KR20220159342A - Polarizing film, laminated polarizing film, image display panel, and image display device - Google Patents

Abstract

A polarizing film in which a transparent protective film is bonded to one side or both sides of a polarizing film, wherein the polarizing film contains a water-soluble radical scavenger, and the general formula (X): 2.0≤a/b (in the general formula (X), a is represents the length (mm) parallel to the absorption axis of the polarizing film, and is a value greater than 200, and b represents the length (mm) orthogonal to the absorption axis of the polarizing film). polarizing film. The polarizing film has a high aspect ratio and is excellent in suppressing the generation of transverse cracks in a direction parallel to the absorption axis of the polarizing film in a high-temperature environment.

Description

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

The present invention relates to 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 high transmittance and high degree of polarization, so they are dyed (containing dichroic substances such as iodine and dichroic dyes). A polyvinyl alcohol-based film is used. The polarizing film is manufactured by subjecting a polyvinyl alcohol-based film to each treatment such as swelling, dyeing, crosslinking, and stretching in a bath, followed by washing treatment and then drying. In addition, 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 using 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 used as an image display cell such as a liquid crystal cell or an organic EL element , It is bonded between a front transparent member such as a front transparent plate (window layer) or a touch panel on the viewing side via an adhesive layer or an adhesive layer, and is used as the above various image display devices (Patent Document 1).

In recent years, these various image display devices are 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, and their applications are expanding. Accordingly, the polarizing film and the laminated polarizing film are required to have high durability under a harsher environment (for example, under a high temperature environment) than has been conventionally required, and to ensure such durability Polarizing films and image display devices have been proposed (Patent Documents 2-3).

Japanese Unexamined Patent Publication No. 2014-102353 Japanese Patent Publication No. 2012-516468 Japanese Unexamined Patent Publication No. 2018-101117

Since the degree of thermal contraction and/or thermal expansion of each member constituting the polarizing film or laminated polarizing film (optical laminate) as described above is different, there is a problem in that the polarizing film cracks when exposed to a high-temperature environment. In addition, there is a problem in that the flexibility of the polarizing film deteriorates due to a decrease in the interaction between molecules of polyvinyl alcohol as polyene formation and growth occur.

On the other hand, the market demands a polarizing film (polarizing film having a high aspect ratio) having a ratio of a length parallel to the absorption axis to a length orthogonal to the absorption axis of the polarizing film from the viewpoint of design in the interior space of the vehicle. It is becoming. In general, the contraction force of the polarizing film in the stretching direction (MD) is greater than that in the stretching direction and the orthogonal direction (TD). In addition, a polarizing film having such a ratio of lengths usually has a larger shrinking force for a given width in the MD direction of the polarizing film than in the TD direction of the polarizing film. Therefore, when exposed to a high-temperature environment, the polarizing film with reduced flexibility cannot withstand the shrinkage force in the MD direction (direction parallel to the absorption axis of the polarizing film), so that the polarizing film in the direction parallel to the absorption axis of the polarizing film It has been found that there is a problem in which transverse cracks (cracks in the orthogonal direction) tend to occur.

In view of the above circumstances, an object of the present invention is to provide a polarizing film having a high aspect ratio, excellent in suppressing effect of transverse cracking in a direction parallel to the absorption axis of the polarizing film in a high temperature environment. .

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

That is, the present invention is a polarizing film in which a transparent protective film is bonded to one side or both sides of a polarizing film, wherein the polarizing film contains a water-soluble radical scavenger, and the general formula (X): 2.0≤a / b (general formula (X ), a represents the length (mm) parallel to the absorption axis of the polarizing film and is a value greater than 200, and b represents the length (mm) orthogonal to the absorption axis of the polarizing film.) It relates to a polarizing film that satisfies the condition of ratio.

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

Further, the present invention relates to an image display panel in which the polarizing film or the laminated polarizing film is bonded to an image display cell.

Further, the present invention relates to an image display device including a front transparent member on the polarizing film or laminated polarizing film side of the image display panel.

Although the detail of the effect mechanism of the effect in the polarizing film of this invention has an unclear part, it estimates as follows. However, the present invention need not be construed as being limited to this mechanism of action.

In the polarizing film of the present invention, a transparent protective film is bonded to one side or both sides of the polarizing film, the polarizing film contains a water-soluble radical scavenger, and the general formula (X): 2.0≤a/b (in the general formula (X) , a represents the length (mm) parallel to the absorption axis of the polarizing film, and is a value greater than 200, and b represents the length (mm) orthogonal to the absorption axis of the polarizing film.) Satisfy the condition. Since the water-soluble radical scavenger can suppress the polyenization of the polarizing film under a high temperature environment and maintain the mechanical strength of the polarizing film, the ratio of the length of the polarizing film perpendicular to the absorption axis to the length parallel to the absorption axis is constant. In the above polarizing film (polarizing film having a high aspect ratio), the effect of suppressing generation of transverse cracks in a direction parallel to the absorption axis of the polarizing film is excellent.

In addition, since the polarizing film of the present invention contains the water-soluble radical scavenger, it can trap radicals that may be generated by the progress of polyenization of the polarizing film. great.

<Polarizing film>

In the polarizing film of the present invention, a transparent protective film is bonded to one side or both sides of the polarizing film.

<Polarizing film>

The polarizing film is formed by adsorbing and orienting a dichroic material such as iodine or a dichroic dye on a polyvinyl alcohol-based film. Iodine is preferable as the dichroic material from the viewpoint of initial polarization performance of the polarizing film.

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

Examples of the material for the polyvinyl alcohol-based film include polyvinyl alcohol or derivatives thereof. Examples of the polyvinyl alcohol derivative include 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 and acrylamides thereof. 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 still more preferably about 1,500 to 4,500. Further, the polyvinyl alcohol preferably has a saponification degree of about 80 to 100 mol%, more preferably about 95 mol% to 99.95 mol%. In addition, the said average degree of polymerization and the said saponification degree can be calculated|required according to JISK6726.

The polyvinyl alcohol-based film may contain additives such as plasticizers and surfactants. As said plasticizer, polyols, such as glycerol, diglycerol, triglycerol, ethylene glycol, propylene glycol, and polyethylene glycol, its condensate, etc. are mentioned, for example. The amount of the additive used is not particularly limited, but, for example, about 20% by weight or less of the polyvinyl alcohol-based film is suitable.

When the polarizing film includes iodine as the dichroic material, the content of iodine is preferably 1% by weight or more and 20% by weight or less. In the polarizing film, the iodine content is preferably 1.5% by weight or more, more preferably 2% by weight or more, and preferably 12% by weight or less from the viewpoint of preventing color loss during durability tests. And, it is more preferable that it is 10% by weight or less.

