JP7219799B2 - Polarizing film, polarizing film, laminated polarizing film, image display panel, and image display device - Google Patents

Description

The present invention relates to a polarizing film, a polarizing film, a laminated polarizing film, an image display panel, and an image display device.

Conventionally, polarizing films used in various image display devices such as liquid crystal display devices and organic EL display devices have been dyed (using iodine, dichroic dyes, etc.) because they have both high transmittance and high degree of polarization. A polyvinyl alcohol-based film containing a dichroic material is used. The polarizing film is produced by subjecting a polyvinyl alcohol-based film to various treatments such as swelling, dyeing, cross-linking and stretching in a bath, followed by washing and drying. The polarizing film is usually used as a polarizing film (polarizing plate) in which a protective film such as triacetyl cellulose is adhered to one or both sides of the polarizing film with an adhesive.

The polarizing film is used as a laminated polarizing film (optical laminate) by laminating other optical layers as necessary, and the polarizing film or the laminated polarizing film (optical laminate) is a liquid crystal cell or an organic EL device. and a front transparent plate (window layer) or a front transparent member such as a touch panel on the viewing side through a pressure-sensitive adhesive layer or an adhesive layer, and the above various image display devices. used (Patent Document 1).

In recent years, such various image display devices have been used in mobile devices such as mobile phones and tablet terminals, as well as in-vehicle image display devices such as car navigation devices and back monitors. there is Along with this, the image display device is required to have higher durability in a harsher environment (for example, in a high temperature environment) than has been conventionally required, and it is necessary to ensure such durability. An image display device for this purpose has been proposed (Patent Document 2).

JP 2014-102353 A JP 2018-101117 A

When a polarizing film or a laminated polarizing film using an iodine-based polarizing film is exposed to a high-temperature environment, the polyvinyl alcohol constituting the polarizing film is converted into polyene by a dehydration reaction, resulting in coloring of the polarizing film. There is a problem that the single transmittance is lowered.

As a result of extensive studies, the present inventors have found that iodine contained in an iodine-based polarizing film promotes polyene formation in a high-temperature environment. Therefore, it is effective to reduce the concentration (content) of iodine in the polarizing film in order to suppress the deterioration of the single transmittance due to the coloring of the polarizing film in a high-temperature environment. On the other hand, by increasing the thickness of the polarizing film, it is possible to obtain a polarizing film having a good degree of polarization with a low iodine concentration. The polarizing film and the laminated polarizing film tended to be easily peeled off during heating.

In view of the circumstances as described above, an object of the present invention is to provide a polarizing film that has a good initial degree of polarization and is excellent in suppressing a decrease in single transmittance due to coloring of the polarizing film in a high-temperature environment. do.

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.

That is, the present invention provides a polarizing film formed by adsorbing and aligning iodine on a polyvinyl alcohol-based film, having an iodine concentration of 3% by weight or more and 10% by weight or less, and an inert film in the generated gas analysis method. The present invention relates to a polarizing film having a peak temperature of 205°C or higher at the maximum intensity of water detected under conditions of a temperature elevation rate of 10°C/min in the presence of a gas and a temperature elevation range of 40°C to 350°C.

The present invention also relates to a polarizing film in which a transparent protective film is attached to at least one surface of the polarizing film.

The present invention also relates to a laminated polarizing film in which the polarizing film is bonded to an optical layer.

The present invention also relates to an image display panel in which the polarizing film or the laminated polarizing film is attached to an image display cell.

The present invention also relates to an image display device comprising a front transparent member on the polarizing film or laminated polarizing film side of the image display panel.

Although the details of the working mechanism of the effects of the polarizing film of the present invention are partly unknown, it is presumed as follows. However, the present invention need not be construed as being limited to this action mechanism.

The polarizing film of the present invention is an iodine-based polarizing film formed by adsorbing and aligning iodine on a polyvinyl alcohol-based film, having an iodine concentration of 3% by weight or more and 10% by weight or less, and in the generated gas analysis method, In the presence of an inert gas, the temperature rise rate is 10°C/min, and the temperature rise range is from 40°C to 350°C. As described above, the iodine-based polarizing film undergoes polyene formation due to the dehydration reaction of polyvinyl alcohol in a high-temperature environment. By setting the peak temperature of the maximum intensity of water detected (observed) at 205° C. or higher, it is possible to suppress a decrease in single transmittance due to coloring of the polarizing film in a high-temperature environment. Furthermore, 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 the evolved gas analysis method is controlled to 205 ° C. or higher. Although it can be done, the initial degree of polarization is good.

On the other hand, the present inventors exposed a polarizing film formed by adsorbing and aligning iodine to an iodine-containing polyvinyl alcohol film in a high-temperature environment for a certain period of time, and observed the generation of radicals from the polarizing film. The timing of the coloring of the polarizing film due to polyene formation and the timing of the generation of radicals were very similar, suggesting a phenomenon in which radicals are generated as the polyene formation of the polarizing film progresses. Therefore, in the polarizing film, in order to set the temperature at which the dehydration reaction described above occurs to a high temperature side, that is, the peak temperature of the maximum intensity of water detected (observed) by the generated gas analysis method is 205 ° C. or higher, the polarized light It is preferable that the membrane contains a compound having a radical scavenging function.

1 is an example of a chart showing peaks of water detected in an evolved gas analysis method using an iodine-based polarizing film as a sample.

<Polarizing film>
The polarizing film of the present invention is an iodine-based polarizing film formed by adsorbing and aligning iodine on a polyvinyl alcohol-based film, having an iodine concentration of 3% by weight or more and 10% by weight or less, and in the generated gas analysis method, In the presence of an inert gas, the temperature rise rate is 10°C/min, and the temperature rise range is from 40°C to 350°C.

As the polyvinyl alcohol (PVA)-based film, a film having translucency in the visible light region and capable of dispersing and adsorbing iodine can be used without particular limitation. In addition, the PVA-based film, which is usually used as a raw material, preferably 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 for the polyvinyl alcohol-based film include polyvinyl alcohol and its derivatives. Derivatives of polyvinyl alcohol include, for example, polyvinyl formal and polyvinyl acetal; olefins such as ethylene and propylene; unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, and those modified with alkyl esters thereof, acrylamide and the like; is mentioned. The polyvinyl alcohol preferably has an average degree of polymerization of about 100 to 10,000, more preferably about 1,000 to 10,000, even more preferably about 1,500 to 4,500. . The polyvinyl alcohol preferably has a degree of saponification of about 80 to 100 mol %, more preferably about 95 mol % to 99.95 mol. The average degree of polymerization and the degree of saponification 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 polyols such as glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol, condensates thereof, and the like. The amount of the additive used is not particularly limited, but is preferably about 20% by weight or less in the polyvinyl alcohol film, for example.

From the viewpoint of improving the initial polarization degree of the polarizing film and controlling the peak temperature of the maximum intensity of water detected by the generated gas analysis method to 205 ° C. or higher, the iodine concentration (content) of the polarizing film is is 3% by weight or more and 10% by weight or less. The iodine concentration (content) of the polarizing film is preferably 3.5% by weight or more, more preferably 4% by weight or more, from the viewpoint of improving the initial degree of polarization of the polarizing film. From the viewpoint of controlling the maximum intensity peak temperature of water detected by the evolved gas analysis method to 205° C. or higher, the content is preferably 9% by weight or less, more preferably 7% by weight or less.

In the generated gas analysis method, the polarizing film has a temperature increase rate of 10 ° C./min in the presence of an inert gas, and the temperature increase range is from 40 ° C. to 350 ° C. The maximum intensity of water detected. shows a peak temperature of 205° C. or higher. In the 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 the generated gas analysis method is set to 205 ° C. or higher, so that it can be used in a high temperature environment. , it is possible to suppress the deterioration of the single transmittance due to the coloring of the polarizing film. On the other hand, when the peak temperature of the maximum strength of water is lower than 205°C or higher, the polarizing film before and after the heat durability test (105°C x 750 hours), which is an index of high-temperature durability required for high-end in-vehicle displays. It becomes difficult to control the amount of change in the single transmittance of 0% or more and 5% or less.

