CN112771419A - Polarizing film, laminated polarizing film, image display panel, and image display device - Google Patents

Polarizing film, laminated polarizing film, image display panel, and image display device Download PDF

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CN112771419A
CN112771419A CN201980063373.4A CN201980063373A CN112771419A CN 112771419 A CN112771419 A CN 112771419A CN 201980063373 A CN201980063373 A CN 201980063373A CN 112771419 A CN112771419 A CN 112771419A
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polarizing film
film
image display
stretching
treatment
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CN112771419B (en
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山下智弘
黑田拓马
西谷良宏
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Nitto Denko Corp
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    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/30Polarising elements
    • G02B5/3025Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state
    • G02B5/3033Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state in the form of a thin sheet or foil, e.g. Polaroid
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/02Physical, chemical or physicochemical properties
    • B32B7/023Optical properties
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B60VEHICLES IN GENERAL
    • B60RVEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
    • B60R11/00Arrangements for holding or mounting articles, not otherwise provided for
    • B60R11/02Arrangements for holding or mounting articles, not otherwise provided for for radio sets, television sets, telephones, or the like; Arrangement of controls thereof
    • B60R11/0229Arrangements for holding or mounting articles, not otherwise provided for for radio sets, television sets, telephones, or the like; Arrangement of controls thereof for displays, e.g. cathodic tubes
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B1/00Optical elements characterised by the material of which they are made; Optical coatings for optical elements
    • G02B1/04Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of organic materials, e.g. plastics
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/30Polarising elements
    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333Constructional arrangements; Manufacturing methods
    • G02F1/1335Structural association of cells with optical devices, e.g. polarisers or reflectors
    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333Constructional arrangements; Manufacturing methods
    • G02F1/1335Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133528Polarisers
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09FDISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
    • G09F9/00Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
    • G09F9/30Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00Electroluminescent light sources
    • H05B33/02Details
    • HELECTRICITY
    • H10SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10KORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K59/00Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
    • H10K59/50OLEDs integrated with light modulating elements, e.g. with electrochromic elements, photochromic elements or liquid crystal elements
    • HELECTRICITY
    • H10SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10KORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K59/00Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
    • H10K59/80Constructional details
    • H10K59/8791Arrangements for improving contrast, e.g. preventing reflection of ambient light

Abstract

The present invention provides a polarizing film formed by adsorbing iodine to a polyvinyl alcohol film and orienting the film, wherein the iodine concentration is 3-10 wt%, and the peak temperature of the maximum strength of water detected in the presence of an inert gas under the conditions of a temperature rise rate of 10 ℃/min and a temperature rise range of 40-350 ℃ is 205 ℃ or higher in a generated gas analysis method. The polarizing film has a good initial polarization degree and is excellent in the effect of suppressing a decrease in the monomer transmittance due to coloring of the polarizing film in a high-temperature environment.

Description

Polarizing film, laminated polarizing film, image display panel, and image display device
Technical Field
The invention relates to a polarizing film, a laminated polarizing film, an image display panel, and an image display device.
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 subjected to dyeing treatment (containing a dichroic material such as iodine or a dichroic dye) has been used in view of having both high transmittance and high degree of polarization. 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.
The polarizing film is used in the form of a laminated polarizing film (optical laminate) in which other optical layers are laminated as necessary, and the polarizing film or the laminated polarizing film (optical laminate) is used in the form of a laminated polarizing film (optical laminate) which is bonded between an image display unit such as a liquid crystal cell or an organic EL element and a front surface transparent plate (window layer) on the viewing side and a front surface transparent member such as a touch panel via an adhesive layer or an adhesive layer to produce the various image display devices described above (patent document 1).
In recent years, such various image display devices are used as in-vehicle image display devices such as car navigation devices and rear view monitors in addition to mobile devices such as mobile phones and tablet terminals, and their applications are expanding. Accordingly, the image display device is required to have higher durability in a more severe environment (for example, a high-temperature environment) than the conventional one, and an image display device for securing such durability has been proposed (patent document 2).
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open publication No. 2014-102353
Patent document 2: japanese patent laid-open publication No. 2018-101117
Disclosure of Invention
Problems to be solved by the invention
When a polarizing film or a laminated polarizing film using an iodine-based polarizing film is exposed to a high-temperature environment, polyvinyl alcohol constituting the polarizing film is polyene-formed by a dehydration reaction, and the polarizing film is colored, resulting in a problem that the monomer transmittance thereof is lowered.
As a result of intensive studies, the present inventors have found that iodine contained in an iodine-based polarizing film promotes polyalkyleneoxide in a high-temperature environment. Thus, in order to suppress a decrease in the monomer transmittance due to coloring of the polarizing film in a high-temperature environment, it is effective to reduce the iodine concentration (content) in the polarizing film. On the other hand, a polarizing film having a good degree of polarization can be obtained with a small iodine concentration by thickening the polarizing film, but when such a polarizing film is used, peeling tends to occur easily when the polarizing film or the laminated polarizing film is heated along with an increase in the size of the panel of the image display device.
In view of the above circumstances, an object of the present invention is to provide a polarizing film having a good initial degree of polarization and having an excellent effect of suppressing a decrease in monomer transmittance due to coloring of the polarizing film in a high-temperature environment.
Another object of the present invention is to provide a polarizing film, a laminated polarizing film, an image display panel, and an image display device 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 film, wherein the iodine concentration is 3% by weight or more and 10% by weight or less, and the polarizing film has a peak temperature of the maximum intensity 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 ℃ of 205 ℃ or more in a generated gas analysis method.
The present invention also relates to a polarizing film having a transparent protective film bonded to at least one surface of the polarizing film.
The present invention also relates to a laminated polarizing film, wherein the polarizing film is bonded to an optical layer.
The present invention also relates to an image display panel, wherein the polarizing film or the laminated polarizing film is bonded to an image display unit.
The present invention also relates to an image display device including a front transparent member on the polarizing film or laminated polarizing film side of the image display panel.
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 an iodine-based polarizing film formed by adsorbing iodine to a polyvinyl alcohol-based film and orienting the film, wherein the iodine concentration is 3 to 10% by weight, and the peak temperature of the maximum strength of water detected in the presence of an inert gas under the conditions of a temperature rise rate of 10 ℃/min and a temperature rise range of 40 to 350 ℃ is 205 ℃ or higher in a generated gas analysis method. As described above, although the iodine-based polarizing film undergoes polyalkylenation due to the 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 the dehydration reaction occurs to a high temperature side, that is, setting the peak temperature of the maximum intensity of water detected (observed) by a generated gas analysis method to 205 ℃. Further, in the polarizing film of the present invention, by setting the iodine concentration in the polarizing film to a certain range, the peak temperature of the maximum intensity of water detected (observed) by a generated gas analysis method can be controlled to 205 ℃ or higher, and the initial degree of polarization can be made good.
