CN112041715B - Method for producing polarizing material, method for producing polarizing film, method for producing laminated polarizing film, method for producing image display panel, and method for producing image display device - Google Patents

Abstract

A method for manufacturing a polarizer, characterized in that it is a method for manufacturing a polarizer obtained by performing a drying process on a polyvinyl alcohol film after performing at least a dyeing process, a crosslinking process and a stretching process, at least one treatment bath contains zinc ions, and the drying process is a process for manufacturing a polarizer with a thickness of less than 20 μm and a moisture content of more than 13 wt % and less than 19 wt % by conveying the polyvinyl alcohol film containing zinc using multiple rollers while drying it, and the multiple rollers include one or more third rollers arranged between a first roller arranged on the most upstream side and a second roller arranged on the most downstream side, and among the one or more third rollers, at least one of the rollers has an angle of less than 90° with the polyvinyl alcohol film. The manufacturing method can obtain a thin polarizer with reduced appearance abnormality (polarization unevenness) and breakage occurring in the drying process and heat durability.

Description

Method for manufacturing polarizing element, method for manufacturing polarizing film, method for manufacturing laminated polarizing film, method for manufacturing image display panel, and method for manufacturing image display device

Technical Field

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

Background Art

In the past, as polarizers used in various image display devices such as liquid crystal display devices and organic EL display devices, polyvinyl alcohol-based films that have been dyed (containing dichroic substances) have been used from the perspective of having both high transmittance and high polarization degree. The polarizer is manufactured by subjecting the polyvinyl alcohol-based film to various treatments such as dyeing, crosslinking, and stretching in a bath and then drying it. In addition, the aforementioned polarizer is usually used in the form of a polarizing film (polarizing plate) obtained by bonding a protective film such as triacetyl cellulose to one or both sides thereof using an adhesive.

The aforementioned polarizing film is laminated with other optical layers as needed and used in the form of a laminated polarizing film (optical laminate). The aforementioned polarizing film or the aforementioned laminated polarizing film (optical laminate) is bonded between an image display unit such as a liquid crystal unit, an organic EL element, and a transparent plate such as a front panel on the visual recognition side and a touch panel with the aid of an adhesive layer, thereby being used as the various image display devices mentioned above.

On the other hand, polarizers are known to contain zinc from the viewpoint of improving heat durability, etc. (Patent Documents 1 to 6). Also, it is known that in a drying step of producing a polarizer, a polyvinyl alcohol-based film is dried while being conveyed by a plurality of rollers to obtain a polarizer (Patent Documents 7 to 10).

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Publication No. 2009-42457

Patent Document 2: Japanese Patent Application Publication No. 2009-42455

Patent Document 3: Japanese Patent Application Publication No. 2006-317747

Patent Document 4: Japanese Patent Application Publication No. 2006-47978

Patent Document 5: Japanese Patent Application Publication No. 2004-61565

Patent Document 6: Japanese Patent Application Publication No. 2003-270439

Patent Document 7: Japanese Patent Application Publication No. 2014-199284

Patent Document 8: Japanese Patent Application Publication No. 2012-47799

Patent Document 9: Japanese Patent Application Publication No. 2012-14001

Patent Document 10: Japanese Patent Application Publication No. 2009-163202

Summary of the invention

Problem that the invention aims to solve

In recent years, with the expansion of the use of various image display devices such as those mentioned above (mobile devices such as mobile phones and tablet terminals, car navigation devices, vehicle-mounted image display devices such as back-monitors, etc.), the polarizing films used are required to be of higher quality and higher performance, and in particular, thin polarizers with heat durability are urgently desired.

On the other hand, the polarizer obtained by the manufacturing method disclosed in the above patent document has good optical properties. However, it is known that when a thin polarizer containing zinc is manufactured by the manufacturing method of the polarizer disclosed in the above patent document, there are the following problems: the obtained polarizer has an abnormal appearance (polarization unevenness) on its surface during the drying process, or the polarizer does not have sufficient heating durability despite containing zinc.

In view of the above circumstances, an object of the present invention is to provide a method for producing a polarizer that can obtain a thin polarizer having heat durability while suppressing appearance abnormality (polarization unevenness) and breakage that occur during a drying process.

Solutions for solving problems

That is, the present invention relates to a method for manufacturing a polarizer, characterized in that it is a method for manufacturing a polarizer obtained by performing a drying step on a polyvinyl alcohol film after performing at least a dyeing step, a crosslinking step and a stretching step, wherein a treatment bath of at least one of the dyeing step, the crosslinking step and the stretching step contains zinc ions, and the drying step is a step of drying a polyvinyl alcohol film containing zinc while conveying it using a plurality of rollers, thereby manufacturing a polarizer with a thickness of less than 20 μm and a moisture content of not less than 13 wt % and not more than 19 wt %, and the plurality of rollers include: a first roller arranged on the upstream side of the conveying direction of the polyvinyl alcohol film, a second roller arranged on the downstream side of the conveying direction of the polyvinyl alcohol film, and one or more third rollers arranged between the first roller and the second roller, and among the one or more third rollers, at least one of the rollers has an embrace angle of less than 90° with the polyvinyl alcohol film.

The present invention also relates to a method for producing a polarizing film, comprising the step of bonding a transparent protective film to at least one surface of a polarizer obtained by the method for producing a polarizer through an adhesive layer.

The present invention also relates to a method for producing a laminated polarizing film, characterized in that it includes a step of laminating an optical layer to a polarizing film obtained by the method for producing a polarizing film.

In addition, the present invention relates to a method for manufacturing an image display panel, characterized in that it includes: a step of bonding a polarizing film obtained by the aforementioned method for manufacturing a polarizing film, or a laminated polarizing film obtained by the aforementioned method for manufacturing a laminated polarizing film, to an image display unit.

Furthermore, the present invention relates to a method for manufacturing an image display device, characterized in that it includes a step of providing a transparent plate on the polarizing film or laminated polarizing film side of the image display panel obtained by the above-mentioned method for manufacturing an image display panel.

Effects of the Invention

The detailed mechanism of action of the effect of the method for producing a polarizer of the present invention is still unclear, but can be inferred as follows. However, the present invention should not be construed in a limiting sense based on this mechanism of action.

The manufacturing method of the polarizer of the present invention is a manufacturing method of the polarizer obtained by performing a drying process after performing a dyeing process, a crosslinking process and a stretching process on a polyvinyl alcohol film, wherein the treatment bath of at least one of the dyeing process, the crosslinking process and the stretching process contains zinc ions, and the drying process is a process of drying the polyvinyl alcohol film containing zinc while conveying it with multiple rollers, thereby manufacturing a polarizer with a thickness of less than 20 μm and a moisture content of more than 13 wt % and less than 19 wt %, wherein the multiple rollers include: a first roller arranged on the most upstream side of the conveying direction of the polyvinyl alcohol film, a second roller arranged on the most downstream side of the conveying direction of the polyvinyl alcohol film, and one or more third rollers arranged between the first roller and the second roller, and among the one or more third rollers, at least one of the rollers has an embrace angle of less than 90° with the polyvinyl alcohol film. The present invention can suppress the appearance abnormality (polarization unevenness) occurring in the drying process by adjusting the moisture content of the obtained thin polarizer to the above-mentioned value in the drying process, and can improve the heating durability of the thin polarizer.