FIG. 1 is an example of a chart showing the peak temperature of water detected by the generated gas analysis method, and the maximum intensity peak temperature of the detected water is 205° C. or higher.

In addition, the above-mentioned generated gas analysis method is an analysis method in which a gas chromatograph and a mass spectrometer are directly connected by an inert metal capillary or the like, and the gas generated when the sample is heated is monitored in real time. Also called EGA/MS method, EGA/TOFMS method, etc.

The polarizing film preferably contains a compound having a radical scavenging function. It is presumed that the compound having the radical scavenging function can capture the radicals generated by heating the polyvinyl alcohol of the polarizing film, and set the temperature at which the dehydration reaction of polyenization occurs to a higher temperature. Examples of the compound having a radical scavenging function include radical scavenging compounds such as hindered phenol, hindered amine, phosphorus, sulfur, benzotriazole, benzophenone, hydroxylamine, salicylate, and triazine compounds. Functional compounds (eg, antioxidants, etc.) can be mentioned. The compound having a radical scavenging function is preferably, for example, a compound having a nitroxy radical or a nitroxide group, from the viewpoint that the temperature at which the dehydration reaction of polyenization occurs can be easily set to a high temperature side.

（一般式（１）中、Ｒ^１は、オキシラジカルを表し、Ｒ^２からＲ^５は、独立して、水素原子、または炭素原子数が１～１０のアルキル基を表し、ｎは０または１を表す。）なお、一般式（１）中の、点線部の左は任意の有機基を示す。 As the compound having a nitroxy radical or a nitroxide group, an N-oxyl compound (as a functional group, C--N(--C)--O ^.) from the viewpoint of having a relatively stable radical in the air at room temperature. ( ^O. represents an oxy radical)), and known compounds can be used. Examples of N-oxyl compounds include compounds having an organic group having the following structure.

(In general formula (1), R ¹ represents an oxy radical, R ² to R ⁵ independently represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, n is 0 or 1 represents an arbitrary organic group.

（一般式（２）中、Ｒ^１～Ｒ^５、およびｎは、上記と同様であり、Ｒ^６は水素原子、または炭素原子数が１～１０のアルキル基、アシル基、もしくはアリール基を表し、ｎは０または１を表す。）

（一般式（３）中、Ｒ^１からＲ^５、およびｎは、上記と同様であり、Ｒ^７およびＲ^８は、独立して、水素原子、または炭素原子数が１～１０のアルキル基、アシル基、もしくはアリール基を表す。）

（一般式（４）中、Ｒ^１からＲ^５、およびｎは、上記と同様であり、Ｒ^９からＲ^１１は、独立して、水素原子、または炭素原子数が１～１０のアルキル基、アシル基、アミノ基、アルコキシ基、ヒドロキシ基、もしくはアリール基を表す。）

（一般式（５）中、Ｒ^１からＲ^５、およびｎは、上記と同様であり、Ｒ^１２は、水素原子、または炭素原子数が１～１０のアルキル基、アミノ基、アルコキシ基、ヒドロキシ基、もしくはアリール基を表す。） Examples of the above organic group-containing compounds include compounds represented by the following general formulas (2) to (5).

(In general formula (2), R ¹ to R ⁵ and n are the same as above, and R ⁶ represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an acyl group, or an aryl group. , n represents 0 or 1.)

(in the general formula (3), R ¹ to R ⁵ and n are the same as defined above; R ⁷ and R ⁸ are independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms; represents an acyl group or an aryl group.)

(in general formula (4), R ¹ to R ⁵ and n are the same as above; R ⁹ to R ¹¹ are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms; represents an acyl group, an amino group, an alkoxy group, a hydroxy group, or an aryl group.)

(In the general formula (5), R ¹ to R ⁵ and n are the same as above, and R ¹² is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an amino group, an alkoxy group, a hydroxy group, or an aryl group.)

In the general formulas (1) to (5), R ² to R ⁵ are preferably alkyl groups having 1 to 6 carbon atoms from the viewpoint of availability, and An alkyl group is more preferred. In general formula (2), R ⁶ is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, more preferably a hydrogen atom, from the viewpoint of availability. In general formula (3), from the viewpoint of availability, R ⁷ and R ⁸ are each preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, preferably a hydrogen atom. is more preferable. In general formula (4), R ⁹ to R ¹¹ are preferably hydrogen atoms or alkyl groups having 1 to 10 carbon atoms from the viewpoint of availability. In general formula (5), R ¹² is preferably a hydroxy group, an amino group, or an alkoxy group from the viewpoint of availability. In general formulas (1) to (5), n is preferably 1 from the viewpoint of availability.

Further, as the N-oxyl compound, for example, N- Oxyl compounds are mentioned.

In addition, the compound having the radical scavenging function preferably has a molecular weight of 1000 or less, more preferably 500 or less, and 300 or less, from the viewpoint of efficiently scavenging the radicals generated in the polyene reaction. is more preferred.

The compound having the radical scavenging function has a viewpoint that it can efficiently soak into the polarizing film together with water during the production of the polarizing film, a viewpoint that it can impregnate the polarizing film at a high concentration, and a thick polyvinyl alcohol film is used. Since the impregnation can be carried out in a short time even in the case of a polarizing film, it is preferable that 1 part by weight or more can be dissolved in 100 parts by weight of water at 25°C, and 1 part by weight or more can be dissolved in 100 parts by weight of water at 25°C. More preferably, 2 parts by weight or more can be dissolved, and more preferably 5 parts by weight or more can be dissolved in 100 parts by weight of water at 25°C.

（一般式（６）中、Ｒは、水素原子、または炭素原子数が１～１０のアルキル基、アシル基、もしくはアリール基を表す。）

Examples of compounds having a nitroxy radical or nitroxide group include the following compounds.

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

When the polarizing film contains the compound having a radical scavenging function, the content of the compound having a radical scavenging function is adjusted from the viewpoint of suppressing a decrease in single transmittance due to coloring of the polarizing film in a high-temperature environment. In the film, it is preferably 0.005% by weight or more, more preferably 0.01% by weight or more, further preferably 0.02% by weight or more, and from the viewpoint of appearance, 15% by weight % or less, more preferably 12 wt % or less, and even more preferably 10 wt % or less.

<Method for manufacturing polarizing film>
In the method for producing the polarizing film, the polyvinyl alcohol film is obtained by subjecting the polyvinyl alcohol film to any swelling step, washing step, and at least dyeing step, cross-linking step, and stretching step. The content of the iodine contained in the polarizing film is the amount of the iodine contained in any one of the treatment baths in the swelling step, the dyeing step, the cross-linking step, the stretching step and the washing step and the iodide such as potassium iodide. It can be controlled by concentration, treatment temperature and treatment time with each of the above treatment baths.

Further, when manufacturing a polarizing film containing the compound having the radical scavenging function, the treatment bath in any one or more of the swelling step, the washing step, the dyeing step, the cross-linking step, and the stretching step includes: It is only necessary to contain the compound having the radical scavenging function. The concentration of the compound having a radical scavenging function contained in any one of the treatment baths cannot be determined indiscriminately because it is affected by the number of treatments, treatment time, treatment temperature, and the like. From the viewpoint of being able to efficiently control the content of the compound having a function, it is usually preferably 0.01% by weight or more, more preferably 0.05% by weight or more, and 0.1% by weight or more. is more preferably 30% by weight or less, more preferably 25% by weight or less, and even more preferably 20% by weight or less.