On the other hand, the present inventors exposed a polarizing film formed by adsorbing iodine to an iodine-containing polyvinyl alcohol film and orienting the film to a high-temperature environment for a certain period of time, and observed that radicals were generated from the polarizing film. Since the time for coloring the polarizing film by the polyalkylenation is very similar to the time for generating the radical, a phenomenon in which the radical is generated by 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 205 ℃ or higher, it is preferable that the polarizing film contains a compound having a radical trapping function.
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, and has an iodine concentration of 3 to 10% by weight, and in a generated gas analysis method, the polarizing film has a peak temperature of a maximum intensity 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 ℃ of 205 ℃ or higher.
The polyvinyl alcohol (PVA) film may be one having a light-transmitting property in a visible light region and obtained by dispersing and adsorbing iodine, without any particular limitation. The PVA film used in the roll film generally has a thickness of about 1 to 100 μm, more preferably about 1 to 50 μm, and a width of about 100 to 5000 mm.
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 obtained by modification with unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, and 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 above-mentioned additive is not particularly limited, and is preferably about 20% by weight or less in the polyvinyl alcohol film, for example.
The iodine concentration (content) of the polarizing film is 3 wt% or more and 10 wt% or less from the viewpoint of making the initial polarization degree of the polarizing film good and controlling the peak temperature of the maximum intensity of water detected by a generated gas analysis method to 205 ℃ or more. The iodine concentration (content) of the polarizing film is preferably 3.5 wt% or more, more preferably 4 wt% or more from the viewpoint of increasing the initial degree of polarization of the polarizing film, and is preferably 9 wt% or less, more preferably 7 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 205 ℃.
In the generated gas analysis method, the polarizing film exhibits a peak temperature of the maximum intensity 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 ℃ of 205 ℃ or higher. In the above polarizing film, by setting the temperature at which the dehydration reaction of polyvinyl alcohol occurs to the high temperature side, that is, by setting the peak temperature of the maximum intensity of water detected by the generated gas analysis method to 205 ℃ or higher, it is possible to suppress the decrease in the monomer transmittance due to the coloring of the polarizing film in a high temperature environment. On the other hand, when the peak temperature of the maximum intensity of water is lower than 205 ℃, 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. × 750 hours), which is regarded as an index of high temperature durability required in high-end in-vehicle displays, to 0% to 5%.
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 205 ℃.
The generated gas analysis method is an analysis method in which a gas chromatograph and a mass spectrometer are directly connected to each other by an inert metal capillary or the like, and a gas generated when a sample is heated by heating 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 compound having a radical trapping function. It is presumed that the compound having the radical trapping function can trap radicals generated by heating polyvinyl alcohol in the polarizing film, and the temperature of the dehydration reaction at which the polyalkyleneoxide is generated is set to a high temperature side. Examples of the compound having a radical-capturing function include: and compounds having a radical trapping function (e.g., antioxidants) such as hindered phenol compounds, hindered amine compounds, phosphorus compounds, sulfur compounds, benzotriazole compounds, benzophenone compounds, hydroxylamine compounds, salicylate compounds, and triazine compounds. The compound having a radical-capturing function is preferably a compound having a nitroxyl radical or nitroxyl group, for example, because the temperature at which the dehydration reaction by the polyalkyleneoxide is carried out can be easily set to a high temperature side.
The compound having a nitroxyl radical or a nitroxyl group may be an N-oxyl compound (a compound having a functional group of C-N (-C) -O (O · represents an oxygen radical)) or a known compound, from the viewpoint of having a relatively stable radical at room temperature and in the air. Examples of the N-oxyl compound include compounds having an organic group having the following structure.
[ chemical formula 1]
Figure BDA0002993657060000051
(in the general formula (1), R1Represents an oxygen radical, R2~R5Independently 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]
Figure BDA0002993657060000061
(in the general formula (2), R1~R5And n is as defined above, R6Represents 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]
Figure BDA0002993657060000062
(in the general formula (3), R1~R5And n is as defined above, R7And R8Independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an acyl group, or an aryl group. )
[ chemical formula 4]
Figure BDA0002993657060000063
(in the general formula (4), R1~R5And n is as defined above, R9~R11Independently 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]
Figure BDA0002993657060000064
(in the general formula (5), R1~R5And n is as defined above, R12Represents 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 acquisition2~R5Preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms. In the general formula (2), R is R from the viewpoint of easy acquisition6Preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably a hydrogen atom. In the general formula (3), R is preferably R from the viewpoint of easy acquisition7And R8Independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, more preferably a hydrogen atom. In the general formula (4), R is R from the viewpoint of easy acquisition9~R11Preferably 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 acquisition12Preferably hydroxyl, amino or alkoxy. In the general formulae (1) to (5), n is preferably 1 from the viewpoint of easy acquisition.
Further, 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.
In addition, the molecular weight of the compound having a radical trapping function 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.
From the viewpoint of efficiently permeating the polarizing film together with water at the time of producing the polarizing film, from the viewpoint of impregnating the polarizing film with a high concentration, and from the viewpoint of impregnating the polarizing film with a high concentration in a short time even when a polyvinyl alcohol-based film having a large thickness is used, the compound having a radical trapping function is preferably soluble in not less than 1 part by weight in 100 parts by weight of 25 ℃ water, more preferably soluble in not less than 2 parts by weight in 100 parts by weight of 25 ℃ water, and still more preferably soluble in not less than 5 parts by weight in 100 parts by weight of 25 ℃ water.
Examples of the compound having a nitroxyl radical or a nitroxyl group include the following compounds.
[ chemical formula 6]
Figure BDA0002993657060000071
(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]
Figure BDA0002993657060000081
[ chemical formula 8]
Figure BDA0002993657060000082
In the case where the polarizing film contains the compound having a radical trapping function, the content of the compound having a radical trapping function in the polarizing film is preferably 0.005% by weight or more, more preferably 0.01% by weight or more, and even more preferably 0.02% by weight or more, and is preferably 15% by weight or less, more preferably 12% by weight or less, and even more preferably 10% by weight or less, from the viewpoint of appearance, from the viewpoint of suppressing a decrease in the monomer transmittance due to coloring 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 the polyvinyl alcohol-based film to at least a dyeing step, a crosslinking step, and a stretching step, optionally followed by a swelling step and a washing 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.
