JP6964798B2 - 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, a polarizing film used in various image display devices such as a liquid crystal display device and an organic EL display device has high transmittance and high polarization degree, and thus has been dyed (such as iodine and dichroic dyes). A polyvinyl alcohol-based film (containing a dichroic substance) 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, washing treatment, and then drying. Further, the polarizing film is usually used as a polarizing film (polarizing plate) in which a protective film such as triacetyl cellulose is bonded to one side or both sides thereof using an adhesive.

The polarizing film is used as a laminated polarizing film (optical laminate) by laminating other optical layers as needed, and the polarizing film or the laminated polarizing film (optical laminate) is a liquid crystal cell or an organic EL element. Etc. and the front transparent plate (window layer) on the visual side and the front transparent member such as a touch panel are bonded to each other via an adhesive layer or an adhesive layer to form the above-mentioned various image display devices. Used (Patent Document 1).

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

Japanese Unexamined Patent Publication No. 2014-102353 Japanese Unexamined Patent Publication No. 2018-10117

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 polyene formed by a dehydration reaction, so that the polarizing film is colored. There was a problem that the single transmittance was lowered.

As a result of diligent 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 iodine concentration (content) in the polarizing film in order to suppress the decrease in the simple substance transmittance due to the coloring of the polarizing film in a high temperature environment. On the other hand, it has been difficult to obtain a polarizing film having a high degree of polarization and a high concentration of iodine.

In view of the above circumstances, the present invention has a good initial degree of polarization in a polarizing film having a high iodine concentration, 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 purpose is to provide a membrane.

Another object of the present invention is to provide a polarizing film using the above-mentioned polarizing film, a laminated polarizing film, an image display panel, and an image display device.

That is, the present invention is a polarizing film formed by adsorption-orientation of iodine on a polyvinyl alcohol-based film, the iodine concentration is 6% by weight or more, and in the generated gas analysis method, in the presence of an inert gas. The present invention relates to a polarizing film in which the peak temperature of the maximum intensity of detected water is 200 ° C. or higher under the conditions that the temperature rise rate is 10 ° C./min and the temperature rise range is 40 ° C. to 350 ° C.

The present invention also relates to a polarizing film in which a transparent protective film is bonded 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 provided with a front transparent member on the polarizing film or laminated polarizing film side of the image display panel.

The details of the mechanism of action of the effect on the polarizing film of the present invention are unknown, but it is presumed as follows. However, the present invention does not have to be construed as being limited to this mechanism of action.

The polarizing film of the present invention is an iodine-based polarizing film formed by adsorbing and orienting iodine on a polyvinyl alcohol-based film, has an iodine concentration of 6% by weight or more, and is an inert gas in a generated gas analysis method. In the presence, the peak temperature of the maximum intensity of detected water is 200 ° C. or higher under the conditions that the heating rate is 10 ° C./min and the temperature rising range is 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, but the polarizing film of the present invention sets the temperature at which this dehydration reaction occurs to the high temperature side, that is, the generated gas analysis method. By setting the peak temperature of the maximum intensity of the water detected (observed) to 200 ° C. or higher, it is possible to suppress a decrease in the single transmittance due to the coloring of the polarizing film in a high temperature environment. Furthermore, in the polarizing film of the present invention, the peak temperature of the maximum intensity of water detected (observed) by the generated gas analysis method is set to 200 ° C. or higher by setting the iodine concentration in the polarizing film to a certain range or higher. Although it can be controlled, the initial degree of polarization is improved.

On the other hand, the present inventors observed the generation of radicals from the polarizing film when the polarizing film formed by adsorbing and orienting iodine on an iodine-containing polyvinyl alcohol-based film was exposed to a high temperature environment for a certain period of time. The timing at which the polarizing film was colored by polyene formation and the timing at which this radical was generated were very similar, suggesting a phenomenon in which radicals are generated due to the progress of polyene formation of the polarizing film. Therefore, in order to set the temperature at which the above-mentioned dehydration reaction occurs in the polarizing film to the high temperature side, that is, to set the peak temperature of the maximum intensity of water detected (observed) by the generated gas analysis method to 200 ° C. or higher, polarization is performed. It is preferable that the membrane contains a compound having a radical scavenging function.

Further, the polarizing film of the present invention is useful as a thin polarizing film from the viewpoint of preventing panel warpage during heating of the polarizing film or the laminated polarizing film as the panel of the image display device becomes thinner.

This is an example of a chart showing the peak of water detected in the generated 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 orienting iodine on a polyvinyl alcohol-based film, has an iodine concentration of 6% by weight or more, and is an inert gas in a generated gas analysis method. In the presence, the temperature rise rate is 10 ° C./min, the temperature rise range is from 40 ° C. to 350 ° C., and the peak temperature of the maximum intensity of detected water is 200 ° C. or higher.

As the polyvinyl alcohol (PVA) -based film, a film having translucency in the visible light region and dispersing and adsorbing iodine can be used without particular limitation. Further, the PVA-based film usually used as a raw material preferably has a thickness of about 1 to 100 μm, more preferably about 1 to 50 μm, and preferably a width of about 100 to 5000 mm.

Examples of the material of the polyvinyl alcohol-based film include polyvinyl alcohol or a derivative thereof. Examples of the polyvinyl alcohol derivative include polyvinyl formal, polyvinyl acetal; olefins such as ethylene and propylene; unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, and alkyl esters and acrylamides thereof. Can be 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, and 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 K 6726.

The polyvinyl alcohol-based 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, and condensates thereof. The amount of the additive used is not particularly limited, but is preferably about 20% by weight or less in the polyvinyl alcohol-based film, for example.

The polarizing film has an iodine concentration (content) of 6% by weight or more from the viewpoint of improving the initial degree of polarization of the polarizing film. From the viewpoint of improving the initial degree of polarization of the polarizing film, the iodine concentration (content) is preferably 7% by weight or more, more preferably 8% by weight or more, and From the viewpoint of controlling the peak temperature of the maximum intensity of water detected by the generated gas analysis method to 200 ° C. or higher, it is preferably 12% by weight or less, and more preferably 10% by weight or less.

The polarizing film has the maximum intensity of water detected in the generated gas analysis method under the conditions that the temperature rise rate is 10 ° C./min and the temperature rise range is 40 ° C. to 350 ° C. in the presence of an inert gas. The peak temperature of is 200 ° C. or higher. By setting the temperature at which the dehydration reaction of polyvinyl alcohol occurs on the high temperature side, that is, the peak temperature of the maximum intensity of water detected by the generated gas analysis method at 200 ° C. or higher, the polarizing film is used in a high temperature environment. , It is possible to suppress a decrease in the single transmittance due to coloring of the polarizing film. On the other hand, when the peak temperature of the maximum intensity of water is lower than 200 ° C., the polarizing film before and after the heating durability test (95 ° C. × 750 hours), which is an index of high temperature durability required for low-end in-vehicle displays. It becomes difficult to control the amount of change in the single transmittance of No. 1 to 0% or more and 5% or less.