It can be inferred that the reason is that the polarizer containing a certain moisture content or more is softer than the polarizer with a low moisture content, and therefore, the appearance abnormality (polarization unevenness) caused by the surface deformation of the polarizer caused by the zinc precipitated on the surface of the polyvinyl alcohol film being crushed by the roller (rolling) during the drying process can be suppressed. And it is inferred that: the above-mentioned polarizer containing a moisture content below a certain value can suppress the deterioration of the polarizer caused by the moisture in the polarizer based on the heat resistance test due to the small total moisture content in the polarizer, so it has heating durability. In particular, when a protective film with low moisture permeability is used as a protective film in the polarizing film, it is difficult for the moisture in the polarizer to penetrate to the outside, and therefore, the polarizer of the present invention is useful for such a scheme.

Furthermore, the present invention is characterized in that the contact time between the polyvinyl alcohol film and the roller (conveying roller) is reduced in a manner that can suppress the above-mentioned appearance abnormality (polarization unevenness) by avoiding the influence of the roller pressure as much as possible, and the above-mentioned appearance abnormality (polarization unevenness) is suppressed, and the hug angle between the roller and the polyvinyl alcohol film is adjusted to be below a certain level. In particular, it can be inferred that the above-mentioned appearance abnormality (polarization unevenness) can be suppressed by adjusting the hug angle between the third roller and the polyvinyl alcohol film to be below a certain level during the drying of the polarizer. It should be noted that the first roller and the second roller are rollers just after drying and before drying is about to end, and it can be inferred that the hug angle during the drying operation (processing) has little effect on the roller pressure.

It is further inferred that the third roller is provided in the drying step to prevent the distance between adjacent rollers (idle distance) from being too long, thereby reducing the deflection of the polyvinyl alcohol film during transportation and thereby suppressing the occurrence of breakage of the polarizer.

Furthermore, it can be inferred that the present invention can reduce the contact time between the polyvinyl alcohol film and the roller (conveying roller) by adjusting the ratio of the contact distance of the zinc-containing polyvinyl alcohol film relative to the third roller to the total conveying distance of the zinc-containing polyvinyl alcohol film (contact distance/total conveying distance) to below 0.1 in the above-mentioned drying process, thereby further suppressing the appearance abnormality (polarization unevenness) caused by the surface deformation of the above-mentioned polarizer.

It is also estimated that the present invention can further suppress the occurrence of polyvinyl alcohol film breakage occurring during the conveyance distance ( _idle distance) of the polyvinyl alcohol film between adjacent rollers by adjusting the ratio (L _MAX /W ₁ ) of the maximum distance (L MAX ) between the plurality of rollers to the width (W ₁ ) of the zinc-containing polyvinyl alcohol film before the drying step to 2 or less.

It is inferred that the polarizer obtained by the manufacturing method of the present invention can suppress shrinkage in the width direction of the polarizer during the drying process and suppress the occurrence of wrinkles at the ends of the polarizer because the ratio (W 2 /W ₁ ) of the width (W ₁ ) of the zinc-containing polyvinyl alcohol film before the drying process to the width ( _{W 2} ) of the polarizer obtained after the drying process is greater than 0.9 and less than 1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the hug angle between the roller and the polyvinyl alcohol film of the present invention.

FIG. 2 is a schematic diagram showing one embodiment of the drying process of the present invention.

FIG. 3 is a schematic diagram showing a drying process used in Comparative Examples 3 and 7. FIG.

FIG. 4 is a schematic diagram showing a drying step used in Comparative Example 4. FIG.

FIG. 5 is a schematic diagram showing a drying process used in Example 5. FIG.

DETAILED DESCRIPTION

<Method for Manufacturing Polarizer>

The manufacturing method of the polarizer of the present invention is a manufacturing method of the polarizer obtained by performing a drying process on a polyvinyl alcohol film after performing at least a dyeing process, a crosslinking process and a stretching process, wherein the treatment bath of at least one of the dyeing process, the crosslinking process and the stretching process contains zinc ions, and the drying process is a process of drying the polyvinyl alcohol film containing zinc while conveying it using multiple rollers, thereby manufacturing a polarizer with a thickness of less than 20 μm and a moisture content of not less than 13 wt % and not more than 19 wt %, and the multiple rollers include: a first roller arranged on the upstream side of the conveying direction of the polyvinyl alcohol film, a second roller arranged on the downstream side of the conveying direction of the polyvinyl alcohol film, and one or more third rollers arranged between the first roller and the second roller, and among the one or more third rollers, at least one of the rollers has an embrace angle of less than 90° with the polyvinyl alcohol film.

The polyvinyl alcohol (PVA) film can be used without particular limitation, and is a film having light transmittance in the visible light region and dispersing and adsorbing dichroic substances such as iodine and dichroic dyes. In addition, the thickness of the PVA film used as a blank is preferably about 10 to 100 μm, more preferably about 15 to 80 μm, and further preferably about 20 to 60 μm, and the width is preferably about 100 to 5000 mm.

As materials for the polyvinyl alcohol-based film, polyvinyl alcohol or its derivatives can be listed. As derivatives of the polyvinyl alcohol, for example, polyvinyl formal, polyvinyl acetal, materials modified with olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid and their alkyl esters, acrylamide, etc. can be listed. The average degree of polymerization of the polyvinyl alcohol is preferably about 100 to 10,000, more preferably about 1,000 to 10,000, and further preferably about 2,000 to 4,500. In addition, the saponification degree of the polyvinyl alcohol is preferably about 80 to 100 mol%, more preferably about 95 mol% to 99.95 mol%. It should be noted that the average degree of polymerization and the saponification degree can be obtained according to JIS K 6726.

The polyvinyl alcohol film may contain additives such as plasticizers and surfactants. Examples of the plasticizer include polyols such as glycerol, diglycerol, triglycerol, ethylene glycol, propylene glycol, polyethylene glycol, and condensates thereof. The amount of the additive is not particularly limited, and is preferably about 20% by weight or less in the polyvinyl alcohol film.

The method for producing a polarizer of the present invention is a method for producing a polarizer by subjecting the polyvinyl alcohol film to at least a dyeing step, a crosslinking step, and a stretching step, and then subjecting the polyvinyl alcohol film to a drying step, wherein the treatment bath of at least one of the dyeing step, the crosslinking step, and the stretching step contains zinc ions. By containing zinc ions in the treatment bath of at least one of the steps, the polyvinyl alcohol film can contain zinc, and the obtained polarizer contains zinc.

<Dyeing process>

The aforementioned dyeing process is a treatment process in which the polyvinyl alcohol film is immersed in a dye bath (iodine solution), which can make the polyvinyl alcohol film absorb dichromatic substances such as iodine or dichromatic dyes and orient. The aforementioned iodine solution is usually preferably an iodine aqueous solution, containing iodine and an iodide as a dissolution aid. It should be noted that, as the aforementioned iodide, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. can be listed. Among these, potassium iodide is suitable.

