetal; olefins such as ethylene and propylene; and derivatives modified with unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, alkyl esters thereof, acrylamide, and the like. The polyvinyl alcohol preferably has an average polymerization degree of about 100 to 10000, more preferably about 1000 to 10000, and further preferably about 1500 to 4500. The saponification degree of the polyvinyl alcohol is preferably about 80 to 100 mol%, more preferably about 95 to 99.95 mol%. The average polymerization degree and the saponification degree can be determined according to JIS K6726.

The polyvinyl alcohol film may contain additives such as a plasticizer and a surfactant. Examples of the plasticizer include: and polyhydric alcohols such as glycerin, diglycerin, triglycerol, ethylene glycol, propylene glycol, and polyethylene glycol, and condensates thereof. The amount of the additive is not particularly limited, and is preferably about 20 wt% or less in the polyvinyl alcohol film, for example.

The polyvinyl alcohol film may be a laminate in which a polyvinyl alcohol resin layer (PVA type resin layer) containing a polyvinyl alcohol resin (PVA type resin) is formed on one side of a long thermoplastic resin base material. As a method for producing the laminate, any suitable method can be adopted, and examples thereof include: a method of applying a coating solution containing the PVA-based resin on the surface of the thermoplastic resin substrate and drying the coating solution. The thickness of the thermoplastic resin substrate is preferably about 20 to 300. Mu.m, and more preferably about 50 to 200. Mu.m. The thickness of the PVA based resin layer is preferably about 3 to 40 μm, more preferably about 3 to 20 μm.

As the constituent material of the thermoplastic resin substrate, any suitable thermoplastic resin can be used. Examples of the thermoplastic resin include: ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. Of these, norbornene-based resins and amorphous (non-crystalline) polyethylene terephthalate-based resins are preferable, and amorphous (non-crystalline) polyethylene terephthalate-based resins are preferably used from the viewpoint that the thermoplastic resin substrate is very excellent in stretchability and can be inhibited from crystallizing during stretching. Examples of the amorphous (noncrystalline) polyethylene terephthalate resin include copolymers containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acid, and copolymers containing cyclohexanedimethanol and diethylene glycol as diol.

The thermoplastic resin substrate may be subjected to a surface treatment (e.g., corona treatment) before the PVA-based resin layer is formed, 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. The thermoplastic resin substrate may be stretched before the PVA-based resin layer is formed.

The coating liquid is a solution obtained by dissolving a PVA-based resin in a solvent. Examples of the solvent include: water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine are preferable. These solvents may be used alone, or two or more kinds may be used in combination. The concentration of the PVA-based resin in the coating solution is preferably about 3 to 20 parts by weight per 100 parts by weight of the solvent, from the viewpoint of forming a uniform coating film which adheres to the thermoplastic resin substrate.

From the viewpoint of improving the orientation of the polyvinyl alcohol molecules by stretching, a halide may be blended in the coating liquid. As the halide, any suitable halide can be used, and examples thereof include iodide, sodium chloride, and the like. Examples of the iodide include: potassium iodide, sodium iodide, lithium iodide, and the like, with potassium iodide being preferred. The concentration of the halide in the coating liquid is preferably about 5 to 20 parts by weight, more preferably about 10 to 15 parts by weight, based on 100 parts by weight of the PVA-based resin.

Further, an additive may be added to the coating liquid. Examples of the additives include: plasticizers such as ethylene glycol and glycerin; and surfactants such as nonionic surfactants.

As a method for applying the coating liquid, any suitable method can be adopted, and examples thereof include: roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and blade coating (comma coating, etc.).

In the stretching step, the PVA-based film is typically stretched unidirectionally by a factor of about 3 to 7. The stretching direction may be the longitudinal direction (MD direction) of the film or the width direction (TD direction) of the film. The stretching direction is preferably the TD direction from the viewpoint of roll-to-roll lamination with the transparent protective film or the optical functional film. The stretching method may be dry stretching or wet stretching, or a combination thereof. The PVA-based film may be stretched in the crosslinking step, the swelling step, the dyeing step, or the like. The stretching step may be performed in one stage or in multiple stages. In the case of performing in multiple stages, the stretching magnification is the product of the stretching magnifications in the respective stages. The stretching direction may correspond to the absorption axis direction of the obtained polarizing film.