In the case of producing a polarizing film containing the compound having a radical trapping function, the compound having a radical trapping function may be contained in one or more treatment baths selected from the swelling step, the washing step, the dyeing step, the crosslinking step, and the stretching step. The concentration of the compound having a radical trapping function contained in any of the treatment baths is affected by the number of treatments, the treatment time, the treatment temperature, and the like of each treatment, and therefore cannot be determined in a general manner, 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 compound having a radical trapping function in the polarizing film.
In particular, when the washing step is performed after the dyeing step, the crosslinking step, and the stretching step are performed, the content of the iodine or the compound having a radical trapping function can be easily adjusted to a desired range in the washing step, in consideration of the treatment conditions in the dyeing step, the crosslinking step, and the stretching step, and in view of allowing components such as iodine or the compound having a radical trapping function to be eluted from or adsorbed to the polyvinyl alcohol film.
In addition, additives such as zinc salt, pH adjuster, pH buffer, and other salts may be contained in each treatment bath 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.
The swelling step is a treatment step of immersing the polyvinyl alcohol-based film in a swelling bath, and can remove dirt, an anti-blocking agent, and the like on the surface of the polyvinyl alcohol-based film, and can suppress uneven dyeing by swelling the polyvinyl alcohol-based film. The swelling bath generally uses a medium containing water as a main component, such as water, distilled water, or pure water. The swelling bath may be added with a surfactant, an alcohol, or the like as appropriate according to a conventional method.
The temperature of the swelling bath is preferably about 10 to 60 ℃, more preferably about 15 to 45 ℃, and further preferably about 18 to 30 ℃. The immersion time in the swelling bath is not generally determined because the swelling degree of the polyvinyl alcohol-based film is affected by the temperature of the swelling bath, and is preferably about 5 to 300 seconds, more preferably about 10 to 200 seconds, and still more preferably about 20 to 100 seconds. The swelling step may be performed only 1 time, or may be performed a plurality of times as needed.
The dyeing step is a treatment step of immersing the polyvinyl alcohol-based film in a dyeing bath (iodine solution), and iodine can be adsorbed to the polyvinyl alcohol-based film to orient the film. The iodine solution is preferably an aqueous iodine solution, and more preferably contains iodine and an iodide as a dissolution aid. The iodide includes 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. Among these, potassium iodide is preferable from the viewpoint of controlling the potassium content in the polarizing film.
The concentration of iodine in the dyeing bath is preferably about 0.01 to 1 wt%, more preferably about 0.02 to 0.5 wt%. The concentration of the iodide in the dyeing bath is preferably about 0.01 to 20 wt%, more preferably about 0.05 to 10 wt%, and still more preferably about 0.1 to 5 wt%.
The temperature of the dyeing bath is preferably about 10 to 50 ℃, more preferably about 15 to 45 ℃, and further preferably about 18 to 30 ℃. The immersion time in the dyeing bath is not generally determined because the degree of dyeing of the polyvinyl alcohol-based film is affected by the temperature of the dyeing bath, and is preferably about 10 to 300 seconds, and more preferably about 20 to 240 seconds. The dyeing step may be performed only 1 time, or may be performed a plurality of times as needed.
The crosslinking step is a treatment step of immersing the polyvinyl alcohol film in a treatment bath (crosslinking bath) containing a boron compound, and the polyvinyl alcohol film can be crosslinked by the boron compound to adsorb iodine molecules or dye molecules to the crosslinked structure. Examples of the boron compound include: boric acid, borates, borax, and the like. The crosslinking bath is generally an aqueous solution, and may be, for example, a mixed solution of an organic solvent miscible with water and water. In addition, from the viewpoint of controlling the potassium content in the polarizing film, the crosslinking bath may contain potassium iodide.
The concentration of the boron compound in the crosslinking bath is preferably about 1 to 15 wt%, more preferably about 1.5 to 10 wt%, and still more preferably about 2 to 5 wt%. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and still more preferably about 2 to 5% by weight.
The temperature of the crosslinking bath is preferably about 20 to 70 ℃, and more preferably about 30 to 60 ℃. The immersion time in the crosslinking bath is not generally determined because the degree of crosslinking of the polyvinyl alcohol-based film is affected by the temperature of the crosslinking bath, and is preferably about 5 to 300 seconds, and more preferably about 10 to 200 seconds. The crosslinking step may be performed only 1 time, or may be performed a plurality of times as needed.
The stretching step is a treatment step of stretching the polyvinyl alcohol-based film in at least one direction at a predetermined magnification. In general, a polyvinyl alcohol-based film is uniaxially stretched in the transport direction (longitudinal direction). The method of stretching is not particularly limited, and any of wet stretching and dry stretching may be employed. The stretching step may be performed only 1 time, or may be performed a plurality of times as needed. The stretching step may be performed at any stage in the production of the polarizing film.
In the wet stretching method, a solvent such as water or a mixed solution of an organic solvent miscible with water and water is usually used as the treatment bath (stretching bath). From the viewpoint of controlling the content of the potassium in the polarizing film, the stretching bath may contain potassium iodide. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1 to 15 wt%, more preferably about 2 to 10 wt%, and still more preferably about 3 to 6 wt%. In addition, the boron compound may be contained in the treatment bath (stretching bath) from the viewpoint of suppressing film breakage during stretching, and in this case, the concentration of the boron compound in the stretching bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and further preferably about 2 to 5% by weight.
The temperature of the stretching bath is preferably about 25 to 80 ℃, more preferably about 40 to 75 ℃, and still more preferably about 50 to 70 ℃. The immersion time in the stretching bath is not generally determined because the degree of stretching of the polyvinyl alcohol-based film is affected by the temperature of the stretching bath, and is preferably about 10 to 800 seconds, and more preferably about 30 to 500 seconds. The stretching treatment in the wet stretching method may be performed together with any one or more treatment steps of the swelling step, the dyeing step, the crosslinking step, and the washing step.
Examples of the dry stretching method include: an inter-roll stretching method, a heated roll stretching method, a compression stretching method, and the like. The dry drawing method may be performed together with the drying step.
The total stretching ratio (cumulative stretching ratio) of the polyvinyl alcohol-based film may be set as appropriate according to the purpose, and is preferably about 2 to 7 times, more preferably about 3 to 6.8 times, and still more preferably about 3.5 to 6.5 times.