The concentration of iodine in the dyeing bath is preferably about 0.01 to 1 wt%, more preferably about 0.02 to 0.5 wt%. The concentration of iodide in the dyeing bath is preferably about 0.01 to 10 wt%, more preferably about 0.05 to 5 wt%.

When the dye bath contains zinc ions, it is preferred to use a zinc salt. 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. Among these, zinc sulfate is suitable. In the dye bath, the concentration of the zinc ions is preferably about 0.1 to 10% by weight, more preferably about 0.3 to 7% by weight, and even more preferably about 0.5 to 3% by weight.

The temperature of the dyeing bath is preferably about 10 to 50° C., more preferably about 15 to 45° C. In addition, the time of immersion in the dyeing bath cannot be generalized 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, more preferably about 20 to 240 seconds. The dyeing step may be performed only once or multiple times as needed.

<Cross-linking process>

The cross-linking process is a process in which the polyvinyl alcohol film dyed by the dyeing process is immersed in a treatment bath (cross-linking bath) containing a boron compound, and the polyvinyl alcohol film is cross-linked by the boron compound, and iodine molecules or dye molecules can be adsorbed to the cross-linked structure. As the boron compound, for example, boric acid, borate, borax, etc. can be listed. The cross-linking bath is usually an aqueous solution, and can be, for example, a mixed solution of an organic solvent and water that is miscible with water. In addition, the cross-linking bath can include iodides such as potassium iodide.

In the cross-linking 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 further preferably about 2 to 5% by weight. In addition, when an iodide such as potassium iodide is used in the cross-linking bath, the concentration of the iodide such as potassium iodide in the cross-linking bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight.

When the cross-linking bath contains zinc ions, a zinc salt is preferably used. 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. Among these, zinc sulfate is suitable. In the cross-linking bath, the concentration of the zinc ions is preferably about 0.1 to 10% by weight, more preferably about 0.3 to 7% by weight, and further preferably about 0.5 to 3% by weight.

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

<Stretching process>

The aforementioned stretching process is a treatment process of stretching the polyvinyl alcohol film to a specified ratio along at least one direction. Generally speaking, the polyvinyl alcohol film is uniaxially stretched along the conveying direction (length direction). The aforementioned stretching method is not particularly limited, and wet stretching method, dry stretching method (roller-to-roller stretching method, heated roller stretching method, compression stretching method, etc.) can be adopted, but in the present invention, it is preferred to use a wet stretching method. The aforementioned stretching process can be implemented only once, or it can be implemented multiple times as needed. The aforementioned stretching process can be carried out at any stage in the manufacture of polarizers.

The treatment bath (stretching bath) in the wet stretching method can generally use water, or a solvent such as a mixed solution of an organic solvent miscible with water and water. The stretching bath may contain an iodide such as potassium iodide. When an iodide such as potassium iodide is used in the stretching bath, the concentration of the iodide such as potassium iodide in the stretching bath is preferably about 1 to 15% by weight, more preferably about 2 to 10% by weight. In addition, the treatment bath (stretching bath) may contain the boron compound in order to increase the degree of crosslinking. In this case, the concentration of the boron compound in the stretching bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight.

When the stretching bath contains zinc ions, a zinc salt is preferably used. 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. Among these, zinc sulfate is suitable. In the stretching bath, the concentration of the zinc ions is preferably about 0.1 to 10% by weight, more preferably about 0.3 to 7% by weight, and further preferably about 0.5 to 3% by weight.

The temperature of the stretching bath is preferably about 25 to 80° C., more preferably about 40 to 75° C. In addition, the time of immersion in the stretching bath cannot be generalized 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, more preferably about 30 to 500 seconds. It should be noted that the stretching treatment in the wet stretching method can be carried out simultaneously with any one or more of the treatment steps of the dyeing step, the cross-linking step, the swelling step described later, and the washing step described later.

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

The manufacturing method of the polarizer of the present invention is a manufacturing method in which a drying step is performed after at least the dyeing step, the cross-linking step and the stretching step are performed on the polyvinyl alcohol film. However, a swelling step may be performed before the dyeing step. In addition, a cleaning step may be performed before the drying step.

<Swelling process>

The swelling step is a treatment step of immersing the polyvinyl alcohol film in a swelling bath, which can remove dirt, adhesives, etc. on the surface of the polyvinyl alcohol film. In addition, uneven dyeing can be suppressed by swelling the polyvinyl alcohol film. The swelling bath generally uses a medium containing water, distilled water, pure water, etc. as a main component. Surfactants, alcohols, etc. can be appropriately added to the swelling bath according to conventional methods.

The temperature of the swelling bath is preferably about 10 to 60° C., more preferably about 15 to 45° C. In addition, the time of immersion in the swelling bath cannot be generalized 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, more preferably about 10 to 200 seconds. The swelling step may be performed only once or multiple times as needed.

<Cleaning process>

The cleaning step is a treatment step of immersing the polyvinyl alcohol film in a cleaning bath, which can remove foreign matter remaining on the surface of the polyvinyl alcohol film. The cleaning bath generally uses a medium containing water, distilled water, pure water, or the like as a main component. In addition, the cleaning bath may use an iodide such as potassium iodide. In this case, the concentration of the iodide such as potassium iodide in the cleaning bath is preferably about 1 to 10% by weight, more preferably about 2 to 4% by weight, and even more preferably about 1.6 to 3.8% by weight.

The temperature of the cleaning bath is preferably about 5 to 50° C., more preferably about 10 to 40° C., and even more preferably about 15 to 30° C. In addition, the time of immersion in the cleaning bath cannot be determined in general terms because the degree of cleaning of the polyvinyl alcohol-based film is affected by the temperature of the cleaning bath, but is preferably about 1 to 100 seconds, more preferably about 2 to 50 seconds, and even more preferably about 3 to 20 seconds. The swelling step may be performed only once or multiple times as needed.

<Drying process>

The drying step is a step of drying a zinc-containing polyvinyl alcohol film while conveying it using a plurality of rollers, thereby manufacturing a polarizer having a thickness of less than 20 μm and a moisture content of more than 13 wt % and less than 19 wt %, wherein the plurality of rollers include a first roller arranged on the upstream side of the conveying direction of the polyvinyl alcohol film, a second roller arranged on the downstream side of the conveying direction of the polyvinyl alcohol film, and one or more third rollers arranged between the first roller and the second roller, and among the one or more third rollers, at least one roller has an angle of less than 90° with the polyvinyl alcohol film.

The plurality of rollers are a plurality of conveying rollers arranged inside a drying process section such as a dryer, an oven, or a heating furnace. The first roller is a conveying roller that is disposed at the most upstream side of the conveying direction of the zinc-containing polyvinyl alcohol-based film in the drying process section and is the first conveying roller that the zinc-containing polyvinyl alcohol-based film contacts in the drying process section. In addition, the second roller is a conveying roller that is disposed at the most downstream side of the conveying direction of the zinc-containing polyvinyl alcohol-based film in the drying process section and is the last conveying roller that the zinc-containing polyvinyl alcohol-based film contacts in the drying process section. In addition, the third roller is one or more conveying rollers disposed between the first roller and the second roller in the drying process section.