The swelling step is performed before the dyeing step, if necessary. The swelling step is performed by, for example, immersing the PVA-based membrane in a swelling bath. As the swelling bath, water such as distilled water or pure water is generally used. The swelling bath may contain any suitable other components besides water. Examples of the other components include: solvents such as alcohols, additives such as surfactants, and iodides. Examples of the iodide include: potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, and the like, with potassium iodide being preferred. The temperature of the swelling bath is, for example, about 20 to 45 ℃. The immersion time is, for example, about 10 to 300 seconds.

The dyeing step is a step of dyeing the PVA-based film with a dichroic substance. Examples of the adsorption method include: a method of immersing a PVA-based membrane in a dyeing solution containing a dichroic substance; a method of applying the staining solution to a PVA film; a method of spraying the dyeing solution onto the PVA-based film is preferably a method of immersing the PVA-based film in the dyeing solution from the viewpoint of good adsorption of the dichroic substance.

Examples of the dichroic substance include: iodine or a dichroic dye, preferably iodine. When iodine is used as the dichroic material, an aqueous iodine solution is preferably used as the dyeing liquid. The iodine content of the aqueous iodine solution is preferably about 0.04 to 5.0 parts by weight relative to 100 parts by weight of water. In addition, in order to increase the solubility of iodine in water, it is preferable to add iodide to the aqueous iodine solution. As the iodide, potassium iodide is preferably used. The content of the iodide is preferably about 0.3 to 15 parts by weight relative to 100 parts by weight of water. From the viewpoint of obtaining a polarizing film having good optical characteristics, the ratio of the contents of iodine and iodide in the aqueous iodine solution is preferably about 1. The temperature of the dyeing liquid is, for example, 20 to 50 ℃. The immersion time is, for example, 5 seconds to 5 minutes.

In the crosslinking step, a boron compound is generally used as a crosslinking agent. Examples of the boron compound include: boric acid, borax, etc., preferably boric acid. The boron compound is usually used in the form of an aqueous solution. The concentration of the boron compound in the aqueous solution containing the boron compound is, for example, about 0.5 to 15% by weight, preferably about 1 to 10% by weight. The aqueous solution containing the boron compound may contain an iodide such as potassium iodide.

Examples of the crosslinking step include: a method of impregnating a PVA-based film in an aqueous solution containing a boron compound; a method of applying an aqueous solution containing a boron compound to a PVA-based film; a method of spraying an aqueous solution containing a boron compound onto the PVA-based film, and a method of immersing in an aqueous solution containing a boron compound is preferable.

In the crosslinking step, the temperature of the aqueous solution containing the boron compound is, for example, 25 ℃ or higher, preferably about 30 to 85 ℃, and more preferably about 40 to 70 ℃. The immersion time is, for example, about 5 to 800 seconds, preferably about 8 to 500 seconds.

The washing step is performed after the crosslinking step as necessary. The cleaning step is typically performed by immersing the PVA-based membrane in a cleaning liquid. As a representative example of the cleaning liquid, pure water is given. The cleaning liquid may contain an iodide such as potassium iodide. The temperature of the cleaning liquid is, for example, about 5 to 50 ℃. The immersion time is, for example, about 1 to 300 seconds.

In the case of producing a polarizing film containing the radical scavenger, the radical scavenger may be contained in one or more treatment baths selected from the group consisting of the swelling step, the washing step, the dyeing step, the crosslinking step, and the stretching step. The concentration of the radical scavenger contained in any of the treatment baths is not generally determined because it is affected by the number of treatments, the treatment time, the treatment temperature, and the like of each treatment, and is preferably 0.01 wt% or more, more preferably 0.05 wt% or more, further preferably 0.1 wt% or more, and preferably 30 wt% or less, more preferably 25 wt% or less, and further preferably 20 wt% or less, from the viewpoint of efficiently controlling the content of the radical scavenger in the polarizing film.

In addition, additives such as zinc salts, pH regulators, pH buffers, and other salts may be contained in the treatment baths in the swelling step, the dyeing step, the crosslinking step, the stretching step, and the washing step. Examples of the zinc salt include: zinc halides such as zinc chloride and zinc iodide; inorganic zinc salts such as zinc sulfate and zinc acetate. Examples of the pH adjuster include: strong acids such as hydrochloric acid, sulfuric acid and nitric acid, and strong bases such as sodium hydroxide and potassium hydroxide. Examples of the pH buffer include: carboxylic acids such as acetic acid, oxalic acid and citric acid and salts thereof, and inorganic weak acids such as phosphoric acid and carbonic acid and salts thereof. Examples of the other salts include: chlorides such as sodium chloride, potassium chloride, and barium chloride, nitrates such as sodium nitrate and potassium nitrate, sulfates such as sodium sulfate and potassium sulfate, and salts of alkali metals and alkaline earth metals.