The cleaning step is a treatment step of immersing the polyvinyl alcohol-based film in a cleaning bath, and can remove foreign matter remaining on the surface of the polyvinyl alcohol-based film. The cleaning bath usually uses a medium containing water as a main component, such as water, distilled water, or pure water. In addition, from the viewpoint of controlling the potassium content in the polarizing film, potassium iodide may be contained in the cleaning bath, and in this case, the concentration of potassium iodide in the cleaning bath is preferably about 1 to 10% by weight, more preferably about 1.5 to 4% by weight, and further preferably about 1.8 to 3.8% by weight.
The temperature of the cleaning bath is preferably about 5 to 50 ℃, more preferably about 10 to 40 ℃, and further preferably about 15 to 35 ℃. The immersion time in the cleaning bath is not generally determined because the degree of cleaning of the polyvinyl alcohol-based film is affected by the temperature of the cleaning bath, and is preferably about 1 to 100 seconds, more preferably about 2 to 50 seconds, and still more preferably about 3 to 20 seconds. The swelling step may be performed only 1 time, or may be performed a plurality of times as needed.
The method for producing a polarizing film of the present invention may be provided with a drying step. The drying step is a step of drying the polyvinyl alcohol-based film cleaned in the cleaning step to obtain a polarizing film, and the polarizing film having a desired moisture content can be obtained by drying. The drying is carried out by any suitable method, and examples thereof include: natural drying, air-blowing drying, heating drying.
The drying temperature is preferably about 20 to 150 ℃, and more preferably about 25 to 100 ℃. The drying time is not generally determined because the degree of drying of the polarizing film is affected by the drying temperature, and is preferably about 10 to 600 seconds, and more preferably about 30 to 300 seconds. The drying step may be performed only 1 time, or may be performed a plurality of times as needed.
The thickness of the polarizing film is preferably 1 μm or more, more preferably 2 μm or more from the viewpoint of improving the initial polarization degree of the polarizing film, and is preferably 20 μm or less, more preferably 18 μm or less, and further preferably 15 μm or less from the viewpoint of preventing heat peeling. In particular, in order to obtain a polarizing film having a thickness of about 8 μm or less, a method for producing a thin polarizing film using a laminate comprising a thermoplastic resin substrate and a polyvinyl alcohol resin layer formed on the thermoplastic resin substrate as the polyvinyl alcohol film can be applied.
< method for producing thin polarizing film >
The method for manufacturing a thin polarizing film includes: forming a polyvinyl alcohol resin layer (PVA type resin layer) containing a polyvinyl alcohol resin (PVA type resin) on one side of a long thermoplastic resin base material to prepare a laminate; and sequentially performing auxiliary stretching treatment in a gas atmosphere, dyeing treatment, stretching treatment in an aqueous solution, and drying shrinkage treatment on the laminate. In particular, in order to obtain a polarizing film having high optical characteristics, a two-stage stretching method in which an auxiliary stretching treatment (dry stretching) in a gas atmosphere and a stretching treatment in an aqueous solution in an aqueous boric acid solution are combined is selected.
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 μm, and more preferably about 50 to 200 μm. The thickness of the PVA based resin layer is preferably about 3 to 40 μm, and more preferably about 3 to 20 μm.
The thermoplastic resin base absorbs water to significantly reduce the tensile stress, and the water absorption rate is preferably about 0.2% or more, more preferably about 0.3% or more, from the viewpoint of enabling stretching at a high rate. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably about 3% or less, more preferably about 1% or less, from the viewpoint of preventing a defect such as deterioration in appearance of the polarizing film obtained due to a significant decrease in dimensional stability of the thermoplastic resin substrate. The water absorption can be adjusted by, for example, introducing a modifying group into the constituent material of the thermoplastic resin substrate. The water absorption is a value determined in accordance with JIS K7209.
The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably about 120 ℃ or lower from the viewpoint of suppressing crystallization of the PVA-based resin layer and sufficiently ensuring stretchability of the laminate. In view of plasticization of the thermoplastic resin substrate with water and favorable stretching in an aqueous solution, the glass transition temperature (Tg) is preferably about 100 ℃ or lower, and more preferably about 90 ℃ or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably about 60 ℃ or higher from the viewpoint of preventing a defect such as deformation of the thermoplastic resin substrate when the coating liquid is applied and dried and producing a good laminate. The glass transition temperature can be adjusted by, for example, introducing a modifying group into the constituent material of the thermoplastic resin substrate and heating the resultant with a crystallizing material. The glass transition temperature (Tg) is a value determined in accordance with JIS K7121.
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. Among 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 a copolymer containing isophthalic acid and/or cyclohexanedicarboxylic acid as a dicarboxylic acid, and a copolymer containing cyclohexanedimethanol and diethylene glycol as a 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, and water is preferred. 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, it is preferable to add a halide to 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, etc., 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.). The drying temperature of the coating liquid is preferably about 50 ℃.
In the auxiliary stretching treatment in the gas atmosphere, the laminate may be stretched at a high stretch ratio so that the thermoplastic resin substrate can be stretched while crystallization thereof is suppressed. The stretching method for assisting the stretching treatment in the gas atmosphere may be fixed-end stretching (for example, a method of stretching using a tenter) or free-end stretching (for example, a method of uniaxially stretching a laminate by passing the laminate between rolls having different peripheral speeds), and from the viewpoint of obtaining high optical characteristics, free-end stretching is preferable.
The stretching ratio in the auxiliary stretching in the gas atmosphere is preferably about 2 to 3.5 times. The auxiliary stretching in the gas atmosphere 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 each stage.
The stretching temperature in the auxiliary stretching in the gas atmosphere may be set to any suitable value depending on the material for forming the thermoplastic resin substrate, the stretching method, and the like, and is preferably not lower than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably not lower than the glass transition temperature (Tg) +10 ℃, and still more preferably not lower than the glass transition temperature (Tg) +15 ℃. On the other hand, the upper limit of the stretching temperature is preferably about 170 ℃ from the viewpoint of suppressing rapid progress of crystallization of the PVA type resin and suppressing defects caused by crystallization (for example, inhibiting orientation of the PVA type resin layer by stretching).
If necessary, after the stretching treatment in the gas atmosphere and before the stretching treatment in the aqueous solution, an insolubilization treatment may be performed. The insolubilization is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing insolubilization treatment, water resistance can be imparted to the PVA-based resin layer, and the PVA can be prevented from being degraded in orientation when immersed in water. The concentration of the boric acid aqueous solution is preferably about 1 to 5 parts by weight relative to 100 parts by weight of water. The liquid temperature of the insolubilization treatment bath is preferably about 20 to 50 ℃.