The aforementioned multiple rollers are substantially circular rollers, and the size is not particularly limited. For example, from the viewpoint of damage to the polarizer caused by the curvature during transportation, the diameter is preferably about 10 to 1000 mm, and more preferably about 30 to 500 mm. In addition, the aforementioned multiple rollers may be the same or different. In addition, the aforementioned multiple rollers may be heated rollers (hot rollers) or non-heated rollers. From the viewpoint of less concern about zinc precipitation on the surface of the polarizer when the rollers contact the polarizer, non-heated rollers are preferred.

In the aforementioned third roller, the embrace angle between at least one roller and the aforementioned zinc-containing polyvinyl alcohol film is 90° or less. A schematic diagram of the aforementioned embrace angle is shown in FIG1. The aforementioned embrace angle is an angle θ (°) formed when the zinc-containing polyvinyl alcohol film W is conveyed by means of a roller R. More specifically, it is an angle formed by the initial point and the final point of contact between the zinc-containing polyvinyl alcohol film W and the roller R, with the center point of the roller R as the reference point. From the viewpoint of reducing the contact time between the zinc-containing polyvinyl alcohol film and the roller and suppressing the appearance abnormality (polarization unevenness) of the polarizer, the aforementioned embrace angle is preferably less than 90°, for example, preferably less than 80°, more preferably less than 70°, further preferably less than 60°, and further preferably less than 50°. In addition, from the viewpoint of suppressing the appearance abnormality (polarization unevenness) of the polarizer, the lower limit of the aforementioned embrace angle is not particularly limited, and from the viewpoint of, for example, suppressing scratches on the polarizer caused by insufficient roller rotation, it can be exemplified as more than 10° and more than 30°.

The number of the third rollers cannot be determined uniformly because it is affected by the temperature and drying time of the drying process, but it is usually preferred that about 1 to 30 rollers be provided in the drying treatment section, and more preferably about 2 to 20 rollers be provided.

Furthermore, in the drying step, the ratio of the contact distance of the zinc-containing polyvinyl alcohol film relative to the third roller to the total conveying distance of the zinc-containing polyvinyl alcohol film (contact distance/total conveying distance) is preferably 0.1 or less. From the viewpoint of reducing the contact time between the zinc-containing polyvinyl alcohol film and the roller and further suppressing the appearance abnormality (polarization unevenness) of the polarizer, the contact distance/total conveying distance is preferably 0.09 or less. Furthermore, from the viewpoint of improving the conveying performance of the polyvinyl alcohol film, the contact distance/total conveying distance is preferably 0.01 or more, more preferably 0.03 or more.

Furthermore, in the drying step, the ratio (L _MAX /W ₁ ) of the maximum distance (L _MAX ) between the plurality of rollers to the width (W ₁ ) of the zinc-containing polyvinyl alcohol film before the drying step is preferably 2 or less. The maximum distance between the plurality of rollers refers to the longest distance among the conveying distances (idle distances) (L 1 ) between adjacent rollers (between the upstream roller and the downstream roller) from the position where the zinc-containing polyvinyl alcohol film leaves the upstream roller to the position where the zinc-containing polyvinyl alcohol film first contacts the downstream roller. From the viewpoint of reducing the deflection of the zinc-containing polyvinyl alcohol film during conveyance and suppressing the breakage of the obtained polarizer, the L _MAX / _{W 1} is preferably 1.5 or less, and more preferably 1 or less. From the viewpoint of suppressing the breakage of the polarizer, the lower limit of the L _MAX /W ₁ is not particularly limited, and for example, from the viewpoint of improving the conveyability of the polyvinyl alcohol film, it can be 0.1 or more, 0.2 or more.

As long as the thickness of the obtained polarizer is less than 20 μm and the moisture content is more than 13 wt % and less than 19 wt %, the drying temperature is not particularly limited, for example, preferably about 15 to 150° C., more preferably about 20 to 100° C., and further preferably about 25 to 50° C. In addition, the drying time cannot be generalized because the degree of drying of the polarizer is affected by the drying temperature, and is preferably about 30 to 600 seconds, more preferably about 60 to 300 seconds. The drying step can be performed only once, or multiple times as needed.

The thickness of the polarizer obtained by the manufacturing method of the present invention is less than 20 μm, and the moisture content is more than 13% by weight and less than 19% by weight. Considering the transportability of the polyvinyl alcohol film and the polarizer, the thickness of the aforementioned polarizer is preferably more than 5 μm, more preferably more than 10 μm, and from the viewpoint of improving the heating durability of the polarizing film, the thickness is preferably less than 19 μm. In addition, in the aforementioned polarizer, from the viewpoint of suppressing the appearance abnormality (polarization unevenness) caused by the surface deformation of the polarizer, the moisture content is preferably more than 13.5% by weight, more preferably more than 14% by weight, and from the viewpoint of improving the heating durability of the polarizing film, the moisture content is preferably less than 18.5% by weight, more preferably less than 18% by weight. It should be noted that the moisture content of the polarizer is calculated by the following formula based on the initial weight of the sample (polarizer) cut into a size of 100 mm square and the dry weight after drying at 120°C for 2 hours.

Water content (weight %) = {(initial weight - dry weight) / initial weight} × 100

The ratio (W ₂ /W ₁ ) of the width (W ₁ ) of the zinc-containing polyvinyl alcohol film before the drying step to the width (W ₂ ) of the polarizer obtained after the drying step is preferably 0.9 or more and less than 1. From the viewpoint of suppressing the generation of wrinkles at the end of the polarizer during the drying step, W ₂ /W ₁ is preferably 0.92 to 0.98, more preferably 0.94 to 0.98.

<Method for producing polarizing film>

The method for producing a polarizing film of the present invention includes the step of bonding a transparent protective film to at least one surface of the polarizer via an adhesive layer.

The aforementioned transparent protective film is not particularly limited, and various transparent protective films used in polarizing films in the past can be used. As the material constituting the aforementioned transparent protective film, a thermoplastic resin having excellent transparency, mechanical strength, thermal stability, moisture barrier, isotropy, etc. can be used. As the aforementioned thermoplastic resin, there can be listed, for example, cellulose ester resins such as cellulose triacetate; polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyamide resins such as polyethersulfone resins, polysulfone resins, polycarbonate resins, nylon, and aromatic polyamide; polyolefin resins such as polyimide resins, polyethylene, polypropylene, and ethylene-propylene copolymers; (meth) acrylic resins; cyclic polyolefin resins (norbornene resins) having a cyclic system and/or a norbornene structure, polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. In addition, the transparent protective film may use a cured layer formed by a thermosetting resin or ultraviolet curing resin such as (meth) acrylic acid, urethane, acrylic urethane, epoxy, silicone, etc. Among these, cellulose ester resins, polycarbonate resins, (meth) acrylic resins, cyclic polyolefin resins, and polyester resins are suitable.