FIG. 1 is an example of a chart showing the peak of water detected by the above-mentioned generated gas analysis method, and the peak temperature of the maximum intensity of detected water is 200 ° C. or higher.

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

The polarizing film preferably contains a compound having a radical scavenging function. It is presumed that the compound having a radical scavenging function can scaveng the radicals generated by heating by the polyvinyl alcohol of the polarizing film and set the temperature at which the dehydration reaction of polyene formation occurs on the high temperature side. Examples of the compound having a radical trapping function include radical trapping of hindered phenol-based, hindered amine-based, phosphorus-based, sulfur-based, benzotriazole-based, benzophenone-based, hydroxylamine-based, salicylate ester-based, and triazine-based compounds. Examples thereof include compounds having a function (for example, antioxidants). The compound having a radical scavenging function is preferably, for example, a nitroxy radical or a compound having a nitroxide group from the viewpoint that the temperature at which the dehydration reaction of polyene formation occurs can be easily set on the 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。Examples of the compound having a nitroxyl radical or a nitroxide group, at room temperature, from the viewpoint of having a relatively stable radical in air, as N- oxyl compound (functional group, the C-N (-C) -O ^· compounds having (O ^· is an oxy radical)) can be mentioned, known materials can be used. Examples of the N-oxyl compound include compounds having an organic group having the following structure.

(In the 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, and n is 0 or 1. In addition, in the general formula (1), the left side of the dotted line part shows 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 compound having an organic group include compounds represented by the following general formulas (2) to (5).

(In the general formula (2), R ^{1 to} R ⁵ and n are the same as above, and R ⁶ represents a hydrogen atom or 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 above, and R ⁷ and R ⁸ are independently hydrogen atoms or alkyl groups having 1 to 10 carbon atoms. Represents an acyl group or an aryl group.)

(In the general formula (4), R ¹ to R ⁵ and n are the same as described above, and R ⁹ to R ¹¹ are independently hydrogen atoms or alkyl groups 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 or an alkyl group having 1 to 10 carbon atoms, an amino group, an alkoxy group and a hydroxy group. Represents a 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, and have 1 to 3 carbon atoms, from the viewpoint of availability. It is more preferably an alkyl group. Further, in the general formula (2), from the viewpoint of availability, R ⁶ is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably a hydrogen atom. Further, in the general formula (3), from the viewpoint of availability, R ⁷ and R ⁸ are preferably hydrogen atoms independently or alkyl groups having 1 to 10 carbon atoms, and are hydrogen atoms. Is more preferable. Further, in the general formula (4), from the viewpoint of availability, R ⁹ to R ¹¹ are preferably hydrogen atoms or alkyl groups having 1 to 10 carbon atoms. Further, in the general formula (5), from the viewpoint of availability, R ¹² is preferably a hydroxy group, an amino group, or an alkoxy group. In the general formulas (1) to (5), n is preferably 1 from the viewpoint of availability.

Further, as the N-oxyl compound, for example, N- described in JP-A-2003-64022, JP-A-11-222462, JP-A-2002-284737, International Publication No. 2016/047655 and the like. Oxyl compounds can be mentioned.

Further, the compound having a radical scavenging function preferably has a molecular weight of 1000 or less, more preferably 500 or less, and more preferably 300 or less, from the viewpoint of efficiently capturing radicals generated in the polyene conversion reaction. Is even more preferable.

As the compound having a radical trapping function, a thick polyvinyl alcohol-based film was used from the viewpoint of being able to efficiently soak into the polarizing film together with water during the production of the polarizing film, from the viewpoint of being able to impregnate the polarizing film at a high concentration. Even in this case, it can be impregnated in a short time, so from the viewpoint of increasing the productivity of the polarizing film, it is preferable that it can be dissolved in 1 part by weight or more with respect to 100 parts by weight of water at 25 ° C. It is more preferable that it can be dissolved in an amount of 2 parts by weight or more, and it is more preferable that it can be dissolved in an amount of 5 parts by weight or more with respect to 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。）

In addition, examples of the compound having a nitroxyl radical or a nitroxide group include the following compounds.

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

When the polarizing film contains a compound having the radical trapping function, the content of the compound having the radical trapping function is the polarization from the viewpoint of suppressing a decrease in the 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 15% by weight from the viewpoint of appearance. % Or less, more preferably 12% by weight or less, and even more preferably 10% by weight or less.

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

Further, when a polarizing film containing the compound having a radical scavenging function is produced, the treatment bath of any one or more of the swelling step, the washing step, the dyeing step, the cross-linking step, and the stretching step is used. It may contain the compound having the radical scavenging function. The concentration of the compound having a radical scavenging function contained in any of the treatment baths cannot be unconditionally determined because it is affected by the number of treatments, the treatment time, the treatment temperature, etc. of each treatment, but the radicals are trapped in the polarizing film. From the viewpoint of efficiently controlling 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. It is more preferably 30% by weight or less, more preferably 25% by weight or less, still more preferably 20% by weight or less.

In particular, when the cleaning step is performed after the dyeing step, the cross-linking step, and the stretching step, the cleaning step takes into consideration the treatment conditions in the dyeing step, the cross-linking step, the stretching step, and the like, and iodine and the radical. The content of the iodine and the compound having a radical trapping function is adjusted to a desired range from the viewpoint that components such as a compound having a trapping function can be eluted from the polyvinyl alcohol-based film or adsorbed on the polyvinyl alcohol-based film. 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. You may. Examples of the zinc salt include zinc halides such as zinc chloride and zinc iodide; and 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 alkali metals and alkaline earth metals. Examples include salt.

The swelling step is a treatment step of immersing the polyvinyl alcohol-based film in a swelling bath, and can remove stains and blocking agents on the surface of the polyvinyl alcohol-based film, and dyes the polyvinyl alcohol-based film by swelling it. Unevenness can be suppressed. As the swelling bath, a medium containing water as a main component, such as water, distilled water, and pure water, is usually used. A surfactant, alcohol, or the like may be appropriately added to the swelling bath according to a conventional method.