In particular, when the washing step is performed after the dyeing step, the cross-linking step, and the stretching step, the washing step should consider the treatment conditions in the dyeing step, the cross-linking step, the stretching step, etc., and the iodine and the radicals From the viewpoint that components such as compounds having a scavenging function can be eluted from the polyvinyl alcohol-based film or adsorbed to the polyvinyl alcohol-based film, the content of the iodine and the compound having a radical scavenging function is adjusted to a desired range. easy to do

Further, each treatment bath in the swelling step, the dyeing step, the cross-linking step, the stretching step and the washing step contains additives such as zinc salts, pH adjusters, pH buffers and other salts. may 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, weak inorganic 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; Salt etc. are mentioned.

The swelling step is a treatment step in which the polyvinyl alcohol film is immersed in a swelling bath, which can remove stains, blocking agents, etc. on the surface of the polyvinyl alcohol film, and can be dyed by swelling the polyvinyl alcohol film. Unevenness can be suppressed. As the swelling bath, a medium containing water as a main component, such as water, distilled water, or pure water, is usually used. Surfactants, alcohols and the like may be appropriately added to the swelling bath according to conventional methods.

The temperature of the swelling bath is preferably about 10 to 60°C, more preferably about 15 to 45°C, even more preferably about 18 to 30°C. In addition, the immersion time in the swelling bath cannot be unconditionally determined because the degree of swelling of the polyvinyl alcohol film is affected by the temperature of the swelling bath, but it is preferably about 5 to 300 seconds, more preferably 10 to 200 seconds. About 20 to 100 seconds is more preferable. The swelling step may be performed only once, or may be performed multiple times as necessary.

The dyeing step is a treatment step in which the polyvinyl alcohol film is immersed in a dyeing bath (iodine solution), and iodine can be adsorbed and oriented on the polyvinyl alcohol film. The iodine solution is usually preferably an aqueous iodine solution containing iodine and iodide as a dissolution aid. Examples of the iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and iodide. Titanium etc. are mentioned. Among these, potassium iodide is preferable from the viewpoint of controlling the content of potassium in the polarizing film.

The concentration of iodine in the dyeing bath is preferably about 0.01 to 1% by weight, more preferably about 0.02 to 0.5% by weight. The concentration of the iodide in the dye bath is preferably about 0.01 to 20% by weight, more preferably about 0.05 to 10% by weight, and about 0.1 to 5% by weight. It is even more preferable to have

The temperature of the dyeing bath is preferably about 10 to 50°C, more preferably about 15 to 45°C, even more preferably about 18 to 30°C. In addition, the immersion time in the dyeing bath cannot be determined unconditionally because the degree of dyeing of the polyvinyl alcohol film is affected by the temperature of the dyeing bath, but it is preferably about 10 to 300 seconds, and 20 to 240 seconds. It is more preferable to be a degree. The dyeing step may be performed only once, or may be performed multiple times as necessary.

The crosslinking step is a treatment step of immersing the polyvinyl alcohol-based film in a treatment bath (crosslinking bath) containing a boron compound, and the polyvinyl alcohol-based film is crosslinked by the boron compound, and the iodine molecules or dye molecules are crosslinked It can be adsorbed on the structure. Examples of the boron compound include boric acid, borates, and borax. The cross-linking bath is generally an aqueous solution, but may be, for example, a mixed solution of an organic solvent miscible with water and water. Moreover, the cross-linking bath may contain potassium iodide from the viewpoint of controlling the content of potassium in the polarizing film.

The concentration of the boron compound in the crosslinking bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, more preferably about 2 to 5% by weight. preferable. Further, when potassium iodide is used in the cross-linking bath, the concentration of potassium iodide in the cross-linking bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight. More preferably, it is about 2 to 5% by weight.

The temperature of the cross-linking bath is preferably about 20 to 70°C, more preferably about 30 to 60°C. The immersion time in the cross-linking bath cannot be unconditionally determined because the degree of cross-linking of the polyvinyl alcohol film is affected by the temperature of the cross-linking bath, but it is preferably about 5 to 300 seconds, more preferably 10 to 200 seconds. It is more preferable to be a degree. The cross-linking step may be performed only once, or may be performed multiple times as necessary.

The stretching step is a processing step of stretching the polyvinyl alcohol-based film in at least one direction at a predetermined magnification. Generally, a polyvinyl alcohol film is uniaxially stretched in the transport direction (longitudinal direction). The stretching method is not particularly limited, and either a wet stretching method or a dry stretching method can be employed. The stretching step may be performed only once, or may be performed multiple times as necessary. The stretching step may be performed at any stage in the production of the polarizing film.

The treatment bath (stretching bath) in the wet stretching method can usually use a solvent such as water or a mixed solution of an organic solvent miscible with water and water. The stretching bath may contain potassium iodide from the viewpoint of controlling the content of potassium in the polarizing film. When potassium iodide is used in the drawing bath, the concentration of potassium iodide in the drawing bath is preferably about 1 to 15% by weight, more preferably about 2 to 10% by weight. More preferably, it is about 6% by weight. The treatment bath (stretching bath) may contain the boron compound from the viewpoint of suppressing film breakage during stretching. In this case, the concentration of the boron compound in the stretching bath is 1 to 15. It is preferably about weight %, more preferably about 1.5 to 10 weight %, and more preferably about 2 to 5 weight %.

The temperature of the drawing bath is preferably about 25 to 80°C, more preferably about 40 to 75°C, even more preferably about 50 to 70°C. In addition, the immersion time in the stretching bath cannot be unconditionally determined because the degree of stretching of the polyvinyl alcohol film is affected by the temperature of the stretching bath, but it is preferably about 10 to 800 seconds, more preferably 30 to 500 seconds. It is more preferable to be a degree. The stretching treatment in the wet stretching method may be performed together with any one or more of the swelling step, the dyeing step, the cross-linking step, and the washing step.

Examples of the dry drawing method include a roll-to-roll drawing method, a heated roll drawing method, a compression drawing method, and the like. The dry stretching method may be applied together with the drying step.

The total draw ratio (cumulative draw ratio) applied to the polyvinyl alcohol film can be appropriately set according to the purpose, but it is preferably about 2 to 7 times, and about 3 to 6.8 times. More preferably, it is even more preferably about 3.5 to 6.5 times.

The washing step is a treatment step in which the polyvinyl alcohol film is immersed in a washing bath, and foreign matter remaining on the surface of the polyvinyl alcohol film can be removed. As the cleaning bath, a medium containing water as a main component, such as water, distilled water, or pure water, is usually used. Further, from the viewpoint of controlling the content of potassium in the polarizing film, the cleaning bath may contain potassium iodide. In this case, the concentration of potassium iodide in the cleaning bath is 1 to 10% by weight. %, more preferably about 1.5 to 4% by weight, even more preferably about 1.8 to 3.8% by weight.

The temperature of the washing bath is preferably about 5 to 50°C, more preferably about 10 to 40°C, even more preferably about 15 to 35°C. The immersion time in the cleaning bath cannot be unconditionally determined because the degree of cleaning of the polyvinyl alcohol film is affected by the temperature of the cleaning bath, but it is preferably about 1 to 100 seconds, more preferably 2 to 50 seconds. About 3 to 20 seconds is more preferable. The swelling step may be performed only once, or may be performed multiple times as necessary.

The method for producing a polarizing film of the present invention may include a drying step. The drying step is a step of drying the polyvinyl alcohol-based film washed in the washing step to obtain a polarizing film, and the drying provides a polarizing film having a desired moisture content. The drying is performed by any appropriate method, and examples thereof include natural drying, air drying, and heat drying.

The drying temperature is preferably about 20 to 150°C, more preferably about 25 to 100°C. In addition, the drying time cannot be generally determined because the degree of drying of the polarizing film is affected by the drying temperature, but it is preferably about 10 to 600 seconds, more preferably about 30 to 300 seconds. preferable. The drying step may be performed only once, or may be performed multiple times as necessary.