The dyeing treatment is performed by dyeing the PVA-based resin layer with iodine. Examples of the adsorption method include: a method of immersing a PVA-based resin layer (laminate) in a dyeing solution containing iodine; a method of applying the dyeing liquid to a PVA-based resin layer; a method of spraying the dyeing solution on the PVA-based resin layer, and the like, a method of immersing the PVA-based resin layer (laminate) in the dyeing solution containing iodine is preferable.
The amount of iodine in the dyeing bath is preferably about 0.05 to 0.5 parts by weight based on 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add the iodide to an aqueous iodine solution. The amount of the iodide is preferably about 0.1 to 10 parts by weight, more preferably about 0.3 to 5 parts by weight, based on 100 parts by weight of water. In order to suppress the dissolution of the PVA based resin, the liquid temperature of the dyeing bath is preferably about 20 to 50 ℃. From the viewpoint of ensuring the transmittance of the PVA-based resin layer, the immersion time is preferably about 5 seconds to 5 minutes, and more preferably about 30 seconds to 90 seconds. From the viewpoint of obtaining a polarizing film having good optical characteristics, the ratio of the contents of iodine and iodide in the iodine aqueous solution is preferably about 1:5 to 1:20, and more preferably about 1:5 to 1: 10.
If necessary, the crosslinking treatment may be performed after the dyeing treatment and before the stretching treatment in an aqueous solution. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing the crosslinking treatment, water resistance can be imparted to the PVA-based resin layer, and the orientation of the PVA can be prevented from being lowered when the PVA is immersed in high-temperature water during subsequent stretching in an aqueous solution. The boric acid concentration of the aqueous boric acid solution is preferably about 1 to 5 parts by weight relative to 100 parts by weight of water. In addition, when the crosslinking treatment is performed, it is preferable to further add the iodide to a crosslinking bath in the crosslinking treatment. The iodine compound can suppress elution of iodine adsorbed on the PVA-based resin layer. The amount of the iodide is preferably about 1 to 5 parts by weight based on 100 parts by weight of water. The liquid temperature of the crosslinking bath (aqueous boric acid solution) is preferably about 20 to 50 ℃.
The stretching treatment in the aqueous solution is performed by immersing the laminate in a stretching bath. The stretching treatment in an aqueous solution allows stretching at a temperature lower than the glass transition temperature (typically, about 80 ℃) of the thermoplastic resin substrate or the PVA type resin layer, and allows stretching at a high magnification while suppressing crystallization of the PVA type resin layer. The stretching method in the aqueous solution stretching treatment may be fixed-end stretching (for example, a method of stretching using a tenter) or free-end stretching (for example, a method of uniaxially stretching a laminate by passing the laminate between rolls having different peripheral speeds), and from the viewpoint of obtaining high optical characteristics, free-end stretching is preferable.
The stretching treatment in an aqueous solution is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in an aqueous boric acid solution). By using an aqueous boric acid solution as a stretching bath, the PVA-based resin layer can be provided with rigidity capable of withstanding the tension applied during stretching and water resistance insoluble in water. The boric acid concentration of the aqueous boric acid solution is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, based on 100 parts by weight of water. In addition, an iodide may be added to the stretching bath (aqueous boric acid solution). The liquid temperature of the stretching bath is preferably about 40 to 85 ℃, and more preferably about 60 to 75 ℃. The immersion time of the laminate in the stretching bath is preferably about 15 seconds to 5 minutes.
The stretching ratio in the stretching in the aqueous solution is preferably about 1.5 times or more, and more preferably about 3 times or more.
The total stretch ratio of the laminate is preferably about 5 times or more, and more preferably about 5.5 times or more, with respect to the original length of the laminate.
The drying shrinkage treatment may be performed by heating the entire area to perform area heating, or may be performed by heating a transport roller (using a so-called heating roller), and both of them are preferably used. By drying with a hot roller, the laminate can be efficiently inhibited from curling by heating, and a polarizing film having excellent appearance can be produced. In addition, the shrinkage rate in the width direction of the laminate subjected to the drying and shrinking treatment is preferably about 1 to 10%, more preferably about 2 to 8%, from the viewpoint of improving the optical properties of the obtained polarizing film by shrinking the laminate in the width direction during the drying and shrinking treatment.
The drying conditions can be controlled by adjusting the heating temperature of the transport roller (temperature of the heating roller), the number of heating rollers, the contact time with the heating roller, and the like. The temperature of the heating roller is preferably about 60 to 120 ℃, more preferably about 65 to 100 ℃, and further preferably 70 to 80 ℃. The number of the conveying rollers is usually about 2 to 40, preferably about 4 to 30, from the viewpoint of increasing the crystallinity of the thermoplastic resin and suppressing the curling satisfactorily. The contact time (total contact time) between the laminate and the heating roller is preferably about 1 to 300 seconds, more preferably 1 to 20 seconds, and still more preferably 1 to 10 seconds.
The heating roller may be installed in a heating furnace, or may be installed in a general manufacturing line (room temperature environment), and is preferably installed in a heating furnace provided with an air blowing mechanism. By using drying with a heating roller and hot air drying in combination, a rapid temperature change between the heating rollers can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of hot air drying is preferably about 30-100 ℃. The hot air drying time is preferably about 1 to 300 seconds.
It is preferable to perform the washing treatment after the stretching treatment in the aqueous solution and before the drying shrinkage treatment. The cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.
In the case of producing a thin polarizing film containing the compound having a radical trapping function, the compound having a radical trapping function may be contained in a treatment bath of at least one of dyeing treatment, stretching treatment in an aqueous solution, insolubilization treatment, crosslinking treatment, and washing treatment. The concentration of the compound having a radical trapping function contained in any of the treatment baths is affected by the number of treatments, the treatment time, the treatment temperature, and the like of each treatment, and therefore cannot be determined in a general manner, 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 compound having a radical trapping function in the polarizing film.
In particular, when the washing treatment is performed, the contents of iodine and the compound having the radical trapping function can be easily adjusted to a desired range in view of allowing components such as iodine and the compound having the radical trapping function to be eluted from or adsorbed to the polyvinyl alcohol-based film in consideration of the treatment conditions in the dyeing treatment, the stretching treatment in an aqueous solution, and the like in the washing treatment.
< polarizing film >
The polarizing film of the present invention is obtained by laminating a transparent protective film on at least one surface of the polarizing film.
The transparent protective film is not particularly limited, and various transparent protective films used for polarizing films can be used. As materials constituting the transparent protective film, for example: a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, isotropy and the like. 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), polyacrylic 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.