Examples of the drying step include: natural drying, air-blowing drying, reduced-pressure drying, heat drying, and the like, and heat drying is preferable. When the heat drying is performed, the heating temperature is, for example, 30 to 100 ℃. The drying time is, for example, 20 seconds to 10 minutes.

< polarizing film >

The polarizing film of the present invention is obtained by laminating a film such as a transparent protective film or an optical functional film on at least one surface of the above polarizing film.

The transparent protective film is not particularly limited, and various transparent protective films used in polarizing films can be used. As a material constituting the transparent protective film, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy, and the like can be used. Examples of the thermoplastic resin include: cellulose ester resins such as cellulose triacetate, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins such as nylon and aromatic polyamide, polyimide resins, polyolefin resins such as polyethylene, polypropylene and ethylene-propylene copolymers, (meth) acrylic resins, cyclic polyolefin resins having a cyclic or norbornene structure (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. The transparent protective film may be a cured layer formed of a thermosetting resin or an ultraviolet-curable resin such as a (meth) acrylic resin, a urethane resin, an acrylic urethane resin, an epoxy resin, or a silicone resin. Among these, cellulose ester resins, polycarbonate resins, (meth) acrylic resins, cyclic polyolefin resins, and polyester resins are preferable.

The thickness of the transparent protective film may be suitably determined, and is generally preferably about 1 to 500 μm, more preferably about 1 to 300 μm, and still more preferably about 5 to 100 μm, from the viewpoints of strength, handling properties such as handling properties, and thin layer properties.

The transparent protective film may contain any suitable additive such as an ultraviolet absorber, an antioxidant, a lubricant, a plasticizer, a mold release agent, a coloring inhibitor, a flame retardant, an antistatic agent, a pigment, and a colorant. In particular, when the transparent protective film contains an ultraviolet absorber, the light resistance of the polarizing film can be improved.

The optical functional film is not particularly limited, and for example, an optical functional film used in the formation of a liquid crystal display device or the like may be used, such as a 1-layer or 2-layer or more reflection plate, semi-transmission plate, retardation plate (including 1/2, 1/4, and the like wave plate), viewing angle compensation film, and luminance improvement film such as linearly polarized light separation film. Examples of the polarizing film having the optical functional film include: a reflective polarizing film or a semi-transmissive polarizing film obtained by further laminating a reflective plate or a semi-transmissive reflective plate on the polarizing film, an elliptical polarizing film or a circular polarizing film obtained by further laminating a phase difference plate on the polarizing film, a wide viewing angle polarizing film obtained by further laminating a viewing angle compensation film on the polarizing film, or a polarizing film obtained by further laminating a brightness improving film on the polarizing film.

When the above-mentioned transparent protective film, optical functional film or the like is laminated on both surfaces of the above-mentioned polarizing film, the films on both surfaces may be the same or different.

Functional layers such as a hard coat layer, an antireflection layer, an adhesion prevention layer, a diffusion layer, and an antiglare layer may be provided on the surface of the film not bonded to the polarizing film. The functional layers such as the hard coat layer, the antireflection layer, the adhesion prevention layer, the diffusion layer, and the antiglare layer may be provided as a layer different from the film, in addition to the film itself.

The polarizing film and the film or the polarizing film and the functional layer are usually bonded together via an adhesive layer or an adhesive layer.

As the adhesive for forming the adhesive layer, various adhesives used for a polarizing film can be applied, and examples thereof include: rubber-based adhesives, acrylic-based adhesives, silicone-based adhesives, urethane-based adhesives, vinyl alkyl ether-based adhesives, polyvinyl alcohol-based adhesives, polyvinyl pyrrolidone-based adhesives, polyacrylamide-based adhesives, cellulose-based adhesives, and the like. Among these, acrylic adhesives are preferred.