The temperature of the swelling bath is preferably about 10 to 60 ° C, more preferably about 15 to 45 ° C, and even more preferably about 18 to 30 ° C. The immersion time in the swelling bath cannot be unconditionally determined because the degree of swelling of the polyvinyl alcohol-based film is affected by the temperature of the swelling bath, but is preferably about 5 to 300 seconds, preferably 10 to 200 seconds. It is more preferably about 20 to 100 seconds. The swelling step may be carried out only once, or may be carried out 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 and oriented on the polyvinyl alcohol-based film. The iodine solution is usually preferably an aqueous iodine solution and contains iodine and iodide as a solubilizing agent. The iodide includes potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and iodide. Examples include titanium. Among these, potassium iodide is preferable from the viewpoint of controlling the content of potassium in the polarizing film.

In the dyeing bath, the iodine concentration is preferably about 0.01 to 1% by weight, more preferably about 0.02 to 0.5% by weight. In the dyeing bath, the concentration of the iodide 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 more preferable to have.

The temperature of the dyeing bath is preferably about 10 to 50 ° C., more preferably about 15 to 45 ° C., and even more preferably about 18 to 30 ° C. The immersion time in the dyeing bath cannot be unconditionally determined because the degree of dyeing of the polyvinyl alcohol-based film is affected by the temperature of the dyeing bath, but is preferably about 10 to 300 seconds, preferably about 20 to 240 seconds. More preferably. The dyeing step may be carried out only once, or may be carried out a plurality of times as needed.

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

In the crosslinked bath, the concentration of the boron compound is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and more preferably about 2 to 5% by weight. preferable. 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, 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-based film is affected by the temperature of the cross-linking bath, but is preferably about 5 to 300 seconds, preferably 10 to 200 seconds. More preferably. The cross-linking step may be carried out only once, or may be carried out a plurality of times as needed.

The stretching step is a treatment step of stretching a polyvinyl alcohol-based film to a predetermined magnification in at least one direction. Generally, a polyvinyl alcohol-based 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 adopted. The stretching step may be carried out only once, or may be carried out a plurality of times as needed. The stretching step may be performed at any stage in the production of the polarizing film.

As the treatment bath (stretching bath) in the wet stretching method, a solvent such as water or a mixed solution of water and an organic solvent miscible with water can be usually used. The stretching bath may contain potassium iodide from the viewpoint of controlling the content of the potassium in the polarizing film. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1 to 15% by weight, more preferably about 2 to 10% by weight, and 3 More preferably, it is about 6% by weight. Further, the treatment bath (stretching bath) can 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% by weight, more preferably about 1.5 to 10% by weight, and even more preferably about 2 to 5% by weight.

The temperature of the stretching bath is preferably about 25 to 80 ° C, more preferably about 40 to 75 ° C, and even more preferably about 50 to 70 ° C. The immersion time in the stretching bath cannot be unconditionally determined because the degree of stretching of the polyvinyl alcohol-based film is affected by the temperature of the stretching bath, but is preferably about 10 to 800 seconds, preferably about 30 to 500 seconds. More preferably. 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 stretching method include an inter-roll stretching method, a heating roll stretching method, and a compression stretching method. The dry stretching method may be performed together with the drying step.

The total draw ratio (cumulative draw ratio) applied to the polyvinyl alcohol-based film can be appropriately set depending on the intended purpose, but is preferably about 2 to 7 times, and preferably about 3 to 6.8 times. More preferably, it is 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 washing bath, and can remove foreign substances remaining on the surface of the polyvinyl alcohol-based film or the like. As the washing bath, a medium containing water as a main component, such as water, distilled water, and pure water, is usually used. Further, from the viewpoint of controlling the content of potassium in the polarizing film, the washing bath may contain potassium iodide, and in this case, the concentration of potassium iodide in the washing bath is 1 to 10 weight by weight. It is preferably about%, more preferably about 1.5 to 4% by weight, and 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, and even more preferably about 15 to 35 ° C. The immersion time in the washing bath cannot be unconditionally determined because the degree of washing of the polyvinyl alcohol-based film is affected by the temperature of the washing bath, but is preferably about 1 to 100 seconds, preferably 2 to 50 seconds. It is more preferably about 3 to 20 seconds. The swelling step may be carried out only once, or may be carried out a plurality of times as needed.

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 drying obtains a polarizing film having a desired moisture content. The drying is carried out by any suitable method, and examples thereof include natural drying, blast drying, and heat drying.

The drying temperature is preferably about 20 to 150 ° C, more preferably about 25 to 100 ° C. The drying time cannot be unconditionally determined because the degree of drying of the polarizing film is affected by the drying temperature, but is preferably about 10 to 600 seconds, more preferably about 30 to 300 seconds. preferable. The drying step may be carried out only once, or may be carried out a plurality of times as needed.

The polarizing film preferably has a thickness of 1 μm or more, more preferably 2 μm or more, and 15 μm or less from the viewpoint of preventing warpage of the panel, from the viewpoint of improving the initial degree of polarization of the polarizing film. It is more preferably 10 μm or less, and even more preferably 8 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 base material is used as the polyvinyl alcohol-based film, and the following thin type is used. A method for producing a polarizing film can be applied.

<Manufacturing method of thin polarizing film>
The method for producing a thin polarizing film is to form 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 form a laminate. This includes subjecting the laminate to an aerial 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 characteristics, a two-stage stretching method that combines an aerial auxiliary stretching treatment (dry stretching) and an underwater stretching treatment in a boric acid aqueous solution is selected.

Any suitable method is adopted as the method for producing the laminate. For example, a method of applying a coating liquid containing the PVA-based resin to the surface of the thermoplastic resin base material and drying the laminate can be mentioned. Be done. The thickness of the thermoplastic resin base material is preferably about 20 to 300 μm, more preferably about 50 to 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 0.3, from the viewpoint of absorbing water, significantly reducing the stretching stress, and being able to stretch at a high magnification. More preferably, it is about% or more. On the other hand, the thermoplastic resin base material has a water absorption rate of 3 from the viewpoint that the dimensional stability of the thermoplastic resin base material is remarkably lowered and problems such as deterioration of the appearance of the obtained polarizing film can be prevented. It is preferably about% 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 K 7209.

The thermoplastic resin base material has a glass transition temperature (Tg) of about 120 ° C. or less from the viewpoint of being able to sufficiently secure the stretchability of the laminate while suppressing the crystallization of the PVA-based resin layer. Is preferable. Further, in consideration of plasticization of the thermoplastic resin base material with water and good stretching in water, the glass transition temperature (Tg) is more preferably about 100 ° C. or lower, and more preferably about 90 ° C. or lower. Is even more preferable. On the other hand, the glass transition temperature of the thermoplastic resin base material is a viewpoint that a good laminate can be produced by preventing problems such as deformation of the thermoplastic resin base material when the coating liquid is applied and dried. 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 base material or heating with a crystallization material. The glass transition temperature (Tg) is a value obtained according to JIS K 7121.