The polarizing film includes a water-soluble radical scavenger. The above water-soluble radical scavengers may be used alone or in combination of two or more. The water-soluble radical scavenger can efficiently permeate into the polarizing film together with water during manufacture of the polarizing film, can be impregnated into the polarizing film at a high concentration, and can be impregnated in a short time even when a thick polyvinyl alcohol-based film is used. It can be impregnated, and from the viewpoint of increasing the productivity of the polarizing film, it is preferable that it is a compound that can dissolve 1 part by weight or more with respect to 100 parts by weight of water at 25 ° C., and 2 parts by weight with respect to 100 parts by weight of water at 25 ° C. It is more preferable that it is a compound that can dissolve more than, and it is more preferable that it is a compound that can dissolve 5 parts by weight or more with respect to 100 parts by weight of water at 25°C.

It is estimated that the water-soluble radical scavenger can suppress polyenization of the polarizing film under a high-temperature environment. Examples of the water-soluble radical scavenger include hindered phenol-based, hindered amine-based, phosphorus-based, sulfur-based, benzotriazole-based, benzophenone-based, hydroxylamine-based, salicylic acid ester-based, and triazine-based compounds having a radical scavenging function A compound having The water-soluble radical scavenger is preferably a compound having a nitroxy radical or a nitroxide group, from the viewpoint of radical species generated in the polarizing film, for example.

As the compound having a nitroxy radical or nitroxide group, from the viewpoint of having a radical that is relatively stable at room temperature and in the air, an N-oxyl compound (a compound having C-N(-C)-O as a functional group (O represents an oxy radical) )), known ones can be used. As an N-oxyl compound, the compound etc. which have the organic group of the following structures are mentioned, for example.

(In 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 represents 0 or 1.) The left side of the dotted line in Formula (1) represents an arbitrary organic group.

As a compound which has the said organic group, the compound etc. represented by the following general formula (2) - (5) are mentioned, for example.

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

(In formula (3), R ¹ to R ⁵ and n have the same definitions as above, and R ⁷ and R ⁸ independently represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, an acyl group, or an aryl group. )

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

(In Formula (5), R ¹ to R ⁵ and n have the same definitions as above, and R ¹² represents a hydrogen atom or 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), from the viewpoint of availability, R ² to R ⁵ are preferably alkyl groups having 1 to 6 carbon atoms, more preferably alkyl groups having 1 to 3 carbon atoms. Further, in the above 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, more preferably a hydrogen atom. Further, in the general formula (3), from the viewpoint of availability, R ⁷ and R ⁸ are independently preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, more preferably a hydrogen atom. 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. Moreover, in the said General formula (5), it is preferable that R< ¹² > is a hydroxyl group, an amino group, or an alkoxy group from a viewpoint of availability. In the general formulas (1) to (5), n is preferably 1 from the viewpoint of availability.

In addition, as the N-oxyl compound, for example, N described in Japanese Patent Laid-Open No. 2003-64022, Japanese Patent Laid-Open No. 11-222462, Japanese Patent Laid-Open No. 2002-284737, International Publication No. 2016/047655, etc. -An oxyl compound is mentioned.

Moreover, as a compound which has the said nitroxy radical or nitroxide group, the following compounds etc. are mentioned, for example.

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

Further, the water-soluble radical scavenger preferably has a molecular weight of 1000 or less, more preferably 500 or less, and even more preferably 300 or less, from the viewpoint of suppressing polyenization of the polarizing film under a high temperature environment.

It is preferable that the content of the water-soluble radical scavenger in the polarizing film is 20% by weight or less. In the polarizing film, the content of the water-soluble radical scavenger is preferably 0.005% by weight or more, more preferably 0.01% by weight or more, still more preferably 0.02% by weight or more, from the viewpoint of suppressing polyenization of the polarizing film in a high-temperature environment. It is preferably less than or equal to weight%, more preferably less than or equal to 12% by weight, and still more preferably less than or equal to 10% by weight.

The polarizing film has the general formula (X): 2.0≤a/b (in the general formula (X), a represents the length (mm) parallel to the absorption axis of the polarizing film and is a value greater than 200, and b is the polarizing film represents the length (mm) orthogonal to the absorption axis) satisfies the condition of the ratio of lengths expressed as The above "parallel" also includes the case of being substantially parallel. Here, “substantially parallel” includes the case of 0°±5.0°, preferably 0°±3.0°, more preferably 0°±1.0°. In addition, the said "orthogonal" also includes the case where it orthogonally crosses substantially. Here, "substantially orthogonal" includes the case of 90°±5.0°, preferably 90°±3.0°, more preferably 90°±1.0°. In addition, the ratio of the lengths of the polarizing films is usually the same as the ratio of the lengths of the polarizing films.

When the a/b is less than 2.0, since the shrinkage force in the MD direction with respect to a certain width decreases, transverse cracks of the polarizing film in a high-temperature environment are less likely to occur. Further, the above a may be 200 (mm) or more from the viewpoint of the image display size of the display in the vehicle interior space, preferably 250 (mm) or more, and may be 2000 (mm) or less from the viewpoint of contraction force, Preferably it may be 1500 (mm) or less. The above a/b is preferably 2.8 or more from the viewpoint of design in the vehicle interior space, and preferably 15 or less from the viewpoint of suppressing transverse cracks, and more preferably 10 or less.

<Method for producing polarizing film>

The method for producing a polarizing film of the present invention is obtained by subjecting the polyvinyl alcohol-based film to an arbitrary swelling step and a washing step, and at least a dyeing step, a crosslinking step, and an stretching step, and the swelling step, the washing step, and the dyeing step , The treatment bath in any one or more treatment steps of the crosslinking step and the stretching step contains a water-soluble radical scavenger. The polarizing film is preferably an iodine-based polarizing film from the viewpoint of initial polarization performance, and the content of the water-soluble radical scavenger and the content of iodine in the polarizing film are determined by a swelling process, a dyeing process, a crosslinking process, a stretching process, and a washing process can be controlled by the concentration of the water-soluble radical scavenger contained in any one of the treatment baths, the concentration of iodine, etc., and the treatment temperature and treatment time of each treatment bath. In particular, when the washing process is performed after the dyeing process, the crosslinking process, and the stretching process, the washing process considers treatment conditions in the dyeing process, crosslinking process, and stretching process, and then, components such as a water-soluble radical scavenger or iodine are added to polyvinyl chloride. It is easy to adjust the content of the water-soluble radical scavenger and the content of the iodine to a desired range from the viewpoint of being eluted from the alcohol-based film or adsorbed on the polyvinyl alcohol-based film.