As a method of forming the above adhesive layer, for example: a method in which the adhesive is applied to a separator or the like which has been subjected to a peeling treatment, and dried to form an adhesive layer, and then transferred to a polarizing film or the like; or a method of applying the adhesive to a polarizing film or the like and drying the adhesive to form an adhesive layer. The thickness of the pressure-sensitive adhesive layer is not particularly limited, and is, for example, about 1 to 100 μm, preferably about 2 to 50 μm.

As the adhesive forming the adhesive layer, various adhesives used for a polarizing film can be applied, and examples thereof include: isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latexes, water-based polyesters, and the like. These adhesives are generally used in the form of an adhesive (aqueous adhesive) formed from an aqueous solution, and contain 0.5 to 60% by weight of a solid content.

The aqueous adhesive may contain a crosslinking agent. As the crosslinking agent, a compound having at least 2 functional groups reactive with a component such as a polymer constituting the adhesive in 1 molecule is generally used, and examples thereof include: alkylene diamines; isocyanates; epoxy resin; aldehydes; amino-formaldehydes such as methylolurea and methylolmelamine. The amount of the crosslinking agent in the adhesive is usually about 10 to 60 parts by weight per 100 parts by weight of the components such as the polymer constituting the adhesive.

Examples of the adhesive include those described aboveAn active energy ray-curable adhesive such as an ultraviolet ray-curable adhesive or an electron beam-curable adhesive is obtained. Examples of the active energy ray-curable adhesive include (meth) acrylate adhesives. Examples of the curable component in the (meth) acrylate adhesive include: a compound having a (meth) acryloyl group, a compound having a vinyl group. Examples of the compound having a (meth) acryloyl group include: alkyl (meth) acrylates such as alkyl (meth) acrylates having 1 to 20 carbon atoms, alicyclic alkyl (meth) acrylates, and polycyclic alkyl (meth) acrylates; a hydroxyl group-containing (meth) acrylate; epoxy group-containing (meth) acrylates such as glycidyl (meth) acrylate, and the like. The (meth) acrylate-based adhesive may contain a nitrogen-containing monomer such as hydroxyethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, or (meth) acryloylmorpholine. The (meth) acrylate adhesive may contain tripropylene glycol diacrylate, 1, 9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, cyclic trimethylolpropane formal acrylate, or bis (meth) acrylate

A polyfunctional monomer such as alkylene glycol diacrylate or EO-modified diglycerol tetraacrylate as a crosslinking component. Further, as the cationic polymerization curing adhesive, a compound having an epoxy group or an oxetane group may be used. The compound having an epoxy group is not particularly limited as long as it has at least 2 epoxy groups in the molecule, and various curable epoxy compounds generally known can be used.

The adhesive may contain an appropriate additive as needed. Examples of the additives include: silane coupling agents, coupling agents such as titanium coupling agents, bonding accelerators such as ethylene oxide, ultraviolet absorbers, deterioration prevention agents, dyes, processing aids, ion trapping agents, antioxidants, tackifiers, fillers, plasticizers, leveling agents, foaming inhibitors, antistatic agents, heat-resistant stabilizers, hydrolysis-resistant stabilizers and the like.

The adhesive may be applied to either the film side (or the functional layer side) or the polarizing film side, or to both sides. After the bonding, a drying step is performed to form an adhesive layer formed by coating a dry layer. After the drying step, ultraviolet rays and electron beams may be irradiated as necessary. The thickness of the adhesive layer is not particularly limited, and is preferably about 30 to 5000nm, more preferably about 100 to 1000nm in the case of using an aqueous adhesive or the like, and is preferably about 0.1 to 100 μm, more preferably about 0.5 to 10 μm in the case of using an ultraviolet-curable adhesive, an electron beam-curable adhesive or the like.

The transparent protective film and the polarizing film, or the polarizing film and the functional layer may be laminated with a surface modification treatment layer, an easy adhesion layer, a barrier layer, a refractive index adjustment layer, or the like interposed therebetween.

Examples of the surface modification treatment for forming the surface modification layer include: corona treatment, plasma treatment, undercoating treatment, saponification treatment, and the like.

Examples of the easy adhesive agent for forming the easy adhesive layer include: a material for forming various resins including a polyester skeleton, a polyether skeleton, a polycarbonate skeleton, a polyurethane skeleton, silicones, a polyamide skeleton, a polyimide skeleton, a polyvinyl alcohol skeleton, and the like. The easy-adhesion layer may be provided on the film in advance, and the easy-adhesion layer side of the film may be laminated on the polarizing film with the pressure-sensitive adhesive layer or the adhesive layer interposed therebetween.