Any suitable thermoplastic resin can be adopted as the constituent material of the thermoplastic resin base material. Examples of the thermoplastic resin include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. And so on. Among these, norbornene-based resin and amorphous (amorphous) polyethylene terephthalate-based resin are preferable, and further, the thermoplastic resin base material is extremely excellent in stretchability and crystallization during stretching can be suppressed. , Amorphous (amorphous) polyethylene terephthalate resin is preferably used. Examples of the amorphous (amorphous) polyethylene terephthalate resin include a copolymer containing isophthalic acid and / or cyclohexanedicarboxylic acid as a dicarboxylic acid, and a copolymer containing cyclohexanedimethanol or diethylene glycol as a glycol.

The thermoplastic resin base material may be surface-treated (for example, corona treatment or the like) before forming the PVA-based resin layer, or the easy-adhesion layer may be formed on the thermoplastic resin base material. .. By performing such a treatment, the adhesion between the thermoplastic resin base material and the PVA-based resin layer can be improved. Further, the thermoplastic resin base material may be stretched before forming the PVA-based resin layer.

The coating liquid is a solution in which a PVA-based resin is dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylpropane, 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 base material. ..

The coating liquid preferably contains a halide from the viewpoint of improving the orientation of the polyvinyl alcohol molecules by stretching. As the halide, any suitable halide can be adopted, and examples thereof include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide, lithium iodide and the like, and potassium iodide is preferable. 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 additive include plasticizers such as ethylene glycol and glycerin; and surfactants such as nonionic surfactants.

Any suitable method can be adopted as the coating method of the coating liquid, and for example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, and a spray coating method can be adopted. , Knife coat method (comma coat method, etc.) and the like. The drying temperature of the coating liquid is preferably about 50 ° C. or higher.

Since the aerial auxiliary stretching treatment can be stretched while suppressing the crystallization of the thermoplastic resin base material, the laminated body can be stretched at a high magnification. The stretching method of the aerial auxiliary stretching treatment may be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). ), But free-end stretching is preferable from the viewpoint of obtaining high optical characteristics.

The draw ratio in the aerial auxiliary stretching is preferably about 2 to 3.5 times. The aerial auxiliary stretching may be performed in one step or in multiple steps. When performed in multiple stages, the draw ratio is the product of the draw ratios of each stage.

The stretching temperature in the aerial auxiliary stretching can be set to an arbitrary appropriate value depending on the material for forming the thermoplastic resin base material, the stretching method, and the like, and for example, the glass transition temperature (Tg) of the thermoplastic resin base material. ) 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 from the viewpoint of suppressing the rapid progress of crystallization of the PVA-based resin and suppressing defects due to crystallization (for example, hindering the orientation of the PVA-based resin layer due to stretching). , It is preferably about 170 ° C.

If necessary, an insolubilization treatment may be performed after the aerial auxiliary stretching treatment and before the dyeing treatment or the underwater stretching treatment. The insolubilization treatment is typically performed by immersing a PVA-based resin layer in an aqueous boric acid solution. By performing the insolubilization treatment, it is possible to impart water resistance to the PVA-based resin layer and prevent the orientation of PVA from deteriorating 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 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 a PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of applying the dyeing solution to the PVA-based resin layer, and a method of applying the dyeing solution to the PVA-based resin layer. Examples thereof include a method of spraying, and a method of immersing a PVA-based resin layer (laminate) in a dyeing solution containing iodine is preferable.

The blending amount of iodine in the dyeing bath is preferably about 0.05 to 0.5 parts by weight with respect to 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 blending 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. The liquid temperature of the dyeing bath is preferably about 20 to 50 ° C. in order to suppress the 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 characteristics, the ratio of the iodine and iodide contents in the iodine aqueous solution is preferably about 1: 5 to 1:20, preferably about 1: 5 to 1:10. More preferably.

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 a PVA-based resin layer in an aqueous boric acid solution. By performing the cross-linking treatment, water resistance can be imparted to the PVA-based resin layer, and the orientation of PVA can be prevented from being lowered when immersed in high-temperature water by subsequent stretching in water. The boric acid 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. Further, when the cross-linking treatment is performed, it is preferable to 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 blending amount of the iodide is preferably about 1 to 5 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the cross-linked 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 base material or 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 crystallized. It can be stretched at a high magnification while suppressing it. The stretching method of the underwater stretching treatment may be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). However, free-end stretching is preferable from the viewpoint of obtaining high optical characteristics.

The underwater stretching treatment is preferably carried out by immersing the laminate in a boric acid aqueous solution (boric acid underwater stretching). By using an aqueous boric acid solution as the stretching bath, it is possible to impart rigidity to withstand the tension applied during stretching and water resistance that does not dissolve in water to the PVA-based resin layer. The boric acid concentration of the boric acid aqueous 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. Further, iodide may be blended in the stretching bath (boric acid aqueous solution). The liquid temperature of the stretching bath is preferably about 40 to 85 ° C, more preferably about 60 ° C to 75 ° C. The immersion time of the laminate in the stretching bath is preferably about 15 seconds to 5 minutes.

The stretching ratio in the underwater stretching is preferably about 1.5 times or more, and more preferably about 3 times or more.

The total draw ratio of the laminated body is preferably about 5 times or more, and more preferably about 5.5 times or more with respect to the original length of the laminated body.

The drying shrinkage treatment may be performed by heating the entire zone, or by heating the transport roll (using a so-called heating roll). Preferably, both are used. By drying using a heating roll, it is possible to efficiently suppress the heating curl of the laminate to produce a polarizing film having an excellent appearance, and it is possible to dry the laminate while maintaining it in a flat state. Therefore, not only curl but also wrinkles can be suppressed. Further, from the viewpoint that the optical characteristics of the obtained polarizing film can be improved by shrinking in the width direction during the drying shrinkage treatment, the shrinkage rate in the width direction of the laminate by the drying shrinkage treatment is 1 to 10%. It is preferably about 2 to 8%, and more preferably about 2 to 8%.

The drying conditions can be controlled by adjusting the heating temperature of the transport roll (temperature of the heating roll), the number of heating rolls, the contact time with the heating roll, and the like. The temperature of the heating roll is preferably about 60 to 120 ° C., more preferably about 65 to 100 ° C., and even more preferably 70 to 80 ° C. From the viewpoint of being able to satisfactorily increase the crystallinity of the thermoplastic resin and satisfactorily suppress curling, the number of transport 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, and even more preferably 1 to 10 seconds.

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

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

Further, in the case of producing a thin polarizing film containing the compound having a radical scavenging function, the radical is added to one or more of the treatment baths of the dyeing treatment, the stretching treatment in water, the insolubilization treatment, the cross-linking treatment, and the washing treatment. It may contain a compound having a scavenging function. The concentration of the compound having a radical scavenging function contained in any of the treatment baths cannot be unconditionally determined because it is affected by the number of treatments, the treatment time, the treatment temperature, etc. of each treatment, but the radicals are trapped in the polarizing film. From the viewpoint of efficiently controlling 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. It is more preferably 30% by weight or less, more preferably 25% by weight or less, still more preferably 20% by weight or less.