In addition, each treatment bath in the swelling step, the dyeing step, the crosslinking step, the stretching step, and the washing step may contain additives such as zinc salt, pH adjuster, pH buffering agent, and other salts. 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, etc. are mentioned. As said pH adjuster, strong acids, such as hydrochloric acid, sulfuric acid, and nitric acid, and strong bases, such as sodium hydroxide and potassium hydroxide, are mentioned, for example. Examples of the pH buffering agent include carboxylic acids such as acetic acid, oxalic acid and citric acid and salts thereof, and 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, and salts of alkali metals and alkaline earth metals.

Although the concentration of the compound having the water-soluble radical scavenger included in any one of the treatment baths cannot be determined uniformly because it is affected by the number of treatments, treatment time, treatment temperature, etc., water-soluble radicals are captured in the polarizing film. From the viewpoint of efficiently controlling the content of the agent, it is usually preferably 0.01% by weight or more, more preferably 0.05% by weight or more, still more preferably 0.1% by weight or more, and preferably 30% by weight or less, and 25% by weight It is more preferable that it is % or less, and it is more preferable that it is 20% by weight or less.

The swelling step is a treatment step in which the polyvinyl alcohol-based film is immersed in a swelling bath, and stains and blocking agents on the surface of the polyvinyl alcohol-based film can be removed, and dyeing unevenness can be reduced by swelling the polyvinyl alcohol-based film. can be suppressed The swelling bath usually uses a medium containing water as a main component, such as water, distilled water, or pure water. The swelling bath may be suitably added with a surfactant, an alcohol, or the like 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 still more preferably about 18 to 30°C. In addition, the immersion time in the swelling bath cannot be determined uniformly 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, about 10 to 200 seconds It is more preferable, and it is still more preferable that it is about 20 to 100 seconds. The said swelling process may be performed only once, and may be performed multiple times as needed.

The dyeing process is a treatment process in which the polyvinyl alcohol-based film is immersed in a dyeing bath (iodine solution), and iodine can be adsorbed and oriented on the polyvinyl alcohol-based film. The iodine solution is preferably an aqueous solution of iodine, and contains iodine and iodide as a solubilizing agent. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide and titanium iodide. Among these, potassium iodide is suitable 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 iodide in the dyeing bath is preferably about 0.01 to 20% by weight, more preferably about 0.05 to 10% by weight, and still more preferably about 0.1 to 5% by weight.

The temperature of the dyeing bath is preferably about 10 to 50°C, more preferably about 15 to 45°C, and still more preferably about 18 to 30°C. In addition, the immersion time in the dyeing bath cannot be determined uniformly because the degree of dyeing of the polyvinyl alcohol-based film is affected by the temperature of the dyeing bath, but it is preferably about 10 to 300 seconds, and about 20 to 240 seconds. is more preferable. The said dyeing process may be performed only once, and may be performed multiple times as needed.

The cross-linking step is a treatment step in which the polyvinyl alcohol-based film is immersed in a treatment bath (cross-linking bath) containing a boron compound, and the polyvinyl alcohol-based film is cross-linked by the boron compound to form iodine molecules or dye molecules into the cross-linked structure. can be adsorbed on As said boron compound, boric acid, a borate, borax etc. are mentioned, for example. The crosslinking bath is generally an aqueous solution, but may be, for example, a mixed solution of a water-miscible organic solvent and water. Further, the crosslinking bath may contain potassium iodide from the viewpoint of controlling the potassium content 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. In addition, when potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and about 2 to 5% by weight. is more preferable.

The temperature of the crosslinking bath is preferably about 20 to 70°C, and more preferably about 30 to 60°C. In addition, the immersion time in the crosslinking bath cannot be determined uniformly because the degree of crosslinking of the polyvinyl alcohol-based film is affected by the temperature of the crosslinking bath, but it is preferably about 5 to 300 seconds, and about 10 to 200 seconds. is more preferable. The said crosslinking process may be performed only once, and may be performed multiple times as needed.

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

The treatment bath (stretching bath) in the above wet stretching method may use a solvent such as water or an organic solvent miscible with water and a mixed solution of water. The stretching bath may contain potassium iodide from the viewpoint of controlling the potassium content 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 preferably about 3 to 6% by weight. more preferable In addition, the treatment bath (stretching bath) may contain the boron compound from the viewpoint of suppressing film breakage during stretching, and in this case, the concentration of the boron compound in the stretching bath is preferably about 1 to 15% by weight , It is more preferably about 1.5 to 10% by weight, and 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 still more preferably about 50 to 70°C. The immersion time in the stretching bath cannot be determined uniformly because the degree of stretching of the polyvinyl alcohol-based film is affected by the temperature of the stretching bath, but it is preferably about 10 to 800 seconds, and about 30 to 500 seconds. is more preferable. In addition, the stretching treatment in the wet stretching method may be performed together with any one or more treatment steps of the swelling step, the dyeing step, the crosslinking step, and the washing step.

Examples of the dry stretching method include an inter-roll stretching method, a heated roll stretching method, and a compression stretching method. In addition, you may carry out the said dry stretching method together with the said drying process.

The total draw ratio (cumulative draw ratio) given to the polyvinyl alcohol-based film can be appropriately set depending on the purpose, but it is preferably about 2 to 7 times, more preferably about 3 to 6.8 times, and 3.5 to 3.5 times. It is more preferable that it is about 6.5 times.

The cleaning process is a treatment process in which the polyvinyl alcohol-based film is immersed in a cleaning bath, and foreign substances remaining on the surface of the polyvinyl alcohol-based film and the like can be removed. The washing bath usually uses a medium containing water as a main component, such as water, distilled water, or pure water. In addition, from the viewpoint of controlling the potassium content in the polarizing film, the washing bath may contain potassium iodide. In this case, the concentration of potassium iodide in the washing bath is preferably about 1 to 10% by weight, and 1.5 to 1.5 to 10% by weight. It is more preferably about 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 still more preferably about 15 to 35°C. In addition, the immersion time in the cleaning bath cannot be determined uniformly because the degree of cleaning of the polyvinyl alcohol-based film is affected by the temperature of the cleaning bath, but it is preferably about 1 to 100 seconds, and about 2 to 50 seconds. It is more preferable that it is, and it is still more preferable that it is about 3 to 20 seconds. The said swelling process may be performed only once, and may be performed multiple 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 a polarizing film having a desired moisture content is obtained by drying. The drying is performed by any appropriate method, and examples thereof include natural drying, air drying, and heat drying.