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 degree of polarization of the polarizing film, and 20 μm or less from the viewpoint of preventing thermal peeling. It is preferably 18 μm or less, more preferably 15 μm or less. In particular, in order to obtain a polarizing film having a thickness of about 8 μm or less, a laminate containing a polyvinyl alcohol-based resin layer formed on a thermoplastic resin substrate is used as the polyvinyl alcohol-based film, and the following thin film is used. A method for manufacturing a polarizing film can be applied.

<Method for producing a thin polarizing film>
A method for producing a thin polarizing film includes forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin base material to produce a laminate. and subjecting the laminate to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order. In particular, in order to obtain a polarizing film having high optical properties, a two-step drawing method is selected in which an auxiliary drawing treatment in air (dry drawing) and a drawing treatment in water in an aqueous boric acid solution are combined.

As a method for producing the laminate, any appropriate method can be adopted. For example, a method of applying a coating liquid containing the PVA-based resin to the surface of the thermoplastic resin substrate and drying the coating liquid can be used. be done. The thickness of the thermoplastic resin substrate is preferably about 20-300 μm, more preferably about 50-200 μm. The thickness of the PVA-based resin layer is preferably about 3 to 40 μm, more preferably about 3 to 20 μm.

The thermoplastic resin base material preferably has a water absorption rate of about 0.2% or more, preferably about 0.3%, from the viewpoint that the thermoplastic resin base material absorbs water to significantly reduce the drawing stress and can be drawn at a high magnification. % or more is more preferable. On the other hand, the thermoplastic resin substrate has a water absorption rate of 3 from the viewpoint of preventing problems such as deterioration of the appearance of the obtained polarizing film due to a significant reduction in the dimensional stability of the thermoplastic resin substrate. % or less, and more preferably about 1% or less. The water absorption rate can be adjusted, for example, by introducing a modifying group into the constituent material of the thermoplastic resin base material. The water absorption rate is a value obtained according to JIS K7209.

The thermoplastic resin substrate has a glass transition temperature (Tg) of about 120° C. or less from the viewpoint of being able to sufficiently ensure the stretchability of the laminate while suppressing crystallization of the PVA-based resin layer. is preferred. Furthermore, considering the plasticization of the thermoplastic resin substrate with water and the excellent stretching in water, the glass transition temperature (Tg) is more preferably about 100° C. or less, and about 90° C. or less. is more preferred. On the other hand, the glass transition temperature of the thermoplastic resin substrate prevents problems such as deformation of the thermoplastic resin substrate when the coating liquid is applied and dried, and a good laminate can be produced. Therefore, it is preferably about 60° C. or higher. The glass transition temperature can be adjusted, for example, by introducing a modifying group into the constituent material of the thermoplastic resin substrate, or by heating using a crystallizing material. The glass transition temperature (Tg) is a value determined according to JIS K7121.

Any appropriate thermoplastic resin may be employed as a constituent material of the thermoplastic resin base material. Examples of the thermoplastic resin include ester-based resins such as polyethylene terephthalate-based resins, cycloolefin-based resins such as norbornene-based resins, olefin-based resins such as polypropylene, polyamide-based resins, polycarbonate-based resins, and copolymer resins thereof. etc. Among these, norbornene-based resins and amorphous (amorphous) polyethylene terephthalate-based resins are preferable, and furthermore, the thermoplastic resin base material has extremely excellent stretchability, and from the viewpoint that crystallization during stretching can be suppressed. , an amorphous (amorphous) polyethylene terephthalate resin is preferably used. Amorphous (amorphous) polyethylene terephthalate resins include copolymers containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers containing cyclohexanedimethanol and diethylene glycol as glycols.

The thermoplastic resin substrate may be subjected to surface treatment (for example, corona treatment) before forming the PVA-based resin layer, 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. Moreover, the thermoplastic resin substrate may be stretched before forming the PVA-based resin layer.

The coating liquid is a solution obtained by dissolving a PVA-based resin in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. preferable. These can be used alone or in combination of two or more. The PVA-based resin concentration of the coating liquid is preferably about 3 to 20 parts by weight with respect to 100 parts by weight of the solvent, from the viewpoint of being able to form a uniform coating film in close contact with the thermoplastic resin substrate. .

From the viewpoint of improving the orientation of polyvinyl alcohol molecules by stretching, the coating liquid preferably contains a halide. Any suitable halide can be employed as the halide, and examples thereof include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide, lithium iodide, etc. Potassium iodide is 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, with respect to 100 parts by weight of the PVA-based resin.

In addition, additives may be added to the coating liquid. Examples of the additives include plasticizers such as ethylene glycol and glycerin; surfactants such as nonionic surfactants.

Any appropriate method can be adopted as the method for applying the coating liquid, and examples thereof include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, and spray coating. , a knife coating method (such as a comma coating method), and the like. Moreover, it is preferable that the drying temperature of the coating liquid is about 50° C. or more.

Since the auxiliary in-air stretching treatment enables stretching while suppressing crystallization of the thermoplastic resin substrate, the laminate can be stretched at a high magnification. The stretching method of the in-air auxiliary stretching treatment may be fixed-end stretching (e.g., a method of stretching using a tenter stretching machine), or free-end stretching (e.g., a method of uniaxially stretching a laminate through rolls having different peripheral speeds). ) may be used, but from the viewpoint of obtaining high optical properties, free-end stretching is preferable.

The draw ratio in the auxiliary in-air drawing is preferably about 2 to 3.5 times. The in-air auxiliary stretching may be performed in one stage or in multiple stages. When it is carried out in multiple stages, the draw ratio is the product of the draw ratios in each step.

The stretching temperature in the in-air auxiliary stretching can be set to any appropriate value depending on the material forming the thermoplastic resin substrate, the stretching method, etc. For example, the glass transition temperature (Tg ) or higher, more preferably the glass transition temperature (Tg) + 10°C or higher, and even more preferably the glass transition temperature (Tg) + 15°C or higher. On the other hand, the upper limit of the stretching temperature is set from the viewpoint that it is possible to suppress rapid crystallization of the PVA-based resin and suppress problems caused by crystallization (for example, hindrance of orientation of the PVA-based resin layer due to stretching). , about 170°C.

If necessary, an insolubilizing treatment may be performed after the above-mentioned auxiliary stretching treatment in air and before dyeing treatment or stretching treatment in water. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The insolubilization treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA when immersed in water. The concentration of the boric acid aqueous solution is preferably about 1 to 5 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilizing treatment bath is preferably about 20 to 50°C.

The dyeing treatment is performed by dyeing the PVA-based resin layer with iodine. Examples of the adsorption method include a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of coating the PVA-based resin layer with the dyeing solution, and a method of applying the dyeing solution to the PVA-based resin layer. Examples include a method of spraying, and a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine is preferred.

The content of iodine in the dyeing bath is preferably about 0.05 to 0.5 parts by weight per 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add the iodide to the aqueous iodine solution. The amount of the iodide compounded is preferably about 0.1 to 10 parts by weight, more preferably about 0.3 to 5 parts by weight, per 100 parts by weight of water. The liquid temperature of the dyeing bath is preferably about 20 to 50° C. in order to suppress dissolution of the PVA-based resin. The immersion time is preferably about 5 seconds to 5 minutes, more preferably about 30 seconds to 90 seconds, from the viewpoint of ensuring the transmittance of the PVA-based resin layer. From the viewpoint of obtaining a polarizing film having good optical properties, the content ratio of iodine and iodide in the aqueous iodine solution is preferably about 1:5 to 1:20, more preferably about 1:5 to 1:10. It is more preferable to have

If necessary, a cross-linking treatment may be performed after the dyeing treatment and before the underwater stretching treatment. The cross-linking treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. The cross-linking treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA when immersed in high-temperature water in the subsequent underwater stretching. The concentration of boric acid in the boric acid aqueous solution is preferably about 1 to 5 parts by weight with respect to 100 parts by weight of water. In the case of carrying out a cross-linking treatment, it is preferable to further add the iodide to the cross-linking bath in the cross-linking treatment. By blending the iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The amount of the iodide compounded is preferably about 1 to 5 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the cross-linking bath (boric acid aqueous solution) is preferably about 20 to 50°C.