The thickness of the transparent protective film can be appropriately determined. Generally, from the viewpoints of strength, workability such as handling, thin-layer properties, etc., it is preferably about 1 to 500 μm, more preferably about 1 to 300 μm, and even more preferably about 5 to 100 μm. In addition, from the viewpoint of reducing the moisture permeability of the transparent protective film, the thickness of the transparent protective film is preferably about 10 to 100 μm, more preferably about 20 to 100 μm, and even more preferably about 30 to 100 μm.

From the viewpoint of suppressing the reduction of polarization performance under high temperature or high temperature and high humidity environment, the moisture permeability of the transparent protective film is preferably 800 g/(m ² ·24h) or less, more preferably 400 g/(m ² ·24h) or less, further preferably 200 g/(m ² ·24h) or less, and further preferably 150 g/(m ² ·24h) or less. In addition, the moisture permeability of the transparent protective film on one side of the polarizer is preferably 200 g/(m ² ·24h) or less, more preferably 150 g/(m ² ·24h) or less. It should be noted that the moisture permeability can be calculated as follows: According to the moisture permeability test (cup method) of JIS Z0208, a sample cut into a diameter of 60 mm is placed in a moisture permeable cup containing about 15 g of calcium chloride, and the sample is placed in a thermostat at a temperature of 40°C and a humidity of 90% RH, and the weight gain of calcium chloride before and after standing for 24 hours is measured to calculate the moisture permeability.

When the transparent protective films are bonded to both surfaces of the polarizer, the transparent protective films on both surfaces may be the same or different.

The transparent protective film may use a phase difference plate having a front phase difference of 40 nm or more and/or a thickness direction phase difference of 80 nm or more. The front phase difference is usually controlled to a range of 40 to 200 nm, and the thickness direction phase difference is usually controlled to a range of 80 to 300 nm. When the phase difference plate is used as the transparent protective film, the phase difference plate also functions as a transparent protective film, so that thinning can be achieved.

As the aforementioned phase difference plate, for example, birefringent films obtained by uniaxially stretching or biaxially stretching polymer raw materials, oriented films of liquid crystal polymers, and products obtained by supporting the oriented layer of liquid crystal polymers with a film, etc. can be listed. The thickness of the phase difference plate is not particularly limited, and is usually about 20 to 150 μm. It should be noted that the aforementioned phase plate can be used by laminating a transparent protective film without phase difference.

The transparent protective film may be subjected to a surface modification treatment. Examples of the surface modification treatment include corona treatment, plasma treatment, primer treatment, and saponification treatment.

The surface of the transparent protective film not bonded with the polarizer may be subjected to hard coating, anti-reflection treatment, treatment for the purpose of anti-adhesion, diffusion and/or anti-glare. It should be noted that the hard coating, treatment for the purpose of anti-reflection layer, anti-adhesion layer, diffusion layer and/or anti-glare, etc., in addition to being provided on the transparent protective film itself, may also be separately provided as an optical layer from the transparent protective film.

The transparent protective film may contain any appropriate additives such as an ultraviolet absorber, an antioxidant, a lubricant, a plasticizer, a release agent, an anti-coloring agent, a flame retardant, an antistatic agent, a pigment, a colorant, and the like.

Examples of the adhesive include water-based adhesives, solvent-based adhesives, emulsion-based adhesives, solvent-free adhesives, active energy ray-curable adhesives (e.g., ultraviolet-curable adhesives, electron-beam-curable adhesives), and thermosetting adhesives. The adhesive is preferably a water-based adhesive from the viewpoint of having a desired cured viscosity or pre-cured viscosity and excellent adhesion to the polarizer.

The water-based adhesive may be any appropriate water-based adhesive, but is preferably a water-based adhesive containing a PVA-based resin. From the viewpoint of adhesiveness, the average degree of polymerization of the PVA-based resin is preferably about 100 to 5,500, more preferably about 1,000 to 4,500. In addition, from the viewpoint of adhesiveness, the average degree of saponification of the PVA-based resin is preferably about 85 mol% to 100 mol%, more preferably about 90 mol% to 100 mol%.

From the viewpoint of excellent adhesion to polarizers and protective films and excellent durability, the aforementioned PVA-based resin preferably contains acetoacetyl groups. The PVA-based resin containing acetoacetyl groups can be obtained, for example, by reacting the PVA-based resin with diketene using any method. The acetoacetyl modification degree of the PVA-based resin containing acetoacetyl groups represents 0.1 mol% or more, preferably about 0.1 mol% to 40 mol%, more preferably about 1 mol% to 20 mol%, and further preferably about 2 mol% to 7 mol%. It should be noted that the acetoacetyl modification degree is a value measured by NMR.

The resin (solid content) concentration of the water-based adhesive is preferably about 0.1% by weight to 15% by weight, more preferably about 0.5% by weight to 10% by weight.

The coating of the adhesive can be performed on any of the transparent protective film and the polarizer, or on both. After lamination, a drying process is performed to form an adhesive layer including a coated dry layer. The lamination of the polarizer and the transparent protective film can be performed by a roll laminator or the like. After the drying process, ultraviolet rays or electron beams can be irradiated as needed. The thickness of the adhesive layer is not particularly limited, but is preferably about 30 to 5000 nm, and more preferably about 100 to 1000 nm.

<Method for producing laminated polarizing film>

The method for producing a laminated polarizing film (optical laminate) of the present invention includes the step of laminating an optical layer to the polarizing film.

The optical layer is not particularly limited, and for example, one or more layers of reflective plates, semi-transmissive plates, phase difference plates (including 1/2, 1/4, etc. wavelength plates), viewing angle compensation films, etc., which are sometimes used to form optical layers of liquid crystal display devices, etc., can be used. As the laminated polarizing film, in particular, a reflective polarizing film or a semi-transmissive polarizing film formed by further laminating a reflective plate or a semi-transmissive reflective plate on the polarizing film, an elliptically polarizing film or a circularly polarizing film formed by further laminating a phase difference plate on the polarizing film, a wide viewing angle polarizing film formed by further laminating a viewing angle compensation film on the polarizing film, or a polarizing film formed by further laminating a brightness enhancement film on the polarizing film can be cited.

An adhesive layer for laminating image display units such as liquid crystal cells, organic EL elements, and other components such as transparent plates such as transparent plates such as front surface transparent plates and touch panels on the visual recognition side may be provided on one or both sides of the aforementioned polarizing film or the aforementioned laminated polarizing film. As the adhesive layer, an adhesive layer is suitable. The adhesive forming the aforementioned adhesive layer is not particularly limited, and an adhesive having polymers such as acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyethers, fluorine systems, and rubber systems as base polymers may be appropriately selected and used. It is particularly preferred to use an adhesive having excellent optical transparency, showing appropriate wettability, cohesiveness, adhesion, weather resistance, or heat resistance, etc., as an adhesive comprising an acrylic polymer.

The adhesive layer can be provided on one or both sides of the aforementioned polarizing film or the aforementioned laminated polarizing film by an appropriate method. As for the provision of the adhesive layer, for example, an adhesive solution is prepared and it is directly provided on the aforementioned polarizing film or the aforementioned laminated polarizing film by an appropriate development method such as a casting method or a coating method; or an adhesive layer is formed on an insulator and transferred to the aforementioned polarizing film or the aforementioned laminated polarizing film. The thickness of the aforementioned adhesive layer can be appropriately determined according to the purpose of use, adhesive strength, etc., and is usually 1 to 500 μm, preferably 5 to 200 μm, and more preferably 10 to 100 μm.