It is preferable that the temperature of the said drying is about 20-150 degreeC, and it is more preferable that it is about 25-100 degreeC. The drying time cannot be determined uniformly because the degree of drying of the polarizing film is affected by the drying temperature, but is preferably about 10 to 600 seconds, and more preferably about 30 to 300 seconds. The said drying process may be performed only once, and may be performed multiple times as needed.

The thickness of the polarizing film is preferably about 1 to 50 μm, more preferably about 1 to 25 μm, and still more preferably about 4 to 20 μm, from the viewpoint of breaking strength and shrinkage force under a high temperature environment. In particular, in order to obtain a polarizing film having a thickness of 8 μm or less, manufacture of the following thin polarizing film using a laminate comprising a polyvinyl alcohol-based resin layer formed on a resin substrate such as a thermoplastic resin as the polyvinyl alcohol-based film. method can be applied.

<Method for producing polarizing film (thin polarizing film)>

A method for producing a polarizing film (thin polarizing film) includes a step of preparing a laminate by forming a polyvinyl alcohol-based resin layer containing a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate; Obtained by subjecting the layered product to any insolubilization treatment step, a crosslinking treatment step, a washing treatment step, and at least an air assisted stretching treatment step, a dyeing treatment step, and an underwater stretching treatment step, while being conveyed in the longitudinal direction, to the above-mentioned laminate, and the insolubilization treatment The treatment bath in any one or more treatment steps among the step, the crosslinking treatment step, the washing treatment step, the dyeing treatment step, and the above-mentioned underwater stretching treatment step contains a water-soluble radical scavenger. The content of the water-soluble radical scavenger and the content of iodine in the polarizing film are determined in each treatment in the insolubilization treatment step, the crosslinking treatment step, the washing treatment step, the dyeing treatment step, and the underwater stretching treatment step. It can be controlled by the concentration of the water-soluble radical scavenger contained in any one of the baths, the concentrations of iodine and potassium iodide, etc., and the treatment temperature and treatment time of each treatment bath. In particular, when the washing treatment step is performed, in the washing treatment step, components such as a water-soluble radical scavenger or iodine are eluted from the polyvinyl alcohol-based film or poly It is easy to adjust the content of the water-soluble radical scavenger and the content of the iodine to a desired range from the viewpoint of adsorption to the vinyl alcohol-based film.

The concentration of the water-soluble radical scavenger included in any one of the treatment baths cannot be uniformly determined because it is affected by the number of treatments, treatment time, treatment temperature, etc. of each treatment. From the viewpoint of efficiently controlling the content of the compound having an oxide group, it is usually preferably 0.01% by weight or more, more preferably 0.05% by weight or more, still more preferably 0.1% by weight or more, and preferably 30% by weight or less. And, it is more preferably 25% by weight or less, and more preferably 20% by weight or less.

<Process of preparing a laminated body>

Any suitable method is adopted as a method of producing the laminate, for example, a method of applying a coating liquid containing the polyvinyl alcohol-based resin (PVA-based resin) to the surface of the thermoplastic resin substrate and drying it. can be heard It is preferable that the thickness of the said thermoplastic resin substrate is about 20-300 micrometers, and it is more preferable that it is about 50-200 micrometers. It is preferable that the thickness of the said PVA system resin layer is about 3-40 micrometers, and it is more preferable that it is about 3-20 micrometers.

The thermoplastic resin substrate has a water absorption of preferably about 0.2% or more, more preferably about 0.3% or more, from the viewpoint of being able to absorb water, greatly reduce stretching stress, and be stretched at a high magnification. On the other hand, the thermoplastic resin substrate preferably has an absorption rate of about 3% or less, and preferably about 1%, from the viewpoint of being able to prevent defects such as significantly lowering the dimensional stability of the thermoplastic resin substrate and deteriorating the appearance of the obtained polarizing film. It is more preferable that it is below. In addition, the said water absorption rate can be adjusted by introduce|transducing a modifier into the constituent material of the said thermoplastic resin base material, for example. The water absorption is a value determined according to JIS K 7209.

The thermoplastic resin substrate preferably has a glass transition temperature (Tg) of about 120° C. or less from the viewpoint of sufficiently securing the stretchability of the laminate while suppressing crystallization of the PVA-based resin layer. Further, considering 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 less, and even more preferably about 90°C or less. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably about 60 ° C. or higher from the viewpoint of preventing defects such as deformation of the thermoplastic resin substrate during application and drying of the coating liquid and producing a good laminate. The glass transition temperature can be adjusted, for example, by introducing a modifier into the constituent material of the thermoplastic resin base material and heating it using a crystallization material. The glass transition temperature (Tg) is a value determined according to JIS K 7121.

Any appropriate thermoplastic resin may be employed as a constituent material of the thermoplastic resin substrate. 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 the like. Copolymer resin etc. are mentioned. Among these, norbornene-based resins and amorphous (amorphous) polyethylene terephthalate-based resins are preferable, and thermoplastic resin substrates have very excellent stretchability and from the viewpoint that crystallization during stretching can be suppressed, amorphous ( Amorphous) A polyethylene terephthalate-based resin is preferably used. As the amorphous (amorphous) polyethylene terephthalate-based resin, a copolymer containing isophthalic acid and/or cyclohexane dicarboxylic acid as dicarboxylic acid, or a copolymer containing cyclohexanedimethanol or diethylene glycol as glycol can be heard

The thermoplastic resin substrate may be subjected to surface treatment (for example, corona treatment) before forming the PVA-based resin layer, or an easily bonding layer may be formed on the thermoplastic resin substrate. By performing such a process, the adhesiveness of a thermoplastic resin base material and a PVA system resin layer can be improved. In addition, 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. , and water is preferred. These can be used individually or in combination of 2 or more types. The concentration of the PVA-based resin in 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 adhered to the thermoplastic resin substrate.

It is preferable that a halide is blended in the coating liquid from the viewpoint of improving orientation of polyvinyl alcohol molecules by stretching. Arbitrary appropriate halides can be employed as the halide, and examples thereof include iodide and sodium chloride. As said iodide, potassium iodide, sodium iodide, lithium iodide etc. are mentioned, for example, 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.

Moreover, you may mix|blend additives with the said coating liquid. Examples of the additive include plasticizers such as ethylene glycol and glycerin; Surfactants, such as a nonionic surfactant, etc. are mentioned.

Any suitable method can be employed as the coating method for the coating solution, and examples include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating. A coat method (comma coat method etc.) etc. are mentioned. In addition, it is preferable that the drying temperature of the said coating liquid is about 50 degreeC or more.