The barrier layer is a layer having a function of preventing impurities such as oligomers and ions dissolved from the film from moving (entering) into the polarizing film. The barrier layer may be any layer that has transparency and can prevent impurities from eluting from the film or the like, and examples of the material forming the barrier layer include: urethane prepolymer-based forming materials, cyanoacrylate-based forming materials, epoxy-based forming materials, and the like.

The refractive index adjustment layer is provided to suppress a decrease in transmittance due to reflection between the film and a layer having a different refractive index such as a polarizing film. Examples of the refractive index adjusting material for forming the refractive index adjusting layer include: the material for forming the resin composition contains various resins including silica-based resins, acrylic-styrene resins, melamine resins, and the like, and additives.

The polarization degree of the polarizing film is preferably 99.98% or more, and more preferably 99.99% or more.

An adhesive layer for bonding other members may be provided on one or both surfaces of the polarizing film. The adhesive layer is preferably an adhesive layer. The pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer is not particularly limited, and for example, a pressure-sensitive adhesive using a polymer such as an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyether, a fluorine polymer, or a rubber as a base polymer can be suitably selected and used. In particular, a pressure-sensitive adhesive which is excellent in optical transparency, exhibits appropriate wettability, cohesiveness and adhesiveness, and is excellent in weather resistance, heat resistance and the like, such as a pressure-sensitive adhesive containing an acrylic polymer, can be preferably used.

The adhesive layer may be provided on one or both surfaces of the polarizing film in an appropriate manner. Examples of the pressure-sensitive adhesive layer include: a method of preparing an adhesive solution and directly applying the adhesive solution to the polarizing film by a suitable spreading method such as a casting method and a coating method; or a method of forming an adhesive layer on a separator and transferring the adhesive layer to the polarizing film. The thickness of the pressure-sensitive adhesive layer may be suitably determined depending on the purpose of use, the adhesive strength, and the like, and is generally 1 to 500. Mu.m, preferably 5 to 200. Mu.m, and more preferably 10 to 100. Mu.m. The polarizing film having a pressure-sensitive adhesive layer on at least one surface thereof is also referred to as a pressure-sensitive adhesive layer-attached polarizing film.

The exposed surface of the pressure-sensitive adhesive layer is preferably covered by a temporary adhesive film for the purpose of preventing contamination or the like until the pressure-sensitive adhesive layer is actually used. This can prevent contamination of the pressure-sensitive adhesive layer and the like in a normal handling state. As the separator, for example, a separator obtained by coating an appropriate thin layer body such as a plastic film, a rubber sheet, paper, cloth, nonwoven fabric, net, foamed sheet, metal foil, or a laminate thereof with an appropriate release agent such as silicone, long-chain alkyl, fluorine, or molybdenum sulfide, as necessary, can be used.

Examples

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

< example 1 >

< polarizing film and polarizing film production >

As the thermoplastic resin substrate, a film (thickness: 100 μm) of polyethylene terephthalate isophthalate (IPA-copolymerized PET) was used. One surface of the substrate was subjected to corona treatment, and an aqueous solution containing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, acetoacetyl-modification rate 4.6%, saponification degree 99.0 mol% or more, manufactured by japan synthetic chemical industries co., ltd., trade name "Gohsefimer Z200") at a ratio of 9. The obtained laminate was stretched in a gas atmosphere of 4.5 times at 140 ℃ in a direction orthogonal to the longitudinal direction of the laminate using a tenter stretcher (stretching treatment). Next, the laminate was immersed in a dyeing bath (aqueous solution having an iodine concentration of 1.0 wt% and a potassium iodide concentration of 7.0 wt%) at a liquid temperature of 25 ℃ for 12 seconds to be dyed (dyeing treatment). Subsequently, the resultant film was immersed for 21 seconds in a crosslinking bath (an aqueous solution having a boron concentration of 1.0 wt%, a potassium iodide concentration of 1.0 wt%, and a concentration of a compound represented by general formula (9) of 5.0 wt%) at a liquid temperature of 60 ℃ (crosslinking treatment). Next, the laminate was immersed in a cleaning bath (aqueous solution having a potassium iodide concentration of 4.5 wt%) at a liquid temperature of 25 ℃ for 10 seconds (cleaning treatment). Subsequently, the laminate was dried in an oven at 60 ℃ for 21 seconds (drying treatment), and a laminate having a PVA-based resin layer (polarizing film) with a thickness of 1.2 μm was obtained. Next, a linearly polarized light separation film (product name "DBEF" manufactured by 3M) was laminated on the polarizing film side of the obtained laminate having the PVA-based resin layer (polarizing film) through an acrylic pressure-sensitive adhesive layer having a thickness of 20 μ M, and then the thermoplastic resin substrate was peeled off, and the acrylic pressure-sensitive adhesive layer having a thickness of 20 μ M was applied to the peeled surface to prepare a polarizing film having a monomer transmittance of 39.7%.