The exposed surface of the adhesive layer is preferably covered by temporarily adhering a separator for the purpose of preventing contamination until it is put into practical use. This can prevent contamination of the adhesive layer under conventional handling conditions. As the separator, for example, a suitable sheet such as a plastic film, a rubber sheet, paper, cloth, a nonwoven fabric, a net, a foam sheet, a metal foil, or a laminate thereof, which is coated with a suitable release agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide-based release agent as required can be used.

<Method for Manufacturing Image Display Panel and Method for Manufacturing Image Display Device>

The manufacturing method of the image display panel of the present invention includes the step of laminating the aforementioned polarizing film or the aforementioned laminated polarizing film to the image display unit. In addition, the manufacturing method of the image display device of the present invention includes the step of providing a transparent plate on the polarizing film or laminated polarizing film side (visual recognition side) of the aforementioned image display panel.

As the aforementioned image display unit, for example, a liquid crystal unit, an organic EL unit, etc. can be listed. As the aforementioned liquid crystal unit, for example, any of a reflective liquid crystal unit that utilizes external light, a transmissive liquid crystal unit that utilizes light from a light source such as a backlight, and a semi-transmissive and semi-reflective liquid crystal unit that utilizes both light from the outside and light from the light source can be used. When the aforementioned liquid crystal unit utilizes light from a light source, the image display device (liquid crystal display device) also configures a polarizing film on the side of the image display unit (liquid crystal unit) opposite to the visual recognition side, and further configures a light source. The polarizing film on the light source side and the liquid crystal unit are preferably adhered to each other by means of an appropriate adhesive layer. As the driving mode of the aforementioned liquid crystal unit, any type of driving mode, such as VA mode, IPS mode, TN mode, STN mode, bent orientation (π type), etc. can be used.

As the organic EL unit, for example, an organic EL unit having a light emitter (organic electroluminescent light emitter) formed by sequentially stacking a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate can be appropriately used. The organic light-emitting layer is a laminate of various organic thin films, and can be composed of various layers, such as a laminate of a hole injection layer containing a triphenylamine derivative and a light-emitting layer containing a fluorescent organic solid such as anthracene; a laminate of these light-emitting layers and an electron injection layer containing a perylene derivative; or a laminate of a hole injection layer, a light-emitting layer, and an electron injection layer.

As the transparent plate arranged on the visual recognition side of the aforementioned image display unit, for example, a front surface transparent plate (window layer), a touch panel, etc. can be listed. As the aforementioned front surface transparent plate, a transparent plate with appropriate mechanical strength and thickness can be used. As such a transparent plate, for example, a transparent resin plate such as an acrylic resin, a polycarbonate resin, or a glass plate can be used. As the aforementioned touch panel, various touch panels such as a resistive film type, an electrostatic capacitance type, an optical type, an ultrasonic type, etc. can be used; a glass plate, a transparent resin plate, etc. having a touch sensor function can be used. When a touch panel of an electrostatic capacitance type is used as the aforementioned transparent plate, it is preferred that a front surface transparent plate comprising a glass or a transparent resin plate is provided closer to the visual recognition side than the touch panel.

Example

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>

<Manufacturing of Polarizer>

A polyvinyl alcohol film having an average degree of polymerization of 2,400, a saponification degree of 99.9 mol%, a thickness of 45 μm, and a width of 2600 mm was prepared. The polyvinyl alcohol film was immersed in a swelling bath (water bath) at 28° C. between rollers having different peripheral speed ratios for 30 seconds to swell and was stretched to 2.4 times in the conveying direction (swelling step), and then immersed in a dyeing bath (an aqueous solution having an iodine concentration of 0.03 wt % and a potassium iodide concentration of 0.3 wt %) at 25° C. for 45 seconds to dye and was stretched to 3.7 times in the conveying direction based on the original polyvinyl alcohol film (polyvinyl alcohol film not stretched at all in the conveying direction) as a reference (dyeing step). Next, the dyed polyvinyl alcohol film was immersed in a crosslinking bath (aqueous solution of 3.0 wt% boric acid, 3.0 wt% potassium iodide, 3.6 wt% zinc sulfate (1.5 wt% zinc ion concentration)) at 40°C for 20 seconds, and stretched to 4.2 times along the conveying direction based on the original polyvinyl alcohol film (crosslinking step). Furthermore, the obtained polyvinyl alcohol film was immersed in a stretching bath (aqueous solution of 4.0 wt% boric acid, 5.0 wt% potassium iodide, 5.0 wt% zinc sulfate (2.0 wt% zinc ion concentration)) at 65°C for 50 seconds, stretched to 6.0 times along the conveying direction based on the original polyvinyl alcohol film (stretching step), and then immersed in a cleaning bath (aqueous solution of 2.5 wt% potassium iodide) at 27°C for 5 seconds (cleaning step). A polarizer was produced by drying the cleaned polyvinyl alcohol film at 25°C for 2 minutes using an oven having a roller configuration as shown in FIG2 (the total number of rollers was 10; the third roller had a maximum embrace angle of 43°). The ratio of the contact distance of the polyvinyl alcohol film relative to the third roller to the total conveying distance of the polyvinyl alcohol film (contact distance/total conveying distance) was 0.09. In addition, the ratio (L _MAX /W 1 ) of the maximum distance between the rollers among the multiple rollers in the oven to the width (W ₁ ) of the aforementioned zinc-containing _polyvinyl alcohol film before the drying process was 0.21. The thickness of the obtained polarizer was 18 μm, the moisture content of the polarizer was 17.2% by weight, _and W ₂ /W ₁ was 0.97.

<Production of polarizing film>

As the adhesive, an aqueous solution containing an acetoacetyl group-containing polyvinyl alcohol resin (average degree of polymerization: 1,200, degree of saponification: 98.5 mol %, degree of acetoacetylation: 5 mol %) and methylolmelamine at a weight ratio of 3:1 was used. A 30 μm thick transparent protective film (saturated water absorption: 0.2 g/m 2 , moisture permeability: 125 g/(m ² ·24 h)) made of (meth) acrylic resin (modified acrylic polymer having a lactone ring structure) as a second transparent protective film was laminated to one side (image display unit side) of the polarizer obtained above using the adhesive by a roll laminator. Furthermore, a 40 μm thick triacetyl cellulose film (moisture permeability: 342 g/(m ² ·24 h), manufactured by Konica Minolta Co., Ltd., trade name: "KC4UYW") as a first transparent protective film was laminated to the other side (visual recognition side) of the polarizer obtained above using a roll laminator. The films ^were then dried by heating in an oven (temperature: 88° C., time: 10 minutes) to prepare polarizing films having transparent protective films laminated to both sides of the polarizer.