In particular, when a cleaning treatment is performed, the cleaning treatment elutes components such as iodine and the compound having a radical scavenging function from a polyvinyl alcohol-based film, or polyvinyl, in consideration of treatment conditions such as dyeing treatment and stretching treatment in water. From the viewpoint that it can 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 has a transparent protective film bonded to at least one surface of the polarizing film.

The transparent protective film is not particularly limited, and various transparent protective films used for the polarizing film can be used. As the material constituting the transparent protective film, for example, a thermoplastic resin having excellent transparency, mechanical strength, thermal stability, moisture blocking property, isotropic property and the like is used. Examples of the thermoplastic resin include cell roll ester resins such as triacetyl cellulol, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyether sulfone resins, polysulfone resins, polycarbonate resins, nylon and fragrances. Polyamide-based resin such as group polyamide, polyimide-based resin, polyethylene, polypropylene, polyolefin-based resin such as ethylene / propylene copolymer, (meth) acrylic-based resin, cyclic polyolefin-based resin having a cyclo-based or norbornene structure (norbornene-based resin) ), Polyallylate-based resin, polystyrene-based resin, polyvinyl alcohol-based resin, and mixtures thereof. Further, as the transparent protective film, a cured layer formed of a thermosetting resin such as (meth) acrylic, urethane, acrylic urethane, epoxy, silicone or the like or an ultraviolet curable resin can be used. Among these, cell roll ester-based resins, polycarbonate-based resins, (meth) acrylic-based resins, cyclic polyolefin-based resins, and polyester-based resins are preferable.

The thickness of the transparent protective film can be appropriately determined, but in general, it is preferably about 1 to 500 μm, preferably about 1 to 300 μm, from the viewpoint of workability such as strength and handleability, and thin layer property. More preferably, it is more preferably about 5 to 100 μm.

When the transparent protective film is attached to both sides of the polarizing film, the transparent protective films on both sides may be the same or different.

As 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 phase difference is usually controlled in the range of 40 to 200 nm, and the thickness direction phase difference is usually controlled 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, so that the thickness can be reduced.

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

The transparent protective film contains any suitable additives such as UV absorbers, antioxidants, lubricants, plasticizers, mold release agents, color inhibitors, flame retardants, antistatic agents, pigments, colorants and the like. You may. 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, a sticking prevention layer, a diffusion layer and an antiglare layer can be provided on the surface of the transparent protective film to which the polarizing film is not bonded. The functional layers such as the hard coat layer, the antireflection layer, the sticking prevention layer, the diffusion layer and the antiglare layer can be provided on the protective film itself, or may 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 bonded via an adhesive layer or an adhesive layer.

As the pressure-sensitive adhesive forming the pressure-sensitive adhesive layer, various pressure-sensitive adhesives used in polarizing films can be applied. Examples thereof include alkyl ether adhesives, polyvinyl alcohol adhesives, polyvinyl porolidone adhesives, polyacrylamide adhesives, cellulose adhesives and the like. Among these, an acrylic pressure-sensitive adhesive is preferable.

As a method for forming the pressure-sensitive adhesive layer, for example, a method in which the pressure-sensitive adhesive is applied to a separator or the like that has been peeled off and dried to form a pressure-sensitive adhesive layer and then transferred to a polarizing film or the like, or the pressure-sensitive adhesive is polarized. Examples thereof include a method of applying to a film or the like and drying to form an adhesive layer. The thickness of the pressure-sensitive adhesive layer is not particularly limited, and is, for example, about 1 to 100 μm, preferably about 2 to 50 μm.

As the adhesive for forming the adhesive layer, various adhesives used for the polarizing film can be applied. For example, isocyanate-based adhesives, polyvinyl alcohol-based adhesives, gelatin-based adhesives, vinyl-based latex-based adhesives, and the like. Water-based polyester and the like can be mentioned. These adhesives are usually used as an adhesive (water-based adhesive) composed of an aqueous solution, and contain 0.5 to 60% by weight of a solid content.

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 having reactivity with a component such as a polymer constituting the adhesive is usually used, and for example, alkylenediamines; isocyanates; epoxies; Aldehydes: Amino-formaldehyde and the like such as methylol urea and methylol melamine can be mentioned. The blending amount of the cross-linking agent in the adhesive is usually about 10 to 60 parts by weight with respect to 100 parts by weight of the components such as the polymer constituting the adhesive.

In addition to the above, examples of the adhesive include active energy ray-curable adhesives such as an ultraviolet curable adhesive and an electron beam curable adhesive. Examples of the active energy ray-curable adhesive include (meth) acrylate-based adhesives. Examples of the curable component in the (meth) acrylate-based adhesive include a compound having a (meth) acryloyl group and a compound having a vinyl group. Examples of the compound having a (meth) acryloyl group include alkyl (meth) acrylates having 1 to 20 carbon atoms, such as chain alkyl (meth) acrylates, alicyclic alkyl (meth) acrylates, and polycyclic alkyl (meth) acrylates. ) Acrylate; hydroxyl group-containing (meth) acrylate; epoxy group-containing (meth) acrylate such as glycidyl (meth) acrylate can be mentioned. The (meth) acrylate-based adhesives are hydroxyethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, (meth) acrylamide, and (meth). It may contain a nitrogen-containing monomer such as acrylamide. The (meth) acrylate-based adhesive contains tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecanedimethanol diacrylate, cyclic trimethylolpropane formal acrylate, dioxane glycol diacrylate, and EO as cross-linking components. It may contain a polyfunctional monomer such as modified diglycerin tetraacrylate. Further, a compound having an epoxy group or an oxetanyl group can also be used as the 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 generally known curable epoxy compounds can be used.

The adhesive may contain an appropriate additive, if necessary. Examples of the additive include a silane coupling agent, a coupling agent such as a titanium coupling agent, an adhesion promoter such as ethylene oxide, an ultraviolet absorber, a deterioration inhibitor, a dye, a processing aid, an ion trap agent, and an antioxidant. Examples thereof include agents, tackifiers, fillers, plasticizers, leveling agents, foaming inhibitors, antistatic agents, heat-resistant stabilizers, and hydrolysis-resistant stabilizers.