[ chemical formula 9]

[ method for measuring iodine content (% by weight) in polarizing film ]

The iodine concentration (% by weight) of the polarizing film was determined by the following equation using a fluorescent X-ray analyzer (product name "ZSX-PRIMUS IV" manufactured by KOHK Co., ltd., measurement diameter.: 20 mm).

Iodine concentration (wt%) =14.474 × (fluorescent X-ray intensity)/(film thickness) (kcps/μm)

The coefficient for calculating the concentration differs depending on the measuring apparatus, and the coefficient can be obtained by using an appropriate calibration curve. The results are shown in Table 1.

[ analysis of generated gas ]

The polarized film was introduced into a heating furnace type pyrolyzer (PY-2020 iD, product of Frontier Lab), and the generated gas was directly introduced into a TOFMS (JMS-T100 GCV, product of JEOL), to carry out a generated gas analysis (EGA/TOFMS). The results are shown in Table 1.

[ measurement conditions ]

Temperature rise conditions: 40 ℃ → 10 ℃/min → 350 DEG C

Interface: a deactivated fused quartz tube of 2.5 mm x 0.15mm id

Carrier gas: he (1.0 mL/min)

Injection port temperature: 300 deg.C

Filling port: flow splitting ratio of 20

Interface temperature: 300 deg.C

Mass spectrometry: TOFMS

An ionization method: EI method

The mass range is as follows: m/z =18

[ method for measuring the content (% by weight) of the radical scavenger in the polarizing film ]

About 20mg of the polarizing film was collected and quantified, and the solution was dissolved in 1mL of water under heating, and then diluted with 4.5mL of methanol, and the resulting extract was filtered through a membrane filter, and the concentration of the radical scavenger was measured by HPLC (ACQUITY UPLC H-class Bio, manufactured by Waters). The results are shown in Table 1.

[ evaluation of degree of polarization ]

The degree of polarization of the polarizing film can be measured using a spectrophotometer (product name "V7100" made by japan spectrophotometers). As a specific method for measuring the degree of polarization, the parallel transmittance (H0) and the orthogonal transmittance (H90) of the polarizing film can be measured according to the formula: the polarization degree (%) = { (H0-H90)/(H0 + H90) }1/2 × 100. The parallel transmittance (H0) is a transmittance value of a parallel laminated polarizing film produced by laminating 2 identical polarizing films so that absorption axes thereof are parallel to each other. The orthogonal transmittance (H90) is a transmittance value of an orthogonal laminated polarizing film produced by laminating 2 identical polarizing films so that absorption axes thereof are orthogonal to each other. These transmittances are Y values obtained by visibility correction with a 2-degree field of view (C light source) of JlS Z8701-1982. The results are shown in Table 1.

[ evaluation of monomer transmittance in high-temperature Environment ]

The polarizing film obtained above was cut into a size of 5.0 × 4.5cm so that the absorption axis of the polarizing film was parallel to the long side, and a 1.3mm alkali-free glass plate was attached to the adhesive layer of the polarizing film to prepare a laminate. The obtained laminate was left standing in a hot air oven at a temperature of 105 ℃ for 96 hours, and the monomer transmittance (Δ Ts) before and after charging (heating) was measured. The monomer transmittance was measured using a spectrophotometer (product name "V7100" manufactured by japan spectrophotometers) and evaluated based on the following criteria. The measurement wavelength was 380 to 700nm (5 nm interval), and the results are shown in table 1.

ΔTs(％)＝Ts ₉₆ －Ts ₀

Here, ts ₀ Is the monomer transmittance of the laminate before heating, ts ₉₆ The monomer transmittance of the laminate after heating for 96 hours. The above Δ Ts (%) is preferably 5. Gtoreq.Δ Ts (%) More preferably 3. Gtoreq.0, still more preferably 3. Gtoreq.Ts (%). Gtoreq.0.