<Air Assisted Stretching Process>

In the air assisted stretching treatment step, since the thermoplastic resin substrate can be stretched while suppressing crystallization, the laminate can be stretched at a high magnification. The stretching method in the air assisted stretching treatment step may be fixed end stretching (for example, stretching using a tenter stretching machine), or free end stretching (for example, by passing the laminate between rolls having different circumferential speeds, A method of axial stretching) may be used, but free end stretching is preferable from the viewpoint of obtaining high optical properties.

It is preferable that the draw ratio in the above air assisted stretching treatment step is about 2 to 3.5 times. The air assisted stretching treatment may be performed in one step or may be performed in multiple steps. When performing in multiple steps, the draw ratio is the product of the draw ratios of each step.

The stretching temperature in the air-assisted stretching treatment step can be set to any suitable value depending on the material for forming the thermoplastic resin substrate, the stretching method, etc., for example, the glass transition temperature (Tg) of the thermoplastic resin substrate. Preferably, It is more preferable that the glass transition temperature (Tg) + 10 ℃ or more, and it is more preferable that the glass transition temperature (Tg) + 15 ℃ or more. On the other hand, the upper limit of the stretching temperature is 170° C. from the viewpoint of suppressing rapid crystallization of the PVA-based resin and suppressing defects due to crystallization (for example, obstruction of orientation of the PVA-based resin layer by stretching). It is preferable that it is about °C.

<Insolubilization treatment process>

If necessary, you may perform an insolubilization treatment process after the above-mentioned air assisted stretching treatment process and before a dyeing treatment process or an underwater stretching treatment process. The said insolubilization treatment process is typically performed by immersing a PVA system resin layer in boric acid aqueous solution. By performing the insolubilization treatment process, water resistance can be imparted to the PVA-based resin layer, and orientation degradation of PVA when immersed in water can be prevented. The concentration of the aqueous solution of boric acid is preferably about 1 to 5 parts by weight based on 100 parts by weight of water. The liquid temperature of the insolubilization treatment bath is preferably about 20 to 50°C.

<Dyeing process>

The dyeing treatment step is performed by dyeing the PVA-based resin layer with iodine. As the adsorption method, for example, a method of immersing a PVA-based resin layer (laminate) in a dye containing iodine, a method of applying the dye solution to a PVA-based resin layer, and a method of applying the dye solution to a PVA-based resin layer. The method of spraying etc. is mentioned, The method of immersing a PVA system resin layer (laminate) in the staining 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 blend the iodide in an aqueous solution of iodine. 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 dissolution of the PVA-based resin. Moreover, it is preferable that it is about 5 second - 5 minutes, and, as for immersion time, it is more preferable that it is about 30 second - 90 second from a viewpoint of ensuring the transmittance|permeability of a PVA system resin layer. From the viewpoint of obtaining a polarizing film having good optical properties, the ratio of iodine and iodide in the iodine aqueous solution is preferably about 1:5 to 1:20, and more preferably about 1:5 to 1:10.

<Crosslinking process>

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

<Underwater stretching treatment process>

The underwater stretching treatment step is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment step, stretching can be performed at a temperature lower than the glass transition temperature (typically about 80° C.) of the thermoplastic resin substrate or the PVA-based resin layer, and the PVA-based resin layer is stretched at a high magnification while suppressing its crystallization. can do. The stretching method in the underwater stretching treatment step may be fixed end stretching (for example, stretching using a tenter stretching machine), or free end stretching (for example, uniaxially by passing the laminate between rolls having different circumferential speeds). Stretching method) may be used, but free end stretching is preferable from the viewpoint of obtaining high optical properties.

It is preferable to perform the said underwater extending|stretching process by immersing a layered product in boric acid aqueous solution (boric acid underwater extending|stretching). By using a boric acid aqueous solution as a stretching bath, rigidity that can withstand the tension applied during stretching and water resistance that does not dissolve in water can be imparted to the PVA-based resin layer. The concentration of boric acid in the aqueous solution of boric acid is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, based on 100 parts by weight of water. In addition, iodide may be blended into the stretching bath (boric acid aqueous solution). The liquid temperature of the stretching bath is preferably about 40 to 85°C, and more preferably about 60 to 75°C. It is preferable that the immersion time of the laminated body in the stretching bath is about 15 seconds to 5 minutes.

It is preferable that it is about 1.5 times or more, and, as for the draw ratio in the said underwater stretching treatment process, it is more preferable that it is about 3 times or more.

In addition, the total draw ratio of the laminate is preferably about 5 times or more, and more preferably about 5.5 times or more with respect to the original length of the laminate.

<Cleaning treatment process>

It is preferable to perform a washing treatment process after the above-mentioned underwater stretching treatment process. The washing treatment step is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide.

In addition, additives such as zinc salt, pH adjuster, pH buffer, and other salts are added to each treatment bath in the dyeing treatment step, the underwater stretching treatment step, the insolubilization treatment step, the crosslinking treatment step, and the washing treatment step. It may contain. 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, etc. are mentioned. As said pH adjuster, strong acids, such as hydrochloric acid, sulfuric acid, and nitric acid, and strong bases, such as sodium hydroxide and potassium hydroxide, are mentioned, for example. Examples of the pH buffering agent include carboxylic acids such as acetic acid, oxalic acid and citric acid and salts thereof, and 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, and salts of alkali metals and alkaline earth metals.

<Transparent protective 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 having excellent transparency, mechanical strength, thermal stability, water barrier properties, 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 the like. Polyamide-based resins such as aromatic polyamides, polyimide-based resins, polyolefin-based resins such as polyethylene, polypropylene, and ethylene-propylene copolymers, (meth)acrylic-based resins, and cyclo- or cyclic polyolefin-based resins having a norbornene structure. (norbornene-based resins), polyarylate-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, and mixtures thereof. In addition, the transparent protective film may use a cured layer formed of a thermosetting resin or an ultraviolet curable resin such as (meth)acrylic, urethane, acrylurethane, epoxy, or silicone. Among these, cellulose ester-type resin, polycarbonate-type resin, (meth)acrylic-type resin, cyclic polyolefin-type resin, and polyester-type resin are suitable.

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

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

The transparent protective film may use a retardation plate having a front retardation of 40 nm or more and/or a thickness direction retardation of 80 nm or more. The frontal retardation is usually controlled in the range of 40 to 200 nm, and the thickness direction retardation is usually controlled in the range of 80 to 300 nm. In the case of using a retardation plate as the transparent protective film, since the retardation plate also functions as a transparent protective film, thinning can be achieved.

Examples of the retardation plate include a birefringent film obtained by uniaxially or biaxially stretching a polymeric material, an orientation film of liquid crystal polymer, and one in which an orientation layer of 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. Alternatively, the phase plate may be bonded to a transparent protective film having no retardation before use.