The adhesive may be applied to either the transparent protective film side (or the functional layer side) or the polarizing film side, or both. After bonding, a drying step is performed to form an adhesive layer composed of a coating and drying layer. After the drying step, ultraviolet rays or electron beams can be irradiated 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, and an ultraviolet curable adhesive. When an electron beam curable adhesive or the like is used, it is preferably about 0.1 to 100 μm, and 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 block 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 for forming the easy-adhesive layer include a forming material containing various resins having a polyester skeleton, a polyether skeleton, a polycarbonate skeleton, a polyurethane skeleton, a silicone-based, a polyamide skeleton, a polyimide skeleton, a polyvinyl alcohol skeleton, and the like. Can be mentioned. The easy-adhesive layer is usually provided in advance on a protective film, and the easy-adhesive layer side of the protective film and the polarizing film are laminated by the adhesive layer or the adhesive layer.

The block layer is a layer having a function for preventing impurities such as oligomers and ions eluted from the transparent protective film and the like from migrating (invading) into the polarizing film. The block layer may be a layer having transparency and capable of preventing impurities eluted from the transparent protective film or the like, and examples of the material forming the block layer include urethane prepolymer-based forming materials and cyanoacrylates. Examples include system-forming materials and epoxy-based forming materials.

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

The polarizing film preferably has a degree of polarization of 99.98% or more, and more preferably a degree of polarization of 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, but is used for forming a liquid crystal display device such as a reflecting plate, a semitransparent plate, a retardation plate (including a wavelength plate such as 1/2 or 1/4), and a viewing angle compensation film. One or two or more optical layers that may be used can be used. The laminated polarizing film is particularly a reflective polarizing film or a semi-transmissive polarizing film in which a reflecting plate or a semi-transmissive reflecting plate is further laminated on the polarizing film, and a retardation plate is further laminated on the polarizing film. Examples thereof include an elliptically polarizing film or a circularly polarizing film, a wide viewing angle polarizing film in which a viewing angle compensating film is further laminated on the polarizing film, and a polarizing film in which a brightness improving film is further laminated on the polarizing film.

On one surface or both surfaces 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 another front transparent member such as a front transparent plate or a touch panel on the viewing side are used. An adhesive layer for bonding the members may be attached. As the adhesive layer, an adhesive layer is suitable. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited, and for example, those using a polymer such as an acrylic polymer, a silicone-based polymer, a polyester, a polyurethane, a polyamide, a polyether, a fluorine-based polymer, or a rubber-based polymer as a base polymer are used. It can be appropriately selected and used. In particular, a pressure-sensitive adhesive containing an acrylic polymer, which has excellent optical transparency, exhibits appropriate wettability, cohesiveness, and adhesiveness, and has excellent weather resistance, heat resistance, and the like is preferably used.

The pressure-sensitive adhesive layer may be attached to one or both sides of the polarizing film or the laminated polarizing film by an appropriate method. The pressure-sensitive adhesive layer may be attached, for example, by preparing a pressure-sensitive adhesive solution and directly attaching the pressure-sensitive adhesive solution onto the polarizing film or the laminated polarizing film by an appropriate developing method such as a casting method or a coating method, or a separator. Examples thereof include a method in which an adhesive layer is formed on the coating film and the pressure-sensitive adhesive layer is transferred 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, and more preferably 10 to 100 μm. Such a polarizing film or a laminated polarizing film having an adhesive layer provided on at least one surface thereof 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 or the like until it is put into practical use. As a result, contamination of the adhesive layer can be prevented under normal handling conditions. As the separator, for example, an appropriate thin leaf such as a plastic film, a rubber sheet, a paper, a cloth, a non-woven fabric, a net, a foam sheet or a metal foil, or a laminate thereof can be used, if necessary, a silicone-based or long-chain alkyl-based separator. Those coated with an appropriate release agent such as fluorine-based or molybdenum sulfide are used.

<Image display panel and image display device>
In the image display panel of the present invention, the polarizing film or the laminated polarizing film is attached to the image display cell. Further, the image display device of the present invention includes a front transparent member on the polarizing film or laminated polarizing film side (visual 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 of the semi-reflective liquid crystal cells may be used. When the liquid crystal cell uses light from a light source, in the image display device (liquid crystal display device), a polarizing film is also arranged on the side opposite to the viewing side of the image display cell (liquid crystal cell), and the light source is further arranged. Be placed. It is preferable that the polarizing film on the light source side and the liquid crystal cell are bonded to each other 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 and bend orientation (π type) can be used.

As the organic EL cell, for example, a cell in which a transparent electrode, an organic light emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light emitting body (organic electroluminescence light emitting body) or the like is preferably used. The organic light emitting layer is a laminate of various organic thin films, for example, a laminate of a hole injection layer made of a triphenylamine derivative or the like and a light emitting layer made of a fluorescent organic solid such as anthracene, or these. Various layer configurations can be adopted, such as a laminate of an electron-injected layer composed of the light-emitting layer and a perylene derivative, or a laminate of a hole-injected layer, a light-emitting layer, and an electron-injected layer.

Examples of the front transparent member arranged on the visual side of the image display cell include a front transparent plate (window layer) and a touch panel. As the front transparent plate, a transparent plate having appropriate mechanical strength and thickness is 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 is used. As the touch panel, for example, various touch panels such as a resistive film method, a capacitance method, an optical method, and an ultrasonic method, a glass plate having a touch sensor function, a transparent resin plate, and the like are used. When a capacitance type touch panel is used as the front transparent member, it is preferable to provide a front transparent plate made of glass or a transparent resin plate on the visual side of the touch panel.

Since the polarizing film of the present invention 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, the polarizing film of the present invention and the polarizing film are used. The polarizing film, the laminated polarizing film, the image display panel, and the image display device are suitable for use in an in-vehicle image display device such as a car navigation device and a back monitor.