<Production of Analog Image Display Device>

The polarizing film obtained above was cut into a size of 150×50 cm in such a way that the absorption axis of the polarizer became the long side, and a glass plate (simulated image display unit) was bonded to one side of the polarizing film (the side on the transparent film A side) with the aid of a 20 μm thick acrylic adhesive layer, and another glass plate was bonded to the other side of the polarizing film (the side on the transparent film B side) with the aid of a 200 μm thick adhesive free of acrylic monomer (manufactured by Nitto Denko Corporation, trade name "LUCIACS CS9868") to produce a simulated image display device.

[Evaluation of abnormal appearance (uneven polarization)]

The appearance of the polarizing film obtained above was evaluated by visual inspection according to the following criteria.

○: No abnormality in appearance or less than 10 pieces/ ^m2 of polarization unevenness occurs.

×: Polarization unevenness of 10 pieces/m ² or more occurs.

[Evaluation of breakage of polarizer]

The appearance of the polarizer obtained above was evaluated by visual inspection according to the following criteria.

○: No visible breakage of the polarizer occurred.

×: Visually recognizable breakage of the polarizer occurred.

[Evaluation of Heating Durability]

The simulated image display device obtained above was left to stand in a hot air oven at a temperature of 95° C. for 500 hours, and the appearance after the exposure (heating) was evaluated by visual inspection according to the following criteria.

○: No abnormality in appearance.

×: Visually recognizable unevenness occurs in the polarizer.

<Example 2>

<Production of polarizer, polarizing film, and analog image display device>

In the preparation of the polarizer, the drying temperature in the drying step was set to 35° C., and the polarizer was prepared by the same operation as in Example 1. The thickness of the obtained polarizer was 17 μm, the moisture content of the polarizer was 14.3% by weight, and W ₂ /W ₁ was 0.95. Using the obtained polarizer, a polarizing film and a simulated image display device were prepared by the same operation as in Example 1.

<Example 3>

<Production of polarizer, polarizing film, and analog image display device>

A polyvinyl alcohol film having an average degree of polymerization of 2,400, a saponification degree of 99.9 mol%, a thickness of 30 μm, and a width of 2,600 mm was prepared. The polyvinyl alcohol film was immersed in a swelling bath (water bath) at 20° C. between rollers having different peripheral speed ratios for 30 seconds to swell and was stretched to 2.4 times in the conveying direction (swelling step), and then immersed in a dyeing bath (an aqueous solution having an iodine concentration of 0.045 wt % and a potassium iodide concentration of 0.45 wt %) at 25° C. for 45 seconds to dye and was stretched to 3.7 times in the conveying direction based on the original polyvinyl alcohol film (polyvinyl alcohol film not stretched at all in the conveying direction) as a reference (dyeing step). Next, the dyed polyvinyl alcohol film was immersed in a crosslinking bath (aqueous solution of 3.0 wt% boric acid, 3.0 wt% potassium iodide, 3.6 wt% zinc sulfate (1.5 wt% zinc ion concentration)) at 40°C for 20 seconds, and stretched to 4.2 times along the conveying direction based on the original polyvinyl alcohol film (crosslinking step). Furthermore, the obtained polyvinyl alcohol film was immersed in a stretching bath (aqueous solution of 4.0 wt% boric acid, 5.0 wt% potassium iodide, 5.0 wt% zinc sulfate (2.0 wt% zinc ion concentration)) at 65°C for 50 seconds, stretched to 6.0 times along the conveying direction based on the original polyvinyl alcohol film (stretching step), and then immersed in a cleaning bath (aqueous solution of 3.0 wt% potassium iodide) at 20°C for 5 seconds (cleaning step). A polarizer was prepared by drying the cleaned polyvinyl alcohol film at 18°C for 2 minutes using an oven having a roller configuration as shown in FIG2 (the total number of rollers was 10; the maximum embrace angle of the third roller was 43°). The ratio of the contact distance of the polyvinyl alcohol film relative to the third roller to the total conveying distance of the polyvinyl alcohol film (contact distance/total conveying distance) was 0.09. In addition, the ratio (L _MAX /W 1 ) of the maximum distance between the rollers among the multiple rollers in the oven to the width (W ₁ ) of the aforementioned zinc-containing _polyvinyl alcohol film before the drying process was 0.20. The thickness of the obtained polarizer was 12 _μm , the moisture content of the polarizer was 17.6% by weight, and W ₂ /W ₁ was 0.97. Using the obtained polarizer, a polarizing film and a simulated image display device were prepared using the same operation as in Example 1.

<Example 4>

<Production of polarizer, polarizing film, and analog image display device>

In the preparation of the polarizer, the drying temperature in the drying step was set to 25° C., and the polarizer was prepared by the same operation as in Example 3. The thickness of the obtained polarizer was 12 μm, the moisture content of the polarizer was 14.5 wt %, and W ₂ /W ₁ was 0.95. Using the obtained polarizer, a polarizing film and a simulated image display device were prepared by the same operation as in Example 1.

<Example 5>

In the production of the polarizer, an oven having a roller configuration as shown in FIG. 5 (the total number of rollers is 8; in the third roller, the maximum embrace angle is 88°) is used in the drying process, and the polarizer is produced by drying at 28° C. for 3 minutes. The same operation as in Example 1 is used to produce the polarizer. The ratio of the contact distance of the polyvinyl alcohol film relative to the third roller to the total conveying distance of the polyvinyl alcohol film (contact distance/total conveying distance) is 0.09. The thickness of the obtained polarizer is 18 μm, and the moisture content of the polarizer is 15.0% by weight, and W ₂ /W ₁ is 0.92. In addition, the ratio (L _MAX /W ₁ ) of the maximum distance between the rollers among the multiple rollers in the oven to the width (W ₁ ) of the aforementioned _zinc -containing polyvinyl alcohol film before the drying process is 0.82. Using the obtained polarizer, a polarizing film and a simulated image display device are produced by the same operation as in Example 1.

<Comparative Example 1>

<Production of polarizer, polarizing film, and analog image display device>

In the preparation of the polarizer, the drying temperature in the drying step was set to 45° C., and the polarizer was prepared by the same operation as in Example 1. The thickness of the obtained polarizer was 17 μm, the moisture content of the polarizer was 12.5% by weight, and W ₂ /W ₁ was 0.91. Using the obtained polarizer, a polarizing film and a simulated image display device were prepared by the same operation as in Example 1.

<Comparative Example 2>

<Production of polarizer, polarizing film, and analog image display device>

In the preparation of the polarizer, the drying temperature in the drying step was set to 17° C., and the polarizer was prepared by the same operation as in Example 1. The thickness of the obtained polarizer was 18 μm, the moisture content of the polarizer was 19.1% by weight, and W ₂ /W ₁ was 0.98. Using the obtained polarizer, a polarizing film and a simulated image display device were prepared by the same operation as in Example 1.