The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin substrate and the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80° C.), and the PVA-based resin layer can be prevented from crystallizing. It can be stretched to a high magnification while suppressing the stretching. The stretching method of the underwater stretching treatment may be fixed-end stretching (e.g., a method of stretching using a tenter stretching machine) or free-end stretching (e.g., a method of uniaxially stretching a laminate through rolls having different peripheral speeds). However, from the viewpoint of obtaining high optical properties, free end stretching is preferable.

The stretching treatment in water is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be imparted with rigidity to withstand tension applied during stretching and water resistance that does not dissolve in water. The concentration of boric acid in the boric acid aqueous solution is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, per 100 parts by weight of water. In addition, an iodide may be added to the stretching bath (boric acid aqueous solution). The liquid temperature of the drawing bath is preferably about 40 to 85°C, more preferably about 60 to 75°C. The immersion time of the laminate in the stretching bath is preferably about 15 seconds to 5 minutes.

The draw ratio in the underwater drawing is preferably about 1.5 times or more, more preferably about 3 times or more.

The total draw ratio of the laminate is preferably about 5 times or more, more preferably about 5.5 times or more, relative to the original length of the laminate.

The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or by heating the transport roll (using a so-called heating roll). Preferably both are used. By drying with a heating roll, heat curling of the laminate can be efficiently suppressed, a polarizing film with an excellent appearance can be produced, and the laminate can be dried while being kept flat. Therefore, not only curling but also wrinkles can be suppressed. In addition, from the viewpoint that the optical properties of the obtained polarizing film can be improved by shrinking in the width direction during the drying shrinkage treatment, the shrinkage ratio in the width direction of the laminate due to the drying shrinkage treatment is 1 to 10%. It is preferably about 2 to 8%, more preferably about 2 to 8%.

The drying conditions can be controlled by adjusting the heating temperature of the transport rolls (the temperature of the heating rolls), the number of heating rolls, the contact time with the heating rolls, and the like. The temperature of the heating roll is preferably about 60 to 120.degree. C., more preferably about 65 to 100.degree. C., even more preferably 70 to 80.degree. From the viewpoint of being able to favorably increase the crystallinity of the thermoplastic resin and satisfactorily suppress curling, the number of conveying rolls is usually about 2 to 40, preferably about 4 to 30. The contact time (total contact time) between the laminate and the heating roll is preferably about 1 to 300 seconds, more preferably 1 to 20 seconds, even more preferably 1 to 10 seconds.

The heating roll may be provided in a heating furnace, or may be provided in a normal production line (under room temperature environment). Preferably, it is provided in a heating furnace equipped with air blowing means. By using both heating roll drying and hot air drying, abrupt temperature changes between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The hot air drying temperature is preferably about 30 to 100°C. Also, the hot air drying time is preferably about 1 to 300 seconds.

It is preferable to perform a washing treatment after the underwater stretching treatment and before the drying shrinkage treatment. The cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide.

Further, when manufacturing a thin polarizing film containing the compound having the radical scavenging function, the treatment bath for any one or more of the dyeing treatment, the underwater stretching treatment, the insolubilization treatment, the cross-linking treatment, and the washing treatment contains the radical A compound having a trapping function may be contained. The concentration of the compound having a radical scavenging function contained in any one of the treatment baths cannot be determined indiscriminately because it is affected by the number of treatments, treatment time, treatment temperature, and the like. From the viewpoint of being able to efficiently control the content of the compound having a function, it is usually preferably 0.01% by weight or more, more preferably 0.05% by weight or more, and 0.1% by weight or more. is more preferably 30% by weight or less, more preferably 25% by weight or less, and even more preferably 20% by weight or less.

In particular, when washing treatment is performed, the treatment conditions for dyeing treatment, underwater stretching treatment, etc. are taken into consideration, and components such as iodine and the above-mentioned radical-scavenging compound are eluted from the polyvinyl alcohol film, or polyvinyl alcohol film is removed. From the viewpoint of being able to be adsorbed on an alcohol-based film, it is easy to adjust the content of the iodine and the compound having a radical scavenging function within a desired range.

<Polarizing film>
The polarizing film of the present invention is obtained by bonding a transparent protective film to 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 a material constituting the transparent protective film, for example, a thermoplastic resin that is excellent in transparency, mechanical strength, thermal stability, water barrier property, isotropy, etc. is used. Examples of the thermoplastic resin include cellulose ester-based resins such as triacetyl cellulose, polyester-based resins such as polyethylene terephthalate and polyethylene naphthalate, polyethersulfone-based resins, polysulfone-based resins, polycarbonate-based resins, nylon and aromatic resins. Polyamide resins such as group polyamides, polyimide resins, polyolefin resins such as polyethylene, polypropylene, ethylene/propylene copolymers, (meth)acrylic resins, cyclic polyolefin resins having a cyclo or norbornene structure (norbornene resins ), polyarylate-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, and mixtures thereof. The transparent protective film may be a cured layer formed from thermosetting resins such as (meth)acrylic, urethane, acrylic urethane, epoxy, and silicone or ultraviolet curable resins. Among these, cellulose ester-based resins, polycarbonate-based resins, (meth)acrylic-based resins, cyclic polyolefin-based resins, and polyester-based resins are suitable.

The thickness of the transparent protective film can be determined as appropriate, but in general, it is preferably about 1 to 500 μm, more preferably about 1 to 300 μm, from the viewpoint of strength, workability such as handleability, and thinness. is more preferable, and about 5 to 100 μm is even more preferable.

When the transparent protective films are laminated on both sides of the polarizing film, the transparent protective films on both sides may be the same or different.

For the transparent protective film, a retardation plate having a front retardation of 40 nm or more and/or a thickness direction retardation of 80 nm or more can be used. The front retardation is usually controlled in the range of 40-200 nm, and the thickness direction retardation is usually controlled in the range of 80-300 nm. When a retardation plate is used as the transparent protective film, the retardation plate also functions as a transparent protective film, so that thickness reduction can be achieved.

Examples of the retardation plate include a birefringent film obtained by uniaxially or biaxially stretching a polymer material, an oriented film of a liquid crystal polymer, and a film in which an oriented layer of a liquid crystal polymer is supported. Although the thickness of the retardation plate is not particularly limited, it is generally about 20 to 150 μm. The retardation plate may be attached to a transparent protective film having no retardation.

The transparent protective film contains any appropriate additives such as ultraviolet absorbers, antioxidants, lubricants, plasticizers, mold release agents, anti-coloring agents, flame retardants, antistatic agents, pigments, colorants, and the like. You can In particular, when the transparent protective film contains an ultraviolet absorber, the light resistance of the polarizing film can be improved.

Functional layers such as a hard coat layer, an antireflection layer, an antisticking layer, a diffusion layer, and an antiglare layer can be provided on the surface of the transparent protective film on which the polarizing film is not attached. The functional layers such as the hard coat layer, antireflection layer, anti-sticking layer, diffusion layer, and antiglare layer can be provided on the protective film itself, or can be provided separately from the protective film. can.

The polarizing film and the transparent protective film, or the polarizing film and the functional layer are usually laminated via a pressure-sensitive adhesive layer or an adhesive layer.

As the adhesive that forms the adhesive layer, various adhesives used in polarizing films can be applied. Alkyl ether-based adhesives, polyvinyl alcohol-based adhesives, polyvinyl porolidone-based adhesives, polyacrylamide-based adhesives, cellulose-based adhesives, and the like can be mentioned. Among these, acrylic pressure-sensitive adhesives are preferred.