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

<Example 1>
<Preparation of polarizing film>
As the thermoplastic resin base material, an amorphous isophthal copolymer polyethylene terephthalate film (thickness: 100 μm) having a long shape, a water absorption rate of 0.75%, and a Tg of about 75 ° C. was used. One side of the resin substrate was corona-treated. 100 weight of PVA-based resin in which polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer Z410") are mixed at a ratio of 9: 1. 13 parts by weight of potassium iodide was added to the part to prepare a PVA aqueous solution (coating liquid). The PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60 ° C. to form a PVA-based resin layer having a thickness of 13 μm to prepare a laminate. The obtained laminate was uniaxially stretched at the free end 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130 ° C. (aerial auxiliary stretching treatment). Next, the laminate was immersed in an insolubilizing bath (an aqueous solution having a boric acid concentration of 4.0% by weight) at a liquid temperature of 40 ° C. for 30 seconds (insolubilization treatment). Next, the finally obtained polarizing film is placed in a dyeing bath having a liquid temperature of 30 ° C. (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water). It was immersed for 60 seconds while adjusting the concentration so that the iodine concentration was 9.3% (dyeing treatment). Then, it was immersed in a cross-linking bath (an aqueous solution having a potassium iodide concentration of 3.0% by weight and a boric acid concentration of 5.0% by weight) at a liquid temperature of 40 ° C. for 30 seconds (cross-linking treatment). Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 4.0% by weight) at a liquid temperature of 70 ° C., the total draw ratio is 5.5 in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds. Uniaxial stretching was performed so as to double (underwater stretching treatment). Then, the laminate is subjected to a washing bath at a liquid temperature of 20 ° C. (potassium iodide concentration 3% by weight, an aqueous solution having a compound concentration of 1.0% by weight represented by the following general formula (9) as a compound having a radical scavenging function). ) (Washing treatment). Then, while drying in an oven kept at 90 ° C., it was brought into contact with a heating roll made of SUS whose surface temperature was kept at 75 ° C. for about 2 seconds (dry shrinkage treatment). In this way, a polarizing film having a thickness of 5 μm was formed on the resin substrate. Further, in the obtained polarizing film, the peak temperature of the maximum intensity of water detected by the generated gas analysis method is 204 ° C., and the content of the compound represented by the following general formula (9) in the polarizing film is high. It was 0.3% by weight.

[Measuring method of iodine concentration (% by weight) in polarizing film]
The iodine concentration (% by weight) of the polarizing film was determined using the following formula using a fluorescent X-ray analyzer (manufactured by Rigaku Corporation, trade name "ZSX-PRIMUS IV", measurement diameter: ψ20 mm).
Iodine concentration (wt%) = 14.474 × (fluorescent X-ray intensity) / (film thickness) (kcps / μm) The coefficient for calculating the concentration differs depending on the measuring device, but the coefficient is an appropriate calibration curve. Can be obtained using.

[Generated gas analysis method]
The polarizing film is introduced into a heating furnace type pyrolyzer (PY-2020iD manufactured by Frontier Lab), and the generated gas is directly introduced into TOFMS (JEOL, JMS-T100GCV) to perform a generated gas analysis (EGA / TOFMS) method. rice field.
[Measurement condition]
Heating conditions: 40 ° C → + 10 ° C / min → 350 ° C
Interface: Inactive Fused Silica Tube, 2.5m x 0.15mm id
Carrier gas: He (1.0 mL / min)
Injection port temperature: 300 ° C
Injection: split ratio 20: 1
Interface temperature: 300 ° C
Mass spectrometer: TOFMS
Ionization method: EI method Mass range: m / z = 18

[Method for measuring the content (% by weight) of a compound having a radical scavenging function in a polarizing film]
Approximately 20 mg of the polarizing film was collected, quantified, heated and dissolved in 1 mL of water, diluted with 4.5 mL of methanol, the obtained extract was filtered through a membrane filter, and the filtrate was HPLC (ACQUITY UPLC manufactured by Waters). The concentration of the compound having a radical trapping function was measured using H-class Bio).

<Manufacturing of polarizing film>
As an adhesive, a polyvinyl alcohol resin containing an acetoacetyl group (average degree of polymerization of 1,200, saponification degree of 98.5 mol%, acetoacetylation degree of 5 mol%) and methylol melamine in a weight ratio of 3: The aqueous solution contained in 1 was used. Using this adhesive, a (meth) acrylic resin (modified acrylic polymer having a lactone ring structure) is formed on the surface (image display cell side) of the polarizing film obtained above opposite to the resin base material. transparent protective film having a thickness of 30 [mu] m (manufactured by Nippon Shokubai Co., moisture permeability ^{125g / (m 2 · 24h)} ) was laminated using a bonding roll combined machine. Next, the resin base material was peeled off, and HC was formed on a triacetyl cellulose film (manufactured by Fuji Film, trade name "TJ40UL") as a transparent protective film on the peeled surface (visual side). humidity bonded at ^{380g / (m 2 · 24h)} ) and through a UV curing adhesive machine bonding roll, then, curing the adhesive from the transparent protective film surface is irradiated with UV light, a polarizing film Made.

[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 the 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 a value of the transmittance of a parallel type laminated polarizing film produced by superimposing two same polarizing films so that their absorption axes are parallel to each other. The orthogonal transmittance (H90) is a value of the transmittance of an orthogonal laminated polarizing film produced by superimposing two identical polarizing films so that their absorption axes are orthogonal to each other. These transmittances are Y values obtained by correcting the luminosity factor with the 2 degree field of view (C light source) of JlS Z 8701-1982. The results are shown in Table 1.

[Evaluation of single transmittance in high temperature environment]
The polarizing film obtained above is cut into a size of 5.0 × 4.5 cm so that the absorption axis of the polarizing film is parallel to the long side, and the thickness is formed on the protective film surface on the image display cell side of the polarizing film. A glass plate (pseudo-image display cell) was laminated 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 obtained laminate was allowed to stand in a hot air oven at a temperature of 95 ° C. for 750 hours, and the single transmittance (ΔTs) before and after charging (heating) was measured. The 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). The results are shown in Table 1.
ΔTs (%) = Ts _{750 -Ts 0}
Here, Ts ₀ is the single transmittance of the laminated body before heating, and Ts ₇₅₀ is the simple substance transmittance of the laminated body after heating for 750 hours. The ΔTs (%) is preferably 5 ≧ ΔTs (%) ≧ 0, and more preferably 3 ≧ ΔTs (%) ≧ 0.

[Evaluation of panel warpage]
The polarizing film is cut into a size of 145 x 105 mm so that the absorption axis of the polarizing film is parallel to the long side, and the thickness is formed on the protective film surface of the polarizing film on the image display cell side via an acrylic adhesive layer having a thickness of 20 μm. A glass plate having a size of 0.4 mm and a size of 155 × 115 mm was laminated. The obtained glass (pseudo-panel) sample with a polarizing film was allowed to stand in a hot air oven at 85 ° C. for 5 hours, and then allowed to stand in a normal temperature and humidity environment for 1 hour, and then the amount of warpage of the glass was evaluated. Warpage refers to the amount of warpage in which the glass and the polarizing plate are convex downward. The results are shown in Table 1.
〇: Warp amount less than 1.0 mm ×: Warp amount 1.0 mm or more

<Example 2>
<Manufacturing of polarizing film and polarizing film>
In the production of the polarizing film, the polarizing film was operated 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 was 6.3% by weight. And a polarizing film was prepared. The obtained polarizing film has a peak temperature of the maximum intensity of water detected by the generated gas analysis method of 207 ° C., and the content of the compound represented by the above general formula (9) in the polarizing film is 0. It was 3% by weight, and the thickness of the polarizing film was 5 μm.