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

A functional layer such as a hard coat layer, an antireflection layer, an antisticking layer, a diffusion layer, or an antiglare layer may be formed on the surface of the transparent protective film to which the polarizing film is not bonded. In addition, functional layers such as the hard coat layer, antireflection layer, antisticking layer, diffusion layer, and antiglare layer may be formed on the protective film itself or separately from the protective film.

The polarizing film and the transparent protective film or the polarizing film and the functional layer are usually bonded through a pressure-sensitive 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. For example, rubber-based pressure-sensitive adhesives, acrylic pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, urethane-based pressure-sensitive adhesives, vinylalkyl ether-based pressure-sensitive adhesives, polyvinyl alcohol-based pressure-sensitive adhesives, polyvinyl A polylidone-type adhesive, a polyacrylamide-type adhesive, a cellulose-type adhesive, etc. are mentioned. Among these, an acrylic adhesive is suitable.

As a method of forming the pressure-sensitive adhesive layer, for example, a method of applying the above-mentioned pressure-sensitive adhesive to a separator or the like subjected to peeling treatment and drying to form a pressure-sensitive adhesive layer, followed by transferring the pressure-sensitive adhesive to a polarizing film or the like, or applying the above-mentioned pressure-sensitive adhesive to a polarizing film or the like and drying to form the pressure-sensitive adhesive layer. A method of formation and the like can be exemplified. The thickness of the pressure-sensitive adhesive layer is not particularly limited, and is, for example, about 1 to 100 μm, preferably about 2 to 50 μm.

As the adhesive forming the adhesive layer, various adhesives used in polarizing films can be applied, and examples thereof include isocyanate-based adhesives, polyvinyl alcohol-based adhesives, gelatin-based adhesives, vinyl-based latex-based adhesives, and water-based polyesters. have. These adhesives are usually used as adhesives made of an aqueous solution (water-based adhesives) and contain 0.5 to 60% by weight of solid content. Among these, polyvinyl alcohol-based adhesives are preferable, and polyvinyl alcohol-based adhesives containing an acetacetyl group are more preferable.

The water-based adhesive may contain a crosslinking agent. As the crosslinking agent, a compound having at least two functional groups in one molecule having reactivity with components such as polymers constituting the adhesive is usually used, and examples thereof include alkylenediamines; isocyanates; epoxies; aldehydes; and amino-formaldehyde such as methylol urea and methylol melamine. The compounding amount of the crosslinking agent in the adhesive is usually about 10 to 60 parts by weight based on 100 parts by weight of components such as polymer constituting the adhesive.

In addition to the above, examples of the adhesive include 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-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 such as chain alkyl (meth)acrylates having 1 to 20 carbon atoms, alicyclic alkyl (meth)acrylates, and polycyclic alkyl (meth)acrylates. ) acrylate; hydroxyl group-containing (meth)acrylate; Epoxy group-containing (meth)acrylates, such as glycidyl (meth)acrylate, etc. are mentioned. (Meth) acrylate-based adhesives include hydroxyethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, ( A nitrogen-containing monomer such as meth)acrylamide and (meth)acryloylmorpholine may be included. (Meth)acrylate-based adhesives include tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, cyclic trimethylolpropane formal acrylate, and dioxane glycol diacrylate as crosslinking components. You may contain polyfunctional monomers, such as an acrylate and EO modified|denatured diglycerol tetraacrylate. Moreover, 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 suitable additives as needed. Examples of the additives include coupling agents such as silane coupling agents and titanium coupling agents, adhesion promoters such as ethylene oxide, ultraviolet absorbers, deterioration inhibitors, dyes, processing aids, ion trapping agents, antioxidants, tackifiers, and fillers. , plasticizers, leveling agents, foam inhibitors, antistatic agents, heat-resistant stabilizers, hydrolysis-resistant stabilizers and the like.

The adhesive may be applied to either the transparent protective film side (or the functional layer side) or the polarizing film side, or both. After bonding, a drying process is performed, and an adhesive layer composed of a coating and drying layer is formed. After the drying process, ultraviolet rays or electron beams may be irradiated as needed. 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 when an ultraviolet curable adhesive, an electron beam curable adhesive, or the like is used, it is 0.1 nm. It is preferably about 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 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 easily adhesive forming the easily adhesive layer include various resins having a polyester skeleton, a polyether skeleton, a polycarbonate skeleton, a polyurethane skeleton, a silicone base, a polyamide skeleton, a polyimide skeleton, a polyvinyl alcohol skeleton, and the like. A forming material to be used may be mentioned. The easily adhesive layer is usually formed on a protective film in advance, and the easily adhesive layer side of the protective film and the polarizing film are laminated with the pressure-sensitive 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 or the like from migrating (invading) into the polarizing film. The block layer may be a layer that has transparency and can prevent impurities eluted from a transparent protective film or the like. As a material forming the block layer, for example, a urethane prepolymer-based forming material or a cyanoacrylate-based forming material , epoxy-based forming materials, and the like.

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

<Laminate polarizing film>

In the laminated polarizing film (optical laminate) of the present invention, the polarizing film is bonded to the optical layer. The optical layer is not particularly limited, but is used for forming, for example, a liquid crystal display device such as a reflector, a transflective plate, a retardation plate (including a 1/2 or 1/4 wave plate), and a viewing angle compensation film. One layer or two 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 further laminating a reflector or a transflective reflector on the polarizing film, an elliptically polarizing film or a circular polarizing film obtained by further laminating a retardation plate on the polarizing film, and the polarizing film. A wide viewing angle polarizing film formed by further laminating a visual compensation film on the film, or a polarizing film formed by further laminating a brightness enhancing film on the polarizing film.

On one 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 other members such as a front transparent member such as a front transparent plate or a touch panel on the viewing side. An adhesive layer for bonding may be provided. 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, an acrylic polymer, a silicone-based polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymers are appropriately selected as base polymers, and can be used In particular, those having excellent optical transparency, exhibiting moderate hygroscopicity, cohesiveness, and adhesiveness, and having excellent weatherability, heat resistance, and the like are preferably used, such as a pressure-sensitive adhesive containing an acrylic polymer.

A pressure-sensitive adhesive layer may be applied to one side or both sides of the polarizing film or the laminated polarizing film by an appropriate method. As the application of the pressure-sensitive adhesive layer, for example, a pressure-sensitive adhesive solution is prepared and applied directly on the polarizing film or the laminated polarizing film by an appropriate spreading method such as a casting method or a coating method, or a method of forming an adhesive layer on a separator and a method of transferring it onto the polarizing film or the laminated polarizing film. The thickness of the pressure-sensitive adhesive layer can be appropriately determined depending on the purpose of use or adhesive strength, and is generally 1 to 500 μm, preferably 5 to 200 μm, and more preferably 10 to 100 μm. In this way, a polarizing film with a pressure-sensitive adhesive layer or a laminated polarizing film with a pressure-sensitive adhesive layer is referred to as a polarizing film with an adhesive layer or a laminated polarizing film with a pressure-sensitive adhesive layer.