When the transparent protective films are bonded to both surfaces of the polarizing film, the transparent protective films may be the same or different.
The transparent protective film may be a retardation plate having a front retardation of 40nm or more and/or a thickness direction retardation of 80nm or more. The front retardation is usually controlled to be in the range of 40 to 200nm, and the thickness direction retardation is usually controlled to be in the range of 80 to 300 nm. When a retardation plate is used as the transparent protective film, the retardation plate also functions as a transparent protective film, and therefore, the thickness can be reduced.
Examples of the phase difference plate include: birefringent films obtained by subjecting a polymer material to uniaxial or biaxial stretching treatment, alignment films of liquid crystal polymers, retardation plates obtained by supporting alignment layers of liquid crystal polymers with films, and the like. The thickness of the retardation plate is not particularly limited, and is usually about 20 to 150 μm. The retardation plate can be used by laminating the retardation plate on a transparent protective film having no retardation.
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.
A functional layer 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 transparent protective film which is 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 the protective film itself, or may be provided separately from the protective film.
The polarizing film and the transparent protective film, or the polarizing film and the functional layer are generally 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 adhesive layer, for example: a method in which the adhesive is applied to a separator or the like subjected to a peeling treatment, dried to form an adhesive layer, and then transferred to a polarizing film or the like; or a method in which the adhesive is applied to a polarizing film or the like and dried to form an adhesive layer. The thickness of the 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 wt% 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 can be usually used, and examples thereof include: alkylene diamines; isocyanates; epoxy resin; aldehydes; amino-formaldehydes such as methylol urea and methylol melamine. 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.
The adhesive may be an active energy ray-curable adhesive such as an ultraviolet-curable adhesive or an electron beam-curable adhesive, in addition to the above. 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 C1-20 chain alkyl (meth) acrylates, 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) acrylic adhesive may contain tripropylene glycol diacrylate, 1, 9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, cyclic trimethylolpropane formal acrylate, and ditrimethylolpropane formal acrylate
Figure BDA0002993657060000191
A polyfunctional monomer such as alkylene glycol diacrylate or EO-modified diglycerol tetraacrylate as a crosslinking component. Further, as the cationic polymerization curing adhesive, an adhesive having an epoxy group and oxygen may be usedA heterocyclic butyl compound. 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 transparent protective 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 applying 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 when an aqueous adhesive or the like is used, and is preferably about 0.1 to 100 μm, more preferably about 0.5 to 10 μm when an ultraviolet-curable adhesive, an electron beam-curable adhesive or the like is used.
The transparent protective film and the polarizing film, or the polarizing film and the functional layer may be laminated via a surface modification treatment layer, an adhesive layer, a barrier layer, a refractive index adjustment layer, or the like.
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: the material for forming the resin composition includes various resins having 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 in advance on a protective film, and the easy-adhesion layer side of the protective film may be laminated on the polarizing film with the 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 eluted from the transparent protective film from migrating (entering) into the polarizing film. The barrier layer may be any layer that has transparency and can prevent impurities from eluting from a transparent protective film or the like, and examples of materials for 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 transparent protective film and the polarizing film or other layers having different refractive indices. Examples of the refractive index adjusting material for forming the refractive index adjusting layer include: the composition contains various resins containing silica, acrylic acid-styrene, melamine 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.
< laminated polarizing film >
In the laminated polarizing film (optical laminate) of the present invention, the polarizing film is bonded to an optical layer. The optical layer is not particularly limited, and for example, optical layers that are used in the formation of liquid crystal displays and the like may be used, such as 1-layer or 2-layer or more reflective plates, semi-transmissive plates, retardation plates (including wave plates such as 1/2 and 1/4), and optical compensation films. The laminated polarizing film may be, in particular, a reflective polarizing film or a semi-transmissive polarizing film in which a reflective plate or a semi-transmissive reflective plate is further laminated on the polarizing film, an elliptical polarizing film or a circular polarizing film in which a phase difference plate is further laminated on the polarizing film, a wide-viewing-angle polarizing film in which a viewing angle compensation film is further laminated on the polarizing film, or a polarizing film in which a brightness enhancement film is further laminated on the polarizing film.
An adhesive layer for bonding an image display unit such as a liquid crystal cell or an organic EL element to another member such as a front transparent plate on the viewing side or a front transparent member such as a touch panel may be provided on one surface or both surfaces of the polarizing film or the laminated 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 excellent in optical transparency, exhibiting appropriate wettability, aggregability, adhesiveness, weather resistance, heat resistance and the like, such as a pressure-sensitive adhesive containing an acrylic polymer, can be preferably used.
The pressure-sensitive adhesive layer may be provided on one or both surfaces of the polarizing film or the laminated polarizing film in an appropriate manner. Examples of the adhesive layer include: a method of preparing an adhesive solution and directly applying the adhesive solution to the polarizing film or the laminated polarizing film by a suitable development method such as a casting method or a coating method; or a method of forming an adhesive layer on a separator and transferring the adhesive layer to the polarizing film or the laminated polarizing film. The thickness of the pressure-sensitive adhesive layer may be suitably determined depending on the purpose of use, adhesion 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 provided on at least one surface thereof is referred to as a pressure-sensitive adhesive layer-attached polarizing film or a pressure-sensitive adhesive layer-attached laminated 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.
< image display panel and image display device >
The image display panel of the present invention is formed by laminating the polarizing film or the laminated polarizing film to an image display unit. The image display device of the present invention includes a front transparent member on the polarizing film or laminated polarizing film side (viewing side) of the image display panel.
Examples of the image display means include: liquid crystal cells, organic EL cells, and the like. As the liquid crystal cell, any of a reflective liquid crystal cell using external light, a transmissive liquid crystal cell using light from a light source such as a backlight, and a transflective liquid crystal cell using both light from the outside and light from the light source can be used, for example. In the case where the liquid crystal cell uses light from a light source, the image display device (liquid crystal display device) is also provided with a polarizing film on the side opposite to the viewing side of the image display cell (liquid crystal cell) and a light source. The polarizing film on the light source side and the liquid crystal cell are preferably bonded together with an appropriate adhesive layer interposed therebetween. Examples of the driving method of the liquid crystal cell include: VA mode, IPS mode, TN mode, STN mode, bend (bend) orientation (pi-type), and the like.