< example 2 >

A polarizing film and a polarizing film were produced in the same manner as in example 1, except that in the above-mentioned < production of a polarizing film and a polarizing film >, the crosslinking bath was changed to a crosslinking bath (an aqueous solution having a boron concentration of 1.0 wt%, a potassium iodide concentration of 1.0 wt%, and a concentration of the compound represented by the above general formula (9) of 10.0 wt%). The results of the measurement and evaluation of the polarizing film and the polarizing film are shown in table 1.

< example 3 >

A polarizing film and a polarizing film were produced in the same manner as in example 1, except that in the above-mentioned < production of a polarizing film and a polarizing film >, the crosslinking bath was changed to a crosslinking bath (an aqueous solution having a boron concentration of 1.0 wt%, a potassium iodide concentration of 1.0 wt%, and a concentration of the compound represented by the general formula (8) of 10.0 wt%). The results of the measurement and evaluation of the polarizing film and the polarizing film are shown in table 1.

< example 4 >

A polarizing film and a polarizing film were produced in the same manner as in example 1, except that in the above-mentioned < production of a polarizing film and a polarizing film >, the crosslinking bath was changed to a crosslinking bath (an aqueous solution having a boron concentration of 1.0 wt%, a potassium iodide concentration of 1.0 wt%, and a concentration of the compound represented by the above general formula (7) of 10.0 wt%). The results of the measurement and evaluation of the polarizing film and the polarizing film are shown in table 1.

< example 5 >

In the above-mentioned < production of polarizing film and polarizing film >, a polarizing film and a polarizing film were produced by the same operation as in example 1 except that a laminate was produced by forming a PVA-based resin layer so that the thickness of the finally obtained polarizing film became 4.8 μm, and the crosslinking bath was changed to a crosslinking bath (an aqueous solution having a boron concentration of 1.0 wt%, a potassium iodide concentration of 1.0 wt%, and a concentration of the compound represented by the general formula (9) of 10.0 wt%). The results of the measurement and evaluation of the polarizing film and the polarizing film are shown in table 1.

< example 6 >

In the above-mentioned < production of polarizing film and polarizing film >, a polarizing film and a polarizing film were produced by the same operation as in example 1 except that the dyeing bath was changed to a dyeing bath (an aqueous solution having an iodine concentration of 0.7 wt% and a potassium iodide concentration of 4.9 wt%) and the crosslinking bath was changed to a crosslinking bath (an aqueous solution having a boron concentration of 1.0 wt%, a potassium iodide concentration of 1.0 wt%, and a concentration of the compound represented by the general formula (9) of 10.0 wt%). The results of the measurement and evaluation of the polarizing film and the polarizing film are shown in table 1.

< example 7 >

A polarizing film and a polarizing film were produced in the same manner as in example 1, except that in the above-mentioned < production of a polarizing film and a polarizing film > the PVA-based resin layer was formed so that the thickness of the finally obtained polarizing film became 2.5 μm to produce a laminate, the dyeing bath was changed to the dyeing bath (aqueous solution having an iodine concentration of 0.5 wt% and a potassium iodide concentration of 3.5 wt%), and the crosslinking bath was changed to the crosslinking bath (aqueous solution having a boron concentration of 1.0 wt%, a potassium iodide concentration of 1.0 wt%, and a compound represented by the general formula (9) concentration of 10.0 wt%). The results of the measurement and evaluation of the polarizing film and the polarizing film are shown in table 1.

< example 8 >

In the above-mentioned < production of polarizing film and polarizing film >, a polarizing film and a polarizing film were produced by the same operation as in example 1 except that the PVA-based resin layer was formed so that the thickness of the finally obtained polarizing film became 4.8 μm to produce a laminate, the dyeing bath was changed to the dyeing bath (aqueous solution having an iodine concentration of 0.5 wt% and a potassium iodide concentration of 3.5 wt%), and the crosslinking bath was changed to the crosslinking bath (aqueous solution having a boron concentration of 1.0 wt%, a potassium iodide concentration of 1.0 wt%, and a compound represented by the general formula (9) of 10.0 wt%). The results of the measurement and evaluation of the polarizing film and the polarizing film are shown in table 1.