It is preferable to cover the exposed surface of the pressure-sensitive adhesive layer by temporarily attaching a separator for the purpose of preventing contamination or the like until it is put into practical use. Thereby, contamination of the adhesive layer or the like can be prevented in the usual handling condition. As the separator, for example, a plastic film, rubber sheet, paper, cloth, nonwoven fabric, net, foam sheet, metal foil, or a laminate thereof, etc., may be selected as necessary. What was coated with a suitable release agent, etc. 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 bonded to an image display cell. Furthermore, the image display device of the present invention is provided with a front transparent member on the polarizing film or laminated polarizing film side (visible side) of the image display panel.

As said image display cell, a liquid crystal cell, an organic electroluminescent cell, etc. are mentioned, for example. As the liquid crystal cell, for example, a reflection type liquid crystal cell using external light, a transmissive liquid crystal cell using light from a light source such as a backlight, or a transflective liquid crystal cell using both external light and light from a light source. You may use it. When the liquid crystal cell uses light from a light source, the image display device (liquid crystal display device) has a polarizing film disposed on the side opposite to the viewing side of the image display cell (liquid crystal cell), and a light source is further disposed. It is preferable that the polarizing film and the liquid crystal cell on the side of the light source are bonded through an appropriate adhesive layer. As the driving method of the liquid crystal cell, any type such as VA mode, IPS mode, TN mode, STN mode, or bend alignment (π type) can be used, for example.

As the organic EL cell, for example, a light emitting body (organic electroluminescent light emitting body) formed by sequentially laminating a transparent electrode, an organic light emitting layer, and a metal electrode on a transparent substrate 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 and the like and a light-emitting layer made of a fluorescent organic solid such as anthracene, or an electronic light-emitting layer made of these light-emitting layers and a perylene derivative. Various layer configurations can be employed, such as a laminate of an injection layer or a laminate of a hole injection layer, a light emitting layer, and an electron injection layer.

As a front transparent member arranged on the viewer side of the said image display cell, a front transparent board (window layer), a touch panel, etc. are mentioned, for example. As the front transparent plate, a transparent plate having appropriate mechanical strength and thickness is used. As such a transparent plate, a transparent resin plate such as an acrylic resin or a polycarbonate resin, a glass plate, or the like is used, for example. As said touch panel, various touch panels, such as a resistive film method, a capacitance method, an optical method, and an ultrasonic method, a glass plate, a transparent resin board, etc. provided with a touch sensor function are used, for example. When a capacitance type 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 formed further on the viewing side than the touch panel.

Example

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

<Example 1>

<Production 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 45 µm was prepared. The polyvinyl alcohol film is immersed for 30 seconds in a swelling bath (water bath) at 20 ° C. between rolls with different peripheral speed ratios, and stretched 2.2 times in the conveying direction while swelling (swelling step), followed by a dyeing bath (100 parts by weight of water) at 30 ° C. Iodine solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7) in the original polyvinyl alcohol film ( It was stretched 3.3 times in the conveying direction on the basis of a polyvinyl alcohol film not stretched in the conveying direction at all) (dyeing step). Next, the dyed polyvinyl alcohol film was immersed for 28 seconds in a crosslinking bath (boric acid concentration of 3.5% by weight, potassium iodide concentration of 3.0% by weight, and zinc sulfate concentration of 3.6% by weight) at 40 ° C. to recover the original polyvinyl alcohol. Based on the film, it was stretched up to 3.6 times in the transport direction (crosslinking step). Further, the obtained polyvinyl alcohol film was immersed for 60 seconds in a stretching bath (boric acid concentration of 4.5% by weight, potassium iodide concentration of 5.0% by weight, and zinc sulfate concentration of 5.0% by weight) at 64 ° C. for 60 seconds to prepare the original polyvinyl alcohol film. After stretching up to 6.0 times in the transport direction as a guide (stretching step), a washing bath at 27 ° C. (potassium iodide concentration is 2.3% by weight, the concentration of the compound represented by the following general formula (9) as a water-soluble radical scavenger is 1.0 % by weight aqueous solution) for 10 seconds (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 determined by the following measuring method. The content of the compound represented by the following general formula (9) in the polarizing film was 0.3% by weight, and the thickness of the polarizing film was 18 µm. In addition, the compound represented by the following general formula (9) is a compound that dissolves 1 part by weight or more with respect to 100 parts by weight of water at 25°C.

[Method for measuring iodine concentration (% by weight) in polarizing film]

For the polarizing film, the iodine concentration (% by weight) was determined using a fluorescence X-ray analyzer (manufactured by Rigaku Corporation, trade name "ZSX Primus IV", measuring diameter: φ20 mm) using the following formula.

Iodine concentration (% by weight) = 14.474 × (fluorescence X-ray intensity) / (film thickness) (kcps / μm)

In addition, the coefficient for calculating the concentration varies depending on the measuring device, but the coefficient can be obtained using an appropriate calibration curve.

[Measurement method of content (wt%) of water-soluble radical scavenger 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, and the resulting extract was filtered through a membrane filter, and the filtrate was HPLC (manufactured by Waters Corporation, ACQUITY UPLC H-class Bio). The concentration of the water-soluble radical scavenger was measured using

<Production of polarizing film>

As an adhesive, an aqueous solution containing a polyvinyl alcohol resin containing an acetacetyl group (average degree of polymerization: 1,200, degree of saponification: 98.5% by mole, degree of acetoacetylation: 5% by mole) and methylolmelamine at a weight ratio of 3:1 was used. Using this adhesive, a transparent protective film (NIPPON SHOKUBAI CO., LTD., LTD. product, with a water vapor permeability of 125 g/(m² 24 h)), and a triacetyl cellulose film (manufactured by FUJIFILM Corporation, trade name "TJ40UL") on the other side (visible side) with HC formed thereon, and a transparent protection with a thickness of 49 μm. After bonding the film (water vapor transmission rate of 300g/(m2 24h)) with a roll bonding machine, it is then heated and dried in an oven (temperature: 90°C, time: 10 minutes) to form a transparent protective film bonded to both sides of the polarizing film. A polarizing film was produced.