As the organic EL unit, for example, an organic EL unit in which a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially stacked on a transparent substrate to form a light-emitting body (organic electroluminescent light-emitting body) can be suitably used. The organic light-emitting layer is a laminate of various organic thin films, and various layer structures including, for example: a laminate of a hole injection layer made of triphenylamine derivative or the like and a light-emitting layer made of a fluorescent organic solid such as anthracene, a laminate of these light-emitting layers and an electron injection layer made of perylene derivative or the like, a laminate of a hole injection layer, a light-emitting layer, and an electron injection layer, and the like.
Examples of the front transparent member disposed on the visible side of the image display unit include: a front surface transparent plate (window layer), a touch panel, and the like. As the front surface transparent plate, a transparent plate having appropriate mechanical strength and thickness can be used. As such a transparent plate, for example, a transparent resin plate such as an acrylic resin or a polycarbonate resin, a glass plate, or the like can be used. As the touch panel, for example, various touch panels of a resistive film type, a capacitive type, an optical type, an ultrasonic type, and the like, a glass plate having a touch sensor function, a transparent resin plate, and the like can be used. In the case of using a capacitive touch panel as the front surface transparent member, a front surface transparent plate made of glass or a transparent resin plate is preferably provided on the side closer to the visible side than the touch panel.
The polarizing film of the present invention has a good initial polarization degree 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, and therefore, the polarizing film of the present invention, and the polarizing film, laminated polarizing film, image display panel, and image display device using the polarizing film are suitable for use in an in-vehicle image display device such as a car navigation device and a rear view monitor.
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 >
< preparation of polarizing film >
A polyvinyl alcohol film having an average polymerization degree of 2400, a saponification degree of 99.9 mol% and a thickness of 30 μm was prepared. The polyvinyl alcohol film was immersed between rolls having different peripheral speed ratios for 30 seconds in a swelling bath (water bath) at 20 ℃ to swell the film and stretched 2.2 times in the transport direction (swelling step), and then immersed for 30 seconds in a dyeing bath (aqueous iodine solution prepared by blending iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at 30 ℃ so that the concentration of iodine in the finally obtained polarizing film was 3.8% by weight, and stretched 3.3 times in the transport direction while dyeing the original polyvinyl alcohol film (polyvinyl alcohol film which was not stretched at all in the transport direction) (dyeing step) while adjusting the concentration for 30 seconds. Next, the dyed polyvinyl alcohol film was immersed in a crosslinking bath (aqueous solution having a boric acid concentration of 3.5 wt%, a potassium iodide concentration of 3.0 wt%, and a zinc sulfate concentration of 3.6 wt%) at 40 ℃ for 28 seconds, and the original polyvinyl alcohol film was stretched 3.6 times in the transport direction (crosslinking step). Further, the obtained polyvinyl alcohol film was immersed in a stretching bath (an aqueous solution having a boric acid concentration of 4.5 wt%, a potassium iodide concentration of 5.0 wt%, and a zinc sulfate concentration of 5.0 wt%) at 64 ℃ for 60 seconds, stretched 6.0 times in the transport direction based on the original polyvinyl alcohol film (stretching step), and then immersed in a cleaning bath (an aqueous solution having a potassium iodide concentration of 2.3 wt%, and a compound concentration of 1.0 wt% represented by the following general formula (9) which is a compound having a radical trapping function) at 27 ℃ for 10 seconds (cleaning step). The washed polyvinyl alcohol film was dried at 40 ℃ for 30 seconds to prepare a polarizing film. The iodine concentration of the polarizing film was determined by the following measurement method. In addition, the peak temperature of the maximum intensity of water detected by the generated gas analysis method was 210 ℃ for the obtained polarizing film, the content of the compound represented by the following general formula (9) in the polarizing film was 0.3% by weight, and the thickness of the polarizing film was 12 μm.
[ chemical formula 9]
Figure BDA0002993657060000231
[ method for measuring iodine concentration (% 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 of Shigaku corporation, trade name: ZSX-PRIMUS IV, measurement diameter: 20 mm).
Iodine concentration (wt%): 14.474 × (fluorescent X-ray intensity)/(film thickness) (kcps/. mu.m)
The coefficient for calculating the concentration differs depending on the measurement device, but the coefficient can be obtained by using an appropriate calibration curve.
[ analysis of generated gas ]
The polarizing film was introduced into a heating furnace type pyrolyzer (PY-2020 iD, manufactured by Frontier Lab), and the generated gas was directly introduced into TOFMS (JMS-T100 GCV, manufactured by JEOL), thereby performing a generated gas analysis (EGA/TOFMS) method.
[ measurement conditions ]
Temperature rising conditions are as follows: 40 ℃ → 10 ℃/min → 350 DEG C
Interface: deactivated fused silica tube, 2.5m × 0.15mm id
Carrier gas: he (1.0mL/min)
Injection port temperature: 300 deg.C
Filling port: split ratio 20:1
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 a compound having a radical-capturing function in a polarizing film ]
About 20mg of the polarizing film was collected and quantified, and the polarizing film was dissolved in 1mL of water under heating, and then diluted with 4.5mL of methanol, and the obtained extract was filtered through a membrane filter, and the concentration of the compound having a radical trapping function was measured with respect to the filtrate by HPLC (ACQUITYUPLC H-class Bio, manufactured by Waters).
< production of polarizing film >
As the adhesive, an aqueous solution containing a polyvinyl alcohol resin having an acetoacetyl group (average polymerization degree of 1200, saponification degree of 98.5 mol%, acetoacetylation degree of 5 mol%) and methylolmelamine at a weight ratio of 3:1 was used. A transparent protective film (made of a Japanese catalyst and having a moisture permeability of 125 g/(m) was laminated on one surface (image display unit side) of the polarizing film obtained above using the adhesive and a roll laminator, and the transparent protective film was 30 μm thick and was formed from a (meth) acrylic resin (a modified acrylic polymer having a lactone ring structure)224h)), and a transparent protective film (having a moisture permeability of 380 g/(m) and having a thickness of 47 μm and formed with HC by bonding a cellulose triacetate film (fuji film, trade name "TJ 40 UL") to the other surface (visible side) thereof224 hours)), and then dried by heating in an oven (temperature 90 ℃ for 10 minutes), a polarizing film was produced in which transparent protective films were laminated on both sides of the polarizing film.