As a method for forming an adhesive layer, for example, the adhesive is applied to a separator that has been subjected to a release treatment, dried to form an adhesive layer, and then transferred to a polarizing film or the like, or the adhesive is polarized. A method of applying to a film or the like and drying to form an adhesive layer can be exemplified. 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 that forms the adhesive layer, various adhesives used in polarizing films can be applied. Examples include isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latex adhesives, water-based polyester and the like. These adhesives are usually used as adhesives consisting of an aqueous solution (water-based adhesives) and contain 0.5 to 60% by weight of solids.

The water-based adhesive may contain a cross-linking agent. As the cross-linking agent, a compound having at least two functional groups in one molecule that are reactive with components such as polymers constituting the adhesive is usually used. Examples include alkylenediamines; isocyanates; epoxies; Aldehydes: amino-formaldehydes such as methylol urea and methylol melamine. The amount of the cross-linking agent compounded in the adhesive is usually about 10 to 60 parts by weight per 100 parts by weight of components such as polymers constituting the adhesive.

Examples of the adhesive include, in addition to the above, active energy ray-curable adhesives such as ultraviolet-curable adhesives and electron beam-curable adhesives. 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 and a compound having a vinyl group. Examples of compounds having a (meth)acryloyl group include alkyl (meth)acrylates having 1 to 20 carbon atoms, chain alkyl (meth)acrylates, alicyclic alkyl (meth)acrylates, and polycyclic alkyl (meth)acrylates. ) acrylates; hydroxyl group-containing (meth)acrylates; and epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate. (Meth)acrylate adhesives include hydroxyethyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, (meth)acrylamide, (meth) Nitrogen-containing monomers such as acryloylmorpholine may also be included. (Meth)acrylate-based adhesives contain tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecanedimethanol diacrylate, cyclic trimethylolpropane formal acrylate, dioxane glycol diacrylate, and EO as crosslinking components. Polyfunctional monomers such as modified diglycerin tetraacrylate may be included. A compound having an epoxy group or an oxetanyl group can also be used as a cationic polymerization-curable adhesive. The compound having an epoxy group is not particularly limited as long as it has at least two epoxy groups in the molecule, and various commonly known curable epoxy compounds can be used.

The adhesive may contain appropriate additives as necessary. Examples of the additives include silane coupling agents, coupling agents such as titanium coupling agents, adhesion promoters such as ethylene oxide, ultraviolet absorbers, deterioration inhibitors, dyes, processing aids, ion trapping agents, and antioxidants. agents, tackifiers, fillers, plasticizers, leveling agents, foaming inhibitors, antistatic agents, heat stabilizers, hydrolysis stabilizers, and the like.

The adhesive may be applied to either the transparent protective film side (or the functional layer side), the polarizing film side, or both. After lamination, a drying process is performed to form an adhesive layer consisting of a coated dry layer. After the drying step, ultraviolet rays or electron beams can be applied, if necessary. The thickness of the adhesive layer is not particularly limited, and when a water-based adhesive or the like is used, it is preferably about 30 to 5000 nm, more preferably about 100 to 1000 nm. When using an electron beam curing adhesive or the like, the thickness is preferably about 0.1 to 100 μm, more preferably about 0.5 to 10 μm.

The transparent protective film and the polarizing film, or the polarizing film and the functional layer may be laminated via an intervening layer such as a surface modification treatment layer, an easy-adhesive layer, a blocking layer, or a refractive index adjusting layer. .

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

Examples of the easy-adhesive agent that forms the easy-adhesion layer include forming materials containing various resins having a polyester skeleton, a polyether skeleton, a polycarbonate skeleton, a polyurethane skeleton, a silicone system, a polyamide skeleton, a polyimide skeleton, a polyvinyl alcohol skeleton, and the like. mentioned. The easy-adhesion layer is usually provided in advance on a protective film, and the easy-adhesion layer side of the protective film and the polarizing film are laminated by the pressure-sensitive adhesive layer or the adhesive layer.

The blocking layer is a layer having a function of preventing impurities such as oligomers and ions eluted from the transparent protective film or the like from migrating (intruding) into the polarizing film. The block layer may be any layer as long as it has transparency and can prevent impurities eluted from a transparent protective film or the like. Examples of materials for forming the block layer include urethane prepolymer-based forming materials and cyanoacrylate. Examples include system-forming materials, epoxy-based forming materials, and the like.

The refractive index adjusting layer is a layer provided to suppress a decrease in transmittance due to reflection between layers having different refractive indices such as the transparent protective film and the polarizing film. Examples of the refractive index adjusting material for forming the refractive index adjusting layer include forming agents containing various resins such as silica-based, acrylic-based, acrylic-styrene-based, and melamine-based resins and additives.

The polarizing film preferably has a degree of polarization of 99.98% or more, more preferably 99.99% or more.

<Laminated polarizing film>
The laminated polarizing film (optical laminate) of the present invention is obtained by bonding the polarizing film to an optical layer. The optical layer is not particularly limited. One or more optical layers may be used. As the laminated polarizing film, in particular, a reflective polarizing film or a semi-transmissive polarizing film obtained by laminating a reflector or a semi-transmitting reflector on the polarizing film, and a retardation plate further laminated on the polarizing film. An elliptically polarizing film or a circularly polarizing film, a wide viewing angle polarizing film in which a viewing angle compensation film is laminated on the polarizing film, or a polarizing film in which a brightness enhancement film is laminated on the polarizing film.

On one side or both sides of the polarizing film or the laminated polarizing film, an image display cell such as a liquid crystal cell or an organic EL element, and a front transparent member such as a front transparent plate or a touch panel on the viewing side. An adhesive layer may be added for bonding the members together. A pressure-sensitive adhesive layer is suitable as the adhesive layer. The pressure-sensitive adhesive that forms the pressure-sensitive adhesive layer is not particularly limited. They can be appropriately selected and used. In particular, a pressure-sensitive adhesive containing an acrylic polymer, which is excellent in optical transparency, exhibits appropriate wettability, cohesiveness and adhesiveness, and is excellent in weather resistance, heat resistance, etc., is preferably used.

Attachment of the pressure-sensitive adhesive layer to one side or both sides of the polarizing film or the laminated polarizing film can be performed by an appropriate method. As the attachment of the adhesive layer, for example, a method of preparing an adhesive solution and directly attaching it on the polarizing film or the laminated polarizing film by an appropriate development method such as a casting method or a coating method, or a separator Examples include a method of forming an adhesive layer thereon and transferring it onto the polarizing film or the laminated polarizing film. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use, adhesive strength, etc., and is generally 1 to 500 μm, preferably 5 to 200 μm, more preferably 10 to 100 μm. Such a polarizing film or laminated polarizing film provided with an adhesive layer on at least one surface is referred to as a polarizing film with an adhesive layer or a laminated polarizing film with an adhesive layer.

It is preferable that the exposed surface of the pressure-sensitive adhesive layer is temporarily covered with a separator for the purpose of preventing contamination and the like until the adhesive layer is put into practical use. As a result, contamination of the pressure-sensitive adhesive layer, etc., can be prevented under normal handling conditions. Examples of the separator include suitable thin sheets such as plastic films, rubber sheets, paper, cloth, nonwoven fabric, nets, foam sheets, metal foils, and laminates thereof. A film coated with an appropriate release agent such as fluorine-based or molybdenum sulfide is used.

<Image display panel and image display device>
The image display panel of the present invention comprises an image display cell and the polarizing film or the laminated polarizing film bonded together. In the image display device of the present invention, a front transparent member is provided on the polarizing film or laminated polarizing film side (viewing side) of the image display panel.