<Preparation of acrylic adhesive>

A monomer mixture containing 99 parts of butyl acrylate and 1 part of 4-hydroxybutyl acrylate was charged into a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser. In addition, 0.1 part of 2,2'-azobisisobutyronitrile as a polymerization initiator with respect to 100 parts of the monomer mixture (solid content) was added together with 100 parts of ethyl acetate, and nitrogen gas was introduced while stirring slowly to replace nitrogen, The liquid temperature in the flask was maintained at around 55°C, polymerization was carried out for 8 hours, and a solution of an acrylic polymer having a weight average molecular weight (Mw) of 1,800,000 was prepared. Thereafter, 0.02 part of an isocyanate crosslinking agent (manufactured by Tosoh Corporation, trade name "TAKENET D110N", trimethylolpropane/xylylene diisocyanate adduct), a silane coupling agent (Shin-Etsu Chemical Co., Ltd. product, brand name "X-41-1056") 0.2 part was mix|blended, and the solution of the acrylic adhesive composition was prepared. Next, the solution of the acrylic pressure-sensitive adhesive composition obtained above was applied to one side of a polyethylene terephthalate film (manufactured by Mitsubishi Chemical Polyester Film Corporation, trade name "MRF38", separator film) treated with a silicone-based release agent, and the thickness of the pressure-sensitive adhesive layer after drying was 20 μm. It was applied as much as possible, and dried at 90°C for 1 minute to form an adhesive layer on the surface of the separator film. Next, the adhesive layer formed on the separator film was transferred to one surface of the polarizing film produced above, and a polarizing film having an adhesive layer was produced.

[Evaluation of single transmittance change in high temperature environment]

The polarizing film with a pressure-sensitive adhesive layer obtained above was cut into a size of 300 × 100 mm so that the absorption axis of the polarizing film was the long side, and a glass plate (simulated image display cell) was bonded through the pressure-sensitive adhesive layer, followed by an auto temperature of 50°C and 0.5 MPa for 15 minutes. The clave process was carried out to produce a sample of the laminated body. The obtained layered product was left still in a hot air oven at a temperature of 105°C for 1000 hours, and the single transmittance (ΔTs) before and after injection (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. In addition, the measurement wavelength is 380 to 700 nm (every 5 nm). The results are shown in Table 1.

ΔTs(%) = Ts ₁₀₀₀ -Ts ₀

Here, Ts ₀ is the single transmittance of the laminate before heating, and Ts ₁₀₀₀ is the single transmittance of the laminate after heating for 1000 hours.

The ΔTs(%) is preferably 5≥ΔTs(%)≥0, and more preferably 3≥ΔTs(%)≥0.

[Evaluation of generation of transverse cracks in a direction parallel to the absorption axis of the polarizing film in a high temperature environment]

After the sample of the laminate was left still in a hot air oven at a temperature of 105 ° C. for 1000 hours, it was taken out of a clean room set at a temperature of 23 ° C. and a relative humidity of 55%. .

○: There is no generation of transverse cracks in a direction parallel to the absorption axis of the polarizing film.

×: Transverse cracks occurred in a direction parallel to the absorption axis of the polarizing film.

<Example 2>

A laminate was produced in the same manner as in Example 1 except that the polarizing film with an adhesive layer was cut into a size of 850 x 300 mm so that the absorption axis of the polarizing film was the long side, and a glass plate (simulated image display cell) was bonded through the adhesive layer. did.

<Example 3>

A laminate was produced in the same manner as in Example 1 except that the polarizing film with an adhesive layer was cut into a size of 440 × 115 mm so that the absorption axis of the polarizing film was the long side, and a glass plate (simulated image display cell) was bonded through the adhesive layer. did.

<Example 4>

In preparation of the polarizing film, a polyvinyl alcohol film having a thickness of 30 μm was prepared, and a laminate was produced in the same manner as in Example 1 except that the iodine concentration of the finally obtained polarizing film was 4.2% by weight. The content of the compound represented by the general formula (9) in the polarizing film was 0.3% by weight, and the thickness of the polarizing film was 12 µm.

<Example 5>

A laminate was produced in the same manner as in Example 1 except that the polarizing film with an adhesive layer was cut into a size of 680 x 80 mm so that the absorption axis of the polarizing film was the long side, and a glass plate (simulated image display cell) was bonded through the adhesive layer. did.

<Example 6>

A laminate was produced in the same manner as in Example 4 except that the polarizing film with an adhesive layer was cut into a size of 1260 × 300 mm so that the absorption axis of the polarizing film was the long side, and a glass plate (simulated image display cell) was bonded through the adhesive layer. did.

<Example 7>

In the production of the polarizing film, a polyvinyl alcohol film having a thickness of 20 μm was prepared, and the iodine concentration of the finally obtained polarizing film was 5.4% by weight, and in the cleaning step, a washing bath at 18 ° C. (potassium iodide concentration of 3.6% by weight) %, an aqueous solution having a concentration of 1.0% by weight of a compound represented by the following general formula (9) as a water-soluble radical scavenger). The content of the compound represented by the general formula (9) in the polarizing film was 0.3% by weight, and the thickness of the polarizing film was 7 µm.

<Comparative Example 1>

In preparation of the polarizing film, a laminate was produced in the same manner as in Example 1, except that the above formula (9) was not added as a water-soluble radical scavenger to the cleaning bath.

<Comparative Example 2>

In the production of the polarizing film, a laminate was produced in the same manner as in Example 2, except that the above formula (9) was not added as a water-soluble radical scavenger to the cleaning bath.

Said evaluation was performed using the laminated body of the Example and the comparative example obtained above. The results are shown in Table 1.

Claims (6)

A polarizing film in which a transparent protective film is bonded to one side or both sides of a polarizing film,
The polarizing film includes a water-soluble radical scavenger, and
Formula (X): 2.0≤a/b
[In formula (X), a represents the length (mm) parallel to the absorption axis of the polarizing film and is a value greater than 200, and b represents the length (mm) orthogonal to the absorption axis of the polarizing film.] A polarizing film characterized in that it satisfies the condition of the ratio of lengths represented by . According to claim 1,
The polarizing film, characterized in that the thickness of the polarizing film is 4 ~ 20㎛. According to claim 1 or 2,
The polarizing film, characterized in that the water-soluble radical scavenger is a compound having a nitroxy radical or a nitroxide group. A laminated polarizing film characterized in that the polarizing film according to any one of claims 1 to 3 is bonded to an optical layer. An image display panel characterized in that the polarizing film according to any one of claims 1 to 3 or the laminated polarizing film according to claim 4 is bonded to an image display cell. An image display device comprising a front transparent member on the side of the polarizing film or laminated polarizing film of the image display panel according to claim 5.