[ evaluation of degree of polarization ]
The degree of polarization of the polarizing film can be measured using a spectrophotometer (product name "V7100" by japanese spectral system). As a specific method for measuring the degree of polarization, the parallel transmittance (H0) and the orthogonal transmittance (H90) of a polarizing film can be measured according to the formula: the polarization degree (%) { (H0-H90)/(H0+ H90) }1/2 × 100 was determined. The parallel transmittance (H0) is a transmittance value of a parallel laminated polarizing film produced by laminating 2 identical polarizing films so that their absorption axes 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 their absorption axes are orthogonal to each other. These transmittances are Y values obtained by correcting visibility 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, a glass plate (analog image display unit) was bonded to the protective film surface of the polarizing film on the image display unit side via an acrylic pressure-sensitive adhesive layer having a thickness of 20 μm, and autoclave treatment was performed at 50 ℃ and 0.5MPa for 15 minutes to prepare a laminate. The obtained laminate was left to stand in a hot air oven at a temperature of 105 ℃ for 750 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" by japanese spectrophotometers) and evaluated based on the following criteria. The measurement wavelength is 380 to 700nm (5nm interval). The results are shown in Table 1.
ΔTs(%)=Ts700-Ts0
Wherein, Ts0Is the monomer transmittance of the laminate before heating, Ts700The monomer transmittance of the laminate after heating for 700 hours. The Δ Ts (%) is preferably 5. gtoreq.DELTA.Ts (%). gtoreq.0, and more preferably 3. gtoreq.DELTA.Ts (%). gtoreq.0.
[ evaluation of thermal peeling ]
The polarizing film was cut into dimensions of 680X 250mm so that the absorption axis was parallel to the long side. A glass plate (analog image display unit) was prepared on the protective film surface on the image display unit side of the polarizing film via an acrylic pressure-sensitive adhesive layer having a thickness of 20 μm. The appearance of the laminate sample obtained after standing still in a hot air oven at 105 ℃ for 750 hours was evaluated by visual observation according to the following criteria. The results are shown in Table 1.
O: there was slight peeling or foaming at the end, but there was no problem in practical use.
And (delta): peeling or foaming is observed at the end, but there is no problem in actual use as long as it is not a particular use (for example, a narrow frame display or the like in which the distance from the end of the polarizing plate to the Active Area (Active Area) where an image is displayed is short).
X: the peeling was noticeable at the end, and there was a problem in practical use.
< example 2 >
< preparation of polarizing film and polarizing film >
A polarizing film and a polarizing film were produced in the same manner as in example 1, except that the iodine concentration in the dyeing bath was adjusted so that the iodine concentration of the finally obtained polarizing film became 4.3 wt%. The peak temperature of the maximum intensity of water detected by the generated gas analysis method of the obtained polarizing film was 208 ℃, the content of the compound represented by the above general formula (9) in the polarizing film was 0.3% by weight, and the thickness of the polarizing film was 12 μm.
< example 3 >
< preparation of polarizing film and polarizing film >
A polarizing film and a polarizing film were produced in the same manner as in example 1, except that the iodine concentration of the dyeing bath was adjusted so that the iodine concentration of the finally obtained polarizing film was 3.5 wt% in the polyvinyl alcohol film having a thickness of 45 μm. The peak temperature of the maximum intensity of water detected by the generated gas analysis method of the obtained polarizing film was 210 ℃, the content of the compound represented by the above general formula (9) in the polarizing film was 0.2% by weight, and the thickness of the polarizing film was 18 μm.
< example 4 >
< preparation of polarizing film and polarizing film >
A polarizing film and a polarizing film were produced in the same manner as in example 1, except that the iodine concentration in the dyeing bath was adjusted so that the iodine concentration of the finally obtained polarizing film became 3.7 wt%, and a compound represented by the general formula (8) was added to the bath in the washing step at a concentration of 1.0 wt% instead of the general formula (9) as the compound having the radical trapping function. The peak temperature of the maximum intensity of water detected by the generated gas analysis method of the obtained polarizing film was 211 ℃, the content of the compound represented by the above general formula (8) in the polarizing film was 0.3% by weight, and the thickness of the polarizing film was 12 μm.
< comparative example 1 >
< preparation of polarizing film and polarizing film >
A polarizing film and a polarizing film were produced in the same manner as in example 2, except that the compound represented by the general formula (9) as the compound having a radical trapping function was not added to the cleaning bath in the production of the polarizing film. The peak temperature of the maximum intensity of water detected by the generated gas analysis method of the obtained polarizing film was 197 ℃, the content of the compound represented by the above general formula (9) in the polarizing film was 0% by weight, and the thickness of the polarizing film was 12 μm.
< comparative example 2 >
< preparation of polarizing film and polarizing film >
A polarizing film and a polarizing film were produced in the same manner as in example 1, except that the iodine concentration in the dyeing bath was adjusted so that the iodine concentration of the finally obtained polarizing film became 2.5 wt%, and the compound represented by the general formula (9) as the compound having the radical trapping function was not added to the cleaning bath. The peak temperature of the maximum intensity of water detected by the generated gas analysis method of the obtained polarizing film was 206 ℃, the content of the compound represented by the above general formula (9) in the polarizing film was 0% by weight, and the thickness of the polarizing film was 12 μm.
The polarizing films of the examples and comparative examples obtained above were used to perform the above-described [ evaluation of degree of polarization ], [ evaluation of monomer transmittance in high-temperature environment ], and [ evaluation of thermal peeling ]. The results are shown in Table 1.
[ Table 1]
Figure BDA0002993657060000271

Claims (10)

1. A polarizing film formed by adsorbing iodine to a polyvinyl alcohol film and orienting the film,
the iodine concentration is 3 to 10 wt%,
in the generated gas analysis, the peak temperature of the maximum intensity of water detected by the polarizing film in the presence of an inert gas under the conditions of a temperature rise rate of 10 ℃/min and a temperature rise range of 40 ℃ to 350 ℃ is 205 ℃ or higher.
2. The polarizing film according to claim 1, having a thickness of 20 μm or less.
3. The polarized film according to claim 1 or 2 comprising a compound having a radical trapping function.
4. The polarized film according to claim 3, wherein,
the compound with the free radical capturing function is a compound with a nitroxyl free radical or a nitroxyl group.
5. A polarizing film comprising the polarizing film according to any one of claims 1 to 4 and a transparent protective film bonded to at least one surface thereof.
6. The polarizing film according to claim 5, wherein the degree of polarization is 99.98% or more.
7. A laminated polarizing film, wherein,
the polarizing film of claim 5 or 6 is laminated to an optical layer.
8. An image display panel comprising an image display unit and the polarizing film according to claim 5 or 6 or the laminated polarizing film according to claim 7 bonded thereto.
9. An image display device comprising a front surface transparent member on the polarizing film or laminated polarizing film side of the image display panel according to claim 8.
10. The image display device according to claim 9, which is an in-vehicle image display device.
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