<Comparative Example 3>

<Production of polarizer, polarizing film, and analog image display device>

In the production of the polarizer, an oven having a roller configuration as shown in FIG. 3 (a total of 18 rollers; the third roller has a maximum embrace angle of 176°) is used in the drying process, and the polarizer is produced by drying at 28° C. for 5 minutes. In addition, the polarizer is produced by the same operation as in Example 1. In addition, the ratio (L _MAX /W ₁ ) of the maximum distance between the rollers among the multiple rollers in the oven to the width (W ₁ ) of the aforementioned zinc-containing polyvinyl alcohol film before the drying process is 0.82. The thickness of the obtained polarizer is 17 μm, the moisture content of the polarizer is 14.3% by weight, _and W ₂ /W ₁ is 0.84. Using the obtained polarizer, a polarizing film and a simulated image display device are produced by the same operation as in Example 1. It should be noted that the ratio of the contact distance of the polyvinyl alcohol film relative to the third roller to the total conveying distance of the polyvinyl alcohol film (contact distance/total conveying distance) is 0.13.

<Comparative Example 4>

<Production of polarizer, polarizing film, and analog image display device>

In the production of the polarizer, an oven having a roller configuration as shown in FIG. 4 (the total number of rollers is 6; in the third roller, the maximum embrace angle is 134°) is used in the drying process, and the polarizer is produced by drying at 31° C. for 3 minutes. Otherwise, the polarizer is produced by the same operation as in Example 1. The thickness of the obtained polarizer is 17 μm, the moisture content of the polarizer is 14.3% by weight, and W ₂ /W ₁ is 0.88. In addition, the ratio (L _MAX /W ₁ ) of the maximum distance between the rollers among the multiple rollers in the oven to the width (W ₁ ) of the aforementioned zinc-containing polyvinyl alcohol film _before the drying process is 0.98. Using the obtained polarizer, a polarizing film and a simulated image display device are produced by the same operation as in Example 1. It should be noted that the ratio of the contact distance of the polyvinyl alcohol film relative to the third roller to the total conveying distance of the polyvinyl alcohol film (contact distance/total conveying distance) is 0.08.

<Comparative Example 5>

<Production of polarizer, polarizing film, and analog image display device>

In the preparation of the polarizer, the same operation as in Example 1 was performed except that the drying step was performed at 25° C. for 2 minutes using an oven without a roller. The thickness of the obtained polarizer was 18 μm, the moisture content of the polarizer was 17.4% by weight, and W ₂ /W ₁ was 0.81. Using the obtained polarizer, a polarizing film and a simulated image display device were prepared in the same operation as in Example 1.

<Comparative Example 6>

<Production of polarizer, polarizing film, and analog image display device>

In the preparation of the polarizer, zinc sulfate was not used in the crosslinking bath and the stretching bath, and the polarizer was prepared by the same operation as in Example 1. The thickness of the obtained polarizer was 18 μm, the moisture content of the polarizer was 17.2% by weight, and W ₂ /W ₁ was 0.96. Using the obtained polarizer, a polarizing film and a simulated image display device were prepared by the same operation as in Example 1.

<Comparative Example 7>

<Production of polarizer, polarizing film, and analog image display device>

A polyvinyl alcohol film having an average degree of polymerization of 2,700, a saponification degree of 99.9 mol%, a thickness of 75 μm, and a width of 2600 mm was prepared, and the concentration of the dye bath was adjusted to an iodine concentration of 0.02 wt% and a potassium iodide concentration of 0.2 wt%. In the drying process, an oven having a roller configuration as shown in FIG. 3 (a total of 18 rollers; the third roller had a maximum angle of 176°) was used to dry the film at 45° C. for 5 minutes to produce a polarizer. The same operation as in Example 1 was used to produce a polarizer. In addition, the ratio (L _MAX /W ₁ ) of the maximum distance (L _MAX ) between the rollers in the oven to the width (W ₁ ) of the zinc-containing polyvinyl alcohol film before the drying process was 0.82. The thickness of the obtained polarizer was 28 μm, the moisture content of the polarizer was 14.5 wt%, and W ₂ /W ₁ was 0.86. The obtained polarizer was used in the same manner as in Example 1 to prepare a polarizing film and a simulated image display device.

The above-obtained polarizers of Examples 2 to 5 and Comparative Examples 1 to 7 and the simulated image display device were used to perform the above-mentioned evaluations of [evaluation of abnormal appearance (polarization unevenness)], [evaluation of breakage of polarizer], and [evaluation of heating durability]. The results are shown in Table 1.

[Table 1]

Description of Reference Numerals

W Zinc-containing polyvinyl alcohol film

R Roller

θ is the angle of the hold angle

L ₁ empty distance

Claims (8)

1. A method for producing a polarizer, characterized in that the method comprises performing a dyeing step, a cross-linking step and a stretching step on a polyvinyl alcohol-based film, and then performing a drying step to obtain the polarizer. The treatment bath of at least one of the dyeing step, the crosslinking step and the stretching step contains zinc ions, The drying step is a step of drying the zinc-containing polyvinyl alcohol film while conveying it with a plurality of rollers, thereby manufacturing a polarizer having a thickness of 20 μm or less and a moisture content of 13 wt % or more and 19 wt % or less. The plurality of rollers include: a first roller disposed on the most upstream side in the conveying direction of the polyvinyl alcohol film, a second roller provided on the most downstream side in the conveying direction of the polyvinyl alcohol-based film, and one or more third rollers are provided between the first roller and the second roller, Among the one or more third rollers, at least one roller has an embrace angle with the polyvinyl alcohol film of 90° or less. The ratio W ₂ /W ₁ of the width W ₁ of the zinc-containing polyvinyl alcohol-based film before the polarizer drying step to the width W ₂ of the polarizer obtained after the drying step is 0.9 or more and less than 1, In the drying step, a ratio of a contact distance of the zinc-containing polyvinyl alcohol film with respect to the third roller to a total conveyance distance of the zinc-containing polyvinyl alcohol film, that is, contact distance/total conveyance distance, is 0.01 or more and 0.1 or less. 2 . The method for manufacturing a polarizer according to claim 1 , wherein a ratio L _MAX /W ₁ of a maximum distance L _MAX between the plurality of rollers and a width W 1 of the zinc-containing polyvinyl alcohol film before the drying step is ₂ or less. 3. A method for producing a polarizing film, comprising the step of bonding a transparent protective film to at least one surface of the polarizer obtained by the method for producing a polarizer according to claim 1 or 2 via an adhesive layer. 4 . The method for producing a polarizing film according to claim 3 , wherein the adhesive forming the adhesive layer is a water-based adhesive. 5 . The method for producing a polarizing film according to claim 3 , wherein the water vapor permeability of the transparent protective film is 200 g/(m ² ·24 h) or less. 6 . A method for producing a laminated polarizing film, comprising the step of laminating an optical layer to a polarizing film obtained by the method for producing a polarizing film according to claim 3 . 7. A method for manufacturing an image display panel, characterized in that it includes the following steps: a step of laminating a polarizing film obtained by the method for manufacturing a polarizing film according to any one of claims 3 to 5, or a laminated polarizing film obtained by the method for manufacturing a laminated polarizing film according to claim 6, to an image display unit. 8. A method for manufacturing an image display device, comprising the step of providing a transparent plate on the polarizing film or laminated polarizing film side of the image display panel obtained by the method for manufacturing an image display panel according to claim 7.