Examples of the image display cell include a liquid crystal cell and an organic EL cell. Examples of the liquid crystal cell include a reflective liquid crystal cell that uses external light, a transmissive liquid crystal cell that uses light from a light source such as a backlight, and a semi-transmissive liquid crystal cell that uses both external light and light from a light source. Any semi-reflective liquid crystal cell may be used. When the liquid crystal cell utilizes light from a light source, the image display device (liquid crystal display device) has a polarizing film disposed on the opposite side of the image display cell (liquid crystal cell) from the viewing side, and the light source is placed. The polarizing film on the light source side and the liquid crystal cell are preferably bonded together via an appropriate adhesive layer. As the driving method of the liquid crystal cell, for example, any type such as VA mode, IPS mode, TN mode, STN mode, or bend orientation (π type) can be used.

As the organic EL cell, for example, a light-emitting body (organic electroluminescence light-emitting body) formed by laminating a transparent electrode, an organic light-emitting layer and a metal electrode on a transparent substrate in this order is preferably used. The organic light-emitting layer is a laminate of various organic thin films. and a laminate of an electron injection layer made of a perylene derivative or the like, or a laminate of a hole injection layer, a light emitting layer, and an electron injection layer.

Examples of the front transparent member arranged on the viewing side of the image display cell include a front transparent plate (window layer) and a touch panel. A transparent plate having appropriate mechanical strength and thickness is used as the front transparent plate. As such a transparent plate, for example, a transparent resin plate such as acrylic resin or polycarbonate resin, or a glass plate is used. As the touch panel, for example, various types of touch panels such as resistive type, capacitive type, optical type, ultrasonic type, etc., and glass plates and transparent resin plates having a touch sensor function are used. When a capacitive touch panel is used as the front transparent member, it is preferable that a front transparent plate made of glass or a transparent resin plate is provided on the viewing side of the touch panel.

The polarizing film of the present invention has a good initial degree of polarization, and is excellent in the effect of suppressing a decrease in single transmittance due to coloring of the polarizing film in a high-temperature environment. The polarizing film, the laminated polarizing film, the image display panel, and the image display device described above are suitable for use as an in-vehicle image display device such as a car navigation device and a back monitor.

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

<Example 1>
<Preparation of polarizing film>
A polyvinyl alcohol film having an average degree of polymerization of 2,400, a degree of saponification of 99.9 mol % and a thickness of 30 μm was prepared. A polyvinyl alcohol film is immersed in a swelling bath (water bath) at 20° C. for 30 seconds between rolls having different circumferential speed ratios, and stretched by 2.2 times in the conveying direction while swelling (swelling step). In a dyeing bath (iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at 30° C., the iodine concentration of the finally obtained polarizing film is While adjusting the concentration so as to be 3.8% by weight, it is immersed for 30 seconds and dyed while the original polyvinyl alcohol film (polyvinyl alcohol film not stretched at all in the conveying direction) is used as a reference in the conveying direction. Stretched twice (dyeing process). Then, the dyed polyvinyl alcohol film is placed in a 40° C. crosslinking bath (an aqueous solution with a boric acid concentration of 3.5% by weight, a potassium iodide concentration of 3.0% by weight, and a zinc sulfate concentration of 3.6% by weight). for 28 seconds and stretched up to 3.6 times in the conveying direction with respect to the original polyvinyl alcohol film (crosslinking step). Further, the obtained polyvinyl alcohol film was placed in a drawing bath (an aqueous solution having a boric acid concentration of 4.5% by weight, a potassium iodide concentration of 5.0% by weight, and a zinc sulfate concentration of 5.0% by weight) at 64°C. for 60 seconds and stretched up to 6.0 times in the transport direction based on the original polyvinyl alcohol film (stretching step), then washed in a washing bath at 27 ° C. (potassium iodide concentration is 2.3% by weight, radical scavenging It was immersed for 10 seconds in an aqueous solution having a concentration of 1.0% by weight of a compound represented by the following general formula (9) as a functional compound (washing step). The washed polyvinyl alcohol film was dried at 40° C. for 30 seconds to prepare a polarizing film. The iodine concentration of the polarizing film was obtained by the following measuring method. In the obtained polarizing film, the peak temperature of the maximum intensity of water detected by generated gas analysis is 210°C, and the content of the compound represented by the following general formula (9) in the polarizing film is The content was 0.3% by weight, and the thickness of the polarizing film was 12 μm.

[Method for measuring iodine concentration (% by weight) in polarizing film]
The iodine concentration (% by weight) of the polarizing film was determined using the following formula using an X-ray fluorescence spectrometer (manufactured by Rigaku, trade name “ZSX-PRIMUS IV”, measurement diameter: ψ20 mm).
Iodine concentration (wt%) = 14.474 × (fluorescent X-ray intensity) / (film thickness) (kcps / μm) Note that the coefficient for calculating the concentration varies depending on the measuring device, but the coefficient is an appropriate calibration curve can be obtained using

[Evolved gas analysis method]
The polarizing film is introduced into a heating furnace pyrolyzer (Frontier Lab PY-2020iD), and the generated gas is directly introduced into a TOFMS (JEOL JMS-T100GCV) to perform the evolved gas analysis (EGA/TOFMS) method. rice field.
[Measurement condition]
Temperature rising conditions: 40°C → +10°C/min → 350°C
Interface: inert fused silica tubing, 2.5m x 0.15mm id
Carrier gas: He (1.0 mL/min)
Inlet temperature: 300°C
Inlet: split ratio 20:1
Interface temperature: 300°C
Mass spectrometer: TOFMS
Ionization method: EI method Mass range: m/z=18

[Method for measuring content (% by weight) of compound having radical scavenging function in polarizing film]
About 20 mg of the polarizing film was collected, quantified, dissolved by heating in 1 mL of water, diluted with 4.5 mL of methanol, the resulting extract was filtered through a membrane filter, and the filtrate was subjected to HPLC (Waters ACQUITY UPLC H-class Bio) was used to measure the concentration of the compound having a radical scavenging function.

<Preparation of polarizing film>
As an adhesive, polyvinyl alcohol resin containing an acetoacetyl group (average degree of polymerization: 1,200, degree of saponification: 98.5 mol%, degree of acetoacetylation: 5 mol%) and methylol melamine at a weight ratio of 3: The aqueous solution contained in 1 was used. Using this adhesive, a 30 μm-thick transparent film made of (meth)acrylic resin (modified acrylic polymer having a lactone ring structure) was applied to one surface (image display device cell side) of the polarizing film obtained above. A protective film (manufactured by Nippon Shokubai, moisture permeability is 125 g / (m ² · 24 h)), and on the other side (visible side), a triacetyl cellulose film (manufactured by Fujifilm, product name “TJ40UL”) with HC After laminating the formed transparent protective film having a thickness of 47 μm (water vapor permeability of 380 g/(m ² · 24 h)) with a roll laminating machine, it was subsequently dried by heating in an oven (temperature: 90°C, time: 10 minutes). Thus, 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 (manufactured by JASCO Corporation, product name "V7100"). As a specific method for measuring the degree of polarization, the parallel transmittance (H0) and orthogonal transmittance (H90) of the polarizing film are measured, and the formula: degree of polarization (%) = {(H0-H90)/(H0+H90)}. It can be obtained from 1/2×100. The parallel transmittance (H0) is the transmittance of a parallel laminated polarizing film produced by laminating two identical polarizing films so that their absorption axes are parallel to each other. The orthogonal transmittance (H90) is the transmittance of an orthogonal laminated polarizing film produced by stacking two identical polarizing films so that their absorption axes are orthogonal to each other. It should be noted that these transmittances are Y values corrected for visual sensitivity using a 2-degree field of view (C light source) of JlS Z 8701-1982. Table 1 shows the results.