< comparative example 1 >

A polarizing film and a polarizing film were produced in the same manner as in example 1, except that in the above-mentioned "production of a polarizing film and a polarizing film", the crosslinking bath was changed to a crosslinking bath (an aqueous solution having a boron concentration of 1.0 wt% and a potassium iodide concentration of 1.0 wt%). The results of the measurement and evaluation of the polarizing film and the polarizing film are shown in table 1.

< comparative example 2 >

In the above-mentioned < production of polarizing film and polarizing film >, a polarizing film and a polarizing film were produced by the same operation as in example 1 except that the dyeing bath was changed to a dyeing bath (aqueous solution having an iodine concentration of 0.5 wt% and a potassium iodide concentration of 3.5 wt%) and the crosslinking bath was changed to a crosslinking bath (aqueous solution having a boron concentration of 1.0 wt%, a potassium iodide concentration of 1.0 wt%, and a concentration of the compound represented by the general formula (9) of 10.0 wt%). The results of the measurement and evaluation of the polarizing film and the polarizing film are shown in table 1.

< comparative example 3 >

In the above-mentioned < polarizing film and polarizing film production > a polarizing film and a polarizing film were produced by the same operation as in example 1 except that a linearly polarized light separating film (trade name "DBEF" manufactured by 3M) was laminated on the polarizing film side of a laminate having a PVA type resin layer (polarizing film) through an acrylic pressure-sensitive adhesive layer having a thickness of 20 μ M, the thermoplastic resin substrate was peeled off, a treatment liquid (an aqueous solution of 0.5 wt% sodium bicarbonate and 50 wt% isopropyl alcohol: ph 6.0) was applied to the peeled surface using a wire bar coater, and the resultant was dried at 50 ℃ for 60 seconds, and then an acrylic pressure-sensitive adhesive layer having a thickness of 20 μ M was applied to produce a polarizing film. The results of the measurement and evaluation of the polarizing film and the polarizing film are shown in table 1.

< comparative example 4 >

A polarizing film and a polarizing film were produced in the same manner as in example 1, except that in the above-mentioned < production of a polarizing film and a polarizing film >, the dyeing bath was changed to a dyeing bath (an aqueous solution having a potassium iodide concentration of 15.0 wt% and a ferric sulfate n-hydrate of 2.0 wt%). The results of the measurement and evaluation of the polarizing film and the polarizing film are shown in table 1.

The polarizing film in the examples, in which the content of iodine exceeded 10% by weight, the monomer transmittance was 41% or less, and the peak temperature of the maximum intensity of water in the generated gas analysis was 175 ℃ or more, was excellent in the effect of suppressing the decrease in the monomer transmittance due to the coloration of the polarizing film in a high-temperature environment.

On the other hand, the polarizing film of comparative example 1 had a peak temperature of 173 ℃ at the maximum intensity of water in the generated gas analysis, and therefore, the effect of suppressing the decrease in the monomer transmittance due to the coloring of the polarizing film in a high-temperature environment was not good. In addition, the polarizing film of comparative example 2 had a monomer transmittance of 41.5%, and thus did not satisfy the criterion of the monomer transmittance of the present invention. In addition, comparative examples 3 and 4 correspond to the polarizing films disclosed in patent documents 1 and 2 of the prior art documents, and have a peak temperature of the maximum intensity of water in the generated gas analysis of less than 175 ℃.

Claims

1. A polarizing film formed by adsorbing iodine to a polyvinyl alcohol film and orienting the film,

the polarizing film has an iodine content of more than 10 wt% and a monomer transmittance of 41% or less,

in the generated gas analysis, the peak temperature of the maximum intensity of water detected by the polarizing film is 175 ℃ or higher in the presence of an inert gas under the conditions that the temperature rise rate is 10 ℃/min and the temperature rise range is 40-350 ℃.

2. The polarizing film according to claim 1, which has a thickness of 10 μm or less.

3. The polarized film of claim 1 or 2 comprising a free radical scavenger.

4. The polarized film according to claim 3, wherein,

the weight ratio of the content of the radical scavenger to the content of the iodine (content of the radical scavenger/content of iodine) is 0.01 or more.

5. The polarized film according to claim 3 or 4,

the radical scavenger is a compound having a nitroxyl radical or nitroxyl group.

6. A polarizing film comprising the polarizing film according to any one of claims 1 to 5 and, bonded to at least one surface thereof, a transparent protective film or an optically functional film.

7. The polarizing film according to claim 6, wherein the degree of polarization is 99.98% or more.