<Example 3>
<Manufacturing of polarizing film and polarizing film>
A polyvinyl alcohol film having an average degree of polymerization of 2,400, a saponification degree of 99.9 mol%, and a thickness of 30 μm was prepared. The polyvinyl alcohol film was immersed in a swelling bath (water bath) at 20 ° C. for 30 seconds between rolls having different peripheral speed ratios and stretched 2.2 times in the transport direction while swelling (swelling step), followed by The iodine concentration of the polarizing film finally obtained in a dyeing bath at 30 ° C. (an iodine aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water) 3.3 in the transport direction with reference to the original polyvinyl alcohol film (polyvinyl alcohol film that is not stretched in the transport direction at all) while immersing and dyeing for 30 seconds while adjusting the concentration so that it is 6.1% by weight. It was stretched twice (dyeing step). Next, the dyed polyvinyl alcohol film is placed in a cross-linked bath at 40 ° C. (an aqueous solution having 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). It was immersed for 28 seconds and stretched up to 3.6 times in the transport direction with reference to the original polyvinyl alcohol film (crosslinking step). Further, the obtained polyvinyl alcohol film is placed in a stretching bath at 64 ° C. (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). After immersing in for 60 seconds and stretching up to 6.0 times in the transport direction with reference to the original polyvinyl alcohol film (stretching step), a washing bath at 27 ° C. (potassium iodide concentration 2.3% by weight, radical trapping) As a compound having a function, it was immersed for 10 seconds in an aqueous solution having a compound concentration of 1.0% by weight represented by the following general formula (6) (washing step). The washed polyvinyl alcohol film was dried at 40 ° C. for 30 seconds to prepare a polarizing film. The obtained polarizing film has a peak temperature of the maximum intensity of water detected by the generated gas analysis method of 209 ° C., and the content of the compound represented by the above general formula (9) in the polarizing film is 0. It was 2% by weight, and the thickness of the polarizing film was 12 μm.

Subsequently, as an adhesive, a polyvinyl alcohol resin containing an acetoacetyl group (average degree of polymerization of 1,200, saponification degree of 98.5 mol%, acetoacetylation degree of 5 mol%) and methylol melamine are weighted. An aqueous solution containing a ratio of 3: 1 was used. Using this adhesive, a transparent (meth) acrylic resin (modified acrylic polymer having a lactone ring structure) having a thickness of 30 μm is formed on one surface (the cell side of the image display device) of the polarizing film obtained above. protective film (manufactured by Nippon Shokubai Co., moisture permeability ^{125g / (m 2 · 24h)} ), also on the other surface (viewing side), triacetyl cellulose film HC in (Fuji film Co., Ltd., trade name "TJ40UL") transparent protective film of the formed thickness 47 [mu] m (moisture permeability ^{380g / (m 2 · 24h)} ) after bonding with a roll lamination coupling device, is subsequently heated and dried in an oven (temperature 90 ° C., the time is 10 minutes) Then, a polarizing film in which a transparent protective film was bonded to both sides of the polarizing film was produced.

<Example 4>
<Manufacturing of polarizing film and polarizing film>
In the production of the polarizing film, the iodine concentration of the dyeing bath was adjusted so that the iodine concentration of the finally obtained polarizing film was 7.9% by weight, and as a compound having a radical trapping function in the bath of the washing step. The polarizing film and the polarized light were carried out in the same manner as in Example 1 except that the compound represented by the general formula (8) was added in an amount of 1.0% by weight instead of the general formula (9). A film was made. The obtained polarizing film has a peak temperature of the maximum intensity of water detected by the generated gas analysis method of 206 ° C., and the content of the compound represented by the above general formula (8) in the polarizing film is 0. It was 3% by weight, and the thickness of the polarizing film was 5 μm.

<Comparative example 1>
<Manufacturing of polarizing film and polarizing film>
In the production of the polarizing film, the iodine concentration of the dyeing bath is adjusted so that the iodine concentration of the finally obtained polarizing film is 8.5% by weight, and the above-mentioned general as a compound having a radical trapping function in the washing bath. A polarizing film and a polarizing film were produced by the same operation as in Example 1 except that the compound represented by the formula (9) was not added. The obtained polarizing film has a peak temperature of the maximum intensity of water detected by the generated gas analysis method of 193 ° C., and the content of the compound represented by the above general formula (9) in the polarizing film is 0 weight by weight. The thickness of the polarizing film was 5 μm.

<Comparative example 2>
<Manufacturing of polarizing film and polarizing film>
In the production of the polarizing film, the iodine concentration of the dyeing bath is adjusted so that the iodine concentration of the finally obtained polarizing film is 5.6% by weight, and the above-mentioned general as a compound having a radical trapping function in the washing bath. A polarizing film and a polarizing film were produced by the same operation as in Example 1 except that the compound represented by the formula (9) was not added. The obtained polarizing film has a peak temperature of the maximum intensity of water detected by the generated gas analysis method of 203 ° C., and the content of the compound represented by the above general formula (9) in the polarizing film is 0 weight by weight. The thickness of the polarizing film was 5 μm.

Using the polarizing films of Examples and Comparative Examples obtained above, the above-mentioned [evaluation of degree of polarization], [evaluation of simple substance transmittance in a high temperature environment], and [evaluation of panel warpage] were performed. The results are shown in Table 1.

Claims (9)

A polarizing film formed by adsorption orientation of iodine on a polyvinyl alcohol-based film.
Iodine concentration is 6% by weight or more,
The polarizing film contains 0.02% by weight or more of a compound having a molecular weight of 1000 or less and having a radical scavenging function capable of dissolving 1 part by weight or more in 100 parts by weight of water at 25 ° C.
In the generated gas analysis, the peak temperature of the maximum intensity of water detected is 200 ° C. under the conditions that the temperature rise rate is 10 ° C./min and the temperature rise range is 40 ° C. to 350 ° C. in the presence of an inert gas. A polarizing film characterized by the above. The polarizing film according to claim 1, wherein the thickness is 15 μm or less. The polarizing film according to claim 1 or 2, wherein the compound having a radical scavenging function is a nitroxy radical or a compound having a nitroxide group. A polarizing film, characterized in that a transparent protective film is bonded to at least one surface of the polarizing film according to any one of claims 1 to 3. The polarizing film according to claim 4, wherein the degree of polarization is 99.98% or more. A laminated polarizing film, wherein the polarizing film according to claim 4 or 5 is bonded to an optical layer. An image display panel, wherein the polarizing film according to claim 4 or 5 or the laminated polarizing film according to claim 6 is attached to the image display cell. An image display device according to claim 7, wherein a front transparent member is provided on the polarizing film or laminated polarizing film side of the image display panel. The image display device according to claim 8, wherein the image display device is for in-vehicle use.

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