[Evaluation of single transmittance under high temperature environment]
The polarizing film obtained above was cut into a size of 5.0 × 4.5 cm so that the absorption axis of the polarizing film was parallel to the long side, and the protective film surface on the image display cell side of the polarizing film had a thickness of A glass plate (pseudo-image display cell) was attached via a 20 μm acrylic pressure-sensitive adhesive layer, and autoclaved at 50° C. and 0.5 MPa for 15 minutes to prepare a laminate. The laminate thus obtained was placed in a hot air oven at a temperature of 105° C. for 750 hours, and the single transmittance (ΔTs) before and after the introduction (heating) was measured. Single transmittance was measured using a spectrophotometer (manufactured by JASCO Corporation, product name "V7100") and evaluated according to the following criteria. The measurement wavelength is 380 to 700 nm (every 5 nm). Table 1 shows the results.
ΔTs (%) = Ts ₇₅₀ - Ts ₀
Here, Ts ₀ is the single transmittance of the laminate before heating, and Ts ₇₅₀ is the single transmittance of the laminate after heating for 750 hours. The ΔTs(%) preferably satisfies 5≧ΔTs(%)≧0, and more preferably satisfies 3≧ΔTs(%)≧0.

[Evaluation of heat peeling]
Cut the polarizing film into a size of 680 × 250 mm so that the absorption axis of the polarizing film is parallel to the long side. A plate (pseudo image display cell) was produced. The appearance of the obtained laminate sample after standing in a hot air oven at 105° C. for 750 hours was visually evaluated according to the following criteria. Table 1 shows the results.
◯: Slight peeling or foaming at the edge, but no practical problem.
△: Peeling or foaming at the edge, but practical unless it is a special application (for example, a narrow frame display with a short distance from the edge of the polarizing plate to the active area where the image is displayed) No problem above.
x: Remarkable peeling at the edge, which poses a practical problem.

<Example 2>
<Preparation of polarizing film and polarizing film>
A polarizing film was prepared in the same manner as in Example 1, except that the iodine concentration in the dyeing bath was adjusted so that the iodine concentration in the finally obtained polarizing film was 4.3% by weight. and a polarizing film. The resulting polarizing film had a peak temperature of 208° C. at the maximum intensity of water detected by the generated gas analysis method, and the content of the compound represented by the above general formula (9) in the polarizing film was 0.5°C. 3% by weight, and the thickness of the polarizing film was 12 μm.

<Example 3>
<Preparation of polarizing film and polarizing film>
In the preparation of the polarizing film, except that the iodine concentration of the dyeing bath was adjusted so that the iodine concentration of the polarizing film finally obtained from the polyvinyl alcohol film having a thickness of 45 μm was 3.5% by weight. A polarizing film and a polarizing film were produced in the same manner as in 1. The resulting polarizing film had a peak temperature of 210° C. at the maximum intensity of water detected by the generated gas analysis method, and the content of the compound represented by the above general formula (9) in the polarizing film was 0.5°C. The content was 2% by weight, and the thickness of the polarizing film was 18 μm.

<Example 4>
<Preparation of polarizing film and polarizing film>
In the preparation of the polarizing film, the iodine concentration in the dyeing bath was adjusted so that the iodine concentration in the finally obtained polarizing film was 3.7% by weight. , Instead of the general formula (9), the polarizing film and the polarizing A film was produced. The resulting polarizing film had a peak temperature of 211° C. at the maximum intensity of water detected by the generated gas analysis method, and the content of the compound represented by the above general formula (8) in the polarizing film was 0.5°C. 3% by weight, and the thickness of the polarizing film was 12 μm.

<Comparative Example 1>
<Preparation of polarizing film and polarizing film>
In the preparation of the polarizing film, a polarizing film and a polarizing film were prepared in the same manner as in Example 2, except that the compound represented by the general formula (9) was not added to the cleaning bath as a compound having a radical scavenging function. A film was produced. The resulting polarizing film had a peak temperature of 197° C. at the maximum intensity of water detected by generated gas analysis, and the content of the compound represented by the general formula (9) in the polarizing film was 0 weight. %, and the thickness of the polarizing film was 12 μm.

<Comparative Example 2>
<Preparation of polarizing film and polarizing film>
In the production of the polarizing film, the iodine concentration in the dyeing bath is adjusted so that the iodine concentration in the finally obtained polarizing film is 2.5% by weight. A polarizing film and a polarizing film were produced in the same manner as in Example 1, except that the compound represented by (9) was not added. The resulting polarizing film had a peak temperature of 206° C. at the maximum intensity of water detected by the generated gas analysis method, and the content of the compound represented by the general formula (9) in the polarizing film was 0 weight. %, and the thickness of the polarizing film was 12 μm.

Using the polarizing films of Examples and Comparative Examples obtained above, the above [Evaluation of degree of polarization], [Evaluation of single transmittance under high temperature environment], and [Evaluation of heat peeling] were performed. Table 1 shows the results.

Claims (9)

A method for producing a polarizing film in which iodine is adsorbed and oriented on a polyvinyl alcohol-based film,
Optionally, the polyvinyl alcohol-based film is subjected to a swelling step, a washing step, and at least a dyeing step, a cross-linking step, and a stretching step, and the swelling step, the washing step, the dyeing step, the cross-linking step, and Any one or more treatment baths in the stretching step contain a compound having a radical scavenging function capable of dissolving 1 part by weight or more in 100 parts by weight of water at 25° C., and the iodine concentration is 3% by weight or more and 7% by weight . % or less of obtaining a polarizing film containing a compound having a radical scavenger function , or
A polyvinyl alcohol-based resin layer containing a polyvinyl alcohol-based resin is formed on one side of a long thermoplastic resin substrate to prepare a laminate, and the laminate is optionally subjected to insolubilization treatment, cross-linking treatment, and Washing treatment, at least in- air auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment, and said dyeing treatment, said underwater stretching treatment, said insolubilization treatment, said cross-linking treatment, and said washing treatment Any one or more of the treatment baths contains a compound having a radical scavenging function that can dissolve 1 part by weight or more in 100 parts by weight of water at 25 ° C., and the iodine concentration is 3% by weight or more and 7% by weight or less . including a step of obtaining a polarizing film containing a compound having a certain radical scavenging function ;
The obtained polarizing film containing the compound having a radical scavenging function was tested in the generated gas analysis method in the presence of an inert gas at a temperature elevation rate of 10°C/min and a temperature elevation range of 40°C to 350°C. Under the conditions of , confirm that the peak temperature of the maximum intensity of water detected is 205 ° C. or higher, and the difference in single transmittance before and after the heat resistance test at 105 ° C. x 750 hours (ΔTs (%)) A method for producing a polarizing film, comprising a step of designing the polarizing film so that 5≧ΔTs(%)≧0. 2. The method of manufacturing a polarizing film according to claim 1, wherein the polarizing film has a thickness of 20 [mu]m or less. 3. The method of manufacturing a polarizing film according to claim 1, wherein the compound having a radical scavenging function is a compound having a nitroxy radical or a nitroxide group. A method for producing a polarizing film, comprising a step of bonding a transparent protective film to at least one surface of the polarizing film obtained by the method for producing a polarizing film according to any one of claims 1 to 3 . 5. The method for producing a polarizing film according to claim 4, wherein the polarizing film has a degree of polarization of 99.98% or more. 6. A method for producing a laminated polarizing film, comprising a step of bonding an optical layer to the polarizing film obtained by the method for producing a polarizing film according to claim 4 or 5 . A step of bonding the polarizing film obtained by the method for producing a polarizing film according to claim 4 or 5 or the laminated polarizing film obtained by the method for producing a laminated polarizing film according to claim 6 to an image display cell. A method for manufacturing an image display panel characterized by: 8. A method for manufacturing an image display device, comprising the step of providing a front transparent member on the polarizing film or laminated polarizing film side of the image display panel obtained by the method for manufacturing an image display panel according to claim 7 . 9. The method of manufacturing an image display device according to claim 8, wherein the image display device is for vehicle use.

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